VIBRATIONAL SPECTRA OF SOME
ORGANOMETALLIC COMPLEXES
'/IB!V\TIONIŒ; SPEC7P-A OF sor-m . -
T Rl\N SI T l ON ME T i\L
ORGANOHE'I'ALLIC CmlP:r.JE~~;::S
Ph.D.
Gabriel George Barna
ABSTRc'\.CT
Chemistry
Department
The vapour phase and solution i. r. spectra of Mn (CO) 4NO
have been investigated in the 5250-33 cm- l region. The spectral data are in accord with a C3v trigonal bipyramidal geometry for
the molecule. Complete vibrational assignments have been
proposed. These assignments are supported in part by a simple
force constant calculation. The ionization potential of this
complex has been determined by mass spectrometry.
A ne,., route has been developed for the synthesis of
Fe(CO)2(NO)2. ~le soluLion i.r., far-infrared and Raman spectra substantiate further the previously assigned fundarnentals of
this species. Assignments are also proposed for the low
frequency modes of bm of the organophosphorus derivatives that
have been investigated. These assignments verify experimentally
the postulated frequency ranges of the Fe-C-O and Fe-N-O
fl.lndarnentals.
Partial vibrational assignments have been put forvlard for
the i. r. and P.aman spectra of the cyclic àiene Group VI 1~ !netal
complexes, (C7HaHl(CO)4· 'Ihe deviations in the observed spectra, in the v(C-O) regions, from what is expected on the basis of
J
C2v geometry, are explained by accidentaI degeneracies. Fermi
resonance arguments have unequivocally designated the coordinated
v (C=C) modes. The !'l-C-O fundamentals ha.ve been attributed to
certain frequency ranges, while the v (M-olefin) modes have been
assigned specifically. The norbornadiene ligand apparently
undergoes no change in stereochemistry upon coordination.
Limi 1:ed vibrational assignments have also been suggested
for the i.r. and Raman spectra of [(COD)RhCI]2' [(COD)CuCI]2
and (COD)2CuCI04' For the last compound, a novel structure
has been proposed on the basis of available spectral data.
The first vibrational assignments for thiocarbonyl complexes
have been achieved for CpMn(CO)2CS and Cp Mn (CO) (CS)2' The
Mn-C-S stretching and bending modes occur at similar positions
and with comparable intensities to the analogous Mn-C-O funda
mentaIs. ~A "slo~..," rotation of the rine; has been postulated ta
cause the apparent clecrease in the symmetry of both the Cp-Mn
and Mn(CO)2CS moieties in solution.
The vibrational spectra of transition metal carbonyl-
nitrosyl cOITlplexes have been investigated. For Hn(CO) 4NO,
in the vapour phase and in solution, a C3v molecular geometry
and complete vibrational assignments have been proposed. The
ionization potential of this cornplex has also been determined
by mass spectrometry. A new synthesis of Fe(CO)2(NO)2 has
been developed. The i.r. and Raman spectra of this complex
anà sorne of i ts organr)phosphorus deri vati ves, ha'le also been
s·tudied.
Partial vibrational assignrr.ents ha.ve been put fOr\vard
for the i.r. and Raman spectra of olefin complexes such as
(NBD)M(CO)4' [(COD)HCI]2 and (COD)2CuCI04. The C=C and metal
ole fin stretching fundamentals are discussed and assigned. A
structure is postulated for the last compound.
The first vibrational assignments for thiocarbonyl
complexes have been achieved for CpHn(CO)2CS and CpI1n{CO) (CS}2'
resulting in the identification of the IOvl-frequency Mn-C-S
fundamental vibrations.
RESUME
L'étude des spectres infra-rouge du 1'-ln (CO) 4NO en phase
vapeur ou en solution a été confinée dans la région 5250-33 cm- l
Les résultats concordent avec une géométrie trigonale bi-
pyramidale C3v de la molécule. On propose une attribution
compléte des vibrations, supportée en partie par un sirnple calcul
de constante de force. Le potentiel d'ionisation de ce complexe
fut déterminé par spectroscopie de masse.
Une nouvelle méthode de synthèse du Fe(CO)2(NO)2 fut mise
au point. Les spectres i.r., i.r. lointain et Raman sur
solutions supportent les attributions fondamentales précédemment
reporteés de cé composé. On propose également les attributions
correspondant aux modes de basse fréquence de deux des dérivès
organophosphorés qui ont été étudiés. Ces attributions vérifient
expérimentalement les intervalles de fréquence postulés pour les
vibrations fondamentales de Fe-C-O et Fe-N-O.
L'attribution de vibrations partielles est avancée pour les
spectres·i.r. et Raman des complexes cyclodiènemétal du groupe
VI A, (C 7Ha)M(CO)4. On explique les déviations du spectre
observé dans les régions v (C-O) , par rapport aux résultats
prévus pour une géométrie C2v ' par un phénomène de dégénérescence
accidentelle. La résonance de Fermi met, sans équivoque, en
relief les modes de coordination v (C=C). Les bandes fonda-
mentales M-C-O ont été attribuées à certaines régions de
fréquence tandis.que les modes V (M-oléfine) ont été attribuées
spécifiquement. Le ligand norbornadiéne semble ne pas changer
de stéréochimie lorsqu'il est coordonné.
Un attribution vibrationnelle limitée est suggérée pour les
spectres i.r. et Raman de [(COD)RhClJ 2 , [(COD)CuClJ 2 et
(COD)2CUCl04' Pour ce dernier composé, une nouvelle structure,
se basant sur les données spectrales à notre disposition, est
proposée.
La premiére attribution vibrationnelle des complexes
thiocarbonyles a été effectuée pour le CpMn (CO) 2CS et le
CpMn (CO) (CS) 2 . Les vibrations de valence et de déformation
du Mn-C-S apparaissent dans des régions similaires et avec des
intensités comparables aux vibrations fondamentales analogues
du Mn--C-O. Pour expliquer la diminution dans la symétrie des
deux composés Cp-Mn et Mn(CO)2CS en solution, on a postulé la
présence d'une "lente" rotation du cycle.
....
VIBR1\TION2\L SPECTRZI. OF SOHE
'l'Ri\..l\JSI'l'ION rrLETl'.L
O~(Gp.~'W:mThLLIC C0l-1PLEXES
Gabriel George Barna
.!-\. 'l'~1e3is Sllbmi t tcd to the FacuL:y cf
Graduate Studies and Research at
McGill University in Partial Fulfillment
of the Requirements for the
Degree of Doctor of Philosophy
Fro~ the Inorgru1ic Chemistry Laboratory
under the Supervision of
Dr. :;:.8. Butler
~lcGill University,
Montreal, Quebec.
@ Gabriel George Barna
----- - -------.
1973
"------ --
Septernber 1972
Î
To My Parents
TABLE OF CONTENTS
ACKNOHLEDGENENTS
LIST OF ABBREVIATIONS
LIST OF TABLES
LIST OF ILLUSTRATIONS
PART l
METAL CARBONYL-NITROSYL COMPLEXES
CHAPTER 1. INTRODUCTION
CHAPTER 2. LOt-J FREQUENCY VIBRATIONAL ASSIGN.1'-lENTS FOR
METAL NITROSYL CO!-1PLEXES
A. METlI-.L CARBONYL-NITROSYL COl-1POUNDS
B. OTHER METAL NITROSYL COMPLEXES
CHAPTER 3. NIT ROSYLTETRACARBONYIJ.1ANGANESE (0)
A. INTRODUCTION
B. EXPERIMENTAL
1. Vibrational Spectra
2. !-1ass Spectra
C. RESULTS AND DISCUSSION
1. Vibrational Assignments
PAGE
v
vi
vii
x
1
3
3
5
Il
Il
13
13
15
16
20
a. c-o and N-O Stretching Vibrations 20
b. Low Frequency Vibrations (700-
350 -1 cm ) 34
c. Low Frequency Vibrations Below
150 cm -1 29
i
2. Force Constant Calculations
3. Mass Spectroscopie Investigation
D. CONCLUSION
CHAPTER 4. DINI'I'ROSYLDICARBONYLIRON(O) AND SŒ-1E
DE RIVA'l'IVES
A. INTRODUCTION
B. EXPERIMENTAL
1. Syntheses
2. Vibrational Spectra
C. RESULTS fu~D DISCUSSION
D. CONCLUSION
PART II
SELECTED CYCLIC DIENE CŒ\1PLEXES OF
CHROHIUH, HOLYBDENUM, 'l'iJNGSTEN, IRON A.~D COPPER
PAGE
43
44
49
52
52
53
53
55
57
69
CHAPTER 1. INTRODUCTION 73
CH]I.PTER 2. REVIEiil OF VIBRATIONAL ASSIGNHENTS FOR METAL-
OLEFIN COMPLEXES 75
CHAPTER 3. TETRACARBONYL1.~ORBORNADIENEMETF_L (0) COHPLEXES 82
A. INTRODUCTION 82
B. EXPERH1ENTAI ..
C. RESULTS AND DISCUSSION
1. Norbornadiene
2. Vibrational Assignrnents of Norbornadiene
83
84
84
Complexes 90
ii
a. C-O Stretching Vibrations
b. C=C Stretching Vibrations
c. Low Frequency Vibrations
PAGE
102
104
109
3. Geometry of Free and Complexed Ligand 113
D. CONCLUSION
CHAPTER 4. 1,5 -CYCLOOCTADIENE CO,l\1PLEXES
A. INTRODUCTION
B. EXPERHillNTAL
C. RESULTS AND DISCUSSION
1. l, 5'-Cyclooctadiene
2. Vibrational l.ssignments for [( COD) RhCl] 2
and [ (COD) CuCl] 2
a. C=C Stretching Vibrations
b. H-Cl Stretching Fundamentals
c. M-L Stretching Vibrations
116
117
117
118
119
119
125
134
135
136
3. Vibrational Assignments for (COD)2CuCI04 137
D. CONCLUSION
PART III
7T-CYCLOPENTADIENYL!·1ANGANESE (I) THIOCARBONYLS,
CpMn(CO)2CS AND CpMn(CO) (CS)2
CHAPTER 1. INTRODUCTION
CHAPTER 2. EXPERH1ENTAL
CHAPTER 3. RESULTS AND DISCUSSION
A. RING VIBRA~IONS
B. Nn-C-O AND !-1n-C-S VIBRATIONS
iii
148
149
151
153
153
172
CHAPTER 4. CONCLUSION
BIBLIOGRAPHY
CONTRIBUTIONS TO KNŒ'iTLEDGE
ERRATA
iv
PAGE
182
183
192
194
AC1:N0l-1LEDGEI'lENTS
The author \'iishes to thank Dr. 1. S. Butler for his guidance
and encouragement, the latter being especially invaluable in
times of seemingly overwhelming crisis. His I,varm friendship
made the author's sojourn at I-lcGill most pleasant and rewarding.
The following are thanked for their specifie contributions
to this work:
Mr. W.A. Budd for the mass spectra,
Mr. A.E. Fenster for the componnds CpMn(CO) 2CS and
CpIvln ( CO) (CS) 2 '
Mr. R.J. Gale for the synthesis of (COD)2CuCI04'
t-1iss. D.A. Johansson for the (NBD) M(CO) 4 complexes.
The author is thankful to his wife, Betty, for her limitless
patience and perseverance in the typing of this thesis and the
arranging of the Figures.
The author reco9nizes the benefits he derived from tha
occasionally relevant, but perpetually stimulating discussions
with the other members of the laboratory.
The National Research Council of Canada is thanked for the
award of a Bursary and a Scholarship.
v
LIST OF ABBREVIATIONS
Spectral
\'1 - weak
lU - medium
s - strong
v - very
p - totally p01arized
p - polarized
dp - depolarized
p - depolarization ratio
m'i-v - millülatt
nm - nanometer
eV - electron volt
v - stretching mode
ë - bending mode
Chemical
HCBD - hexachlorobutadiene
COD - I,S-cyclooctadiene
NBD - norbornadiene
COT - 1,3,5,7-cyclooctatetra.ene
Cp - cyclopentadienyl
vi
J
LIST OF 'J'ABLES
T/I.BLE PART l PAGE
1. STRETCHING P.ND BEN DING FUNDAMENTJ\L FREQUENCIES OF
TRANSITION HETAL NITROSYL COtvlPLEXES (cm -1) • 8
II. DISTRIBUTION OF NORIl.t.AL 1-i0DES FOR l'ln (CO) 4~W 20
III. SYMHETRIES OF THE FUNDMlliNTAL MODES OF Mn (CO) 4NO
IV.
V.
(C3v
SYMHETRY) •
OBSERVED INFRARED ABSORPTIONS OF !lin (CO) 4NO
TEr1PERATURE STUDY IN THE v (C-O) AND v (N-O)
FUNDAf'.1.ENTAL REGIONS (cm -1) •
-1 (cm ).
VI. EXPECTED Fl~D OBSERVED OVERTONE Ai'\ID CŒIBINA'l'ION
FREQUENCIES OF Mn(CO)4NO IN THE 5250-3500 cm- l
22
23
32
REGION (CC14
SOLU'rION) • 33
VII. EFFECT OF SOLVENTS ON THE FREQUENCY OF v5
, THE al
Mn-N STHETCHING FUNDA!llENTAL (cm -1) • 36
VIII. CO!l'lPARISON OF THE FUNDAHENTAL FREQUENCIES OF -1
Hn (CO) 4NO J..ND Fe (CO) 5 VAPOURS (cm ). 40
IX. OBSERVED I~D CALCULATED v(C-O) FUND/ll1ENTALS (cm- l ). 43
X. C-O FORCE CONSTANTS OF CARBONYL-NITROSYL CŒ1PLEXES o
(mdyn/A) • 44
XI. ORDER OF DECREASING AB UN DAN CE OF Mn (CO) 4NO
FFAGMENTS
XII. FREQUENCY SHIFTS OF THE Fm~DAMENTAL MODES OF THE
Fe(NO)2(CO)L COMPLEXES (cm- l ).
XIII. VIBRF.TIONAL SPECTfu"\ OF THE PPh3
DERIVATI\I"ES OF -1
Fe(CO)2(NO)2 (cm ).
vii
45
62
63
TABLE
XIV.
XV.
INFRARED FREQUENCIES OF THE P(OMe) 3 DERIVATIVES
OF Fe (CO) 2 (NO) 2 (cm -1) .
-1 FUNDAHENTAL FREQUENCIES OF Fe(CO)2{NO)2 (cm ).
PART II
PAGE
66
70
XVI. ASSIGNED v(C=C) FUNDAHENTALS OF ETHYLENE COHPLEXES
(cm -1) • 76
XVII. SHIFT IN BANDS RELATED TO v(C=C) VIBRATIONS 78
XVIII. lI.8SIGNED FUNDAMENT1...LS OF f.lETlI.L-CYCLOOCTADIENE
SYSTEMS (cm-l ). BO
XIX. ASSIGNED FUNDAHEN'l'ALS OF VARIOUS HETAL-OLEFIN
COMPLEXES (cm- l ). 81
XX. VIBRATIONAL FREQUENCIES OF NORBORNADIENE (cm- l ). 88
XXI. INFRARED FREQUENCIES OF THE (NBD)M(CO)4 COMPLEXES
(cm-l ) . 95
XXII. -1
RlI.MA.N FREQUENCIES OF THE (NBDHl( CO) 4 COHPLEXES (cm ). 98
XXIII . SYH~,ETRIES OF THE FUNDAHENTAL I-IODES OF THE
(NBD)M(CO)4 COMPLEXES. 102
XXIV. FREQUENCIES RELEVANT TO THE FERMI PESONANCE
CALCULATIONS (cm-1 ). 108
XXV. ASSIGNMENT OF FUNDAMENTlI.L .MODES OF THE (NBD) N(CO) 4
COMPLEXES (cm- l ). 112
XXVI. MOLECULAR PAR1J-1ETERS FOR BONDED .P-.ND NONBONDED NBD. 114
XXVII. -1
VIBRATIONAL FREQUENCIES OF 1,5-CYCLOOCTADIENE (cm ). 121
XXVIII. DISTRIBUTION OF NOrurlAL MODES OF COD.
XXIX. SY~~ETRY AND ACTIVITY OF THE [(COD)RhCl]2 and
[ (COD) Cuel] 2 FUNDAHEN'rl'.LS.
viii
124
127
Tl\BLE PAGE
XXX. VIBRATIONAL FREQUENCIES OF [{COD)RhCl]2 AND -1
[(COD) CuCl] 2 (cm ). 131
XXXI. VIBRKfIONAL FREQUENCIES AND ASSIGN~œNT OF -1
(COD)2CuCI04 (cm ). 140
XXXII. NUMBER OF VIBRATIONAL MODES FOR 'l'IlE POSSIBLE
STRUCTURES OF (COD)2Cu(I) ION. 144
XXXIII. CORRELATION DIAGRk~ FOR THE Td h~D C3v PERCHLOP~TE IONS. 146
XXXIV. ASSIGNED FUNDl'J1ENTAL HODES (cm -1) OF [( COD) RhC1] 2
A..~ D [( COD) CuCl] 2 • 147
PART III
XXXV. SPECTRAL PREDICTIONS FOR CpNn(CO) 2CS. 154
XXXVI. INFRARED FREQUENCIES .Po.ND ASSIGNI1E~Jl'S FOR -1
[CpFe(CO) 3]BPh 4 AND [CpFe(CO) 2CS]BPh'1 (cm -) • 155
XXXVII. SOLID STATE IKFRARED AND RAI".J',N DA'l',,; (cm -1) AND
ASSIGNHENTS FOR CpMn(CO)2CS Jl..ND Cp?-ln(CO) (CS)2. 161
XXXVIII. INFRARED DATA AND COMPLETE VIBRATIONAL ASSIGNNENT
XXXIX.
XL.
XLI.
XLII.
FOR CpHn(CO)2CS IN SOLUTION.
CONPARISON OF THE RING VIBRATIONS (cm -1) OF
Cp!1n (CO) 3 A~D ITS THIOCARBONYL DERIVATIVES.
-1 COMPARISON OF \) (C-O) vJITH \)2 A..l\JD \)7 (cm ).
CORRELATION BETWEEN Mn (CO) 3 AND ITS CS
DERIVATIVES
VIBRATIONAL FREQUENCIES AND ;....sSIGNr-1EtYfS FOR -1
SOLID CpNn(CO) 3 (cm ).
XLIII. EFFECT OF SOINENTS ON SO~1E OF THE FUNDAHEN'TAL
-' MODES OF Cpr-1n(CO)2 CS (cm .L.).
ix
164
168
170
174
175
181
LIST OF ILLUSTRATIONS
FIGURE PART l
1. Possible trigonal bipyramidal structures for
Mn(CO)4NO •
PAGE
12
2. Polarization orientations in the spectrophotometer. 15
3. Infrared spectrum of Mn (CO) 4NO vapour (8 m.~ Hg) • 18
4. Infrared spectrum of ~~(CO)4NO (CS 2 solution). 18
5. Far-infrared spectrum of Mn(CO)4NO (benzene
solution) •
6. Infrared spectrum of Mn(CO)4NO illustrating the
3000-2200 and 1500-700 cm- l overtone and
combination regions (CS2
solution) •
7.
8.
Overton'e and combination spectrum of Mn (CO) 4NO
in the 5250-3800 cm- l region (CC14
solution).
Infrared spectrum of Mn(CO)4NO in the c-o and
N-O stretching regions (cyclohexane solution) .
9. c-o stretching modes for r-In (CO) 4~W (C3v symmetry) i
only one component of the doubly degenerate e mode
shown.
10.
Il.
12.
13.
Approximate description of the normal modes of
Fe(CO) 5 and Mn(CO)4NO.
+ Clastograms for three fragments of the Ivln (CO) 4NO
ion.
Plot of abundance vs. electron energy(eV) for
CS2
+ and Mn(CO)4NO+.
Infrared spectrum of Fe(CO)2(NO)2 (CS 2 solution).
14. Far-infrared spectrum of Fe(CO)2(NO)2 (benzene
solution) .•
x
18
21
21
21
30
37
48
50
59
59
FIGURE
15.
16.
Raman spectrum of Fe(CO)2(NO)2 (CS 2 and CC1 4 solutions) .
Solid state Raman spectrum of Fe(CO) (NO)2PPh3'
17. Infrared spectrum of Fe(NO)2[P(OMe) 3]2 (neat
liquide
PART II
18. Possible metal-olefin bonding schemes.
19. Infrared spectrum of norbornadiene (neat
liquid) .
20. Raman spectrum of norbornadiene (-196°C).
21. Infrared spectrum of (NBD)Cr(CO)4 (CS 2 and
C2 C1 4 solutions) •
22.
23.
24.
25.
26.
27.
28.
29.
30.
Raman spectrum of (NBD)Cr(CO)4 (solid state).
Infrared spectrum of (NBD)MO(CO)4 (CS 2 and
C2C1 4 solutions) •
Raman spect~um of (NBD)Mo(CO)4 (solid state).
Infrared spectrum of (NBD)lV(CO) 4 (Nujol and
HCBD mulls) •
Raman spectrum of (NBD)W(CO)4 (solid state).
Bar-graph representations of the (NBD)M(CO)4
infrared spectra. (M = Cr,Mo,W)
Bar-graph representations of the (NBD)M(CO)4
Raman spectra. (M = Cr,Mo,W)
Probable structure of the (NBD)H(CO)4 complexes.
Vapour phase structure of .norbornadiene.
31. Infrared ·spectrum of 1,5-cyclocctadiene (neat:
liquid) .
xi
",
PAGE
60
61
61
79
86
86
91
91
92
92
93
93
94
94
101
113
120
FIGURE
32. Raman spectrum of 1,5·-cyclooctadiene (-196°C)
33. Molecular structures for [(COD)RhCl]2 and
[ (COD) CuCl] 2 .
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
Infrared spectrum of [(COD)RhCl]2 (Nujol and
HCBD mulls) .
Raman spectrum of [(COD)PbCl]2 (solid state).
Infrared spectrum of [(COD)CuCl]2 (KBr pellet).
Raman spectrum of [(COD)CuCl]2 (solid state).
Bar-graph representations of the infrared spectra
of COD and its complexes.
Bar-graph representations of the Raman spectra of
COD and its complexes.
Infrared spectrum of (COD)2CUC104 (KBr pellet).
Raman spectrum of (COD)CuCl04 (solid state).
+ Five possible structures for the (COD)2Cu ion.
Postulated structure for (COD)2CuCI04.
PART III
Infr'ared spectrum of Cp Mn (CO) 2CS (vapour phase) •
Infrared spectrum of CpMn(CO)2CS (CS 2 solution).
46. Far-infrared spectrum of Cpr-1n (CO) 2 CS (benz~ne
solution) •
47.
48.
49.
Raman spectrum of CpMn(CO)2CS (solid state).
Infrared spectrum of CpMn(CO) (CS)2 (solid state).
Raman spectrum of CpMn(CO) (CS)2 (solid state).
xii
"
PAGE
120
126
128
128
129
129
130
130
139
139
143
145
158
158
158
158
159
159
'-
FIGURE PAGE
50. Bar-graph representations of the infrared
spectra of CpMn(CO) 3 and its CS derivatives.
51. Bar-graph representations of the Ra~an spectra
of Cp Mn (CO) 3 and its CS derivatives.
xiii
160
160
PART l
~ŒTAL CAill10NYL-NITROSYL COMPLEXES
- l -
CHAPTER J. INTRODUCTION
At the beginning of the research to be described in this
part of the thesis, several revie"ls on the physical and chemical
properties of transition metal nitrosyl complexes had already
1-4 been published . In the sections dealing \-Ji th the vibrational
spectra of these complexes, reference was frequently made to
the lack of Raman data. Although vibrational assignments can,
and have, been made solely on the basis of i.r. data, it was
pointed out that the current ava.ilability of commercial laser
Raman spectrophotometers would stimulate research into more
complete vibrational studies of these systems.
In the present work, i t ",as planned to carry out Raman
studies on a variety of transition rnetal ni trosyl cOTI!plexes.
The new spectral evidence so obtained would then be used to
confirm or reject sorne of the previous assignments that had
been made purely on the basis of i.r. data. It was also hoped
to extend the vibrational assignments of sorne simple metal
carbonyl-nitrosyl complexes of the type, M(CO)x(NO)y. Previously,
only Fe(CO)2(NO)2 5 and CO(CO)3N06-a had received any significant
attention.
Vibrational assignments have been proposed for a variety
of transition metal carbonyl complexes by a nurrber of independent
research groups. From these assignments, certain trends in the
low frequency modes have become apparent. Firstly, the rnetal
carbon'yl bending modes (8 (M-C-O)] generally occur at higher
9 '0 frequencies than the metal-carbon stretching modes [v(H-C)]- , .....
2
Second, the former modes are more intense in the i.r. while
the latter are more intense in the Raman. One aim of the
present study \vas to ascertain if there are sirnilar trends for
the low frequency modes of metal nitrosyls.
Before the results of the author 's own work on the spectra
of metal nitrosyl complexes are presented, the published
vibrational assignments for metal nitrosyl cornpounds are
reviewed briefly (Chapter 2). Next, the complete vibrational
assignment of Mn(CO)4NO, together with details of a force
constant calculation and a rnass spectroscopie investigation,
are given in Chapter 3. Finally, spectroscopie data for
Fe(CO)2(NO)2 and sorne of its derivatives are presented and
discussed in Chapter 4.
- 3 -
CHAPrrER 2. L01'J FREQUENCY VIBRl\TIŒJAL ASSICNr-1ENTS FOR
HETAL NITROSYL CŒ-IPLEXES
This revievl is divided into blO sections: metal carbonyl
nitrosyls and metal nitrosyl complexes containing ligands other
than CO. The approach \vill be an historical one. The review
is considered to be complete until June l, 1972. The proposed
vibrational assignments for the low frequency region (below
700 cm-l) are tabulated at the end of this review. The very
low frequency modes (in the 150-50 cm-l region) of the type
o (C-M-N) are not considered, owing to the scarcity of assignments in this region ..
A. METAL CJl.RBONYL-NITROSYL COMPOUNDS
The first complete vibrational assignment for any metal
nitrosyl complex was reported by MeDowell gt aZ. (MHy)6 in
1961. These workers investigated the i.r. spectrum of CO(CO)3NO in the vapour phase. Together with additional data from isotopie substitution (13 CO and 15NO) and supported by the vibrational
assignments for Ni (CO) 4' the follovTing results were obtained. The stretching fundamental, v (Co-N) , was assigned to the band at "594 cm-l, higher than -the bending mode, o(Co-N-O) ëit 565 cm- l
However, the normal coordinate calculation performed by the
vlilson FG method showed a marked diserepancy betvleen the
caleulated and observed values for these biO modes. Moreover,
the potential energy distribution indieated that the v(Co-N)
and the 0 (Co-C-O), as vlell as the 0 (Co-N-O) and v (Co-C)
- 4 -
fundamentals, are considcrably mixed.
The i. r. and Raman spectra of liquid Co (CO) 3NO were
investigated by Mann et aZ. 7 in 1967. On the basis of
admittedly indefinite depolarization ratios, the v(Co-N) mode
was reassigned to a medium intensity Raman band at 627 cm- l
A force constant calculation again shm'led considerable mixing
between the 6 (Co-N-O) and 6 (Co-C-O) modes.
The compound was also studied in the solid state by
Cataliotti et al. 8 in 1971. 'l'he i.r. active fundamentals were
assigned taking into account the observed solid state correlation
spli t·tings of the bands. In this s tudy, th C 0: 1 \) (Co-N)
-1 fundamental was assigned to a band at 612 cm , i. e. in agree-
-1 ment with the original vapour phase value of 594 c~ of MHY.
This assignment is not really inconsistcnt ,vi th the Raman data
of Mann because in Raman spectra al modes are generally found
to be the most intense. On this basis, i·c could have been
anticipated that the strong Raman band at 603 cm- l (594 cm- l in
the vapour) is indeed the a, ·v (Co-N) mode.
From the spectroscopie data of the three independent
research groups, it can be concluded that for the vapour phase
-1 v(Co-N) is at 594 cm ,while 6 (Co-N-O) is lower in energy at
565 -1 cm Furthermore, the intensity of the ô mode is more than
ten times grèater than that of the v mode.
The vibration al spectrum of the C2 carbonvl-nitrosvl v . -
complex, Fe(CO)2(NO)2' \'las assigned5 in 1968. For this species,
the al and b l v (Fe-N) modes ,';ere assigned to the vapour phase
bands at 619 and 658 cm- l respectively; ~ .. lhile the al' li l and b 2
- 5 -
6 (Fe-N-O) modes \Vere assigned to bands at 654, 648 and 614 cm-1
respectively. These assignments were based on i.r. data and
were supported by a complete force constant calculation. The
relative intensities of the absorptions due to the two types of
mode are again markedly different. Both the syrnmetric and
asyrnmetric stretching modes appear as \veak shoulders on the
sides of the very strong peaks assigned to the bending
fundamenta1s.
The on1y other carbony1-nitrosyl mo1ecu1e that has been
investigated is Na [Fe (CO) 3NO} 11. The s tretching mode l ',) (Fe-N) ,
was assigned te the band at 664 cm-1 in the solid state, at a
higher frequency than the ô (Fe-N-O) mode at 630 cm-1 . Both
these modes occur at a higher frequency ·than the corresponding
fundamentals of the isoe1ectronic molecule, CO(CO)3NO. Of course,
this is related to the effect of the negative charge on aIl of
the modes of this anionic species - the extra e1ectron enhancing
the Fe-N and Fe-C bond orders. A force constant ca1culation
yie1ded a' good fit between the observed and calculated values
for these modes. As in the previous cases, the stretching mode
appears as a very weak shou1der on the side of a very strong
bending fundarnenta1.
The data discussed in this section are summarized in Table I.
B. OTHER METAL NITROSYL COMPLEXES
12 In 1963, Fe1tham and Fate1ey assigned the fundamentals
of CpNiNO by ana10gy wi th those of Co (CO) 3NO. Thus, the H-N-O
- 6 -
-1 fundamentals \'Vere assigned as follows: v(Ni-N) 640 cm
6 (Ni-N-O) 570 cm-l. Raman data13 later eonfirmed that the
stretching fundamental \-las at 640 cm -l, while the bending mode
-1 had to be reassigned to a band at 490 cm •
Comprehensive studies have been carried out for a series
of HX5 (NO) complexes. In 1966, the al v (Ru-N) mode of
K2 [RuIS (NO)] was assigned14 to a band at 598 cm -l, while the
e 0 (Ru-N-O) fundamental VoTas assigned to a doublet at 573 and
552 em- l (the splitting caused by solid state effeets). Two
years later, Miki 15 prepared similar eompounds lof chromium and
ruthenium with normal isotopie abundances, and with enriched
l5NO • The· i. r. shifts betv!een the fundamentals of the two speeies
were eompared with those caleulated on two t~eoretieal three-body
models, M-N-O and M-O-N. The models indieated definitely that
the ni trosyl group \-las eoordinated to the mctal atom through
the ni trogen, \-lÏ th the stretehing mode al\vays oeeurring at a
higher frequeney than the bending mode. Prior to this work, the
linkage had been taci tly assumed to be M-N-O in ni trosyl complexes.
The validity of this model was/eonfirmed by applying it to
Co (CO) 3NO. Assuming HHY 1 S assignment of v (Co-N) and 0 (Co-N-O) ,
the calculated isotopie shifts based upon this thre.e-body model
\'Vere found to match elosely the observed isotopie shifts, as well
as the ones caleulated by MHY using the complete nine-body model.
Low frequency'metal nitrosyl fundamentals have also been
assigned 'for a series of [H (CN) 5 (NO) 1 n- complexes, chiefly on
the basis of i.r. data alone. In 1967, polarized icr.
- 7 -
measurements on a single crystal of Na2 [Fe(CN)S(NO)] 02H20, led
, l' 16 to unequlvoca asslgnments . The o(Fe-N-O) and v (Fe-N) modes
-1 were assigned to bands at 662 and 650 c~ , respectivelyo These
assignments are supported by two more recent studies (single
crystal Raman17 and lSNO substitution18). The bending mode
has a calculated and observed lSNO isotopie shift of 16 cm- l
while the shift in the stretching fundamental is only 2
The relative magnitudes of the isotopie shifts of these
-1 cm
f d 1 h b f ' d b h' t' ~ 19 un amenta save een con lrme y yet ot er lnves 19a~ors .
In K3 [Mn(CN) S(NO) ], the bending and stretching fundamentals
20 -1 were found to be accidentally degenerate at 660 cm 0 In the
dihydrate, perturbation spli ts this degeneracy: 6 (I-1n-N-O) is at
-1' -1 663 cm , and v (Mn-N) is at 653 cm 0 This assignment was
contradicted in 1971 by a more thorough study by Miki et aZ. 21
of the compounds K3 [Hn (CN) SNO] , K3 [!-ln (CN) s~JO] 02H 20 and
Ag2 [Mn(CN)SNO]. Using the same three-body calculaticns as
mentioned above lS , the M-N-O arrangement was again favouredo The ,
stretching modes, v (Mn-N) , were assigned at higher frequencies
than the bending modes, 0 (Mn-N-O) 0 In the unhydrated potassium
saI t, the bending and stretching fundamen·tals are accidentally
degenerate at 659 cm-li however, 15NO substitution splits this
degeneracy such that v(~~-N) is at 661 cm-1 and 6(Mn-N-O) is at
648 cm-l. In every case, the assignments were substantiated by
calculationo
AlI the assignments disGussed above are. sUInrnarized in 'l'able 10
Complex
K3 [Cr (CN) 5NO ] .H2 O
[Cr(NII 3 ) 5NO] C1 2
[Cr(NH 3 )5NO ] (CI04 )2
K3 [Mn (CN) 5NO ]
15 K3 [Hn (CN) 5 NO]
K3 [Mn(CNj 5NO ] .2H 2 O
15 K
3[Mn(CN)5 NO].2H 2 O
TABLE I.
STRETCHING AND BENDING FUNDAI-1ENTAL FREQUENCIES
OF TRANSITION METAL NITROSYL COMPLEXES (em- 1 ).
v (M-N) 15 (M-N-O) r-1edium
620 s 610 sh a,b ,e
573 s 535 m a,b,e
577 vw 531 s a,b ,e
659 s 659 s a,b ,e
660 s 660 s a,b,e
661 w 648 s a,b ,e
663 m 663 fi a,b ,e
653 663 a,b ,e
660 w 651 w} a,b ,e 646 m
Study Ref.
IR 15
IR 15
IR 15 00
IR 21
IR 20
IR 21
IR 21
IR 20
IR 21
J
Fe(CO)2 (NO) 2 619 sh(a1 ) 654 s (al) d IR 5
658 sh (b1 ) 648 sh (b1 )
614 s(b2 )
Na [Fe (CO) 3NO] 664 w 630 vs· bic IR Il
Na2 [Fe(CN)SNO] .2H2O 650 m 662 5 e IR 16
657 ms 666s e R 17
652 m 663 m e IR 18
K2
[RuC15
(NO)] 606 w 588 s a ,b ,e IR 15
K2 [RuBr5 (NO) ] 606 'Il 573 s a ,b ,e IR 15
[NEt 4 ] [RuBr5 (NO) ] 609 'Il 573 w a IR 14 '-0
K2 [RUI 5 (NO) ] 598 vw 573 vw} a IR 14 552 w
Co(CO)3NO 594 w 565 vs d IR 6
602 rn 564 s f IR 8
612 rn 568 vs g IR 8
627 m 566 'Il f R 7
CpNiNO 640 m 570 Vvl f IR 12
640 rn 484 m f R 13
640 vs 490 s g R 13
L_ --'
CS 2 [OsC1 5 (NO) ]
Cs 2 (OsBr5 (NO)]
K[IrC1 5 (NO)]
K [IrBr 5 (NO) ]
a Nujol mull
b HCBD mull
C KBr disk d vapour
e single crystal
f l' 'd J.qUl
g frozen solid
h microcrystalline solid
615 vw
612 (7)
617 w
615 (3)
567 ~l
560 (2)
562 w
558 (2)
595 w a
598 (2) h
586 m a
585 (1)' ·h
578 w a
580 w h
550 m a
550 w h
IR
R
IR
R
IR
R
IR
R
19
19
19
19
19
19
19
19
1-' o
j
- Il -
CH~.PTER 3. * NITROSYLTETRJ."\CARBONYU1J..NGJllJESE (0)
A. INTRODUCTION
During the past few years, several transition metal
carbonyl-ni trosyl complexes, isoelectronic vli th binary metal
carbonyls, have been discovered. A vast nunmer of the carbonyl
compounds and their derivatives have been investigated by means
of vibrational spectroscopy. In contrast to this, the spectra
of the carbonyl-nitrosyl complexes - with the exception of
Co (CO) 3NO, Fe (CO) 2 (NO) 2 and Ha [Fe (CO) 3NO] - have recei ved li ttle
attention. In particular, the i.r. spectrum of the five-
coordinate complex, ~ln (CO) 4NO, has been investigated only in
the C-O and N-O stretching regions 23 ,24 On the basis of three
C-O stretching absorptions observed in tetrachloroethylene
solution, a C3v trigonal bipyrarnidal structure, with the NO
group in one of the axial positions (Figure la) , has been
proposed for the complexe
A lm ... temperature (-110°) three-di!l1ensional X-ray study of
Mn(CO)4NO, frozen into its crystalline state, has been reported
25 recently • This study indicates that under these conditions
the most reasonable structure for the complex is a "trigonal
bipyramid wi th C2v rather than C3v symmetry, i. e. , 'id th the
NO group occupying one of the equatorial positions rather than
an axial one (Figure lb) •
* Part of the vlcrk described in this Chapter has already been
published22 .
(a)
o N
C3v
- 12 -
o
(b)
o c
oc;,,_f ,/ Mn ~~~ ~~-~ NO './ ------Cv-------
c o
Figure 1. Possible trigonal bipyramidal structures
for Hn(CO)4NO.
The purpose of the present study ~vas to obtain i. r. an.d
Raman data throughout the whole spectral region and to propose
a complete vibrational assignment for the molecule. In
addition, it was hoped to establish its molecular geometry in
the vapour phase and in solution.
- 13 -
B. EXP:CRHJENTAL
N-t t j'OS !lUe t Y'oc:aY'b oiZy Z manpanes e (0 )_' I-1n (CO) 4 NO, was
prepared and purified by the method of King26 The purity
of the deep red liquid \Vas established by the absence of any
impurity peaks in its mass spectrum and in the c-o and N-O
stretching regions of its solution infrared spectra.
1. Vibrational Spectra
The instrumentation used to record the vibrational
spectra of aZZ the compounds that are considered in this
thesis will be·described here. Solvents, unless otherwise
noted, were a1ways of spectrograde quali ty.
'rhe far-infrared spec·tra were recorded on a Perkin
Elmer FIS-3 spectrophotometer using 1.0 mm polyethylene
solution cells. The spectra were calibrated against the low
frequency spectrum of water vapour; the frequencies are
-1 precise to ±4 cm
Infrared spectra in the 4000-350 -1
cm region \'lere
recorded on a Perkin Elmer 521 spectrophotometer using the
1653.3 and 667.3 cm- l bands of water vapour as calibrations.
-1 '-1 The errors on the frequencies are ±4 cm (4000-2000 cm
region) and ±2 cm-1 (2000-350 cm-l region). The C-O ~~d
N-O stretching ::cegions were aiso recorded on a Perkin Elmer
337 spectrophotometer coupled to a Texas Instruments Servo-
Ri ter N.odel II expansion scale recorder. These spectra \vere
- 14 -
calibrated against the 2143.2 cn- l band of CO and the 1583.1 -1 cm
band of polystyrene i the observed frequencies are precise to
-1 ±l cm • A matched pair of 1.0 mm KBr solution cells were used
for all the spectra. The vapour spec·trum \Vas obtained using
a 10 cm gas cell, fi tted wi th KBr \',indŒvs.
The 5250-3800 cm- l region was recorded on a Perkin Elmer
350 spectrophotometer using 10 cm pyrex solution cells. The
4288.3 cm-l band of CO \Vas useCi to calibrate the spectrai the
precision of the frequencies is ±5 cm- l •
Raman spectra were obtained on a Jarrell-Ash Model 25-300
laser Raman spectrophoton.eter, equipped with a Coherent Radiation
krypton ion laser. Although the laser erni ts eight exciting lines,
only the 647.1 nm (red) and 520.8 nm (green) ones were used. The
maximum effective power of t.hese lines at t.he sample was about
100 and 50 rntJ, respectively. The plane of the incident beam was
always perpendicular to the plane of the slit. The polarization
of the incident and scattered beams are diagrammed in Figure 2.
The IIparallelll and "perpendicularll planes used for the depolar-
ization measurements are also shown in the Figure. To nullify
any orientational anisotropy in the rnonochromator~ depolarization
measurements were always obtained with a polarization scrarnbler
placed directly before the slit. The peaks were calibrated
against the 730.1 and 533.7 cm- l peaks of indene. Sar.lples were
rUl1 either as solutions in a quartz solution cell or as powdered
solids in capilla~J tubes.
.- 15 -
l Il
b
s
Figure 2. Polarization orientations in the spectrophotometer.
a - polarization of incident beam
b - plane of slit
i - incident beam
s - scattered beam
S - sample
l - plane of polarization for "perpendicular"
measurements
- plane of polarization for "parallel" measurements
2. M.ass Spectra
Mass spectra were obtained on an AEI MS902 mass
spectrometer. Samples ~lere generally run at a nominal energ-j
of 70 eV.
For the ionization potential (IP) determination, a
special procedure ~las employed. The voltage across the source
was monitored by means of a DANA Module 550 digital voltmeter.
Since this voltmeter was floating on 8000 volts, it was
insulated careiully to prevent it from grounding. The
'--'
- 16 -
vol t.meter \-ïas pmvered by a 12 V oc battery connected to a CDE
Powercon Model 12B8 AC generator.
The clast.ograms were obtained as follows. The compound
vias vapourized into a large bulb connected to the ionization
chamber through the cold inlet system. The amount of compound
leaking into the source was constant throughout the experi~ent.
The spectrometer was focused onto a given mie peak. As the
voltage across the source was varied, the nu~er of ions
arri ving at the analyser was read étirectly off the "Collector"
scale on the instrument. At given intervals, the voltage was
reset to sorne specific value to check the reproducibility of
numbers read off the IICollector". By this method, the nurnbers
were found to be reproducible (± 10%). Since the "Multiplier"
setting was kept constant, the relative abundances of the
different fragments are on the same scale.
C. RESULTS AND DISCUSSION
~ving to the extreme air and light sensitivity and poor
scattering properties of the complex, aIl attempts to obtain
vapour phase, solution· or solid state laser Raman spectra
using the 647.1 nm krypton excitation, failed. Even when
frozen onto an evacuated cOld-finger at -196°, the compound
decomposed rapidly. However, despite the lack of Raman data,
vibrational and structural assignrncnts could be achieved for
this species.
The cow.mon structures for a five-coordinate molecule are
- 17 -
a square pyramid or a trigonal bipyramicl. The former can be
* eliminated on the basis of group theoretical arguments. The
latter is generally found in five-coordinate complexes. More-
over, the isoelectronic species, Fe(CO)S' has this configuration.
Two trigonal bipyramidal structures are possible for
Hn(CO) 4NO. The ~~O group can be axially or equatorially situated
giving rise to C3v and C2v molecular sYl®letries, respectively.
The twenty-seven normal modes, for both of these geometries, are
tabulatedaccording to their vibrational activities in Table II.
These fllildamentals are expected to appear in three spectral
regions:
(i) ·2150-1700 cm-l : v (C-O) and v (N-O)
(ii) 750-350 cm -1: v (!l'm-C) and \) (Mn-N)
o (1fu-C-O) and 0 (Mn-N-O)
(iii) below 150 cm- l c-r·ln-C and C-r.'In-N deformations
In addition to these fundamentals, è. number of overtone and
combination bands are expected, particularly in the 5250-2200
and 1400-700 cm- l regions.
The vapour phase and CS 2 solution i.r. spectra of Mn(CO)4NO
in the 4000-350 -1 region shm-m in Figures 3 and 4,. cm are
respectively. The far-infrared spectrum (400-33 -1 c~ ) in
benzene solution is sho\'1n in Figure 5. These spectra are in
* For C4v symmetry (apical NO group): 6al
(IR/R) + a 2 (inact.)
+ 4b l (R) + 2b2
(R} + 7e(IR/R). For Cs symmetry (eql1atorial NO
group): 17 a' (IR/R) + 10a 1/ (IR/R) •
- 18 -
(A) Figure 3. Infrared spectrum of Nn(CO)4HO vapour (8 mm Hg).
(B) Figure 4. Infrared spectrum of Mn(CO)4NO (CS 2 solution).
(C) Figure 5. Far-infrared spectrum of MnCCO)4NO (benzene
solution) •
J
r (A)
! i 1
j 1
L_
--~-_._~
(--.-
~-~ r~ -'--
1
1
1
r~
3~';'1l!"~~:----_. ___ .1 § <:
(B)
3:JNV lllWSN't/èil
(C)
o o ~
o o C\J
o o CV)
- 19 -
accord \vi th the general predictions made ab ove . Furthermore,
i t is readily apparent that the vapour phase and CS2
solution
spectra are remarkably simple and almost identical. A band
-1 count over the entire 4000-33 cm region yields about fifteen
bands which most probably can be regarded as fundamentals. In
view of this, the C3v structure is favoured for !-1n (CO) 4NO both
* in the vapour and in solution. It seems somewhat unlikely that
nine of the fundamentals expected for the C2v structure would be
too weak to be observed or accidentally coincident with other
fundamentals. In addition, almost aIl the i.r. active
fundamentals expected for the carbonyl-nitrosyls, CO(CO)3N07 and
5 Fe(CO)2(NO)2 ' are observ~ble directly. Presumably, crystal
packing forces are responsible for !J'm(CO) 41'W adopting the C2v
structure in the solid state.
Based on a C3v molecular geometrj, the symmetries of aIl
the fundamentals are collected together in Table III.
The observed frequencies for the vapour phase and solution
* Rapid intramolecular isomerization Ylithin this geometry, of 27 the type established by Udovich and Clark for the compounds
Mn (NO) (CO)4_x(PF3)x' has not been observed. For these PF3 derivatives, as \vell as some solvolysis products, the conclusion
that isomerization was occurring was based on the e:{Cess number
of v (C-O) and v (N-O) bands. No snch res'..ll t was observed for
~1n (CO) 4NO. It shoulà be noted that \"lhile this above mentioned
isomerization \"las developed for a model Ylith an equatorial NO
group·, the results can be explained as well, and for sorne cases
better, using a rnodel with an axial NO group.
Ho1ecu1ar Synunetry
- 20 _.
TABLE II.
DISTRIBUTION OF NORNAL HODES
FOR Hn (CO) 4NO
Symmetry of normal modes and their spectral activity
10al(IR/R) + 3a2 (R)
+ 7b l (IR/R) + 7b 2 (IR/R)
8a l (IR/R) + a2
(R)
+ ge (IR/R)
No. of i.r. active modes
24
17
i.r. spectra of ~~(CO)4NO, together with the assignments
proposed on the basis of C3v synunetry, are given in Table IV.
Typical spectra illustrating the various overtone and combination
regions are shown in Figures 6 and 7.
1. Vibrational Assignrnents
a. c-o and N-O Stretching Vibrations
Four i.r. active fundamentals [C-O stretching (2a1 + e)
and N-O stretching (al)] are expected for Hn(CO)4NO in the
-1 2200-1700 cm region. The i.r. spectrllm in cyclohexane
solution for this region is shm,m in Figure 8.
- 21 -
(A) Figure 6. Infrared spectrun of ~n(CO)4NO illustrating the
3000-2200 anQ 1500-700 crn- l overtone and
cornbination regions (CS 2 solution) .
(B) Figure 7. Overtone and combination spectrurn of Mn(CO)4NO
in the 5250-3800 crn- l region (CC1 4 solution).
(C) Figure 8. Infrared spectrurn of Mn(CO)4NO in the c-o and
N-O stretching regions (cyclchexane solution) .
-----=~-]
1 Lg I~
r ~o
o 'E
lis ____ ilr~
(A)
() o ,n
'"
5000 4500 4000 3800 cm-1 1
CB)
w u z <i tt--2 V)
z <t: 0:: t-
( C)
- 22 -
TABLE III.
SYNMETRIES OF THE r"UNI?PJ;iENTAL HODES
OF Mn (CO) 4NO (C3v SYMi'lETRY)
Fundamenta1 Symmetry No. i. r. bands
v (C-Q) 2a1 + e 3
v (N-O) al 1
v (lo·L'1. - C) 2a1 + e 3
v (Mn-N) . al 1
o (Hn-C,""O) al + a2 + 2e 3
o (Mn-N-O) e 1
o (C-Mn-C) 2e 2
o (C-r1n-N) al + 2e 3
-1 . The very strong band at 1766 cm ~s clearly due to v3 ,
the al N-O stretching mode. The weak band at 1730 cm-1 is
most probab1y the 15NO isotope band resulting from
15 . Mn(CO)4( NO), present in natura1 abundance (0.4%). The 15N_O
stretching vibration in Co (CO) 3 (15NO) is shifted dO\lm simi1ar1y
by 36 cm-1 from the 14N_O stretching vibration in CO(CO)3(14NO)6.
The position of the v(N-O) frequency indicates that it is a
Vapour (8nun Hg)
3546 w
c CS 2 soln.
3977 w
3942 vw
3861 v\'/
3503 m
TABLE IV.
OBSERVED INFRARED ABSORPTIONS
OF Mn(CO)4NO (cm-1 )a,b
CC1 4 soln.
5230 '.!w
4183 m
4103 s
4068 s
4026 m
3979 s
3943 w,sh
3864 w
3780 Vw
3715 vw
3503 vs
Cy c10hexane soln.
Assignment
3v3
2v1
N
vI + v 10 LoJ
v 1 + \12
2v10
\1 2 + v 10
2 \.1 2
v 1 + v 3
v 3 + v10
v 2 + v 3
2v3
j
2763 W 2761 W vI + vII
2747 W 2744 W vI + v 12
2679 w,sh v 10 + vII
2666 w 2666 w v 10 + 'J 12
2639 w 2631 w v 4 + v 10 ' v 2 + vIl
2609 vw 2602 vw vI + vS' v 2 + v 4
2566 vw 2560 ID 2558 ID vI + v 13
2522 V\v 2520 vw vI + v 14
2487 w 2477 fi 2476 ID v 10 + 'V 13
2444 w,br 2425 5 2426 5 V3 + VII
2400 vw,sh 2401 vw,sh v2 + v14 ' l'V v 3 + v 12 ,t>.
2372 'l-l,sh 2374 vw,sh v 2 + v6 ' v 7 + v IO '
v 3 + \'4
2325 vw,sh 2333 v\'/ ')2 + v 7
2310 vw,sh v 3 + vII - vIS'
v3 + vII - v16
2288 ID 2289 ID v3 + Vs
2206 vw 2202 ID v 3 + v13
2132 T,lW VI + V17 ' vI + v18
.J
21.16 vw,sh
2111 s 2098 s 2094 s
2092 sh 2087 sh 2082 sh
2020 vs. 2027 vs 2021 vs
1996 vs 1990 vs 1974 vs
1970 sh
196:; m 1946 sh 1945 w
1900 vvw
1870 vvw 1865 sh 1865 sh
1836 vw
1781 vs 1761 vs 1757 vs
1749 w,sh 1728 sh 1732 sh
1490 ID
J.445 sh 1450 w
2099 s
2088 sh
2058 vw
2023 vs
2018 sh
1982 vs
1947 w
1869 w
1766 vs
1730 w
v 10 + v 15 ' v3 + v 7 '
v 10 + v 16
vI
v(13C- O)
v2 + v 8
v10
vI - v 8
v2
vI - vIS' vI - v16 v (13C_O)
v10 - vIS' v 10 - v 16
v 3 + vIS' v3 + v16
v2 - v 8 v 3 v (15N_O)
vI - v 4
vI - v12
t\J U1
j
1420 sh
1365 sh
1356 w 1359 m
1313 vw 1318 w
1257 w 1260 m
1214 w 1214 w,sh
1187 m,br. 1186 m,br
10 B9 vw 1075 w 1069 m,sh
1047 w 1049 m,sh
10?1 moJ 1015 s 1019 s
990 w,sh
930 w,sh
907 vVl 899 m,sh 901 m,sh
B81 vw 875 m 880 s
815 mol 815 m
748 vw 751 w
914 vw
873 vw
820 vw
753 vw
vI - vII
v 10 - v 12
v 10 - vII
2v 11
2v12 , v 4 + v 12
2v 4
v 5 -1- vII
vII + v 14 ' v 4 + v 13
2v5 , \)6 + vII'
v 12 + v 14
v7 + vII
v7 + v 12
v5 ;- v 14
2v13
\)13 + v 14 ' v 5 + \)7
V 7 + v 13 ' v6 + v 14
vII + v15 ' vII + v 16 ,
V6 + V7
r.,) 0"\
J
715 w,sh
657 vs 653 vs 640 vs,br
641 vs
615 vl,sh
546 sh
. 524 m 523 s 532 m,br
489 w,sh
456 m 459 s} 456 s
417 vw,sh 417 w,sh
398 vw 398 w
357 \-1
308 m,br
270 m,br
647 vs,br
554 vw
531 s} 517 s
460 s} 454 s
428 sh
397 m
3:;9 m
2v 7 , v 4 + vIS'
v 4 + v 16
rl8
v 12
v 4
v 13 + vIS' v13 + v 16
Vs v13 - v 17 , v 13 - v18
v 13
v 14
v6
v-I
V14 - VIS' v14 - v16
v6 - vIS' \)6 - v 16
l'V -.J
j
L
102 m,br
66 w
52 w
v 15 ' v 16 \)
8
v17 ' v 18
a Where necessary each 1ist of frequencies has been divided into severa1 sections and the
intensities given are relative to the most intense peak within each section; s = strong,
TIl = medium, w = weak, sh = shou1der, br = broad, v very.
b The c-o and N-O stretching region (2200-1700 cm-l ) has a1so been recorded in n-hexane
solution. The observed frequencies are; 2097 m, 2088 sh, 2024 vs, 2018 sh, 1980 vs, 1947 w,
and 1767 vs.
c The far-infrared frequencies (below 350 cm- l ) given in this list were recorded in benzene
solution. N 00
- 29 -
* neutral NO group that is bonded to manganese.
-1 file three very strong bands at 2099, 2023, ruld 1982 cm
are assigned to vI' v lO ' and v 2 ' -i.e., the al (radial), e, and
a l (axial) C-O stretching modes, respectively (Figure 9).
These assignments are supported by the appearance of weak l3co
isotope bands due to Mn(CO)3(13 CO)NO molecules, present in
na-tural abundance (3% 13cO-radial a..'1d 1% l3co-axial). ~'i1hen
l2CO . ln an H-CO system is substituted by 13CO , a dmvmv-ard shift
-1 31 -1 of about 45 çm is expected for a frequency of 2000 cm •
This is the maxiumum shift anticipated, and vïOuld be obtained
only if aIl the CO groups involved in a particular vibr~tional
mode of the parent mole cule were substituted by l3co . When the
* Due to the three-electron bond in free nitric oxide, the
nitrosyl group can be coordinated in three possible valence
states: NOT, NO, or NO. A linear M-H-O bond is generally
viewed as being due to NO+, vlhile a coordinated NO- species
gives rise to a bent ~1-N-0 grouping. The stretching fundamental
of the coordinated ni trosyl group shmvs a marked dependence on
the electronic configuration of this group. The correlation is
evident from the comparison of X-ray data with the v(N-O)
frequency for. the follovJÏng three dihydrated species.
° M-N-O ~-l\; (l~)
Na2 [Fe (CN) SNO] .2H2O 178.3° 1.63
1<3 [Ivln (CN) SNO] .2H 2O 174.3° 1.66
K3 [V(CN) SNO] .2H2O 171.4° 1.66
N-O (A)
1.13
1.21
1.29
-1 (N-O) cm
1939
1725
1530
Ref.
28
29
30
The N-O bond 1engt..l1s and stretching frequencies are obviously
i!1dicative of the fact that in the -three molecu1es, the
ni trosyl groups are bonded as 1'10+, NO and IK'- respectively.
The M-N-O bond angles are a1so in line vii th the previously
postulated idea.
- 30 -
------------_._------------,
a, (axial) e
Figure 9. c-o stretching modes for Mn (CO) 4NO (C3v sylluuetry) ;
only one component of the doubly degenerate e mode shown.
parent molecule is only partially substituted, the shifts would be close to 45 -1 cm for those vibrations whi.ch involve mainly the substituted CO groups, near zero for those involving only
unsubstituted CO groups, and of intermediüte values for
32 vibrations involving.both types of CO groups .
The 35 cm-1 shift (44 cm- l in CS2
) between the band at
1982 cm- l and the isotope band at 1947 cm-1 indicates that the
1982 cm- l band is due mainly ta the vibration of the axial CO
group, i. e., the al (axial) c-o stretching mode ('v 2) .
vii th respect to the s·tructural assignment " there are hm
pie ces of information to be obtained from the spectrum in the
J
- 31 -
-1 2000 cm region. First, the three peaks observed in the v(C-O)
region are in agreement ",i th the nUIPber expected for C3v
geometry. Second, the observed 35 cm- l isotopie shift (44 cm- l
in CS 2 ) is in itself strongly indicative of ê_ symmetrically
unique CO group. For the molecule of C2v geometry, there are
two sets of two synunetrically equivalent CO groups. For the
monosubstituted l3 co species, all the vibrational modes
involving the 13co group would still con-tain a 12co group.
Th us , an isotope shift of 44 cm- l would not be expected for
any of the fundamental modes. This presence of a unique CO
group further corroborates the C3v structure.
The relatively low intensity of the 2099 cm- l band
-1 compared to the bands at 2023 end 1982 cm suggests that this
band is due to the al(radial) c-o stretching mode (vI) because
this mode is expected to exhibit tl1e weakest i.r. activity33
Horeover, such a totally syrnnetric c-o stretching mode is always
the highest of aIl tl1e c-o stretching frequencies of a metal
carbonyl complex of any stereochernistry33. 7he sma11 shift
(11 cm -1) observed between the 2099 cm-1 band and the isotope
b d 2088 -l, d f 13 ub 't' , an at co ~s expecte or mono- CO s st~ ut~on ~n a
vibration involving three equivalent CO groups. Therefore, this
-1 observation also supports the assignment of the 2099 cm band
as vl
•
-1 From the ?.bove discussion, the assignment of the 2023 cm
band to the e c-o stretching mode (v 10 ) follows automatica1ly.
A variable ter.!perature study was undertaken on the spectrllirL
hexane soIn.
2097
2024
2018
1980
1766
- 32 -
TABLE V.
TEHPERATURE STUDY IN THE \i (C-O) and \i (N-O)
FUNDAJ.1ENTAL REGIONS (cm-1 )
cy c10hexane soIn. (-82°)
2098
2022
2018
1977
1765
hexane solid (-110°)
2098
2023
2018
1977
1767
of J.VI'.n (CO) 4NO in solution. Spectra \V'ere obtained in the 2000-
-1 1700 cm region at room tempe rature , for the solution at -82°,
and for the sarrv1e frozen into a solid solvent matrix at -110°.
The data are presented in Table V. Except for the fact that the
spectral features are sharpened at 10wer temperatures, thus
making the 2018 cm-1 shoulder more pronounced, there is no change
in either 'the band structures or their relative intensi ties •
This implies that the molecular geometry of the species is
unchanged under the conditions emp1oyed.
'l'he consistenc..-y of these assignments is 'lerified by tl1e
-1 overtone and combination spectrum in the 5250-3500 cm region.
AlI the predic,ted frequencies are observed (Table VI). That
TABLE VI.
EXPECTED AND OBSERVED OVERTONE AND COMBINATION FREQUENCIES OF
Mn(CO)4NO IN THE 5250-3500 em-1 REGION (CC14
SOLUTION).
VCO
VNO
VI v 10 v
2 \)3 a
2094 2021 1974 1757
\)1 4188 ca1"c 4115 ca1c 4068 ca1c 3851 calc
2094 4183 w 4103 s 4068 s 3864 w
\)10 4042 ca1c 3995 cale 3778 ca1c
2021 4026 m 3979 s 'V3780 vw
\.12 3948 ca1c 3731 cale
1974 3943 m,sh 3715 vw
v 3 3514 ca1c
1757 3503 vs
a The third overtone of this mode is a11mved and is expected at -1 -1 5271 cm ; it is observed at 5230 cm
w w
J
- 34 -
there is a rather close fit between the calculated and observed
frequencies is a good indication that the c-o and N-O
stretching vibrations are not too anharmonic. This is also the
case for Co (CO) 3NO 7 but not for Fe (CO) 2 (NO) 2 5 . The weakest
bands in the 5250-3500 cm- l region result from the combinations
of the N-O stretching mode with the three C-O stretching modes.
A siw~lar situation exists for the overtones and combinations
of the C-O and N-O stretching modes in CO(CO)3N07 and
5 Fe ( CO) 2 (NO,) 2 •
The other bands which appear in -1
the 2200-1700 cm region
as shoulders on the main bands or as very weak bands, particularly
in the vapour spectrum, are assigned to combination or difference
vibrations (see Table IV).
b. Low Frequency Vibrations (700-350 cm- l )
The i.r. active fundamentals expected for Mn(CO)4NO in
the 700-350 cm- l region are: Mn-N-O bending (e), Mn-N
stretching (al)' Mn-C-O bending (al + 2e), and Mn-C stretching
(2a l + e). The assignments proposed here are supported by the
pub lished assignrnents for Co (CO) 3HO 7 , Fe (CO) 2 (NO) 25 , and Fe (CO) 534
which have been substantiated by force constant calculations.
In particular, the Mn-N-O bending and Mn-N stretching vibrations
should arise at higher frequencies than the I-1n-C-O bending and
Mn-C stretching vibrations. Horeover, the 1·1n-C-O in-plane
bending mode (v12) should occur at a higher frequency than the
5 Mn-C-O out-of-plane bending modes (v 4 and v 13 ) • AIse, the
- 35 -
relative intensities of the peaks can be used to give sorne
indication as to their possible origine It is now a weIl
established fact that the ô (lvl-N-Q) modes are generall~l more intense than the v(l.l-C) modes in the i.r. In the assigned i.r. spectra of the three carbonyl-nitrosyl systems considered in
the Review, (vide sup:r>a p. 9) a similar trend was noted for the metal-ni trogen vibrations vi z., the 0 (N-N-O) modes are much more intense than the v (M-N) modes.
On the basis of the preceeding arguments, the two fundamentals arising from the !-111-N-O g:.couping are expected at the high
frequency end of this region. Noreover, the v (lm-N) l'uode is anticipated to be one of the weaker bands. This particular
fundamental, however, can be assigned independently from other experimental evidence.
A solvent-effect study of the lm" freguency fundamentals
of Fe (CO) 2 (NO) 2 has s11mm that t..."1e Fe-N stre"cching modes shift to higher frequencies on going from the vapour to polar solvents, while the other modes remain alrnost unaffected or shift slightly
l . 5 to ower frequenc1es Infrared spectra of !-111 (CO) 4NO in CS 2, cyclohexane, CC1 4 , CHCI 3 , and acetone solutions indicate that
only the absorption at 524 cm- l in the vapour phase spectr~~ sho\'1s any appreciable solvent sensitivity. 'L'his band shifts to higher frequencies on going from ~~e vapour to polar solvents
(Table VII). Consequently, this rr.ode is assigned to the al ~m-N
stretching funda~ental (vS).
The highest frequency strong band in the vapour phase
1
a
- 36 -
TlillLE VII.
EFFECT OF SOLVENTS ON THE FREQUENCY OF VS'
THE al l'-1n-N STRETCHING FUNDAHENTAL (cm -1) .
Solvent V (Mn-N) V (vap.) -v (sol.)
Vapour 524
Carbon disulphide 523 +1
Cyclohexane 524 a 0
Carbon tetrachloride 532 -8
Chloroform- 537 -13
Acetone 573 -49
Average value of the bITO components of a doublet at 531 and
517 cm-l •
spectrum at 653 cm- l appears as a doublet (657 and 641 cm-l )
in the CS 2 solution spectrum. The 657 cm- l band is assigned
to the e Mn-N-O bending mode (Vll
) , while the band at 641 cm- l
is attributed to the e l'-1n-C-O in-plane bending mode (V12 ).
This last assignment is supported by evidence for the
isoelectronic and isostructural complex, Fe(CO)5. The e in
plane Fe-C-O bending mode (vll ) of this species, occurs at
646 cm- l • Observing the modes diagrarr@ed in Figure 10, it can
- 37 -
Figure 10. Approximate description of the normal modes of
Fe(CO)S and Mn(CO)4NO.
l
1
Fe(CO) 5 Mn (CO) 4NO Fe(CO)s !-1n (CO) 4NO
- 38 -
be seen that the axial groups do ~ot take part in this
fundamental vibration. Since the configuration of the
Equatorial plane is identical for the two species and
moreover, the masses of the iron and manganese atorns are
very similar, it is reasonable to expect that these modes
will occur at similar frequencies.
Theother Mn-C-O bending mode can similarly be assigned
by analogy with the bending modes of Pe(CO)r.. By comparison ::>
with the v7 mode of Fe(CO)5' the al (v 4) Hn-C-O bending mode
-1 i5 assigned to the weak band in the vapour spectrum at 615 cm
The three Hn-C st:cetching modes are expected to fall in
the region below 500 cm- l . The complimentary nature of the
C-O and M-C bond orders is weIl established. In vie\v of this,
the order of the al (radial) and the al (axial) Nn-C stretching
modes is expected to be opposite to that for the corresponding
C-O stretching modes. Moreover, both !1n-C stretching modes
should occur near 400 -1 cm • Consequently, the bands at 398
-1 and 357 cm in the CS 2 solution spectrum are assigned to v
6
and v 7 , respectively.
Since the e l-m-C stretching mode (v 14 ) of Hn(CO) 4NO is
similar to the e' Fe-C stretching mode (v 13 ) cf Fe . (CO) 5'
these two modes are expected te absorb in approximately the
same region. The v13 mode of Fe(CO)5 vapour falls at 431 cm-li
therefore, the weak band at 417 cm- l in the l\1...'1(CO) 4l\!û vapour
spectrum is assigned to v 14 •
- 39 -
-,1 By elimination, the 456 cm band is assigned to the e
(v13 ) Mn-C-O bending mode. This assignment is supported by
the expected position [higher than the v (r\1n-C) modes] and
intensi ty [greater than that of the v (r-1n-C) modes] of this
band. Also, it is split slightly into a doublet in CS 2 and
cyclohexane solution.
c. -1 Lmv Frequency Vibrations Below 150 cm
The i.r. active fundamentals expected for Mn(CO)4NO in
-1 the region below 150 cm are: C-Mn-C deformations (al + 2e)
and C-Mn-N deformations (2e). The far-infrared spectrum in
benzene solution (Figure 5) exhibits three bands in this
region at 102, 66, and 52 cm- l The 102 cm- l band is broad
and rather unsyrnrnetrical, ~vhile the other hw bands are
reasonably sharp.
The assignments proposed for this region must be regarded
as speculative because two of the modes expected are not
observed. By analogy with the v 14 ' vg , and vIS modes of
Fe(CO)S 33 which occur at 104, 72, and 68 -1 respecti vely34 , , cm
the three Mn (CO) 4NO bands are assigned in order of decreasing
frequency to vIS' v 8 ' and v17 • Since the e C-Mn-N.in-plane
5 ~ -1 deformation (V 16 ) is also expected ,1 to occur near 100 cm ,
the broad asyrnrnetrical band at 102 cm-l is attributed to this
mode as well as to vIS. The e C-Mn-N out-of-plane deformation
-1 (vIS) is anticipated in the neighbourhood of 50 cm '].'his mode
-1 is assigned tentatively, along with v17 ' to the band at 52 cm •
Normal mode
al Symmetry
v1 v2
v3
v 4 v 5
v6
v7
va
a" Symmetry û
v e 9
TABLE VIII.
COMPARISON OF THE FUNDAMENTAL FREQUENCIES
OF Mn(CO)4NO AND Fe(CO) 5 VAPOURS (cm- l ).
Mn(CO) 4NOa
Approx. Descrip.
C-O radial str.
C-O axial str.
N-Q str.
l'1n-C-O bend
~1rl-N str.
Mn-C axial str.
1-1n-C radial str.
C-Mn-C def.
Mn-C-Q bend
Freq.
2111
1996
1781
615
524
398
357d
66
Norma.l mode
al' Symmetry
vI
v2
v3 v4
a2
1 Symmetry
v 5
a2 " Symmetry
v6
v7
v 8
Fe(CO) b 5
Approx. Descrip.
C-O str.
c-o str.
Fe-C str.
Fe-C str.
Fe-C-O bend
c-o str.
Fe-C-O bend
Fe-C str.
Freq.
2117 "'" 0
1984
414
377
593c
2014
620
474
j
L
e Symmetry v9 C-Fe-C def. 72 f
v IO c-o str. 2020 e' Symmetry
vII Nn-N-Q bend 657 v IO c-o str. 2034
v 12 Mn-C-O bend 641 vII Fe-C-O bend 646
v 13 Mn-C-O bend 456 v12 Fe-C-O bend 544
\)14 . Mn-C str. 417 v13 Fe-C str. 431
vIS C-Mn-C def. 102 v 14 C-Fe-C def. 104
v16 C-Mn-N def. 102 g vIS C-Fe-C def. 68
v17 C-Mn-C def. 52 e" Symmetry
vIa C-Mn-N def. 52h V 16 Fe-C-O bend 487 c
vI? Fe-C-O bend 614
v 18 C-Fe-C def. 95
a Those frequencies below 150 cm- l are taken from the far-infrared data recorded in benzene
solution.
b Except \vhcre otherwise mentioned, the fundamental frequencies listed are those of
W.F. Edgell et aZ.~ Speatroahim .. 4ata~ 19, 863 (1963).
c From solid-state i.r. spectrum (ref. 34)
.f;:>.
f-'
.j
d In CS2
solution.
e This mode is i.r. inactive.
f From the laser Raman spectrum of the liquid [M. Bigorgne, J. Organometa~. Chem. 3 24, 211
(1970)].
g Presumable coincident with vlS •
h presumably coincident with v17 •
~ N
j
-- 43 -
TABLE IX.
OBSERVED AND CALCULATED
v(C-O) FUNDA1'1ENTALS (cm- l ).
Fundamental Observed Calculated
VI 2095 2093
vI ( l3CO) 2084 2086
v lO 2022 2022
v.., ... 1978 1979
v 2 ( l3CO) 1946 1946
The vibraticnal assignments proposed above for the
fundamentals in the three s2ectral regions are collected together
and compared with those of Fe (CO) 5 in Table VIII c
2. Force Constant Calculations
Force constant calculations were performed on the "CO
block" of Mn(CO)4NO, using the standard program of ., ,-
SchachtschneiderJo! modificd sligh tly by Dr. H.K. Spendjian
to run on the i-lcGill University IBH 360-75 computer. With
the nitrosyl group included in the calculation, convergence
cou Id not be obtained.
Using the assignment of the CO peaks proposed earlier
- 44 -
TABLE X.
C-O FORCE CONSTANTS OF
o Cl\Rl30NYL-NITROSYL COMPLEXES (mdyn/A).
1'-1n (CO) 4NO Fe (CO) 5 Fe (CO) 2 (NO) 2 Co (CO) 3NO
fC-O, eq. 16.69 16.57 } 16.92 16.55
fC-O, aXe 16.42 16.95
f 0.19 0.40 } CO,CO; eq. ,eq. 0.51 0.40 f 0.51 0.28
CO,COi eq. ,ax.
ref. 37 5 5
very good agreemen"t \.".as obtained betvleen the calculated and
observed frequencies. These l1urnbers are 1isted in Table IX.
No other assignment gave such a good correlation between the
t'VlO sets of frequencies. The resu1 ting force constants are
simi1ar to those obtained for re1ated species by more
sophisticated ca1cu1ations (Table X) .
3. ~ass Spectroscopie Investisation
F ' d' 38,39 d' 't' t t' 1* ragmentatlon stu les an lonlza lon po en la
* 'l'he term "ionization potentia1 11 shou1d strict1y be I!ionizaticn
energy" . However, since the former is the common1y employed
phrase, i t V/i1l be used in this thesis.
l
mie
055
169
83
141
197
85
41.5
113
III
55.5
69.5
139
- 45 -
TABLE XI.
ORDER OF DECREASING ABUNDANCE
OF !-1n (CO) 4NO FRAGMENTS
Ion
Mn+
[Mn (CO) 3NO] +
[l'ln (CO) ] +
Will (CO) 2NO] +
[Mn (CO) 4NO] +
[1-1nNO) +
[!-1n (CO) ] ++
[l'in (CO) NO] +
[Mn (CO) 2] +
[!-1n ( CO) 2] ++
[Mn (CO) ] ++ 3
[Mn (CO) 3] +
Relaotive Abundance
56
21
15
Il
10
7
5
4
3
2
2
1
determinations 40 have been carried out on several organometallic
complexes similar to Hn(CO)4NO. The ionization potentials of
CO(CO)3NO, Fe(CO)2(NO)2 and CpNiNO are 8.75, 8.45 and 8.50 eV,
respectively40. For both of the carbonyl-nitrosyls, the
- 46 -
[P - NO]+ ion concentration was negligible compared to that
of the [P - CO]+ ion.
The fragments obtained from electron bombardment of
Nn(CO)4NO, at 70 eV, are listed in Table XI in the order of
decreasing abundance.
As expected, the [P - NO]+ fragment is missing, in line
with other carbonyl-nitrosyls. Also, none of the doubly charged
ions contain the NO group. Two opposing trends are observed for
the order of the relative abundances of the two fragment types:
wi th and wi thout the NO group.
[Mn] + > > [Mn ( CO) ] + > > [!:4n ( CO) 2] + > [Mn (CO) 3] +
[Mn(CO)3NO]+»[Mn(CO)2NO]+>[~m(co) 4NO]+> [MnNO]+> [Mn(CO)N01+
The first trend is readily explained. As the NO group is
split off from the parent ion, the [Mn(CO) 4]+ ion fragments with
the successive 105s of the CO groups. The second trend cannot be
explained through the monotonic loss of any group. It seems to
suggest.that as long as the NO group is attached to the ionic
fragment, sorne other process, besides the simple loss of neutral
groups, may be occurring. Supportive of this suggestion are t.'l-te
non-characteristic clastograms obtained in the ionization
potential determination.
To obtain the IP of the parent ion, the ahundance of the
mie 197 ion was monitored as the voltage across the source was
gradually decreased. (The procedure is des cribed :).n detail in
the Experimental section). Whereas the resul ting curve was
- 47 -
expected to change monotonically, a condition for which the
Warren plot41 gives the value of the IP, well-defined sharp
peaks \vere observed. To determine whether this effect vIas
real or not, the s ame measurements \vere carried out for several
of the other ion fragments. The clastograms of the [P]+,
[P - CO]+ and [p - 2CO]+ ions are shown in Figure Il. It should
be noted that the ordinate represents the absolute, not the
fractional, abundances of the ions. A fresh sample, at a later
tirne, showed similar characteristic curves, indicating that these
curves are indeed reproducible.
There is indication for the step\vise unirnolecular decom-
position of Mn(CO)4NO. (Organometallic complexes, HMn(CO) 5 in
particular39 , have been shown to undergo such processes) •
* 2 r-ietastable peaks (m = rn2 Iml
) were found for the follmling steps:
[~ill(CO)4NO]+ --+ [Mn (CO) 3N01+ + CO
[Mn (CO) 3NO] + ~ [{\1n (CO) 2NO] + + CO
* rn = 145.0
= 117.6
The parallelism bet\veen the curves for the [Nn (CO) 4NO] + and
[Mn(CO)2NO]+ ions seems to be more than purely coincidental.
These curves suggest that there is sorne close interdependence
between these two fragments. There is not only a stepwise loss
of neutral CO groups as this -,vould gi ve rise to re lati ve
+ abundances of the three groups similar to those for the [Hn(CO) x]
fragments. It is felt that sorne unspecified secondary process
is responsible for the obvious intensi ty relationship bet"vleen the
two fragments. \'1h~ther this process is rea} , or just sorne curious
Figure 11.
- 48 -
+ Clastograms for three fragments of the Hn(CO)4NO
ion.
p+ - molecular ion, Mn(CO)4NO+
40
30 Q) u c 0 "0 C :J
..0 « 20
1 1
1 '10 1
1 1
1 1
1 1
1 1
1 1
1
1 1 1
10 30 50 70 Electron Energy (eV)
- t19 --
experiment.al artifact, remair.s to be established.
Further evidence for the fact that there is sorne other
process besides the straight loss of neutral CO groups, is found
in the value of the ionization poten·tial. The semilog curves
for the abundances of the parent ion, and. CS 2 + reference ion,
vs. the eV across the source, are shown in Figure 12. Carbon
42 disulphide has an IP of 10.1 eV • By inspection, the IP of
Mn (CO) 4NO is determined to be 11.5 ± 0.3 eV. This value is
considerably greater than the IP of other carbonyl-nitrosyl
systems ("'8.5 eV). This high value could also be an indication
of the fact that the appearance of the molecular ion is not due
to a simp18 ionization process.
These data, taken in conjunction, do indicate that further'
investigation is vlarranted into this phenomenon.
D. CONCLUSION
A complete vibrational assignment has been proposed for the
binary carbonyl-nitrosyl complex, .t-ln(CO)4NO. The i.r. data
obtained for the vapour and in solution dre interpreted best ih
terrns of a C3v trigonal bipyrarnidal structure rather than the C2v
one which is favoured for the complex in its crystalline state
at -110°C, on the basis of X-ray evidence. This conclusion is
based principally on the fact. that there are significantly fewer
fundamentals observed, than are expected for the C2v structure.
It is further supported by 13c-satellite evidence for a
syrrunetrically unique carbonyl group. A simple force constant
- 50 -
Figure 12. Plot of abundance vs. e'ectron energy(eV) for
CS 2+ and Mn(CO)4NO+.
p+ - rnolecular ion, Mn(CO)4NO+
w u z « o z
10
~ 1.0 «
9 Electron Energy (eV)
p+ !
14
- 51 -
calculation on the "CO block" of this molecule supports the
assignment of the v(C-O) modes and gives rise to force constants
in line with those of related species.
The ionization potential of Mn(CO)4NO has been determined
for the first time. The actual value is Il.5 ± 0.3 eV i.e. 1
significantly higher than the ionization potentials of related
carbonyl-nitrosyl complexes. A reproducible, but unexplained,
curious phenomenon has been observed for the fragmentation of
Mn(CO)4NO in the mass spectrcmeter. This process is postulated
to be one of the factors giving rise to such an unusually high
value of the ionization potential.
- 52 -
CHAPTBR 4. DINITROSYLDICl'-:.lffiONYLIP.ON (0) A~D SO!-lE DERIVA'J.'IVES
A. INTP.ODUCTION
As mentioned in the Review, there are fe\v Raman data for
metal nitrosyl complexes. From the author's own experience,
this is because metal nitrosyls generally give rise to po or
quality Raman spectra owing to their intense colour (usually
* deep red) and weak scattering properties.
In this Chapter, new vibrational data will be presented for
Fe(CO)2(NO)2 and a few of its derivatives. The Raman data are of
particular interest as they are the first ever obtained for iron(O)
nitrosyl complexes. In addition, the far-infrared spectrum of
Fe(CO)2(NO)2 has been recorded for the first time. The new
experimental evidence obtained provides support for the majority
of the previously published5 assignments for Fe(CO)2(NO) 2 but
places doubt on sorne others.
The low frequency spectra of four tertiary phosphine and
phosphite ceri vatives of Fe (CO) 2 (NO) 2 have been recorded in the
900-350 cm- l region. These data are among the relatively few
that have ever been measured in this spectral region. The general
practice in reporting the vibrational spectra of such compounds
is simply to list only the CO and NO stretching frequencies. A
* A Raman spectrum could not be obtained for the stable, y8llow
complex, [CPMn(CO)2NO]PF6. Since complexes of this colour are
usually ammeanable to Raman spectra, it appears that the
scattering property of this particular nitrosyl complex is the
limiting factor.
- 53 -
few vibrational assignments are proposed for the organophosphorus derivatives discussed here.
A new convenient route has been developed for the synthesis
of Fe(CO)2(NO)2. The method compares favourably with the most commonly used one of Hieber and Beutner43 •
B. EXPERIHENTAL
1. Syntheses
Di ni tY'OS 1/ Z. di c:aT'b ony Zi T'on (0), Fe (CO) 2 (NO) 2' was prepared b l th d . th [ ( , ] . 44 . t d' t Y a nove me 0 uSlng e Fe CU/
4H lon as an ln erme J.a e.
AlI operations were carried out strictly under nitrogen.
A mixture of 4 ml of Fe (CO) 5 (29 mmol) and 60 ml of
deaerated NH40H was stirred magnetically at room tempe rature
for 24 hr. The solution trJas then filtered and the [Fe (CO) 4H]
ion was precipitated by the dropwise addition of 5.1 9 of
(Et)4NCl (31 mmol) ~issolved in 30 ml of deaerated water. The resul ting pink precipi tate \\'as washed wi th t\rJO 10 ml aliquots
of deaerated water and an equal volume of pentane. This
precipitate was suction dried for 30 min.
To the solution of the [(Etj4N] [Fe(CO)4H] dissolved in 50 ml deaerated l ,2-dichloroethane, 13.3 9 of Diazald (N-methyl-N-
nitroso-p-toluenesulfonemide) (62 rnmol) was added. This
solution was then stirred magnetically for l hr., the excess
pressure being relieved through an oil-bubbler connected to the
flask. The flask was connected to a vacuum line and the solution was degassed by means of the usual vacuum line technique. A
- 54 -
dark red solution was distilled over into a-196° trap on
the vacuum line, from the room tempe rature reaction mixture.
This process resulted in a pure solution of Fe(CO)2(NO)2 in
1,2-dichloroethane. Performing this reaction step in chloro-
ethane instead of 1,2-dichloroethane, produces pure liquid
Fe(CO)2(NO)2 - the complex can be trapped out at -64°. Yields
of 60-75%, based on Fe(CO)5' can be obtained. The 1,2-dichloro
ethane solution can be stored, '>lithout any decomposition, for
weeks under vacuum in the dark.
DinitrosyZaarbonyZ(triphenyZvhosphineJiron(OJ, Fe(NO)2(CO)PPh3 ,
dinitrosyZbis(triphenyZphosphineJiron(O), Fe(NO)2(PPh 3 )2' and
dim: t ros.y Z aarb ony Z (tri me th'fll ph os phi te) i('on (0 J, Fe (NO) 2 (CO) [P (OHe) 3]
45 viere prepared according to published syntheses . The puri ty of
each compound \l7as estab1ished by t.l.c., its identi-ty by
comparison of the i.r. spectrum ,vith the pllblished one.
Dini-/;rosyZb1:'S (trimethl1Zphosphite)iron(O) 1 Fe (l-JO) 2 [P(OHe) 3]2'
was prepared by a method similar to the preparation of the mono-
trimethylphosphi te deri vati ve. A 5 ml solution of Fe (CO) 2 (NO) 2
('V2 rnrnol) in dichloroethane and 1.2 ml of P (Œ1e) 3 (9 mmol) was
stirred, under nitrogen, for 24 hr at 85°. During this time,
the starting material was converted, almost quantitatively, to
the bis-derivative. The resulting mixture \ojas purified by
chromatography on a silica gel coluœl. The first colourless
fraction (excess trimethylphosphite) was eluted WiL~ CH 2C12 •
The eluant was then changed to a 1:1 mixture of acetone and
hexane i this concentra.ted and eventually \l7ashed out a red band.
- 55 -
The resulting solution was rechromatographed on silica gel.
Finally, the solvent VIas removed at reduced pressure, leaving
the desired product as a red, oily material. This product • .,as
ShO\VD to be pure by t .1. c. r-t could be s tored in the dark,
under nitrogen, \.,ithout decomposition.
rt should be noted that a concerted effort to synthesize
similar PF3 derivatives, failed. The attempted synthesis was
similar to that used to prepare the tertiary phosphine
derivatives. In absence of tetrabutylammonium bromide as
catalyst, no reaction occurred. However, with the catalyst,
substitution of the CO groups did occur, as evide:1ced by
changes in the i.r. spectrum. The spectra aiso indicated the
presence of the tetrabutylammonium cation. n1is ion could not
be separated out by any chromatographie me ans . Conductance
measurements in nitromethane solution did indeed verify that
the reaction product was an ionic compound. Assuming a molecular
-1 weight of 400 g mole , the specifie conductance at 25° was
l l .... à t be 63 cm- l mhos- 1 M- l . E' . l l (C H) ca cu a ... e. 0 .Lemen-ca ana yses ,
failed to substantiate the molecular formula for any reasonable
compound that could be proposed. Mass spectroscopie analysis
also yielded no positive results. The dichotomy in the
behaviour of PF 3 and PPh 3 in their reactions with Fe(CO)2(NO)2
is not understood.
2. Vibrational Spectra
The i.r. spectrum of Fe(CO)2(NO)2 .in CS 2 solution was
-,
- 56 -
obtained using a pair of matched 1.0 mm KBr cells. The spectra
of triphenylphosphine, Fe (NO) 2 (CO) (PPh 3) and Fe (NO) 2 (PPh 3) 2
were recorded as Nujol mulls sand\oJiched bet\veen KBr plates.
The i.r. spectra of the two trimethylphosphite derivatives and
the free ligand, were measured for the neat liquids squeezed
between KBr plates.
The far-infrared spectra were obtained for benzene solutions,
and were run against pure benzene as reference in 1.0 mm Beckmann
polyethylene solution cells.
The Raman spectrum of Fe (CO) 2 (NO) 2 was obtained wi th the
647.1 nm exciting line at 50 mW power. OWing to the poor
scattering p.coperty of this compound, very \'Jide slits (9-10 cm- l )
had to be ernployed. Spectra were recorded for CS 2 and CC1 4
solutions. The regions of CS 2 solvent scattering 'VJere clear
for the CC1 4 solution spectrum. In this way, a composite Raman
spectrum in the 2100-1700 and 700-250 cm- l regions was obtained.
An attempt to record the Raman spectrum of the neat liquid,
failed.
The Raman spectrum of Fe(NO)2(CO) (PPh 3) was run for the
powdered solid in a pyrex capillary. Since the compound
decomposed in t.he laser beam at room temperature, a special low
temperature sample handling system, diagrarnrrled on the next page,
was constructed. With this system, temperatures down to -80 0
could easily be achieved. This sarnple was run at -10 0 using
the 647.1 nm exciting line at 80 roW power. A po or quality, but
reproducible, spectrum lIJas obtained. The spectrurn of Fe(NO)2(PPh3)2
- 57 -
p
i - incident laser beam
s - scattered laser beam
n - cold N2 inlet
p - pyrex capillary (sample)
t - ther~ocouple
e - evacuated
was also attempted at room and low temperatures. Although the
compound did not visibly decompose, only a very noisy baseline
was obtained and no peaks could be discerned.
Attempts to obtain the Raman spectra of the trimethylphosphite
derivatives also failed.
C. RESULTS AND DISCUSSION
To facilitate the assignment of the fundamentals of
Fe(CO)2(NO)2 and its derivatives, certain trends noted for
other carbonyl-nitrosyl complexes will be introduced.
A good linear correlation can be obtained46 ,47 between
the shifts in the v(C-O) and v(N-O) fundamental frequencies
with changes in L for complexes of the type M(CO)x(NO)yL. The
shifts are dependent on the 1f-acceptor abilities of the
- 58 -
* ligands.
Assuming a significant TI-contribution to the bonding scheme,
a number of a priori predicitons can be made for Fe(CO)2(NO)2
and its derivatives. The 1T-acceptor abilities of the ligands
in question are generally accepted48 ,49 to be in the order of
CO>P (OR) 3>PR3 . On this basis, "through cornmon "rr-bonding
arguments, certain shifts in the fundamental modes can be
predicted (Table XII). It is evident from the assignments also
presented in this Table that these predictions are verified
experimentally ..
The solution i.r., far-infrared and solution Raman spectra
of Fe (CO) 2 (NO) 2 are shown in ?'igures 13, 14 and 15 respecti vely.
The Raman spectrum of the crystalline comple}{, Fe(NO)2(CO) (PPh 3),
is reproduced in Figure 16. A typical i.r. spectrQ~ of cne of
the organophosphorus derivative3 is also demonstrated in Figure
17. The frequencies relevant to these spectra, as weIl as to aIl
the other complexes discussed in this Chapter, are listed in
Tables XIII, XIV, and XV.
Although i.r. spectra of Fe(CO)2(NO)2 in the vapour phase
5 and liquid state have been published previously by Poletti et a~.
there are no reports in the literature dealing with the i.r.
spectrum in solution. In the present study, the i.r. spectrum
of Fe(CO)2(NO)2 in CS 2 solution has been recorded. This spectrum
* The author acknowledges the fact that cr-effects also play an
important role in metal-CO and metal-NO bonding. In particular,
they are concomitant to the TI-effects - a gcod 'IT-accepting ligand . . d . 48 belng slmultaneoulsy a poor a-donor an v~ae ~ersa
l
- 59 -
(A) Figure 13. Infrared spectrum of Fe(CO)2(NO)2 (CS 2 solution).
(B) Figure 14. Far-infrared spectrurn of Fe(CO)2(NO)2 (benzene
solution) .
w u z <! r-r-2 tJ) z <! 0:: r-
1
2000 1700
(A)
r
1
600 400 -1 cm
-,
w u z ;:! 1-
2 li) z <r Ct: 1-
300 100
(B)
- 60 -
Figure 15. Raman spectrum of Fe (CO) 2 (NO) 2 (CS 2 and CC1 4 solutions) .
Instrument 580-420b 700-580
c 2100-1980b
Controls a 350-250 420-360 1830-1730 Dnits ----
Excitation 647.1 647.1 647.1 nm
Power 50 50 50 mW
Slit 9.5 9.0 8.0 -1 cm
Sensitivity 5 10 2 x 10 10 -1 " sec
Time Constant 10 10 40 sec
Scan 20 10 5 cm -1 min -1
Chart 24 12 6 in/hr
a In the subsequently reproduced Raman spectra, for the sake of
brevity, the instrument controls will be named in short form and
the units will be ommitted.
b CS 2 solution.
c CC1 4 solution.
1 =s:~
-==--~ ~
-~ ~ ~
A1ISI'13.lNI
.-lE u
0 0 ~
0 0 <D
o o co ~-
o o o C\J
l
- 61 -
(A) Figure 16. Solid state Raman spectrum of Fe(CO) (NO)2PPh3.
Instrument Contro1s
Exc.
Power
Slit
Sens.
T.C.
Scan
Chart
920-350
647.1
85
5.5
5 x 10
40
5
12
2100-1680 -----647.1
85
4.4
5 x 10
40
5
12
(B) Figure 17. Infrared spectrum of Fe (NO) 2 [P (011e) 3] 2 (neat
1iquid) •
: f.
1
( A)
~------------------------------------------,~
=-
<
3:JN\t .1.11 V\JSNV'til (B)
lE u
o o ~
o o cD
.,
Mode
\l (C-O)
\l (N-O)
\l (Fe-C)
\l (Fe--N)
ô (Fe-N-O)
*
Predicted
* shift in mode
decrease
decrease
increase
increa.se
increase
TABLE XII"
FREQUENCY SHIFTS OF THE FUNDN~NTAL MODES OF
THE Fe (NO) 2 (CO) L CDr1PLEXES (cm -1) "
L= CO
2083 (al) , 2033 (h 2)
1806 (al)' 1763 (h 1)
659 (b 1)
647 (al)
610 (h 2)
Observed for Fe(NO)2(CO)L
P(OMe)3
2025 (a' )
1778 (a'), 1733 (a ")
669 (a ")
667 (a' )
619 (a' )
With L changing as CO, P(OMe)3' PPh 3 "
PPh 3
2009 (a' )
1759 (a'),1714 (a ") 0-, N
690 (ail )
669 (a' )
622 (a 1)
J
PPh3
IR
851 (6) b
753 (vw ,sh)
745 (v\'! ,sh)
741 (60)
ï~l (sh)
TABLE XIII.
VIBRATIONAL SPECTRA OF THE PPh3
DERIVATIVES OF Fe{CO)2{NO)2 (cm-1 ).
Ramanc
742 (8)
Fe{NO)2{PPh3 )2
IR
1712 (vs)
1667 (vs)
850 (7)b
843 (5)
a
803 (7,br)
750~ 744 (50)
740 J
723 (5)
Fe (NO) 2 (CO) (PPh 3 )
IR
2009 (vs) a
1759 (vs)
1714 (vs)
854 (10)b
849 ( 7)
748 (54)
724 (sh)
c Raman
2007
1742
1708
846 ( 6)
760 (5)
750 (5)
0'1 w
J
705 (32) 707 (30) 706 (8)
693 (63) 693 (sh) 693 (50) 696 (50) 692 (7)
679 (35) 685 (w,sh) 690 (w,sh)
672 (5) 669 (30) 660 (15)
627 (4)
620 {5} 616 (25) 617 (3) 622 (37) 617 (14)
618 (w,sh)
580 (20)
541 (3) 564 (3) 564 (20)
528 (3) 521 (70) 525 (52) 523 (6)
512 (45) 509 (sh) 505 (50) 507 (55) (l',
~
4981 495 (13) f (45) 490 490 (5) 489 (10)
466
1 458 (2) 458 (3) 458 (22)
441 (20) 450 439 (6)
430 (11) 429 (sh) 428 (5) 426 (12)
419 (12) 421 (16) 421 (s11)
396 (4) 403 (18) }
397 (2) 402 (3)
386 (10) 387 (:,)
J
396 (s) d
375 (3)
327 (3)
268 (sh) 268 (sh)
248 (m) 246 (90)
206 (m) 208 (50)
192 (sh) 1951 [(40)
185
a Spectrum obtained for CH2 C12 solution in the 2100-1700 cm- l region. b Spectrum recorded for Nujol. mull in the 900-350 cm- I region. c Spectrum run for a microcrystal1ine sample (at -lOoe for the iron complex) . d The far-infrared spectrum was obtained for the sample dissolved in benzene.
0) (JI
.J
P(OMe)3
851 (4)b
824 ( 10)
766 (sh)
726 ( 50)
512 (5)
- 66 -
TJ.I.BLE XIV.
INFRJl.RED FREQUENCIES OF THE P (OMe) 3
DERIVATIVES OF Fe(CO)2(NO)2 (cm-1).
2025 (vs)
1747 (vs) 1778 (vs)
1698 (vs) 1733 (vs)
853 ( 32)
801 (sh)
791 (46 ,br) 791 (28)
759 (sh) 754 (26)
737 (46)
678 (15)
667 (sh) 669 (s11)
663 (sh) 667 (17)
603 ( 21) 619 (20)
526 (33) 526 (10)
467 (sh) 475 (2)
420 (sh)
a
a -1 Samp1es ,.vere run as cyclohexane solutions in the 2100-1700 cm
region.
b Spectra were recorded
region.
for -1 the nE:at liquids in the 900-400 cm
,- 67 -
is of higher quali ty than the knO'.vn vapour and liquid spectra
bands previously appearing as shoulders are now distinctly
resolved.
The Raman spectrum of Fe(CO}2(NO}2 in the high frequency
-1 region (2100-1700 cm ) is in accord with the previous vibra'tional
assignment of this complex \vhich \Vas based on i. r. data alone 5 •
Unfortunately, reliable Raman depolarization ratios could only be
obtained for the CO stretching modes o";:ling to graduaI decom-
position of the complex in solution. Four Raman active modes
[v(C-O), al + h 2 ; v(N-O), al + hl] are expected in this region.
The highest frequency band in the CO strc=tching region at 2083 cm- l
is polarized, whereas the other CO band at 2033 cm- l is depolarized.
These data confirm the previous assignment of the two bands te the
* al (vI) and b 2 (')17) modes, rE'.!specti vely. 'l'he relative in tensi ty
-1 of the two peaks at 1806 and 1763 cm suggests they should be
associated with the al (v2 ) and hl (v 12 ) modes, respectively.
There is sorne evidence for reversing the previous assign-
ments of the v 5 a.né!. v 19 fundamentals. Bo t."L \',"ere assigned to
Fe-C-O bending modes. Based on the new Raman data, the s'tronger
560 cm -1 band ls reassignedto the al (v 5) bending mode, leaving
-1 the 477 cm peak as the h2
(v19 ) mode. This reassignment is
supported by a closer inspection of the available data. From
the published table of "Potential Energy Distribution Arnong The
* The fundamentals described by poletti et al. 5 have been re
nurnbered to conform to the more usual convention of decreas:i..ng in
frequency in each syn~~etry block.
"
- 68 -
Syrnmetry Coordinates ", i t can be seen that \) 18 and \) 19 nlix.
Using the reassigned value for \)19' a combination band due to
the interaction of these two fundamenta1s can be expected at
-1 482 + 614 = 1096 cm . 1>_ Il rather strong" band was observed aoc
1095 cm -1. Al though this band was previous 1y assigned to a
combination between 658 + 436 = 1094 cm-l, this seems somewhat
unlike1y because both of these bands are weak shou1ders, whereas
-1 the 614 and 482 cm bands are more intense. The stronger
fundarnentals would be more 1ike1y to give rise to a "rather
strong" combination band.
The previous assignment of the Fe-N-O and Fe-C-O funda
-1 mentals for Fe{CO)2(NO)2 to the 700-600 and 500-400 cm regions,
respectively, is substantiat~d experimentally. In the i.r.
spectra of the bis-P (OMe) 3 derivative, (Table XIV), for which
-1
the two CO groups have been re?laced, the peaks in the 500-400 cm
region disappear, while t.he others are only shifted. The shift
in the Fe-N-O fundarnentals in going from othe parent compound to
the mono-phosphite and phosphine derivatives is to higher
frequency, as predicted (vide supra, p.62). The relevant
assignments are shown in Table XII. To the best of the author's
knowledge, these are the first low frequency data that have been
used in such an argument. In general, only the \)(C-O) and \)(N-O)
high frequency fundamental frequencies ar.e considered owing to
the relative comp1exity of the low frequency region.
There is a strong band in the high reso1ution CS 2 solution
i. r. spectrum of Fe (CO) 2 (NO) 2 at 591 cm- l (Figure l3) , which
- 69 -
apparently was not observed in the published lower resolution
vapour phase or liquid state spectra. The Fe-N-O twisting mode
-1 of a2 symmetry (v 9 ) has been calculated to be at 590 cm •
Consequently, this 591 cm- l band is assigned tentatively to
either v 9 (made active by the solvent interaction) or to a
combination band (whose intensity has been enhanced by Fermi
resona.nce with the 610 cm- l mode) .
Four fundamentals (2al + b l + b 2 ) should appear in the
-1 100-50 cm region. The far-infrared spectrum of Fe(CO)2(NO)2
in benzene, down to 60 cm-l, was obtained. The only features
are a broad band centered at 87 cm -1 wi°th a weak shoulder at
-1 72 cm • rrhe former is in excellent agreement wi th the
-1 calculated value (86 cm ) for the N-Fe-N deformation mode (V 7 )
-1 and is tentati vely assigoned to this mode. The 72 cm band is
probably due to either v 8 or v 21 I.vhich are calculated to lie at
66 and 78 cm-l, respectively.
The proposed vibrational assignments for Fe(CO)2(NO)2 are
presented in Table XV. These assignments a.re based upon the
work on Poletti et aZ. S and differ only in the assignments of
D. CONCLUSION
The new far-infrared, i.r. and Raman spectra obtained for
Fe(CO)2(NO)2 substa~tiate the previously published vibrational
assignrnents for this co~plex. The only significant difference . is the assignments for the Vs and v 19 modes. The new vibrational
- 70 -
Tl.BLE XV.
-1 FUNDl'1-1ENTAL FREQUENCIES OF Fe (CO) 2 (NO) 2 (cm ).
Solutiona
Normal Mode Approx. Descrip. IRb Ramanc
al Syrrunetry
'\)1 c--o str. ~O83 2082
v 2 N-O str. 1806 1806
v 3 Fe-N-O bend. 647 647
v 4 Fe-N str. 624
v 5 Fe-C-O bend. 560 560
v 6 Fe-C str. 380 383
v 7 N-Fe-N def. 87
v 8 C-Fe-C dei. 72
a2 Syrrunetry
v9 Fe-N-O bend. 591
v 10 Fe-C-O bend.
v Il C-Fe-N def.
b 1 Symmetry
v 12 N-O str. 1763 1762
v 13 Fe-N str. 659
v 14 Fe-N-Q bend.
v 15 Fe-C-O bend. 436 426
v 16 C-Fe-N def.
Vapour
IRd
2118
1847
654
619
482
382
180H
658
648
436
J
- 71 -
h 2 Symmetry
"17 c-o str. 2033 2034 2061
"18 Fe-N-O bend. 610 614
"19 Fe-C-O bend. 476 477 559
"20 Fe-C str. 445 447
"21 C-Fe-N def. 72
a Other bands, not assigned to fundamental modes, were observed
at: 835, 324, 313, 272 cm-1 in i.r. and 322, 307, 270 cm-1 in
Raman.
b -1 The solvents used in the different regions are: 2100-300 cm -1 (CS 2), 300-60 cm (benzene) .
c Obtained for CS 2 solution in the 2100-1700 and 850-250 cm-1
regions. For the regions obscured by the solvent, the spectrum
was run for the CC1 4 solution.
d From reference 5.
J
- 72 -
data have a1so been successfu1ly used in correlc.ting bonding
effects in Fe(CO)2(NO)2 and its derivatives. In particular,
-1 sorne assignments in the low frequency (700-400 cm ) region
are uniquely based upon such arguments. The assignment of
the Fe-N-O and Fe-C-O fundamentals of Fe(CO)2(NO)2 to speciZic
frequency ranges, has also been experimental1y verified.
PART II
SELECTED CYCLIC DIENE COHPLEXES OF
CHRmnUM, 110LYBDENUM, TUNGSTEN, IRON AND COPPER
- 73 -
CHAPTER 1. IN'.L'?ODUCTION
Although a large number of metal-olefin compounds have been
synthesized since the early 1950'5, the vibrational spectra of
these complexes have received little attention. Complete
vibrational assignments have been achieved only for Zeise's
salt, K[Pt(C2H4
)C13
].2H20, and the corresponding dimer,
50-52 [Pt(C2H4 )C1 2 ]2' as weIl as for their palladium analogues •
However, even for these relatively simple systems, arguments
have been raised recently concerning the assignment of the
coordinated v (C=C) mode. Partial vibraticnal assignments have
been attempted·only for u few of the more complex metal-olefin
systems containing ole fins such as butadiene, 1,5-cyclooctadiene
(COD) , bicyclo[2.2.1]hepta-2,5-diene (norbornadiene, NBD) , and
1,3,5,7-cyclooctatetraene (COT).
In this \-'lOrk, i t was planned to obtain vibrational assign-
rnents for two sets of complexes containing t\\·o of the above-
mentioned larger ligands viz., NBD and COD. Ir. metal-olefin
complexes of the types to be discussed, there are two important
parameters that characterize the bond between the rnetal and the
ole fin. Firstly, the shift in the position of the v (C=C)
fundamental provides sorne clue as to the change in electron
density in the C=C group upon coordination. Second, the strength
of the metal-olefin bond is reflected in the position of the
* V (~l-I,)
*
stretching mode. For the (NBD)H(CO)4 complexes to be
In this Part, M-L will ahvays refer to a metal-olefin bO!1d.
- 74 -
considered here, only one v(C=C) vibration has ~een assigned53 ,
,.,rhereas two a.re expected. Furthermore, no mention has been made
of the v(~-L) vibrations. In the case of one of the COD complexes
that are also dealt with here, a partial vibration al assignment
54 was published when this vlork ha.d just been completed . Again,
only one \1 (C=C) mode \'las assigned, and the v (r.1-L) vibrations
were considered in a somewhat curious fashion.
The work describeë: in this Part of the thesis was undertaken
in order to furnish a unified approach to the problem of the
assignment of the v (C=C) and v (H-L) fundamentals of metal-olefin
complexes. These complexes a!?pear frequently in transition metal
chemistry,' They are often intermediates in the heterogeneous
reduction of olefins, they also appear in catalysis and as
intermediates in synthetic problems, ~-;rhile they have been widely
used, they have been li·ttle charvcterized. Before presenting the
results of the author's own work, the pres8ntly available
vibrational assignments for metal-ole fin complexes ':lill be
reviewed in Chapter 2. In Chapter 3, vibrational assigmnents
will be proposed for NBD and (NBD)f.1(CO)4 (1'1 = Cr,Mo,W) complexes.
Finally 1 in Chapter 4, vibrational assignrnents v]ill be suggested
for [(COD) RhCl] 2' [(COD) cuCl1 2 and (COD) 2CuC104' A molecular
structure is also offered for the last species.
1
- 75 -
CHAPTER 2. REvrmv or VIBHi"\TIONAL ASSIGNI'-ŒNTS FOR
!.ffiTAL-OLEFIN COHPLEXES
This review will be presented in historical sequence \oTith
emphasis being placed upon the published assignments for v (C=C)
and v (M-L) modes. There \.;ill be no attempt to try and duplicate
the several very comprehensive reviews on metal-olefin
55-58 complexes . The review is considered to be complete until
June 1972.
In 1958, Powell and Sheppard50 assigned the v (C=C) modes
for several ethylene complexes (T~le XVI) •
v (C=C) lies in the 1530-1500 cm- l region.
For these molecules,
-1 A weak band, at 410 cm ,
at the far limi t of the range of their instrument, \'las assigned
tentatively to the metal-ethylene s·tretching vibration, v (M-L) •
Subsequent work 51 on Zeise's salt, including a force constant
calculation, confirmed these assignments. Force constant
calculations have also been carried out on Zeise's dimer and its ··2
palladium analogue::>. The data from both these studies are also
presented in Table XVI. These force constant calculations
emphasize the need to consider the metal-olefin stretching force
constant for an accurate estimate of the C=C bond strength, since
the position of the v (C=C) band is strongly influenced by the
o(CH2) mode coupled to it.
A controversy arose in 1969 when Hiraishi 59 reassigned v (C=C)
in Zeise's salt to 1243 cm-l, on the hasis of Raman data. This
low frequency is consistent with a bonding scheme in which the
ethylene is bonded to ~he metal atom through sing~e bonds from
[Pd(C2H4 ) C1 2 ] 2
[Pt(C2H4 )C12 ]2
K[Pt(C2H4)C1 3 ]·H2O
K[Pt(C2H4)C13 ]
[Pt(C2H4 )C1 2 (NH 3)]
- 76 -
Tlill LE XVI.
ASSIGNED v (C=C) FUNDAMENTALS
OF ETHYLENE COHPLEXES a (cm-1).
V(C=C)50 v(C=C)52
1525 w 1527 w
1506 \'1 1516 w
1516 1526 b vw w
1516 vw
1520 w
v(H_L)52
427 s
406 s, 408 s (R)
407 sb
383
a Samp1es were aIl run in the solid state, cither as pressed
disks or as Nujo1 and HCBD mu11s.
b Re ference 51.
each carbon atome In view of this, tl1e two expected v (I\i-L) modes
were assigned to peaks at 493 and 403 cm- 1 . Sirni1ar1y, assign-
ments were proposed for the ais and trans-C4H8 analogues of
.', 1 60 Zelse s sa t • It was concluded that although there is no
definite experimental supporting evidence, it is at least possible
to assign the C=C stretching modes to bands in the 1260 crn-1
region. As in the case of the ethy1ene compOl ... nds f the v (toi-L)
modes were assigned to bands around 490 and 400 -1 cm
61 In an attempt ta reso1ve this controversy, Powell gt al.
- 77 -
carried out i.r. and Raman studies on a series of Pt-olefin and
Ag-olefin complexes and reported their results earlier this year.
In this work, they introduced the follovling formalisme The C=C
vibration in the 1500 cm- l region is labelled Band l and the
o(CH2 ) mode in the 1260 cm- l region is referred to as Band II.
These two modes are considered to be coupled, wi th the 'J (C=C)
vibration distributed among the two bands. The summed percentage
changes of Bands l and II, upon coordination, are related to the
metal-olefin bond strength. Also, assuming that "the maj or part
of the combined frequency change will be associated wi th the band
of greatest fractional v (C=C) character", i t is seen tha't Band 1,
-1 in the 150'0 cm region, is due mainly to the v(C=C) mode in all
the substituted Ethylene complexes ('rable XVII). For the Ethylene
complexes themselves, this work supports the assignrnent of
H' • h' 59 b 1 è' h . 1" f h ( ) __ .!.ra1S 1 , Y conc u .1n<] t at there 1S al: _ m1X.l.ng 0 t e v C=C
mode in Bands l and II.
Two extreme bonding possibilities for a metal-olefin bond
are shmvn in Figure 18. It is, of course, probable that the "real"
bonding picture is a mixture of the two. In the case of the
ethylene complexes, it seems that Figure l8B is a more accurate
description of the ethylenic bonding in view of the C=C
assignments. This implies that there should be two l-i-L stretching
fundamentals: a symmetric and asymnletric one, as diagrarr~ed below.
\ / C
M-: "c /\
L
ethy1ene
[Ag.L] +
K [PtCl3 .,L]
ais -2 -butene
[Ag. L] +
K [PtC13
.L]
trans-2-butene
[Ag.L] +
K [PtC1 3 • L] ,
- 78 -
'l'ABLE XVII.
SHIFT IN BANDS RELATED
TO v(C=C) VIBRATIONS
Band l Band II
1623 1324
1579 2.5 1320 1.5
1515 6.5 1240 7.5
1660 1255
1597 4.0 1250 0.5
1503 9.5 1242 1.0
ln 75 1308
1615 3.5 1302 0.5
1526 9.0 1263 3.5
4.0 275
14.0 493, 405
4.5 280
10.5 489, 404
4.0 290
12.5 493, 386
However, a1though two were assigned in the case of the p1atinum
comp1ex, (Table XVII), on1y one was assigned to the sil ver comp1ex.
The reverse bonding picture is indicated for the substituted
ethy1ene complexes. But there still seems to be a discrepancy
between the predicted single v(M-L) fundamenta1 assigned for the
sil ver complexes and the two such fundamenta1s assigned for the
platinlli~ complexes.
;'-
\/ c
M~II C /\
- 79 -
(A)
Figure 18. Possible metal-olefin bonding schemes.
(B)
54 In a study published six months ago, Powell and Leedham
extended their vibrational studies to a series of 1,5-cyclo-
octadiene complexes. The Band l and II formalism was used in
the same \vay as above. It was concluded 'chat the v (C=C)
-1 fundamental is again predominantlyassociated with the 1500 cm
band. The proposed vibrational assignments are given in Table
XVIII. There seems ta be an inherent contradiction in t.he way
the v (C=C) and v (H-L) modes are assigned. Naintaining that the
C=C vibrations are in the neighbourhood of 1500 cm-l, a bonding
scheme represented by diagram A in Figure 18, is implied. In
this case, for the palladium and platinum complexes, there should
be only two M-L vibrations, instead of the four that were assigned.
In addition, blO v (C=C) modes are expected for these C2v complexes,
and four for the D2h rhodium dimer. Only in the case of the
palladium complex was mention made of a second v(C=C} mode.
Vibrational assignments have been made for' a nurnber of o~~er
metal-olefin complexes. The proposed assignments are collected
together in Table XIX. For aIl of these complexes, except
(C4H6 }Fe(CO}3 and, (COT)Fe(CO}3' the same problem mentioned above
COD
(COD)PdC1 2
(COD)PtC1 2
[(COD) RhC1] 2
- 80 .-
TABLE XVIII.
ASSIGNED FUNDAl'ŒNT1\LS OF
HETAL-CYCLOOCTADIENE SYSTEMS (cm- 1).
'J (C=C) 'J (M-L)
IR Raman IR
1658 s 1644 s
1524 s 1522 vs 570 m, 464 vs 569
1511 rr....v 415 w, 350 w 413
1496 m 1500 vs 588m, 480 s 587
461 m, 378 \v 461
1474 m 1476 vs 583 \'1 , 490 vs 586
476 vs, 388 ms 480
Raman
mw, 464 TIl
vs 1 352 m
m, 482 m
vs, 385 m
rnw , 480 vs
vs, 393 s
is encountered viz. on1y one C=C fundamenta1 is assigned to a
meta1-diene system.
(NBD) Cr(CO) 4
(NBD) Mo (CO) 4
(NBD) W (CO)4
(NBD) PtC12
(NBD) RuC1 2
(NBD) RUBr2
2CuBr.NBD
2AgN03 ·NBD
(COT) Fe (CO) 3
[(COT) RhC1] 2
(C4H6 jFe(CO) 3
- 81 -
TABLE XIX.
ASSIGNED FUNDAMENTALS OF VARIOUS
HETAL-OLEFIN COMPLEXES (crn-1).
v (C=C) 'J (H-L)
IR Raman Raman Medium
1438 solution
1438
1420
1436 m mu11
1420 vw
1438 fil
1471 \I!
1470 m
1562 a 1562 a solution m m
1490 TIl 1460 5 330 vs
1630 wa mu11
1410 w
1439 m 1477 w 351 3 neat 1ig.
a Vibrationa1 mode of an uncomplexed C=C group.
ReL
53
62
63
64
65
- 82 -
CHJ..PTER 3. TETRACl\FŒONYLI.JORBORNADIENEj·;ETAL (0) COMPLEXES
A. INTRODUCTION
It appears from the Revie'i,v that vibrational assignments of
metal-olefin species have been restricted mainly to complexes
containing small olefins. In particular, little systematic
work has been done on metal-olefin complexes of the bicyclic
ligand norbornadiene (bicyclo[2.2.l]hepta-2,S-diene, C7H8).
\\1hen the syntheses of the Group VIII complexes, (NBD) RuC1 2 ,
[(NBD)RhCl]2' (NBD)PtC1 2 and (NBD)PdC1 2 were reported, a few
frequencies were reported but none were assigned66 . Infrared
data for (NBD) Fe(CO) 3 have been published but only the v (C-H)
and v (C-O) bands were assigned67 . P..l though t'flO v (C=C) modes
are expected for 1T-bonded diei1e complexes, on1y one has been
assigned for each of the following complexes in the region
indicated in parentheses: (NBD)PtX2 and (NBD)PdX 2 (1440-
-1 68 -1 62 1430 cm ) ,(NBD)HX2
(1470-1420 cm ) ,(ilBD)M(CO)4 (1438-
1420 cm- l )S3.
The work described in this Part of the thesis was initiated
in order to provide sorne definitive assignments for the vib-
rational spectra of the three (NBD)M(CO)4 complexe~ (M = Cr,Mo,W).
The focus of interest was the determination of reliable assign-
ments for both the v(C=C) and metal-olefin stretching vibrations.
Since no X-ray data were available on these compounds, i t "vas
also of interest to ascertain whether or not there is a
spectroscopically observable change in the geometry of the
- 83 -
ligand upon coordination. In addition, it was hoped to make
sorne tentative assignments for the vibrational spectra of the
free ligand itself.
B. EXPERIMENTAL
'l'etracal>DonyZnorboï.'nadienechromium(OJ, (NBD) Cr(CO) 4'
tetraaarbonyZnorbornadienemoZybdenum(OJ, (NBD) Mo(CO) 4' and
tetracarbonyZnorbornadienetungsten(Oj, (NBD)W(CO) 4 were prepared
by Miss. D. Johanssoni the chromium and molybdenum species by
the direct method of King69 , the tungsten complex through the
t ' t' t '1 d ' t' 70 h f tl "" r1.s-ace on1. r1. e er1. va 1. ve . Eac 0 le compounL<.s \"as
resublimed by the author before spectra were run. To ensure
that there was no polymerization of the free ligand, it was
vacuum distilled (125 mm IIg/33°) immediately prior ta use. The
resul ting liquid gave one sharp peak in agas chromatograph.
The i. r. of "the ligand was run as a neat liquid, the
chromium and molybdenum complexes were run as CS 2 and CC1 4
solutions in a pair of 1.0 mm KBr solution cells. The spectrum
of the tungsten complex was obtained for Nujol and hexachloro-
butadiene (HCBD) mulls.
The Raman spectra of the complexes were obtained for the
powdered solids in Pyrex capillary tubes, using the 647.1 and
520.8 nm laser lines for excitation. A partial solution spectruID
of (NBD)W(CO)4 in freshly dried and deaerated benzene was also
obtained in a qual:"tz solution cell (647.1 nm/40m~'1). The spectrum
of the free ligand was also obtained in this solution cell. The
- 84 -
solid state spectrum of NBD \'las recorded at liquid ni trogen
temperature using the apparatus sketched below.
s~
"'e r' \
c. RESt1'I~TS AND DISCUSSION
1. Norbornadiene
e - evacuated
i - incident laser bearn
5 - scattered laser beam
A partial spectroscopie investigation of this, olefin in the
solid, liquid and vapour phases has been carried out recently by
Baglin71 • On the basis of both i.r. and Raman data, aIl the
bands in the v(C-H) region were assigned. Furthe~more, the
antisymmetric v(C=C) mode was assigned tentatively to the i.r.
-1 band at 1543 cm •
- 85 -
The i.r. and solid state (-196°) Raman spectra of NBD
* recorded in the present \'lOrk are shown in Figures 19 and 20;
the actual frequencies are listed in Table xx. The data in the
v (C-H) region are in good agreement \Vi th those of Baglin. In
this work, the solid state Raman spectrum at -196° was also
recorded. Extremely good resolution \vas obtained throughout
the whole spectral region; peaks which appeared as shoulders in
the spectrum of the liquid \vere clearly resolved in that of the
solide
As Baglin pointed out, there are two extra polarized bands
in the v(C-H) region. He attributed these to Fermi resonance 72
between the v(C-H) fundamentals and the lower energy v(C=C) and
o (CH2 ) modes. It will be shown shortly (vide infra, pp.105) that
this suggestion i5 substantiated by the spectra of the (NBD) H(CO) 4
complexes. A comparison of the solid state and liquid Raman
spectra of NBD reveals two additional small peaks at 3085 and
-1 3050 cm • These are assigned tentatively to correlation field
spli tting. Baglin' s reasons for his assignments can be appre-
ciated but it is a little'difficult to see how he distinguished
50 readily between the various hl and b 2 modes without actually
seeing hi5 i..r. vapour spectrum.
The two v (C=C) fundamen'tals (a~ and b 1) are expected to J. ....
appear somewhere in the 1700-1500 cm- l region. The al mode
* Some of the subsequently shown Raman spectra are reproduced in
such a TJlay 'that the intensities of the peaks across the 2pectral
range are not relative to each other.
('or
- 00 -
(A) Figure 19. Infrared spectrum of norbornadiene (neat
1iquid) .
(B) Figure 20. Raman spectrum of norbornadiene (-196°C).
Instrument Contro1s 1680-20 3160-2830
Exc. 647.1 647.1
Power 55 80
Slit 4 4
Sens. 10 3 5 x 10 2
T.C. 2 2
Scan 20 20
Chart 24 24
(A)
.~.':..
o o
1 ~Q
t ~ ~~ 1
r 1
r~ 1
1
r
o c -----s;
(B)
.- 87 -
should be strong and polarized in the Raman, but weak in the i.r.
spectrum. The b l mode is expected to be stronger in the i.r • .....
spectrum. On this basis, the strong polarized Raman band for
-1 the liquid at 1574 cm , \.,i th no i. r. counterpart, is assigned
to the al v (C=C) mode. -1 The strong i.r. band at lS44 cm is
assigned to the corresponding b1
mode.
Certain other somewhat tentative conclusions may be inferred
73 74 from the assigned i.r. and Raman spectra ' of the C2v species,
cyclopentene (C5
H6). In the Raman spectrum of liquid C
SH
6, aIl
the strong bands are due exclusively to al fundamentals.
Similarly, the strong bands in the R~man spectrurn of liquid NBD
should also be due to al vibrations; this is indeed found to be
true on the basis of depolarization measurements. The very
intense polarized band a'c 1108 cm- 1 is assigned to an al ring
-1 mode by analogy with the al ring mode in C
SH6 at 1107 cm In
addition, the very strong totally polarized band at 937 cm- l is
also assigned to a symmetric al ring mode.
For C? syrnmetry, NBD should exhibit 31 i.r.-active modes _v
(12 al + 9b l + 10b2 ) and 39 Raman active modes (the above + 8a2 ).
Eight of these modes {3al + a2 + 2b l + 2b 2 } are accounted for
by the v(C-H) vibrations. As expected, nine polarized lines are
-1 observed in the 1600-400 cm regioni however, one of these at
1601 cm- l is most probably due to a cornbination band. Both the
i. r. and Raman spectra exhibi t fewer than the anticipated number
of fundamentals. However, since the molGcular geometry has been
, l' h d . h J 75,76. t ,., -estao 1.8 e as C2~ l.n t e vapour plase , l.t seems IllOS _].KeLy
IR
1iquid
3148 (sh)
3125 (11)
3105 (11)
3070 (32)
2991 (50)
2975 (sh)
2938 ( 44)
2873 ( 34)
1641 ( 4)
1600 (2)
1544 (34)
- 88 -
TABLE XX.
VIBRATIONAL FREQUENCIES
OF NORBORNADIENE (cm-1 ).
Raman
1iquid solid(-196°} Assignment
3148 (1) 3146 (3)
3125 (2) 3119 (5) vinyl b 2
3103 ( 14) 3098 (26) viny1 al F. R.
3085 (2) solid state sp1ito
3075 (sh) 3070 (25)
3065 ( 14) 3060 (24) vinyl al F.R.
3050 (5) solid state split.
2993 ( 13) 3001 (40) bridgehead al
2988 (52)
2970 (sh) 2973 (32)
2939 ( 8) 2934 (1.4 ) met,hy1ene al F.R.
2871 ( 6') 2867 (14) methy1ene al F.R.
* 1601 ( 7) P 1603 (2)
1574 (42) P 1575 (24) \) (C=C) al
1,560 ( 4)
\) (C=C) b 1
\) (C-H)
- 89 -
1450 (9) 1451 (4) op 1447 (10)
1391 (1)
1334 (sh)
1311 (50)
1269 (2) 1271 (3) dp 1274 ( 2)
1249 ( 1)
1240 (6)
1226 (20) 1230 (12) P 1228 ( 22)
1204 ( 18) 1209 ( 3)
1149 ( 8) 1150 (2) 1150 ( 12)
1104 ( 4) 1103 ( 77) P 1114 (26) ring al
1107 (sh)
1102 ( 88)
1071 (5)
1062 ( 4) 1062 (5)
1015 ( 4) 1018 (2) 1017 (9)
956 ( 24)
934 ( 15) 937 (72) P 934 ( 110) ring al
911 (6) 910 (sh) P 913 (25)
891 (sh) 891 (sh) dp 897 ( 24)
880 ( 17)
873 (40) 876 (12) P 874 ( 7)
797 (35) 797 ( 1) 802 (10)
774 (2) ïï5 (27) "" 775 (19) 1::
726 (70) 729 ( 2) 733 ( 2)
710 (1)
- 90 -
665 (60) 667 (4)
541 (6 ) 542 (8) dp 543 (50)
501 (30)
444 ( 8) dp 446 ( 31)
421 (20) 423 (10) P 430 ( 42)
101 ( 60)
74 (26)
58 (10)
42 ( Il)
* In this and the following Taoles, "p Il denotes a totally
polarized Raman band \vhile "p" signifies a polarized band wi th
a depolarization ratio (p) of 0<p<3j4.
that a number of the fundamentals are too Vleak to be observed.
The assignments that can be made wi th any confidence are
given in Table xx.
2. Vibrational Assignments of Norbornadiene Complexes
The i.r. and Raman spectra of the (NBD)M(CO)4 (M = Cr,Mo,W)
complexes are shown in Figures 21-26. The vibrational frequencies
of the compounds in the various phases are listed in Tables XXI
and XXII. For the purposes of easier comparison, the spectra
of the complexes and of the free ligand are presented in bar
·graph form in Figures 27 and 28.
- 91 -
(A) Figure 21. Infrared spectrum of (NBD)Cr(CO)4 (CS 2 and
C2C1 4 solutions) .
(B) Figure 22. Raman spectrum of (NBD)Cr(CO)4 (solid state).
Instrument Controls 2100-20 3150-2830
Exc. 647.1 647.1
Power 40 40
Slit 4 4
Sens. 2 x 10 3 10 2
T.C. .5 10
Scan 50 10
Chart 48 48
i 1
!
._~ .. ~ C7"_ ~ -- _ .
i ,;---~~~~7-
C (~-'---
;--r:::..
~::.: --:.~ .,.-- .~_ ..
j:. i .. ,
(
f~-< 1
1 1
\ ~-
3JNVllIVIISNV<i1
(A)
-==
{
---J
------------~
-"==-=-------~ '-,
-', ? .:.
1. }
-"'->------------.-:- ---._-=:;. -------~
-,.-._~-- ---~-------"?~
(
A1ISN3.LNI
o o o C\J
o o al C\J
o o M
(B)
.. -..:........:.-:.-:.:.::::.'?:'-~.- ---~~.s.-_ ..... ;:=-._:;.:~----::- .. -:-::.-=::'- ------sa
-------~.:.-=..:..:::...--
-==-=====-~-: - ----
"E u
o o ..
g CO
- 92 ..
(A) Figure 23. Infrared spectrum of (NBD)Mo(Cù)4 (CS 2 anà
C2C1 4 solutions) •
(B) Figure 24. Raman spectrum of (NBD) Mo(CO) 4 '(solid state) .
Instrument Contro1s 760-20 1480-760 2200-1840 3160-2830
Exc. 520.8 520.8 520.8 520.8
Power 40 40 40 40
Slit 4 4 4 4
Sens. 2 x 10 3 5 x 10 2 2 x 10 3 10 2
T.C. 2 2 2 10
Scan 20 20 50 10
Chart 48 48 48 24
\
~
1
·1 1
i 1
l._:::~
c--------·-~..::--=-~ -----
(A)
o o Cl)
--" - ---_. __ ._--
-~»
. \ 1
._-----._. -----'
U IStJ:31 NI
(B)
. ....
. '~
.. i
\[1 ~ ,~
'" .' i '- . i
1
1
1 1
1
1
. --'---. -
.......
(B)
- 93 -
(A) Figure 25. Infrared spectrum of (NBD)H(CO)4 (Nujo1 and
HCBD mu11s) •
(B) Figure 26. Raman spectrum of (NBD) ~q(CO) 4 (solid sta·te) .
Instrument 2080·-1830 Contro1s 1380-20 1480-1380 3180-2930
Exc. 647.1 647.1 647.1
Power 30 30 30
Slit 4 4 6
Sens. 10 2 5 x 10 5 x 10
T.C. 10 10 40
Scan 10 10 5
Chart 24 24 12
~--_._----~~-=-~
3:)N'~ 1.1.IV'lJSNV'è::Il
(A)
o o <r
o o co
o L.O
C\I ..-
o o o «)
~"
':"liSN31NI
:.C.
o 8 C\I
o
I~
1
~
(B)
•
-.:.> -----
'.
;-.~
i
< "
:i
.. }
" " -.::. , . ~ .~
i " " 1
~ , 1
,,' 1
~
} ....
-< ;·f ~ . . ~
"
). ~ .: ..
:" ~.)
'/ . -1 "}
} .~ J { , l'
~ ~.
t 1 1
!
I§
1
1
i , ___ , __________ .-J
~11SN31NI
~::' ::..
"~
~ .......
;r
A11S"'431NI
(Bj
-. ) l 'c ~ .. ~
'.
~ )
1 / , (
~ ~
t (
~
','
') , ,
) , -......
' . . , .. ~ .
.' " -'1 .. Y i "-
ID t , LO
i '" ) 1
{
1 " S ? 1
t 1 1 .. 1 ~
! ~j
<:~ "'=' ~ j' l .... > 1 ( 1
___ ._.J
_. 94 -
(A) Figure 27. Bar-graph representations of the {NBD)M(CO)4
infrared spectra. (M = Cr,Mo,N)
(B) Figure 28. Bar-graph representations of the (NBD) M(CO) 4
Raman spcctra. (M = Cr,Mo,W)
j
J 1
---.. ----1 1
J
@"Q i z :::l 1
g i
i 1
i 1
---{ _----1 _--"l ---1
-=f --1 1
1
--1 1
.l:
1
-- --1 1
...{.;
-----J 1
1
! i-
l
cr ~ C 1 o 0 .
~ +.
Ô -6 dl CIl '
~
-_._----' 1 --; L
--' 1 1
i
--J -1 ._.J
-i -,
. _ ... _ 0 o N
.. -
___ ___ --j=1 ,-
-L Ig I~ 1
r
1
-,,- .. ·---rl .. ---. -. - -'1
.) ~
1
__ 1
(!-\) __ ~ _________ J
1 -Ï
(B)
(NBD) Cr (CO) 4
solutiona
3958 (4)
3928 (2)
3884 (1)
3844 (2)
3797 (1)
3094 (1)
3078 Cl)
3004 (15)
2963 (11)
2927 (5)
2906 (sh)
2849 (9)
2034 s
2006 w (13 CO)
1959 m
1944 vs
- 95 -
Tf.BLE XXI.
INFRARED FREQUENCIES
-1 OF 'l'HE (NBD)H(CO)4 COHPLEXES (cm ).
(NBD) Ho (CO) 4
, . a SO.Lutlon
3978 (8)
3939 (3)
3896 (2)
3835 (5)
3790 (3)
3091 (3)
3074 (sh)
3002 (27)
2965 (17)
2940 (1)
2924 (15)
2884 (2)
2847 (7)
2044 s
2031 w (13 CO)
1958 s
1925 \ol (13 CO)
(NBD)1tl (CO) 4
solidb
3093 (14)
3080 (8).
3015 (15)
3003 (24)
2970 (14)
2932 (13)
2889 (2)
2845 (3)
2044 s
2031 w (13 CO)
1957 s
19 2 4 w (13 CO )
Assignment
l v (C-OJ
1 :::=:::::ons
v{C-H)
- 96 -
1915 vs 1911 s 1910 s v (C-Q)
1885 \'1 (13 CO) 1882 \'1 (13 CO) 1881 w ( 13 CO )
1455 (4 ) 1456 ( 17) 1446 (6 ) o (CH 2 )
1433 (10) 1435 (37) 1428 ( Il) } V (C~C)
1426 (sh) 1429 (sh) 1418 ( 3)
1309 ( 17) 1304 ( 35) 1306 (19)
1251 (2)
1237 (2) 1233 (4) 1237 (4)
1225 ( 1) 1219 ( 3)
1184 (34) 1182 (35) 1181 (12)
1158 ( 7) 1150 ( 15) 1160 (10)
1124 ( 1) 1121 (1)
1103 ( 1) 1102 ( 1) 1108 ( 7)
1087 ( 8) 1082 ( 15) 1080 ( 15)
1042 (5) 1036 (16) 1039 ( Il)
1007 ( 3) 1007 (5) 1008 ( 2)
946 ( 5) 960 (10) 980 ( 4)
930 ( 3) 940 ( 13) 946 ( 4)
920 ( 8) 926 ( 8)
911 ( 7)
899 (2) 895 (9) 897 ( 8)
867 ( 3) 869 ( 1) 860 ( 3)
797 (2 ) 791 (3 ) 799 (4 )
785 (6) 779 (15) 783 (9)
759 (9 ) 724 (10) 749 ( 2)
.. 97 -
667 ( 35) 655 ( 4)
643 (sh)
635 ( 22)
621 ( 22) 616 (39) 616 (2 )
602 (25) 592 (2) 606 (22) cS (r·l-C-O)
570 (35) 570 ( 21)
549 ( 34) 547 (19)
515 (17) 503 ( 25) 511 ( 18)
496 (sh) 492 ( 7)
482 (6 )
494 (20)
466 ( 15) 462 ( 14)
448 (6) 437 ( 24) 446 (20) v (M-C)
433 ( 3) 39 J. (2) 391 ( 22)
326 ( 3)
a Obtained for CS2
and C2
C14
solutions. '"
b Recorded for Nujo1 and hexachlorobutadiene rou11s.
c v(C-Q) region was obtained for cyc~ohexane solution.
(NBD) Cr (CO) 4
solid
3102 (60 )
3097 (sh)
3083 (48)
3013 ( 45)
3003 (65)
2968 (20 )
2938 ( 20)
2924 (sh)
2849 ( 8)
2019 ( 22)
1961 (6)
1938 ( 60)
1922 (5)
1903 (3 )
1879 (37)
1456 ( 15)
- 98 -
Tli.BLE XXII.
RA1>11'.N FREQUENCIES
-1 OF THE (NBD)M(CO)4 COHPLEXES (cm ).
(NBD) Mo(CO) 4
solid
3100 (75)
3084 (58)
3014 (48)
3003 (67)
2969 (22)
2942 (10)
2928 (12)
2851 ( 10)
2033 (100)
1967 (20)
1943 (sh)
1932 ( 140)
1900 (5)
1876 (100)
1458 (40)
(NBD) W (CO) 4
solid
3097 ( 45)
3092 (sh)
3097 (34)
3013 (35)
3003 ( 35)
2968 (12)
2936 ( 12)
2926 ( 12)
2846 (6)
2030 (40)
1966 ( 8)
1938 (sh)
1929 (50 )
1895 (5)
1869 (43)
1447 (9)
. ta Ass~gnmen
1
v (C-H)
J
l 1
r v (C-O)
j ë (CH;2)
-- 99 .-
- 100 _.
469 ( 8) 464 (5 ) l 454 (46) 433 (200 ) 444 (80)
431 (sh) v (M-C)
411 (55) 405 (100 ) 414 (sh)
387 (10) 394 ( 3)
251 (42) 241 (28) 237 ( 18) } V (M-Ll
239 (35) 220 (100) 217 (45 )
142 (10) 136 (200) 137 (60 )
120 (110)
105 (170) 104 (sh) 99 (400 )
95 (1000) o (C-r.1-C)
82 (12) 77 (sh) 77 (30) o (C-Ivl-L)
52 (30) 63 (10) o (L-M-L)
41 ( 8) 48 (180 ) 49 (sh) 1attice
43 (40) modes
31 (25) 28 (100) 25 (sh)
a Specifie assignments for both the i.r. and Raman spectra are
presented in Table xxv.
- 101 -
o 1
C
0" 1 t: c,"'-t----~~ 1 M~" 1 1
~ 1" :1~ O.,.C'--------::-:::...I '~~
C 1 o
Figure 29. Probable structure of. the (NBD)fJl(CO) 4 complexes.
X-ray studies have not becn perfo:crned on these cornpounds.
However, the rnolecular geornetry can be little else than
octahedral C2v ' with two of the ais positions being occupied
by the two olefinic groups (Figure 29). Based on this ffiolecular
configuration, the calculated number and symmetry of the
fundament.al modes are tabulated in Table XXIII.
The spectra will be considered in t.~ree distinct regic!ls:
\) (C-Q) , \) (C=C) and 10\'1 frequ.ency vibrations.
- 102 -
TABLE XXIII.
SYHBETRIES OF' THE FUNDl'..MENTAL MODES
OF THE (NBD) M(CO)'1 C0i-1PLEXES a
Fundamenta1 Symmetry No. IR/R bands
\) (C-O) 2a1 + b l + b 2 4/4
\) (M-C) 2a 1 + b l + b 2 4/4
\) (M-L) al + b l 2/2
\) (C=C) al + b l 2/2
o (M-C-O) 2a 1 + 2a 2 + 2b 1 + 2b 2 6/8
o (C-H-C) 2a1 + 0. 2 + b l + b 2 4/5
o (C-M-L) a 2 + b 1 + b 2 2/3
o (L-M-L) 0.1 1/1
a <Ming to the comp1exity of the ligand, the various bending,
stretching and deformation modes associated with NBD, except for
\) (C=C) and \) (~1-L) , ,vere not considered.
a. C-O Stretching Vibrations
From Table XXIII, one predicts four IR/R active CO
-1 fundamentals (2a
1 -1- b
l + b
2) in the 2050-1850 cm region. Only
three bands are observed in the solid state Raman and solution
i.r. spectra (execpt for the i.r. spectrum of the chromium
- 103 -
complex) which can be attributed to these fundamentals. Since
a molecular geometry having a symmetry higher than C2v is
di fficult to imagine, ei "ther there is an accident al degeneracy
between two of the modes or one of the fundamentals is too weak
to be observed. The first suggestion is supported by several
arguments. The observed stretching frequencies for (NBD) vi (CO) 4
in benzene solution are 2040 (S/P), 1943 (s,dp) and 1891 (m,dp)cm- l .
As expected77 , the 2040 cm- l band is one of the al modes. The
middle bands in the Raman spectra of the three complexes are
always more :intense than the highest frequency al peaks. This
observation supports the assumption - deouced by inspection of
the i.r. spectra of the three compounds - that the middle two
bands in the i.r. spectrum of the chromium complex coalesce to
give one band in the spectra of the molybdenum and tungsten
complexes. It seems likely that the intensity of the central
Raman band for each of the three complexes is enhanced by the al
component of this accidentally degenerate pair of lines. ~1is
postulated degeneracy is clearly supported by measurements of the
* absolute integrated i.r. intensities of these bands.
As a consequence of these arguments, the c-o regions of the
~he absolute integrated i.r. intensities of the v(C-Q) bands
of these complexes, in order of decreasing frequency, are
tabulated on the next page (designated, for the sake of simplici ty , ·-1 -2
as vI to \)4). The units are H cm ,the values quoted are fOI"
10 -4 E, where E is the absolute in tegrated in tensi ty obf;ained by
W;lson and Wells method78 . 1~1' D J 1 -.... _ \1' lSS • • 0 1ansson, persor~a.!.
conununication) •
- 104 -
vibrational spectra have been assigned. The highest frequcncy
band has been shmln to be a polaLized al mode. In addition,
the middle bands are due to overlapping of the other al mode
with either b l or b 2 • From the Ra..'11an depolarization measure
ments for the tungs ten complex, the lo\vest frequency CO funda
mentaIs at ~1870 cm- l must be attributed to either the b l or b 2
modes. No further distinction can be made in the absence of
polarized single crystal measurements. In partial support of aIl
these assignments, a similar situation exists 79 ,80 for the
structurally related isoelectronic tetracarbonyl complex,
ais-Fe (CO) 4I2.
The three v.'eak peaks in the solid s tab.:: :Raman spectra are
due either to factor group splitting of the CO fundamentals or
to combination vibrations.
b. C=C Stretching Vibrations
The C=C vibrations of the NBD ligand, shift to lower
" .. h th f l' 61 frequency upon coord~nat~on. In Ilne w~t e orma lsm
discussed in the Review (vide supra, p. 77 ), "Band I" in the
(NBD)M(CO)4 complexes can be considered to be tl1e bands near
* Footnote continued from previous page.
(NBD)M(CO)4 10-4 E
M "1 "2 "., "4 .;)
Cr 3.54 ± 0.42 2.26 ± 0.52 9.57 ± 1. 24 7.99 ± 0.28
Mo 2.57 ± 0.25 13.8 ± 0.50 9.90 ± 0.52
W 2.79 ± 0.08 14.4 ± 1.0 8.37 i 0.43
1420 -1
cm
.- 105 _.
The shift in these bands, from 1574 and 1544 cm- l
in the free ligand, is in the order of 10%. Considering "Band III!
as the strong Raman bands a·t '\.01220 cm-l, the maximum shift in
these bands upon coordination is 0.4%. Thus, in accordance wi th
Powell et al' s formalism, the fra.ctional v (C=C) character is
much greater in Band 1. Therefore, the v (C=C) fundamentals can
be assigned to peaks in the 1450-1400 cm- l region. However,
there are three bands in this spectral region for each of the
complexes. Presumably, two of these are due to the v(C=C)
fundamentals of the complexed olefin, while the third is due to
the 0 (CH2
) methylene bending Ip.ode, also present in this region
in the spectrum of the free ligand. These bands can be assigned
unequivocally by considering carefully the modes in the v(C-H)
region.
Baglin found tvlO extra polarized lines in the Raman spectrt.lli1
of liquid NBD in the v (C-H) region. He at tributed these bands
to Fermi resonance between the C-H and 10\ver-lying fundamentals.
A Fermi doublet vias assigned to the peaks observed in ·the
-1 present work at 3103 and 3065 cm . This results from the
interac·tion of the firs t overtone of the b 1 v (C=C) mode at
-1 1544 cm wi th the al component of -the vinyl stretch ealeulated
to be near 3080 cm -1. In ·the NBD complexes, both C=C funda-
ment.als are shi fted to lovler frequencies upon coordination.
Consequen·tly, this Fermi resonance is expect.ed to disappear.
This is indeed found to be the case. -1 The 3065 cm Raman band
of the free ligand, as weIl as the i.r. bands at 3105 and 3070 cm- l
- 106 -
disappear in the solid state spectra of the complexes. Also,
a new strong band appears in the Raman spectra of the complexed
species in the 3085-3079 cm- l region. This band is not due to
solid state splitting in the Raman spectra (cf. solution and
solid state i.r.). These bands, together with the corresponding
weak bands in the i.r., are assigned to the vinyl al stretching
modes. Their freqllencies are in good agreement with the
ealaulated value of the undisturbed vinyl al stretching mode in
the free ligand at 3080 cm- l (The relative intensities of these
bands in the i. r. and Raman are also in accord wi th the assign-
ment. Such symmetric fundamentals are expected to be strong in
Raman and weak in i.r.) -1 'The hand near 3100 cm ,strong in Raman
and weak in i.r., is considered to be the 3125 cm- l band of the
free ligand that has shifted to lower frequency upon coordination.
A second Fermi doublet \17as assigned by Baglin to the pair
-1 of lines at 2939 and 2871 cm • They ,,,ere postulated to result
from the inte~action of the first overtone of the methylene al
bending mode at 1451 cm-l and the al methylene C-H stretching
fundamental. This undisturbed methylene stretching mode can be
caZaulated to be near 2908 cm- l in the free ligand.
The sa~e Fermi resonance is also assumed to be present in
the spectra of the complexes. -1 The low frequency band 'Ù2850 cm
is assigned as one component of the Fermi doublet involving the
al methy lene bending and stretching fundamenotals. Since the
atoms of the methylene group are the farthest from the coor~ination
si tes in the ligand, i t is reasonable to assume tha"i::o the -v·ibrati.ons
- 107 -
of this group will be lit tle affected by coordination of the
ligand. Thus, considering the Fermi doublet in the complex to
be centered at about the same frcquency as in the free ligand,
the other component of the doublet can be taken as the peak at
-1 2968 cm . Fermi resonance can be expected to occur if, in
-1 conjunction with the 2968 and 2850 cm doublets, the highest
frequency band in the 1450-1400 cm- l region is assigned to the
hl mechylene bending mode. The result of these calculations
using the frequencies obtained from the Raman spectra and the
following equation
o (CH 2 ) cale = F.R.l + F.R.2 - 2 [05 (CH 2 ) obs]
(F.R. referring. to one peak of the Fermi doublets) 1 are shown in
Table XXIV. These values indicate that there is a high
probabili ty of Fermi resonance bet~-Jeen the firs t overtone of
the methylenic cS (CH 2 ) vibration and the v (CH2 ) fundamental.
In the case of the chromium complex, for exan~le, 2 x o(CH2 ) = -1 2 x 1456 = 2912 cm ,which is close enough to the ealculated
fundamental at 2905 cm- l for interaction to occur. These
caZcuZated values are in good agreement with the caZcuZated value
-1 of the s ame mode in the free ligand at 2908 cm • It should be
emphasized that assignment of the peak around 2940 cm- l as the
second component of the Fermi doublet, as in the case of the
free ligand t gives rise to an improbable situation. No matter
which of the bands in the vicinity of 1430 cm- l is assigned to
the cS (CH 2 ) mode, Fe::-mi resonance would have to occur behleen
bands si tuated at least 60 cm-- l apart.
F.R.l (obs)
F. R.2 (obs)
2 X ô(CII 2 ) (obs)
V(CH 2 ) ( cale)
- 108 -
TABLE XXIV.
FPEQUENCIES RELEVANT TG THE
FEPJH RESONANCE CALCULATIONS (cm -1) .
(NBD) Cr (CO) 4 (NBD) Ho (CO) 4
2849 2851
2968 2959
2 x1456=2912 2x1458=2916
2905 2904
(NBD) W (CO) 4
2846
2968
2x1447=2894
2920
On the basis of the arguments given above, the highest
frequency band in the 1450-1400 cm- l range of the spectra of the
three (NBD)H(CO) 4 complexes is assigned to t.~e ô (CH 2 ) fundamental.
This leaves the other two bands to be attributed to the al and
hl v(C=C) fundamental vibrations. From intensity arguments, the
middle band, strong in i.r. and weak in Raman, is assigned to
the hl m,ode; the 10'\vest band, strong in Raman and weak in i.r.,
is assigned to the al mode. These assignments were later con
firmed by a Raman spectrum of the tungsten complex in benzene
solution. -1 Of the three bands nt 1451, 1431 and 1407 cm ,only
the lowest one is totally polarized.
The proposed assignments are in accord with observed spectra
of other NBD complexes. For instance, in the i.r. spectra of the
- 109 -
cornpounds (NBD)PtX 2 and (NBD)PdX 2 , three bands were reported in
-1 68 the 1450-1390 cm region The pattern is the sarne as in the
carbonyl complexes v'i z. a high frequency mode in the region of
1449-1437 cm-1 and a pair of lines in the 1410-1390 cm-1 region.
In view of the arguments presented abOVê, these bands are assigned
* to the o(CH 2 ) and the two v(C=C) modes, respectively. The
position of the ô (CH 2 ) mode in the complexes, compared to that in
the free ligand (1451 -1 cm ), again il1ustrates that this mode is
little affected by coordination of the ligand. As expected, this'
is not the case for the olefinic stretching vibrations.
The 150 cm-1 ('\,10%) decrease in frequency of the v(C=C) modes
upon coordination is in agreement with that observed for similar
metal-olefin complexes. Accepting the fact that these C=C funda-
mentaIs must be coupled considerably with lower-lying funda-
51 52 mentaIs ' ,no attempt will be made to correlate the metal-
ligand bond strength with the frequency decrease of the v(C=C)
modes.
c. Lm-, Frequency Vibrations
In the spectra of the (NBD)M(CO)4 complexes, two v(M-L)
fundamentals (al + bl) are expected. In similar complexes, such
modes generally lie in the 500-300 cm- l region. In the present
case, however, these funda.mentals are assigned to the two Raman
* In an independe!1t study concurrent. with this onc.:: D.M. Adams and
W.S. Fernando have reached the same assignment for ti::ese complexes.
(Personal communication) .
- 110 -
bands in the 250-215 -1
CHl region. For these compounds, no other
fundamental mode could possibly appear in this range. The
func.:1amental rE:gions for metal-carbonyl mOÎt:ties have been
clearly delineated through assignments of a legion of carbonyl
cornplexes 9,10 . In particular, the v (M-C) modes do not fall below
360 cm-l, while the lattice vibrations and the C-M-C deformation
-1 modes do not come higher than about 150 cm . Furthermore, in
the solid state Raman spectrum of the free ligand, there are no
-1 bands in the 430-100 cm region. It follows, therefore, that
-1 the two strong Raman bands in the 250-215 cm region can be
assigned to the al and b l v(M-L) modes. On the basis of relative
intensit.ies, the stronger band is assigned to the al mode, the
weaker to the b l mode. These assignments are supported by
depolarization measurements for the tungsten complex in a benzene
solution; the 218 cm- l band is totally polarized, while the 234 cm- l
band is depolarized. These observations are in line with the
assignment of the stronger band to the al mode. Only in the case
of the chromium complex is the stronger al mode at a higher
* frequency than the hl mode. This assignment of the v(M-L)
vibrati~ns for these (NBD)M(CO)4 complexes is of particular
interest because this is one of the few times that they have been
assigned definitively without resorting to such exotic techniques
* D.M. Adams anà vl.S. Fernando, who have also studied the vibra
tional spectra of the (NBD)Cr(CO)4 complex, agrE:E: with the assign
ment of the biO low frequency bands as v (M-r.). Moreover, they
found the stronger band at 249 cm- l to be polarized. (Persol1al
communication)
- III -
as metal-isotope studies 99 .
'l'he bands due to the a (N-C-Q) and \i (M-C) fundamentals are
expected to appear in the '100-400 cm- l region. The bending
fundamentals should be observed at higher frequency than the
t t h · 9 ,10 s re c.lng ones . In addition, the bending modes should be
more intense in the i.r. and the stretching modes stronger in 65 81 the Raman ' • These expectations are fulfilled for the NBD
complexes. The four lowest frequency bands in this region,
strong in Raman and relativcly weak in i.r., are assigned to the
four. M-C stretching fundarnentals. Specifically, these are the
bands in the region of 497-411, 464-387 and 446-391 cm- l in the spectra of the chromiurn, molybdenum and tungsten complexes,
respecti vely. The two s trong Raman bands in each of these regions
are assigned to the ·two al M-C vibrational modes" The six or so bands falling above the prcviously mentioned regions and below 680 cm -1 are assigned to the r1-C-O bending fundamentals. E!ach
of these complexes exhibits a weak Raman band at ~55S cm- l
which is assigned tentatively to an a2
c(M-C-O) mode, owing to
its absence in the i.r. spectra.
The spectra below 150 cm- l should display altogether nine
C-M-C, C-M-L and L-M-L deformation modes, as weIl as various
lattice modes. About seven bands are observed but it is
impossible at this stageto gi ve ass ignments for these.
The vibrational assignments proposed above fer the three
NBD complexes are collected together .in Table XXV.
Fundamen·ta1
\) (C-H) viny 1 b~. .c..
\) (C-H) vinyl al
** \) ( CH 2) al·
\)(CH 2 ) *'k
al
\)(C-O) al
- 112 -
TABLE xxv.
l'..8SIGNMENT OF Fffi\!DA11EN'J'A.L r-mDES
-1 * OF THE (NBD)H(CO)4 CONPLEXES (cm).
(NBD) Cr (CO) 4 (NBD) Ho (CO) 4
IR R IR R
3102 3100
3078 3083 3074 3084
2963 2968 2965 2969
2849 2849 2847 2851
2034 2019 2044 2033
\) (C-O) a 1+b 1 or b~. 1959 1938 1958 1932 ,t..
1944
\) (C-O) b 1 or b 2 1915 1879 1911 1876
o(CH 2) b 1 1455 1456 1456 1458
\) (C=C} b 1 1433 1430 1435
\) (C=C) al 1426 1425 1429 1431
o (H-C-O) a2 552 554
\) (M-C) al 448 454 437 433
\) (M-C) al 433 411 405
\) (M-L) al 251 220
\) (M-L) b l 239 241
* The values used are from Tables XXI and XXII.
** Fermi doublet
(NBD)W(CO) 4
IR R
3097
3080 3079
2970 2968
2845 2846
2044 2030
1957 1929
1910 1869
1446 1447
1428 1426
1418 1412
556
446 444
431
217
237
- J.13 -
3. Geometry of Free and Complexed Ligand
Since the crystal structures of the (NBD)M(CO)4 complexes
have not been investigated, it is of interest to consider
whether or not there is any spectroscopically observable change
in the configuration of the ligand upon coordination. 'Th.ro
vapour phase electron diffraction studies have been carried out
on the uncomplexed ligand75 ,76. Both of these studies indicate
that the molecular syrnrnetry is approximately C2v . There have
also been X-ray studies on the complexed ligand. In [(NBD)CuCI]4'
the functional unit is a tetramer82 with the copper and chlorine
atoms forming én eight-ffiembered tub shape ring and only one of
the olefinic double bonds of NBD being coordinated to the copper.
In (NBD)PdCl 2 , both of the double bonds are coordinated to the
83 palladium atom • The NBD ligand retains it C2 symmetry in both _v
of these crystal structures. The relevant crystallographic data
are presented in Table XXVI.
rf,he apparent differences in the molecular parameters of the
free and éomplexed NBD Inolecule are Ilot really significant ..
Using a 3a criterion, meaningful differences exist only in the
C6 -CI -C2 angle (Figure 30) - this angle decreases upon coordination
of the ligand.
7
3
Figure 30. Vapour phase structure of l1orbornadiene.
- 1.14 -
TABLE XXVI.
MOLECULAR PARl>-,~1ETERS FOR BONDED N-ID NONBONDED NBD.
NBD75 [ (NBD) CuCl1 4 82 (NBD) PdC12
83
(C=C) (A) 1.356(2) 1.345(11) 1.366(1)
1.317(11) a
C1-C2 (A) 1.549 (5) 1.537 (10) 1.554(56)
c1 -c7 (A) 1.567(12) 1.526(12) 1.547(59)
C6
-C1-C
2 106.4(6)° 102.7(7) ° 100.3(3)°
C1-C7
-C4 96.4° 93.3(6)° 94.5 ob
1vl- (C=C) ° 1.971(8) 2.159 (37) (A)
2.166(36)
v (C=C) 1574,1544 -1 1560
_la 142 8 , 1410 cm
_lc
cm cm
1460 cm -1
a Free C=C.
b Ca1cu1ated by Dr. IJ. Lerbscher using pub1ished data (persona1
corrununication)
c From reference 68.
- 115 -
Taking the C-H and C=C regions as monitors for the stereo-
chemistry of the ligand, it is concluded that in the (NBD)f.1(CO)4
complexes there is no significant change in the geometry of the
ligand upon coordination, as is the case for the (NBD)PdC1 2
compound. This conclusion can be substantiated in two ways.
First, the v(C=C) modes of the carbonyl complexes are in the same
region as the analogous modes of the palladium compound. This
implies that the metal-ligand bonding is similar in the two
species. Since there is no significant change between the
geometry of the free and complexed ligand for the palladium
compound, this can also be assumed to be true for the carbonyl
complexes. Second, a careful comparison of the spectra in the
C-H region of the free NBD and of the complexed NBD in
(NBD) l-1 (CO) 4' shows them to be very much alike. The apparent
changes in the Raman spectra in the 3100-3060 cm- l region become
less significant if the disappearance of the Fermi resonance is
taken into account .. The shift of the 3125 cm- l band in the free
lig.and to around 3100 cm -1 in the complexes is also explainable
on grounds other than a change in geometry. The effect of
coordination should be most prevalent on the vinyl group.
Therefore, this shift in the vin~ll C-H fundamental is a
consequence of complexation and not of a change in geometry.
-1 The changes in the spectra in the 3000-2900 cm region, have
already been accounted for in terms of changes in Fermi
resonance.
- 116 -
D. CONCLUSION
Partial vibrational assignments have been proposed for NBD
and the three (NBD) H (CO) 4 (M = Cr ,No ,m complexes. For the free
ligand, the two v (C=C) fundamentals, as weIl as blO of the ring
modes have been assigned. In the case of the complexes, assign
ments have been proposed for the modes of particular interest
for compounds of this type.
The apparent difference in the v(C-O) fundamental regions of
the three complexes has been accounted for, and assignments are
made for the modes of each of these complexes. 'l'he Fermi
resonances proposed previously for free NED have been sub
stantiated experimentally. On the basis of Fermi resonance
arguments, the coordinated v(C=C) modes have been assigned
unequivocally to bands in the range of 1430-1410 cm- l i.e. ,
approximately 10% lower than for t~e free ligand. The two M-L
fundamentals have ceen assigned definitively to the 250-210 cm-1
region. This range is the lowest yet observed for vibratIons of
this type. The cS (M-C-O) and v (N-C) modes have been assigned to '
the expected regions, with the al stretching modes being clearly
identified.
From the spectroscopie data obtained, it is concluded that
NBD undergoes little change in stereochemistry upon coordination.
- 117 -
CHAPTER 4. 1,5-CYCLOOCrrADIENE COMPLEXES
A. INTRODUCTION
1,5-Cyclooctadiene (CSH12 ) complexes of transition metals
have been little investigated from the standpoint of vibrational
spectroscopy. A.part from the recently published i.r. and Raman
data of Pm.,ell et aZ. 54 for sorne palladium, platinum and rhodium
complexes, rnost of the earlier ~vork has been preparati ve in
nat.ure. For example, the syntheses of (COD) PdCJ.2 84, [( COD) R.hCl] 2 85
86 and (COD) Fe (CO) 3 ' were reported about twel ve years ago. More
recently, several papers have been published on the far-infrared
spectra of the [(COD)RhCl]2 dimer 87 - 89 • These studies were
concerned with the vibrational modes of the bridging halogen
groups. The reaetions 9 0 of this rhodium dimer \.,i th tertiary
* phosphine and phosphite ligands have also been investigated.
There have been other preparative papcrs dealing with the . 91 92 chernistry of rhodlurn COD complexes ' , as weIl as sorne on the
kinetics and mechanism of the reactions of complexes of the type (COD) Rh(ASPh
3)C1 93 ,94.
The work described in this Chapter, together with the work
* It should be mentioned in passing that an a·ttempt was made to study the kinetics of the briège-breaking reaction of [(COD) R~Cl] 2 and its iodo-ana.logue with organophosphorus ligands. It was hoped that the results would yield kinetic data suitable for comparison with those of similar halogen-bridge breaking reactions. Preliminary studies showed that th8se rea.ctions \vere complete in less than 10 seconds. Consequently, they are too fast to be monitored by conventional. spectroscopie methods.
- 118 -
on the l'lBD complexes, \-las underta.1(en \'li th a view 'to\-lards
obtaining reliable assignments for ole fin complexes of the
transition metals. In particular, the vibrational spectra of
the free COD ligand and three of its complexes are considered.
In the case of the first two complexes, [( COD) RhCl] 2 and
[(COD)CuCl]2' the molecular structures have been determined by
X-ray Cl.ystallography95,96. For these complexes, vibrational
assignments are proposed. For the third complex, (COD)2CuCI04'
the molecular structure is unknown. Using the spectra of the
first two compounds as internal references, vibrational and
structural assignments are made for this complexe
The vibrational spectrum of l,5-cyclooctadiene has been
published twice97 , 54 i in nei ther case were detailed vibrational
assignments proposed. In the first case, the liquid state i.r.
and Raman spectra, and the solic1 state i.r., \Vere recorded in
the 1700-450 cm- l region. In the second, the complete i.r.,
but only a partial Raman spectrum (without depolarization data)
were published. In this thesis, these data are supplemented by
a complete solution Raman spectrum (including depolarization
measurements), and a solid state Raman spectrum.
B. EXPERIMENTAL
Di -'Il-oh Zorobis [ 1~ 5 -ay aZooetadiene rhodi um (I) ], [( COD) RhCI] 2'
was prepared by the method of Chatt and Venarlzi 85 . The iodo··
analogue '\Tas also prepared by the same published method. The
purity of these compounds was confirmed bl' t.l.c.
- 119 -
Vi -"fJ.-ah lOl'obi s [1.,5 - aNa looa tadiene covne r (I) ], [( COD) CuCl] 2'
was prepared under nitrogen by rnethod lb of reference 96. The
whi te crystals obtained \vere \vashed thoroughly to rernove any
rernaining reactants.
Bis(l,5-ayclooatadiene)aopper(I) perchlorate, (COD)2CUCI04'
was synthesized electrochernically by ï-lr. R.J. Gale, using the
method of Manahan98 . The identity (and purity) of the compound
was established by elernental analysis. (Calcd: C, 50.7; HI 6.4.
Found: C, 50.4; H, 6.6.)
To prevent polyrnerization, the COD was vacuum distilled
before i ts spectra were ~-ecorded. The fraction distilling at
21 mm Hg/33° was collected. The spectra were in good agreement
with the published results 54 . The solid state (-196°) Raman
spectrum of COD was obtained in the sarne manner as that of NBD,
described previously. The Raman spectra of the complexes were
obtained for the powdered solids in Pyrex capillaries using the
647.1 nm Kr+ line. The i.r. spectra of the copper complexes were
obtained for KBr pellets; the rhodium dimer was run as a mull in
Nujol and hexachlorobutadiene (HCBD).
C. RESULTS AND DISCUSSION
1. 1,5-Cyclooctadiene
The i.r. and solid state Raman (-196°) spectra of COD are
shown in Figures 31 and 32; the observed frequencies are given
in Table XXVII. The calculated vibrational modes and their
spectral activities for the C2v "tub" and Ci "chair" configur
ations of the free ligand are listed in Table XXVIII.
- 120 -
(A) Figure 31. Infrared spectrum of 1,5'-cyclooctadie~e (neat
liquid) •
(B) Figure' 32. Raman spectrum of 1, 5-cyclooctadiene (-196 OC) .
Instrument 3050-2780 Controls 1700-20
Exc. 647.1
Power 60
Slit 4.5
Sens. 2 x 10 2
T.C. 2
Scan 50
Chart 48
\
~
3JN'111IV\lSN'1~1
(A)
l<ïg
[8 -~
o o (l)
~
~~
i .J.
(B)
- 121 -
TABLE XXVII.
VIBRl"\TIONAL FP..EQUENCIES
OF 1,5-CYCLOOCTADIENE (cm-1 ).
IR Raman
liquid liquid
3075 (5)
3009 ( 65) 3012 (60 ) P 3019 (6)
2989 (sh) 2996 (sh) P 2997 (30)
2978 (6)
2956 (sh) 2957 (10) dp 2948 ( 8)
2938 (40 )
2919 (sh) 2919 (70) P 2916 (15)
2892 (sh)
2883 (67) 2884 (95) P 2884 (50)
2838} (25)
2826 2829 (30) P 2827 (6)
* ** 1657 (20) 1661 (150) P 1658 (38)
1487 (40) 1487 (20) dp 1495 ( 14)
1447 (15) 1451 (sh) dp 1442 ( 3)
1425 ( 35) 1430 (60 ) p 1430 (50)
1407 (shj dp 1411 (6)
1356 (6 ) 1351 ( 13) P 1~51 (6 )
1321 ( 1) 1317 (16) dp 1319 (23)
- 122 -
1266 (6 ) 1275 (65) P 1276 ( 55)
1235 (10) 1239 (5)
1208 (16) 1210 (12) P 1215 (9)
1190 (sh)
1151 ( 4)
1084 (14) 1085 (22) P 1087 (10)
1015 (30) dp 1014 ( 21)
1003 (16) 1000 (sh) dp 997 ( 8)
966 ( 3) 970 ( 14) dp 976 ( 18)
905 ( 3) 904 (5 br) dp 909 ( 5)
840 (sh)
822 ( 12)
798 ( 25) 800 (110) P 804 (42)
753 (sh)
718 (sh)
708 ( 32) 708 (90) P 711 (20)
697 ( 5)
649 (35) 657 (7) dp 655 ( 12)
497 ( 10) 496 ( 12) P 501 ( 12)
466 ( 8) 467 (15) P 472 ( 10)
351 (22) P 352 (25)
332 ( 20) dp
266 (90) dp 270 (75)
237 (95) dp 249 (GO)
111 ( 10)
*
**
- 123 -
Assigned to the h v (C=C) mode. l
Assigned to the al v(C=C) mode.
88 (50)
56 (ï5)
42 (50)
Molecular Symmetry
C2v
& C. ~
~
- 124 -
TABLE XXVIII.
DISTRIBUTION OF NORr1AL 1'1ODES OF COD.
Fundamental Modes
l4a l + l4a2 +
l3b l + l3b 2
v(C-H)
3al + 3a 2 +
3b l + 3b 2
v (C=C)
al + b l
27ag + 27a u
v (C-H)
6a g + 6a u
v (C=C)
ag + a u
No. IR bands
40
9
2
27
6
1
No. Raman bands (pol.)
54 (14)
12 (3)
2 ( 1)
27 (27)
6 (6)
1 (1)
No. Coincidences
40
9
2
0
0
0
Considering the experimental data, there are two pertinent
observations that can be made. Firstly, in the Raman spectrum
of liquid COD there are 16 polarized bands; 5 in the v(C-H)
region and Il in the region below 1700 cm-1 Second 1 there are
a large nurnber of coincidences between the i. r. and Raman bands
- 125 -
throughout the whole vibra tional range. In conjunction ~'li th the
calculations outlined in Table XXVIII, these data indicate that
the ligand adapts the C2v "tub" configuration. A similar
conclusion was reached previously on the basis of limited data97 .
Pourteen polarized Raman bands are expected for the C2 v
speciesi 3 in the C-H stretching region, and Il in the lower
frcquency range. The blO extra polarized bands in the v (C-H)
s t.retching region, as in the case of NBD, are probab ly due to
Fermi resonance between the C-H stretching modes and the over-
tones of the C-H bending fundamentals in the neighbourhood of
1430 cm-1 . In particular, it seems likely that there is a Fermi
interaction between the 2884 and 2829 cm- 1 bands and the over-
-1 tone of the 1430 cm bending fundamental.
-1 The two v(C=C) fundamentals are expected in the 1700-1500 cm
region. Therefore: the very strong 1661 -1 cm polarized Raman band
is assigned to the al v(C=C}
is attributed to the hl mode.
mode, while -1 the 1657 cm i.r. peak
These values are somewhat higher
than the similar fundamentals of other olefinic sys te ms ; C2H4
(1623 cm-1}100, HBD (1574, 1544 cm-1), COT (1653,1635 cm-1)*,
butadiene (1638,1599 cm-1} 65, cyclooctene (1648 cm-1} 101.
2. Vibrational Assignments for [(COD}RhCl]2 and [(COD}CuCl]2
For the rhodium complex, an X-ray investig'.ltion has
established a square-planar coordination around the rhodium atom
* The spectrum of this compound was run incidentally in the
preliminary stages of the work described in this thesis.
- 126 -
with a coplanar arrangement of the four C=C centers, ·the two
rhodium, and the two c;hlorine atoms95 . The space group is C~h
with four molecules per unit celli the molecular symmetry is
D2h and the COD rings are in a tub configuration. In the case
of the copper complex, the Cu(I) is quasi-tetrahedrally co-
ordinated to the two chlorine atoms and the cent6rs of the two
double bonds of COD 96 . The COD is again in the tub configuration~
There are two molecules, of D211 symmetry, per unit cell (space
group Pl). The molecular confiCJurations of these two species
are shown in Figure 33.
Figure 33. Molecular structures for [(COD)RhCl]2 and [(COD)CuCIJ 2 •
Owing to the complexi ty introduced by the large liga.nd, vibra-
tional assignments will be made only for the fundamentals
involved directly in the olefin-metal-halogen bonding. The
symmetrj and activity of these fundamentals are described in
Table XXIX.
l
- 127 -
TABLE XXIX.
SYNMETRY AND ACTIVI'l'Y OF THE
[(COD) RhCl] 2 and [(COD) CuCl] 2 FUNDANENTALS.
Fundamental [ (COD) RhCl] 2 [(COD) CuCl] 2
\l (M-L) a g + bIg + b 2u + b 3u a g + b 2g + b lu + b 3u
\l (C=C) a g + bIg + b 2u + b 3u a + bIg + b 2u + b 3u g
\l (M-X) a + b, + b 2u + b 3u a + b 2g + b + b 3u g log g lu
Activity: a g' b -19
Raman active
b 2u ' b 3u - infrared active
OWing to the center of symmetry, each of the above types of mode
should exhibi t two bands in the i. r. and two in the Raman wi th
no coincidences between them (Hutual Exclusion principle) .
The solid state i.r. and Raman spectra of the two complexes
are shown in Figures 34-37. For the purpose of easier comparison
between the three COD complexes and the free ligand, these spectra
are also shown in bar-graph from in Figures 38 and 39. The
frequencies are listed in Table XXX. The spectra \vill be
considered in the distinct regions of the three fundamentals
mentioned in Table XXIX.
- 128 -
(A) Figure 34. Infrared spectrum of [(COD)RhCl]2 (Nujol and
HCBD mul1s) .
(B) Figure 35. Raman spectrum of [(COD)RhCl]2 (solid state).
Instrument Controls 200 -60 1630-160 3080 -2 830
Exc. 647.1 647.1 647.1
Power 80 80 80
Slit 5 7 6
Sens. 5 x' 10 2 2 x 10 2 102
T.C. 10 10 40
Scan 10 10 5
Chart 12 12 6
\ \ \ '\
\
---'---l" ~. o o ~
::>:)N';'l.lI:r-JSN\>'H.l
(A)
o o ru
o o C\l
o o ~Q
)"1ISN3.!NI
(E)
-_ ... _----_._----- ---- ---- ------ ._------ "!::-
--------.- <:- -----... '-------,.
~ -----_ . .---':li._. _~ _.-
-------~
-~ .. --------._------_. --- --=-_._---~~
-t-~:.~ ...
À1ISt~31tJ:
(B)
o o N
o o 1.0
- 129 -
(A) Figure 36. Infrared spectrum of [(COD)CuC1]2 (KBr pellet).
(B) Figure 37. Raman spectrum of [(COD)CuCl]2 (solid state).
Instrument 3130-2780 ContraIs 1670-160 200-30
Exc. 647.1 647.1
Power 90 90
Slit 5.5 5.5
Sens. 5 x 10 2 x 10 2
T.C. 40 10
Scan' 5 10
Chart 6 12
,,--:>
( \
\ '---- --
~-=- --.: :---:::::=----~,
~~
~
\. 3::lN, 0' WlllV~('"N"'ë.1
(A)
- ----l"E u
a a oq
a f6
o o ~
a a a C\J
----
;"1 1 SI\! 3 lN 1
(B)
-~:-~..:.-.......
AlISN::iHJ!
(B)
l,-lE u
o
o o 10
o -16
- 130 -
(A) Figure 38. Bar-graph representations of the infrared spectra
of COD and its complexes.
(B) Figure 39. Bar-graph representations of the Raman spectra
of COD and its complexes.
J ~-~ --=1- 1
'" l <f ""...:'1 :J '0 U U = .c"Q 0Sl 0: ëi 0 8 <Il .Y.. Q
(A)
OV o -. '0 (1 .= C\J 0
Ô <Il
o ~J
1'7 .. _ 't:
u
o o <;f
o o CO
.----~------- 1 ~ --- ---. ---------- --- ._ ___ -- - - -1. _____ - __ - --
- ---.---- --._----
U "0 î) ~ () If)
------------ -1---- __ -----_.--
(B)
=C';I u " -g u '0 8 ." Q
'ïE u
o o ~
o ~-- ------------- 0
:0
-t~ ------------t ----
- 0 o
jg
IR
3030
3006
2993
2981
2944
2916
2879
2834
1477
1469
1446
1430
1424
1372
1330
1324
1300
- 131 -
Ti\BLE xxx.
VIBRATIONAL FREQUENCIES OF
-1 * [(COD)RhCl]2 ~BD [(COD)CuCIJ 2 (cm ).
[ (COD) RhCl] 2 [(COD)CuCl]2
Raman IR Raman
(5 ) 3026 (sh) 3085 (6)
(sh) 3006} 3066 (6)
(30) ( 22) 2990 3011 ( 17) 3008 ( 18)
(sh) 2971 (sh) 2983 ( 22) 2978 (5)
( 30) 2936 (sh) 2954 ( 27) 2955 (5)
(sh) 2911 ( 20) 2926 (30) 2924 (30)
(32) 2877 (75) 2885 (40) 2881 ( 52)
(28) 2831 ( 40) 2832 (27) 2829 (12)
(sh) 1478} 1611 (12
( 20) ( 22) 1467 1550 ( 3) 1563 (12
(6) 1446 (sh) 1474 ( 32) 1486 ( 12)
(sh) 1432 (20 ) 1450 ( 15) 1446 (sh)
( 15) 1428 ( 51) 1428 (50)
(2) 1372 (10) 1393 ( 1)
(sh) 1385 (7 )
(25) 1325 (10) 1344 ( 13) 1341 ( 10)
( 17) 1299 {l2} 1316 ( 4) 1318 (10)
br)
br)
- 132 ..
1226 ( 5) 1236 ( 40) 1311 ( 10)
1210 ( 10) 1212 ( 8) 1260 (53)
1189 ( 22) 1237 (29)
1169 (24) 1175 (19) 1200 (12)
1149 (16) 1185 ( 18)
1076 ( 10) 1076 (6) 1161 ( 3)
1004 ( 25) 1082 ( 13) 1082 (6)
993 ( 52) 994 (sh) 1101 ( 20)
960 ( 100) 961 ( 25) 993 ( 23) 980 (sh)
879 ( 15) 880 ( 45) 956 (25) 959 ( 50)
866 (16) 901 (5)
831 ( 12) 864 ( 10)
816 (50) 844 (l8)
795 (5) 817 ( 29)
773 ( 28) 776 ( 70) 806 (sh) 811 (85)
695 (5) 742 (63)
583 (2) 58'2 (27) '129 (2'5)
514 (2) 513 ( 55) 714 ( 45)
488 (9) 671 ( 7)
477 (6) 477 ( 120) 647 (27)
393 (60) 515 (20)
387 (11) 385 ( 50) 480 (5) 481 ( 20)
351 (37) 455 ( 2)
** 278 266 (32) 411 (5) 409 (50)
** 260 249 ( 30) 348 (4) 350 ( 15)
, 165 {sh)
*
**
***
- 133 -
*** 137 (25) 349 (w)
126 (la) 291 (95)
102 (15 0) 223 (sh)
89 (20) 177 (s)
82 (l5) 151 (100)
115 (sh)
102 (80)
73 ( 100)
AlI data refer to solid state spectra.
From reference 88.
Far-infrared spectrum run for Nujol mull (reproduced be1ow) .
w u z ~ 1-~ lfl Z <l: 0:: 1-
'--"--~I ~ 100 cm-1 300
- 134 -
a. C=C Stretching Vibrations
The v(C=C) frequencies of bonded polyolefins such as NBD,
-1 COD, and COT seem to fall in the 1500-1400 cm region (cf.
Review). In the (NBD) 1-1 (CO) 4 series presented earlier in this
thesis, the coordinated C=C modes were assigned quite unambiguously
-1 to the two bands in the 1430-1410 cm region.
-1 In the case of [(COD) RhCl] 2' assignrnents in the 1500-1400 cm
region are hindered by the obvious interference of the C-H bending
fundamentals of the free ligand (Figures 38 and 39). ~vi th sorne
uncertain·ty as to which of thesc fundamentals are transmi tted
into the spectrum of the comp1ex, only tentative assignments can
be made. In this way, the Raman doublet at 1478 and 1467 cm-1
-1 and the i. r. peaks at 1469 and 1424 cm are assigned to the biO
gerade and the two ungerade coordinated v(C=C) fundamentals,
* respective1y.
For the copper dimer, a more complex situation exists, In
* It is of interest to note the influence of the electronic
interaction around the ring on the position of the coordinated
v(C=C) mode.
v (C=C) -1 Ref. cm
C2H4 1623 100
[ (C2H 4) 2RhC1 ] 2 1520 102
[ (COD) RhCl] 2 1480-1420 this work
[(COT) RhCl] 2 1410 64
~vi th an increasing degree of conjugation, th.e C=C double bond
loses i ts strict double bon(l character.
- 135 -
the paper dea1ing \vith its X-ray structure, an i.r. band at
1612 cm- l was assigned to a v (C=C) mode96 . In this work 1 tvlO
unusua11y broad bands are found in the Raman at 1611 and 1563 -1 cm ,
but there is no i.r. peak corresponding to the published one.
From the nature and position of the Raman bands, it is concluà.ed
L~at they are not fundamentals. Since the i.r. spectrum of the
complex is featureless in the 3600--3400 cm-1 region, these bands
are not due to water in the sample. Possibly, they are
combinations and/or overtones of lower frequency vibrations. The
-1 1428 cm' IR/R bands correspond closely with strong bands found
for the free ligand. Assigning these bands to ligand vibrations,
-1 -1 the 1474 and 1450 cm i.r. peaks and the 1486 and 1446 cm
Raman bands are assigned to the four v (C=C) fundamentals. As
expected, these i.r. and Raman bands do not coincide.
b. M-C1 Stretching Fundamentals
The four fundamental vibrations due to the bridging CI-M-Cl
-1 group (a + b l + b
2 + b 3 ) are expected in the 300-200 cm g g u u
region - two should be Raman active and two i.r. active.
-1 Consequently, it is reasonable for the bands at 278 and 260 cm -
in the far-infrared spectrurn of the rhodium species to have been
, d th" t' - ~ 1 88 assJ.gne 0 t. e ewo 1. r. aC_l ve tunaalf.enta s • In the present
-1 work, the b.ro strong Raman bands at 266 and 249 cm were
assigned to the t\vO expected Raman active modes. This is supported
by the disappearance of these two pea~s in the Raman spectrum of
the iodo-complex. The noncoincidence of these i.r. and Raman
- 136 -
fundamentals further domonst:cates that t.~e D2h molecl.l1ar symmetry
of the dimer is indeed reflected by the vibr.J.tional spectra.
In a series of bridged Cu(II)-Cl complexes, the v(Cu-Cl)
fundamentals have been identified in the 328-222 cm- l range l03
It is generally accepted that such metal-halogen stretching
fundamentals should decrease in frequency as the oxidation state
of the metal is loweredl04 • As an outgrO'\.olth of this, the strong
Ra~an bands at 291 and 151 cm- l and the i.r. bands at 223 and
177 cm -1 for the Cu (1) dimer are assigned ·to the bridging v (Cu-Cl)'
modes. Again there is a noncoincidence in these fundamentals in
line with the D2h molecular syw~etry.
c. M-L Stretching Vibrations
From the fe\ol assigned M- (C=C) frequencies, these vibrations
are expected to fall in the 500-300 cm-l region. The bands in
the neighbourhood of 350 cm- l in the Raman (present in aIl the
three complexes and the free ligand) are assigned to a ligand
vibration. For t.he rhodium complex, the strong Raman band at
513 cm -1 (wi th a coincident \oleak i. r. line at 514 cm -1) is also
attributed to a ligand mode. This leaves only three bands in
this 500-300 cm- l region, in both the i.r. and Raman! two of which
are necr::;ssarily the metal-olefin stretching vibrations. The very
-1 -1 strong 477 cm Raman band (472 cm in CS 2 , totally polarized)
is assigned to the symmetric a v (M-L) vibration, \vhile either 9 -,
the 393 or 385 cm ... band must be due to the other Raman active
mode. This 393/385 -1
Gffi doublet is not a solid state effect
-- 137 -
because both bands appear in solution. In addition, the i.r.
-1 peaks at 488 and 387 cm are assigned to the v (M-L) lib " modes. u
In the case of the copper dimer, the range of V(M-L)
frequencies is quite clearly defined. -1 Ignoring tl1e 350 cm
ligand IR/R peaks, there ure on1y three other bands in the
-1 520-400 cm region. ~vo of thesc, in boti1 the i.r. and Raman,
must be due to the H-L vibrations, there being no oilier
unaccounted bands in the 600-150 cm-1 region. On the basis of
i ts intensi ty, the 409 cm -1 Raman band is assigned ta ilie a mode. g
The other Raman active fundamental (b 2g) must ilierefore be the
-1 1 band at 515 cm . Sirni1ar1y, the 455 and 411 cm- ·i.r. peaks are
attributed to the two lib U" fundalllentals.
3. Vibrational Assignments for (COD)2CuCI04
In the paper desc~·ibing the electrochemical preparation of
98 this compound , blO characteristic i.r. bands were cited at
1638 and 1595 cm-1 • Ass~ming that these were due to v(C=C) modes,
it was conclnded that there is a non-equiva1ent coordination of
the two COD groups. This author fee1s that these data do not
prove the existence of symmetrica11y non-equiva1ent groups, at
best on1y that the dienes do not coordinate in a tetrahedra1
fashion with the Cu(I). For examp1e, in a C2v configuration,
four IR/R active v (C=C) modes are expect.ed, despi te the fact tha1:
the C=C groups would be equiva1ent1y bonded. Moreover f during
the CO'..lrse of an extremely câ!.-eful spectroscopie investigation,
the 1595 cm-1 band was found to be real, while the 1638 cm-1
- 138 -
peak \Vas ne va r reproduced. HO\vever, in one case 1 for a vlet KBr
disk, an additional band \'las found at '\"1630 cm- l - bands in this
neighbourhood are typical1y attributed to ,vater.
The solid state i.r. and Raman spectra are reproduced in
Figures 40 and 41, the spectral data are listed in Table XXXI.
The most striking feature in the i.r. and Raman spectra of
(COD) 2CuC10 4 is the very strong Raman band at 1591 cm -l, coinciden·t
with a medium intensity i.r. band at 1590 cm- l • Such a frequency
is too high for a coordinated double bond. However, it is
precisely in the region that a non-cool'dinated double bond of
a complexed polyene is anticipated (vide supra, p. 81 ). This
observation is further supported by the appearance of a strong
i.r. band
cis- (C=C)
-1 at 763 cm ,
105 group
which is i.ndicative of an uncomplexed
Accepting that there is a non-bonded C=C group and tllat
there are two COD groups per copper atom (from elemental analysis
data), five reasonable structures can be postulated for the
complex in the solid state. These are shown in Figure 42. The
spectra, as in the case of the other COD complexes, will be
conside!:ed in the \.l (C=C) and \.l (H-L) regions.
As mentioned above, one band characteristic of an uncornplexed
double bond is observed, [1591 (R) /1590 cm- l (IR)]. The vibra-
tions of the complexed dow)le bonds are again anticipated to be
in the 1500-1400 -1 cm region. The 8(Or 2 ) vibrations of the free
olefin rnask this regioll, alloKing only tentative assj gnment.s to
be made. -1
Thus 1 the three Harou.n bands at 1485, 1455 and 1403 cm
- 139 -
(A) Figure 40. Infrared spectrum of (COD)2cuCI04 (KBr pellet).
(13) Figure 41. Raman spectrœn of (COD) 2CuC104 (solid state).
Instrument 3100-2730 Contro1s 1720-40
Exc.
Power
Slit
647.1
Sens.
T.C.
Scan
Chart
5 x
70
4
10
10
5
6
L __ _
f
t '< ~~---~=:=.~=--'--::.:."-~-~
-------~-~~-::=:::;~~=~~-
(
\
\ \,
'-.. -. . ~-:.:. .. ~-
<jE u
o o o (Il
1
,l.liSN31NI
(B)
o o N ~
o o ~q
) - :-.. -.~ .. - -----::::,.
... _.~ -.
~ ~ --y
)
o () o
IR
3032
3013
2951
2937
2894
2845
1590
1483
1450
1430
1387
1348
1323
1257
1234
118R
1165
- 140 -
TABLE XXXI.
VIBRATIONAL FREQUENCIES AND ASSIGNMENT
-1 a OF (COD)2CUC104 (cm ).
Raman Assignment
(sh) 3020 (15)
(5)
( 17) 2963 (sh) v (C-H)
(3) 2932 (15)
( 32) 2898 ( 42)
(20) 2847 ( 12)
( 10) 1591 (90) v(C=C)free
( 32) 1485 ( 8) v (C=C) coord.
(10) 1455 ( sh) v (C=C) coord.
( 33) 1440 (23) ô (CH 2)
(5) 1403 (5 ) v(c=C)coord.
( Il) 1350 ( 4)
( 18) 1325 ( 4)
1309 (3)
(sh) 1260 (50)
( 15)
1203 ( 15)
(6) 1192 (sh)
( 8)
-- 141 -
10901 1090 (6) l
} b J(65 br) · .... '0 v 4
1080 1080 (6) "'-- 4
1015 ( 17)
9 86 ( 15) 995 (16) ClO4 vI
938 (2) 932 ( 65) CI04 v 2
907 ( 17) 910 ( 10)
868 ( 3)
852 (20)
823 ( 35) 832 (55)
763 (46) 750 ( 13)
734 ( 35)
680 ( 3)
663 ( 17) CI04 \i 3
653 (sh)
638 (sh)
625 (57) 624 ( 10) C104 v 5
520 (3) 520 ( 14) v (Cu-L)
498} 498 (h\ v{Cu-L) ,- , (3)
488 ligand
453 (2 ) 458 ( 12) C104 v6
413 ( 10) 415 ( 22) \i (Cu-L)
355 ( 22) ligand
289 ( 37) v (Cu-Q)
141 ( 32)
._---_.
a Solid state values.
b Fundamenta1s of C104 described in Table XXXIII.
- J.42 -
-1 with corresponding i.r. bands at 1483 and 1450 cm are assigned
to the fundamentals of the coordinated C=C bonds.
In the low frequency region (600-300 cm- l ) , there are two
easily eliminated interfering vibrations. The Raman peak at
-1 350 cm is assigned to a ligand mode, as in aIl the previous
cases. -1 . The very weak 488 cm l.r. band, absent in Raman; is
also attribu·ted to a ligand mode. In addition, the i.r. and
Raman absorptions at 453 and 458 cm-l, respectively, are due ta
the v 6 fundamental of the perchlorate ion (vide infra, Table
XXXIII). This leaves three sets of IR/R bands: 520/520, 498/498
and 413/415 cm-l, to be attributed ta the v(M-L) vibrations.
The calculated nuIiÙJer of v(C=C) and v(M-L) modes for each
of the possible structures (shown in Figure 42) and the nurnber
actually observed are cornpared in Table XXXII. The data indicate .J_
that structure III ls the most reasonable one for (COD) 2cu' ion
in the solid state.
The structure proposed thus far is based on a three-coordinate
Cu(I). Although Cu(I) is generally tetrahedrally coèrdinated,
there are specifie examples of trigonally bonded species. For
instru1ce, the X-ray structures of both [(NBD)CUCIJ 482 ~nd
[(COT) CuCl] 106 indicate a CI-Cu-Cl chain \"ith only one C==C group n
of the ole fin being coordinated ta the copper atom. Despite
these examples, i t still remains questionable \Olhy the fourth
double bond [in (COD)2CuCI04] does not coordir-ate to the
potEmtially available bonding si te on the copper atom. One
possible explanat2.oTI is that ·the oxygen atom of the C104 group
- 143 -
Figure 42. Five possible structures for the (COD)2cu+ ion.
0f1----CU--U &--cu---ç;f~ l II
"
III
IV
v
- 144 -
TABLE XXXII.
NU~1BER OF VIBRI\TIONAL MODES
FOR THE POSSIBLE STRUCTURES OF (COD)2CU(I) ION.
Structure Syrcunetry \1 (C=C) free v(C=C)coord. \) (M-L)
l C2v 2 IR/R 2 IR/R 2 IR/R
II C2h l IR, l R l IR, l R l IR, l R
III C l IR/R s 3 IR/R 3 IR/R
IV C2v 2 IR/R 6 IR/R 6 IR/R
V C2h l IR, l R 3 IR, 3 R 3 IR, 3 R
No. observed l IR/R 2 IR/R, 1 R 3 IR/R
liE~s close ene·ugh to' the copper atom to satisfy this fourth
coordination site. A closer examination of the spectra does
indeed support this hypothesis.
Although Cl04 is generally considered as a non-coordinating
ligand, there are instances where the oxygen atoms are coordinated.
coorc1inated octahedrally by four sulfur ane t\"c oxygen 107 atoms .
'l'he Co-O distance is 2. 341L o Since this distance is O.l-O.3A
longer than other Co(II)_o bonds, it supports ~1e argument that
the anion is only vleakly bonded ~ nevertneless, i t is bO!:1deà.
A coordinated perchlorate group shou1.d give rise to a l'ilet.al-
- 145 -
oxygen stret.ching vibration. In a series of M-(acac) complexes,
including Cu (II), one of the hlO \) (M-O) frequencies has been
assigned in the 300-290 cm- l regionl08 In view of this, the
t b d f ( ) 1 2 89 -l, 'd s rong Raman an or COD 2CuC_04 at cm lS asslgne to
the \.' (Cu-O) mode. l'li th one of the oxygen a-toms bonded, the
tetrahedral perchlorate group undergoes a C3v
perturbation.
8uch a perturbation of the CI04 group has been considered
109 previously for a Cu(II) compound, Cu(CI04)2.2H2o . The cor-
relation between tl1e free (T~) and coordinated (C3 ) ion is Q v
shown in Table XXXIII. This perturbation should be, and is,
manifested in the vibrational spectrum of (COD)2CUCI04. As
seen in 'l'able XXXI, i t is possible to assign bands to aIl of
the expected modes of the perturbed perchlorate grou.p. Based
solely on the spectroscopie evidenee presented above, the final
postulated structure for (COD)2CuCI04 i5 shown in Figure 43.
AlI the proposed vibrational assignments for the three
COD complexes ean be found in 'l'a'Jles XXXI and XXXIV.
Figure 43. Pcstu1ated structure for (COD)2cuCI04.
KCI04 -·1 IR( cm )
932 VVl
460
1110 vs
626 vs
TABLE XXXIII.
CORRELATION DIAGRi\H FOR
THE Td m~D C3v PERCHLORATE IONS. a
CI04-(T
d) * M-O -CI0 3 (C3v)
* VI al (R) sym. str. ) v 2 al (IR/R) CIO str.
\)2 e (R) sym. bend. ) \) 6 e (I R/ R) rock
~ \)1 al (IR/R) CI03
str. \)3 t 2 (IR/R) asym. str.
* ~ \)4 e(IR/R) CIO asym. bend.
~ \)3 al (IR/R) CI03 sym. bend. \)4 t 2 (IR/R) asym. bend.
~\)5 e(IR/R) CI03 asym. bend.
a From reference 109.
CU(CI04 )2· 2H 20
-1 IR( cm )
920 vs
480 m
1030 vs
1158 vs
648 s
62O} 605 s
1-' ,!:.
~
- 147 -
TABLE XXXIV.
ASSIGNED FUNDM1ENTAL I-10DES (cm- 1 )
* OF [(COD)RhCl]2 AND [(COD)CuCl]2.
[ (COD) RhCl] 2 [(COD) CUC1] 2
IR Raman IR Raman
v (C=C) sym. 1478 1486
v (C=C) sym. 1467 1446
v (C=C) asym. 1469 1474
v (C=C) asym. 1424 1450
ligand 514 513 480 418
v (M-L) asym. 488 455
v (M-L) a g 477 409
v (M-L) bIg 393 515 (b2g
) 385
v (I-1-L) asym. 387 411
ligand 351 348 350
v (M-C1) asym. 278 223
v (M-Cl) sym. 266 291
v (M-C1) asyrn. 260 177
v (M-C1) sym. 249 151
* Frequencies from 'rab1e xxx.
- 148 -
D. CONCLUSION
Vibrational assignments have been proposed for the i.r.
and Raman spectra of COD, [(COD)RhCl]2' [(COD)CuCl]2 and
(COD) 2CuC104. The data for liquid COD verify that othe ligand
exists in a IItub ll configuration. Due to interference by ligand
modes, the v(C=C) fllndamentals of the bonded COD can be only
tentatively assigned to the 1480-1400 cm- l region - a range
proposed previously for modes of this type. The H-L stretching
frequencies have also been designated, in sorne cases quite
specifically, to bands in the 520-380 cm- l region. This range,
in contrast tothat for the M- (NBD) stretching frequencies, falls
within the previously established range for such fundamentals.
Assignments have also been made for the v(M-Cl) stretching modes
of the rhodium and copper dimers. In the case of the copper
-1
complex, one of these modes occurs at a lower frequency (151 cm -)
than usual.
On the basis of spectroscopie evidence, a structure !las
been proposed for the complex, (COD)2cuC104. The main points
of the argument are as follovlS. Firstly 1 there certainly exists
a non-bonded ethylenic group. Second, a low frequency Raman
band can be attributed to a Cu-O vibration. Further evidence
points to the reduction of symmetry of the C10 4 group. Since
there are also ~~10 COD groups per copper atom, the postulated
structure is the only one t.hat agrees wi th the available data.
PART III
7r-CYCLOPENTADIENYLMANGANESE (I) THIOCARBONYLS,
CpMn(CO)2CS AND CpMn(CO) (CS)2
- 149 -
CHAPTER 1. IN'rRODUCTION
In the literatnre, untold numbers of carbonyl complexes
have been documenteà for essentially aIl ·the transition metals.
In contrast to this, the analogous ·thiocarbonyl complexes
containing the terminal CS grouping are known for only a limited
number of metals; in fact, only abou·\: 25 such complexes have
been identified. Moreover, most of these thiocarbonyl complexes
contain Group VIII metals such as ruthenium, rhodium and iridiumllO •
As yet, to the best of the author's knowledge, a detailed
vibrational assignment for a Uliocarbonyl complex has not been
reported. To date, the approach to the spectra of thiocarbcnyls
has been ra"ther·limited. In every case, only the i.r. active
(C S) f d t 1 · b t dlll-118 d th ~ v - un amen a s nave een repor e ,an even .en on.Ly
frcr!:l the viewpoint of characterization of the complexes. These
fundamentals oocur in the 1380-1250 cm-l regionl19 •
This vlOrk was u!lder'caken follovling the serendipi tous
c1isc:V'3.r:y in t.his lél. .. ~oratory of the complex, CpHn(CO) 2CS. This
compound is obviously similar to the analogous tricarbonyl
complex, for which the vibrational spectra have been thoroughly
.... '" dl20-l23 s\.-ua~e . rrhus, it vias deemed of interest to investigat.e
the vibrational spectrum Qf this thiocarbonyl complex. It ".tlas
hoped that the fundameni:.als associated wi th the Mn-C-S moiety,
-1 particularly in the low frequency (700-300 cm ) region, could
be located and assigned. Such assignrnents \"10uld establish a
precedent for the subsequent interpretation of t.~e spectra of
other thiocarbonyl complexes.
,
- 150 -
Before the resul ts are discussed in Chapt.er 3 , the
experimental procedure will be described briefly in Chapter 2.
- 151 -
CHAPTER 2. EXPEfUHENT1\L
!n-CycZopentadienyZ)dicarbonyZ(thiocarbonyZ)manganese(I),
CpMn(CO)2CS and (TI-cyqZopentadienyZ)carbonylbi~(thiocapbonyZ)-
124 manganese(I) , CpMn(CO) (CS)2' were prepared by Mr. A.E. Fenster •
The first compound was purified by vacuum sublimation at room
temperature, before the spectra were obtained. In contrast to
this, successive sublimations of the latter compound did not
eliminate aIl of the mono-Qliocarbonyl complex. The amount of
this remaining impurity, however~ is estimated to be in the
order of 1%. The iron complexes, [CpFe(CO)3]BPh4 and
[CpFe(CO)2CS]BPh4, were prepared by the author through pLilllished
methods 125,126 .'
The Raman spectrum of the powdered CpMn (CO) 2CS ',vas obtained
in a capillary, using the 647.1 nm ex ci ting line at 45 mlv pm'ler.
The solid state spectra, at room temperature and at -78°C, did
not show any significant difference. Solution Raman spectra
were attempted several times, however, under aIl the varied
conditions, the solutions decomposed rapidly.. The Raman spectrum
of CpNn(CO) (CS) 2 was run for the solid s·tate sample (647.1 nm/
60 mW). The iron complexes yielded only very low quali ty Raman
spectrai the majority of the bands were those resulting from
the BPh4 anion.
The i.r. spectra of Cp!-1n(CO) 2CS \olere obtained in a host of
solvent.s and in the solid state (KBr disk). The solid state
i . r. spectra of Cpr.1n (CO) (CS) 2 and the tvlO iron complexes ~vere
recorded for the sarnples pressed in KBr disks. The vapour
- 152 -
phase i.r. spectrum of the mono-thiocarbonyl complex was obtained
for the sample heated to lOQoe in an evacuated Beckman heated
gas celle The far-infrared spectrum was cbtained for the
compound dispersed in a Nujol mUll, and dissolved in benzene.
- 153 -
CHAPTER 3. RESULTS k~D DISCUSSION
In discussing the vibrationa1 modes of CpMn(CO)2CS and
CpHn (CO) (CS) 2' the now \ve11-established concept of "local
symmetry", as proposed by Cotton et aZ. 127 , will be employed.
As a consequence of this theory, to a first approximation,
Cp~1n (CO) 2CS can be considered as two distinct non-interacting
parts: the Cp-Mn group of CSv symmetry, and the Mn(CO)2CS group
of Cs sy~~etry. The same approach is taken for the groupings
of CpMn(CO) (CS)2. (It will be determined later to what extent
this assumption of non-interaction between the two parts of L~e
molecules is justified.)
In keeping with this approach, the vibrational spectra of
these complexes will be considered in the two distinct parts:
the vibrations of the Cp-Mn moiety, and those of the Mn(CO) (CS)L
group. The symmetries of the fundamental modes of these groups
[for CpMn(CO)2CS] are listed in Table XXXV.
A. RING VIBRATIONS
The common point of comparison of the vibrational spectra
* of the three similar compounds, CpMn(CO) 3' CpMn(CO)2CS, and
CpMn(CO) (CS)2' is the assessment of the ring vibrations of
* The isoelectronic analogues, (CpFe(CO)3]BPh 4 and [CpFe(CO)2CS]BPh4,
of the first two compounds, have also been synthesized. The
observed frequencies, minus those definitely attributable to BPh4 are listed in Table XXXVI. Assignments can be proposed for these
compounds, or.ly in the regions where t.he BPh 4 vibrations ào not
interfere.
- 154 -
TABLE xxxv.
* SPECTHAL PREDICTIONS FOR Cpt'ln (CO) 2CS.
** Mn(CO)2 CS
Fundarnental 122 Syrnrnetry Fundarnental Syrnmetry
C-H str. al + el + e 2 c-o str. a' + ail
C-H bend. (1) al + el + e 2 c-s str. a' ·0 *** ring breath. al Mn-C str. a' + ail
C-H bend. (II) a2 + el + e 2 l' CS 'ln- str. a'
C=C str. al + e 2 Mn-C-O bend. 2a ' + 2a"
C=C benè.. Cl) e 2 rtill-C-S bend. a' + ail
c=c bend. (li) e 2 C-Mn-C dei. a'
Cp-Hn str. al C-Mn-C ' def. a' + ail
Avtivitics fOl:' CSv: al (IR/R) , a" (inact.) ... , el(IR/R) , e 2 (R)
C : s a' (IR/R) , ail (IR!R)
* The ring-to-I'h1 (CO) 2 CS skeletal modes are: Cp-~1n s tr. (a ') ,
ring tilt (al), ring twist (ail).
** ***
For the modes of the r.ln(CO) (CS)2 moiety, interchange o and S.
In this Parc the Mn-C stretching modes will be differentiated
as being either a Mn-carbonyl or Mn-thiocarbonyl type, by the
a.ppropriate superscript on the C atome
- 155 -
TABLE XXXVI.
* INFRARED FREQUENCIES AND ASSIGN~ŒNTS
-1 FOR [CpFe(CO) 3]BPh4 AND [CpFe(CO)2CS].BPh4 (cm ).
+ [CpFe(CO)2 CS ]
solid
3117 w
3097 m
2092 vs < a')
2058 vs (ail)
2027 w,sh
1416 m,sh
1347 vs
833 w
764 w,sh
+ [CpFe(CO) 3]
solid
3107 sh
3099 s
2121 vs (al)
2076} vs (e)
2068
2040 w,sh
2025 w,sh
1705 vw
1440 w
1419 sh
1361 vw
1342 vw
1114 m
1015 w
907 w
764 w,sh
Assignment
C-H stretch. al
C-H stretch. el
C-O stretch.
C=C stretch. el
C-S stretch. a'
ring breath. ~1
C-H bend. <n) el
C-H bend. (1) al
- 156 -
730 s 732 m,sh
720 m,sh
597 s
1 572 s 578 s Fe-C-O bend.
565 sh
480w
463 w
439 w
401 vw Fe-C stretch.
387 w Fe-ring stretch.
375 vw Fe-ring tilt
** 364 vw
345 \'1 349 w
310 w
* Bands directly attributable to the BPh4 anion, are not recorded
in this Table.
** The Raman spectra of both complexes have been rune The only
significant peaks obtained are those for the tricarbonyl cornplex
at 365 (w) and 315 (w) cm-l.
- lS7 -
these complexes. The vibrations of the TI-cyclopentadienyl ring
have been studied extensively for various complexes by Parker
and Stiddard122 • Their approach will be employed here.
The vibrational spectra of CpI'in (CO) 2 CS are reproduced in
Figures 44 (vapour phase i.r.), 4S (soluti.on i.r.), 46 (far-
infrared), and 47 (solid state Raman). The solid state i. r. and
Raman spectra of Cp~m(CO) (CS)2 are shown in Figures 48 and 49.
The observed frequencies are collected together in Tables XXXVII
and XXXVIII. Fer comparative purposes, the solid state i.r. and
Raman spectra are also represented in bar-graph form in Figures
50 and 51.
Not surprisingly, there is good agreement between the
frequencies observed for the relateü modes of the three complexes
(Table XXXIX). The only exception is the appearance of the e 2
Raman band (v 9) at ~2970 cm-l in the spectra of the thiocarbonyl
complexes. Previously, this mode had not been observed for any
TI-cyclopentadiellylmetal carbonyl complex, and consequently had
been assumed to be accidentally degenerate with VSo In the
present work, it is possible that the v9 mode has been shifted
('\1120 cm -1) by a weak hydrogen bonding effect in the crystal
bet\veen adj acent TI-CSH5
rings 12 B
From Table XXXIX, it is immediately evident that the ring
modes of the CS deri.vati ves of Cp~..n (CO) 3 conform much more
closely to the predicted activities, based on CSv geometry, than
dû those of CpHl'1 (CO) 3' In particular, the IR/R inactive v 4 mode
which is masked by 'J (C-S) in the case of CpM...'1. (CO) 2CS is defini tely
not observed in the spectrum of the CpMn{CO) (CS)2 complexo Of aIl
- 158 -
(A) Figure 44. Infrared spectrum of CpMn(CO)2 CS (vapour phase) •
(B) Figure 45. Infrared spectrum of CpIVm (CO) 2 CS (CS 2 solution) •
( C) Figure 46. Far-infrared spectrum of CpMn(CO)ZCS (benzene
solution) •
(D) Figure 47. Raman spectrum of CPMn(CO)2CS (solid state).
Instrument Contro1s 3200-3050 2100-520 520-100
Exc. 647.1 647.1 647.1
Power 45 45 45
Slit 4.5 5 4
Sens. 2 x 10 2 x 10 2 5 x 102
T.C. 40 10 10
Scan 5 20 20
Chart 6 24 24
3:JN'9' llli'\lSN'9'èll
(A)
o o <:
0 0 co
0 0 ~
0 0 '!2
0 0 0 C\j
o o ll1 N
o o o CO)
,-------'.,5 - <::::...-
~ ---- --
==--c----- -- -r---~=-
ç r~
.. --=---
(---~
)
! ?
c!-<; f:'~
'<-- _. - ---~-~-=----)
'f C-.--
~~ a 0 co
[§
0 a
~"
0 0 a N
a a ,g
l,__ 1 '---~:: .-.,-- J
--_._-
(B)
:3:)N'\11 l 1 V'-l SN "lèi l ( C)
1'1 E u
o o ~
o o C")
Al1SN31.NI
(0)
o o <0 ....
o o o C\I
o o .... fi')
------- ~~
LL-_~===-=::::::: ~
AliSN31NI
(D)
o o '<f
o o a:J
o o
l" 1
- 159 -
(A) Figure 48. Infrared spectrum of Cp!.1n(CO) (CS) 2 (solid state) •
(B) Figure 49 • Raman spectrum of CpHn(CO) (CS)2 (solid state) •
Instrument Controls 3160-2900 2100-150 150-20
Exc. 647.1 647.1 647.1
Power 60 60 60
Slit 5 4 4
Sens. 5 x 10 10 2 10 3
T.C. 40 10 2
Scan 10 20 50
Chart 12 24 48
,.--_._._~----_.~
.~-.-
3:JNXflJ.'iI'ISN"'~1
(A)
o o CO
o o (\j
o o ~
o o o M
-
(B)
Al.l9Gl.NI
.. ------ .. - '---".,
} }
..-'" ~
o ~
§ c.'
8 ...
- 160 -
(A) Figure 50. Bar-graph representations of the infrared spectra
of CpMn(CO)3 and its CS derivatives.
(B) Figure 51. Bar-graph representations of the Raman spectra
of CpMn(CO)3 and its CS derivatives.
1 :E ~
u
0 0
~ "'"
~ ~
~ 0 0 CO
1
j ~=t l
1 !
N ~
l 1
N ;j') 1 f§ ~ l' 1 ~ - & ~
B B 1 B t CCI C 2 2 2 a a a U U U
1 .
--l
1 2
1 1 J ,1.
1 f~ ~ -=t
(A)
9-' ~ --- -
1
,
----~ --~ ---
--
1
- ~
,.sJ I..f' Ul U ~ 1 Â" Ô 0 !d .!::I c c ::E ::E a a U U
1
l + j 1
1
(B)
-. -
~I o o .;r
~ 1
o o
'0 C\:
TABLE XXXVII.
SOLID STATE INFRARED AND RAMAN DATA (cm -1)
AND ASSIGNMENTS FOR CpMn(CO)2CS AND CpMn(CO) (CS)2.
CpMn (CO) (CS) 2 CpMn(CO)2 CS
IRa Ramanb IRa Ramanb Assignment
3110 vw 3115 3120 w 3124 C-H stretch. al
2972 2971 C-H stretch. e 2 1--'
'" 1-' 1997} 2009 vs 1986 (50) C-O stretch. a' 1989 vs 1980 1981 (15)
1933 vs 1953 (90 ) C-O stretch. ail
1914 w,sh
1424 m 1422 m 1427 (8) C-C stretch. el
1338 (18)
1298 vs 1260 vs C-S stretch. a'
1289 sh
1235 sh 1213 sh
1220 vs C-S stretch. ail
1113 (60) 1115 w 1116 (130) ring breath. al
1060 "vVl 1064 m 1068 (9) C-H bend. (1) e 2
1011 vw 1005 w C-H bend. (II) el
923 vw
865 vw
845 vw,sh 845 (10) C-H bend. (1) el
832 s 834 (12) 835 s C-H bend. (1) al '\
625 m 645 s 646 (8)
590 s 607 s 609 ( 4) 1-'
570 s 0\ IV
, Mn-C-O and 499 m 500}(10) 516 s 511 (15)
494 Mn-C-S bend.
479 rn 478 (30) 473 vw
448 vw 437 sh ~
429 V'il 428 (85) 458 vw 460 (140) Mn-Co stretch. al
437 vw 437 (43) 0 . i'ln-C stretch. ail
419 '\'1 (360 + 60)
404 (43) Mn-Cs stretch.
382 w 383 (w,sh) ring tilt al
364 w
359 (55)
350 (vw,sh)
321 (500) 339 w
135 s c
115 (55) 110 m,br
92 (vs) 92 w,sh
72 (vvs) 60 m,br
39 (vvs)
a Spectrum run for pressed KBr disk.
b Recorded for the powdered sample in a capillary.
c Far-infrared data for Nujol mull.
367 (55)
338 (150)
136 (50)
120 (180)
83 (800)
s Mn-C stretch. al
Mn-Cs stretch.
ring tilt al
ring-Mn stretch. al
def. and
lattice modes
....... 0'\ W
- 164 -
TABLE XXXVIII.
INFRARED DATA AND COMPLETE VIBRATIONAL ASSIGNMENT
-1 CS
2 (cm )
4005 s
3940 vvs
3900 s
3121 s
2719 w
2656 ID
2613 s
2562 rn
2521 s
2477 s
2438 w,sh
2424 m
2389 m
2365 VVi ,sh
401.2 s
* FOR CpMn (CO) 2 CS IN SOI,UTION.
4016 ID (2007 + 2007)
3942 vs 3946 s (2007 + 1956)
3904 s 3910 ID (1956 + 1956)
3117 s 3125 ID C-H stretch.
2719 w (3121 - 399)
2670 w 2660 w (2007 + 645)
2617 ID 2615 ID (2007 + 612) ,
2562 ID 2564 w (1956 + 612) ,
2523 s 2527 ID (2007 + 519) ,
(1266 ;. 1266)
2476 s 2485 ID (1956 ;. 528) ,
2442 ID 2446 w,sh (2007 + 430)
2432 ID 2430 w (2007 + 409)
2391 w 2393 w (1956 + 430)
2365 w (2007 + 360) ,
2334 ID 2340 m (1962 + 379)
2273 ID 2279 w (1270 + 1005)
2135 \"l (2007 + 122)
al
(2007 + 605)
( 1956 + 605)
(2007 + 513) ,
(1956 + 519)
(1956 + 409)
i'
2007 vs 2016 s
1996 vw 1999 w
1956 vs 1962 s
1946 vw,sh
* 1924 w ( CO) 1930 w
1879 m,sh 1888 Ir.
1836 s 1835 s
1757 m,sh 1760 w,sh
1724 vs 1734 vs
1699 vs 1706 vs
1663 s 1656 s
1602 vvs
1520 m
1266 vs 1272 s,br
1226 w
1156 w 1154 vs
1113 w 1113 s
1074 m
1061 m 1060 ln
- 165 -
2017 s
1959 vs
1931 sh
1885 w
1840 m
1759 w,sh
1729 m
1704 m
1667 w
1598 s
1425 vvs
1394 w,sh
1359 w,sh
1270 vs
1228 w,sh
1157 m
1114 w
1074 w
1061 m
C-O stretch. al
13c_o stretch. a'
c-o stretch. ail
(1113 + 824)
13C_O stretch. ail
(1266 + 612)
(917 + 917)
(1266 + 513)
(917 + 825)
(1266 + 430)
(1266 +,399)
(1266 + 330)
C-C stretch. e 2
C-C stret~h . el
{1266 + 122)
(1266 + 103)
C-s stretch. a' 13 c-s stretch. a'
C-H bend. (II) e 2
ring breath. al
(645 + 430)
C-H bend. (1) e 2
'\
- 166 -
1039 vw 1035 w,sh 1040 w (612 + 430)
1006 s lOlO w,sh 1005 s C-H bend. ( Il ) el
998 vs (645 + 360) , (605 + 399)
978 w 979 m (645 + 330)
947 m (612 + 330)
917 m 914 vs 917 m C-C bend. (II) e 2
825 vs 824 s 825 w/br C-H bend. (1) al
645 vs 646 s 645 s
612} 613 vs 613 s vs
605 605 sh 607 sh Mn-C-Q and
528 w,sh Mn-C-S bend.
519} S20}m vs 513 512 s 514
430 w 432 w 431 w Mn-Co stretch. ail
409 m (330 + 78)
399 sh 379 vw 383 vw ring tilt
360 w 361 w 364 w r.m-cs stretch. al
C6
H6
377 w ring tilt
360 s Mn-Cs stretch. al
330 w Mn-ring stretch. al
122 w ~ C-M-C and
103 C-M-C I def. w J 78 vw ring twist ail
- 167 -
Footnote to Table XXXVIII.
* The lists of frequencies have been divided into several
sections; the intensities are quoted relative to the most
intense peak within each section.
** '!he frequencies used for assignment of the cOIT~ination bands
are from the CS 2 solution data, except i.n the regions where
these are not available.
*** The frequencies observed in the vapour phase i.r. spectrum are:
3119 vw, 2973 w, 2025 vs, 1979 vvs, 1947 w, 1279 vs, 10B4 m,
1025 s, 818 s, 643 w, 610 m, 515/509 vw, 423/417 vvw, 397 w.
3125 IR/R
837 IR/R
1114 IR/R
1266 IR
3096 IR/R
lOl4} IR 1007
- 168 -
TABLE XXXIX.
COHPARISON OF THE RING VIBRZi.TIONS (cm -1)
OF CpMn (CO) 3 AND ITS THIOCARBONYL DERIVA'l'IVES.
CpMn ( CO) (CS) 2
IR Raman IR Ré".rnan
3120 w 3124 (15) 3110 3115
835 s 832 s 834
1115 w 1116 (130) 1113
masked
1005 w 1011 vw
( 12)
( 60)
Mode
(\) . } ~
1
2
3
4
5
6
Symmetry
al (IR/R)
a2
848 IR/R 845 ( 10) 845 vw 7 el (IR/R)
l424} a] IR/R 1422 m 1427 ( 8) 1424 m 1420
3096 IR/R 2971 (12) 2972 9
1154 IR 10
lO64} IR/R 1064 m 1068 (9) 1060 vw Il
1059 e2
(R)
1520 IR 12
941 IR 923 'i'W 13
611 masked masked masked 14
a The i.r. frequencies quoted are from reference 122, the solid
state Raman activities from the author's work.
- 169 -
the modes v9-v13 , which are strictly i.r. inactive, only vII is
observed in the i.r. spectrum of CpMn(CO)2CS. In addition, none
of the degenerate e modes are split in the i.r. or Raman spectra.
These observations can be interpreted to mean that there is
little intramolecular interaction in the thiocarbonyl complexes.
Thus, the tendency to lmqer the local CSv syrnmetry of the ring
to the molecular Cs symmetry, is much less in the CS compounds
than in Cp~~(CC)3. In the series constructed by Parker and
Stiddard (p. 488 of reference 122), for the order of decreasing
local symmetrj for the Cp-M moiety, CPMn(CO)2CS would fit in the
same place as CpV( CO) 4. In view of this, the possibili t l" that
the 610 crci- l ban.d in the spectra of the thiocarbonyl complexes
is due to the v14 ring mode, is considered remote, since this
mode only becomes i.r. active much farther down the series.
This means that the G10 cm- l band can then be attributed to a
Ô (Mn-C-O) fundamental. The impor.tance of this conclusion will
become evident shortly.
The fa ct that vII is the first and only e 2 mode to become
i.r. active is rationalized on the basis that this C-H (1)
bending vibration is the one that interacts most strongly with
the metal atome Such an interaction is not unreasonable when
one notes the trends observed for the frequencies of the v(C-C)
and the two other ô(C-H) (1) modes (v 2 and v7 ) for a series of
n-cyclopentadienyl complexes including the CS compounds. There
is an apparent correspondence between the charge density on the
metal atom and the position of these bending modes (Table XL) •
Complex
CpM.'1 (CO) 2NO +
CpMn(CO) 3
CpMn(CO)2 CS
CpMn(CO) (CS)2
CpMn(CO)2PPh3
- liO -
TABLE XL.
CŒ-1PARISON OF \) (C-O)
1j7ITH \)2 AND \17 (cm -1) • a
\) (C-O)
2096, 2049 885
2027, 1944 847
2009, 1933 845
'\11990 845
1934, 1864 842
852
837
835
834
829
a The data, except for the thiocarbonyls, are from Table 11
of reference 122.
- 171 -
In contrast to CPMn(CO)3' aIl the ring modes observed in
the solid state i.r. spectrum of CpMn(CO)~CS are also present ... in the solution spectrum. The relative intensities of the bands
under the two conditions are approximately the same, including
those of VIl. This indicates that there is no increase in the
symmetry of the Cp-~m moiety in CpMn(CO)2CS in going from the
solid to the solution state. In addition, v IO ' v12 and v 13
appear in the solution i.r. spectr.um, although they are not
present in the solid state i.r. spectrum. Since these are all
e 2 modes that should be i.r. inactive, it seems that in fact the
Cp-Mn moiety has a Zo~er local symmetry in solution than in the
solid state. Since gross intermolecular effects are generally
considered to be negligible in solution, it must be intra-
molecular interaction between the Cp-Mn part and the rest of the
molecule that is responsible for the lowering of the ~yrnmetry.
One possible explanation for this phenomenon is the slow (longer
than the vibration al time scale) rotation of the Cp ring around
the Cp-I411 axis [of. (COT) Fe (CO) 3 reference 63]. Such a motion
is more likely to occur in solution than in the condensed solid
state. This "TOuld result in a lcwering of the overall symmetry
of the molecule. This hypothesis is further justified by the
splitting of several of the low frequency modes in solution and
in the vapour phase (the vapour phase data are given in the
footnotes to Table XXXVIII) •
- 172 -
B. Hn-C-O AND Mn-C-S VIBRATIONS
When one contemplates the complete vibrational spectra of
the thiocarbonyl complexes, the most striking observation is the
total absence of the v(C-S) fundamental in the Rfu~an spectra.
This is even more surprising since sulfur is generally con-
sidered to be a readily polarizable atomi and thus, CS might
be expected to give rise to a strong Raman effect. The reason
for this apparent anomaly is not yet understood.
Since CS is nmv believed to be a better TI-accepting ligand
than C0129-131, it is expected that in the thiocarbonyls the
v(C-O) frequencies will be higher, and the v(Mn-C) and ô(~m-C-O)
frequencies lower, than the corresponding modes in Cp~m(CO)3.
These predictions can be seen to be validated in the bar-graph
xepresentations of the spectra (Figures 50 and 51) •
Such generalized bonding arg~ments can also be utilized in
+ the comparison of the Mn with the isoelectronic Fe' complexes.
The decrease in electron density around the central metal atom,
+ in going from ~m to Fe , is manifested by the observed shifts
in certain of the vibrational modes. Thus, the v(C-O} and
v(C-S) frequencies are found to be higher, and the ô(M-C-O) and
the V(M-C) frequencies lower in the Fe+ than the Mn complexes
(Tables XXXVI and XXXVII). This is attributable to the decrease
in backbonding to the CO and CS groups.
Since it has been established that the Cp-Mn moiety can be
treated successfully by the method of "local symmetryll, the
remainder of the mole cule will aIse be considered as an
- 173 -
independent unit. The C3v symmetry of the Mn(CO)3 moiety is,
of course, lowered by the substitution of the CS groups. This
change is shown in the correlation diagram between Mn{CO)3 and
its CS derivatives (Table XLI). The fundamental modes will be
discussed in order of decreasing frequency. The values quoted
are from the solid state i.r. spectra, unless otherwise noted.
The 2009 and 1933 cm- l bands are assigned to the a 1 and ail
v(C-O) modes of CPMn(CO)2CS respectively. These assignments are
proposed in view of the fact that the highest frequency mode of
a metal carbonyl complex is invariably the in-phase totally
t . 77 symme r1.C one • However, in the absence of depolarization
measurements, it is possible that these assignments may be
reversed, particularly since the 1933 cm- l Raman band is the more
intense one. For the bis-thiocarbonyl derivative, the triplet
-1 . peak at ~1990 cm 1.S attributed to the al v(C-O) mode; the
splitting must be due to solid state effects. The 1260 cm- l band
in the i.r. spectrum of the mono-thiocarbonyl and the 1298 and
1220 cm- l bands in the i.r. spectrum of the bis-thiocarbonyl are
assigned to the v(C-S) fundamenta1s of these compounds.
The lower frequency modes will be considered next. As it
was shown before, the bands in this region shift to lower
frequency upon increasing replacement of CO by CS groups in
CpMn(CO) 3. These shifts are of importance in correlating the
fundamentals ·of CpMn(CO)3' CpMn(CO)2CS and CpMn(CO) (CS)2.·The
proposed assignments are based on those120-l23 of CPMn(CO)3.
It should be noted that L~e solid state Raman data presented
Fundamental
v (C-O)
v(C-S)
ô (M-C-O)
v (M-C)
ô (C-M-C)
- 174 -
TABLE XLI.
CORRELATION BETWEEN
Mn (CO) 3 AND ITS CS DERIVATIVES
Mn(CO) 3
C3v
al + e
al + a2 +
a'
a'
2a ' 2e"""""" ~a'
.",a ' al + e ---~a'
"a 1
al + e----~a'
+ an
+ 2a"
+ ail
+ ail
+ ail
Mn (CO) (CS)2
Cs
a'
a' + ail
a' + a"
2a ' + 2a"
a'
a' + ail
a'
a' + a"
Fundamental
'J (C-O)
v (C-S)
ô (M-C-O)
6 (M-C-S)
v (M-Co)
v (M-Cs )
ô (C-M-C)
ê (C-M-C ')
here for the tricarbonyl (Table XLII) are the first complete data
to be reported.. Al though ,the Raman spectrum of the CO s tretching
region has been studied before, no solid state data were recorded
f th ~h ob tO 1 ° 123 or e o~ er V1 ra 10na reg10ns
In the tricarbonyl, the very strong Raman band at 354 cm-l
has been assigned to the al v(Cp-Mn} rncde. Consequently ~~e ve~'
high intensity lowest frequency Raman bands at 338 and 321 cm-l
are assigned to the a'\) (Cp-Mn) modes of the 'two CS complexes.
* IR
3126 m
3098 w
2022} vs
2018
1954 s
1937} vs
1922
1914 sh
142S}s 1420
1359 m
lO62}S 1057 m
1008
849 s
834 s
668} vs
663
- 175 -
TABLE XLII.
VIBRATIONAL FREQUENCIES A~D ASSIGNMENTS -1 FOR SOLID CpHn(CO} 3 (cm ).
Raman
3131
3093
2015 (20)
1944 (40)
1921 (53)
1914 (w,sh)
1429 (7)
1361 (6)
1114 (67)
1062 (12)
846 } (7)
836
668 (4)
** Assignment
C-H stretch.
C-H stretch.
C-O stretch.
c-o stretch.
c-o stretch.
c-o stretch.
c=c stretch.
al
el
el
ring breath. al
C-H bend. <1> e 2
C-H bend. el
C-H bend. <1> el
C-H bend. <1> al Mn-C-O bend. e
· )
* IR
3126 rn
3098 w
2022} vs
2018
1954 s
1937} vs
1922
1914 sh
142S}s 1420
1359 rn
lO62}S 1057 m
1008
B49 s
834 s
66B} vs
663
- 175 -
TABLE XLII.
VIBRATIONAL FREQUENCIES .AI.~D ASSIGN~.ENTS
-1 FOR SOLID Cp.Hn (CO) 3 (cm ).
Raman
3131
3093
2015 (20)
1944 ( 40)
1921 (53)
1914 (w,sh)
1429 ( 7)
1361 (6)
1114 (67)
1062 (12)
846} 7)
836
668 (4)
** Assignment
C-H stretch.
C-H stretch.
C-O stretch.
c-o stretch.
c-o stretch.
c-o stretch.
c=c stretch.
al
el
el
ring breath. al
C-H bend. ' l , '-LI e 2
C-H bend. el
C-H bend. <1> el
C-H bend. (1) al
Mn-C-O bend. e
- 176 _.
643 vs,br Mn-C-O bend. e
609 m 607 ( 3) C-C bend. (1) e 2
541 s 545 (7) Mn-C-O bend. al
499 w 500 (58) r.1n-C stretch • al
487 w 489 (sh) Mn-C stretch. e
373 w 385 (20) } ring tilt e 367 (sh)
357 w 354. (350) ring-Mn stretch. al
140r ,br 120
107 w 113 (240) def. and
97 (sh) 1attice modes
55 (sh)
46 (sh)
39 (sh)
* Infrared data from reference 120.
** . 120-123 Based upon various previous ass1.gnments
.- 177 -
-1 Similarly, the weak Raman bands at 383 and 350 cm are assigned
to the al ring tilt modes of CpMn(CO)2CS and CpMn(CO) (CS)2'
respecti vely.
-1 In the region below 500 cm and above the Cp-Mn stretching
frequencies assigned previously, three strong bands appear in the
Raman spectra of the thiocarbonyl complexes. Since only two and
one v(Mn-Co ) modes are expected for CpMn(CO)2CS and CpMn(CO} (CS)2
respecti vely, the remaining bands mus t be due to the v (Mn-Cs)
fundamentals. Thus, the two Raman bands for Cp~m(CO)2CS at 460
and 437 cm- l are assigned to the al and ail V(Mn-Co ) modes -
syrnrnetries assigned on the basis of relative intensities - whi1e
the 10wer frequ~ncy band (due to the mass effect expected for
sulfur) at 367 cm-1 is assigned to the v(Mn-Cs ) fundarnenta1. In
o the vapour phase i.r. spectrum ç the lower frequency v(Mn-C ) mode
-1 is split into a doublet at 423/417 cm • For CpMn(CO) (CS)2' the
assignments are as fo1lows: al V (Mn-Co) at 428 cm-l, the two
v (Mn-Cs) modes at 40'4 and 359 cm- l
In the solid state i.r. spectrurn of CP!~(CO)2CS, there are
four bands in the region usua1ly associated wi th the 0 (M-C··O)
modes (650-470 cm-l ) i while there are six for cprvln(CO) (CS) ..... ~
However, for these compounds there shou1d be four and two
o (Mn-C-O) modes, respective1y, in this region. The only other
-1 type of fundamental expected in the 700-300 cm region is the
o (Mn-C-S) • Consequently, the extra bands in the case of the
bis-thiocarbony1 complex must be due to the o(X4n-C-S) modes.
Moreover, since the predictions based on the "local sym .. netryll
- 178 -
arguments for the Cp-Mn and Hn(CO)2CS moieties have been shown
to be valid, it must be accidentaI degeneracies that are the
cause of the apparently too few bands in this region of the
spectra of the mono-thiocarbonyl complexe This reasoning is
supported by the splitting of two of these bands into doublets,
in the solution i.r. spectra. A similar observation was found
earlier for the ring modes i.e. the appearance of extra bands in
solution indicates an apparently lower molecular symmetry in
solution than in the solid state.
Thus, for CpMn(CO)2CS and CpMn(CO) (CS)2 the bands in the
645-473 and 625-448 cm- l regions, respectively, are assigned to
the 0 (Mn-C-O) and ô (r.lln-C-S) fundamental vibrations. Conclusive
assignments for these modes cannot be made at this time. Hcwever,
it is deemed significant that at least the regions for the
ô (M-C-S) and V(M-Cs ) fundamentals can be assigned unequivocally.
Also, it is interesting to note that the relative intensities of
these sulfur containing modes are the same in i.r. and Raman as
those of the carbonyls i.e. ô (Mn-C-S) is strong in i.r. and weak
in Raman, while V(Mn-Cs ) is strong in Raman and weak in i.r.
The bands below 150 cm- l are assigned to the three C-Mn-C
modes, the ring twisting mode and. the lattice vibrations. lUI
the assignments proposed above~ for these complexes in the solid
state, are collected in Table XXXVII.
The solution i.r. data for CpMn(CO)2CS, and a complete
vibrational assignment (in the 4000-60 cm-l region) are presented
in Table XXXVIII. It should be noted that aIl the cornbination
- 179 -
and overtone bands of CpMn(CO)2CS have been assigned vlithout
requiring combinations between modes associated with the Cp and
Mn(CO) 2CS moieties. This further substantia·tes the initial
assumption that the vibrations of these two fragments can be
assigned on the basis of "local syrnrnetry Il •
Sorne of the cornbination bands, which are considered to be
important to the arguments presented in this Chapter, will nOtIl
be discussed.
The 2273 cm- l band cannot be explained on the basis of any
cornbination other than that between the inactive a2 ring mode
-1 (v 4 ) and the el ring mode (v 6 ) nea.r 1000 cm . This would place
v 4 at 1270' cm-l, in good agreement with the frequency of this
mode, observed in other complexes in the 1266-1259 cm- l
region122 The other alternative, that v(C-S) combines with v6
,
is considered unlikely, since no other ring modes are found to
co~bine with either v(C-O) or v(C-S). This same type of reasoning
-1 substantiates the previous assignment of the 612 cm band (CS 2
solution) to a 8 (Mn-C-O) mode, rather than the \1 14 ring mode.
The co~bination of this band with both the v(C-O) and v(C-S)
vibrations designates this fundamental to the r.1n(CO)2CS moiety.
A close examination of the cornbinations between the low frequency
(benzene solu,tion) fundamentals and the other assigned modes,
-1 indicates that the 122 and 103 cm bands can be assigned
tentatively to the c-r-1n-C and C-Hn-C 1 deformation modes, while
the 78 cm-l peak °b-'..L.t ob t d t th Il ° can poss~_iy oe a~ r~ u e 0 e a r~ng
t\'listing mode.
- 180 -
In contrast to all ·the other fundament.als, the 399 cm -1
(CS2
solution) and 330 cm -1 bands combine \.,ri th both the Cp and
~m(CO)2CS fundarnentals. The latter mode has been clearly
identified as the al Cp-Mn vibration. Since this mode involves
stretching of the bond connecting the two fragments of the
molecule, it could have been anticipated that it would combine
with the fundamentals of both the ring and the Mn(CO)2CS
fragments.
A corollary to the previous argument is the assignment of
the 399 cm- l band (in CS2
) to the al ring tilt vibration of
CpMn (CO) 2CS. This assignment leads to another note\vorthy point.
In a solvent shift study (Table XLIII) perforrned on CpMn(CO)2CS,
it is this 399 cm- l band that is the most significantly solvent
dependent. Since solvent shifts are generally correlated with
bond polarities, it can be concluded that this Cp-Mn bond is
the most polar one in this molecule, in particular, more polar
than the c-o and C-S·bonds. (The al Cp-Mn fundarnental in solution
is just out of the practical range of the available instrumentation).
CS 2
V (C-O) al 2007
v (C-O) ail 1956
v(C-S) al 1266
Ô (C-H) el 1006
Ô (C-H) al 825 r
645
612 ô (M-C-O)
605 Ô (M-C-S)
519
513
0 \.1 (l4-C ) ail 430
ring tilt al 399
s v(r4n-C ) al 360
TABLE XLIII.
EFFECT OF SOLVENTS ON SOME OF THE FUNDAMENTAL
MODES OF CpMn(CO)2 CS (cm- l ).
C6H12 CC1 4 C6H6 CH 2C1 2 CHC13 CH 3I
2016 2017 2003 2011 2015 2011
1962 1959 1954 1956 1954
1272 1270 1269 1269
998 1005 1007 1005
824 825 824 632
646 645 645 646
613 613 614 613 613
605 607 602 607 608 607
520 517 517 517
512 514
432 431 435 436 435
379 383 382 383 381
361 364 364 365 361 363
CH 3CN CH 3N02 bv
2014 2009 13
1952 1951 11
1264 8
1005 8 1-' co
842 841 17 ......
646 1
613 2
6 '1
518 515 l 8
J 434 429 7
395 20
350 367 17
- 182 -
CHAPTER 4. CONCLUSION
The first vibrational assignment for a thiocarbonyl complex
has been achieved for CpMn(CO)2CS in both the solid and solution
states. Sorne of the fundarnental modes of CpMn(CO) (CS)2 have
also been assigned. The.' ô (.Mn-C-S) and \.\ (Mn-Cs) modes occur
in the sarne regions (with the sarne relative i.r. and Raman
intensities) as the corresponding carbonyl fundamentals. In a
solvent shift study, the frequency of the Cp-Mn ring tilt mode
is the most solvent sensitive.
The method of "local symmetry" has been found to be much
more meaningful for the thiocarbonyls than for CpMn (CO) 3. In
the solid state'especially, the thiocarbonyls exhibit little
intrarnolecular interaction. The "slow" rotation of the ring
in solution causes an apparent decrease in the syrnmetry of both
the Cp-Mn and Mn(CO)2CS moieties.
- 183 -
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- 192 -
CONTRIBUTIONS 'ro Ki.'W'iVLEDGE
PART l
1. The molecular geometry of Mn(CO)4NO, in the vapour phase
and in solution, has been determined to be a C3v trigonal
bipyramidal one.
2. The infrared spectrum of ~~(CO)4NO has been assigned in
-1 the 5250-33 cm region.
3. The ionization potential of Hn(CO)4NO has been determined
by mass spectrometry.
4. A ne\V' route has been developed for the synt.hesis of
Fe (CO) 2 (NO).2·
5. The solution i.r., far-infrared and Raman spectra of
Fe(CO)2(NO}2 have been assigned.
6. Low frequency assignments h.ave been put forward for the
complexes Fe(NO)2(CO}PPh 3 and Fe(NO)2(Co)p(OMe}3.
PART. II
1. For the (NBD)M(CO)4 complexes, the coordinated C=C and the
metal-olefin stretching fundamentals have been assigned.
2. Vibrational assignments have been proposed for the olefin-
metal-halogen linkages of [(COD}RhCl]2 and [(COD)CuCl]2.
3. A vibrational assignment, and a novel geometry, have been
suggested for the species (COD)2CUCl04.
- 193 -
Pl--RT III
1. The firs"t vibrational assignrnents for thiocarbonyl complexes
have been achieved for CpMn(CO)2CS and CpMn(CO) (CS)2'
resulting in the identification of the low·-frequency !-ln-C-S
fundamental vibrations.
- 194 -
EHRA'rZ\
l. p. 35, l. 3 : o (M- ~\!-O) should be 6 (M-C-O) •
2. p. 35, l. 9 : preceding.
3. p. 58, 1- 3 : predictions.
4. p. 60, footnote a: omitted.
5. p. 87, l. 9 : The compound discussed in refs. 73, 74 is
cyclopentadiene, CS
H6 , not cyclopentene.
6. p. 102, last line: excepte
7. p. 136, l. 1: demonstrates.
8. p. 154, Table XXXV heading: This should be CSHSMn.