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Advanced Inorganic Chemistry
Alireza [email protected]
Department of Chemistry, Yazd University
1. Crystal Field Theory CFT
2. Ligand Field Theory LFT
3. Molecular Orbital Theory MOT
Bonding in Coordination Chemistry
پیوند در شیمی کوئوردیناسیون
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π-acceptor ligands
CN-, CO, PR3, C2H4
ML π-bonding (π-back bonding)
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1d-d transition
Ligand Field transition
The Electronic Spectra of Coordination Compounds
طیف الکترونی ترکیبات کوئوردیناسیون
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The aim of this chapter is to demonstrate how to interpret the origins of the
electronic spectra of coordination comps and to correlate these spectra with bonding.
The spectrum of the d3 complex [Cr(NH3)6] in aqueous solution
The Electronic Spectra of Coordination Compounds
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The classification of microstates
We start the analysis by setting up a table of microstates of the d2
configuration;have been only the microstates allowed by the pauli
principle have been included.The largest value of ML, which for a d2
configuration is +4. This state must belong to a term with L=4 (a G
term).
We can concluded that the terms of a 3d2 configuration are 1G, 3F, 1D, 3P, and 1S. These terms account for all 45 permitted states
Term Number of state1G 9x1 = 93F 7x3 = 211D 5x1 = 53P 3x3 = 91S 1x1 = 1
Total: 45
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It is possible to identify the term of lowest energy by using Hund’s rule
1. For a given configuration, the term with the greatest multiplicity
lies lowest in energy. For the d2 configuration, this rule predicts that
the ground state will be either 3F or 3P.
2. For a term of given multiplicity, the greater value of L, the lower
the energy. In this case, the 3F term is lower in energy than 3P
term.The ground term of a d2 species such as Ti2+ is expected to be 3F.
Thus, for d2 the rules predict the order
3F 3P 1G 1D 1S
but the order observed for Ti2+ from spectroscopy is
3F 1D 3P 1G 1S
The energies of the term
The Racah Repulsion Parameters
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Energies of d2 free ion terms
3F 1D 3P 1G 1S
Values for Racah Parameters
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Splitting of d2 free ion terms in Octahedral field
Splitting of d2 free ion terms in Octahedral field
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Splitting of dn free ion terms in Ligand fields
Tanabe-Sugano diagram for d2 config. Orgel diagram for d2 config.
1
2
31
2
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3T1g
3T2g
3T1g
3A2g
Electronic Transitions of d2
ion in Octahedral Field
4T1g
4T2g
4T1g
4A2g
Electronic Transitions of d7
ion in Octahedral Field
d5+2
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Electronic spectrum of [Co(H2O)6]2+
4T1g
4T2g
4T1g
4T1g (P)
4T1g
4A2g
3T2g
3T1g
3T1g
3A2g
4T1g
4T2g
4T1g
4A2g
d5+2d2
d2 , d7 Oh
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Hole Formalism in Electronic Transitions of dn ion
43
d7 d3
d2 d8
d2 d7 dn d10-ndn d5+n
Electronic spectrum of [Cr(OH2)6]3+
1
2
3
4A2g
4T2g
4A2g
4T1g
4A2g
4T1g(P)
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3
Electronic spectrum of [Ni(OH2)6]2+
3A2g
3T2g
3A2g
3T1g
3A2g
3T1g (P)
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d2 , d7 Td
d2 , d7 Oh
d3 , d8 Td
d3 , d8 Oh
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d2 , d7 Ohd3 , d8 Oh
Electronic Transitions of d1 ion in Octahedral FieldThe number of microstates possible for dX configuration is given by formula
)!(!
!
XNX
N
d1 case corresponds to X = 1 and N = 10 (maximum occupancy of the d-level). The number of microstates is then 10 which means that any of the five degenerate d-orbitals may be occupied by an electron with a spin of ½ or - ½.
The orbital angular momentum for Ti3+, L = 2, the spin S = 1/2 and the term is 2D
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2T2g
2Eg
Electronic Transitions of d1 ion in Octahedral Field
lmax
Hole Formalism in Electronic Transitions of dn ion
d4 d9
dn d10-n
d1 d6
dn d5+n
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Td Oh
2T2g
2E
Td Oh
d1 , d6 Td
d1 , d6 Oh
d4 , d9 Td
d4 , d9 Oh
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12T2g
2Eg
2T2g
2Eg
15T2g
5Eg
Electronic spectrum of [Fe(OH2)6]2+
5T2g
5Eg
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Electronic spectrum of [Cr(H2O)6]2+
15Eg(D) 5T2g
5Eg(D)
5T2g
5
5
5
Electronic spectrum of [Cu(OH2)6]2+ 12Eg
2T2g
2Eg
2T2g
2
2
2
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d5 metal complexes• Terms of free d5 metal ions are 6S, 4G, 4F, 4D, 4P, 2I, 2H, 2G, 2G, 2F, 2F, 2D, 2D, 2D, 2P, 2S (16 terms, 252
microstates). The lowest energy term is 6S.
• In the octahedral ligand field the 6S term will NOT be split. It gives rise to a single 6A1g term.
• The 6A1g term is the ground state term at weak ligand fields. NO terms of the same multiplicity exists and thus NO spin-allowed e-e transition is possible.
• At strong ligand fields spin pairing occurs (t23e2 t2
5). As a result, the ground state term and the multiplicity change from 6A1g to 2T2g(I)
.
4G
(t2)5
(t2)4(e)1
(t2)2(e)3
(t2)1(e)4
octahedral and tetrahedral d5
2T2
6A1
4P
4T1
4T2
4E
4T1
4T1
4T2
4E
4A2
6S
free ion weak field strong field
Configuration (example) Ground
state
Excited states w/same S # Abs.bands
d1 oct (Ti(H2O)63+), d9 tetr. 2T2
2E2 1
d2 oct (V(H2O)63+), d8 tetr. 3T1 (F) 3T2,
3T1 (P), 3A2 3
d3 oct (Cr(H2O)63+), d7 tetr. 4A2
4T2, 4T1 (F), 4T1 (P) 3
d4 oct (Cr(H2O)62+), d6 tetr. 5E2
5T2 1
d5 oct (Mn(H2O)62+) or tetr. 6A1 none 0
d6 oct (Fe(H2O)62+), d4 tetr. 5T2
5E2 1
d7 oct (Co(H2O)62+), d3 tetr. 4T1 (F) 4T2,
4T1 (P), 4A2 3
d8 oct (Ni(H2O)62+), d2 tetr. 3A2
3T2, 3T1 (F), 3T1 (P) 3
d9 oct (Cu(NH3)62+), d1 tetr. 2E2
2T2 1
Summary
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Summary
Electronic Transitions in Low Spin Complexes
low spin
high spin Orgel Diagram
Tanabe-Sugano Diagram
Tanabe-Sugano Diagram
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Tanabe – Sugano Diagram
d2 A=0 C/B=4.42
E(1S)= A+14B+7C E(1S)= 14B+7C E(1S)/B= 14+7C/B 44.9 52.9E(1G)= A+4B+2C E(1G)= 4B+2C E(1G)/B= 4+2C/B 12.8 20.8
E(1D)= A-3B+2C E(1D)= -3B+2C E(1D)/B= -3+2C/B 5.8 13.8
E(3P)= A+7B E(3P)= +7B E(3P)/B= +7 7 15E(3F)= A-8B E(3F)= -8B E(3F)/B= -8 -8 0
Tanabe – Sugano Diagram
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low spin high spin low spin high spin
low spin high spin low spin high spin
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The Nephelauxetic Effect[V(H2O)6]
3+. B = 610 cm-1
V3+(g) B = 861 cm-1
This value indicates that electron repulsions are weaker than in the free ion. This
weakening occurs because the occupied moleculer orbitals are delocalized over the
ligands and away from the metal.
nephelauxetic parameter = B (comp)/ B(free ion)
The values of depend on the metal ion and the ligand. They vary along the
nephelauxetic series:
Br- Cl- CN- NH3 H2O F-
A small value of indicates a large measure of d-electron delocalization on to the
ligands and hence a significant character in the complex.The softer ligand, the
smaller the nephelauxetic parameter.
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Determination of O and B
O
OO
d1, d3, d4, d6, d8, d9 1=O
d2, d7 3 - 1 =O
CrF63-
14900, 22700 , 34400 cm-1
= 14900 cm-1
2 + 3 - 3 1 = 15B’ = 12400
15B’ = 12400
B’ ≈ 827 cm-1
d3, d81 =
2 = 7.5B’ + 1.5 - 0.5 [225 B’2+2-18B’]1/2
3 = 7.5B’ + 1.5 + 0.5 [225 B’2+2-18B’]1/2
(2 +3 -31)/15=B’
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V(H2O)63+ (d2)
1 = 17800 (3T1g 3T2g)
2 = 25700 (3T1g3T1g(P)) cm-1
The third expected transition 3 (3T1g(F) 3A2g) is far in the UV region and is masked by other absorptions. We can calculate the 3.
2/1 = 1.44
2:
2/B = 42(approximately): B= 2/42 = 25700cm-1/42 = 610 cm-1
1:
1/B = 29 (approximately): B= 1/29 = 17800 cm-1/29= 610 cm-1
Since o/B= 31, o= 31xB = 31x 610 cm-1 = 19000cm-1
3 ≈ (60)(610)=37210 cm-1
1
2
UV/VIS spectra of three
chromium(III) complexes:
a) [Cr(en)3]3+
b) [Cr(ox)3]3-
c) [CrF6]3-
look for the shift of the two
absorption peaks 1 and 2
to lower frequencies.
a)
b)
c)
a) [Cr(en)3]3+
b) [Cr(ox)3]3-
c) [CrF6]3-
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[Ni(en)3]2+(purple)
9000 cm-114000 cm-1
25000 cm-1
[Ni(H2O)6]2+(green)
B1g B2g
B1g Eg
Free ion term Oh D4h
When degenerate orbitals are asymmetrically occupied, J-T distortions arelikely
John-Teller Distortion in Spectrum
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Eg A1gEg B1g
12T2g
2Eg
2- Charge Transfer Transitions
[email protected] 74Ligand to Metal Charge Transfer Metal to Ligand Charge Transfer
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Ligand to Metal Charge Transfer (LMCT)
Ligand to Metal Charge Transfer
Ligand to Metal Charge Transfer (LMCT)
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Metal to Ligand Charge Transfer (MLCT)
Metal to Ligand Charge Transfer
Intensity & Selection Rule
Bear-Lambert
A: جذب
b: cm طول مسیرعبور نور
A = log(I0/I)
: M-1cm-1 ضریب جذب مولی
c: M غلظت
A = bc
A
l
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Intensity & Selection Rule
i
j Transition Moment Integral
0
0 dO ji
Forbiden
Allowed
غیر مجاز
مجاز
اربیتیاسپینی
g g
u u
غیر مجاز
S0غیر مجاز
Intensity & Selection Rule
اسپین تقارن (M-1cm-1)
d-d (Oh) مجاز
(S=0)
غیرمجاز
g g
20-200
d-d (Td) مجاز
(S=0)
مجاز >250
d-d غیرمجاز
(S0)
<1
CT مجاز
(S=0)
مجاز 1000-50000
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The spectrum of the d3 complex [Cr(NH3)6] in aqueous solution
The Electronic Spectra of Coordination Compounds
Electronic spectrum of [Mn(H2O)6]2+
Why is absorption by [Mn(H2O)6]2+
so weak?6A1Excited states is no spin-allo-wed absoption, may be very weakforbidden transitions to excited stateof spin multiplicity other than 6
S0 غیر مجازاسپین
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Vibronic Coupling
Absorption
, cm-12500012500
Absorption of a TMC in the UV and visible regions results from transitions of electrons between the energy levels available in the metal complex.
Of our interest will be:
1) The number of absorption bands
2) The energy of absorption bands
3) The intensity of absorption bands
4) The band width of absorption bands
1
2
