ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net 2012, 9(4), 2532-2539
Syntheses, Magnetic and Spectral Studies on the
Coordination Compounds of the Polystyrene-
anchored Thiazolidin-4-one
DINESH KUMAR*a AND AMIT KUMAR
b
aDepartment of Chemistry, National Institute of Technology, Kurukshetra, 136119,
Haryana, India bDepartment of Chemistry, Haryana College of Technology & Management, Kaithal,
136027, Haryana, India
Received 17 October 2011; Accepted 30 December 2011
Abstract: The reaction between polystyrene 3-formylsalicylate and
thiophene-2-carboxylic acid hydrazide in DMF in the presence of ethyl
acetate results in the formation of polystyrene N-(2-carbamoylthienyl)-
3'-carboxy-2'-hydroxybenzylideneimine (I). A benzene suspension of I
reacts with mercaptoacetic acid and forms the polystyrene N-(2-
carbamoylthienyl)-C-(3'-carboxy-2'-hydroxyphenyl) thiazolidin-4-one,
PSCH2–LH2 (II). A DMF suspension of II reacts with Zn(II), Co(II),
Cu(II), Zr(OH)2(IV) and MoO2(VI)
ions and forms the corresponding
polystyrene-anchored coordination compounds, [PSCH2–LZn(DMF)]
(III), [PSCH2–LCo(DMF)3] (IV), [PSCH2–LHCu(OAc)] (V),
[PSCH2–LH2Zr(OH)2(OAc)2] (VI) and [PSCH2–LHMoO2(acac)] (VII)
respectively. The polystyrene-anchored coordination compounds have
been characterized on the basis of elemental analyses, spectral (IR,
reflectance, ESR) studies and magnetic susceptibility measurements. II
acts as a neutral tridentate ONS donor ligand in VI, a monobasic
bidentate OS donor ligand in VII, a monobasic tridentate ONS donor
ligand in V and a dibasic tridentate ONO donor ligand in III and IV.
The acetato groups behave as monodentate ligands in V and VI. A
square-planar structure for V, a tetrahedral structure for III, an
octahedral structure for IV and VII and a pentagonal-bipyramidal
structure for VI are suggested.
Keywords: Thiazolidin-4-one, Polystyrene-anchored coordination compounds,
Magnetically dilute, Strong field and Covalent character.
Syntheses, Magnetic and Spectral Studies on the Coordination Compounds 2533
Introduction
In recent years there has been considerable interest in the syntheses and use of
functionalized polymers having chelating abilities due to their practical convenience,
operational flexibility and formation of coordination compounds with high metal to polymer
bond energies1. A structural study of polymer-anchored compounds seems useful in view of
their numerous applications in organic synthesis2, immobilization of enzymes
3, biological
systems4, water treatment
5 and as catalysts
6 etc. Thiazolidin-4-ones belong to an important
group of heterocyclic compounds with carbonyl group at fourth position7. They show broad
spectrum of biological activities due to their ready accessibility and diverse chemical
reactivity8. They are involved in variety of applications such as antimicrobial, antibacterial,
anticonvulsant, antifungal, anti-HIV, antiproliferative, anti-inflammatory, cystic fibrosis and
antithyroid9-11
etc. Many drugs possess modified pharmacological properties in the form of
the metal complexes12
. These facts prompted us to explore the coordination behavior of
thiazolidin-4-one (II) derived from the Schiff base (I) (obtained from the condensation of
polystyrene 3-formylsalicylate and thiophene-2-carboxylic acid hydrazide) towards Zn(II),
Co(II), Cu(II), Zr(OH)2(IV) and MoO2(VI)
ions. A perusal of the literature indicates that
several polymer-anchored ligands containing O atom(s) like crown ethers13
, acetylacetone14
and iminodiacetic acid15
have been reported, however there is no report on the coordination
compounds of polymer-anchored ligand containing thiazolidin-4-one moiety.
In this paper, we describe the syntheses and characterization of polystyrene-anchored
thiazolidin-4-one, PSCH2–LH2 (II) and its coordination compounds with above ions.
Experimental
Chloromethylated polystyrene, PSCH2–Cl (containing 1.17 mmol of Cl per g of resin and
1% crosslinked with divinylbenzene) [Sigma Chemical Co (USA)]. Copper(II) acetate
monohydrate, zinc(II) acetate dihydrate [SD’s Fine]; cobalt(II) acetate tetrahydrate,
hexadecaaquaoctahydroxotetrazirconium(IV) chloride [BDH]; ammonium molybdate(VI)
tetrahydrate, acetylacetone [Ranbaxy]; thiophene-2-carboxylic acid hydrazide [Acros
Organics (USA)] were used as supplied for the syntheses. Polystyrene 3-formylsalicylate,
bis(acetylacetonato)dioxomolybdenum(VI), hexadecaaquaoctahydroxotetrazirconium(IV)
acetate and 3-formylsalicylic acid were synthesized by following the reported
procedures16-19
.
The elemental analyses, IR, reflectance spectral studies, ESR spectra and magnetic
susceptibility measurements were carried out as described in our previous report 20
.
O
OO
C
HH
PS
C
H
N N
H
C
OH
CS S
C
OH
C
H
NN
H
C
PS
H
H
C
O O
O
[I (keto form)] [I (enol form)]
DINESH KUMAR 2534
O
OO
C
H
H
PS
C
H
N N
H
C
OH
CS
OH
C
S C
HH H H
CS
C
SC
OH
C
H
NN
H
C
PS
H
C
O O
O O
[II (keto form)] [II (enol form)]
SC
O
N
N
C
H
S
C
H
O
O
C
H
A
H
H
CPS C
O
O Zn
H
H
CPS
C
O
N
N
C
C
H
SC
H
O
O
O
C
H A
A
A
O
S
Co
[III, A = DMF] [IV, A = DMF]
H
C
O
O
O
H
CS
H
C
C
N
N
O
C S
PS C
H
H
Cu
OAc
HO
OH
C
O
C
H
S
C
C
HH
H
N S
C
N
O
OH
HO
Ac
Zr
O
O
H
H
CPS O
OAc
[V] [VI]
O
C
H
PS C
H
O
O
O
Mo
N C SN
O
H2
C
C
C
S
H H
O
O
O
C
CC
H
Me
Me
O
[VII]
Synthesis of polystyrene N-(2-carbamoylthienyl)-3'-carboxy-2'-hydroxybenzylideneimine (I)
Polystyrene 3-formylsalicylate (1.0 g) was allowed to suspend and swell in DMF (100 mL)
for 45 min. To this suspension, a DMF solution (60 mL) of thiophene-2-carboxylic acid
hydrazide (0.66 g, 4.68 mmol) and ethyl acetate (100 mL) were added, while stirring
magnetically. The mixture was refluxed for 8 h and then cooled to room temperature. The
polystyrene-anchored Schiff base, I obtained was suction filtered, washed with DMF and
ethyl acetate. It was dried in vacuo at room temperature.
Syntheses, Magnetic and Spectral Studies on the Coordination Compounds 2535
Synthesis of polystyrene N-(2-carbamoylthienyl)-C-(3'-carboxy-2'-hydroxyphenyl)
thiazolidin-4-one, PSCH2–LH2 (II)
Mercaptoacetic acid (0.32 g, 3.51 mmol) was added to the swollen suspension of I (1.0 g) in
benzene (100 mL). The mixture was refluxed for 12 h on a water bath and then cooled to
room temperature. The solid product was filtered and washed with 10% sodium bicarbonate
solution followed by chilled distilled water. The product was dried as mentioned above. IR
bands (KBr): 1695 cm-1
[ν(C==O)(thiazolidinone ring)], 1652 cm-1
[ν(C==O)(amide)], 1580
cm-1
[ν(C––N)(thiazolidinone ring)], 1532 cm-1
[ν(C––O)(phenolic)], 830 cm-1
[ν(C––
S)(thiazolidinone ring)] and 648 cm-1
[ν(C––S)(thiophene ring)].
Syntheses of coordination compounds of II
1.0 g of II was allowed to suspend and swell in DMF (100 mL) for 1 h. A DMF solution of
appropriate metal salt (2.34 mmol) was added to the above suspension. The mixture was
refluxed on water bath for 8-10 h and the products obtained were suction filtered, washed
several times with ethyl acetate and DMF. The products were then dried as mentioned
above.
Results and Discussion The reaction between polystyrene 3-formylsalicylate and thiophene-2-carboxylic acid
hydrazide in DMF in the presence of ethyl acetate results in the formation of polystyrene
N-(2-carbamoylthienyl)-3'-carboxy-2'-hydroxybenzylideneimine (I). The cyclization of I
with mercaptoacetic acid in benzene forms polystyrene N-(2-carbamoylthienyl)-C-(3'-
carboxy-2'-hydroxyphenyl)thiazolidin-4-one, PSCH2–LH2 (II). A DMF suspension of II
reacts with Zn(II), Co(II), Cu(II), Zr(OH)2(IV) and MoO2(VI)
ions in 1:2 molar ratio and
forms the corresponding polystyrene-anchored coordination compounds of the types,
[PSCH2–LZn(DMF)] (III), [PSCH2–LCo(DMF)3] (IV), [PSCH2–LHCu(OAc)] (V),
[PSCH2–LH2Zr(OH)2(OAc)2] (VI) and [PSCH2–LHMoO2(acac)] (VII) respectively. The
percent reaction conversion of III-VII lies between 45.3-74.3 and the metal binding capacity
of II lies between 0.32-0.55 mmol of corresponding metal per g of the resin (Table 1).
Table 1. Analytical, MBC and PRC values of polystyrene-anchored coordination compounds of II.
Compound
obsd(calcd)%
MBCa mmol/g of
resin
PRCb
M DMF
III 2.9 (4.96) 3.3 (5.54) 0.44 58.5
IV 3.0 (4.04) 11.2
(15.02) 0.51 74.3
V 3.5 (4.87) - 0.55 71.9
VI 2.9 (6.40) - 0 .32 45.3
VII 3.3 (6.81) - 0.34 48.5
Abbreviations: aMBC = [M% (observed) 10] /(atomic weight of metal)
bPRC = [M% (observed) 100] / M% (calculated) on the basis of 100% reaction conversion
of polystyrene-anchored ligand to polystyrene-
anchored coordination compounds.
DINESH KUMAR 2536
Infrared spectral studies
The infrared spectra of I-VII were recorded in KBr and the prominent peaks are shown in
Table 2. The ν(C==N)(azomethine) stretch of I occurs at 1620 cm
-1. This band disappears
and a new band appears in II at 1580 cm-1
due to the ν(C––N)(thiazolidinone ring) stretch21
,
indicating the formation of corresponding thiazolidin-4-one. The formation of II is further
supported by the appearance of a new band at 830 cm-1
due to the ν(C––S) (thiazolidinone
ring) stretch22
. II occurs in the keto-form23
as evident by the presence of a strong band due to
the ν(C==O)(amide) stretch at 1652 cm-1
. This band remains almost at the same energy in
V, VI and VII indicating the non-involvement of the keto O atom towards coordination. III
and IV do not display the ν(C==O)(amide) stretch but show new band at 1260 and 1245 cm-
1 respectively suggesting the conversion of –C(O)NH– moiety (keto-form) into –
C(OH)==N– moiety (enol-form) followed by the deprotonation of enolic OH group and
subsequently involvement of enolic O atom towards coordination. The ν(C––O)ф stretch23
of II occurs at 1532 cm-1
. This band remains unchanged in VI indicating the non-
involvement of phenolic O atom towards coordination. However, the shifting of this band
towards higher energy (≤ 10 cm-1
) in the remaining compounds favours the formation of a
bond between phenolic O atom and the corresponding metal ions. The
ν(C==O)(thiazolidinone) stretch24
of II occurs at 1695 cm-1
. This band shows a negative
shift by 45 cm-1
in VI indicating the coordination through O atom of the carbonyl group of
thiazolidinone moiety. The occurrence of this band almost at the same energy in the
remaining compounds indicates the non-involvement of the carbonyl O atom towards
coordination. The [ν(C––N)(thiazolidinone ring)] stretch21
of II shifts from 1580 cm-1
to
lower energy by 35-42 cm-1
in the III, IV and V lending support for the involvement of ring
N atom towards coordination. However, this band remains almost at the same energy in VI
and VII. The [ν(C––S)(thiazolidinone ring)] stretch22
of II occurring at 830 cm-1
shifts to
lower energy by 29 cm-1
in VII, on the other hand, it remains unchanged in the remaining
polystyrene-anchored coordination compounds. The ν(C––S)(thiophene ring) stretch25
of II
occurring at 648 cm-1
shifts to lower energy by 35 and 43 cm-1
in V and VI respectively. On
the other hand, it remains unchanged in the remaining polystyrene-anchored coordination
compounds. The νas(COO) and νs(COO) stretches of free acetate ions occur at 1560 and
1416 cm-1
respectively26
. The νas(COO) and the νs(COO) stretches occur at 1585, 1350; and
1595, 1370 cm-1
in V and VI respectively. The magnitude of energy separation (ν = 225
and 235 cm-1
) between νas(COO) and νs(COO) is > 144 cm-1
and it indicates the
monodentate nature of acetato groups26
, since in the event of bidentate coordination, the
energy separation between νas(COO) and νs(COO) is < 144 cm-1
. DMF shows a band at 1680
cm-1
due to the ν(C==O) stretch27
. This band shifts to lower energy by 40 and 35 cm-1
in III
and IV indicating the involvement of O atom towards coordination27
. The absence of a band
between 835-955 cm–1
, characteristic of ν(Zr==O) stretch28
in VI suggests its structures as
[PSCH2–LH2Zr(OH)2(OAc)2] and not as [PSCH2–LH2ZrO(H2O)(OAc)2]. The appearance of
a band at 1128 cm-1
due to the δ(Zr––OH) bending mode also supports the suggested
structure of the compound26
. VII exhibits the νs(O==Mo==O) and νas(O==Mo==O) stretches
at 924 and 938 cm-1
respectively and these bands occur in the usual range (892-964 cm-1
;
842-928 cm-1
) reported for the majority of MoO2(VI) compounds26
. The presence of
νs(O==Mo==O) and νas(O==Mo==O) bands indicates a cis-MoO2 structure as the
compounds with trans-MoO2 structure exhibit only the νas(O==Mo==O) since the
νs(O==Mo==O) is IR inactive29
.
Magnetic measurements
The room temperature magnetic moments of the polystyrene-anchored coordination
compounds of II are presented in Table 2. The magnetic moment of V is 1.88 B.M. This
Syntheses, Magnetic and Spectral Studies on the Coordination Compounds 2537
value lies within the range (1.70–2.20 B.M.) reported for the magnetically dilute Cu(II)
compounds30
. The magnetic moment of IV is 4.89 B.M and this value lies within the range
reported for the high-spin octahedral Co(II) compounds
31. III, VI and VII are diamagnetic.
Table 2. IR, reflectance spectral data (cm-1
) and ma g ne t i c mo me nt s o f polystyrene-
anchored coordination compounds.
Compound
ν(C–O)
Φ
ν(C–N)
(thiazoli-
dinone)
ν(C–O)
(enolic)
ν(C–S)
(thio-
phene)
ν(C=O)
(DMF)
max
Mag.
moment
(B. M.)
II 1532 1580 - 648 - - Diamagnetic
III 1540 1538 1260 648 1640 - Diamagnetic
IV 1541 1545 1245 648 1645
8910,
13100,
20100
4.89
V 1542 1540 - 613 - 17220 1.88
VI 1532 1580 - 605 - - Diamagnetic
VII 1540 1580 - 648 - - Diamagnetic
Reflectance spectral studies
The electronic spectra of the compounds could not be recorded in the nujol mull as the
polystyrene-anchored compounds do not form a good mull. Therefore, their reflectance
spectra were recorded (Table 2). The compounds being insoluble in common solvents, their
solution electronic spectra also could not be recorded. IV exhibits three bands at 8910,
13100 and 20100 cm-1
due to the 4T1g(F) →
4T2g(ν1),
4T1g(F) →
4A2g(ν2) and
4T1g(F) →
4T1g(ν3)
transitions, respectively suggesting an octahedral structure
32. The ν3/ν1 value is 2.26
which lies in the usual range (2.00-2.80) reported for the majority of octahedral Co(II)
coordination compounds32
. The parameters are: 10Dq = 10080 cm
-1, B' = 824 cm
-1, β = B'/B
= 0.85, β0 = 15% and CFSE = −96.4 kJ mol
-1. The reduction of Racah parameter from the
free ion value of 971 cm-1
to 824 cm-1
and the β0
value (15%) indicate the covalent nature of
the compound and the strong field nature of the ligand respectively. V exhibits a band at
17220 cm-1
which is assigned to 2B1g →
2A1g,
2B2g and
2Eg transitions for square-planar
arrangement of ligand around Cu(II) ions
33. The absence of a band in the range: 8000-10000
cm-1
precludes the presence of a tetrahedral structure34
.
ESR studies
The ESR spectrum of V exhibits g|| = 2.26 and g = 2.09 indicating the presence of a
tetragonal type symmetry about the Cu(II) ion
35. The spectral parameters
35 are: A|| = 1.963 ×
10-2
cm-1
, A = 4.67 × 10-3
cm-1
, G = 2.93, gav = 2.15, 2
Cu = 0.88, (')2 = 0.18, = 0.54 and
Pd = 1.92 × 10-2
cm-1
. The trend that g|| > g and A|| > A is indicative of the presence of an
unpaired electron in 22 yxd
orbital
36. The g|| value (2.26) indicates that metal-ligand bond in
the compound is covalent. The G value (2.93) indicates the strong field nature of the
DINESH KUMAR 2538
polystyrene-anchored ligand37
. The values of 2
Cu (0.88) and (')2
(0.18) indicate the
covalent nature of the compound. The positive value of (0.54) suggests that A|| should be
greater than A35
and this trend in A|| and A values was also observed by us. The lower value
(1.92 10-2
cm-1
) of Pd in comparison to that of the free ion value (3.5 10-2
cm-1
)
indicates the presence of covalent character between the metal-ligand bonding. The
spectrum does not show any band ~1500 G due to the ∆Ms = 2 transition and this precludes
the presence of M––M interaction.
Conclusion
The elemental analyses, IR, reflectance, ESR spectral and magnetic susceptibility
measurements suggest a square-planar structure (V) for [PSCH2–LHCu(OAc)], a tetrahedral
structure (III) for [PSCH2–LZn(DMF)], the octahedral structures (IV and VII) for [PSCH2–
LCo(DMF)3] and [PSCH2–LHMoO2(acac)] respectively and a pentagonal-bipyramidal
structure (VI) for [PSCH2–LH2Zr(OH)2(OAc)2].
Acknowledgement One of the authors (Amit Kumar) is grateful to the Director of his Institute for financial
assistance and encouragement for this work.
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