syntheses, magnetic and spectral studies on the...

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

[email protected]

[email protected]

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.

mailto:[email protected]

mailto:[email protected]

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.


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


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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