SYNTHESES , SPECTROSCOPIC AND MAGNETIC PROPERTIES OF POLYSTYRENE-ANCHORED COORDINATION COMPOUNDS OF THIAZOLIDINONE

ABSTRACT. The reaction between polystyrene 3-formylsalicylate and furoic acid hydrazide in DMF in the presence of ethyl acetate results in the formation of polystyrene N-(2-carbamoylfuranyl)-3'-carboxy-2'hydroxybenzylideneimine (I). A benzene suspension of I reacts with mercaptoacetic acid and forms the polystyrene N-(2-carbamoylfuranyl)-C-(3'-carboxy-2'-hydroxyphenyl)thiazolidin-4-one, PSCH2–LH2 (II). A DMF suspension of II reacts with Mn(II), Ni(II), Cd(II), Fe(III) and UO2(VI) ions and forms the polystyrene-anchored coordination compounds of the types, [PSCH2–LMn(DMF)3], [PSCH2–LNi(DMF)3], [PSCH2–LCd(DMF)], [PSCH2–LH2FeCl3] and [PSCH2–LHUO2(NO3)(DMF)]. The polystyrene-anchored coordination compounds have been characterized on the basis of elemental analyses, spectral (IR, reflectance) studies and magnetic susceptibility measurements. II acts as a neutral tridentate ONO donor ligand in [PSCH2–LH2FeCl3], a monobasic tridentate ONO donor ligand in [PSCH2–LHUO2(NO3)(DMF)], a dibasic tridentate ONO donor ligand in [PSCH2–LMn(DMF)3], [PSCH2–LNi(DMF)3] and [PSCH2–LCd(DMF)]. A tetrahedral structure for Cd(II) and an octahedral structure for Mn(II), Ni(II), Fe(III) and a square-antiprism geometry for UO2(VI) complex are suggested.


INTRODUCTION
There has been considerable interest in the synthesis and use of functionalized polymers having chelating abilities in recent years due to their practical convenience, operational flexibility and formation of coordination with high metal to polymer bond energies [1].Chloromethylated styrene-divinylbenzene copolymer, in particular, is one of the most widely employed macromolecular supports for the synthesis of functionalized polymers.Heterogenization or immobilization of active metal complexes on polymeric supports has evolved as a promising strategy for combining the advantages of homogeneous and heterogeneous catalysts due to their easy isolation from the products by filtration and the possibility of recycling them or continuous operation in a reactor [2].A structural study of polymer-anchored compounds seems useful in view of their numerous applications in analytical chemistry [3], metal ion removal [4], immobilization of enzymes [5], antimicrobial activities [6], as catalysts [7][8], as solid supports [9], as substrate carriers [10] and a s ion-exchanger [11], etc.
Thiazolidin-4-ones belong to an important group of heterocyclic compounds with carbonyl group at fourth position.They show broad spectrum of biological activities due to their ready accessibility and diverse chemical reactivity [12,13].They are involved in variety of applications such as antimicrobial, antibacterial, anticonvulsant, antifungal, anti-HIV, antiproliferative, anti-inflammatory, cystic fibrosis and antithyroid [14], etc.Many drugs possess modified pharmacological properties in the form of the metal complexes [15].
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 3formylsalicylate and furoic acid hydrazide) towards Mn(II), Ni(II), Cd(II), Fe(III) and UO 2 (VI) ions.
A perusal of the literature indicates that several polymer-anchored ligands containing oxygen atom(s) like crown ethers [16], Imidazole [17], iminodiacetic acid [18] and iminodipropionic acid, amino acid [19] have been reported.However, there is less number of papers available on the coordination compounds of thiazolidin-4-one moiety [20].
In this paper, we describe the syntheses and characterization of polystyrene-anchored thiazolidin-4-one, PSCH 2 -LH 2 (II) and its coordination compounds with Mn(II), Ni(II), Cd(II), Fe(III) and UO 2 (VI) ions.The structures of I and II is represented in Figure 1. were used as received for the syntheses.Polystyrene 3-formylsalicylate was synthesized by following the reported procedure [21].

Analyses and physical measurements
A known weight (~1.0 g) of the polystyrene-anchored coordination compound of Mn(II), Ni(II) and Cd(II) ions was warmed slowly with 6 M CH 3 COOH.The organic skeleton left was filtered off and then washed repeatedly with hot 2 M CH 3 COOH and distilled water.The leached Mn(II), Ni(II) and Cd(II) ions were estimated by complexometric titration method against standardized EDTA solution using eriochrome black-T, murexide and xylenol orange as indicators respectively.The Fe(III) compound was leached with 6N HCl.The organic skeleton left was filtered off, washed thoroughly with 2 M HCl followed by hot distilled water.The leached Fe(III) ions were reduced to Fe(II) with aqueous SnCl 2 and then were estimated against standard K 2 Cr 2 O 7 solution using N-phenylanthranilic acid as an indicator.The estimation of U was carried out gravimetrically as U 3 O 8 after decomposing the compound with a few drops of conc.HNO 3 and then igniting the residue.The coordinated DMF molecules were determined by heating the corresponding polystyrene-anchored coordination compound in an air oven at a definite temperature for 3 h.DMF was completely lost between 160-225 o C respectively on heating the compounds of Mn(II), Ni(II), Cd(II) and UO 2 (VI) ions.The IR spectra of II and its coordination compounds were recorded using KBr pellets (4000-400 cm -1 ) on a Nicolet Fourier transform infrared spectrophotometer calibrated with polystyrene.The diamagnetic corrections were computed by following a procedure specially designed for the polystyrene-anchored coordination compounds [21].The reflectance spectra were recorded on a Beckmann DU spectrophotometer attached with a reflectance arrangement.The magnetic susceptibility measurements were carried out at room temperature, using Hg[Co(NCS) 4 ] as the standard [22].The diamagnetic corrections were computed using Pascal's constants.The magnetic susceptibilities were corrected for temperature independent paramagnetism term (TIP) [22] using value of 200 × 10 -6 cgs units for Ni(II), zero for Mn(II) and Fe(III) ions.

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 Scheme 3. Preparation of polystyrene-anchored coordination compounds.

Infrared spectral studies
The infrared spectra of PSCH 2 -LH 2 (II) and its coordination compounds 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 1575 cm -1 due to the ν(C--N)(thiazolidinone ring) stretch [23] indicating the formation of corresponding thiazolidinone.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) stretch [24].II occurs in the keto-form [25] as evident by the presence of a strong band due to the ν(C=O)(amide) stretch at 1650 cm -1 .This band remains almost at the same energy in Fe(III) and UO 2 (VI) compounds indicating the noninvolvement of the keto O atom towards coordination.The Cd(II), Mn(II) and Ni(II) compounds do not display the ν(C=O)(amide) stretch but show a new band between 1235-1260 cm -1 suggesting the conversion of -C(O)NH-moiety (keto-form) into -C(OH)=N-moiety (enolform) followed by the deprotonation of enolic OH group and subsequently involvement of enolic O atom towards coordination.The ν(C--O)ф stretch [25] of II occurs at 1535 cm -1 .This band remains unchanged in the Fe(III) and UO 2 (VI) compounds 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) stretch [26] of II occurs at 1690 cm -1 .This band shows a negative shift by 30-50 cm -1 in the Fe(III) and UO 2 (VI) compounds 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)] stretch [23] of II shifts from 1575 cm -1 to lower energy by 28-34 cm -1 in the Mn(II), Ni(II) and Cd(II) compounds lending support for the involvement of ring N atom towards coordination.However, this band remains almost at the same energy in the remaining compounds.The [ν(C--S) (thiazolidinone ring)] stretch [24] of II occurred at 830 cm -1 .This band remains unchanged in the compounds indicating the non-involvement of S atom towards the coordination.The ν(C--O--C)(furan ring) stretch [27] of II occurring at 1085 cm -1 shifts to lower energy by 60 and 70 cm -1 in Fe(III) and UO 2 (VI) compounds respectively.On the other hand, it remains unchanged in the remaining compounds.DMF shows a band at 1675 cm -1 due to the ν(C=O) stretch [28].This band shifts to lower energy by 20-38 cm -1 in Cd(II), Mn(II), Ni(II) and UO 2 (VI) compounds indicating the involvement of O atom towards coordination [28].The absence of a band between 820-860 cm -1 in the Fe(III) compound, precludes the presence of a (Fe-O-Fe) bridged structure [28].[PSCH 2 -LHUO 2 (NO 3 )(DMF)] exhibits the ν as (O=U=O) stretch at 908 cm -1 and this band occurs in the usual range (870-950 cm -1 ) observed for the majority of trans-UO 2 compounds [29].The force constant (f U--O ) and the U--O bond length are 6.85 mdyn/Å and 1.74 Å.These values are in the expected ranges (6.58-7.03mdyn/Å and 1.60-1.92Å) reported for the majority of UO 2 (VI) compounds [29].

Magnetic measurements
The room temperature magnetic moments of the polystyrene-anchored coordination compounds of II are presented in Table 2. [PSCH 2 -LMn(DMF) 3 ] exhibits magnetic moment 5.88 B.M. and it falls in the normal range reported for the majority of high-spin octahedral Mn(II) compounds [32].[PSCH 2 -LNi(DMF) 3 ] exhibits magnetic moment 3.15 B.M. which falls in the normal range reported for the octahedral Ni(II) compounds.This value is also indicative of magnetically dilute nature of the compound [32].[ PSCH 2 -LH 2 FeCl 3 ] exhibits magnetic moment 5.90 B.M. which falls in the normal range reported for the majority of magnetically dilute Fe(III) compounds [32].The Cd(II) and UO 2 (VI) compounds are diamagnetic as expected for the d 10 or f 0 systems.