Syntheses and Characterization of the Coordination Compounds of N-( 2-hydroxymethylphenyl )-C-( 3 ′-carboxy-2 ′-hydroxyphenyl ) thiazolidin-4-one

A dry benzene solution of the Schiff baseN-(2-hydroxymethylphenyl)-3-carboxy-2-hydroxybenzylideneimine upon reactingwith mercaptoacetic acid undergoes cyclization and forms N-(2-hydroxymethylphenyl)-C-(3-carboxy-2-hydroxyphenyl)thiazolidin4-one, LH3 (I). AMeOH solution of I reacts with Co(II), Ni(II), Cd(II), Zr(OH)2(IV), and UO2(VI) ions and forms themonomeric coordination compounds, [M(LH)(MeOH)3] [where M = Co(II), Ni(II)], [M (LH)(MeOH)] [here M = Cd(II), UO2(VI)] and [Zr(OH)2(LH)(MeOH)]. e coordination compounds have been characterized on the bases of elemental analyses, molar conductance, molecular weight, spectral (IR, NMR, and re�ectance) studies, and magnetic susceptibility measurements. I behaves as a dibasic tridentate OOS donor ligand in these compounds. e compounds are nonelectrolytes (ΛM = 3.8–8.9mho cm 2 mol) in DMF. A tetrahedral structure for [Cd(LH)(MeOH)] and an octahedral structure for the remaining compounds are suggested.

Literature survey shows that much has been reported on the syntheses and characterization [11] of a variety of thiazolidin-4-ones, but very less is known about their coordination compounds [12][13][14].
Metal complexes play an important role in plant and animal life due to their physicochemical and biological properties.Metal ions are involved in speci�c interactions with antibiotics, proteins, nucleic acids, and other biomolecules [15].Most of the drugs have improved pharmacological properties in the form of their metal complexes.Transition metal ions play a very important role in the pharmacological action of metal-based drugs and these drugs are more effective against infectious microbes than the uncomplexed drugs [16].
ese facts motivate us to explore the coordination behavior of a newly synthesized thiazolidin-4-one with some transition metal ions.

Analyses and Physical
Measurements.e organic skeleton of the respective coordination compounds was decomposed by the slow heating of ∼0.1 g of the latter, with conc.HNO 3 .e residue was dissolved in a minimum amount of conc.HCl and the corresponding metal ions were estimated as follows: the Ni(II) contents of the respective coordination compound were estimated by complexometric titration method against standardized EDTA solution using murexide as an indicator.e Co(II) and Cd(II) contents in the respective coordination compounds were estimated by the complexometric titration method against standardized EDTA solution using xylenol orange as an indicator.e uranium content in [UO 2 (LH)(MeOH)] was estimated gravimetrically as U 3 O 8 aer decomposing the compound with a few drops of conc.HNO 3 and then igniting the residue.e zirconium contents were estimated gravimetrically as ZrO 2 aer decomposing the corresponding compound with a few drops of conc.HNO 3 and then igniting the residue.e C, H, and N contents of LH 3 and its coordination compounds were determined by CHN Eager analyzer model-300.e S and Cl contents were estimated gravimetrically as BaSO 4 and AgCl, respectively.e molecular weight measurements were carried out by the Rast method using diphenyl as the solvent [19].e molar conductances (Λ M ) of the coordination compounds were measured in DMF with the help of a Toshniwal conductivity bridge (CL01-02A) and a dip-type cell calibrated with KCl solutions.e IR spectra were recorded in KBr pellets (4000-400 cm −1 ) on a Beckman 20 spectrophotometer.e re�ectance spectra were recorded on a Beckmann DU spectrophotometer attached with a re�ectance arrangement.e magnetic susceptibility measurements were carried out at room temperature, using Hg[Co(NCS) 4 ] as the standard [20].e diamagnetic corrections were computed using Pascal's constants.e magnetic susceptibilities were corrected for temperature-independent paramagnetism term (TIP) [20] using a value of 200×10 −6 cgs units for Ni(II) and Co(II) ions.

Synthesis of N-(2-hydroxymethylphenyl)-C-(3 ′ -carboxy-2 ′ -hydroxyphenyl)thiazolidin-4-one (I).
A dry benzene solution of the Schiff base (2.71 g, 10 mmol) and mercaptoacetic acid (0.92 g, 10 mmol) were re�uxed for 12 h in a water bath.e mixture was cooled to room temperature and then was washed with 10% sodium bicarbonate solution.e benzene layer was separated using a separating funnel.e partial evaporation of the benzene layer gave a solid product, which was �ltered, washed with petroleum ether and recrystallized from petroleum ether.e compounds were dried as mentioned above.Yield = 14%.Anal:  and recrystallized from MeOH and were then dried as mentioned above.Yield = 50-75%.e coordination compounds are air-stable at room temperature.ey are insoluble in H 2 O, partially soluble in MeOH, EtOH, and completely soluble in DMSO and DMF.eir molar conductance measurements (Λ M = 3.8-8.9mho cm 2 mol −1 ) in DMF indicate their nonelectrolytic nature.e analytical data of I and its coordination compounds are presented in Table 1.

Infrared Spectral Studies
. e infrared spectra of I and its coordination compounds were recorded in KBr and the prominent peaks (in cm −1 ) are shown in Table 2. e Schiff base exhibits the (C=N)(azomethine) stretch at 1640 cm −1 .is band disappears in I and a new band appears at 1570 cm −1 due to the (C-N)(thiazolidinone ring) stretch [21] indicating the conversion of the Schiff base into I. e formation of I is further supported by the appearance of a new band at 830 cm −1 due to the (C-S)(thiazolidinone ring) stretch [22].A negative shi of 15-35 cm −1 of the (C-S)(thiazolidinone ring) stretch in the coordination compounds indicates the involvement of the S atom of the thiazolidinone moiety in coordination [14].I shows the (C=O)(thiazolidinone ring) stretch [23] at 1710 cm −1 .is band remains unchanged in the coordination compounds indicating the noninvolvement of O atom in the coordination.e (C-O)(alcoholic) stretch [24] of I occurs at 1225 cm −1 which remains unchanged in the complexes.I exhibits a strong band at 2860 cm −1 due to the intramolecular H-bonded OH group of phenolic and/or carboxylic acid moieties [25].is band disappears in the coordination compounds indicating the breakdown of Hbonding and subsequent deprotonation of the OH group followed by the involvement of phenolic and carboxylic acid O atoms in coordination.e presence of a broadband at involvement of the O atom of MeOH in coordination [26].e appearance of two new bands between 1560-1572 cm −1 ,  as (COO) and 1337-1358 cm −1 ,  s (COO) stretches indicates the presence of the coordinated carboxylate group in the coordination compounds.e energy difference (Δ = 213-225 cm −1 ) between these stretches is >210 cm −1 which indicates the monodentate nature of the carboxylate moiety [27].e (C-O) stretch of I occurs at 1520 cm −1 .is band shis to higher energy by 6-10 cm −1 in the coordination compounds indicating the involvement of phenolic O atom of 3-formylsalicylic acid moiety in coordination [26].e absence of a band between 835-955 cm −1 due to the (Zr=O) stretch [28] in the present Zr(OH) 2 (IV) compound suggests its formulation as [Zr(OH) 2 (LH)(MeOH)] and not as [ZrO(H 2 O)(LH)(MeOH)] [29].e presence of a broadband at 3440 cm −1 due to (OH) stretch and the appearance of a new medium intense band at 1135 cm −1 due to the (Zr-OH) bending mode [29] also support the proposed structure of the present Zr(OH) 2 (IV) compound.[UO 2 (LH)(MeOH)] exhibits the  as (O=U=O) stretch at 898 cm −1 and this band occurs in the usual range (870-950 cm −1 ) observed for the majority of trans-UO 2 (VI) compounds [30].e force constant ( U-O ) and U-O bond length in the present dioxouranium(VI) compound are 6.70 mdyn/Å and 1.74 Å, respectively.ese values are in the expected range (6.58-7.03mdyn/Å and 1.60-1.92Å) reported for the majority of UO 2 (VI) compounds [29].e new nonligand bands in the present coordination compounds in the low-frequency region are assigned to the (M-O) (550-570 cm −1 ) and the (M-S) (345-375 cm −1 ) and these bands [31] are in the expected order of increasing energy: (M-S) < (M-O).

NMR Spectral Studies
. e NMR spectra of I and its coordination compounds were recorded in DMSO- 6 .e chemical shis () are expressed in ppm down�eld from TMS. e prominent resonance signals of these compounds were compared with the reported peaks [32].I exhibits a singlet at  17.5 ppm due to the carboxylic proton, a sharp singlet at  13.60 ppm due to phenolic proton, a singlet at  2.35 ppm due to alcoholic proton, multiplets due to methylene protons at  4.70-4.79ppm, and multiplets between  7.34 and 7.50 ppm due to the aromatic protons.e occurrence of the resonance signal at the same frequency ( 2.35 ppm) due to alcoholic proton (CH 2 OH) indicates the noninvolvement of the alcoholic group in coordination.e absence of the signal at  17.5 ppm due to the COOH proton in the coordination compounds indicates the deprotonation of the COOH group, followed by the involvement of its O atom in coordination.e absence of the resonance signal at  13.60 ppm due to the phenolic proton in the coordination compounds indicates the deprotonation of the phenolic OH group followed by its involvement in coordination [26].e appearance of resonance signals at 2.81-2.85ppm due to alcoholic proton and at 3.0-3.1 ppm due to methyl protons in the coordination compounds supports the presence of MeOH in these compounds.
T 1: Analytical, molar conductance (Λ M ), and molecular weight data of I and its coordination compounds.