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Spectrochimica Acta Part A 75 (2010) 983–991

Contents lists available at ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

journa l homepage: www.e lsev ier .com/ locate /saa

ynthesis and electrochemical studies of charge-transfer complexes ofhiazolidine-2,4-dione with � and � acceptors

rashant Singha,c, Pradeep Kumarb, Anju Katyal c, Rashmi Kalrad, Sujata K. Dasse,atya Prakashf, Ramesh Chandrab,c,∗

A.R.S.D. Collage, University of Delhi, Delhi-110007, IndiaDepartment of Chemistry, University of Delhi, Delhi-110007, IndiaDr. B.R. Ambedkar Center for Biomedical Research, University of Delhi, Delhi-110007, IndiaA.N.D. Collage, University of Delhi, Delhi-110007, IndiaV.P.C. Institute, University of Delhi, Delhi-110007, IndiaDepartment of Biomedical Engineering, McGill University, Montreal, H3A 2B4, Canada

r t i c l e i n f o

rticle history:

a b s t r a c t

In the present work, we report the synthesis and characterization of novel charge-transfer complexes

eceived 16 April 2009eceived in revised form 1 December 2009ccepted 3 December 2009

eywords:hiazolidine-2,4-dione

of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorod-icyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemicalproperties and we conclude that these complexes are frequency dependent. Charge-transfer complexbetween thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigmaacceptors are more conducting than with pi acceptors.

© 2009 Elsevier B.V. All rights reserved.

igma/pi acceptorshermal and electrochemical properties

. Introduction

Thiazolidine-2,4-diones (TZDs) reduce insulin resistance anddeally suited for treatment of the cardiovascular metabolic syn-rome. In clinical use so far, rosiglitazone and pioglitazone appearo be devoid of idiosyncratic, fulminate hepatotoxicity. TZDs act asPAR agonist. The primary event in the action of many drugs is oftenreversible association between a drug molecule and a receptor to

orm a transient/stable complex. In such reactions, some drugs canehave as electron donors, forming charge-transfer complexes bylectron transfer from an occupied orbital to an empty orbital of ancceptor molecule.

Charge-transfer complexes are consisted of donor (D) andcceptor (A). It is generally accepted that, for an ideal charge-ransfer (CT) complex DA, in excited state resembles D+A−. Thisffect is expected in terms of Mulliken’s theory for bonding in suchomplexes, which require that there be a slight mixture of the

harge-transfer state so that D and A acquire slight positive andegative charges, respectively [1–4]. The polar solvent moleculesill tend to become oriented in such a way so as to stabilize theseartial charges, and, despite the restriction of the Frank-Condon

∗ Corresponding author at: Department of Chemistry, University of Delhi, ACBR,elhi-110007, India. Tel.: +91 11 27666272.

E-mail address: rameshchandra57@yahooo.co.in (R. Chandra).

386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2009.12.019

principle, these polarized molecules will lead to a greater stabiliza-tion of the excited state, and hence to a low energy shift. Such ashift, however, should be small compared with the ground state,as for the case of alkyl pyridinium iodides [5]. Since, they have avery large interaction with solvent in the ground state. The physicsof charge-transfer were studied mostly in isolated systems of twointeracting molecules. If an electron is transferred from a donormolecule to an acceptor, the hole left behind on the donor willexert a strong attraction towards transferred electron and whichwill dropped back and oscillate between the two orbitals, causing“weak charge-transfer”, in which only a small part of the elec-tron is transferred. Such weak charge-transfer complexes give noelectron spin signal but give a charge-transfer spectrum. The lackof essential achievements in the field of organic conductors andsuperconductors in last two decades from the point of view of theircritical temperature (Tc) has resulted in the search for new solu-tions. One of the most effective ways of improving the conductorsis the search for new donors enabling the enhancement of inter-molecular interactions in the donor–acceptor systems [6–9]. Thecation radical salts of unsymmetrical and flexible donors complywith this requirement. The additional simultaneous interactions

due to the increased number of heteroatoms and non-coplanarityof some rings or outer groups with respect to the central molecu-lar framework should hinder the formation of a dense face-to-facestacked quasi one-dimensional packing that enhancing dimension-ality of the system [10].

9 ca Act

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2

2

oStoo

TS

84 P. Singh et al. / Spectrochimi

In this work, conductimetric and spectroscopic methods haveeen employed to examine the interaction of thiazolidine-2,4-ione as a possible electron donor with several small molecules ofiological importance including iodine. Iodine is well known for itslectron-accepting properties, which may be deduced from molec-lar orbital considerations. It has been used in the past as a modelcceptor to investigate the electron-donating properties of organicolecules. In human biology, iodine is required for the biosyn-

hesis of the thyroid hormones triiodothyronine and thyroxine,hich reguate metabolic rate. Similarly 2,3-dichloro-5,6-dicyano-

,4-benzoquinone (DDQ) and 2,3,5,6-tetra-1,4-benzoquinone aretrong electron acceptor and applied in the determination of severallectron donor drugs containing amino group/active methyleneroup in organic solution. A long term goal of this work is toonstruct a simple model system for elucidation of the biologi-al reactions of thiazolidine-2,4-dione. We envisage to synthesizeharge-transfer complexes of thiazolidine-2,4-dione with sigma asell as pi acceptors.

. Experimental

.1. Reagents and analysis

All reactions were carried out at ambient temperature in

ven-dried glassware. All the chemicals were purchased fromigma–Aldrich and Merck and used without any type of purifica-ion. All reactions were monitored by thin layer chromatographyn gel F254 plates. All NMR spectra in d6-DMOS were recordedn a Bruker Toxispin 300 MHz spectrometer. Mass spectra were

able 1ynthesis of charge-transfer complexes of thiazolidine-2,4-dione with sigma (iodine) as w

S. No. Donor Acceptor Structure of the cha

1 I2

2

3

4

5

a Characterized by FT-IR, NMR and mass spectra.

a Part A 75 (2010) 983–991

recorded on TOF-Mass spectrometer Model No. KC455 and Infrared spectra were recorded on Spectrum Bx2 IR. Electrochemicalproperties were determined from Electrochemical Analyzer CH 201instrument. Thermogravimetric analyses were done using a Perkin-Elmer model Pyris 6 computerized thermal analysis system. Therate of heating of the sample was kept at 10 ◦C per min under nitro-gen flow at 20 ml per min. Copper sulfate pentahydrate was usedas a calibration standard for TG–DTA.

2.2. Charge-transfer complex formed betweenthiazolidine-2,4-dione and iodine

In a round bottom flask (50 ml), 10 mmol of thiazolidine-2,4-dione and 10 mmol of iodine were taken in 20 ml of chloroformand stirred at 30 ◦C for 30 min. Appearance of solid product wasobserved when the reaction mixture was kept undisturbed for 12 hProduct was washed with small quantity of chloroform, filtered anddried. The solid product was recrystallized with acetonitrile anddried in P2O5. Solid product was characterized by FT-IR, 1H NMR,13C NMR, CHNS analysis and TG–DTA techniques. Then electro-chemical studies of the synthesized compound (cyclic voltametry,AC and DC conductivity) were done. Thermal analysis was done inthe environment of N2 gas (compound 1) [11].

2.3. Synthesis of charge-transfer complexes ofthiazolidine-2,4-dione with chloranil/DDQ

In a round bottom flask (50 ml), 10 mmol of thiazolidine-2,4-dione (compound 3a) and 10 mmol of chloranil/2,3-dichloro-4,5-

ell as pi (chloranil, DDQ, duraquinone and picric acid) acceptors.a.

rge-transfer complex Compound no. Time (h) Yield (%)

1 12.5 75

2a 5 70

2b 3 60

3a 24 65

3b 24 70

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P. Singh et al. / Spectrochimi

icyanoquinone were taken in 30 ml of acetonitrile and the reactionixture was refluxed for 3/5 h, respectively. Then the reaction mix-

ure was cooled to room temperature. The solvent was evaporated

nder reduced pressure and the compounds were recrystallizedith acetonitrile and dried in P2O5. Solid product was analyzed

y FT-IR, 1H NMR, 13C NMR and TG–DTA techniques. Then elec-rochemical studies (cyclic voltametry, impedance spectroscopy)ere done of the synthesized charge-transfer complexes. Thermal

Scheme 1. Synthesis of charge-transfer complexes of thiazolidine-2,4-dione w

a Part A 75 (2010) 983–991 985

analyses were done in the environment of N2 gas (compound 2a/2b)[12,13].

2.4. Synthesis of charge-transfer complexes formed betweenthiazolidine-2,4-dione and picric acid/duraquinone

In a round bottom flask, 10 mmol of thiazolidine-2,4-dione and10 mmol of picric acid/duraquinone were taken in 20 ml of hex-

ith (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

986 P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991

omple

a2iCvst

F

TT

Scheme 2. Mechanism for the synthesis of charge-transfer c

ne and the reaction mixture was stirred for 10 min and kept for4 h. Appearance of solid product was observed, filtered and dried

n P2O5. Solid product was analyzed by FT-IR, 1H NMR, 13C NMR,HN and TG–DTA techniques. Then electrochemical studies (cyclic

oltametry, impedance spectroscopy) were done of the synthe-ized charge-transfer complexes. Thermal analyses were done inhe environment of N2 gas (compound 3a/3b) [14].

All solid products synthesized above were characterized byT-IR, 1H NMR, CHNS and 13C NMR techniques. Electrochemical

able 2hermogravimetric-differential thermal analysis of charge-transfer complexes of TZD wi

S. No. C.T. complex DTA analysis

1 TZD-iodine (Fig. 1(a)) 156 and 212 ◦C (endothermic)

2 TZD-chloranil (Fig. 1(b)) 142 and 210 ◦C (endothermic)

3 TZD-DDQ (Fig. 1(c)) 140, 180 and 210 ◦C (endothermic)

4 TZD-picric acid (Fig. 1(d)) 158 and 242 ◦C (endothermic)

5 TZD-duraquinone (Fig. 1(e)) 135 and 320 ◦C (endothermic)

xes of thiazolidine-2,4-dione with (a) chloranil and (b) DDQ.

studies and thermal studies of the synthesized compounds weredone.

3. Result and discussion

As per the structure of thiazolidine-2,4-dione, the moleculecan act as a potential donor and is used for the synthesis ofcharge-transfer complexes of thiazolidine-2,4-dione (Table 1) withsigma and pi acceptors as in Scheme 1 and the mechanisms are

th (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

Decomposition pattern Compound no.

(i) 120–232 ◦C for removal thizol ring. (ii)Beyond 232 ◦C, removal of CH2O, CH3S and I2.

1

(i) 100–210 ◦C for removal thizol ring. (ii)Beyond 210 ◦C, removal of HCl, HNO, CH2O andCH3.

2a

(i) At 90 ◦C for removal thizol ring starts andends at 175 ◦C. (ii) Beyond 175 ◦C, removal ofHCN, HNO, CH2O and CH3S.

2b

(i) At 130 ◦C for removal thizol ring starts andends at 190 ◦C. (ii) Beyond 190 ◦C removal ofHNO2, HNO, CH2O and CH3S.

3a

(i) At 135 ◦C for removal thizol ring starts andends at 200 ◦C. (ii) Beyond 200 ◦C, removal ofHCN, HNO, CH2O and CH3S.

3b

P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991 987

dione

ei

3

idpg

Fig. 1. TG–DTA plots of the charge-transfer complexes of thiazolidine-2,4-

xplained of charge-transfer complexes (Table 1, entries 2 and3) asn Scheme 2.

.1. Thermal analysis (TG–DTA)

Charge-transfer complexes (Table 1) were further character-zed by thermal analysis as in Table 2. Thermo gravimetric analysisetermines the decomposition of the complexes on increasing tem-erature. It was done in nitrogen gas so that no the complex will notet oxidized in the presence of oxygen. Plots were made by plotting

with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

temperature on x-axis and weight % as well voltage on y-axis as inFig. 1.

3.2. Electrochemical analysis

3.2.1. Cyclic voltametryFrom the cyclic voltametry analysis, we determine the maxi-

mum current and potential in which charge-transfer complex wasstable and beyond that the charge-transfer complex gets decom-posed. From the cyclic voltametry plot of all the complexes as in

988 P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991

-2,4-d

FI

2edSds

vtdsr

Fig. 2. Cyclic voltametry plots of the charge-transfer complexes of thiazolidine

ig. 2, we found that the complexes of thiazolidine-2,4-dione with2 and picric acid were stable most.

We could successfully form a complex with thiazolidine-,4-dione and iodine, a well-known electron acceptor whichstablishes that thiazolidine-2,4-dione can act as electrononor. The structure of thiazolidine-2,4-dione also hints that.till we cannot rule out the possibility that thiazolidine-2,4-ione may also act as electron acceptor under some circum-tances.

Cyclic voltametry is a dynamic electrochemical method, where

ariation in current is recorded at well-defined applied poten-ial depending on the scan rate, the current–potential curves arerawn. The measured oxidation potential of an electroactive sub-tance correlates directly with the ionization potential Ip and theeduction potential with the electron affinity Ea. Since the vacuum

ione with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

level potentials of the common reference electrodes can be esti-mated, the band edge positions of electroactive materials can beapproximated. Ideally, one peak couple of oxidation and reduc-tion potential should appear in the cyclic voltagram measurementfor the valence band (VB) and the conduction band (CB), respec-tively. Complexes are first oxidized at the surface of the layerand then the oxidized valence bands are filled up by electronsin the inner non-oxidized region of the layer and reduction takesplace.

From the cyclic voltametry, we determine the maximum range

of current by the variation in potential (voltage) in which the com-plex was stable and beyond the compound decomposed by highcurrent. From the cyclic voltametry plot of all the complexes, wefound the complexes of thiazolidine-2,4-dione with I2 gives thebest result.

P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991 989

,4-dio

3

cWguZac

R

Fig. 3. Impedance spectra of the charge-transfer complexes of thiazolidine-2

.2.2. AC and DC conductivity measurementimpedance spectroscopy technique was used to evaluate the AC

onductivity of the charge-transfer complexes by col and col plot.e found that the complexes of thiazolidine-2,4-dione with iodine

ive the best conductivity as in Fig. 3. impedance (Z) and angle weresed to determine Z cos � and Z sin � and by drawing a plot betweencos � and Z sin �, we get the intercept on x-axis, which is known

s impedance that is resistance. From resistance we can calculateonductivity of the compound from

esistance = Resistivity × LengthArea

(i)

ne with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

and

Conductivity = 1Resistivity

(ii)

We also determined DC conductivity by plotting current vs.voltage as in ohm’s law. The DC conductivity measurements were

done with Kiethley 236 Current Source-meter. The DC conductivity(Fig. 3) and AC conductivity (Fig. 4) of various TZD charge-transfercomplexes synthesized in the study were compared (Table 3). Itwas found that all charge-transfer complexes synthesized had sig-nificant AC conductivity than DC conductivity.

990 P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991

Fig. 4. AC and DC conductivity spectra of the charge-transfer complexes of thiazolidine-2,4-dione with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

TC

able 3omparison AC and DC conductivity of the charge-transfer complexes of TZD.

S. No. Charge-transfer complex AC conductivity (×10−3 m

1 TZD-iodine 6.10112 TZD-chloranil 0.97403 TZD-DDQ 2.51214 TZD-picric acid 2.75755 TZD-duraquinone 1.1148

ho) DC conductivity (×10−10 mho) Compound no.

1.692 10.0505 2a0.08457 2b0.7220 2a0.0544 2b

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Solar Cells 93 (2009), 552–563C.[12] Y. Siham, H.S. Al Qaradawi, A.M. Bazzi, N. El-Metwally, Spectrochim. Acta Part

A: Mol. Biomol. Spectrosc. 71 (2008) 1594–1598.[13] J.A. Tossell, Geochim. Cosmochim. Acta 73 (2009) 2023–2033.[14] R.S. Vagner, R.R. Hercílio, A.B. Juliano, E.T. Henrique, Spectrochim. Acta Part A:

Mol. Biomol. Spectrosc. 71 (2008) 1296–1301.

P. Singh et al. / Spectrochimi

So we conclude that these compounds are frequency dependentot current dependent. We found that conductivity for the complexetween thiazolidine-2,4-dione and iodine is maximum.

. Conclusion

This study reports the synthesis, thermal and electrochemicalroperties of novel charge-transfer complexes of thiazolidine-,4-dione with sigma and pi acceptors. All the charge-transferomplexes have been well characterized by FT-IR, CHNS, 1H NMRnd 13C NMR spectra. Thermal as well as electrochemical studiesf the charge-transfer complexes were done and it was found thathe CT complex between thiazolidine-2,4-dione and iodine is mosttable and gives highest conductivity.

cknowledgements

This work is dedicated to Late Dr. N.N. Ghosh, my mentor andy guide (Prashant Singh).

ppendix A. Analytical data of the synthesized complexess in Table 1

ntry 1. Thiazolidine-2,4-dione–iodine complexC3H3O2NSI2; brown colour and volatile in nature; IR (� = cm−1)3120 (N–H), 2817 (C–CH), 1735 (C O) and 1696 (C O); 1H NMR(ı) amidic N–H (11.99, 1H, singlet), aliphatic C–H (5.92, 2H); 13CNMR (ı) carbonyl carbons (174, 173), aliphatic carbon (36)

ntry 2. Thiazolidine-2,4-dione–chloranil complexC9HO4SNCl2; orange colour solid and crystalline; IR (� = cm−1)3350 (N–H), 2922 (C CH), 1689 (C O), 1679 (C O); 1H NMR (ı)amidic N–H (11.92, 1H, singlet); 13C NMR (ı) carbonyl carbons(199, 174, 173), alkenic carbons (153, 161, 140, 130, 124); massanalysis (M+) ion peak = 290; melting point (◦C) 248–250.

ntry 3. Thiazolidine-2,4-dione–DDQ complex

C11HO4SN3; pale yellow colour; IR (� = cm−1) 3248 (N–H), 2947(C–CH), 2318 (CN), 1734 (C O), 1627 (C O); 1H NMR (ı) amidicN–H (11.00, 1H, singlet); 13C NMR (ı) carbonyl carbons (162, 161),alkenic carbons (129, 128, 123, 122, 121, 130); mass analysis (M+)ion peak = 271; melting point (◦C) 210–212.

a Part A 75 (2010) 983–991 991

Entry 4. Thiazolidine-2,4-dione–picric acid complexC9H6O9SN4; pale yellow colour and crystalline; IR (� = cm−1)3139 (O–H), 3043 (N–H), 2947 (C–CH), 1736 (C O), 1675(C O); 1H NMR (ı) amidic N-H (11.99, 1H, singlet), activemethylene carbon (5.99, 2H), aliphatic methyl protons (4.14,12H); 13C NMR (ı) carbonyl carbons (180, 174, 173, 172),aromatic carbons (172, 150, 136, 133, 129), aliphatic carbons(55, 35).

Entry 5. Thiazolidine-2,4-dione–duraquinone complexC13H15O4SN; pale yellow colour; IR (� = cm−1) 3445 (N–H),2936 (C CH), 1735 (C O), 1640 (C O); 1H NMR (ı) amidicN–H (11.99, 1H, singlet), active methylene carbon (5.99, 2H),aliphatic methyl protons (4.14, 12H); 13C NMR (ı) carbonylcarbons (180, 174, 173, 172), aromatic carbons (172, 150, 136,133, 129), aliphatic carbons (55, 35).

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