Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

Article abstract of DOI:10.1016/j.saa.2009.12.019

In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also ev

Full text of DOI:10.1016/j.saa.2009.12.019

Spectrochimica Acta Part A 75 (2010) 983–991
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and electrochemical studies of charge-transfer complexes of
thiazolidine-2,4-dione with ␴ and ␲ acceptors
Prashant Singha,c, Pradeep Kumarb, Anju Katyalc, Rashmi Kalrad, Sujata K. Dasse,
Satya Prakashf, Ramesh Chandrab,c,∗
a A.R.S.D. Collage, University of Delhi, Delhi-110007, India
b Department of Chemistry, University of Delhi, Delhi-110007, India
c Dr. B.R. Ambedkar Center for Biomedical Research, University of Delhi, Delhi-110007, India
d A.N.D. Collage, University of Delhi, Delhi-110007, India
e V.P.C. Institute, University of Delhi, Delhi-110007, India
f
Department of Biomedical Engineering, McGill University, Montreal, H3A 2B4, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 April 2009
Received in revised form 1 December 2009
Accepted 3 December 2009
In the present work, we report the synthesis and characterization of novel charge-transfer complexes
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 electrochemical
properties and we conclude that these complexes are frequency dependent. Charge-transfer complex
between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma
acceptors are more conducting than with pi acceptors.
Keywords:
Thiazolidine-2,4-dione
Sigma/pi acceptors
© 2009 Elsevier B.V. All rights reserved.
Thermal and electrochemical properties
1. Introduction
principle, these polarized molecules will lead to a greater stabiliza-
tion of the excited state, and hence to a low energy shift. Such a
Thiazolidine-2,4-diones (TZDs) reduce insulin resistance and
ideally suited for treatment of the cardiovascular metabolic syn-
drome. In clinical use so far, rosiglitazone and pioglitazone appear
to be devoid of idiosyncratic, fulminate hepatotoxicity. TZDs act as
PPAR agonist. The primary event in the action of many drugs is often
a reversible association between a drug molecule and a receptor to
form a transient/stable complex. In such reactions, some drugs can
behave as electron donors, forming charge-transfer complexes by
electron transfer from an occupied orbital to an empty orbital of an
acceptor molecule.
Charge-transfer complexes are consisted of donor (D) and
acceptor (A). It is generally accepted that, for an ideal charge-
transfer (CT) complex DA, in excited state resembles D+A−. This
effect is expected in terms of Mulliken’s theory for bonding in such
complexes, which require that there be a slight mixture of the
charge-transfer state so that D and A acquire slight positive and
negative charges, respectively [1–4]. The polar solvent molecules
will tend to become oriented in such a way so as to stabilize these
partial charges, and, despite the restriction of the Frank-Condon
shift, however, should be small compared with the ground state,
as for the case of alkyl pyridinium iodides [5]. Since, they have a
very large interaction with solvent in the ground state. The physics
of charge-transfer were studied mostly in isolated systems of two
interacting molecules. If an electron is transferred from a donor
molecule to an acceptor, the hole left behind on the donor will
exert a strong attraction towards transferred electron and which
will 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 no
electron spin signal but give a charge-transfer spectrum. The lack
of essential achievements in the field of organic conductors and
superconductors in last two decades from the point of view of their
critical temperature (Tc) has resulted in the search for new solu-
tions. One of the most effective ways of improving the conductors
is the search for new donors enabling the enhancement of inter-
molecular interactions in the donor–acceptor systems [6–9]. The
cation radical salts of unsymmetrical and flexible donors comply
with this requirement. The additional simultaneous interactions
due to the increased number of heteroatoms and non-coplanarity
of some rings or outer groups with respect to the central molecu-
lar framework should hinder the formation of a dense face-to-face
stacked quasi one-dimensional packing that enhancing dimension-
ality of the system [10].
∗
Corresponding author at: Department of Chemistry, University of Delhi, ACBR,
Delhi-110007, India. Tel.: +91 11 27666272.
E-mail address: rameshchandra57@yahooo.co.in (R. Chandra).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.12.019

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P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991
In this work, conductimetric and spectroscopic methods have
recorded on TOF-Mass spectrometer Model No. KC455 and Infra
red spectra were recorded on Spectrum Bx2 IR. Electrochemical
properties were determined from Electrochemical Analyzer CH 201
instrument. Thermogravimetric analyses were done using a Perkin-
Elmer model Pyris 6 computerized thermal analysis system. The
rate 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 used
as a calibration standard for TG–DTA.
been employed to examine the interaction of thiazolidine-2,4-
dione as a possible electron donor with several small molecules of
biological importance including iodine. Iodine is well known for its
electron-accepting properties, which may be deduced from molec-
ular orbital considerations. It has been used in the past as a model
acceptor to investigate the electron-donating properties of organic
molecules. In human biology, iodine is required for the biosyn-
thesis of the thyroid hormones triiodothyronine and thyroxine,
which reguate metabolic rate. Similarly 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ) and 2,3,5,6-tetra-1,4-benzoquinone are
strong electron acceptor and applied in the determination of several
electron donor drugs containing amino group/active methylene
group in organic solution. A long term goal of this work is to
construct a simple model system for elucidation of the biologi-
cal reactions of thiazolidine-2,4-dione. We envisage to synthesize
charge-transfer complexes of thiazolidine-2,4-dione with sigma as
well as pi acceptors.
2.2. Charge-transfer complex formed between
thiazolidine-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 chloroform
and stirred at 30 ◦C for 30 min. Appearance of solid product was
observed when the reaction mixture was kept undisturbed for 12 h
Product was washed with small quantity of chloroform, filtered and
dried. The solid product was recrystallized with acetonitrile and
dried 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 in
the environment of N2 gas (compound 1) [11].
2. Experimental
2.1. Reagents and analysis
All reactions were carried out at ambient temperature in
oven-dried glassware. All the chemicals were purchased from
Sigma–Aldrich and Merck and used without any type of purifica-
tion. All reactions were monitored by thin layer chromatography
on gel F254 plates. All NMR spectra in d6-DMOS were recorded
on a Bruker Toxispin 300 MHz spectrometer. Mass spectra were
2.3. Synthesis of charge-transfer complexes of
thiazolidine-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-
Table 1
Synthesis of charge-transfer complexes of thiazolidine-2,4-dione with sigma (iodine) as well as pi (chloranil, DDQ, duraquinone and picric acid) acceptors.a.
S. No.
Donor
Acceptor
Structure of the charge-transfer complex
Compound no.
Time (h)
Yield (%)
1
I2
1
2a
2b
12.5
75
2
3
5
3
70
60
4
3a
3b
24
24
65
70
5
a
Characterized by FT-IR, NMR and mass spectra.

P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991
985
dicyanoquinone were taken in 30 ml of acetonitrile and the reaction
mixture was refluxed for 3/5 h, respectively. Then the reaction mix-
ture was cooled to room temperature. The solvent was evaporated
under reduced pressure and the compounds were recrystallized
with acetonitrile and dried in P2O5. Solid product was analyzed
by FT-IR, 1H NMR, 13C NMR and TG–DTA techniques. Then elec-
trochemical studies (cyclic voltametry, impedance spectroscopy)
were done of the synthesized charge-transfer complexes. Thermal
analyses were done in the environment of N2 gas (compound 2a/2b)
[12,13].
2.4. Synthesis of charge-transfer complexes formed between
thiazolidine-2,4-dione and picric acid/duraquinone
In a round bottom flask, 10 mmol of thiazolidine-2,4-dione and
10 mmol of picric acid/duraquinone were taken in 20 ml of hex-
Scheme 1. Synthesis of charge-transfer complexes of thiazolidine-2,4-dione with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.

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P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991
Scheme 2. Mechanism for the synthesis of charge-transfer complexes of thiazolidine-2,4-dione with (a) chloranil and (b) DDQ.
ane and the reaction mixture was stirred for 10 min and kept for
24 h. Appearance of solid product was observed, filtered and dried
in P2O5. Solid product was analyzed by FT-IR, 1H NMR, 13C NMR,
CHN and TG–DTA techniques. Then electrochemical studies (cyclic
voltametry, impedance spectroscopy) were done of the synthe-
sized charge-transfer complexes. Thermal analyses were done in
the environment of N2 gas (compound 3a/3b) [14].
studies and thermal studies of the synthesized compounds were
done.
3. Result and discussion
As per the structure of thiazolidine-2,4-dione, the molecule
can act as a potential donor and is used for the synthesis of
charge-transfer complexes of thiazolidine-2,4-dione (Table 1) with
sigma and pi acceptors as in Scheme 1 and the mechanisms are
All solid products synthesized above were characterized by
FT-IR, 1H NMR, CHNS and 13C NMR techniques. Electrochemical
Table 2
Thermogravimetric-differential thermal analysis of charge-transfer complexes of TZD with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.
S. No.
1
C.T. complex
DTA analysis
Decomposition pattern
Compound no.
TZD-iodine (Fig. 1(a))
156 and 212 ◦C (endothermic)
(i) 120–232 ◦C for removal thizol ring. (ii)
Beyond 232 ◦C, removal of CH2O, CH3S and I2.
(i) 100–210 ◦C for removal thizol ring. (ii)
Beyond 210 ◦C, removal of HCl, HNO, CH2O and
CH3.
1
2
3
4
5
TZD-chloranil (Fig. 1(b))
TZD-DDQ (Fig. 1(c))
142 and 210 ◦C (endothermic)
140, 180 and 210 ◦C (endothermic)
158 and 242 ◦C (endothermic)
135 and 320 ◦C (endothermic)
2a
2b
3a
3b
(i) At 90 ◦C for removal thizol ring starts and
ends at 175 ◦C. (ii) Beyond 175 ◦C, removal of
HCN, HNO, CH2O and CH3S.
TZD-picric acid (Fig. 1(d))
TZD-duraquinone (Fig. 1(e))
(i) At 130 ◦C for removal thizol ring starts and
ends at 190 ◦C. (ii) Beyond 190 ◦C removal of
HNO2, HNO, CH2O and CH3S.
(i) At 135 ◦C for removal thizol ring starts and
ends at 200 ◦C. (ii) Beyond 200 ◦C, removal of
HCN, HNO, CH2O and CH3S.

P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991
987
Fig. 1. TG–DTA plots of the charge-transfer complexes of thiazolidine-2,4-dione with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.
explained of charge-transfer complexes (Table 1, entries 2 and3) as
in Scheme 2.
temperature on x-axis and weight % as well voltage on y-axis as in
Fig. 1.
3.1. Thermal analysis (TG–DTA)
3.2. Electrochemical analysis
Charge-transfer complexes (Table 1) were further character-
ized by thermal analysis as in Table 2. Thermo gravimetric analysis
determines the decomposition of the complexes on increasing tem-
perature. It was done in nitrogen gas so that no the complex will not
get oxidized in the presence of oxygen. Plots were made by plotting
3.2.1. Cyclic voltametry
From the cyclic voltametry analysis, we determine the maxi-
mum current and potential in which charge-transfer complex was
stable 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
Fig. 2. Cyclic voltametry plots of the charge-transfer complexes of thiazolidine-2,4-dione with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.
Fig. 2, we found that the complexes of thiazolidine-2,4-dione with
I2 and picric acid were stable most.
level potentials of the common reference electrodes can be esti-
mated, the band edge positions of electroactive materials can be
approximated. Ideally, one peak couple of oxidation and reduc-
tion potential should appear in the cyclic voltagram measurement
for the valence band (VB) and the conduction band (CB), respec-
tively. Complexes are first oxidized at the surface of the layer
and then the oxidized valence bands are filled up by electrons
in the inner non-oxidized region of the layer and reduction takes
place.
We could successfully form a complex with thiazolidine-
2,4-dione and iodine, a well-known electron acceptor which
establishes that thiazolidine-2,4-dione can act as electron
donor. The structure of thiazolidine-2,4-dione also hints that.
Still we cannot rule out the possibility that thiazolidine-2,4-
dione may also act as electron acceptor under some circum-
stances.
Cyclic voltametry is a dynamic electrochemical method, where
variation in current is recorded at well-defined applied poten-
tial depending on the scan rate, the current–potential curves are
drawn. The measured oxidation potential of an electroactive sub-
stance correlates directly with the ionization potential Ip and the
reduction potential with the electron affinity Ea. Since the vacuum
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 high
current. From the cyclic voltametry plot of all the complexes, we
found the complexes of thiazolidine-2,4-dione with I2 gives the
best result.

P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991
989
Fig. 3. Impedance spectra of the charge-transfer complexes of thiazolidine-2,4-dione with (a) iodine, (b) chloranil, (c) DDQ, (d) picric acid and (e) duraquinone.
3.2.2. AC and DC conductivity measurement
and
impedance spectroscopy technique was used to evaluate the AC
conductivity of the charge-transfer complexes by col and col plot.
We found that the complexes of thiazolidine-2,4-dione with iodine
give the best conductivity as in Fig. 3. impedance (Z) and angle were
used to determine Z cos ꢀ and Z sin ꢀ and by drawing a plot between
Z cos ꢀ and Z sin ꢀ, we get the intercept on x-axis, which is known
as impedance that is resistance. From resistance we can calculate
conductivity of the compound from
1
Conductivity =
(ii)
Resistivity
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-transfer
complexes synthesized in the study were compared (Table 3). It
was found that all charge-transfer complexes synthesized had sig-
nificant AC conductivity than DC conductivity.
Resistivity × Length
Resistance =
(i)
Area

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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.
Table 3
Comparison AC and DC conductivity of the charge-transfer complexes of TZD.
S. No.
Charge-transfer complex
AC conductivity (×10−3 mho)
DC conductivity (×10−10 mho)
Compound no.
1
2
3
4
5
TZD-iodine
TZD-chloranil
TZD-DDQ
TZD-picric acid
TZD-duraquinone
6.1011
0.9740
2.5121
2.7575
1.1148
1.692
1
2a
2b
2a
2b
0.0505
0.08457
0.7220
0.0544

P. Singh et al. / Spectrochimica Acta Part A 75 (2010) 983–991
991
Entry 4.
Thiazolidine-2,4-dione–picric acid complex
So we conclude that these compounds are frequency dependent
not current dependent. We found that conductivity for the complex
between thiazolidine-2,4-dione and iodine is maximum.
C9H6O9SN4; 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), active
)
methylene 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).
4. Conclusion
This study reports the synthesis, thermal and electrochemical
properties of novel charge-transfer complexes of thiazolidine-
2,4-dione with sigma and pi acceptors. All the charge-transfer
complexes have been well characterized by FT-IR, CHNS, 1H NMR
and 13C NMR spectra. Thermal as well as electrochemical studies
of the charge-transfer complexes were done and it was found that
the CT complex between thiazolidine-2,4-dione and iodine is most
stable and gives highest conductivity.
Entry 5.
Thiazolidine-2,4-dione–duraquinone complex
C13H15O4SN; pale yellow colour; IR (ꢁ = cm−1) 3445 (N–H),
2936 (C CH), 1735 (C O), 1640 (C O); 1H NMR (ı) amidic
N–H (11.99, 1H, singlet), active methylene 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).
References
Acknowledgements
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(2009).
This work is dedicated to Late Dr. N.N. Ghosh, my mentor and
my guide (Prashant Singh).
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Jingli, Polyhedron 27 (2008) 2833–2844.
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362 (2009) 1701–1708.
Appendix A. Analytical data of the synthesized complexes
as in Table 1
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able online (2009).
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Entry 1.
Entry 2.
Thiazolidine-2,4-dione–iodine complex
C3H3O2NSI2; 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); 13
NMR (ı) carbonyl carbons (174, 173), aliphatic carbon (36)
C
Thiazolidine-2,4-dione–chloranil complex
C9HO4SNCl2; 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); mass
analysis (M+) ion peak = 290; melting point (◦C) 248–250.
Entry 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) amidic
N–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.