Studies on novel Cu(II) complexes of 5-(4-hydroxy-phenyl)-1,3,4- thiadiazole-2-thiol and 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione: Synthesis, spectral and structural characterization

Article abstract of DOI:10.1016/j.poly.2012.04.025

Two new mixed ligand complexes, [Cu(en)₂](4-hpythol) ₂·2H₂O (4-hpythol = 5-(4-hydroxy-phenyl)-1,3,4- thiadiazole-2-thiol) (2) and [Cu(en)₂(5-thot)₂] (5-thot = 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thi

Full text of DOI:10.1016/j.poly.2012.04.025

Polyhedron 41 (2012) 52–60
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Studies on novel Cu(II) complexes of 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol
and 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione: Synthesis, spectral and
structural characterization
a
a
a
b
a,
M.K. Bharty a, , A. Bharti , R.K. Dani , S.K. Kushawaha , R. Dulare , N.K. Singh
⇑
⇑
a Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
b Department of Chemistry, P.G. College, Ghazipur, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new mixed ligand complexes, [Cu(en)2](4-hpythol)2ꢀ2H2O (4-hpythol = 5-(4-hydroxy-phenyl)-1,3,4-
thiadiazole-2-thiol) (2) and [Cu(en)2(5-thot)2] (5-thot = 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione
(3), have been prepared, containing en as the co-ligand. The starting ligands, potassium salts of thiohy-
drazide carbodithioate (RCSNHNHCSSK)/hydrazine carbodithioate (RCONHNHCSSK), underwent cycliza-
tion during the crystallization or complexation in the presence of ethylenediamine (en) and converted to
Received 15 March 2012
Accepted 17 April 2012
Available online 3 May 2012
Keywords:
5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol
and
5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione,
Thiadiazole complex
Oxadiazole complex
Copper(II) complexes
Mixed ligand complexes
Supramolecular architecture
respectively. The metal complexes have been characterized with the aid of elemental analyses, IR, mag-
netic susceptibility and single crystal X-ray studies. The ligand 4-hpythol and complexes 2 and 3 crystal-
ꢀ
lize in the triclinic and monoclinic systems, space group P 21/n, P1 and P 21/c, respectively. The ligand is
present in the deprotonated thiol form in [Cu(en)2](4-hpythol)2ꢀ2H2O (2), where it is ionically bonded
through the thiol sulfur atom, while potassium N0-(thiophene-2-carbonyl) hydrazinecarbodithioate after
cyclization is present as the thione form in [Cu(en)2(5-thot)2] (3) and is covalently bonded through the N
atom of the resulting oxadiazole-2-thione. The most noteworthy feature of 4-hpythol (1) is its existence
in the thiol form in the solid state. Complex 3 show irreversible redox behavior, assignable to a M2+/M3+
one electron transfer. ESR signals were registered for complexes 2 and 3. Both complexes contain
extended hydrogen bonding, providing supramolecular frameworks.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
superoxide-dismutase (SOD) mimetic activity. Copper-based
compounds show potential chemotherapeutic properties [5,6].
Copper exhibits considerable biochemical action in humans,
either as an essential trace metal or as a constituent of various
exogenously administered compounds. In its former role it is bound
to ceruloplasmin, albumin and other proteins, while in the latter it is
bound to ligands of various types forming complexes that interact
with biomolecules, mainly proteins and nucleic acids. In particular,
the involvement of copper in human diseases has been described
from a medicinal-chemical [1] and a biochemical view [2], focusing
on the molecular physiology of Cu transport [3]. Current interest
in copper complexes is stemming from their potential use as antimi-
crobial, antiviral, anti-inflammatory, antitumor agents, enzyme
inhibitors or chemical nucleases. Markedly, the biochemical action
of copper complexes with non-steroidal anti-inflammatory drugs
(NSAIDs) has been studied [4], which have reduced side effects,
and their mode of action is attributed to their marked
The toxic effects of copper complexes lead to cell death either by
necrosis or through the activation of the apoptotic process [7].
1,3,4-Thiadiazole and oxadiazole derivatives, which belong to an
important group of heterocyclic compounds, are the subject of
extensive study in recent years because of their diverse biological
activities, such as anti-tuberculostatic, anti-inflammatory, analge-
sic, antipyretic, anticonvulsant, antibacterial and antifungal activi-
ties [8–13]. These compounds have also been shown to exhibit
antimycotic [14] and analgesic action [15]. Some works have
reported on the metal complexes of 2,5-bis(2-pyridyl)-1,3,
4-thiadiazole [16], 5-phenyl-1,3,4-oxadiazole-2-thione [17,18], 5-
(4-pyridyl)-1,3,4-oxadiazole-2-thione [19–20], 5-(3-pyridyl)-1,3,
4-oxadiazole-2-thione [21] and 5-(2-pyridyl)-1,3,4-oxadiazole-2-
thione [22], but no work seems to have been carried out on the com-
plexes of 1,3,4-thiadiazoles-2-thiones/thiols. Therefore it would be
of interest to investigate the mixed ligand complexes of thiadiazole-
2-thiol and oxadiazoles-2-thiones and to compare the mode
of bonding of the ligands and structures of the complexes. In view
of this, we have prepared and characterized the Cu(II) complexes
⇑
Corresponding authors. Tel.: +91 542 6702452.
E-mail addresses: mkbharty@bhu.ac.in (M.K. Bharty), singhnk_bhu@yahoo.com
(N.K. Singh).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.04.025

M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
53
of 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol and 5-thiophen-
2-yl-3H-1,3,4-oxadiazole-2-thione in the presence of ethylenedia-
mine, which acts as a co-ligand.
40%; m.p. 210-215 °C. Anal. Found: C, 45.90; H, 2.25; N, 13.50; S,
30.45%. Anal. Calc. for C8H5N2OS2 (209.28): C, 45.87; H, 2.38; N,
13.37; S, 30.58 (%). IR ( (OH) 3424,
m
cmꢁ1, KBr):
m
m(S–H) 2565,
m
(C@N) 1588, (C–S) 755, m
m
(N–N) 1070s. 1H NMR (DMSO-d6; d
ppm): 8.20–7.54 (m,4H, aromatic protons), 3.60 (s,1H, SH), 3.20
(s, 1H, OH). 13C NMR (DMSO-d6; d ppm): 178.10 (C–S), 158.05
(C@N), 128.42 (C3), 127.50 (C4, C8), 129.20 (C6), 125.94 (C5, C7)
(Scheme 1).
2. Experimental section
2.1. Chemicals and starting materials
Commercial reagents were used without further purification
and all experiments were carried out in the open atmosphere.
Ethyl-2-thiophenecarboxylate (Sigma Aldrich), CS2 (SD Fine Chem-
icals) and KOH (Qualigens) were used as received. All the synthetic
manipulations were carried out in the open atmosphere and at
room temperature. The solvents were dried and distilled before
use following standard procedures. The complexes were analyzed
for their metal content after decomposition with a mixture of conc.
HNO3 and HCl, followed by conc. H2SO4 [23].
2.3.3. Synthesis of potassium N0-(thiophene-2-carbonyl)
hydrazinecarbodithioate [K+(H2thcd)ꢁ]
The potassium N0-(thiophene-2-carbonyl) hydrazinecarbodi-
thioate [K+(H2thcd)ꢁ] was prepared by adding CS2 (1.5 ml,
20 mmol) dropwise to
a suspension of thiophene-2-carbonyl
hydrazide (2.28 g, 20 mmol) in methanol (20 ml) in the presence
of potassium hydroxide (1.2 g, 20 mmol). The reaction mixture
was stirred continuously for 30 min and the white solid
[K+(H2thcd)ꢁ] which separated was filtered, washed with EtOH
and dried. Yield: 77%; m.p. 145–150 °C. Anal. Found: C, 28.10; H,
2.00; N, 10.85; S, 37.65%. Anal. Calc. for C6H5N2S3OK (256): C,
2.2. Physical measurements
Carbon, hydrogen and nitrogen contents were estimated on a
CHN Model CE-440 Analyser and on an Elementar Vario EL III Carlo
Erbo 1108. Magnetic susceptibility measurements were performed
28.12; H, 1.95; N, 10.93; S, 37.50 (%). IR (
cmꢁ1, KBr):
3213, 3140, (C@O) 1666, (N–N) 1062s, m
(C@S) 985. 1H NMR
m
m(NH)
m
m
(DMSO-d6; d ppm): 11.74, 10.48 (s,2H) 7.92–7.14 (m, 3H, aromatic
protons). 13C NMR (DMSO-d6; d ppm): 178.50 (C@S), 160.19 (C@O),
129.18 (C3), 127.68 (C4), 125.97 (C5), 128.40 (C6) (Scheme 2).
at room temperature on
a Cahn Faraday balance using
Hg[Co(NCS)4] as the calibrant, and electronic spectra were re-
corded on a SHIMADZU 1700 UV–Vis spectrophotometer. IR spec-
tra were recorded in the 4000–400 cmꢁ1 region as KBr pellets on a
Varian Excalibur 3100 FT-IR spectrophotometer. 1H and 13C NMR
spectra were recorded in DMSO-d6 on a JEOL AL300 FT NMR spec-
trometer using TMS as an internal reference. ESR spectra of com-
plexes 2 and 3 were recorded on X-band spectrometer, model
Varian E-112, using TCNE as the internal standard. The electro-
chemical experiments were performed with a CHI-660C (CH
Instruments, USA), using three-electrode system with a nickel sup-
port as the working electrode, a platinum wire as the counter elec-
trode (area ꢂ8.0 cm2) and Hg/HgO was used as the reference
electrode.
2.3.4. Synthesis of [Cu(en)2(4-hpythol)2]ꢀ2H2O (2)
A solution of 4-hpythol (1) (0.420 g, 2 mmol) in MeOH (10 ml)
was added to
a
MeOH solution (10 ml) of Cu(OAc)2ꢀ2H2O
(0.200 g, 1 mmol). This mixture was magnetically stirred for 3 h
at room temperature. The resulting black precipitate was filtered
off, then washed thoroughly with methanol. A methanol solution
(10 ml) of ethylenediamine (0.30 ml, 4 mmol) was added to the
methanol suspension of the above compound and magnetically
stirred for 2 h at room temperature. The resulting clear dark blue
solution was filtered off and kept for crystallization. Dark blue sin-
gle crystals of 2 suitable for X-ray analysis were obtained by slow
evaporation of the above solution over a period of 12 days. Yield
58%; m.p. 220 °C. Anal. Found: C,37.20; H, 4.55; N, 17.40; S,
20.30; Cu, 10.10%. Anal. Calc. for C20H30CuN8S4O4 (638.35): C,
2.3. Synthesis
2.3.1. Synthesis of 4-hydroxy-thiobenzoic acid hydrazide
37.58; H, 4.69; N, 17.54; S, 20.20; Cu, 9.94 (%). IR (
(OH) 3430, (NH) 3210, (C@N) 1606, (N–N) 1095s,
745, (Cu–N) 524. B = 1.75 BM. UV–Vis [kmax, DMSO, nm]: 580,
361, 339.
m
cmꢁ1, KBr):
(C–S)
4-Hydroxy-thiobenzoylsulfanyl-acetic acid was prepared by the
literature method [24]. 4-Hydroxy-thiobenzoic acid hydrazide was
prepared by adding a slightly excess amount of hydrazine hydrate
(3.0 mL, 20 mmol) to a solution of 4-hydroxy-thiobenzoylsulfanyl-
acetic acid (4.4 g, 20 mmol) prepared in 1 N aq.NaOH, and keeping
the reaction mixture for 2 h. This mixture was acidified with dil.
acetic acid (20% v/v) whereupon a cream solid of 4-hydroxy-thio-
benzoic acid hydrazide was obtained, which was filtered, washed
with H2O, dried and crystallized in ethanol. Yield: 85%; m.p.
170 °C [24].
m
m
m
m
m
m
l
2.3.5. Synthesis of [Cu(en)2(5-thot)2] (3)
CuCl2ꢀ2H2O (0.170 g, 1 mmol) and freshly prepared potassium
N0-(thiophene-2-carbonyl) hydrazinecarbodithioate [K+(H2thcd)ꢁ]
(0.514 g, 2 mmol) were dissolved separately in 15–20 ml metha-
nol, mixed together and stirred for 2 h. The green solid which sep-
arated was filtered, washed successively with methanol-water
mixture (50:50 v/v) and finally with methanol. A methanol solu-
tion (10 ml) of ethylenediamine (0.30 ml, 4 mmol) was added to
the methanol suspension of the above compound and stirred for
30 min. A clear dark blue solution was obtained, which was filtered
and kept for crystallization. Dark blue crystals of 3 suitable for
X-ray analysis were obtained by slow evaporation of the above
solution over a period of 15 days. Yield: 50%. m.p. 240 °C. Anal.
Found: C, 34.75; H, 4.00; N, 20.40; S, 23.35; Cu, 11.45%. Anal. Calc.
for C16H22CuN8S4O2 (550.25): C, 34.89; H, 3.99; N, 20.35; S, 23.26;
2.3.2. Synthesis of 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol
(4-hpythol) (1)
Potassium N0-(4-hydroxy-thiobenzoyl)-hydrazinecarbodithio-
ate was prepared by adding CS2 (0.9 ml, 10 mmol) dropwise to a
suspension of 4-hydroxy-thiobenzoic acid hydrazide (1.68 g,
10 mmol) in methanol (20 ml) in the presence of potassium
hydroxide (0.6 g, 10 mmol). The reaction mixture was stirred con-
tinuously for 30 min and the separated yellow solid of potassium
N0-(4-hydroxy-thiobenzoyl)-hydrazinecarbodithioate was filtered,
washed with EtOH and dried. Yield: 60%; m.p. 334–338 °C. This so-
lid was dissolved in a MeOH–H2O (50% v/v) mixture and after
7 days colorless crystals of 5-(4-hydroxy-phenyl)-1,3,4-thiadia-
zole-2-thiol, suitable for X-ray analyses, were obtained. Yield:
Cu, 11.54 (%). IR (
1088s, (C–S) 755,
DMSO, nm]: 606, 350.
m
cmꢁ1, KBr):
(Cu–N) 518.
m
(NH) 3231,
m(C–N) 1593, m(N–N)
m
m
lB = 2.02 BM. UV–Vis [kmax,

54
M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
S
S
HO
HO
+ N2H4.H2O
SCH2 COOH
HN
NH2
KOH
MeOH
CS2
S
4
5
7
S
SH
H+
1
S
H
N
2
6
3
HO
HO
N
H
N
N
SK
8
1.Cu(OAc)2.H2O
2. en
NH2
H2N
N
N
S
Cu
S
.
S
OH
2H2O
HO
S
H2N
NH2
N
N
Scheme 1. Synthesis of 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol) (4-hpythol) and its Cu(II) complex (2).
O
2
O
H
N
S
S
S-K+
3
1
NH2
4
N
H
CS2
MeOH
KOH
N
H
S
6
5
CuCl2.2H2O
S
H2N
NH2
O
N
en
60 0
S
S
Green ppt
N
O
N
C
N
Cu
H2N
NH2
S
Scheme 2. Synthesis of potassium N0-(thiophene-2-carbonyl) hydrazinecarbodithioate [K+(H2thcd)ꢁ] and its Cu(II) complex (3).
3. Crystal structure determination
4. Results and discussion
Crystals suitable for X-ray analyses of compounds 1, 2 and 3 were
grown at room temperature. The crystal data were collected on an
Oxford Gemini diffractometer equipped with CrysAlis CCD software
The ligand 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol
reacts with Cu(OAc)2ꢀ2H2O to form a blue precipitate which is
soluble in methanolic solutions of en, yielding [Cu(en)2] (4-hpy-
thol)2ꢀ2H2O (2). A methanol solution of CuCl2ꢀ2H2O on reaction
with potassium N0-(thiophene-2-carbonyl) hydrazinecarbodithio-
ate yields [Cu(en)2(thot)2] (3), suggesting that the potassium
N-acylhydrazine carbodithioate generates 1,3,4-oxadiazole/thiadi-
azole-2-thione on cyclization in the presence of en by an internal
ring closure reaction via desulfurization. A similar cyclization pro-
cess has been described in the literature [17–20]. The elemental
analyses and physical measurements of complex 3 indicate that
both hydrazinic hydrogens from the [–C(O)NHNHC(S)Sꢁ–] moiety
and one sulfur atom are missing from the resulting complex.
using a graphite mono-chromated Mo Ka (k = 0.71073 Å) radiation
source at 293 K for 1, 2 and 3. Multi-scan absorption correction was
applied to the X-ray data collection for all the compounds. The
structures were solved by direct methods (SHELXS-08) and refined
against all data by full matrix least-squares on F2 using anisotropic
displacement parameters for all non-hydrogen atoms. All hydrogen
atoms were included in the refinement at geometrically ideal posi-
tions and refined with a riding model [25]. The MERCURY package
and the ORTEP-3 for Windows program were used for generating
the structures [26,27].

M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
55
Schemes 1 and 2 depict the formation of the complexes which con-
tain the thione/thiol form of the ligand and ethylenediamine as a
co-ligand. Complexes 2 and 3 are insoluble in ethanol and chloro-
form, but are soluble in DMF and DMSO, and melt at 220 and
240 °C, respectively.
free en [28]. Appearance of a new band near 520 cmꢁ1 due to
(M–N) suggests the formation of a chelate with en in complexes
2 and 3. The IR data are thus consistent with the presence of
m
1,3,4-thiadiazole and 1,3,4-oxadiazole moieties in complexes 2
and
2565 cmꢁ1 and the presence of
indicates that the thiol sulfur is ionically bonded to Cu(II). The
slight negative shift in (C–S) and (C@S) in complexes 2 and 3,
3
[29], respectively. This disappearance of
m(S–H) at
m
(C–S) at 745 cmꢁ1 in complex 2
4.1. IR spectra
m
m
respectively, may be due to the involvement of the thiol or thione
The IR spectrum of the ligand 5-(4-hydroxy-phenyl)-1,3,4-thia-
diazole-2-thiol (4-hpythol) in KBr shows absorptions (cmꢁ1) due to
the stretching modes of O–H (3424), S–H (2565), C@N (1588), C–S
(755) and N–N (1070). The IR spectrum of potassium N0-(thio-
phene-2-carbonyl) hydrazinecarbodithioate [K+(H2thcd)ꢁ] in KBr
shows absorptions (cmꢁ1) due to the stretching modes of NH
(3213 m, 3140 m), C@O (1666), C@S (985) and N–N (1062). The
IR spectra of complexes 2 and 3 show bands in the region of
3231–3210 cmꢁ1 due to the N–H stretching vibrations of en, which
are shifted to lower frequency compared to those encountered in
sulfur in hydrogen bonding. In complexes 2 and 3, peaks appearing
at 1593–1606 cmꢁ1 due to
m
(C@N) (endocyclic) and
m(C–S–C)
1285/
m
(C–O–C) 1270 cmꢁ1 suggest cyclization of the dithiolate
moiety to 1,3,4-thiadiazole-2-thiol/1,3,4-oxadiazole-2-thione via
desulfurization.
4.1.1. 1H and 13C NMR spectra
The 1H NMR spectrum of 4-hpythol exhibits signals at d 3.60
and 3.20 ppm due to protons of the thiol and phenyl hydroxyl
Fig. 1. ESR spectrum of [Cu(en)2(4-hpythol)2]ꢀ2H2O (2) in MeOH at LNT.
Fig. 2. ESR spectrum of [Cu(en)2(5-thot)2] (3) at LNT.

56
M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
Table 2
6
4
Interatomic distances (Å) and angles (°) for 4-hpythol (1).
Bond lengths (Å)
Bond angles (°)
S(2)–C(2)
S(2)–C(1)
S(1)–C(1)
C(2)–N(1)
N(2)–C(1)
O(1)–C(6)
N(1)–N(2)
1.734(6)
1.747(6)
1.731(6)
1.300(7)
1.276(7)
1.323(7)
1.425(6)
C(2)–S(2)–C(1)
N(1)–C(2)–S(2)
C(2)–N(1)–N(2)
C(1)–N(2)–N(1)
N(2)–C(1)–S(1)
N(2)–C(1)–S(2)
S(1)–C(1)–S(2)
87.0(3)
112.7(4)
113.6(5)
113.1(5)
127.4(5)
113.6(4)
119.0(3)
2
0
-2
-4
4.2. Electronic spectra and magnetic moments
0.2
0.3
0.4
0.5
0.6
0.7
[Cu(en)2](4-hpythol)2ꢀ2H2O (2) shows a magnetic moment of
1.75 BM, which indicates the presence of one unpaired electron.
The presence of a broad band around 17240 cmꢁ1, assigned to
the envelope of the 2B1g ? 2A1g, 2B2g and 2Eg transitions, suggests
a square planar geometry for the complex. Two other high energy
bands observed at 27665 and 29420 cmꢁ1 may be assigned to
intraligand/charge transfer transitions. [Cu(en)2(thot)2] (3) shows
Potential / V
Fig. 3. Cyclic voltammogram of Cu(en)2(5-thot)2] (3).
groups, respectively. Aromatic protons appear between d 8.20 and
7.54 ppm. The 13C NMR spectrum of 4-hpythol shows signals at d
178.10 and 158.05 ppm due to C–S and C@N carbons, respectively.
The hydroxyl phenyl ring carbons appear at d 128.42, 129.20 (C3,
C6), 127.50, 125.94 (C4, C5) ppm. The NMR data thus indicate that
the ligand 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole is present in the
thiol–thione tautomeric form in solution. The 1H NMR spectrum of
potassium N0-(thiophene-2-carbonyl) hydrazinecarbodithioate
[K+(H2thcd)ꢁ] in DMSO-d6 shows two signals at d 11.74 and
10.48 (s, 2H), ppm due to the presence of two NH protons. The phe-
nyl ring protons appear as a multiplet between d 7.92–7.14 (m, 3H)
ppm. The 13C NMR spectrum of K+(H2thcd)ꢁ shows signals at d
178.50 and 161.19 ppm due to >(C@S) and >(C@O) carbons, respec-
tively. The phenyl ring carbons appear at d 128.40, 129.18 (C3, C6),
127.68 and 125.97 (C4, C5) ppm.
a
magnetic moment of 2.02 B.M. and a broad band at
16500 cmꢁ1, assignable to the 2Eg ? 2T2g transition for an octahe-
dral geometry around Cu(II) [30].
4.3. ESR spectra
The frozen solution EPR spectra of the copper(II) complexes 2
and 3 (Figs. 1 and 2) were recorded in DMSO and methanol, respec-
tively. EPR spectra of Cu(II) complexes on the high field side are
more intense than the low field side, indicating a dx2ꢁy2 ground
state for the copper(II) ion. Analysis of the spectra give g = 2.185
k
and 2.216 and g\ = 2.009 and 2.008 for complexes 2 and 3 respec-
tively. The trend g > g\ > ge (2.0023), observed for the complexes
k
Table 1
Crystallographic data for compounds 1, 2 and 3.
Parameters
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C8H5N2OS2
209.28
monoclinic
P 21/n
C20H30CuN8O4S4
638.35
C16H22CuN8O2S4
550.25
monoclinic
P 21/c
triclinic
ꢀ
P1
103(2)
293(2)
293(2)
k, Mo K
a
(Å)
0.71073
0.71073
0.71073
Unit cell dimensions
a (Å)
b (Å)
c (Å)
8.0624(3)
11.3547(3)
11.2234(3)
90
91.359(3)
90
1027.17(5)
4
1.353
6.5080(6)
7.7549(7)
15.1301(14)
75.869(8)
84.854(8)
68.602(9)
689.45(11)
1
10.6834(18)
8.6081(15)
12.672(2)
90
95.432(16)
90
1160.1(3)
2
1.575
a
(°)
b (°)
c
(°)
V, (Å3)
Z
qcalc (g cmꢁ3
)
1.538
1.138
l
(mmꢁ1
)
0.479
1.332
F(000)
428
331
566
Crystal size (mm3)
0.30 ꢃ 0.27 ꢃ 0.25
2.55–28.75
ꢁ10 6 h 6 10
ꢁ15 6 k 6 14
ꢁ14 6 l 6 15
7007
0.25 ꢃ 0.23 ꢃ 0.21
2.78–28.86
ꢁ4 6 h 6 8
ꢁ10 6 k 6 9
ꢁ18 6 l 6 20
3615
0.31 ꢃ 0.27 ꢃ 0.24
3.04–29.01
ꢁ14 6 h 6 14
ꢁ11 6 k 6 11
ꢁ15 6 l 6 17
3099
h range for data collections (°)
Index ranges
No. of reflections collected
No. of independent reflections (Rint
)
)
2663
1815/0/428
1.048
0.051, 0.1431
0.1845, 0.1891
0.297, ꢁ0.495
1629
3615/0/178
0.942
0.0342, 0.0503
0.0836, 00.0879
0.297, ꢁ0.240
1928
3099/0/142
1.034
0.0576, 0.0787
0.1520, 0.1776
0.782, ꢁ0.877
No. of data/restrains/parameters
Goodness-of-fit on F2
b
R1a, wR2 [(I > 2
r(I)]
b
R1a, wR2 (all data)
Largest difference peak/hole (e Åꢁ3
a
R1
R2 = [
=
R
R
||Fo| ꢁ |Fc||
R|Fo|.
w(|F2o | ꢁ |F2c |)2/
R .
w|F2o |2]1/2
b

M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
57
Fig. 4. ORTEP plot of 4-hpythol (1) showing the atomic numbering scheme, with ellipsoids of 30% probability.
Fig. 5. Showing N–Hꢀ ꢀ ꢀO hydrogen bonding forming a linear structure for 1.
under investigation, also suggests a dx2ꢁy2 ground state for the
the Ag/AgCl reference. The separation between the cathodic and
anodic peak potentials (
irreversible process assignable to the Cu(II)/Cu(III) couple with a
redox potential of 0.471 V (Fig. 3) [35]. However, it is to be noted
Cu(II) ion [31–33]. Also, the observed g values of less than 2.30
D
Ep = Epa ꢁ Epc) of 0.158 V indicates an
k
provide evidence for the appreciable covalent character of bonding
between the Cu(II) ion and the attached ligand in the complexes
[34].
that the peak separation (
pared to that expected for a one electron process.
D
Ep = Epa ꢁ Epc) is quite large as com-
4.4. Electrochemical studies
4.5. Crystal structure description of 4-hpythol (1)
The cyclic voltammogram of complex 3 (Fig. 3) obtained at a
platinum electrode in the potential range +0.2 V to +0.7 V, with a
scan rate of 50 mVsꢁ1, exhibits a cathodic peak at Epc = 0.392 V
and the associated anodic peak at Epa = 0.550 V with respect to
The crystallographic data and structural refinement details for
4-hpythol (1) are given in Table 1 and selected bond distances
and bond angles in Table 2. Fig 4 shows the ORTEP diagram of the
Fig. 6. Molecular structure of [Cu(en)2](4-hpythol)2ꢀ2H2O (2).

58
M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
Table 3
S(1)–C(1) [1.731(6) Å] and endocyclic S(2)–C(2) [1.734(6) Å] bond
lengths are comparable, and they are longer than typical carbon
sulfur double-bonds [S@C (1.56 Å)] [36], which indicate that the
exocyclic sulfur has single bond character and the ligand is present
in the thiol form. This is further supported by the N(2)–C(1) bond
length of [1.276(7) Å], which comes in the range of N@C double
bonds [1.27 Å] [37]. The structure is stabilized by intermolecular
O–Hꢀ ꢀ ꢀN hydrogen bonding occurring between the thiadiazole N
and OH of a nearby molecule, producing a linear chain structure
(Fig. 5). The values found for O–H, Nꢀ ꢀ ꢀH and \O–Hꢀ ꢀ ꢀN are close
to the bond distances and bond angles reported earlier [38,39].
Interatomic distances (Å) and angles (°) for [Cu(en)2](4-hpythol)2ꢀ2H2O (2).
Bond lengths (Å)
Bond angles (°)
Cu(1)–N(3)
Cu(1)–N(4)
N(1)–C(2)
N(3)–C(9)
C(10)–C(9)
S(2)–C(1)
S(1)–C(2)
S(1)–C(1)
N(4)–C(10)
N(1)–N(2)
N(9)–C(9)
N(8)–C(8)
1.993(2)
2.004(2)
1.295(3)
1.469(4)
1.487(4)
1.716(3)
1.725(3)
1.746(3)
1.472(4)
1.391(3)
1.236(7)
1.286(7)
N(3)–Cu(1)–N(3)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)–N(4)#1
C(9)–N(3)–Cu(1)
C(1)–N(2)–N(1)
N(4)–C(10)–C(9)
N(1)–C(2)–C(3)
C(3)–C(2)–S(1)
S(2)–C(1)–S(1)
N(2)–C(1)–S(2)
C(2)–N(1)–N(2)
C(2)–S(1)–C(1)
180.0
85.17(9)
94.83(9)
107.93(19)
113.5(2)
109.3(2)
123.2(2)
123.94(19)
122.99(16)
125.3(2)
113.4(2)
88.60(13)
4.6. Crystal structure description of [Cu(en)2](4-hpythol)2ꢀ2H2O (2)
The crystal structure of complex 2 consists of a complex cation
[Cu(en)2]2+ and the 1,3,4-thiadiazole thiolate (4-hpythol) anion
and two lattice held water molecules. The ethylenediamine mole-
cules chelate Cu(II), and two 1,3,4-thiadiazole-2-thiolate anions
are ionically bonded in every unit of structure 2. This is shown as
the molecular structure of complex 2 in Fig 6, with the atom labeling
scheme and a weak Cuꢀ ꢀ ꢀS interaction. Crystallographic data and
structural refinement details related to complex 2 are given in Table
ligand with the atomic numbering scheme. The most noteworthy
feature of the ligand 4-hpythol (1) is its stabilization in the thiol
form, in contrary to other 1,3,4-thiadiazoles which exist in the
thione form. The dihedral angle between the thiadiazole and the
attached hydroxyl phenyl rings is 9.6(6)°, indicating that both rings
are almost coplanar. The bond lengths and angles in the phenyl
ring and thiadiazole ring are generally normal. The exocyclic
Fig. 7. O–Hꢀ ꢀ ꢀO and N–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀS interactions in [Cu(en)2(4-hpythol)2]ꢀ2H2O (2) (oxygen atoms are shown as a ball and stick model).
Fig. 8.
pꢀ ꢀ ꢀp interactions in [Cu(en)2(4-hpythol)2]ꢀ2H2O (2).

M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
59
Fig. 9. Molecular structure of [Cu(en)2(5-thot)2] (3).
interaction between the thiadiazole and phenyl rings in complex
2. The distance between the thiadiazole and phenyl ring centroids
contacts (Cgꢀ ꢀ ꢀCg) is 3.757 Å (Fig. 8).
Table 4
Interatomic distances (Å) and angles (°) for [Cu(en)2(5-thot)2] (3).
Bond lengths (Å)
Bond angles (°)
Cu(1)–N(3)
Cu (1)–N(4)
N(3)–C(7)
C(4)–C(5)
S(2)–C(6)
C(7)–C(8)
N(1)–N(2)
2.041(3)
2.010(3)
1.476(5)
1.423(6)
1.682(5)
1.499(6)
1.407(5)
N(4)–Cu(1)–N(4)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)–N(4)#1
C(7)–N(3)–Cu(1)
C(8)–N(4)–Cu(1)
N(3)–C(7)–C(8)
N(4)–C(8)–C(7)
180.0(18)
84.16(14)
95.84(14)
108.3(2)
109.6(3)
109.2(3)
108.0(3)
4.7. Crystal structure description of [Cu(en)2(5-thot)2] (3)
Fig. 9 shows the molecular structure of complex 3 with the
atom labeling scheme. Crystallographic data and structural refine-
ment details related to complex 3 are given in Table 1 and selected
bond lengths and angles are in Table 4. The molecular structure of
3 shows that in the centro symmetric unit of [Cu(thot)2(en)2], the
metal ion is six coordinate, bonded with four nitrogens of two en
ligands and two nitrogens of two oxadiazole anions. The dihedral
angle between the plane formed by the oxadiazole and phenyl ring
is 25.78°. The bond angles N(4)–Cu–N(3) 84.16(14) and N(4)–Cu–
N(3) 95.84(14)° indicate a minor deviations from an ideal octahe-
dral geometry. The bond lengths Cu–N(4) and Cu–N(3) are
2.010(3) and 2.041(3) Å, respectively, which is normal for Cu–N
amine coordination. In the solid state the complex is stabilized
via an intermolecular N–Hꢀ ꢀ ꢀS interaction between the thione sul-
fur and NH2 hydrogen atoms of en, and a C–Hꢀ ꢀ ꢀS interaction be-
tween the thione sulfur and CH2 hydrogen atoms of an en
molecule, leading to the formation of a wave-like metal-organic
framework (Fig. 10). The above observed intermolecular and intra-
molecular hydrogen bondings have stabilized the molecular crystal
packing, giving a supramolecular network. The axial and equatorial
Cu–N distances for the complex are 2.010(3) and 2.041(3) Å
respectively, suggesting an axially distorted octahedral geometry
for the copper complex due to Jahn–Teller distortion. The hard
acceptor, viz. Cu(II), shows no tendency for coordination with the
soft donor sulfur, but prefers to bind with the comparatively hard
nitrogen site of the ligand.
1 and selected bond lengths and angles are in Table 3. The Cu–N dis-
tances are in the range 1.993–2.004 Å (Table 3), which is normal for
Cu–N amine coordination. The bite angles for the CuC2N4 five mem-
bered rings are 85.17(9)° and 94.83(9)°, indicating a substantial
distortion in the molecule. Similar geometrical parameters for the
coordination sphere have been reported for other diaquabis (ethy-
lenediamine) Cu(II) salts [40,41]. Each [Cu(en)2]2+ forms a pair of
intermolecular Cuꢀ ꢀ ꢀS interactions with a distance of 3.032 Å, which
is well under the distance of 3.2 Å for the sum of the van der Waals’
radii of Cu and S [42] and greater than a Cu–S covalent bond [43].
The Cu(II) center, in D2h symmetry, is bonded to four nitrogen atoms
of en groups which offer interesting hydrogen bonding packing. The
elements of the structure are joined to each other in the crystal
packing by means of an extended system of H-bonds, where hydro-
gen atoms belonging to en participate in the structure. In the solid
state, the complex is stabilized via an intermolecular N–Hꢀ ꢀ ꢀN inter-
action between the thiadiazole nitrogen atoms and the NH2 hydro-
gen atoms of en. An N–Hꢀ ꢀ ꢀO interaction is present between the
thiol nitrogen and hydrogen atoms of the water molecule, as well
as a weak O–Hꢀ ꢀ ꢀO interaction between the phenolic OH and hydro-
gen of the water molecule (Fig. 7). In addition there is a
pꢀ ꢀ ꢀp
Fig. 10. N–Hꢀ ꢀ ꢀS and C–Hꢀ ꢀ ꢀS hydrogen bonding in complex (3) leading to a wave-like structure.

60
M.K. Bharty et al. / Polyhedron 41 (2012) 52–60
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This paper reports the syntheses, spectral and crystal structure
investigations of two new complexes, [Cu(en)2](4-hpythol)2ꢀ2H2O
(2)
(4-pythol = 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol)
and [Cu(en)2(5-thot)2] (3) (thot = 5-thiophen-2-yl-3H-1,3,4-oxadi-
azole-2-thione), containing en as the co-ligand. It was found that
potassium thiohydrazide carbodithioate cyclized to 1,3,4-thiadia-
zole-2-thiol during crystallization in MeOH–H2O. In complex 3,
the metal-bound N0-(thiophene-2-carbonyl) hydrazine carbodi-
thioate is cyclized to 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thi-
one in the presence of ethylenediamine via desulfurisation. This
strategy has been found to be an easy and facile route to synthesize
mixed ligand complexes of 1,3,4 oxadiazole-2-thione. The struc-
tures of the complexes are stabilized through weak intermolecu-
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