Square planar Ni(II) complexes of pyridine-4-carbonyl-hydrazine carbodithioate, 1-phenyl-3-pyridin-2-yl-isothiourea and 4-(2-methoxyphenyl) piperazine-1-carbodithioate involving N-S bonding: An approach to DFT calculation and thermal studies

Article abstract of DOI:10.1016/j.poly.2013.07.012

Three new complexes [H₂en][Ni(pchc)₂] (1) (pchc = pyridine-4-carbonyl-hydrazine carbodithioate), [Ni(Hppith)₂] (2) (H₂ppith = 1-phenyl-3-pyridin-2-yl-isothiourea) and [Ni(mppcdt) ₂] (3) {mppcdt = 4-(2-methoxyphenyl)piperazine-1-carbodithioate} have been synthesized and characterized by elemental analyses, IR and single crystal X-ray diffraction data. The ligand H₂ppith and complexes [H ₂en][Ni(pchc)₂] (1) [Ni(Hppith)₂] (2) and [Ni(mppcdt)₂] (3) crystallize in monoclinic, orthorhombic, monoclinic and triclinic system with space group P21/n, Icab, C2/c and P1, respectively. The nitrogen and sulfur donor sites of the bidentate ligands chelate Ni(II) forming two five-membered CSN₂M chelate rings in the complex 1, two six membered C₂SN₂M rings in complex 2 and the sulfur donor sites of the bidentate ligand chelate Ni(II) forming two four membered CS₂M rings in complex 3. The Ni(II) complexes are diamagnetic and have distorted square planar geometry. The crystal structure of the complexes are stabilized by various types of inter and intramolecular extended hydrogen bonding providing supramolecular framework. Results obtained from quantum chemical calculations at the density functional theory level corroborate our experimental findings from IR and UV. The course of the thermal degradation of complexes 1,2 and 3 has been investigated by TG-DTA. Thermogravimetric analyses of the complexes indicate NIO/NIS as the end residue.

Full text of DOI:10.1016/j.poly.2013.07.012

Polyhedron 63 (2013) 156–166
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Square planar Ni(II) complexes of pyridine-4-carbonyl-hydrazine
carbodithioate, 1-phenyl-3-pyridin-2-yl-isothiourea and
4-(2-methoxyphenyl)piperazine-1-carbodithioate involving
N–S bonding: An approach to DFT calculation and thermal studies
a
b
a,
P. Bharati a, A. Bharti a, M.K. Bharty a, , B. Maiti , R.J. Butcher , N.K. Singh
⇑
⇑
a Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
b Department of Chemistry, Howard University, 525 College Street NW, Washington, DC 20059, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new complexes [H2en][Ni(pchc)2] (1) (pchc = pyridine-4-carbonyl-hydrazine carbodithioate),
[Ni(Hppith)2] (2) (H2ppith = 1-phenyl-3-pyridin-2-yl-isothiourea) and [Ni(mppcdt)2] (3) {mppcdt = 4-
(2-methoxyphenyl)piperazine-1-carbodithioate} have been synthesized and characterized by elemental
analyses, IR and single crystal X-ray diffraction data. The ligand H2ppith and complexes [H2en][Ni(pchc)2]
(1) [Ni(Hppith)2] (2) and [Ni(mppcdt)2] (3) crystallize in monoclinic, orthorhombic, monoclinic and tri-
Received 22 March 2013
Accepted 10 July 2013
Available online 19 July 2013
Keywords:
ꢀ
clinic system with space group P21/n, Icab, C2/c and P1, respectively. The nitrogen and sulfur donor sites
Ni(II) complexes
Carbodithioate complex
Secondary interactions
Hydrogen bonding
DFT
of the bidentate ligands chelate Ni(II) forming two five-membered CSN2M chelate rings in the complex 1,
two six membered C2SN2M rings in complex 2 and the sulfur donor sites of the bidentate ligand chelate
Ni(II) forming two four membered CS2M rings in complex 3. The Ni(II) complexes are diamagnetic and
have distorted square planar geometry. The crystal structure of the complexes are stabilized by various
types of inter and intramolecular extended hydrogen bonding providing supramolecular framework.
Results obtained from quantum chemical calculations at the density functional theory level corroborate
our experimental findings from IR and UV. The course of the thermal degradation of complexes 1, 2 and 3
has been investigated by TG-DTA. Thermogravimetric analyses of the complexes indicate NIO/NIS as the
end residue.
Thermal analyses
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
M(N,S) and M(S,S) bonded compounds with increased electron
delocalization which may lead to improved biological activity [4–
Nickel(II) complexes of nitrogen sulfur containing chelating li-
gands have recently attracted much attention because of their use
as a model for the nickel center of enzymes such as bifunctional car-
bon monoxide dehydrogenase/acetyl–CoA synthase and nickel-
containing superoxide dismutase [1]. Nickel(II) complexes with
nitrogen and sulfur donor ligands are also highly interesting be-
cause several hydrogenases and carbon monoxide dehydrogenases
contain such nickel complexes as their active site [2,3]. Nickel is a
nutritionally essential trace metal for at least several animal spe-
cies, micro-organisms and plants, and therefore toxicity symptoms
can occur under the conditions of either its deficiency or excess.
Isonicotinic acid hydrazide being an antimicrobial agent has been
used as anti-tubercular drug and its dithio derivatives may exhibit
both N–S and S–S bonded chelating behavior forming interesting
6]. The uninegative thio ligands exhibit different modes of bonding
in mononuclear Ni(II) complexes [7]. The dithiocarbazates and their
substituted derivatives containing nitrogen sulfur donor atoms
have been of great interest to researchers because of their wide var-
iation in structure and properties. Their complexes have tunable
electronic behavior which may result in nonlinear optical (NLO)
materials with unique magnetic and electrochemical properties
[7,8] and show selective biological activity [9–11]. Substituted dith-
iocarbazates containing hetero atoms behave as bidentate [7,8], tri-
dentate [9,10] or multidenate [11] chelating agents. In the
literature, thiosemicarbazone ligands based on aldehydes have gen-
erally formed trans square planar complexes, while ketone based
thiosemicarbazones have formed only cis square planar complexes
[12–14]. Thiourea/isothiourea ligands may exhibit monodentate,
bidentate or multidentate behavior in the resulting complexes
[15–24], which opens a multiplicity of bonding schemes. Thus the
presences of different donor atoms as well as the various structures
of thiourea derivatives result in a variety of complexes. In view of
⇑
Corresponding authors. Tel.: +91 5422318529; fax: +91 5422368127 (N.K.
Singh).
E-mail addresses: manoj_vns2005@yahoo.co.in (M.K. Bharty), singhnk_bhu@
yahoo.com (N.K. Singh).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.07.012

P. Bharati et al. / Polyhedron 63 (2013) 156–166
157
this, we have prepared and characterized the Ni(II) complexes of
pyridine-4-carbonyl-hydrazine carbodithioate, 1-phenyl-3-pyri-
din-2-yl-isothiourea and 4-(2-methoxyphenyl) piperazine-1-car-
bodithioate, all of which contain nitrogen–sulfur donor atoms.
2.3.2. Synthesis of 1-phenyl-3-pyridin-2-yl-isothiourea (H2ppith)
To a solution of pyridine-2-yl amine (1.88 g, 20 mmol) in ben-
zene (20 mL) was added phenylisothiocyanate (2.4 mL, 20 mmol)
and the reaction mixture was refluxed for 4 h. A white precipitate
was obtained upon cooling the reaction mixture in ice, which was
filtered off, washed with methanol and ether and recrystallised
from MeOH:CHCl3 mixture (50:50 v/v). Yield: 0.87 g, 38%; m.p.
455 K. Anal. Calc. for C12H11N3S1 (229.30): C, 62.85; H, 4.83; N,
18.32; S, 13.98. Found: C, 62.87; H, 4.80; N, 18.34; S, 13.97%. IR
2. Experimental
2.1. Chemicals and starting materials
(KBr, cmÀ1):
m(NH) 3219, m(C@N) 1598; m
(C–S) 772. 1H NMR
Commercial reagents were used without further purification
and all experiments were carried out in open atmosphere. Isonicot-
inic acid hydrazide, Pyridine-2-yl amine, Isothiocyanato benzene,
1-(2-methoxyphenyl) piperazine (Sigma Aldrich), CS2 (SD Fine
Chemicals) and KOH (Qualigens) were used as received. All the
synthetic manipulations were carried out in open atmosphere
and at room temperature. The solvents were dried and distilled be-
fore use following the standard procedure. The complexes were
analyzed for their metal content, after decomposition with a mix-
ture of conc. HNO3 and HCl, followed by conc. H2SO4 [25].
(CDCl3; d ppm): 7.25 (s, 2H, NH), 7.32–7.82 (pyridine ring protons),
6.67–7.12 (phenyl ring protons). 13C NMR (CDCl3; d ppm): 180.89
(C@S), 162.09 (C@N), 159.67–118.22 (aromatic carbons). UV–Vis
[kmax, MeOH, cmÀ1]: 43100, 42200 and 33220.
2.3.3. Synthesis of potassium 4-(2-methoxyphenyl)piperazine-1-
carbodithioate [K+(mppcdt)À]
The potassium 4-(2-methoxyphenyl)piperazine-1-carbodithio-
ate was prepared by adding CS2 (1.8 mL, 20 mmol) dropwise to a
suspension of 1-(2-methoxyphenyl) piperazine (3.51 mL,
20 mmol) in methanol (20 mL) in the presence of potassium
hydroxide (1.2 g, 20 mmol). The reaction mixture was stirred con-
tinuously for 30 min in cold condition and the separated white so-
lid potassium 4-(2-methoxyphenyl) piperazine-1-carbodithioate
was filtered, washed with EtOH and dried under reduced pressure
and recrystallized from a MeOH–CHCl3 mixture (50:50 v/v). Yield:
0.211 g, 69%; m.p. 185 °C. Anal. Calc. for C12H15N2S2OK (306.43): C,
47.05; H, 4.92; N, 9.13; S, 20.92. Found: C, 47.08; H, 4.91; N, 9.15; S,
2.2. Physical measurements
Carbon, hydrogen, nitrogen and sulfur contents were estimated
on a CHN Model CE-440 Analyser and on an Elementar Vario EL III
Carlo Erbo 1108. Magnetic susceptibility measurements were per-
formed at room temperature on a Cahn Faraday balance using
Hg[Co(NCS)4] as the calibrant and electronic spectra were recorded
on a SHIMADZU 1700 UV–Vis spectrophotometer. IR spectra were
recorded in the 4000–400 cmÀ1 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 spectrometer
using TMS as an internal reference. Thermogravimetric analyses
(TG-DTA) were completed on a Perkin Elmer-STA 6000 thermal
analyzer at a heating rate of 5 °C/min in N2 atmosphere.
20.90%. IR (KBr, cmÀ1): (C@S) 928; 1H NMR (DMSO-
m(C–N) 1415; m
d6; d ppm): 6.85–7.25 (m, 4H, aromatic protons), 3.08–3.27 (m, 8H,
CH2), 3.88 (s, 3H, CH3). 13C NMR (DMSO-d6; d ppm): 209.56 (C@S),
120.96–140.56 (aromatic carbons), 152.05 (C–N), 44.65–50.73
(CH2), 55.39 (CH3). UV–Vis [kmax, DMSO, cmÀ1]: 31250.
2.3.4. Synthesis of [H2en][Ni(pchc)2] (1)
2.3. Synthesis
A methanol solution (25 mL) of [(H2en)(pchc)2] (0.486 g,
1 mmol) was added slowly to the methanol solution of NiCl2Á6H2O
(0.237 g, 1 mmol) and stirred for 2 h. A clear solution was obtained
which was filtered and kept for crystallization. Blue crystals of 1
suitable for X-ray analyses were obtained by slow evaporation of
the above solution over a period of 15 days. Yield: 0.43 g, 78%;
m.p. (>633) K. Anal. Calc. for C16H20Ni1N8S4O2 (543.35): C, 35.33;
H, 3.68; N, 20.61; S, 23.55. Found: C, 35.36; H, 3.66; N, 20.58; S,
2.3.1. Synthesis of ethylenediammonium-pyridine-4-carbonyl-
hydrazine carbodithioate [(H2en)(pchc)2]
The potassium pyridine-4-carbonyl-hydrazine carbodithioate
was prepared by adding CS2 (1.8 mL, 20 mmol) dropwise to a sus-
pension of isonicotinic acid hydrazide (2.74 g, 20 mmol) in metha-
nol (20 mL) in the presence of potassium hydroxide (1.2 g,
20 mmol). The reaction mixture was stirred continuously for
30 min and the separated yellow solid potassium pyridine-4-car-
bonyl-hydrazine carbodithioate was filtered, washed with EtOH
and dried. The above potassium salt was dissolved in water and
treated with a solution of chloroacetic acid (1.8 g, 20 mmol) neu-
tralized with sodium carbonate. The solution was left overnight
after adjusting the pH at 7. The reaction mixture was cooled in
ice and acidified with conc. HCl, white precipitate was obtained
which was dissolved in the aqueous solution of sodium hydroxide
(1.89 g, 20 mmol) and ethylenediamine (1.6 mL, 25 mmol) diluted
two times with water was added and the reaction mixture was
kept for 3 h and then acidified with dil. HCl (40% v/v) in ice cold
condition which gave a white precipitate. The precipitate was fil-
tered, washed with water, dried under reduced pressure and
recrystallized from a MeOH–CHCl3 mixture (50:50 v/v). Yield:
0.69 g, 58%; m.p. 557 K. Anal. Calc. for C16H22N8S4O2 (486.67): C,
39.48; H, 4.55; N, 22.81; S, 26.35. Found: C, 39.53; H, 4.49; N,
23.57%. IR (KBr, cmÀ1):
m(NH) 3116, m(C@O) 1650, m(N–N) 1032,
m
(C@S) 850, (Ni–N) 503, (Ni–S) 407. 1H NMR (DMSO-d6; d ppm):
10.08 (s, 1H, NH), 7.37–8.70 (m, 4H, pyridine ring protons), 4.59
(–NH3+), 3.03 (d, 4H, –CH2). We have computed IR frequencies
(using electronic structure method as described in Section 4) in
the gas phase. These IR frequencies
m
(cmÀ1) are: (N–H) 3539,
(C@O) 1642, (N–N) 1138, (C@S) 1019 and (Ni–S) 365. The signifi-
cant deviations (in most cases higher in magnitude) in frequencies
are probably due to usage of different phases (experiment in solid
state; computation in gaseous state). Experimental UV–Vis [kmax
,
DMSO, cmÀ1]: 11450. The corresponding computed (using a TD-
DFT: B3LYP/6-31G⁄⁄ method along with PCM model for solvation)
absorption peak appears at 12276 cmÀ1, which is close to the
experimental value.
2.3.5. Synthesis of [Ni(Hppith)2] (2)
A methanol solution (25 mL) of H2ppith (0.228 g, 2 mmol) was
added slowly to the methanol solution of Ni(OAc)2Á4H2O (0.248 g,
1 mmol) and stirred for 2 h. The resulting clear solution was ob-
tained which was filtered off and kept for crystallization. Reddish
black crystals of 2 suitable for X-ray analyses were obtained by
slow evaporation of the above solution over a period of 20 days.
22.63; S, 26.46%. IR (KBr, cmÀ1):
m(N–H) 3250, 3120; m(C@O)
1622; (N–N) 1003;
m
m
(C@S) 904. 1H NMR (DMSO-d6; d ppm):
10.8, 11.5 (s, 2H, NH), 8.00–9.06 (m, 4H, pyridine ring protons),
4.45 (–NH3+), 4.05 (d, 4H, –CH2). 13C NMR (DMSO-d6; d ppm):
170.51 (C@S), 163.94 (C@O), 151.03–120.05 (aromatic carbons),
34.58 (CH2, en).
Yield: 0.58 g, 52%; m.p. 493 K. Anal. Calc. for
C15H20N6S2Ni

158
P. Bharati et al. / Polyhedron 63 (2013) 156–166
Fig. 1. TGA analysis of [H2en][Ni(pchc)2] (1).
Fig. 3. TGA analysis of [Ni(mthppzcdt)2] (3).
equipped with CrysAlis Pro., using a graphite mono-chromated Mo
(k = 0.71073 Å) radiation source. The structures were solved by
Ka
direct methods (SHELXL-2008) and refined against all data by full
matrix least-squares on F2 using anisotropic displacement parame-
ters for all non-hydrogen atoms. All the hydrogen atoms were in-
cluded in the refinement at geometrically ideal positions and
refined with a riding model [26]. The MERCURY package and ORTEP-3
programs were used for generating molecular structures [27,28].
4. Quantum chemical calculation
To get insight into the binding mode and also to verify the
composition of the complexes we have performed quantum
chemical calculations using Density Functional Theory (DFT). A
hybrid version of DFT and Hartree–Fock (HF) methods, namely,
B3LYP density functional theory method [29] is used in our calcu-
lations. In this method the exchange energy from Becke’s ex-
change functional [30] is combined with the exact energy from
Hartree–Fock theory. The three parameters define the hybrid
functional, specifying how much of the exact exchange is mixed
in along with the component exchange and correlation function-
als [31]. We have used 6-31G⁄⁄ (6-31 + G⁄⁄ for N) basis set for all
the atoms except metal atom, Ni. For Ni we have used LanL2DZ
basis set with an effective core pseudo potential [32]. All the
geometry optimizations and frequency calculations were per-
formed to verify a genuine minimum energy structure using
GAUSSIAN 09 suits of program [33].
Fig. 2. TGA analysis of [Ni(Hppith)2] (2).
(515.07): C, 34.97; H, 3.91; N, 16.31; S, 12.44. Found: C, 34.95; H,
3.92; N, 16.32; S, 12.42%. IR (KBr, cmÀ1):
(C–N) 1560, (C–S)
744, (Ni–N) 589,
(Ni–S) 406. 1H NMR (CDCl3; d ppm): 13.66 (s,
m
m
m
m
1H, NH), 7.32–7.82 (pyridine ring protons), 6.67–7.25 (phenyl ring
protons). 13C NMR (CDCl3; d ppm): 162.09 (C@N), 118.57–148.70
(aromatic carbons). UV–Vis [kmax, CHCl3, cmÀ1]: 33550 and 38160.
2.3.6. Synthesis of [Ni(mppcdt)2] (3)
The potassium 4-(2-methoxyphenyl)piperazine-1-carbodithio-
ate was soluble in the mixture of MeOH:CHCl3 (25 mL). This [K+-
(mppcdt)À] (0.306 g, 2 mmol) was added slowly to the methanol
solution of Ni(OAc)2Á4H2O (0.248 g, 1 mmol) and stirred for 5 h.
The resulting clear solution was obtained which was filtered off
and kept for crystallization. Green crystals of 3 suitable for X-ray
analyses were obtained by slow evaporation of the above solution
over a period of 16 days. Yield: 0.53 g, 56%; m.p. 521 K. Anal. Calc.
for C24H30N4NiO2S4 (593.47): C, 48.52; H, 5.05; N, 9.43; S, 21.56.
5. Thermal analyses of the complexes
In general, complexes possessing higher dimensionality usually
have higher thermal stability than those with low dimensional
structures. Most three-dimensional complexes lose little weight
on heating up to nearly 300 °C, while one-dimensional compounds
begin to decompose usually under 200 °C. In detail, the stability of
coordination compounds are decided by the metal ions, substitu-
ents of mixed ligands and coordinated anions, as well as guest mol-
ecules in the lattices. Hydrogen bonding is one of the most
important non-covalent interactions and plays an important role
in building the supramolecular structures, making a great contri-
bution to thermal stabilities. The thermal properties of complexes
1, 2 and 3 were studied by TG and DTA in the temperature range
30–800 °C under a nitrogen atmosphere. Thermo gravimetric anal-
ysis of complex 1 showed that the complex starts decomposing at
190 °C and thermogram exhibits four distinct decompositions at
190, 245, 380 and 610 °C. The first weight loss (14.56%) could be
Found: C, 48.53; H, 5.01; N, 9.46; S, 21.58%. IR (KBr, cmÀ1):
m(C–
N) 1499, (C–S) 791,
m
m
(Ni–S) 488. 1H NMR (CDCl3; d ppm): 6.90–
7.25 (m, 4H, aromatic protons), 3.35–3.96 (m, 8H, CH2), 3.11 (s,
3H, CH3). 13C NMR (CDCl3; d ppm): 187.78 (C–S), 111.51–124.18
(aromatic carbons), 69.59 (–OCH3), 44.33–51.40 (–CH2), UV–Vis
[kmax, CHCl3, cmÀ1]: 30674 and 25380.
3. Crystal structure determination
The X-ray data collection for complexes 1, 2, 3 and ligand H2ppith
were performed on an Oxford Diffraction Gemini diffractometer

P. Bharati et al. / Polyhedron 63 (2013) 156–166
159
O
H
N
S-K+
O
N
stirring
at low temp.
H
NH2
+
CS2
+
KOH
N
S
N
H
N
ClCH2COOH
N
O
H
H
N
O
H
S
N
S
H
H
N+
N
H
O
N
en
NaOH,
N
N
SCH2COOH
H
S
H
N
S
N+
H
dil.HCl
H
N
S
H
H
NiCl2.6H2O
MeOH
2
N
N
(H2en)2+
N
O
O
N
NH
S
Ni
HN
S
S
S
Scheme 1. Synthesis of ethylenediammonium-pyridine-4-carbonyl-hydrazine carbodithioate and the Ni(II) complex.
H
N
H
N
NH2
NCS
Benzene
+
N
Reflux for 6 h
S
N
Phenyl isothiocyanate
Pyridine-2-yl amine
Ni(OAc)2.4H2O
MeOH
H
N
N
N
S
Ni
S
N
N
H
N
Scheme 2. Synthesis of Ni(II) complex of 1-phenyl-3-pyridin-2-yl-isothiourea.
due to loss of one ethylenediamine molecule along with water mol-
ecule and a corresponding endothermic peak at 211 °C was ob-
tained. The second decomposition at 245 °C shows the weight
loss (51.83%) of isonicotinamide molecule from the ligand unit
and the third and fourth decompositions at 380 and 610 °C show
the degradation of the remaining organic moieties, and after
610 °C the residue of 13.08% left corresponds to nickel oxide and
corresponding exothermic peaks in DTA at 280, 567 and 639 °C
were obtained. Complex 2 decomposed at 198 °C with a weight
loss (28.12%) of phenyl ring from the ligand moiety. The complex
also exhibits four distinct decompositions at 198, 240, 355 and
500 °C. The weight loss (35.97%) could be ascribed to the loss of
thiourea group from the ligand and the third and fourth decompo-
sitions show the degradation of the remaining organic moieties

160
P. Bharati et al. / Polyhedron 63 (2013) 156–166
H3C
H3C
O
O
S
stirring
at low temp
N
N
+ CS2
+
KOH
N
NH
S-K+
Ni(OAc)2.4H2O
MeOH
H3C
O
S
S
S
N
Ni
N
N
N
S
O
CH3
Scheme 3. Synthesis of Ni(II) complex of potassium 4-(2-methoxyphenyl)piperazine-1-carbodithioate.
and after 500 °C, the residue of 17.05% left corresponds to nickel
sulfide. The DTA curve of the complex 2 shows four peaks, two cor-
responding endothermic at 205 and 492 °C and two exothermic
peaks at 265 and 553 °C, respectively. [Ni(mppcdt)2] shows the
first weight loss (36.7%) at 261 °C of methoxy phenyl group from
the ligand and the corresponding endothermic peak was obtained
at 265 °C in DTA of the complex. The complex exhibits four distinct
decompositions at 261, 308, 559 and 746 °C, the weight loss
(46.82%) at 308 °C could be due to the loss of piperazine molecule
and corresponding exothermic peak at 291 °C was obtained in DTA
of the complex. The third and fourth decompositions show the deg-
radation of the remaining organic moieties and the corresponding
endo and exothermic peaks were obtained at 438 and 536 °C in
DTA, and after 746 °C the residue of 16.17% left corresponds to
nickel sulfide (Figs. 1–3).
6. Results and discussion
An aqueous solution of the ligand ethylenediammonium-pyri-
dine-4-carbonyl-hydrazine carbodithioate [(H2en)(pchc)2] reacts
with NiCl2Á6H2O and yields [H2en][Ni(pchc)2] (1). The ligand 1-phe-
nyl-3 pyridin-2-yl-isothiourea (H2ppith) on reaction with Ni(OAc)2-
Á4H2O yields [Ni(Hppith)2] (2) whereas the ligand potassium 4-(2-
methoxyphenyl)piperazine-1-carbodithioate [K+(mppcdt)À] reacts
with Ni(OAc)2Á4H2O and forms [Ni(mppcdt)2] (3). Usually the potas-
sium salt of acid hydrazides carbodithioate cyclize during complex-
ation in the presence of metal ion and ethylenediamine and form
octahedral complexes of oxadiazole/thiadiazole, but in the present
case due to the presence of ethylenediammonium salt of pyridine-
4-carbonyl-hydrazine carbodithioate in the solution, the metal ion
forms the complex anion with two moles of pyridine-4-carbonyl-
hydrazine carbodithioate and ethylenediammonium is present as
a cation in the crystal structure of the complex. The ligands [(H2-
en)(pchc)2], H2ppith, [K+(mppcdt)À] and their complexes 1, 2 and
3 are stable towards air and moisture and melt at 557, 455, 458,
>633, 493 and 521 K, respectively. The Schemes 1–3 depict the for-
mation of the complexes from the ligands [(H2en)(pchc)2], H2ppith
and [K+(mppcdt)À]. All the ligands are soluble in methanol and
Fig. 4. ORTEP diagram of [H2en][Ni(pchc)2] (1).
ethanol while complexes 1, 2 and 3 are soluble in DMF and DMSO.
The TG and DTA curves show that all the three complexes are stable
up to 190, 198, 261 °C (according to the first weight loss). There was
a slight weight gain of 1% in complexes 2 and 3 and four-step
decompositions were observed for all the complexes.
6.1. IR spectra
The IR spectrum of the ligand ethylenediammonium-pyridine-
4-carbonyl-hydrazine carbodithioate [(H2en)(pchc)2] shows
absorptions due to the stretching modes of NH 3250, 3120; C@O
1622; C@S 904 and N–N 1003 cmÀ1. The IR spectrum of [H2-
en][Ni(pchc)2] (1) shows two bands at 3245 and 3116 for
of [H2en]2+ and the ligand moiety. The presence of one
(NH) band
indicates that only one hydrazinic hydrogen is present in the
complex. Two new bands for (Ni–N) and (Ni–S) appear at 503
m(NH)
m
m
m

P. Bharati et al. / Polyhedron 63 (2013) 156–166
161
and 407 cmÀ1 indicating bonding of Ni(II) with one hydrazinic
nitrogen and dithio sulfur in complex 1.
IR spectrum of 1-phenyl-3-pyridin-2-yl-isothiourea (H2ppith)
shows absorptions due to
mNH 3219; thioamide I 1598 and thioam-
ide IV 772 {mainly due to
m
(C–S)} and pyridine ring vibration
676 cmÀ1. The thioamide IV and pyridine ring vibrations suffer
negative shifts of 28 and 10 cmÀ1, respectively indicating bonding
through thiol sulfur and pyridine nitrogen in complex 2 [34]. The
appearance of two new bands for
m
(Ni–N) and
m
(Ni–S) at 589 and
406 cmÀ1 together with a negative shift of 28 cmÀ1 in
m
(C–S) indi-
cate that H2ppith is acting as bidentate ligand, bonding through
thiol sulfur and nitrogen of pyridine in complex 2.
The IR spectrum of the ligand potassium 4-(2-methoxy-
phenyl)piperazine-1-carbodithioate [K+(mppcdt)À] shows absorp-
tions due to the stretching modes of C@S 928 and C–N
1415 cmÀ1. The IR spectrum of the [Ni(mppcdt)2] (3) shows a neg-
ative shift of 137 cmÀ1 in the
m(C–S) band due to delocalization of
the negative charge on both the sulfur. A new band for
m(Ni–S) ap-
pears at 488 cmÀ1 indicating bonding of Ni(II) with dithio sulfur in
complex 3. The bonding through sulfur and nitrogen in complexes
1, 2 and 3 are further supported by X-ray data.
Fig. 5. Optimized structure of [H2en][Ni(pchc)2] (1).
6.2. 1H and 13C NMR spectra
The 1H NMR spectrum of [(H2en)(pchc)2] in DMSO-d6 shows sig-
nals at d 11.50, 10.80 and 4.45 ppm for the amide, thioamide and
+
NH3 protons, respectively. The CH2 protons appear as doublet at
4.05 ppm and aromatic protons appear as multiplet between d 8.0
and 9.06 ppm. The 13C NMR spectrum of [(H2en)(pchc)2] shows sig-
nals at d 170.51 and 163.94 ppm due to the >C@S and >C@O, carbons,
respectively. The aromatic carbons appear in the region of d 120.05–
151.03 ppm and methylene group of en appears at d 34.58 ppm. The
1H NMR spectrum of [H2en][Ni(pchc)2] in DMSO-d6 shows absence
of amide proton which suggests the deprotonation of the ligand
during formation of the complex. Two signals appear at d 10.08
+
and 4.59 ppm for thioamide and NH3 protons, respectively. The
methylene protons appear as doublet at 3.03 ppm and aromatic
protons as multiplet between d 7.37 and 8.07 ppm.
The 1H NMR spectrum of H2ppith in CDCl3 shows one signal at d
7.25 ppm for thioamide proton. Phenyl and pyridine ring protons
appear between d 6.67 and 7.82 ppm. The 13C NMR spectrum of H2-
ppith shows a signal at d 180.89 due to the >C@S carbon. The phe-
nyl and pyridine ring carbons appear in the region of d 118.22–
159.67 ppm. The 1H NMR spectrum of [Ni(Hppith)2] in CDCl3
shows a signal at d 13.66 ppm for NH proton. Phenyl and pyridine
ring protons appear between d 6.67 and 7.25 ppm. The 13C NMR
spectrum of [Ni(Hppith)2] shows absence of >C@S carbon signal
Fig. 6. Crystal packing of Ni(II) complex along a axis (en molecules shown as ball
and stick model).
Fig. 7. N–HÁ Á ÁS, N–HÁ Á ÁO and C–HÁ Á ÁS interactions between dithio sulfur and hydrogen of en molecule.

162
P. Bharati et al. / Polyhedron 63 (2013) 156–166
Table 1
Crystallographic data for [H2en][Ni(pchc)2] (1), Hppith, [Ni(ppith)2] (2) and [Ni(mppcdt)2] (3).
Compound
[H2en][Ni(pchc)2]
16H20N8Ni1O2S4
543.35
293(2)
Hppith
[Ni(ppith)2]
[Ni(mppcdt)2]
Empirical formula
Formula weight
T (K)
C
C12H11N3S
229.31
293(2)
C24H20N6Ni1S2
515.29
293(2)
C24H30N4NiO2S4
593.47
293(2)
K
(Mo K
a
) (Å)
0.71073
0.71073
0.71073
0.71073
Crystal system
Space group
a (Å)
b (Å)
c (Å)
orthorhombic
Icab
monoclinic
P21/n
5.8695(4)
22.4750(19)
8.7463(5)
90.00
98.813(7)
90.00
1140.16(14)
4
monoclinic
C2/c
14.165(2)
19.6634(10)
10.2438(13)
90.00
125.461(19)
90.00
2323.9(5)
4
triclinic
P1
ꢀ
12.6233(5)
19.0071(6)
18.6713(8)
90.00
90.00
90.00
4479.8(3)
8
1.611
6.9734(8)
8.2661(14)
11.5779(16)
81.973(13)
85.198(11)
87.513(12)
658.18(16)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (mg mÀ3
)
1.336
0.258
1.473
1.040
1.497
1.084
l
(mmÀ1
)
1.271
F (000)
2240
480.0
1064
310
Crystal size (mm3)
h Range (°)
0.35 Â 0.25 Â 0.18
2.14–28.90
À9 6 h 6 16
À24 6 k 6 24
À24 6 l 6 11
6393
0.30 Â 0.26 Â 0.24
2.97–29.20
À8 6 h 6 7
À30 6 k 6 27
À12 6 l 6 11
4841
0.30 Â 0.27 Â 0.24
3.20–28.80
À19 6 h 6 11
À26 6 k 6 15
À8 6 l 6 13
5338
0.36 Â 0.25 Â 0.17
3.29–29.00
À9 6 h 6 8
À10 6 k 6 11
À13 6 l 6 14
4838
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
2565
2565/0/165
0.916
0.0309, 0.0738
0.0508, 0.0775
0.370, À0.369
2592
2592/0/145
0.663
0.0487, 0.1353
0.0820, 0.1972
0.185, À0.202
3041
3041/36/150
1.040
0.0376, 0.0843
0.0548, 0.0948
0.391, À0.206
2965
2965/0/162
1.058
0.0397, 0.0772
0.0575, 0.0874
0.392, -0.299
Goodness-of-fit (GOF) on F2
b
Final R indices wR2 [I > 2
r
(I)](Rint
)
Final R indices (all data)R1a,wR2
b
Largest difference peak/hole (e ÅÀ3
)
a
R1
R2 = [
=
R
R
||Fo| À |Fc||
R|Fo|.
b
w(|F2o| À |F2c|)2/
R
w|F2o|2]1/2
.
Table 5
Table 2
Interatomic distances (Å) and angles (°) for [H2en][Ni(pchc)2] (1).
Hydrogen bonding parameters for H2ppith.
D–HÁ Á ÁA
D–H
(Å)
HÁ Á ÁA
DÁ Á ÁA
\D–HÁ Á ÁA
Sym
operator
Bond length (Å) Bond angles (°)
Expt.
Ni(1)–N(2) 1.916(17) 1.960
(Å)
(Å)
(°)
Theory
Expt.
Theory
N2–H2Á Á ÁS1
C4–H4Á Á ÁS1
0.86
0.93
2.56
2.82
3.40
3.63
166.70
146.98
1 À x,Ày,Àz
1 À x,Ày,Àz
N(2)–Ni(1)–N(2) 100.41(11) 100.39
Ni(1)–S(1)
S(1)–C(1)
N(3)–C(5)
N(2)–C(2)
S(2)–C(1)
O(1)–C(2)
2.154(6)
1.725(2)
1.331(3)
1.331(3)
1.695(2)
1.250(2)
2.240
1.754
1.344
1.349
1.700
1.255
N(2)–Ni(1)–S(1)
N(2)–Ni(1)–S(1)
S(1)–Ni(1)–S(1)
C(1)–S(1)–Ni(1)
C(2)–N(2)–Ni(1)
163.13(5)
86.16(5)
91.91(4)
98.04(8)
163.14
85.36
92.49
97.56
Table 6
Interatomic distances (Å) and angles (°) for [Ni(Hppith)2] (2).
133.03(14) 136.08
N(1)–N(2)–Ni(1) 114.11(14) 113.11
N(1)–C(1)–S(2) 122.3(17) 120.85
Bond length (Å)
Expt.
Ni(1)–N(1) 1.919(19) 1.965
Ni(1)–S(1)
S(1)–C(6)
N(1)–C(1)
N(3)–C(6)
C(5)–N(2)
N(2)–C(6)
Bond angles (°)
Theory
Expt.
Theory
N(1)–Ni(1)–N(1)
N(1)–Ni(1)–S(1)
S(1)–Ni(1)–S(1)
C(6)–S(1)–Ni(1)
C(5)–N(1)–Ni(1)
C(1)–N(1)–Ni(1)
Ni(1)–N(1)–C(1)
N(1)–C(1)–N(2)
92.06(11)
93.27
169.33
87.89
Table 3
Hydrogen bonding parameters for [H2en][Ni(pchc)2] (1).
2.163(7)
1.761(2)
1.359(3)
1.361(3)
1.373(3)
1.296(3)
2.229
1.775
1.364
1.369
1.362
1.306
170.04(6)
87.57(4)
99.05(8)
126.21(15) 125.72
115.51(15) 114.91
126.21(15) 125.72
97.25
D–HÁ Á ÁA
D–H HÁ Á ÁA DÁ Á ÁA \D–HÁ Á ÁA Sym
(Å)
(Å)
(Å)
(°)
operator
N1–H1NÁ Á ÁS2
C6–H6AÁ Á ÁS1
0.74
0.95
2.68
2.98
1.92
3.389 159.29
1/2 À x,1/2 + y,1 À z
1/2 À x,y,1/2 + z
x,1 À y,1/2 + z
3.76
2.75
139.95
160.62
123.4(2)
123.5
N1S–H1N3Á Á ÁO1 0.87
Table 7
Hydrogen bonding parameters for [Ni(Hppith)2] (2).
Table 4
Interatomic distances (Å) and angles (°) for H2ppith.
D–HÁ Á ÁA
D–H
(Å)
HÁ Á ÁA
DÁ Á ÁA
\D–HÁ Á ÁA
Sym
operator
(Å)
(Å)
(°)
Bond length (Å)
Bond angles (°)
N3–H3Á Á ÁS1
C8–H8Á Á ÁS1
0.86
0.93
2.78
2.90
3.54
3.71
147.40
145.77
1 À x,Ày,Àz
X,Ày,1/2 + z
S(1)–C(6)
N(2)–C(6)
N(2)–C(5)
N(3)–C(6)
N(3)–C(7)
C(5)–N(1)
1.684(3)
1.366(4)
1.407(4)
1.331(4)
1.423(4)
1.319(4)
C(6)–N(2)–C(5)
C(6)–N(3)–C(7)
N(1)–C(5)–N(2)
N(1)–C(5)–C(4)
N(2)–C(5)–C(4)
N(3)–C(6)–N(2)
N(3)–C(6)–S(1)
129.6(3)
125.9(3)
118.8(3)
123.2(3)
118.0(3)
117.0(3)
124.5(2)
at d 180.89 due to complexation. The phenyl and pyridine ring
carbons appear in the region of d 118.57–148.70 ppm. The 1H
NMR spectrum of [K+(mppcdt)À] in DMSO-d6 shows signals at d

P. Bharati et al. / Polyhedron 63 (2013) 156–166
163
Table 8
Interatomic distances (Å) and angles (°) for [Ni(mppcdt)2] (3).
Bond length (Å)
Bond angles (°)
S(1)–Ni(1)
S(2)–Ni(1)
S(1)–C(1)
S(2)–C(1)
N(1)–C(1)
2.205(7)
2.194(7)
1.716(2)
1.708(2)
1.320(3)
C(1)–S(2)–Ni(1)
C(1)–S(1)–Ni(1)
S(2)–Ni(1)–S(1)
S(2)–Ni(1)–S(1)
S(2)–C(1)–S(1)
N(1)–C(1)–S(1)
85.04(8)
84.52(8)
79.61(3)
100.39(3)
110.72(14)
124.75(19)
Table 9
Hydrogen bonding parameters for [Ni(mppcdt)2] (3).
Fig. 8. ORTEP diagram of H2ppith with atomic numbering scheme at 30% probability
level.
D–HÁ Á ÁA
D–H
(Å)
HÁ Á ÁA
DÁ Á ÁA
\D–HÁ Á ÁA
(°)
Sym
operator
(Å)
(Å)
C8–
0.95
2.97
3.51
116.88
x,y,1 + z
H8AÁ Á ÁS2
3.88 ppm for methyl protons and at 3.08–3.27 ppm for CH2 pro-
tons. The aromatic protons appear as multiplet between d 6.85
and 7.25 ppm. The 13C NMR spectrum of [K+(mppcdt)À] shows sig-
nals at d 209.56 and 152.05 ppm due to the >C@S and >C–N, car-
bons, respectively. The CH3 and CH2 carbons are observed at d
55.39 ppm and in the region of d 44.65–50.73 ppm, respectively
while those of aromatic carbons in the region of d 120.96–
140.56 ppm. The 1H NMR spectrum of the complex [Ni(mppcdt)2]
(3) in CDCl3 shows a signal at d 3.11 ppm for the methyl protons.
The methylene protons are observed in 3.35–3.96 ppm region
while aromatic protons appear as multiplet between d 6.90 and
7.25 ppm. The 13C NMR spectrum of [Ni(mppcdt)2] shows a signal
at d 187.78 ppm which is upfield as compared to the ligand due to
delocalization of >C@S carbon in the complex. The CH3 carbon ap-
pears at d 69.59 ppm, CH2 carbons in the region of d 44.33–
51.40 ppm and the aromatic carbons in the region of d 111.51–
124.18 ppm.
Fig. 9. N–HÁ Á ÁS and C–HÁ Á ÁS interactions between thiol sulfur and hydrogen of
thiourea along a axis.
6.3.1. Crystal structure description of [H2en][Ni(pchc)2] (1)
Fig. 4 shows the ORTEP diagram of the complex [H2en][Ni(pchc)2]
(1) together with the atom numbering scheme. The crystallographic
data and structural refinement details related to the complex are gi-
ven in Table 1. The complex has a distorted square-planar geometry
containing a pair of pyridine-4-carbonyl-hydrazinecarbodithioate
ligand coordinated to Ni(II) ion via dithiolato sulfur and hydrazinic
nitrogen forming two five membered CSN2Ni chelate rings around
the metal. In the complex, the crystallographic asymmetric unit
consists of an anion [Ni(pchc)2]2À and a cation [H2en]2+ (protonated
ethylenediamine) held through hydrogen bonding. Selected bond
distances and bond angles for the complex 1 are compiled in Table 2
and hydrogen bonding parameters in Table 3. The C@O bond length
6.3. Electronic spectra and magnetic moments
[H2en][Ni(pchc)2] (1), [Ni(Hppith)2] (2) and [Ni(mppcdt)2] (3)
are diamagnetic in nature suggesting the presence of Ni(II) in
low spin square-planar geometry. The UV–Vis spectrum of com-
plex 1 shows a band at 11450 cmÀ1 assigned to the 2A1g ? 2B1g
(m1) transition, the corresponding computed value has been found
to be 12276 cmÀ1 [35]. Complexes 2 and 3 show two high energy
bands at 33550, 38160 cmÀ1 and 30674, 25380 cmÀ1 due to charge
transfer/intraligand transitions.
Fig. 10. ORTEP plot of [Ni(Hppith)2] (2) with atomic numbering scheme at 30% probability level.

164
P. Bharati et al. / Polyhedron 63 (2013) 156–166
Fig. 11. Optimized structure of [Ni(Hppith)2] (2).
Fig. 12. Showing N–HÁ Á ÁS and C–HÁ Á ÁS interactions forming a linear chain structure in complex 2.
[1.249(3) Å] is purely a double bond which remains uncoordinated
but takes part in the formation of supramolecular architecture
through hydrogen bonding. The C1–S1and C1–S2 bond distances
of 1.725 (2) and 1.695 (2) Å, respectively suggest that they are inter-
mediate between single and double bond [36]. The complex may be
described to have a distorted square planar geometry with the li-
gand–metal–ligand bite angle varying between 86.16(5) [N(2)–
Ni(1)–S(1)] and 91.91(4) [S(1)–Ni–S(1)] in the chelate rings. Both
five membered chelate rings are essentially planar. The average
bond lengths of N2–N1 = 1.400, N1–C1 = 1.316, C1–S2 = 1.695,
C1–S1 = 1.725 Å, suggest considerable delocalization of charge in
the chelate ring [37]. The dihedral angles formed between the che-
late ring and the pyridine ring of the same ligand bonded to Ni(II) is
found to be 24.79° which suggests that the two rings are not copla-
nar but tilted. To get clear picture of binding site and geometry we
have performed geometry optimization of the complex
[H2en][Ni(pchc)2] (1) at B3LYP density functional theory level
(Fig. 5). The computed optimized structure of complex (1) corrobo-
rates geometrical parameters obtained from crystal structure anal-
ysis (see Table 2). The above conclusions are therefore strongly
supported by the present theoretical predictions.
carbonyl oxygen and dithiolato sulfur in which [H2en]2+ acts as a
linker between two units of the complex in the development of
supramolecular architecture. A view of the crystal packing of com-
plex 1 along b axis shows that the arrangement of two [H2en]2+ is
such that it forms a cavity by involvement in N–HÁ Á ÁO and N–HÁ Á ÁS
hydrogen bonding. Furthermore, the crystal packing shows that
both sulfur atoms of each molecule in every row are arranged in
such a way that they face each other. In the crystal of 1, the mole-
cules are stabilized by N–HÁ Á ÁS hydrogen bonding involving the
hydrogen of [H2en]2+ and dithio sulfur. In addition, the crystal
structure of complex 1 is further stabilized by the C–HÁ Á ÁS intermo-
lecular interactions occurring between the hydrogen of [H2en]2+
and dithio sulfur (Fig. 7). The values found for O–H, NÁ Á ÁH, \O–
HÁ Á ÁN and N–H, SÁ Á ÁH, \N–HÁ Á ÁS are close to the bond distances
and bond angles reported earlier [38,39].
6.3.2. Crystal structure description of H2ppith
The crystallographic data and structural refinement details are
given in Table 1 and selected bond distances and bond angles in Ta-
ble 4. Hydrogen bonding parameters of the ligand are listed in Ta-
ble 5. Fig. 8 shows the ORTEP diagram of H2ppith with the atom
numbering scheme. The C–S bond distance of 1.684(3) Å (Table 4)
in H2ppith agrees well with those in other related compounds for a
C@S double bond. The structure of H2ppith is stabilized by inter-
molecular N–HÁ Á ÁS hydrogen bonding occurring between thioam-
ide hydrogen and sulfur atom of other nearby molecule of the
ligand. In addition, the crystal structure is further stabilized by
The crystal packing of the complex 1 shows N–HÁ Á ÁO intramo-
lecular hydrogen bonding (distance 2.75 Å) occurring between
the carbonyl oxygen and hydrogen of [H2en]2+ leading to a wave
like arrangement. The crystal packing of Ni(II) complex along a axis
(Fig. 6) is mainly determined by intermolecular hydrogen bonding
formed between CH2 and NH3 hydrogen of protonated en with

P. Bharati et al. / Polyhedron 63 (2013) 156–166
165
Fig. 13. ORTEP diagram of [Ni(mthppzcdt)2] (3) with atomic numbering scheme at 30% probability level.
Fig. 14. C–HÁ Á Áp stacking and relative shift between piperazine ring hydrogen and phenyl ring centroids in complex 3.
Fig. 15. C–HÁ Á ÁS interactions between dithio sulfur and hydrogen of phenyl ring along b axis in complex 3.
C–HÁ Á ÁS hydrogen bonding between the CH hydrogen of pyridyl
data (see Table 6, Fig. 11). The crystal structure is stabilised via
C–HÁ Á ÁS and N–HÁ Á ÁS hydrogen bonding (Fig. 12).
ring and sulfur atom of other molecule of the ligand (Fig. 9).
6.3.3. Crystal structure description of [Ni(Hppith)2] (2)
6.3.4. Crystal structure description of [Ni(mppcdt)2] (3)
Fig. 10 shows the ORTEP diagram of [Ni(Hppith)2] (2) together
with the atom numbering scheme. The crystallographic data and
structural refinement details are given in Table 1 and selected bond
distances and bond angles are presented in Table 6, along with the-
oretically predicted data at B3LYP level of theory. The hydrogen
bonding parameters of complex 2 are listed in Table 7. Ni(II) ion
has a distorted square-planar coordination and possesses an NiN2-
S2 environment by two nitrogen and two sulfur atoms, from the
two units of thiourea ligand. The dihedral angle between the che-
late ring and phenyl ring is 28.86°. The coordination bond dis-
tances of thiourea moiety Ni(1)–S(1), 2.163(7) Å and Ni(1)–N(1),
1.919(19) Å are same as those of the other Ni(1)–S(1)# and
Ni(1)–N(1)# (Table 6). The C–S bond distance of 1.761 (2) Å is
intermediate between single C–S (1.82 Å) and double C@S
(1.56 Å) bond distances. The structure of 2 adopts a distorted
square planar geometry with N(1)–Ni(1)–S(1) and N(1)–Ni(1)–
S(1)# bond angles of 170.04(6)°. The other angles around the nick-
el(II) ion deviate slightly from the ideal value of 90° ranging from
87.57(4)° to 99.05(8)°. The geometry optimization of the complex
3 at B3LYP level of theory revealed that the bond distances and
bond angles are in very good agreement with the experimental
Fig. 13 shows the ORTEP diagram of [Ni(mppcdt)2] (3) together
with the atom numbering scheme. The crystallographic data and
structural refinement details are given in Table 1 and selected bond
distances and bond angles are presented in Table 8. The hydrogen
bonding parameters of complex 3 are listed in Table 9. Ni(II) ion
has a distorted square-planar coordination and possesses an NiS4
environment by four dithio sulfur, from the two units of the ligand.
The dihedral angle between the chelate ring and phenyl ring is
53.62°. The coordination bonds of dithio moiety Ni(1)–S(1),
2.205(7) Å and Ni(1)–S(2), 2.194(7) Å are same in both the unit
(Table 8). The C–S bond distance of 1.751 (10) Å is intermediate be-
tween single C–S (1.82 Å) and double C@S (1.56 Å) bond distances
[40]. The complex 3 adopts a distorted square planar geometry
with S(2)–Ni(1)–S(2) and S(1)–Ni(1)–S(1) bond angles of
180.00(2)° and 180.00 (2)°, respectively [41]. The other angles of
36.61 (3)° around the nickel(II) atom deviate slightly from the ideal
value of 90°. The crystal structure of 3 is stabilised via C–HÁ Á ÁS
hydrogen bonding occurring between hydrogen of methoxy phenyl
ring and dithio sulfur. In addition, the structure is further stabilized
by C–HÁ Á Á
p interactions between phenyl ring and hydrogen of
piperazine ring. The phenyl ring and hydrogen of piperazine ring

166
P. Bharati et al. / Polyhedron 63 (2013) 156–166
(c) T.I. Doukov, T.M. Iverson, J. Seravalli, S.W. Ragsdale, C.L. Drennan, Science
298 (2002) 567;
(d) J. Wuerges, J.W. Lee, Y.I. Yim, H.S. Yim, S.O. Kang, K.D. Carugo, Proc. Natl.
Acad. Sci. USA 101 (2004) 8569.
are almost parallel (\ABC = 62.48°) but displaced with respect to
each other. The displacement as measured by the angle formed be-
tween the ring centroids A and the normal BC of piperazine ring
plane was found to be 1.386 Å with a displacement angle of
27.41° and the ring centroids contacts (CgÁ Á ÁH) of 3.010 Å is well
within the reported range [42] (Figs. 14 and 15).
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7. Conclusion
Three new ligands ethylenediammonium-pyridine-4-carbonyl-
hydrazine carbodithioate [(H2en)(pchc)2], 1-phenyl-3-pyridin-2-
yl-isothiourea
(H2ppith)
and
potassium
4-(2-methoxy-
phenyl)piperazine-1-carbodithioate [K+(mppcdt)À] and their dia-
magnetic and square planar complexes [H2en][Ni(pchc)2] (1),
[Ni(Hppith)2] (2) and [Ni(mppcdt)2] (3) have been synthesized
and characterized by various physicochemical methods. The crys-
tal structure of the complex 1 shows Ni(N,S)2 bonding and is stabi-
lized through weak intermolecular N–HÁ Á ÁS and C–HÁ Á ÁS
interactions between dithio sulfur and hydrogen of [H2en]2+ and
N–HÁ Á ÁO interactions between carbonyl oxygen and hydrogen of
doubly protonated en and C–HÁ Á ÁO interactions between carbonyl
oxygen and hydrogen of [H2en]2+. The crystal structure of complex
2 is stabilized by weak intermolecular N–HÁ Á ÁS interactions be-
tween sulfur of thiol group and hydrogens of thioamide molecule
as well as C–HÁ Á ÁS interactions between sulfur of thiol group and
hydrogens of phenyl ring. The geometries of the complexes are
optimized at B3LYP density functional theory level and are found
to be corroborated with the experimental data. The crystal struc-
ture of complex 3 is stabilized by weak intermolecular C–HÁ Á ÁS
interactions between sulfur of dithio group and hydrogen of phe-
nyl ring. The TG and DTA studies show that complexes 2 and 3
show similar mode of degradation and produce metal sulfide
whereas in complex 1 the last residue is metal oxide. Only complex
2 melt during the course of heating whereas the rest of the com-
plexes decompose without melting.
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One of the authors Dr. M.K. Bharty is thankful to the Depart-
ment of Science and Technology, New Delhi, India for the award
of a Young Scientist Project (No. SR/FT/CS-63/2011).
Appendix A. Supplementary data
CCDC 840589, 903821, 900638 and 929710 contains the sup-
plementary crystallographic data for [H2en][Ni(pchc)2] (1),
[H2ppith], [Ni(Hppith)2] (2) and [Ni(mppcdt)2] (3). These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk.
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