Nickel(II) and copper(II) complexes of 5-(4-methoxy-phenyl) [1,3,4]-oxadiazole-2-thione: Synthesis and X-ray characterization

Article abstract of DOI:10.1016/j.molstruc.2009.08.006

Two new mixed ligand complexes [Ni(en)₂(mot)₂] (1) and [Cu(en)₂(mot)₂] (2) derived from potassium N′-(4-methoxy-benzoyl) dithiocarbazate [K⁺(H₂L)^-] containing en as the coligand

Full text of DOI:10.1016/j.molstruc.2009.08.006

Journal of Molecular Structure 936 (2009) 257–263
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Nickel(II) and copper(II) complexes of 5-(4-methoxy-phenyl)
[1,3,4]-oxadiazole-2-thione: Synthesis and X-ray characterization
a
a
a
b
N.K. Singh a, , S.K. Kushawaha , M.K. Bharty , Ram Dulare , R.J. Butcher
*
a Department of Chemistry, Banaras Hindu University, Varanas 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:
Received 26 June 2009
Received in revised form 2 August 2009
Accepted 6 August 2009
Available online 11 August 2009
Two new mixed ligand complexes [Ni(en)2(mot)ꢀ2] (1) and [Cu(en)2(mot)2] (2) derived from potassium
+
0
N -(4-methoxy-benzoyl) dithiocarbazate [K (H2L) ] containing en as the coligand have been synthesized.
[K+(H2L)ꢀ] undergoes cyclization in the presence of ethylenediamine and is converted to 5-(4-methoxy-
phenyl [1,3,4]-oxadiazole-2-thione (mot)ꢀ. [Ni(en)2(mot)2] and [Cu(en)2(mot)2] have been characterized
by various physicochemical techniques and single crystal X-ray. In [Ni(en)2(mot)2] and [Cu(en)2(mot)2]
the metal ion has MN6 core with six coordinate octahedral arrangement from four N atoms of two en
and two N atoms from two mot anions.
Keywords:
5-(4-Methoxy-phenyl) [1,3,4]-oxadiazole-
2-thione
Ó 2009 Elsevier B.V. All rights reserved.
Mixed ligand complexes
X-ray structure
Supramolecular architecture
1. Introduction
2. Results and discussion
N-aroyl dithiocarbazates and their salts can be converted to
1,3,4-oxadiazole-2-thiol/thione which exhibit relevant biological
properties and have a wide variety of applications, in both medi-
cine and agriculture [1]. Several methods have been used for the
synthesis of these compounds from acyclic precursors. Some of
them are oxidative cyclization of acyl hydrazone [2], acylthiourea
[3–5] and acylthiosemicarbazide [6–9]. The heterocyclic thiones
represent an important type of compounds in the field of coordina-
tion chemistry because of their potential multifunctional donor
sites, i.e., either exocyclic or endocyclic nitrogen [10]. The cycliza-
tion of 3-acyldithiocarbazate esters, N-aroyl dithiocarbazates and
their salts to the corresponding 1,3,4-oxadiazole in the presence
of a base is reported in the literature [11–15]. It is known that
the salts of N-aroyl dithiocarbazates can be converted to 1,3,4-oxa-
diazole-2-thiol in the presence of a base [13], it was thought
whether the N-aroyl dithiocarbazate bonded to a transition metal
can be converted to 1,3,4-oxadiazole-2-thione. Accordingly the
Cu(II) complex of 4-methoxy-benzoyl dithiocarbazate was reacted
with an excess of ethylenediamine and the results of this investiga-
tion is presented here.
A methanol solution of [Ni(en)2(NCS)2] on reaction with
[K+(H2L)ꢀ] yields [Ni(en)2(mot)2] (1). The reaction of [K+(H2L)ꢀ]
with CuCl2ꢁ2H2O gave a blue precipitate which dissolved in meth-
anolic solution of en on heating at 60 °C to form [Cu(en)2(mot)2]
(2). A simple scheme showing the syntheses of [K+(H2L)ꢀ] and
the complexes 1 and 2 are given below.
The complexes are air stable, non-hygroscopic shiny crystalline
solids, which are insoluble in common organic solvents but soluble
in dimethyl formamide (DMF) and dimethylsulfoxide (DMSO). The
complexes were fully characterized by magnetic susceptibility
measurements, IR, UV–vis and X-ray spectroscopies. Analytical
data of the complexes (recorded in Section 4) corroborated well
with their respective formulations. 1H NMR spectrum of
[K+(H2L)ꢀ] in DMSO-d6 shows signals at d 9.65 (2H, NH) and 3.50
(3H, AOCH3) ppm. The benzene ring protons appear as multiplet
between 7.0 and 7.7 ppm (m, 4H). The 13C NMR spectrum of
[K+(H2L)ꢀ] shows signals at d 178.90, 160.38 and 55.28 ppm which
are due to the C@S, C@O and OCH3 carbons, respectively. The IR
spectrum of [K+(H2L)ꢀ] in KBr is expected to give rise to character-
istic bands due to m(NH), v(C@O), v(NAN) and v(C@S) which occur
at 3246 and 3169; 1637, 1000 and 886 cmꢀ1, respectively. The
absorptions appearing in the region 3244–3122 cmꢀ1 due to NH
stretching vibrations of en are shifted to lower frequency than
* Corresponding author. Address: Department of Chemistry, Banaras Hindu
University, Varanas 221005, Uttar Pradesh, India. Tel.: +915426702452; fax:
+915422368127.
those encountered in the free en [16]. A negative shift in m(NH2)
of en and appearance of a new band due to MAN near 468–
E-mail address: singhnk_bhu@yahoo.com (N.K. Singh).
471 cmꢀ1 suggest formation of a chelate. The IR spectra of the
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.08.006

258
N.K. Singh et al. / Journal of Molecular Structure 936 (2009) 257–263
complexes are devoid of any peak due to v(NH) (hydrazinic)
(3246 cmꢀ1) which was present in the precursor [Cu(HL)2]. Addi-
tionally, v(C@O) (1637 cmꢀ1) disappeared and new peaks appeared
due to the endocyclic C@N and CAOAC at 1608–1585 and 1255–
1226 cmꢀ1, respectively, suggesting cyclization of the dithiocar-
bazate moiety. The IR data are thus consistent with the formation
of 1,3,4-oxadiazole moiety during complexation [17]. The magnetic
moment and electronic spectral data were used to determine the
geometry of the complexes. [Ni(en)2(mot)2] exhibits a magnetic
moment of 2.86 B.M. and shows a band at 17,860 cmꢀ1 which is
Table 1
Crystal data for (1) and (2).
1
2
3
Empirical formula
Formula weight
T (K)
C22H30N8NiO4S2
593.37
295(2)
C22H30CuN8O4S2
598.20
295(2)
considered to arise from the A2g(F) ? 3T1g(F)(v2) transition in an
octahedral geometry around Ni(II) [18]. [Cu(en)2(mot)2] shows a
magnetic moment of 2.01 B.M. and a broad band at 16400 cmꢀ1 as-
signed to the 2T2g ? 2Eg transition for an octahedral geometry
around Cu(II) [18].
k/Å
0.71073
0.71073
Monoclinic
P21/n
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
ꢀ
P1
8.1852
13.404
13.954
111.63
106.561
92.842
1343.5(5)
2
1.467
0.922
9.6756(4)
12.2074(4)
11.5411
90 0
Molecular structures of 1 and 2 were determined crystallo-
graphically. The details of data collection, structure solution and
refinement are listed in Table 1. The Ortep diagram of complex 1
and molecular structure of the complex 2 with atom numbering
scheme are shown in Figs. 1 and 5, respectively. The selected bond
lengths and angles are given in Tables 2 and 3. The single crystal X-
ray diffraction studies indicate that the ligand (motꢀ) adopts the
thione form in 1 and 2. The X-ray structure of complex 1 shows
the presence of two independent complexes in the asymmetric
unit and in each unit the Ni atom is on a center of inversion. The
X-ray crystal structures of both units of 1 show the presence of
two motꢀ as ligand coordinated to Ni(II) in a distorted octahedral
geometry (Fig. 1) having axial bond angles of 90.52(7)° and
87.66(8)° but equatorial bond angles of 82.75(8)° and 82.96(8)°,
respectively in units containing Ni(1) and Ni(2). The coordination
environment is fulfilled by two axial (mot)ꢀ ions at the trans posi-
tions, bonded through oxadiazole nitrogen atoms at the distances
a
(°)
b (°)
107.672(4)o
90 0
c
(°)
V (Å3)
1298.83(8)
2
1.530
Z
Dcalc/Mg mꢀ3
l
(mmꢀ1
)
1.047
Crystal size (mm)
0.53 ꢂ 0.41 ꢂ 0.34
0.57 ꢂ 0.39 ꢂ 0.35
Reflections collected
Independent reflections
Data/restrains/parameters
Goodness-of-fit
40498
24231
9076 (Rint = 0.0423)
9076/0/337
1.062
4428 (Rint = 0.0283)
4428/0/170
1.069
R factor [I > 2
r(I)]
0.0411
0.0291
wR2 [I > 2 (I)]
r
0.1053
0.0732
R factor (all data)
0.0851
0.0609
wR2 (all data)
0.1387
0.826, ꢀ0.465
0.0929
0.631, ꢀ0.241
Largest diff. peak/hole (e Åꢀ3
)
Fig. 1. Ortep plot of [Ni(en)2(mot)2] showing atomic numbering scheme with ellipsoid of 30% probability. Hydrogen atoms are omitted for clarity (symmetry code i = ꢀx,
ꢀy + 1, ꢀz + 1).
Table 2
Selected bond lengths (Å) and bond angles (°) for [Ni(en)2(mot)2].
Ni (1)
Ni (2)
Ni(1)AN(12A)
Ni(1)AN(1A)
Ni(1)AN(11A)
S(1A)AC(1A)
O(1A)AC(2A)
O(1A)AC(1A)
C(1A)AN(1A)
N(11A)#1ANi(1)AN(1A)#1
N(11A)ANi(1)AN(1A)#1
N(12A)#1ANi(1)AN(1A)#1
N(12A)ANi(1)AN(1A)#1
N(12A)#1ANi(1)AN(11A)#1
N(12A)ANi(1)AN(11A)#1
2.144(2)
2.107(17)
2.084(18)
1.699(2)
1.363(2)
1.392(2)
1.312(3)
89.33(7)
90.67(7)
90.52(7)
89.48(7)
82.75(8)
97.25(8)
Ni(2)AN(12B)
Ni(2)AN(1B)
Ni(2)AN(11B)
S(1B)AC(1B)
O(1B)AC(2B)
O(1B)AC(1B)
C(1B)AN(1B)
N(11B)#2ANi(2)AN(1B)#2
N(11B)ANi(2)AN(1B)#2
N(12B)#2ANi(2)AN(1B)#2
N(12B)ANi(2)AN(1B)#2
N(12B)#2ANi(2)AN(11B)#2
N(12B)ANi(2)AN(11B)#2
2.092(18)
2.156(2)
2.102(2)
1.685(2)
1.366(3)
1.399(3)
1.320(3)
90.59(9)
89.41(9)
87.66(8)
92.34(8)
82.96(8)
97.04(8)
#1, ꢀx, ꢀy + 1, ꢀz + 1; #2, ꢀx ꢀ 1, ꢀy + 2, ꢀz + 1.

N.K. Singh et al. / Journal of Molecular Structure 936 (2009) 257–263
259
Table 3
The two NiAN(en) distances in both the units are different. The
Ni(1)AN(12A) bond length is larger than Ni(2)ANi(12B) while
Ni(1)AN(11A) is shorter than Ni(2)AN(11B). Due to stronger
Ni(1)AN(1A) (Noxa) bonding, the C(1A)AS(1A) bond length is long-
er in unit 1 as compared to unit 2. The binding of Ni(II) with en in-
volves the formation of a five membered chelate ring with bite
angle of 82.75(8)° and represents a major distortion from an octa-
hedral geometry. The geometry and bonding parameters within
the en molecule agree with those of related compounds, e.g., Ni
[trans (L)2 (en)2] {L = N-(5-chlorouracilato)} [19], isothiocyanato
[20] and salicylato [21]. Almost planar (motꢀ) ligands in complex
1 bonded to Ni(II) and designated as Ni(1)AN(1A)#1@Ni(1)AN(1A)
2.107(17) and Ni(2)AN(1B)#1@Ni(2)AN(1B) = 2.156(2) Å are com-
parable to those of ca. 2.1090–2.1150 Å encountered in the related
compound [Ni(en)2(3-pyt)2] (3-pyt)ꢀ = 5-(3-pyridyl)-1,3,4-oxadi-
azole-2-thione [10]. The two phenyl rings in the Ni(2) complex
are almost parallel (\BCA = 88.48°) having centroid to centroid
(Cgꢁ ꢁ ꢁCg) separation of 3.621 Å but displaced with respect to each
other. The displacement as measured by the angle formed between
the ring centroids AC and the ring normal BC to the phenyl plane
(Fig. 3) is found to be 0.227 Å with a displacement angle of
Selected bond lengths (Å) and bond angles (°) for [Cu(en)2(mot)2].
CuAN(1)
CuAN(11)
CuAN(12)
O(1)AC(1)
C(1)AN(1)
N(1)AN(2)
C(1)AS
2.485(12)
2.012(12)
2.032(12)
1.383(17)
1.307(2)
N(11)ACuAN(12)
N(11)ACuAN(12)#1
N(11)ACuAN(1)
N(11)#1ACuAN(1)
N(12)ACuAN(1)
84.73(5)
95.27(5)
88.16(5)
91.84(5)
93.41(5)
86.59(5)
1.403(19)
1.697(16)
N(12)#1ACuAN(1)
#1, ꢀx + 1, ꢀy, ꢀz.
Table 4
Hydrogen bonding parameters for Ni(en)2(mot)2 [Å and °].
DAH. . .A
d(DAH)
d(H. . .A)
d(D. . .A)
\(DHA)
N(11A)AH(11E). . .S(1A)#1
N(11A)AH(11F). . .N(2A
N(11A)AH(11F). . .S(1B)
N(12A)AH(12E). . .S(1A)
N(12A)AH(12F). . .N(2A)#1
N(11B)AH(11G). . .S(1B)
N(11B)AH(11H). . .S(1A)#3
N(12B)AH(12G). . .S(1B)#2
N(12B)AH(12H). . .N(2B)
0.90
0.90
0.90
0.90
0.90
0.90
0.90
0.90
0.90
2.60
2.51
2.87
2.97
2.70
3.01
2.91
2.67
2.45
3.3561(19)
3.107(3)
3.614(2)
3.702(2)
3.254(3)
3.711(2)
3.535(2)
3.457(2)
3.013(3)
141.8
123.9
140.6
139.3
120.9
136.0
128.0
147.1
120.5
21.36° which is well within the reported values for
p p interac-
ꢁ ꢁ ꢁ
tion [22]. Weak intermolecular NAHꢁ ꢁ ꢁN interaction between
oxadiazole nitrogen and NH2 hydrogen atoms of en molecule and
NAHꢁ ꢁ ꢁS interactions (Table 4) between thione sulfur and CH2
and NH2 hydrogens of en molecule stabilize the structure of the
#1, ꢀx, ꢀy + 1, ꢀz + 1; #2, ꢀx ꢀ 1, ꢀy + 2, ꢀz + 1; #3, ꢀx ꢀ 1, ꢀy + 1, ꢀz + 1.
of 2.107 Å Ni(1) and 2.156 Å Ni(2), and four equatorial sites are
occupied by the two bidentate N,N-ethylenediamine. The bond
length of Ni(1)AN(1A) (Noxa) is shorter than the corresponding
bond length in Ni(2) showing stronger bonds in Ni(1) than Ni(2).
compound
1
(Fig. 2). The two Nꢁ ꢁ ꢁS distances of 3.535(2)
and 3.457(2) Å (Table 4) are close to the mean Nꢁ ꢁ ꢁS distance for
NHꢁ ꢁ ꢁS hydrogen bond reported earlier [23]. The monomeric
Fig. 2. Perspective view of the crystal packing of [Ni(en)2(mot)2] along the a axis showing NAHꢁ ꢁ ꢁS intermolecular hydrogen bonding.

260
N.K. Singh et al. / Journal of Molecular Structure 936 (2009) 257–263
[Ni(en)2(mot)2] units are held together through NAHꢁ ꢁ ꢁS/N inter-
molecular hydrogen bonding (Table 4). The arrangement of the
monomeric units in the three dimensional architecture along a axis
provides a supramolecular network (Fig. 2). In addition, there are
weak CAHꢁ ꢁ ꢁO interactions between oxadiazole oxygen and CH2
hydrogen of en and between methoxy oxygen and phenyl ring
hydrogen which lead to the formation of chain like pattern in
various layers of the molecular arrangement (Fig. 4).
The molecular structure of 2 shows that in the centrosymmetric
unit of [Cu(en)2(mot)2] the metal ion is six coordinate, bonding
through four nitrogens of en and two oxadiazole nitrogens. The
separation between two planes formed by the oxadiazole rings in
the same complex is 1.525 Å. The dihedral angle between the plane
formed by the oxadiazole and phenyl ring is 21.54°. The phenyl
ring and oxadiazole ring are almost parallel (\CBA = 86.41) having
a centroid–centroid (Cg. . .Cg) separation of 3.846 Å but displaced
with respect to each other. The displacement as measured by the
angle formed between the ring centroids AB and the ring normal
BC to the oxadiazole plane (Fig. 6) is found to be 0.092 Å with a dis-
placement angle of 16.89° which is well within the range [22]. In
addition, the monomeric units of [Cu(en)2(mot)2] are held together
through NAHꢁ ꢁ ꢁS intermolecular and NAHꢁ ꢁ ꢁN intramolecular
hydrogen bonding (Table 5), leading to the formation of metal–or-
ganic framework along a axis (Fig. 7). The shortest intra and inter
chain Cuꢁ ꢁ ꢁCu separations are found to be 11.541 and 8.776 Å,
respectively (Fig. 7). In the solid state the complex is stabilized
via intermolecular NAHꢁ ꢁ ꢁS interaction between thione sulfur
and NH2 hydrogen atoms of en and CAHꢁ ꢁ ꢁS interaction between
thione sulfur and methoxy hydrogen of a nearby molecule. In addi-
tion there are three intramolecular XAHꢁ ꢁ ꢁH (X = N, C) hydrogen
bonding formed between oxadiazole nitrogen and hydrogen of
NH2, CH2 and phenyl ring. The above observed
intermolecular and intramolecular hydrogen bonding have
p p interactions,
ꢁ ꢁ ꢁ
stabilized the molecular crystal packing giving a supramolecular
Fig. 3.
p–p stacking and relative shift between two phenyl ring centroids in complex 1 containing Ni(2).
Fig. 4. Network structure of [Ni(en)2(mot)2] down the a axis forming layers of chain via CAHꢁ ꢁ ꢁO interactions.

N.K. Singh et al. / Journal of Molecular Structure 936 (2009) 257–263
261
Fig. 5. Molecular structure of [Cu(en)2(mot)2] with the atomic labeling scheme. Hydrogen atoms are omitted for clarity. (Symmetry code i = ꢀx + 1, ꢀy, ꢀz).
Fig. 6.
p–p stacking and relative shift between phenyl ring and oxadiazole ring centroids in complex 2.
easy and facile route to synthesize mixed ligand complexes of
1,3,4-oxadiazole-2-thione.
Table 5
Hydrogen bonding parameters for Cu(en)2(mot)2 [Å and °].
DAH. . .A
d(DAH)
d(H. . .A)
d(D. . .A)
\(DHA)
4. Experimental
N(11)AH(11C). . .S#1
N(11)AH(11D). . .N(2)
N(12)AH(12C). . .O(2)#2
N(12)AH(12D). . .S#3
0.90
0.90
0.90
0.90
2.70
2.56
2.18
2.75
3.5058(14)
3.0661(18)
3.0483(18)
3.6171(13)
149.5
116.0
163.2
161.6
4.1. General methods
All reagents were of AR grade and used without further purifi-
cation. Methyl 4-methoxy benzoate (Sigma–Aldrich), CS2 (SD Fine
Chemicals) and KOH (Qualigens) were used as received. 4-Methoxy
benzoic acid hydrazide and [Ni(en)2(SCN)2] were prepared by re-
ported methods [24]. All the synthetic manipulations were carried
out in open atmosphere and at room temperature. The solvents
were dried and distilled before use following the standard proce-
dure. The complexes were analyzed for their metal content, after
decomposition with a mixture of conc. HNO3 and HCl, followed
by conc. H2SO4 [25]. 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 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 cmꢀ1 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.
#1, ꢀx + 1, ꢀy, ꢀz; #2, ꢀx + 1, ꢀy, ꢀz + 1; #3, x ꢀ 1/2, ꢀy + 1/2, z ꢀ 1/2.
network. The axial and equatorial CuAN distances for the complex
are 2.4858(12) and 2.03225(12) Å, respectively, whereas the
respective distances for the nickel complex are 2.0847(18) and
2.1072(17) Å. This suggests an axially distorted octahedral geome-
try for the copper complex due to Jahn–Teller distortion whereas
an almost regular octahedral geometry is found in the case of the
nickel complex. The soft donor site of the ligand motꢀ shows no
tendency for coordination with Ni(II) and Cu(II) as they are hard
metal ions and prefer to bind with comparatively hard nitrogen
site of the ligand.
3. Conclusion
Two new mixed ligand complexes [Ni(en)2(mot)2] (1) and
[Cu(en)2(mot)2] (2) with 5-(4-methoxy-phenyl) [1,3,4]-oxadiaz-
ole-2-thione have been prepared and their structures investigated.
During the formation of these complexes the metal-bound N-(4-
methoxy benzoyl dithiocarbazate is cyclized to 5-(4-methoxy-phe-
nyl) [1,3,4]-oxadiazole-2-thione in the presence of ethylenedia-
mine via desulfurisation. This strategy has been found to be an
4.1.1. Synthesis of [K+(H2L)ꢀ]
This compound was prepared by adding carbon disulfide
(1.2 mL, 20 mmol) drop wise to a mixed solution of 4-methoxy
benzoic acid hydrazide (3.32 g, 20 mmol) and potassium hydroxide

262
N.K. Singh et al. / Journal of Molecular Structure 936 (2009) 257–263
Fig. 7. NAHꢁ ꢁ ꢁS hydrogen bonding and Cuꢁ ꢁ ꢁCu separation in the metal organic framework of [Cu(en)2(mot)2] along a axis.
(1.12 g, 20 mmol) in methanol (30 mL) and stirring the reaction
mixture for 2 h. The solid separated was filtered off, washed with
a mixture of ethanol–ether (10% v/v) and dried in vacuo. Yield
1.44 g, 55%. m.p.: 245 °C. Anal. Calc. for C9H9O2N2S2K (280.40): C,
38.60; H, 3.15; N, 10.11; S, 22.60. Found: C, 38.57; H, 3.10; N,
4.3. Synthesis of [Cu(en)2(mot)2] (2)
A methanolic solution (10 ml) of CuCl2ꢁ2H2O (0.17 g, 1 mmol)
was stirred with an aqueous methanolic solution (50:50 v/v)
(10 mL) of [K+(H2L)ꢀ] (0.56 g, 2 mmol) in a 1:2 M ratio, the precip-
10.00; S, 22.85%. IR data (
m
cmꢀ1, KBr):
(C@S) 886. 1H NMR (DMSO-d6;
m(NH) 3246 m, 3169 m;
itate obtained was filtered and washed with a mixture of
m
(C@O) 1637 s; (NAN) 1000 m;
m
m
H2OAMeOH (50:50 v/v). This precipitate was suspended in
MeOHAH2O to which an excess (0.30 mL, 4 mmol) of ethylenedia-
mine (en) was added and the mixture was heated at 60 °C until to-
tal dissolution of the complex was observed. The resulting solution
was filtered off and kept for 15 days where upon dark brown crys-
tals suitable for XRD were obtained. Anal. Calc. for C22H30N8O4S2Cu
(598.20): C, 44.25; H, 5.02; N, 10.55; S, 10.80; Cu, 10.48. Found: C,
d ppm): 3.80 (s, 3H, OCH3), 7.0–7.7 (d, 4H, C6H5), 9.65 (m, 2H,
NH). 13C NMR (DMSO-d6: d ppm) 178.90 (C@S), 160.38 (C@O),
117.87 (C1), 113.67 (C2), 126.64 (C3), 128.95 (C4), 55.28 (OCH3).
Based on the above physicochemical studies the tentative structure
of the ligand is depicted in Scheme 1.
44.17; H, 5.05; N, 10.71; Cu, 10.62%.
l
B = 2.01 B.M., m.p.: 145 °C. IR
(C@N) 1585 m;
(C@S) 901; (CuAN) 468.
4.2. Synthesis of [Ni(en)2(mot)2] (1)
data ( (NH) 3244 m; 3122 m; m
m
cmꢀ1, KBr):
m
m
(CAOAC) 1226 m;
m
(NAN) 1039 s;
m
m
A
methanolic solution (10 mL) of [Ni(en)2(NCS)2] (0.23 g,
UV–vis [kmax, cmꢀ1 (acetonitrile)]: 16,400.
1 mmol) was mixed with an aqueous methanolic solution (50:50
v/v) (10 mL) of [K+(H2L)ꢀ] (0.56 g, 2 mmol) and the reaction mix-
ture was filtered. The filtrate was kept for crystallization; where
upon orange crystals of the complex 1 were obtained after 10 days.
Anal. Calc. for C22H30N8O4S2Ni (593.37): C, 44.69; H, 5.05; N, 18.75;
S, 10.95; Ni, 9.82. Found: C, 44.53; H, 5.09; N, 18.80; S, 10.84; Ni,
4.4. X-ray crystallography
Crystals suitable for X-ray analyses of the complexes [Ni(en)2-
(mot)2] (1) and [Cu(en)2(mot)2] (2) were grown at room tempera-
ture. Preliminary examination and intensity data were collected
using Bruker three circle diffractometer equipped with a SMART
9.82% (9.90).
lB = 2.86 B.M., m.p.: 218 °C. IR data (m
cmꢀ1, KBr):
m
(NH) 3234 s;
m(C@N) 1608 s; m(CAOAC) 1255 s; m(NAN) 1072 s;
m(C@S) 977;
m
(NiAN) 471 s. UV–vis [kmax, cmꢀ1 (DMF)]: 17,850.
6000 CCD software using a graphite monochromatized Mo Ka
O
H
O
N
S-K+
NH2
N
H
CS2
MeOH
KOH
N
H
S
H3CO
H3CO
[K+(H2L)-]
[Ni(en)2(NCS)2]
CuCl2.2H2O
S
H2N
NH2
O
N
OCH3
en
M
N
O
N
Blue ppt
N
, 60 0
C
H2N
H3CO
NH2
S
M = Ni(II), Cu(II)
Scheme 1. Syntheses of the ligand and complexes.

N.K. Singh et al. / Journal of Molecular Structure 936 (2009) 257–263
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Acknowledgement
One of the authors (S.K. Kushawaha) is thankful to the Depart-
ment of Science and Technology, New Delhi, India for the award of
a Young Scientist Fellowship (No. SR/FTP/CS-35/2005).
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