Synthesis and structural characterization of Ni(II) complexes containing a heterocyclic NO donor ligand

Article abstract of DOI:10.1016/j.poly.2011.08.013

Five novel nickel(II) complexes have been successfully synthesized with a heterocyclic ligand, Opdac, [Ni(Opdac)₂]Cl₂ (1), [Ni(Opdac)₂(CH₃OH)₂]Br₂(CH ₃OH)₂ (2), [Ni(Opdac)₂]I₂ (3), [Ni(Opdac)₂NO₃]NO₃ (4) and [Ni(Opdac) ₂ClO₄]ClO₄ (5) where Opdac = 4-(1-H-1,3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-2-dihydro-3-H-pyrazol-3- one. All the complexes were characterized by elemental analysis, molar conductivity, CHN analysis, magnetic susceptibility measurements, spectroscopic studies and TG/DTA methods. In all the complexes, Opdac acts as a bidentate ligand coordinating to Ni(II) ion via the benzimidazole imine nitrogen and the pyrazolone oxygen atoms. The complexes 1 and 3 have a tetrahedral geometry while 2, 4 and 5 have an octahedral geometry around the Ni(II) center.

Full text of DOI:10.1016/j.poly.2011.08.013

Polyhedron 30 (2011) 2849–2855
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and structural characterization of Ni(II) complexes containing
a heterocyclic NO donor ligand
⇑
P.M. Vimal Kumar, P.K. Radhakrishnan
School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686560, Kerala, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Five novel nickel(II) complexes have been successfully synthesized with a heterocyclic ligand, Opdac,
[Ni(Opdac)2]Cl2 (1), [Ni(Opdac)2(CH3OH)2]Br2(CH3OH)2 (2), [Ni(Opdac)2]I2 (3), [Ni(Opdac)2NO3]NO3 (4)
and [Ni(Opdac)2ClO4]ClO4 (5) where Opdac = 4-(1-H-1,3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-
2-dihydro-3-H-pyrazol-3-one. All the complexes were characterized by elemental analysis, molar conduc-
tivity, CHN analysis, magnetic susceptibility measurements, spectroscopic studies and TG/DTA methods.
In all the complexes, Opdac acts as a bidentate ligand coordinating to Ni(II) ion via the benzimidazole
imine nitrogen and the pyrazolone oxygen atoms. The complexes 1 and 3 have a tetrahedral geometry
while 2, 4 and 5 have an octahedral geometry around the Ni(II) center.
Received 28 February 2011
Accepted 10 August 2011
Available online 26 August 2011
Keywords:
Ni(II) complexes
Schiff base
Spectra
Magnetism
Crystal structure
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental
The heterocyclic NO donor Schiff base ligands play an important
role in the development of coordination chemistry as they readily
form complexes with most of the transition metal ions [1–4]. The
synthesis, structure and properties of coordination complexes still
arouse considerable research interests because of their potential
applications in material science [5]. The Schiff base complexes of
transition metals have acquired a special significance in the do-
main of coordination chemistry because of their diverse range of
applications, such as in organic synthesis, photochemistry and
heterogeneous catalysis, drug design and as models of biological
systems [6–14]. Also the unsymmetrical Schiff bases are very
important as they can bind one, two or more metal centers, involv-
ing various coordination modes, and allow successful synthesis of
homo and/or heteronuclear metal complexes with interesting ste-
reochemistries [15,16].
As part of our continued involvement in the coordination chem-
istry of NO donor Schiff bases, we have recently reported the
metal-binding properties of the Schiff base Opdac to control the ste-
reochemistry at cobalt(II) center [17]. So we were eager to explore
the bonding features of this Schiff base Opdac with respect to nick-
el(II) center in the presence of various counter ions and herein we
report the synthesis and characterization of its five novel Ni(II)
complexes [Ni(Opdac)2]Cl2 (1), [Ni(Opdac)2(CH3OH)2]Br2(CH3OH)2
(2), [Ni(Opdac)2]I2 (3), [Ni(Opdac)2NO3]NO3 (4) and [Ni(Opdac)2-
ClO4]ClO4 (5).
2.1. Materials and instrumentation
High purity 4-antipyrine carboxaldehyde (Aldrich, USA),
O-phenylenediamine, nickel(II) nitrate hexahydrate, and nickel(II)
chloride hexahydrate (E. Merck, India) were purchased from the
respective concerns and used as such. Metal bromide, iodide and
perchlorate salts were prepared by dissolving Analar BDH nickel
carbonate in the respective 50% acids and crystallizing the salts
after concentrating the respective solutions on a steam bath. All
other chemicals and solvents were AR grade and used as such.
The carbon, hydrogen and nitrogen content in the synthesized
compound was determined on a Perkin-Elmer 240 CHN elemental
analyzer. All the complexes were analyzed for their metal, halide
and perchlorate contents by standard methods [18,19]. Molar con-
ductivities were measured using freshly prepared 10À3 M solutions
in dimethylformamide, nitrobenzene and methanol at room tem-
perature, using a Toshniwal conductivity bridge with a dip-type
conductance cell (cell constant 0.9712) which was calibrated with
0.01 M KCl solution. The infrared spectra of the ligands and the
complexes were recorded in the range 4000–400 cmÀ1 on a Shima-
dzu IR 470 spectrophotometer. Solid state electronic spectra in the
range 800–200 nm were recorded using a Shimadzu UV–Vis-2450
spectrophotometer and in the range 800–1500 nm on a Cary 2390
UV–Vis–NIR spectrophotometer. Magnetic susceptibility measure-
ments were performed on pulverized samples at room tempera-
ture on a Sherwood Magway MSB Mk1 balance. The diamagnetic
corrections were calculated by using Pascal’s constants. Thermal
studies were undertaken on Shimadzu DTG-60 thermal analyzer
⇑
Corresponding author. Tel.: +91 4812731036; fax: +91 4812731002.
E-mail address: pkrkn@yahoo.co.in (P.K. Radhakrishnan).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.013

2850
P.M. Vimal Kumar, P.K. Radhakrishnan / Polyhedron 30 (2011) 2849–2855
Table 1
in nitrogen atmosphere in the temperature range 25–700 °C; heat-
ing rate: 10 °C minÀ1
Crystal data and structure refinement parameters for complex 2.
.
The synthesis, structural and electronic features of 4-(1-H-1,
3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-2-dihydro-3-H-
pyrazol-3-one (Opdac) has already been published by the authors
[17].
CCDC No.
Formula
814713
40H48Br2N8NiO6
955.39
0.30 X 0.20 X 0.20
Monoclinic
P21/c
C
Formula weight
Crystal size (mm)
Crystal system
Space group
Unit cell dimensions
a (Å)
2.2. Synthesis of metal complexes
9.1391(2)
13.1308(3)
17.4313(4)
94.0830(10)
2086.51(8)
2
980
0.71073
293(2)
0.0342
À13/14, À13/20, À26/26
2.23 /33.17
32657/7933/5408
7933/0/272
1.011
b (Å)
c (Å)
2.2.1. General procedure for synthesis of nickel(II) complexes
A solution of NiX2Á6H2O (X = Cl, Br, I, NO3 and ClO4) in acetoni-
trile (1 mmol, 10 mL) was added to a hot solution of Opdac
(2 mmol, 20 mL) in ethyl acetate and refluxed for about 3 h. The
precipitated complexes were filtered off, washed with ethyl ace-
tate and dried under vacuum and kept in desiccator. All the com-
plexes were recrystallized from methanol for single crystals by
slow vapor diffusion of ethyl acetate from an adjacent container,
but good quality single crystals, suitable for X-ray crystallography,
of only complex 2 were obtained. The analytical, spectral and mag-
netic data are summarized below.
b (°)
V (Å3)
Z
F(000)
l
Mo K
a
(mmÀ1
)
T (K)
Rint
Range of h, k, l
hmin/max (°)
Reflections collected/unique/observed [I > 2
r(I)]
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0366
wR2 = 0.0907
R1 = 0.0701
wR2 = 0.1038
2.2.2. [Ni(Opdac)2]Cl2 (1)
R indices (all data)
Anal. Calc. for C36H32N8O2Cl2Ni (738.29): C, 58.57; H, 4.37; N,
15.18; Ni, 7.95; Cl, 9.60. Found: C, 58.54; H, 4.33; N, 15.16; Ni,
7.92; Cl, 9.56%. IR (cmÀ1): 1620 [
m
(C@O)], 1604 [
(Ni–O)]; (kM/
152.37 (in DMF), 186.54 in MeOH), 53.81 (in C6H5NO2); (kmax
nm) 380 (n–p⁄), 260 ( p⁄), 638, 1192 (d–d transitions), 290 (C–
T transition); eff = 3.39 BM.
m
(C@N)], 3320
[m
(N–H)], 446
[m
(Ni–N)], 556
[m
X
À1 cm2 molÀ1):
p–
(in C6H5NO2); (kmax, nm) 380 (n–p⁄), 256 ( p⁄), 426, 602, 1009
,
(d–d transitions), 323 (C–T transition); eff = 2.96 BM.
l
p–
Caution! Though we have not met with any incident while
working with the perchlorate compound described here, care
should be taken in handling them as the perchlorates are poten-
tially explosive. They should not be prepared and stored in large
amounts.
l
2.2.3. [Ni(Opdac)2(CH3OH)2]Br2(CH3OH)2 (2)
Anal. Calc. for C40H48N8O6Br2Ni (955.39): C, 50.29; H, 5.06; N,
11.73; Ni, 6.14; Br, 16.73. Found: C, 50.25; H, 5.02; N, 11.69; Ni,
6.11; Br, 16.71%. IR (cmÀ1): 1622 [
m
(C@O)], 1604 [
(Ni–O)]; (kM/
À1 cm2 molÀ1):
164.58 (in DMF), 178.39 (in MeOH), 56.25 (in C6H5NO2); (kmax
nm) 378 (n–p⁄), 256 ( p⁄), 420, 605, 1002 (d–d transitions),
318 (C–T transition); eff = 3.08 BM.
m(C@N)], 3320
2.3. X-ray crystallographic study
[m
(N–H)], 450
[
m(Ni–N)], 555
[m
X
,
The block pale green crystal of [Ni(Opdac)2(CH3OH)2]Br2(CH3-
OH)2 (2) was directly picked up from the mother liquor, attached
to a glass fiber and transferred for the data collection. X-ray single
p–
l
crystal data were collected using Mo Ka (k = 0.7107 Å) radiation on
2.2.4. [Ni(Opdac)2]I2 (3)
a BRUKER APEX II diffractometer equipped with CCD area detector.
Unit cell refinement (Bruker, 2006) [20] data reduction (SAINT) and
structure solution as well as refinement (SHELXL97) [21] were carried
out using the software package of SMART APEX. All structures were
solved by direct method and refined in a routine manner. In most
of the cases, nonhydrogen atoms were treated anisotropically.
Whenever possible, the hydrogen atoms were located on a differ-
ence Fourier map and refined. In other cases, the hydrogen atoms
were geometrically fixed. Molecular graphics were generated by
using the softwares Mercury 2.3 [22] and ORTEP 3 [23]. The details
of the X-ray crystal data and the structure solution as well as the
refinement are given in Table 1.
Anal. Calc. for C36H32N8O2I2Ni (921.19): C, 46.94; H, 3.50; N,
12.16; Ni, 6.37; I, 27.55. Found: C, 46.91; H, 3.47; N, 12.13; Ni,
6.34; I, 27.51%. IR (cmÀ1): 1620 [
m
(C@O)], 1602 [
(Ni–O)]; (kM/
138.14 (in DMF), 172.36 (in MeOH), 54.72 (in C6H5NO2); (kmax
nm) 383 (n–p⁄), 264 ( p⁄), 615, 1180 (d–d transitions), 292 (C–
T transition); eff = 3.49 BM.
m
X
(C@N)], 3320
[m
(N–H)], 446
[m
(Ni–N)], 550
[m
À1 cm2 molÀ1):
,
p–
l
2.2.5. [Ni(Opdac)2NO3]NO3 (4)
Anal. Calc. for C36H32N10O8Ni (791.40): C, 54.64; H, 4.08; N,
17.70; Ni, 7.42. Found: C, 54.60; H, 4.04; N, 17.67; Ni, 7.39%. IR
(cmÀ1): 1622 [
m
(C@O)], 1604 [
(NO3coordinated)], 1384, 823 [
(Ni–N)], 550 (Ni–O)]; (kM/
À1 cm2 molÀ1): 69.37 (in
DMF), 92. 14 (in MeOH), 24.52 (in C6H5NO2); (kmax, nm) 378 (n–
p⁄), 258 ( p⁄), 390, 600, 1006 (d–d transitions), 313 (C–T transi-
tion); eff = 2.95 BM.
m
(C@N)], 3320 [
m(N–H)], 1435,
1240, 1052 [
m
m(NO3uncoordinated)],
443
[m
[m
X
3. Results and discussion
p–
3.1. Properties
l
The crystalline complexes are soluble in common organic sol-
vents such as methanol, ethanol, dimethylformamide and nitroben-
zene, but insoluble in ethyl acetate, chloroform and acetone. The
elemental analysis data suggest that the complexes can be formu-
2.2.6. [Ni(Opdac)2ClO4]ClO4 (5)
Anal. Calc. for C36H32N8O10NiCl2 (886.29): C, 49.91; H, 3.72; N,
12.93; Ni, 6.78; ClO4, 22.43. Found: C, 49.89; H, 3.68; N, 12.91;
Ni, 6.75; ClO4, 22.39%. IR (cmÀ1): 1622 [
m
(C@O)], 1602 [
(N–H)], 1143, 1114, 1024, 945, 630 [ (ClO4coordinated)],
1089, 624 [ (ClO4uncoordinated)], 446 [ (Co–N)], 550 [ (Co–O)].
(kM/
À1 cm2 molÀ1): 78.37 (in DMF), 110.25 (in MeOH), 27.41
m
(C@N)],
lated as Ni(Opdac)2X2 (X = ClÀ, BrÀ, IÀ, NO3 or ClO4À). The molar
À
3320 [
m
m
conductance data reveals that [Ni(Opdac)2]Cl2 (1), [Ni(Opdac)2(-
CH3OH)2]Br2(CH3OH)2 (2) and [Ni(Opdac)2]I2 (3) behave essen-
tially as 1:2 electrolytes whereas [Ni(Opdac)2NO3]NO3 (4) and
m
m
m
X

P.M. Vimal Kumar, P.K. Radhakrishnan / Polyhedron 30 (2011) 2849–2855
2851
[Ni(Opdac)2ClO4]ClO4 (5) complexes behave as 1:1 electrolytic
type [24].
3.2. Infrared spectra
The Infrared spectra of the complexes 1–5 are presented in
Fig. 1. The strong bands observed at 1631 and 1612 cmÀ1 in Opdac
are attributed to the stretching vibrations of the pyrazolone car-
bonyl oxygen [17,25] and benzimidazole imine nitrogen [26],
respectively. In the complexes 1–5 the m(C@O) and m(C@N) bands
show a red shift with respect to those of the free ligand by 9–11
and 8–10 cmÀ1, respectively. The N–H stretching frequency ob-
served in Opdac around 3321 cmÀ1 remains almost unchanged in
all the complexes indicating that the N–H nitrogen of the benz-
imidazole moiety is not coordinated [26]. Thus the IR spectral data
of the solid state complexes show that Opdac acts as a neutral
bidentate ligand coordinating through the imine nitrogen and the
pyrazolone oxygen forming a six membered ring around the cen-
tral metal ion. The presence of additional non-ligand bands in
the spectra of all the complexes around 443–450 and 550–
556 cmÀ1 are attributed to Ni–N and Ni–O stretching frequencies,
respectively [27].
The nitrate complex exhibits vibrational frequencies character-
istic of both uncoordinated and coordinated nitrate ions. A very
strong band at 1384 cmÀ1 and a medium band at 823 cmÀ1 are
attributed to the m3 and m2 vibrations, respectively, of ionic nitrate
of D3h symmetry [28]. The presence of coordinated nitrate is indi-
cated by two bands at 1435 and 1240 cmÀ1 due to the m4 and m1
vibrations, respectively, of the nitrate of C2v symmetry [29]. Since
(m4–m
1) = 195 cmÀ1, the nitrate ion is coordinated in a bidentate
fashion [30].
In the perchlorate complex, the triply split band maxima at
1143, 1114 and 1024 cmÀ1 are due to the m8
, m6 and m1 vibrations,
respectively, of the perchlorate ion of C2v symmetry, indicating the
coordination of the perchlorate ion in a bidentate fashion [31]. But
the presence of a very strong band at around 1089 cmÀ1 is attrib-
uted to the m3 vibration of uncoordinated perchlorate ion of Td
symmetry [32]. The bands observed around 945 and 630 cmÀ1
due to the m2 and m3 vibrations, respectively, of the coordinated
perchlorate (C2v) ion and the band at 624 cmÀ1 due to the
m4 vibra-
tion of the uncoordinated perchlorate (Td) ion also support the co-
existence of both coordinated and uncoordinated perchlorate ion
in the complex [31].
3.3. Electronic spectra and magnetism
The electronic spectra of the complexes 1–5 are presented in
Figs. 2 and 3. The electronic spectrum of Opdac exhibits two main
peaks at about 387 and 252 nm which are assignable to the n–p⁄
and
p–
p⁄ transitions, respectively [17]. In all the complexes, the
n–p⁄ band is blue-shifted to the 378–383 nm region while the
p–
p⁄ band is red-shifted to the 256–264 nm region compared to Op-
dac. The reflectance spectra of the complexes 1 and 3 show bands
in the region 615–638 nm attributable to the 3T1(F) ? 3T1(P) tran-
sition which is consistent with a tetrahedral geometry around the
nickel(II) ion. The low-energy band expected for the
3T1(F) ? 3A2(F) transition in tetrahedral nickel(II) complexes is ob-
served in the region 1118–1192 nm. The observed leff values of
3.39 BM for 1 and 3.49 BM for 3 are in good agreement with the
tetrahedral nickel(II) complexes [27].
Fig. 1. Infrared spectra of the complexes 1–5.
The diffuse reflectance spectra of complexes 2, 4 and 5 are char-
acterized by three main bands in the regions
3A2g(F) ? 3T2g(F), 3A2g(F) ? 3T1g(F)
2 = 600–605 nm
3 = 390–426 nm A2g(F) ? 3T1g(P) and these transitions are indic-
ative of an octahedral geometry around the Ni(II) center. The room
temperature magnetic moments of the complexes 2, 4 and 5 are
m
1 = 1002–1009 nm
3.08, 2.95 and 2.96 BM, respectively, indicating an octahedral
geometry around the Ni(II) ion [33]. Furthermore, all the com-
plexes 1–5 shows a strong band in the region 290–323 nm which
can be assigned to the charge transfer transition.
m
and
3
m

2852
P.M. Vimal Kumar, P.K. Radhakrishnan / Polyhedron 30 (2011) 2849–2855
Fig. 3. UV–Vis–NIR spectra of the complexes 1–5.
Fig. 2. UV–Vis spectra of the complexes 1–5.
3.4. Thermal studies (TG/DTA)
Complex 2 undergoes a two stage decomposition process. During
the first stage (171–315 °C) two iodide ions are decomposed with
an exothermic DTA peak at 305 °C (observed weight loss 27.56%,
calculated 26.96%). The second stage (316–460 °C) occurs with an
exothermic DTA peak at 445 °C, corresponding to the release of
both Opdac molecules (observed weight loss 66.11%, calculated
66.02%). The final residue (8.11%) above 460 °C corresponds to
anhydrous NiO.
The complex 4 is stable up to 161 °C indicating the absence of
either water or solvent molecules in the complex. Two nitrate
ions are decomposed in the first step (161–302 °C) with an exo-
thermic DTA peak at 236 °C (observed weight loss 15.67%, calcu-
lated 15.49%). The second stage (303–474 °C) occurs with an
exothermic DTA peak at 446 °C, corresponding to the release of
both Opdac molecules (observed weight loss 76.95%, calculated
76.19%) leaving anhydrous NiO (9.44%) as the final residue above
474 °C.
The complex 5 is stable up to 186 °C indicating the absence of
either water or solvent molecules in the complex. The first stage
(186–378 °C) with an exothermic DTA shoulder at 344 °C, corre-
sponds to the decomposition of two perchlorate ions (observed
weight loss 22.96%, calculated 22.15%). The second stage with a
mass loss of 69.98% (calculated 70.30%) takes place in the range
of 379–539 °C with an exothermic effect (DTAmax = 482 °C), corre-
sponding to the decomposition of the two Opdac moiety. The final
residue (8.62%) above 539 °C is anhydrous NiO.
The TG and DTA curves of the complexes 1–5 are illustrated in
Fig. 4. The assignment of each decomposition process was based on
the chemical and IR spectral analyses of the intermediate products
and the final residue.
The complex 1 undergoes a two stage decomposition process.
There is no mass loss up to 191 °C indicating the absence of either
water or solvent molecules in the complex. The first stage starts at
191 °C and ends at 454 °C with an exothermic DTA shoulder at
352 °C, corresponding to the removal of one Opdac molecule (ob-
served weight loss 41.24%, calculated 41.08%). The second stage oc-
curs between 455 and 627 °C, resulting the release of remaining
Opdac (observed weight loss 41.24%, calculated 41.12%) with an
exothermic DTA shoulder at 574 °C. The final residue (17.56%)
above 627 °C corresponds to anhydrous NiCl2.
The thermogram of the complex 2 shows that the decomposi-
tion occurs in three steps. During the first stage (52–145 °C) both
the coordinated as well as uncoordinated methanol molecules
are decomposed with an exothermic DTA peak at 98 °C (observed
weight loss 13.41%, calculated 13.15%). Two bromide ions (ob-
served weight loss 16.73%, calculated 16.08%) are decomposed in
second step (146–365 °C) with an exothermic DTA peak at
336 °C. The third stage (366–602 °C) is due to the removal of the
two Opdac molecule (observed weight loss 63.71%, calculated
63.29%) with an exothermic DTA peak at 565 °C leaving anhydrous
NiO (7.81%) as the final residue above 602 °C.
Comparing the temperature ranges of the first weight loss for
complexes 1–5, it can be shown that within the series the bromide
complex is the least stable and the chloride complex is the most
The complex 3 is thermally stable up to 171 °C indicating the
absence of either water or solvent molecules in the complex.

P.M. Vimal Kumar, P.K. Radhakrishnan / Polyhedron 30 (2011) 2849–2855
2853
Fig. 5. [Ni(Opdac)2]Cl2 (1) and [Ni(Opdac)2]I2 (3).
Fig. 6. [Ni(Opdac)2(CH3OH)2]Br2(CH3OH)2 (2).
Fig. 4. TG and DTA curves of the complexes 1–5
stable. The thermal stability of the complexes is in the order:
chloride > perchlorate > iodide > nitrate > bromide.
Based on the above observations the following tentative struc-
tures in Figs. 5–8 may be assigned to the complexes.
3.5. Crystal structure of [Ni(Opdac)2(CH3OH)2]Br2(CH3OH)2 (2)
The crystallographic data are summarized in Table 1. The crys-
tal structure of the complex 2 with the atom numbering scheme is
given in Fig. 9. The selected bond lengths and bond angles are given
in Table 2.
Fig. 7. [Ni(Opdac)2NO3]NO3 (4).

2854
P.M. Vimal Kumar, P.K. Radhakrishnan / Polyhedron 30 (2011) 2849–2855
coordination number, ligated through the benzimidazole imine
nitrogen N(4) and pyrazolone oxygen atom (O1) atoms of two biden-
tate Opdac moieties as well as the oxygen atoms (O2) of two meth-
anol molecules. The Ni–N4 bond distance value [2.0996(13) Å]
conforms to those reported for the similar octahedral Ni(II) com-
plexes with some Schiff bases [34]. The observed value for the Ni–
O1 bond length 2.0191(12) Å is agreeable [1.987(5)–2.039(5) Å] to
related octahedral Ni(II) complexes [35–37]. The Ni(II) center in
the complex 2 is significantly distorted from the octahedral geome-
try as revealed from the corresponding \O–Ni–O and \O–Ni–N an-
gles [89.67(5)–90.32(5)° and 89.22(5)–90.77(5)°, respectively]
(Table 2 for details).
4. Conclusion
A series of mononuclear nickel(II) complexes [Ni(Opdac)2]Cl2 (1),
[Ni(Opdac)2(CH3OH)2]Br2(CH3OH)2 (2), [Ni(Opdac)2]I2 (3), [Ni(Op-
dac)2NO3]NO3 (4) and [Ni(Opdac)2ClO4]ClO4 (5) were prepared
and characterized. In all the cases the Ni(II) ion is coordinated by
the imine nitrogen and pyrazolone oxygen donor sites of the ligand.
In the free ligand moiety Opdac, the imine nitrogen (N4) and pyraz-
olone oxygen (O1) are trans oriented to each other. During chelation,
they rearrange to cis fashion in all the complexes. This cis conforma-
tion of the ligand is necessary for its participation as a bidentate NO
chelate ligand. The complexes 1 and 3 have a tetrahedral geometry
while 2, 4 and 5 have an octahedral geometry around the Ni(II)
center.
Fig. 8. [Ni(Opdac)2ClO4]ClO4 (5).
Acknowledgements
The authors are thankful to the Head, SAIF and IIT Madras for
the single crystal X-ray diffraction measurements.
Appendix A. Supplementary data
CCDC 814713 contains the supplementary crystallographic data
for 2. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/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
References
[1] T. Ueno, M. Ohashi, M. Kono, K. Kondo, A. Suzuki, T. Yamane, Y. Watanabe,
Inorg. Chem. 43 (2004) 2852.
Fig. 9. Molecular structure of complex
displacement parameters are shown at 50% probability level. Hydrogen atoms as
well as solvated methanol molecules are omitted for clarity.
2 with atom labeling scheme. Atomic
[2] S. Pal, A.K. Barik, S. Gupta, A. Hazra, S.K. Kar, S.-M. Peng, G.-H. Lee, R.J. Butcher,
M.S.E.I. Fallah, J. Ribas, Inorg. Chem. 44 (2005) 3880.
[3] N.-N. Hou, Acta Crystallogr., Sect. E61: m (2005) 1197.
[4] S. Shit, S. Sen, S. Mitra, D.L. Hughes, Transition Met. Chem. 34 (2009) 269.
[5] S. Thakurta, J. Chakraborty, G. Rosair, R.J. Butcher, S. Mitra, Inorg. Chim. Acta
362 (2009) 2828.
Table 2
Selected bond distances (Å) and angles (°) of complex 2.
[6] S. Yamada, Coord. Chem. Rev. 190 (1999) 537.
Bond lengths (Å)
Bond angles (°)
[7] S. Akine, T. Taniguchi, W. Dong, S. Masubuchi, T. Nabeshima, J. Org. Chem. 70
(2005) 1704.
[8] W.K. Dong, Y.X. Sun, Y.P. Zhang, L. Li, X.N. He, X.L. Tang, Inorg. Chim. Acta 362
(2009) 117.
Ni(1)–O(1)
Ni(1)–N(4)
Ni(1)–O(2)
C(16)–O(1)
C(18)–N(4)
C(7)–N(4)
C(12)–N(3)
C(17)–C(18)
C(16)–N(2)
C(13)–N(1)
N(1)–N(2)
2.0192(12)
2.0996(13)
2.1122(13)
1.2566(19)
1.331(2)
1.400(2)
1.383(2)
1.443(2)
1.369(2)
N(4)–Ni(1)–O(1)
N(4)–Ni(1)–O(2)
O(1)–Ni(1)–O(2)
C(19)–O(2)–Ni(1)
C(7)–N(4)–Ni(1)
C(16)–O(1)–Ni(1)
C(16)–C(17)–C(18)
C(17)–C(18)–N(4)
N(3) –C(18)–N(4)
C(18) –N(3)–C(12)
C(16) –N(2)–N(1)
89.22(5)
91.00(5)
89.68(5)
[9] T. Katsuki, Coord. Chem. Rev. 140 (1995) 189.
122.09(13)
129.19(11)
121.85(11)
122.25(14)
123.27(14)
112.04(14)
107.32(14)
108.92(13)
[10] P.J. Pospisil, D.H. Carsten, E.N. Jacobsen, J. Eur. Chem. 2 (1996) 974.
[11] Neumann, M. Dahan, Nature 388 (1997) 353.
[12] L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1999) 85.
[13] D.X. West, H. Gebremedhin, R.J. Butcher, J.P. Jasinski, A.E. Liberta, Polyhedron
12 (1993) 2489.
[14] M.F. Summers, L.G. Marzilli, N.B. Pahor, L. Randaccio, J. Am. Chem. Soc. 106
(1984) 4478.
[15] P. Zanello, S. Tamburini, P.A. Vigato, G.A. Mazzocchin, Coord. Chem. Rev. 77
(1987) 165.
1.332(2)
1.378(2)
[16] O. Pouralimardan, A.-C. Chamayou, C. Janiak, H.-M. Hassan, Inorg. Chim. Acta
360 (2007) 1599.
[17] P.M. VimalKumar, P.K. Radhakrishnan, Polyhedron 29 (2010) 2335.
[18] A.I. Vogel, A Text Book of Quantitative Inorganic Analysis, ELBS, London, 1961.
[19] E. Kurz, G. Kober, M. Berl, Anal. Chem. 30 (1958) 1983.
The crystal structure of complex 2 describes a methanol inclusion
coordination complex of Ni(II). The Ni(II) center presents a six

P.M. Vimal Kumar, P.K. Radhakrishnan / Polyhedron 30 (2011) 2849–2855
2855
[20] Bruker, APEX II, SAINT and SADABS, Bruker AXS Inc., Madison, Wisconsin, USA,
2006.
[31] N.T. Madhu, P.K. Radhakrishnan, Synth. React. Inorg. Met. Org. Nano Met.
Chem. 31 9 (2001) 1663.
[21] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[22] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M.
Towler, J. van de Streek, J. Appl. Crystallogr. 39 (2006) 453.
[23] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[24] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[25] R.N. Jadeja, J.R. Shah, Polyhedron 26 (2007) 1677.
[26] R.K. Dubey, C.M. Mishra, P. Baranwal, S.S. Dubey, J. Indian Chem. Soc. 86 (2009)
1025.
[32] R.C. Maurya, D.D. Mishra, P.K. Trivedi, A. Gupta, Synth. React. Inorg. Met. Org.
Nano Met. Chem. 24 (1) (1994) 17.
[33] M. del C.F. Fernandez, R.B. de la Calle, A. Macias, L.V. Matarranz, P.P. Lourido,
Polyhedron 27 (2008) 2301.
[34] I.G. Santos, J. Sanmartin, A.M. Garcia-Deibe, M. Fondo, E. Gomez, Inorg. Chim.
Acta 363 (2010) 193.
[35] E.G. Petkova, R.D. Lampeka, M.V. Gorichko, K.V. Domasevitch, Polyhedron 20
(2001) 747.
[27] K.C. Raju, P.K. Radhakrishnan, Synth. React. Inorg. Met. Org. Nano Met. Chem.
33 (2003) 1037.
[28] B.M. Gatehouse, S.E. Livingstone, R.S. Nyholm, J. Inorg. Nucl. Chem. 8 (1958) 75.
[29] N.T. Madhu, P.K. Radhakrishnan, Transition Met. Chem. 25 (2000) 287.
[30] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fourth ed., Wiley, New York, 1986.
[36] S.B. Raj, P.T. Muthiah, G. Bocelli, L. Righi, Acta Crystallogr., Sect. E 57 (2001) 591.
[37] M. Fondo, A.M. Garcia-Deibe, N. Ocampo, J. Sanmartin, M.R. Bermejo, A.L. Saiz,
Dalton Trans. (2006) 4260.