Nickel(II), copper(II), and cobalt(II) complexes derived from a new unsymmetrical ONS donor schiff base ligand: Synthesis, characterization, crystal structure, and catalytic activities

Article abstract of DOI:10.1080/00958972.2014.946917

A series of Ni(II), Cu(II), and Co(II) complexes, ML₂, of a new thioether containing ONS donors have been synthesized, where L = deprotonated Schiff base. The analytical, spectral (FTIR,¹H NMR, UV–vis), conductivity, and magnetic stu

Full text of DOI:10.1080/00958972.2014.946917

This article was downloaded by: [University of Colorado - Health Science Library]
On: 26 September 2014, At: 10:35
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Nickel(II), copper(II), and cobalt(II)
complexes derived from a new
unsymmetrical ONS donor Schiff base
ligand: synthesis, characterization,
crystal structure, and catalytic
activities
Mukul Kalitaa, Prasanta Gogoia, Pranjit Barmana & Bipul Sarmab
a Department of Chemistry, National Institute of Technology,
Silchar, India
b Department of Chemical Sciences, Tezpur University, Tezpur,
Click for updates
India
Accepted author version posted online: 25 Jul 2014.Published
online: 14 Aug 2014.
To cite this article: Mukul Kalita, Prasanta Gogoi, Pranjit Barman & Bipul Sarma (2014) Nickel(II),
copper(II), and cobalt(II) complexes derived from a new unsymmetrical ONS donor Schiff
base ligand: synthesis, characterization, crystal structure, and catalytic activities, Journal of
Coordination Chemistry, 67:14, 2445-2454, DOI: 10.1080/00958972.2014.946917
To link to this article: http://dx.doi.org/10.1080/00958972.2014.946917
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry, 2014
Vol. 67, No. 14, 2445–2454, http://dx.doi.org/10.1080/00958972.2014.946917
Nickel(II), copper(II), and cobalt(II) complexes derived from
a new unsymmetrical ONS donor Schiff base ligand:
synthesis, characterization, crystal structure, and catalytic
activities
MUKUL KALITA†, PRASANTA GOGOI†, PRANJIT BARMAN*† and
BIPUL SARMA‡
†Department of Chemistry, National Institute of Technology, Silchar, India
‡Department of Chemical Sciences, Tezpur University, Tezpur, India
(Received 9 January 2014; accepted 7 July 2014)
A series of Ni(II), Cu(II), and Co(II) complexes, ML2, of a new thioether containing ONS donors
have been synthesized, where L = deprotonated Schiff base. The analytical, spectral (FTIR, 1H
NMR, UV–vis), conductivity, and magnetic studies showed that the metal complexes possess octa-
hedral geometry and are non-electrolytes. The structures of ligand as well as nickel(II) complex,
NiL2, 2, were determined by single-crystal X-ray diffraction studies. The copper complex shows
very good catalytic activities towards oxidation of organic thioethers to the corresponding sulfoxide
predominantly using H2O2 as the oxidant.
Ni(II), Cu(II), and Co(II) complexes, ML2, with a new thioether containing ONS donors were
synthesized, where L = deprotonated Schiff base. The analytical, spectral (FTIR, 1H NMR, and
UV-vis), conductivity, and magnetic studies show that the metal complexes possess octahedral
geometry and are non-electrolytes. The coordination mode of ligand, 1, and nickel(II) complex,
NiL2, 2, was determined by single-crystal X-ray diffraction studies. Here, the nickel is coordinated
to two oxygens, two nitrogens, and two sulfurs of two tridentate ligands with slightly distorted
octahedral environment around nickel. The copper complex shows very good catalytic activities
towards oxidation of organic thioethers to the corresponding sulfoxide predominantly using H2O2 as
the oxidant.
Keywords: ONS donor ligand; Crystal structure; Thioether; Catalytic activity; Schiff base
*Corresponding author. Email: barmanpranjit@yahoo.co.in
© 2014 Taylor & Francis

2446
M. Kalita et al.
1. Introduction
Schiff bases have led to a renewed interest in coordination chemistry as they can be easily
synthesized, have good coordinating ability to metals, and have potential antibacterial, anti-
cancer, and antifungal properties [1]. Chelating ligands with ONS donors are important in
coordination chemistry owing to their stability, chemical properties, electrochemical activi-
ties, and broad biological activities [2]. Transition metal complexes with such ligands have
versatile structural and functional properties and applications in catalysis, material research,
etc. [3]. Coordination chemistry of copper with ONS donor ligands is interesting as their
structures, spectral properties, redox properties, and medical applications mimic those of
sulfur-containing proteins [4]. New complexes containing nickel provide better understand-
ing of biological systems and also develop new homogeneous catalysts for selective oxida-
tion [5]. Nickel complexes with ONS donors are effective in Co-dehydrogenase, saline
alcoholysis, and also have fungi toxicities [6]. Cobalt complexes are important due to their
anticancer properties, cytotoxic activities, etc. [7].
Metal complex-catalyzed conversion of sulfides to sulfoxides is significant in synthetic
chemistry, offering effective synthesis of important compounds that have industrial and
medical applications [8]. Transition metal complexes like oxido-peroxido tungsten,
vanadium, and molybdenum give good selectivity towards sulfoxide formation from sulfide
[9–12]. Also, nanoparticle-supported vanadium complexes are effective as heterogeneous
catalysts in sulfide oxidation [13]. Copper Schiff base complexes also give predominantly
sulfoxides from sulfides [14]. Nanoparticle-supported manganese complexes are used in the
oxidation of thiol to disulfide [15].
Herein, we report the synthesis and characterization of a new ONS donor Schiff base,
bromo, nitro, N-[2-(benzylthio) phenyl] salicylaldimine and its nickel(II), copper(II), and
cobalt(II) complexes. Crystal structures of ligand and nickel(II) complex are solved by
single-crystal X-ray diffraction studies. In this paper, we describe Schiff base copper com-
plex-catalyzed oxidation of sulfides to their sulfoxides in the presence of H2O2, a process
delivering a high yield and desirable reaction time.
2. Experimental
2.1. Materials and methods
Nickel chloride hexahydrate, copper nitrate trihydrate, and cobalt chloride hexahydrate were
purchased from Merck, India. 3-Bromo-5-nitro salicylaldehyde was purchased from Alfa
Aesar. 2-(Benzylthio)aniline was prepared according to the literature method [16]. Elemental
analyses were recorded on a Perkin-Elmer Model 240C elemental analyzer. Electrical con-
ductivities were measured on a CM-180 conductivity meter (Elico, India). Electronic spectra
were measured on a Cary 100 Bio UV–visible spectrophotometer. Magnetic susceptibilities
were measured on a conventional Gouy balance using freshly prepared Hg[Co(NCS)4] as
calibrant by Magway MSB MK1 Magnetic susceptibility balance, Sherwood Scientific,
Cambridge, UK. Infrared spectra of the ligand and complexes were recorded on an
IR-affinity-I FTIR spectrometer SHIMADZU as KBr pellets. Melting points were recorded
on a Veego melting point apparatus and were uncorrected. The 1H NMR spectra were
recorded on a Bruker 400 DRX spectrometer in CDCl3 solution using TMS as the internal

Unsymmetrical ONS Schiff base
2447
standard. All other reagents and solvents like methanol, ethanol, DMF, DMSO, dichloro-
methane (DCM), and acetonitrile were of commercial grade and employed as received or
purified by standard methods prior to use. All the reactions were carried out at room temper-
ature in open atmosphere.
2.2. Synthesis of HL
2-(Benzylthio)aniline (0.215 g, 1 mM) was dissolved in ethanol and 3-bromo-5-nitro sali-
cylaldehyde (0.233 g, 1 mM) was dissolved in ethanol and added dropwise to the above
solution with continuous stirring. The solution was then refluxed for another 30 min and
the color of the solution changed to yellow. Then, the solution was kept undisturbed for six
hours at room temperature. The formed orange crystalline product was filtered off, washed
several times with ethanol, and dried in vacuum (10−2 torr) (purity was checked by TLC).
Needle-like crystals suitable for XRD analysis were grown by recrystallization from etha-
nol. Yield 91%; m.p. 198 °C. IR (KBr pellet, cm−1): 3460(m), 1603(s), 1444(s), 1329(s),
735(s). 1H NMR (CDCl3, 400 MHz): δ 11.39 (1H, s, OH), 8.55 (1H, s, CH=N), 8.35
(1H, s, Ar–H), 8.25 (1H, s, Ar–H), 6.91–7.42 (9H, m, Ar–H) and 4.11 (2H, s, CH2).
UV–vis (DCM, λmax, nm): 310 (13,193), 473 (1625). Anal. Calcd for C20H15O3N2SBr: C,
54.18; H, 3.38; N, 6.32; S, 3.61. Found (%): C, 53.95; H, 3.27; N, 6.38; S, 3.59.
2.3. Synthesis of complexes
2.3.1. Preparation of NiL2 (2). The ligand, 1 (0.884 g, 2 mM), was dissolved in boiling
methanol (30 mL) followed by the addition of methanolic 2 mM sodium hydroxide. To the
above solution, a solution of nickel chloride hexahydrate (0.237 g, 1 mM) dissolved in
methanol (30 mL) was added. The solution was stirred for 40 min. The color of the solution
changed to brown-black. The solution was kept undisturbed for 24 h. The black-brown nee-
dle-like crystal formed, suitable for X-ray diffraction, was filtered off, washed several times
with 25% methanol–water solution to remove the impurities, and dried under vacuum
(10−2 torr) (purity was checked by TLC). Yield 67.7%; m.p. 274 °C. IR (KBr, cm−1):
1600(s), 1482(s), 1304(s), 756(s), 555(m), 510(m). UV–vis (DCM, λmax, nm): 301 (1150),
387 (1445), 601 (232). Anal. Calcd for C40H28O6N4S2Br2Ni: C, 50.92; H, 2.97; N, 5.94; S,
3.39. Found (%): C, 50.98; H, 2.87; N, 5.81; S, 3.28.
2.3.2. Preparation of CuL2 (3). The preparation of 3 follows the same procedure as that
of 2 except that copper nitrate trihydrate (0.241 g, 1 mM) was used. When the color of the
solution changed to dark green, it was kept undisturbed for 24 h and green microcrystals
were obtained (purity was checked by TLC). Yield 68.6%; m.p. 252 °C. IR (KBr, cm−1):
1598(s), 1455(s), 1315(m), 750(s), 566(m), 524(m). UV–vis (DCM, λmax, nm): 263 (1681),
363 (2071), 617 (117). Anal. Calcd for C40H28O6N4S2Br2Cu: C, 50.66; H, 2.95; N, 5.91; S,
3.37. Found (%): C, 50.54; H, 2.86; N, 5.96; S, 3.32.
2.3.3. Preparation of CoL2 (4). The preparation of 4 follows the same procedure as that of
2 and 3 except that cobalt chloride hexahydrate (0.237 g, 1 mM) was used. When the color
of the solution changes to black, it was kept undisturbed for 2 days. Black microcrystals were

2448
M. Kalita et al.
obtained (purity was checked by TLC). Yield 58.7%; m.p. 264 °C. IR (KBr, cm−1): 1592(s),
1470(s), 1318(m), 752(s), 560(s), 524(m). UV–vis (DCM, λmax, nm): 289 (2264), 372
(1766), 598 (652). Anal. Calcd for C40H28O6N4S2Br2Co: C, 50.91; H, 2.97; N, 5.94; S, 3.39.
Found (%): C, 50.98; H, 2.87; N, 5.83; S, 3.35.
2.4. Oxidation of thioether
The present work also describes the catalytic oxidation of sulfide to sulfoxide and sulfone
using the synthesized copper(II) complex. The H2O2-induced catalytic activity of copper(II)
complex towards oxidation of sulfide under atmospheric conditions is shown in equation
(1). A 30% hydrogen peroxide solution (5 mM) was added to a solution containing the sul-
fide (2 mM), complex (0.5 M %), and 2 ml CH3CN [14]. The reaction mixture was stirred
at room temperature until the completion of reaction and it is monitored using TLC. After
complete conversion of the reactant, the product was extracted with EtOAc and washed
with water. The organic layer was dried over anhydrous Na2SO4. The solvent was removed
under vacuum and the residue was purified by chromatography (eluting with 1:1 hexane/
EtOAc). Here, we have used hydrogen peroxide as an oxidant in the presence of the copper
(II) complex for the oxidation of sulfide to their sulfoxide with high yield. A series of sol-
vents were employed for the reaction; acetone, DCM, and methanol give good yield with
slightly longer reaction times. The conversion was calculated on the basis of the isolated
yields shown in table 1.
2.5. X-ray crystallography
Single-crystal X-ray diffraction data for 1 and 2 were collected at 100 K with Mo Kα radia-
tion (λ = 0.71073 Å) using a Bruker Smart Apex II CCD diffractometer equipped with a
graphite monochromator. SMART [17] software was used for data collection and also for
indexing the reflections and determining the unit cell parameters. Collected data were inte-
grated using SAINT [17]. Structures were solved by direct methods and refined by full-
matrix least-squares calculations using SHELXTL [18] software. Absorption corrections
were done by multiscan method (SADABS) [17]. All non-H atoms were refined in the
anisotropic approximation against F2 of all reflections. The H-atoms were placed at their
calculated positions and refined in the isotropic approximations. We have used SIMU,
DELU, and ISOR commands to find reasonable ADP restraints for C18, C8, and O3.
3. Results and discussion
3.1. Synthesis and formulation
The new ONS donor Schiff base, HL, was synthesized by the reaction of 2-(benzylthio)ani-
1
line and 3-bromo-5-nitro salicylaldehyde in ethanol. The ligand was characterized by H
NMR, FTIR, and elemental analyses. Neutral nickel(II), copper(II), and cobalt(II)

Unsymmetrical ONS Schiff base
2449
Table 1. Oxidation of sulfide catalyzed by CuL2 in different solvents in the presence of 30% H2O2.a
Entry
Substrate
Solvent
CH3CN
Time (h)
5
Sulfoxideb yield (%)
Sulfoneb yield (%)
1
92
6
S
2
CH3CN
4
90
7
S
Cl
Cl
Cl
Cl
3
4
CH3CN
CH3CN
5
3
88
90
9
5
S
NO2
S
O
O
O
5
CH3CN
4
89
8
S
Br
1
2
CH3COCH
CH3COCH
8
7
90
89
8
9
S
S
3
4
CH3COCH
CH3COCH
8
6
85
86
12
10
S
NO2
S
5
CH3COCH
7
85
9
S
Br
1
2
CH2Cl2
CH2Cl2
7
6
91
88
7
9
S
S
3
4
CH2Cl2
CH2Cl2
7
5
87
88
10
8
S
NO2
S
5
CH2Cl2
6
82
10
S
Br
1
2
CH3OH
CH3OH
9
8
89
87
8
S
10
S
(Continued)

2450
M. Kalita et al.
Table 1. (Continued).
Entry
Substrate
Solvent
Time (h)
9
Sulfoxideb yield (%)
85
Sulfoneb yield (%)
9
3
CH3OH
S
NO2
4
5
CH3OH
7
8
88
8
9
S
O
CH3OH
10
S
Br
aReaction condition: substrate (2 mM), complex 1 (0.5 M %), and 30% H2O2 (5 mM) were stirred at room temperature in solvent
(2 mL).
bIsolated yield.
complexes were obtained by the reaction of ligand HL with the corresponding metal salt.
Elemental analyses indicate that metal ions react with the ligand in a 1 : 2 M ratio to afford
the neutral complexes ML2, where L represents the deprotonated mononionic (ONS) ligand.
They are crystalline solids, stable in air, and have melting points in the range 238–296 °C.
They are insoluble in organic solvents such as acetone, but soluble in DMF, DCM, and
DMSO. The elemental analyses data of ligands 2–4 are in agreement with the structure of
the ligand and complexes, respectively. The reaction scheme for the synthesis of metal com-
plexes is given in scheme 1.
3.1.1. FTIR spectra. The FTIR spectrum of 1 exhibits a broad band at 3460 cm−1 due to
ν(O–H), a strong band at 1603 cm−1 due to ν(C=N) and other strong bands from ν(C=C) to
ν(C–S) at 1444 and 735 cm−1, respectively.
The band for ν(OH) disappeared in the spectra of complexes indicating coordination
of phenolic oxygen with metal. The complexes exhibit a band for ν(C=N) in the range
1592–1600 cm−1 showing a shift to lower frequencies by 11–3 cm−1 compared with
ligand, which indicates coordination of ligand with metal via nitrogen. Moreover,
phenolic ν(CO) stretch, which is shifted by 20–32 cm−1 towards lower wavenumbers in
the complexes, indicates coordination of the phenolic oxygen [19]. Again, ν(C–S) in
Scheme 1. Synthesis of metal complexes.

Unsymmetrical ONS Schiff base
2451
complexes shifted to higher frequencies from 735 to 752–756 cm−1, which is evidence
of the M–S bond [20]. The appearance of new bands at 566–555 and 524–510 cm−1 in
complexes supported coordination with oxygen and nitrogen, respectively [19, 20].
3.1.2. Electronic spectra. The ligand shows sharp bands at 473 nm and 310 nm, which
are assigned to n–π* transition of the imine moiety and π–π* transition of phenyl rings,
respectively. The electronic spectrum of 2 exhibited three bands, 601, 387, and 301 nm,
which may be assigned to d–d, n–π*, and π–π* transitions, respectively. The electronic
spectrum of 3 shows a band at 617 nm due d–d transition and at 363 nm which may be due
to n–π* band of the imine. Complex 3 has another band centered at 263 nm which is
assigned to π–π* transition of phenyl rings [5, 21]. Complex 4 shows bands at 598, 372,
and 289 which may be assigned to d–d, n–π*, and π–π* transitions, respectively.
3.1.3. Molar conductivity. The molar conductivities of 2 are at 24.5 s cm2 M−1, 3 at
19.4 s cm2 M−1, and 4 at 29.2 s cm2 M−1. Molar conductivities of 19.4–29.2 s cm2 M−1 in
acetonitrile revealed that all the complexes are non-electrolytes [22].
3.1.4. Magnetic measurement. The magnetic moment (μeff) for 2 is 2.79 BM, close to the
spin-only value of 2.83 BM expected for a d8 system in Oh symmetry. The value obtained
Figure 1. Molecular structure of nickel complex shown with 50% probability ellipsoids. Hydrogens are omitted
for clarity.

2452
M. Kalita et al.
for 3 is in the expected range (1.61 BM) for a d9 configuration [5]. The magnetic moment of
4 is 4.96 BM, consistent with the value suggested for high-spin octahedral Co(II) complex.
3.2. Molecular structure
The ORTEP view with atom numbering of nickel complex is shown in figure 1. The crystal
structure of the ligand from unsubstituted aldehyde and its metal complexes is reported by
Kalita et al. [5]. Here, we report a ligand from substituted aldehyde. In this case, the benzyl
part is tilted outside from the basal plane. This may be due to the presence of bulky bro-
mine and nitro. In 1, N-methylenebenzenamine and 2-hydroxy-3-bromo-5-nitro phenyl rings
are planar. The bromine and nitro of the ligand repel the benzyl part of the ligand, resulting
in the benzyl part being tilted outside from the coordination sphere. The imine double bond
has a trans geometry, indicating that coordination of the ligand with metal ions must be
through ONS donors. The C=N bond length is in the expected range for a typical C=N
bond length of imines. N2S2O2 donor set meridionally made the coordination sphere. The
nickel coordinated with two deprotonated oxygens, two thioether sulfurs, and two imine
nitrogens of the tridentate ligand to form the chelate complex. The two oxygens bonded to
nickel are cis. The two thioether sulfurs also occupy cis positions in the basal plane and the
two imine nitrogens are in axial positions [23]. The distortion around nickel in the complex
Table 2. Crystal structure and structure refinement details for ligand and nickel complex.
Compound
Ligand
Nickel complex
CCDC entry no.
Empirical formula
Formula weight
T (K)
980688
C20H15BrN2O3S
443.31
980689
C40H28Br2N4NiO6S2
943.31
100(2)
100(2)
λ (Ǻ)
0.71073
Monoclinic
P21/c
0.71073
Orthorhombic
Pca21
Crystal system
Space group
Unit cell dimensions
a (Å)
8.6540(2)
21.1839(7)
b (Å)
13.9908(3)
11.0378(4)
c (Å)
14.7051(3)
16.4508(6)
α (°)
90.00
90.00
β (°)
95.2770(10)
90.00
γ (°)
90.00
1772.89(7)
90.00
3846.6(2)
V (Å3)
Z
4
4
DCalcd (Mg/m3)
1.661
2.461
896
0.58 × 0.49 × 0.41
2.01–38.78
−15 ≤ h ≤ 15
1.629
2.744
1896
0.37 × 0.13 × 0.11
1.92–27.48
μ (mm−1
F (0 0 0)
)
Crystal size (mm3)
θ Range for data collection (°)
Index ranges
−19 ≤ h ≤ 27
−24 ≤ k ≤ 22
−5 ≤ k ≤ 14
−25 ≤ l ≤ 25
−21 ≤ l ≤ 13
Completeness (%)
98.8
85.0
Absorption correction
Max and min transmissions
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Semi-empirical from equivalents
0.4319 and 0.3294
Full-matrix least-squares on F2
10,037/0/248
Semi-empirical from equivalents
0.7523 and 0.4301
Full-matrix least-squares on F2
8816/0/496
1.063
1.002
R1 =0.0321, wR2 = 0.0741
R1 =0.0956, wR2 = 0.0944
R1 =0.0613, wR2 = 0.1334
R1 =0.1220, wR2 = 0.1955

Unsymmetrical ONS Schiff base
2453
Table 3. Selected bond lengths (Å) and angles (°) for 2.
Ni1–S1
Ni1–S2
Ni1–N2
Ni1–N4
Ni1–O1
Ni1–O4
S1–C33
S1–C34
S2–C13
S2–C14
N2–C7
N2–C8
N4–C27
N4–C28
O1–C1
O4–C21
2.399(3)
2.464(3)
2.028(9)
2.026(8)
2.010(7)
1.998(7)
1.750(11)
1.849(11)
1.772(11)
1.837(11)
1.300(12)
1.419(12)
1.291(13)
1.457(13)
1.298(13)
1.279(11)
S1–Ni1–O4
S1–Ni1–O1
S1–Ni1–N4
S1–Ni1–N2
S1–Ni1–S2
S2–Ni1–N2
N4–Ni1–S2
N4–Ni1–N2
O1–Ni1–N4
O1–Ni1–S2
O1–Ni1–N2
O4–Ni1–O1
O4–Ni1–N4
O4–Ni1–S2
O4–Ni1–N2
175.0(2)
95.1(2)
85.1(3)
92.4(2)
88.11(10)
81.6(2)
97.3(3)
177.3(4)
91.6(3)
170.8(2)
89.6(3)
85.5(3)
89.9(3)
92.2(2)
92.6(3)
is small as judged from the spread of the cis-angles 85.1(3)°–92.4(2)° and the trans angles
170.8(2)° and 175.0(2)°. The Ni(II)–S (thioether) distances are 2.399(3) and 2.464(3) Å and
are quite typical of Ni(II)–S (thioether) distances observed in complexes of multidentate
ligands with one or more thioether S donors [24]. The Ni(II)–N (imino) distances of the
complex (2.028(9) and 2.026(8) Å) are well within the range when compared with those of
typical Ni(II)–N (imino) distances. The Ni(II)–O bond lengths 1.998(7) and 2.010(7) Å are
in the range of octahedral complexes [25]. The bond length of S2–C13, 1.772(11) Å
increases compared with S2–C13 bond of the free ligand, 1.7610(11) Å. The S2–C14 bond
also increases showing a weak coordination of S with Ni. Imine bond lengths of complex
N2–C7, 1.300(12) Å and N4–C27, 1.291(13) Å increase compared with the free ligand,
1.2863(14) Å, due to delocalization of the imine-bonded electrons. Interestingly, the
O1–C1, 1.298(13) Å and O4–C21, 1.279(11) Å bond lengths decrease compared with the
corresponding bond length of free ligand O1–C1, 1.3348(13) Å, due to delocalization of
the negative charge of oxygen to the ligand backbone giving partial double bond character.
Detailed crystallographic data are given in table 2. Selected bond lengths and angles of
the nickel complex are given in table 3.
4. Conclusion
A new sterically and electronically tunable hydroxyl-imine-thioether tridentate ligand and
three mononuclear Ni(II), Cu(II), and Co(II) complexes were prepared. These compounds
were characterized by different physico-chemical analyses. Single-crystal X-ray diffraction
data, magnetic susceptibility measurements, and electronic spectra revealed slightly dis-
torted octahedral arrangement for 2. The copper complex showed good catalytic activity
towards oxidation of thioether.
Supplementary material
CCDC 980688 and 980689 contain the supplementary crystallographic data for 1 and 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 Center, 12 Union Road, Cambridge
CB2 1EZ, UK; Fax: (+44) 1223 336 033; or E-mail: deposit@ccdc.cam.ac.uk.

2454
M. Kalita et al.
Acknowledgements
Authors thank SAIF, IIT Bombay, and IASST, Guwahati, for spectral and analytical data.
Authors also thank the Director of NIT, Silchar, for financial assistance (M.K.)
References
[1] M. Asadi, S. Esmaielzadeh, K. Mohammadi. Phosphorus, Sulfur Silicon Relat. Elem., 185, 1445 (2010).
[2] A.K. Pramanik, M.S. Jana, T.K. Mondal. J. Coord. Chem., 66, 4067 (2013).
[3] N.V. Kulkarni, N.H. Bevinahalli, V.K. Revankar. J. Coord. Chem., 63, 1785 (2010).
[4] S. Sarkar, P.K. Dhara, M. Nethaji, P. Chattopadhyay. J. Coord. Chem., 62, 817 (2009).
[5] M. Kalita, T. Bhattacharjee, P. Gogoi, P. Barman, R.D. Kalita, B. Sarma, S. Karmakar. Polyhedron, 60, 47
(2013).
[6] S. Acharya, A. Kejriwal, A.N. Biswas, P. Das, D.N. Neogi, P. Bandyopadhyay. Polyhedron, 38, 50 (2012).
[7] R. Manikandan, P. Viswanathamurthi, K. Velmurugan, R. Nandhakumar, T. Hashimoto, A. Endo. J. Photo-
chem. Photobiol., B, 130, 205 (2014).
[8] M. Amini, M. Bagherzadeh, Z. Moradi-Shoeili, D.M. Boghaei, A. Ellern, L.K. Woo. J. Coord. Chem., 66,
464 (2013).
[9] M. Amini, M. Bagherzadeh, B. Eftekhari-Sis, A. Ellern, L.K. Woo. J. Coord. Chem., 66, 1897 (2013).
[10] M. Amini, A. Arab, R. Soleyman, A. Ellern, L.K. Woo. J. Coord. Chem., 66, 3770 (2013).
[11] N.-Y. Jin. J. Coord. Chem., 65, 4013 (2012).
[12] M. Bagherzadeh, M. Zare. J. Coord. Chem., 66, 2885 (2013).
[13] M. Bagherzadeh, M.M. Haghdoost, A. Shahbazirad. J. Coord. Chem., 65, 591 (2012).
[14] P. Gogoi, M. Kalita, T. Bhattacharjee, P. Barman. Tetrahedron Lett., 55, 1028 (2014).
[15] M. Bagherzadeh, M.M. Haghdoost, F.M. Moghaddam, B.K. Foroushani, S. Saryazdi, E. Payab. J. Coord.
Chem., 66, 3025 (2013).
[16] Q.X. Chi, R.W. Lu, Z.X. Zhang, D.F. Zhao. Chin. Chem. Lett., 17, 1045 (2006).
[17] SMART, SAINT and SADABS, Bruker AXS Inc., Madison, WI (2007).
[18] G.M. Sheldrick. Acta Crystallogr., Sect. A, 64, 112 (2008).
[19] G.G. Mohamed, M.M. Omar, A.M. Hindy. Turk. J. Chem., 30, 361 (2006).
[20] T. Rosu, E. Pahontu, C. Maxim, R. Georgescu, N. Stanica, A. Gulea. Polyhedron, 30, 154 (2011).
[21] M.R.P. Kurup, B. Varghese, M. Sithambaresan, S. Krishnan, S.R. Sheeja, E. Suresh. Polyhedron, 30, 70
(2011).
[22] W.J. Geary. Coord. Chem. Rev., 7, 81 (1971).
[23] J.C. Noveron, R. Herradora, M.M. Olmstead, P.K. Mascharak. Inorg. Chim. Acta, 285, 269 (1999).
[24] S. Mandal, P.K. Bharadwaj, Z.Y. Zhou, T.C.W. Mak. Polyhedron, 14, 919 (1995).
[25] P.K. Dhara, S. Sarkar, M.G.B. Drew, M. Nethaji, P. Chattopadhyay. Polyhedron, 27, 2447 (2008).