Synthesis, characterization, structure, redox property, antibacterial and catalytic activity of tridentate Schiff base cobalt(III), nickel(II) and palladium(II) complexes

Article abstract of DOI:10.1016/j.poly.2013.01.010

Ligand, HL, 2-((2-(benzylthio)phenylimino)methyl)phenol, upon reaction with Co(NO₃)₃·6H₂O, Ni(OAc) ₂·4H₂O and PdCl₂ separately afforded complexes [(L)₂Co]NO₃ (1), [(L)₂Ni] (2) and [(L)PdCl] (3) respectively. The new complexes were characterized by usual spectroscopic studies like UV-Vis, IR and NMR and authenticated by X-ray structure determination on [(L)₂Co]NO₃, [(L) ₂Ni]. The analysis of crystal structures revealed that in all the complexes the ligand HL binds the metal center as uni-negative anion; L ^- dissociating phenolic proton and offers (O, N, S) tridentate binding mode to the metal. The compound [Co(L)₂]NO₃ is tested for in vitro antibacterial activity. Complex 3, acts as a catalyst in Heck reaction for a number of substrates. Complexes 1 and 2 exhibited a quasi reversible oxidative responses at 0.97 and 0.85 V, respectively, versus SCE. The electronic spectra and redox properties of the complexes have been explained with DFT computation.

Full text of DOI:10.1016/j.poly.2013.01.010

Polyhedron 51 (2013) 275–282
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Polyhedron
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Synthesis, characterization, structure, redox property, antibacterial and catalytic
activity of tridentate Schiff base cobalt(III), nickel(II) and palladium(II) complexes
b,
c
d
e,1
Poulami Pattanayak a, , Jahar Lal Pratihar , Debprasad Patra , Chia-Her Lin , Sobhana Paul
,
⇑
⇑
Kausiki Chakraborty f,1
a Department of Chemistry, University of Kalyani, Kalyani 741235, India
b Department of Chemistry, Kandi Raj College, Murshidabad 742137, India
c Department of Chemistry, East Calcutta Girls’ College, Kolkata 700089, India
d Department of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan
e Department of Zoology, East Calcutta Girls’ College, Kolkata 700089, India
f Department of Zoology, Derozio Memorial College, Kolkata 700136, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Ligand, HL, 2-((2-(benzylthio)phenylimino)methyl)phenol, upon reaction with Co(NO3)3ꢀ6H2O, Ni(OAc)2-
ꢀ4H2O and PdCl2 separately afforded complexes [(L)2Co]NO3 (1), [(L)2Ni] (2) and [(L)PdCl] (3) respectively.
The new complexes were characterized by usual spectroscopic studies like UV–Vis, IR and NMR and
authenticated by X-ray structure determination on [(L)2Co]NO3, [(L)2Ni]. The analysis of crystal structures
revealed that in all the complexes the ligand HL binds the metal center as uni-negative anion; Lꢁ disso-
ciating phenolic proton and offers (O, N, S) tridentate binding mode to the metal. The compound [Co(L)2]-
NO3 is tested for in vitro antibacterial activity. Complex 3, acts as a catalyst in Heck reaction for a number
of substrates. Complexes 1 and 2 exhibited a quasi reversible oxidative responses at 0.97 and 0.85 V,
respectively, versus SCE. The electronic spectra and redox properties of the complexes have been
explained with DFT computation.
Received 13 December 2012
Accepted 8 January 2013
Available online 19 January 2013
Keywords:
Crystal structure
Redox
Antibacterial activity
Heck reaction
DFT
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
still be developed. Furthermore, Schiff base complexes are very
much important for their interesting applications in biological,
Metal complexes incorporating ONS donor Schiff base ligands
where the ligands containing phenolic OH, the azomethine group
and thioether sulfur are scarce [1]. The Schiff bases are easily syn-
thesized and form complexes with almost all metal ions. There
have been many reports on activity of Schiff base complexes in
homogeneous and heterogeneous catalysis [2–10]. The carbon–
carbon bond forming reactions (Suzuki and Heck) is an important
and reliable tool in organic synthesis [11–18]. The Heck coupling
of an aryl halide with olefins is renowned as the most successful
method for forming a carbon–carbon bond in the synthesis of nat-
ural products, biologically active molecules [19–28] where the
recovery of the palladium catalyst is a challenging task [29–31].
Several strategies reported in the literature include a high catalyst
loading, higher temperature and relatively longer reaction time as
well as the participation of bases, ligands and metal salts additives.
So, the more mild, convenient and efficient catalytic system should
clinical, and pharmacological areas including antibacterial, anti-
fungal, and anticancer [32–43]. Notable examples of the ligand sys-
tems are thiosemicarbazone, semicarbazone and related ligands
which grab our attention due to their activity against influenza,
protozoa, smallpox and viral diseases [32–43]. Our present com-
munication focuses on catalytic activity, redox behavior and anti-
bacterial property of cobalt(III), nickel(II) and palladium(II)
complexes of ONS donor Schiff base ligand.
Herein we report the reactions of tridentate 2-((2-(benzyl-
thio)phenylimino)methyl)phenol, HL, ligand with Co(NO3)3ꢀ6H2O,
Ni(OAc)2ꢀ4H2O and PdCl2 separately to form complexes of compo-
sition [(L)2Co]NO3, 1, [(L)2Ni], 2 and [(L)PdCl], 3, respectively
where, the ligand offers (O, N, S) binding mode to the metal. The
complex formations have been authenticated on the basis of X-
ray studies and 1H NMR spectroscopy. Antibacterial activity of
[(L)2Co]NO3 complex have been studied against some bacteria.
Heck coupling reactions were carried out, in presence of air and
moisture, using [(L)PdCl] as catalysts. The redox property of the
complexes has been studied electrochemically. Plausible descrip-
tions of redox orbitals and electronic spectra have been ascribed
on the basis of single point DFT calculations.
⇑
Corresponding authors. Tel.: +91 33 25828750; fax: +91 33 25828282.
E-mail addresses: pparka@rediffmail.com (P. Pattanayak), jlpr@rediffmail.com
(J.L. Pratihar).
1
Collaborator for experiment related to antibacterial activity.
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.010

276
P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
color of the solution changes from green to olive green. The result-
2. Experimental
2.1. Materials
ing solution was refluxed for 6 h and filtered. Total solution was
kept for crystallization. After few days single crystal was obtained,
these are collected by filtration and washed with MeOH. Yield:
70%. Anal. Calc. for C40H32N2O2S2Ni (695.5): C, 69.01; H, 4.63; N,
4.02. Found: C, 69.36; H, 4.32; N, 3.87%. UV–Vis spectrum (CH2Cl2)
The solvents used in the reactions were of reagent grade (E.
Marck, Kolkata, India) and were purified and dried by reported pro-
cedure [44]. Cobalt nitrate hexahydrate, nickel acetate tetrahydrate,
palladium chloride, benzyl chloride and salicylaldehyde were pur-
chased from Emark, India. 2-Aminothiophenol was purchased from
Aldrich. 2-(benzylthio)aniline and 2-((2-(benzylthio)phenylimi-
no)methyl)phenol was prepared following the reported procedures
[1,45]. Iodobenzene, bromobenzene, 1-iodo-3,5-dimethylbenzene,
1-iodo-3,4-dimethylbenzene, 1-iodo-2-nitrobenzene, 1-iodo-3-
nitrobenzene, 1-bromo-3,5-dimethylbenzene, 1-bromo-2-nitro-
benzene, styrene were purchased from Aldrich.
kmax (e
, Mꢁ1 cmꢁ1) = 460 (1950), 325 (4120), 250 (11130). IR (KBr
pellets, cmꢁ1):
0.85.
m = 1604 (CH@N), 1523 (C–O), 752 (C–S). E1/2 [V]:
2.4.3. [(L)PdCl]
PdCl2 (0.065 g, 0.368 mmol) was dissolved by refluxing in 20 ml
acetonitrile, an orange color solution resulted. To this solution HL
(0.092 g, 0.370 mmol) in acetonitrile (10 ml) was added. The color
of the solution changes from light orange to brown. The mixture
was refluxed for 3 h. Total solution was kept for crystallization.
After few days single crystal was obtained, these are collected by
filtration and washed with acetonitrile. Yield: 80%. Anal. Calc. for
2.2. Physical measurements
Microanalysis (C, H, N) was performed using a Perkin-Elmer
2400 C, H, N, S/O series II elemental analyzer. Infrared spectra were
recorded on a Parkin-Elmer L120-00A FT-IR spectrometer with the
samples prepared as KBr pellets. Electronic spectra were recorded
on a Shimadzu UV-1800 PC spectrophotometer. 1H NMR spectra
were obtained on Bruker 400 NMR spectrometers in CDCl3 using
TMS as the internal standard. Electrochemical measurements were
made under dinitrogen atmosphere using a CH instruments model
600D potentiostat. A platinum disc working electrode, a platinum
wire auxiliary electrode and an aqueous saturated calomel refer-
ence electrode (SCE) were used in a three-electrode configuration.
All electrochemical data were collected at 298 K and are uncor-
rected for junction potentials.
C
20H16NOSClPd (460.31): C, 52.18; H, 3.50; N, 3.05. Found: C,
52.35; H, 3.24; N, 3.18%. UV–Vis spectrum (CH2Cl2) kmax
, Mꢁ1
cmꢁ1) = 455 (3070), 305 (4650), 255 (9000). IR (KBr pellets,
cmꢁ1): = 1606 (CH@N), 1523 (C–O), 758 (C–S). 1H NMR CDCl3:
(e
-
m
d 8.23 (s, 1H), 7.66–7.21 (m, 12H), 6.64 (d, 1H), 4.49 (d, 1H), 4.33
(d, 1H).
2.5. Antibacterial activity
2.5.1. Microorganisms
The microorganisms used in this study included Escherichia coli
DH5, Bacillus subtilis ATCC6623 and Staphylococcus ATCC25923.
These strains were kindly provided by Prof. Prasanta Kr. Bag,
Department of Biochemistry, University of Calcutta, Kolkata, West
Bengal, India.
2.3. DFT calculations
Using the X-ray coordinates of the [(L)2Co]+ and [(L)2Ni] com-
plexes, ground state electronic structure calculations have been
carried out using DFT [47] methods with the Orca 2.7 program
[46]. Becke’s hybrid function [47] with the Lee–Yang–Parr (LYP)
correlation function [48] was used throughout the study. LANL2DZ
valence and effective core potential functions were used. All energy
calculations were performed using the self-consistent field ‘‘tight’’
option of the Orca 2.7 program to ensure sufficiently well con-
verged values for the state energies.
2.5.2. Drug solution
The compound of cobalt [(L)2Co]NO3 (7 mg) was screened for its
antibacterial activity. For this drug was dissolved in 700 ll of 100%
DMSO to get the concentration of 1 mg/ml, which was used as
stock solution. Evaluation of the activity was carried out by broth
dilution technique using Mueller Hinton medium.
2.5.3. Preparation of inoculum
An inoculum of the microorganism was prepared from 4 h MBH
(Mueller Hinton Broth) cultures and suspensions were adjusted
with a turbidity equivalent to that of a 0.5 McFarland standard.
50 ꢂ 106 CFU/ml were inoculated in each bacterial culture tube.
2.4. Syntheses of complexes [(L)2Co]NO3, [(L)2Ni] and [(L)PdCl]
2.4.1. [(L)2Co]NO3
Cobalt nitrate hexahydrate (1 mmol, 291 mg) was mixed with
the methanolic solution of the Schiff bases (2 mmol 756 mg). The
color of the solution changes from pink to redish brown. The
resulting solution was stirred in presence of slight heat for 4 h. To-
tal solution was kept for crystallization. After few days single crys-
tal was obtained. Yield: 60%. Anal. Calc. for C40H32N3O5S2Co
(757.76): C, 63.34; H, 4.22; N, 5.54. Found: C, 63.21; H, 4.29; N,
2.5.4. Determination of minimum inhibitory concentration (MIC) and
determination of minimal bactericidal concentration (MBC)
MIC and MBC of the cobalt compound was assessed using the
broth microdilution method recommended by the National Com-
mittee of Clinical Laboratory Standards [49]. The bacterial culture
tubes were prepared by dispensing 10
into each tube. A 25 l aliquot of the cobalt compound was added.
The concentration of the cobalt compound tested were 2, 20, 32,
80, 100, 128, 200 g/ml. Dilutions of Tetracycline served as posi-
tive control while broth with 25 l of 100% DMSO was used as a
ll of the inoculated broth
l
5.36%. UV–Vis spectrum (CH2Cl2) kmax
(1560), 345 (17300), 270 (35470), 240 (35980). IR (KBr pellets,
cmꢁ1): = 1605 (CH@N), 1529 (C–O), 1337(NO3), 756 (C–S). 1H
(e,
Mꢁ1 cmꢁ1) = 445
l
m
l
NMR CDCl3: d 7.94 (s, 1H), 7.56 (d, 2H), 7.30–7.23 (m, 3H), 7.16
(t, 1H), 7.02–6.96 (m, 3H), 6.76 (d, 2H), 6.57 (t, 2H), 3.71–3.66
(m, 2H). E1/2 [V]: 0.97.
negative control tubes were covered and incubated for 24 h in
ambient air at 37 °C. After incubation MIC were read visually fol-
lowing a reported method [50]. All the contents of the test tubes
were plated to nutrient agar (Hi-Media) and incubated. The mini-
mum bactericidal concentration (MBC) was defined as a 99.9%
reduction in CFU from the starting inoculum after 24 h incubation
interval.
2.4.2. [(L)2Ni]
Nickel acetate tetrahydrate (1 mmol, 250 mg) was mixed with
the methanolic solution of the Schiff bases (2 mmol 756 mg). The

P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
277
Table 1
Crystallographic data for 1 and 2.
Chemical formula
C40H32N2O2S2Co,
NO3
C40H32N2O2S2Ni,
H2O
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
757.76
monoclinic
P 21/c
18.0644(3)
10.1594(1)
20.7710(3)
90
113.2730(10)
90
713.51
monoclinic
P 21/c
12.7395(3)
30.6303(7)
17.6227(4)
90
103.6870(10)
90
a
(°)
b (°)
(°)
c
k (Å)
0.71073
3501.80(9)
1568
0.71073
6681.4(3)
2960
V (Å3)
F(000)
Z
4
4
T (K)
295
1.437
0.660
296
1.415
0.749
D (mg/mꢁ3
)
l
(mmꢁ1
)
h Min–Max (°)
2.0, 28.3
31888
8652 (0.051)
5557
1.4, 29.3
104860
18005 (0.044)
11940
Reflections measured
Unique reflections (Rint
No. of reflections used
)
Fig. 1. UV–Vis spectra of [(L)2Co]NO3
dichloromethane.
(
. . ..), [(L)2Ni] (—) and [(L)PdCl] (—) in
[I > 2
r
(I)]
(I)]
R1 [I > 2
r
0.0444
0.1197
1.02
0.0423
0.1445
0.80
wR2 (all data)
Goodness-of-fit (GOF) on F2
solution was done by direct method with SHELXS-97 program
[51,52]. Full matrix least square refinements on F2 were performed
using SHELXL-97 program [51,52]. The fact to mention here that the
crysꢁtal structure of compound [(L)2Co]NO3, 1 contain a disorder
NO3 ion with refined occupancies for the O atoms of 0.555(11)
& 0.445(11) and the crystal structure of compound [(L)2Ni], 2 crys-
tallizes with two independent complex molecules with two water
molecules of crystallization per asymmetric unit. All non-hydrogen
2.6. General procedure for the Heck reaction
mixture containing styrene (3.5 mmol), aryl halide
A
(3.5 mmol), the palladium complex [(L)PdCl] (0.001 mmol) and
potassium carbonate (8.0 mmol) in methanol (10 ml) were heated
to reflux for 4 h. After evaporation of solvent the product was
poured into water and extracted with diethyl ether. The ether solu-
tion was dried over Na2SO4 and filtered. The ether solution were
passed through silica column (60–120 mesh), the complex remain
trapped. After extraction of desired compound complex was ex-
tracted using dichloromethane. Upon evaporation of the ether, so-
lid of pure products were obtained. The yields of the products
obtained from all the reactions were determined after isolation
and characterized by 1H NMR spectra.
atoms were refined anisotropically using reflections I > 2r(I). The
C-bound hydrogen atoms were included in calculated positions
and refined as riding atoms. It was not possible to locate the water
H atoms for compound 2. Further crystallographic and refinement
details are given in Table 1.
3. Results and discussion
3.1. Syntheses
2.7. Crystallography
The reactions of two equivalent of 2-((2-(benzylthio)phenylimi-
no)methyl)phenol, HL ligand with Co(NO3)3.6H2O and Ni(OAc)2-
ꢀ4H2O separately in methanol afforded brown and green
complexes of compositions [(L)2Co]NO3, 1, and [(L)2Ni], 2,
respectively (Scheme 1). The complex [(L)PdCl], 3 was synthesized
upon reaction of ligand HL with Pd(MeCN)2Cl2 in 1:1 mol ratio in
Single crystals of [(L)2Co]NO3 and [(L)2Ni] were grown by slow
evaporation of methanol solution at 298 K. Data were collected by
x
-scan technique on a Bruker Smart CCD diffractometer with Mo
Ka
radiation monochromated by graphite crystal. Structure
n+
N
O
OH
Cl
O
O
PdCl2
Mn+
N
X-
Pd
M
Reflux
CH3CN
N
S
S
N
MeOH
S
S
HL
3
[(L)PdCl
M = Co(III), n = 1, X = NO 3
Ni(II), n = 0, X =
1 & 2
Scheme 1. Synthesis of [(L)2M]n+ and [(L)PdCl].

278
P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
Fig. 2. Molecular structure of [(L)2Co]+ with atom numbering scheme. Hydrogen atoms and NO3 ion are omitted for clarity.
ꢁ
acetonitrile solution. In all the complexes the ligand binds the met-
als in tridentate (O, N, S) fashion through deprotonated phenolic-O,
imine-N and thioether-S atom forming two fused rings – one six
membered and other five membered. The oxidation state of Co(III)
characteristic of uncoordinated NO3ꢁ [53]. The IR data are collected
in Section 3.
The compositions of complexes [(L)2Co]NO3 and [(L)PdCl]
matched well with the C, H, N analytical data and 1H NMR spectral
data. The O–H proton resonance is absent in the 1HNMR spectra of
[(L)2Co]NO3 and [(L)PdCl] complexes signifying the dissociation of
the phenolic proton upon complexation. The singlet resonance for
the aldimine (N@CH) proton of the HL ligand near d = 8. 47 is
shifted to d = 7.94 and 8.23 in the cobalt(III) and Pd(II) complexes
respectively [1]. The methylene proton resonance appeared as
multiplet in the range d 3.72–3.65 for complex [(L)2Co]NO3
whereas the methylene proton resonance of [(L)PdCl] appeared
as two separate doublet at d 4.49 and d 4.33 due to the non equiv-
alent nature of two methylene protons. The aromatic proton reso-
nances of [(L)2Co]NO3 complex appeared as doublet at d 7.56,
multiplet in the range d 7.32–7.20, triplet at d 7.16, multiplet in
the range d 7.06–6.96, doublet at d 6.76 and triplet at d 6.56. The
aromatic proton resonances of [(L)PdCl] appeared in the region d
7.66–7.21 and one broad singlet at d 6.64 for one proton. Although,
all the aromatic protons for [(L)PdCl] could not be assigned accu-
rately but the protons integrations matched well with the number
of protons. The 1H NMR data are given in Section 3.
ꢁ
in [(L)2Co]NO3, 1, is satisfied by one NO3 ion. The composition of
the complexes is supported by the microanalytical data and 1H
NMR spectra.
3.2. Spectral characterization and solution structures
Compounds 1–3 are soluble in common organic solvents fur-
nishing brown, green and brown color respectively. UV–Vis spectra
of the complexes were recorded in dichloromethane solutions and
characteristic spectra for 1–3 are shown in Fig. 1. The UV–Vis spec-
tral data are given in the experimental section. Compounds 1–3
displayed several absorptions in the visible and ultraviolet regions.
Characteristic low energy absorption bands appeared near 445,
460 and 455 nm for [(L)2Co]NO3, [(L)2Ni] and [(L)PdCl] respectively
which may be due to metal to ligand charge transfer (MLCT) (vide
DFT computation).
The m
(C@N) band in the ligand (1610 cmꢁ1) is shifted to lower
frequency in all the complexes (1604–1606 cmꢁ1), indicating the
coordination of the azomethine nitrogen [1]. Phenolic C–O band
in ligand (1282 cmꢁ1) has been shifted to higher frequency in the
complexes (1385–1389 cmꢁ1) indicating the coordination through
3.3. X-ray structure determination of [(L)2Co]NO3 and [(L)2Ni]
the phenolic oxygen [1]. The
m
(C–S) near 758–752 cmꢁ1 indicates
Suitable crystals of [(L)2Co]NO3 and [(L)2Ni] were grown by the
slow evaporation of methanolic solutions. The X-ray structures of
[(L)2Co]NO3, [(L)2Ni] were determined and the perspective view
the coordination of the thio-benzyl group [1]. A broad band at
1337 cmꢁ1 was observed in cobalt(III) complex which is the

P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
279
Fig. 3. Molecular structure of [(L)2Ni] with atom numbering scheme. Hydrogen atoms are omitted for clarity.
Table 2
Table 3
Selected bond distances (Å) and angles (deg) for compound 1.
Selected bond distances (Å) and angles (°) for compound 2.
Distances
Distances
Co1–S1
Co1–S2
Co1–O1
Co1–O2
Co1–N1
Co1–N2
S1–C13
S1–C14
O1–C1
2.2631(7)
2.2494(8)
1.8871(15)
1.8810(18)
1.9249(18)
1.9223(18)
1.769(2)
N1–C7
N1–C8
N2–C28
N2–C27
O3–N3
O2–C21
O4–N3
O5–N3
1.290(3)
1.432(3)
1.433(3)
1.295(3)
1.262(7)
1.307(3)
1.209(8)
1.114(15)
Ni1–S1
Ni1–O1
Ni1–N1
S1–C13
S2–C34
O1–C1
2.4767(7)
2.0103(16)
2.0243(19)
1.778(3)
1.832(3)
1.304(3)
1.297(3)
1.420(3)
Ni1–S2
Ni1–O2
Ni1–N2
S1–C14
S2–C33
O2–C21
N1–C8
2.5046(7)
1.9779(18)
2.0304(19)
1.832(3)
1.775(2)
1.295(3)
1.414(3)
1.298(3)
N1–C7
N2–C28
1.826(3)
1.323(3)
N2–C27
Angles
Angles
S1–Ni1–S2
S1–Ni1–O2
Ni1–S1–C13
S2–Ni1–O1
Ni1–S2–C34
S2–Ni1–N1
O1–Ni1–O2
O1–Ni1–N2
N1–Ni1–N2
92.50(2)
90.70(6)
93.60(9)
83.58(5)
119.66(11)
95.37(6)
93.90(7)
92.54(7)
175.32(8)
S1–Ni1–O1
S1–Ni1–N1
S1–Ni1–N2
S2–Ni1–O2
S2–Ni1–N2
O1–Ni1–N1
O2–Ni1–N1
O2–Ni1–N2
171.78(5)
82.22(6)
94.06(6)
173.68(5)
81.91(6)
90.93(7)
90.46(8)
92.43(7)
S1–Co1–S2
S1–Co1–O1
S1–Co1–O2
S1–Co1–N1
S1–Co1–N2
S2–Co1–O1
S2–Co1–O2
S2–Co1–N1
S2–Co1–N2
85.89(3)
178.67(6)
92.38(5)
86.75(6)
92.83(6)
92.80(6)
177.36(5)
91.22(7)
87.57(7)
O1–Co1–O2
O1–Co1–N1
O1–Co1–N2
O2–Co1–N1
O2–Co1–N2
N1–Co1–N2
Co1–S1–C13
Co1–S1–C14
C13–S1–C14
88.93(7)
93.55(7)
86.84(7)
86.68(8)
94.51(8)
178.75(10)
97.40(8)
110.55(10)
102.46(13)
center are cis,cis; trans,trans and cis,cis, respectively. The Co(1)–
O(1), Co(1)–N(1), Co(1)–S(1), and C(7)–N(1) lengths for [(L)2Co]+
(1.8870(15), 1.9249(18), 2.2631(7) and 1.290(3) Å, respectively)
and Ni(1)–O(1), Ni(1)–N(1), Ni(1)–S(1), and C(7)–N(1) lengths for
[(L)2Ni] (2.0103(16), 2.0243(19), 2.4767(7) and 1.297(3) Å, respec-
tively) are within the normal range [40,54–56].
of [(L)2Co]+ cation and the [(L)2Ni] molecule along with the atom
numbering scheme are shown in Figs. 2 and 3 and selected bond
distances and angles are collected in Tables 2 and 3. The asymmet-
ric unit of [(L)2Ni] contains two molecules of same structural
parameters. So, structural analysis of one molecule is considered.
The geometry about the metal (Co(III) and Ni(II)) is distorted octa-
hedral, where the two anionic ligands, [Lꢁ], coordinated meridio-
nally giving rise to MN2O2S2 (M = Co, Ni) coordination sphere.
The three donor atoms are deprotonated phenolic oxygen, imine
nitrogen and thioether sulfur. A disorder nitrate (NO3ꢁ) ion satis-
fies the unipositive charge of the complex cation, [(L)2Co]+. The ori-
entations of phenolic-O, imine-N and thioether-S around metal
3.4. Electrochemistry
The electrochemical behavior of complex [(L)2Co]NO3 and
[(L)2Ni] were investigated in dichloromethane acetonitrile mixed
solvent (0.1 M TBAP) by cyclic voltammetry with a scan rate of
50 mV sꢁ1 (Figs. S6–S7). Complexes [(L)2Co]NO3 and [(L)2Ni] exhib-
ited one electron quasireversible oxidative responses with the E1/2

280
P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
Fig. 4. Cyclic voltammogram of (a) [(L)2Co]NO3 and (b) [(L)2Ni].
Fig. 5. (a) HOMO of [(L)2Co]+ and (b) LUMO of [(L)2Co]+; (c) HOMO of [(L)2Ni] and (d) LUMO of [(L)2Ni].
Â
Â
Ãþ
2þ
at 0.97 and 0.85 V versus SCE. The oxidation have been assigned
according to the couple of Eqs. (1) and (2) where [Co(L)2]+ is the
Co(III) analogue of [Co(L)2]2+ and [Ni(L)2] is analogue of [Ni(L)2]+
(see Fig. 4).
ðLÞ2Co ꢀ ½ðLÞ2Coꢃ
ð1Þ
ð2Þ
Ãþ
ðLÞ2Niꢃ ꢀ ½ðLÞ2Ni

P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
281
Table 4
Antibacterial activity of the cobalt compound [(L)2Co]NO3.
Strains
Sensitivity to the cobalt compound
Sensitivity to DMSO (control)
MIC (
lg/ml)
MBC (lg/ml)
Escherichia coli DH5alpha
Bacillus subtilis ATCC6623
Staphylococcus ATCC25923
ꢁ
ꢁ
+
—
—
—
0.0
0.0
32
0.0
0.0
64
ꢁ Shows no antibacterial activity up to 200
l
g/ml, — indicates no inhibition with DMSO.
compound showed no antibacterial strains Escherichia coli DH5
and Bacillus subtilis ATCC6623 up to 200 lg/ml.
Table 5
Heck reaction with catalyst 3.
3.6. Heck reaction
Aryl halide
Product
Isolated yield
95
Heck coupling is an important palladium catalyzed C–C cou-
pling reaction where the substrates are arylhalides (bromoaryls
and iodoaryls) and styrene [11,12]. We have examined the cata-
lytic activity of [(L)PdCl] toward Heck coupling reactions in ambi-
ent condition. Conversions of arylhalides (Br and I) to
corresponding stilbene derivatives upon reaction with styrene
using [(L)PdCl] as catalyst in refluxing methanol and in presence
of K2CO3 have been examined. The results of transformations are
given in Table 5. After reaction the palladium catalyst was isolated
and it was found that the coupling reactions did take place reusing
the isolated catalyst. This reusability of the catalyst was checked
up to three times for a reaction keeping the other conditions in
tact. The products were characterized by 1H NMR spectroscopy.
I
92
I
92
90
I
I
NO2
4. Conclusion
NO2
92
O2N
O2N
Ligand, 2-((2-(benzylthio)phenylimino)methyl)phenol, HL, is
used for the synthesis of [(L)2Co]NO3, [(L)2Ni] and [(L)PdCl]. Com-
plexes were characterized by usual spectroscopy and authenti-
cated by X-ray structure determination on [(L)2Co]NO3, [(L)2Ni].
The redox property of complexes [(L)2Co]NO3 and [(L)2Ni] were
examined and correlate with DFT results. The new [(L)PdCl] com-
plex have been used as catalysts for Heck coupling reactions in
presence of air and moisture. The compound [Co(L)2]NO3 is tested
for in vitro antibacterial activity.
I
82
80
Br
Br
Solvent = MeOH, base = K2CO3, time = 4 h.
Acknowledgments
Special thank to Professor Surajit Chattopadhyay, University of
Kalyani, for his valuable suggestions throughout this work. The
MeOH
Reflux
X
+
ð3Þ
K2CO3
R
R
X = I or Br
R = H, Me, NO2
According to the DFT results the composition of HOMO (Fig. 5(a
and c)) of [(L)2Co]NO3 and [(L)2Ni] are metal centered indicating
the oxidation to be metal centered. The LUMO (Fig. 5(b and d))
are metal ligand mixed centered. Therefore the HOMO ? LUMO
MLCT transition is consistent with the assignment of UV–Vis
spectra.
authors are grateful to Prof. P.K. Bag, Department of Biochemistry,
University of Calcutta, for his valuable guidance during the study of
microbial activity. Author PP acknowledged to DST under WOS-A
(Sanction No. SR/WOS-140/2011) and JP acknowledged to Univer-
sity Grants Commission (under Minor Research Project, Sanction
No. F.PSW/067/2011-12). The necessary laboratory and infrastruc-
tural facility are provided by the Department of Chemistry, Kandi
Raj College and Department of Chemistry, University of Kalyani.
3.5. Antibacterial activity
The compound of cobalt [(L)2Co]NO3 was found to show good
in vitro activity to one bacterial strain-Staphylococcus ATCC25923,
out of the three bacterial strains used in this work (Table 4). Data
revealed that the compound inhibited Staphylococcus aureus MIC
Appendix A. Supplementary material
CCDC 806268 and 912712; contain the supplementary crystal-
lographic data for 1–3. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
32 lg/ml and MBC was found to be 64 lg/ml. However the

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P. Pattanayak et al. / Polyhedron 51 (2013) 275–282
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