Mixed-ligand nickel(II) thiosemicarbazone complexes: Synthesis, characterization and biological evaluation

Article abstract of DOI:10.1016/j.poly.2012.11.031

The syntheses and characterization of some new mixed-ligand nickel(II) complexes {[Ni(L¹)(PPh₃)] (1), [Ni(L¹)(Py)] (2), [Ni(L²)(PPh₃)]·DMSO (3), [Ni(L ²)(Imz)] (4), [Ni(L³)(4-pic

Full text of DOI:10.1016/j.poly.2012.11.031

Polyhedron 50 (2013) 354–363
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Mixed-ligand nickel(II) thiosemicarbazone complexes: Synthesis, characterization
and biological evaluation
b
b
c
c
Saswati a, Rupam Dinda a, , Carla S. Schmiesing , Ekkehard Sinn , Yogesh P. Patil , M. Nethaji ,
⇑
Helen Stoeckli-Evans d, Rama Acharyya a,
⇑
a Department of Chemistry, National Institute of Technology, Rourkela 769008, Orissa, India
b Department of Chemistry, Western Michigan University, Kalamazoo, MI 49008, USA
c Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
d Institute of Physics, University of Neuchâtel, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland
a r t i c l e i n f o
a b s t r a c t
The syntheses and characterization of some new mixed-ligand nickel(II) complexes {[Ni(L1)(PPh3)] (1),
Article history:
Received 28 June 2012
Accepted 9 November 2012
Available online 29 November 2012
[Ni(L1)(Py)] (2), [Ni(L2)(PPh3)]ꢀDMSO (3), [Ni(L2)(Imz)] (4), [Ni(L3)(4-pic)] (5) and [{Ni(L3)}2(
l
-4,40-
byp)]ꢀ2DMSO (6)} of three selected thiosemicarbazones {the 4-(p-X-phenyl)thiosemicarbazones of sali-
cylaldehyde} (H2L1ꢁ3) (A, Scheme 1) are described in the present study, differing in the inductive effect
of the substituent X (X = F, Br and OCH3), in order to observe its influence, if any, on the redox potentials
and biological activity of the complexes. All the synthesized ligands and the metal complexes were suc-
cessfully characterized by elemental analysis, IR, UV–Vis, NMR spectroscopy and cyclic voltammetry. The
molecular structures of four mononuclear (1–3 and 5) and one dinuclear (6) Ni(II) complex have been
determined by X-ray crystallography. The complexes have been screened for their antibacterial activity
against Escherichia coli and Bacillus. The minimum inhibitory concentrations of these complexes and their
antibacterial activities indicate that compound 4 is the potential lead molecule for drug designing.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Thiosemicarbazone
Nickel(II) complexes
X-ray crystal structure
Antibacterial study
1. Introduction
NSO chelating ligands and are known to exhibit diverse biological
activities [32]. However, not only the bioinorganic relevance of the
Nickel(II) complexes with nitrogen and sulfur donor ligands are
highly interesting [1–5] because several hydrogenases and carbon
monoxide dehydrogenases [6] contain such nickel complexes as
their active site. Thiosemicarbazones are an important class of
N,S donor ligand which have considerable pharmacological interest
due to their significant antibacterial, antiviral, antimalarial, anti-
leprotic and anticancer activities [7–10]. Metal complexes of thio-
semicarbazone ligands have shown variable bonding properties
and structural diversity, along with promising biological implica-
tions and ion sensing abilities [9,11–17]. Among the transition
metals, thiosemicarbazone complexes of nickel(II) also show
marked and diverse biological [18–21] as well as catalytic activity
[22,23], but there are a limited number of Ni(II) complexes re-
ported with N1-substituted thiosemicarbazones [24–29].
complexes but also the chemistry of transition metal complexes of
the thiosemicarbazones is receiving significant current attention
because of the variable binding modes displayed by these ligands
in their complexes [34–43]. The variable modes of binding of thio-
semicarbazone ligands and the ability of nickel to take up different
coordination environments (such as octahedral, square-planar and
tetrahedral) has encouraged us to explore the coordination chem-
istry further, and herein we report the syntheses, X-ray structures
and physical properties of some new mixed-ligand nickel(II) com-
plexes of thiosemicarbazone ligands, with special reference to their
antibacterial activity. Three thiosemicarbazones {the 4-(p-X-
phenyl)thiosemicarbazones of salicylaldehyde} (H2L1ꢁ3) have been
used, differing in the inductive effect of the substituent X (X = F, Br
and OCH3) in order to observe its influence, if any, on the redox
potentials and biological activities of the complexes.
Thiosemicarbazones obtained by condensation of ring-substi-
tuted 4-phenyl thiosemicarbazides with salicylaldehyde and
substituted salicylaldehydes [30–33] form a class of versatile NS/
2. Experimental
2.1. Materials
⇑
Corresponding authors. Tel.: +91 661 246 2657; fax: +91 661 246 2022 (R.
Dinda), tel.: +91 661 246 3657; fax: +91 661 246 2022 (R. Acharyya).
E-mail addresses: rupamdinda@nitrkl.ac.in (R. Dinda), r_acharyya@yahoo.co.in
(R. Acharyya).
Reagent grade solvents were dried and distilled prior to use. All
other chemicals were reagent grade, available commercially and
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.11.031

Saswati et al. / Polyhedron 50 (2013) 354–363
355
used as received. HPLC grade DMSO and CH3CN were used for
2.4. Synthesis of the complexes {[Ni(L1)(PPh3)] (1); [Ni(L1)(Py)] (2);
spectroscopic and electrochemical studies, and ethanol and
methanol were used for the synthesis of the ligands and the metal
complexes. Commercially available TEAP (tetra ethyl ammonium
[Ni(L2)(PPh3)]ꢀDMSO (3); [Ni(L2)(Imz)] (4), [Ni(L3)(4-pic)](5) and
[{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6)}
perchlorate) was properly dried and used as
a supporting
electrolyte for recording the cyclic voltammograms of the
complexes.
2.4.1. [Ni(L1)(PPh3)] (1)
To a solution of H2L1 (0.289 g, 0.100 mmol) in hot methanol, tri-
ethylamine (0.202 g, 0.2 mmol) was added, followed by solid
Ni(OAc)2 salt (0.248 g, 0.100 mmol) and triphenylphosphine
(0.262 g, 0.100 mmol). The mixture was refluxed for 3 h and a clear
reddish brown solution was obtained, which was filtered and al-
lowed to evaporate at room temperature. Reddish brown colored
crystals were obtained from the filtrate after 3–4 days. [Ni(L1)
(PPh3)] (1): Yield: 67%. Anal. calc. for C32H25FN3NiOPS: C, 63.18; H,
4.14; N, 6.91. Found: C, 63.13; H, 4.17; N, 6.87%. Main IR peaks
2.2. Physical measurements
Elemental analyses were performed on a Vario ELcube CHNS
Elemental analyzer. IR spectra were recorded on a Perkin-Elmer
Spectrum RXI spectrometer. 1H NMR spectra were recorded with
a Bruker Ultrashield 400 MHz spectrometer using SiMe4 as an
internal standard. Electronic spectra were recorded on a Lamda25,
Perkin-Elmer spectrophotometer. Electrochemical data were col-
lected using a PAR Versastat-II instrument driven by E-CHEM soft-
(KBr, cmꢁ1):
1542 s, 1408 m,
m
(N(1)–H) 3215 s,
m
(C@C) 1627 s,
m
m(–C(8)@N(3))
m(P–C) 1094 s,
(C(7)–S(1)) 739 s. 1H NMR
ware (PAR) at 298 K in
a dry nitrogen atmosphere. Cyclic
(DMSO-d6, 400 MHz) d: 9.45 (s, 1H, –C(7)–N(1)H), 8.66 (s,1H,
voltammetry experiments were carried out with Pt working and
auxiliary electrodes, Ag/AgCl as the reference electrode and TEAP
as the supporting electrolyte.
–N(3)@C(8)–H), 7.78–6.34 (m, 23H, C6H4).
2.4.2. [Ni(L1)(Py)] (2), [Ni(L2)(PPh3)]ꢀDMSO (3), [Ni(L2)(Imz)] (4) and
[Ni(L3)(4-pic)] (5)
2.3. Synthesis of the ligands (H2L1ꢁ3) {H2L1 (4-(p-fluorophenyl)
thiosemicarbazone); H2L2 (4-(p-bromophenyl) thiosemicarbazone)
and H2L3 (4-(p-methoxyphenyl)thiosemicarbazone) of
salicylaldehyde}
Complexes 2–5 were prepared following the same procedure as
complex 1. Reddish brown crystals of Complex 3, suitable for X-ray
crystallography were obtained by slow evaporation from DMSO.
[Ni(L1)(Py)]: (2):Yield: 70%. Anal. calc. for C19H15FN4NiOS: C,
53.68; H, 3.56; N, 13.18. Found: C, 53.65; H, 3.59; N, 13.16%. Main
IR peaks (KBr, cmꢁ1):
(–C(8)@N(3)) 1521 s, 1417 m,
m
(N(1)–H) 3229 s,
m(C@C) 1613 s,
The thiosemicarbazides were prepared from distilled substi-
tuted aniline by a known method, reported ear1ier [44]. The Schiff
base ligands, 4-(p-fluorophenyl)thiosemicarbazone (H2L1), 4-(p-
bromophenyl) thiosemicarbazone (H2L2) and 4-(p-methoxy-
phenyl)thiosemicarbazone (H2L3) of salicylaldehyde were prepared
in 80–90% yield by stirring an equimolar ratio of the substituted
thiosemicarbazide with salicylaldehyde in methanol medium,
using standard procedures [31]. The resulting compound was
filtered, washed thoroughly with methanol and dried over fused
CaCl2. H2L1: Yield: 85%. Anal. calc. for C14H12N3SOF: C, 58.13; H,
4.18; N, 14.52. Found: C, 58.15; H, 4.20; N, 14.51%. Main IR peaks
m
m
(C(7)–S(1)) 736 s. 1H NMR
(DMSO-d6, 400 MHz) d: 9.47 (s, 1H, –C(7)–N(1)H), 8.35 (s, 1H,
–N(3)@C(8)–H), 8.84–6.59 (m, 13H, C6H4). [Ni(L2)(PPh3)]ꢀDMSO
(3): Yield: 65%. Anal. calc. for C34H31BrN3NiO2PS2: C, 54.64; H,
4.18; N, 5.62. Found: C, 54.69; H, 4.19; N, 5.78%. Main IR peaks
(KBr, cmꢁ1):
1545 s, 1425 m,
m
(N(1)–H) 3257 s,
m
(C@C) 1624 s,
m
m(–C(8)@N(3))
m(P–C) 1098 s,
(C(7)–S(1)) 747 s. 1H NMR
(DMSO-d6, 400 MHz) d: 9.58 (s, 1H, –C(7)–N(1)H), 8.69 (s, 1H,
–N(3)@C(8)–H), 7.77–6.35 (m, 23H, C6H4), 2.54 (s, 6H, DMSO).
[Ni(L2)(Imz)] (4): Yield: 68%. Anal. calc. for C17H14BrN5NiOS: C,
42.99; H, 2.97; N, 14.74. Found: C, 42.95; H, 2.99; N, 14.72%. Main
(KBr, cmꢁ1):
3028 s, (C@C) 1605 s,
(C(7)@S(1)) 750 s. 1H NMR (DMSO-d6, 400 MHz) d: 11.81 (s, 1H,
m(O(1)–H) 3357 s,
m(N(1)–H) 3247 s, m(N(2)–H)
IR peaks (KBr, cmꢁ1):
(–C(8)@N(3)) 1556 s, 1428 m,
m
(N(1)–H) 3251 s,
m(C@C) 1619 s,
m
m(C(8)@N(3)) 1543 s, 1438 m,
m
m
(C(7)–S(1)) 741 s. 1H NMR
m
–C(14)–O(1)H), 10.06 (s, 1H, –C(7)–N(1)H), 9.99 (s, 1H,
–C(7)–N(2)H), 8.48 (s, 1H, –N(3)@C(8)–H), 8.11–6.81 (m, 8H,
C6H4). 13C NMR (DMSO-d6, 100 MHz) d: 176.52, 161.25, 158.54,
157.05, 140.52, 135.97, 135.95, 131.81, 128.54, 128.46, 127.48,
120.70, 119.66, 116.48. H2L2: Yield: 88%. Anal. calc. for
(DMSO-d6, 400 MHz) d: 9.60 (s, 1H, –C(7)–N(1)H), 8.71 (s,1H,
–N(3)@C(8)–H), 7.03–6.79 (m, 12H, C6H4). [Ni(L3)(4-pic)] (5) :
Yield: 67%. Anal. calc. for C21H20N4NiO2S: C, 55.90; H, 4.47; N,
12.42. Found: C, 55.87; H, 4.43; N, 12.46%. Main IR peaks (KBr,
cmꢁ1):
1430 m,
m
m
(N(1)–H) 3263 s,
m(C@C) 1622 s, m(–C(8)@N(3)) 1542 s,
(C(7)–S(1)) 739 s. 1H NMR (DMSO-d6, 400 MHz) d: 9.23
C
14H12N3SOBr: C, 48.01; H, 3.45; N, 12.00. Found: C, 48.04; H,
3.40; N, 12.03%. Main IR peaks (KBr, cmꢁ1):
(O(1)–H) 3307 s,
(C@C) 1621 s,
(C(7)@S(1)) 752 s. 1H NMR
m
m
(s, 1H, –C(7)–N(1)H), 8.19 (s, 1H, –N(3)@C(8)–H), 8.68–6.57 (m,
12H, C6H4), 3.69 (s, 3H, –C(4)–OCH3), 2.37 (s, 3H, 4-pic-CH3).
m(N(1)–H) 3297 s,
m
(N(2)–H) 3098 s,
m(C(8)@N(3)) 1522 s, 1412 m,
m
(DMSO-d6, 400 MHz) d: 11.88 (s, 1H, –C(14)–O(1)H), 10.09
(s, 1H, –C(7)–N(1)H), 9.96 (s, 1H, –C(7)–N(2)H), 8.49 (s, 1H,
–N(3)@C(8)–H), 8.09–6.82 (m, 8H, C6H4). 13C NMR (DMSO-d6,
100 MHz) d: 176.07, 157.17, 140.79, 139.09, 132.04, 131.85,
131.28, 129.12, 128.09, 127.53, 120.62, 119.63, 117.82, 116.51.
H2L3: Yield: 87%. Anal. calc. for C15H15N3SO2: C, 59.78; H, 5.02; N,
13.94. Found: C, 59.75; H, 5.04; N, 13.91%. Main IR peaks (KBr,
2.4.3. [{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6)
To a solution of H2L3 (0.301 g, 0.100 mmol) in hot methanol,
triethylamine (0.202 g, 0.2 mmol) was added, followed by solid
Ni(OAc)2 salt (0.248 g, 0.100 mmol) and 4,40-bipyridine (0.078 g,
0.050 mmol). The mixture was refluxed for 3 h and a clear reddish
brown solution was obtained, which was filtered and allowed to
evaporate at room temperature. Reddish brown crystals suitable
for X-ray crystallography were obtained from DMSO by slow evap-
oration. Yield: 65%. Anal. calc. for C44H46N8Ni2O6S4: C, 51.38; H,
4.51; N, 10.89. Found: C, 51.43; H, 4.50; N, 10.84%. Main IR peaks
cmꢁ1):
(C@C) 1623 s,
m
(O(1)–H) 3325 s,
m
(N(1)–H) 3278 s,
m(N(2)–H) 3019 s,
m
m
(–C(8)@N(3)) 1563 s, 1457 m, m
(C(7)@S(1)) 749
s. 1H NMR (DMSO-d6, 400 MHz) d: 11.70 (s, 1H, –C(14)–O(1)H),
10.07 (s, 1H, –C(7)–N(1)H), 9.95 (s, 1H, –C(7)–N(2)H), 8.47 (s, 1H,
–N(3)@C(8)–H), 8.10–6.81 (m, 8H, C6H4), 3.76 (s, 3H,
–C(4)–OCH3). 13C NMR (DMSO-d6, 100 MHz) d: 176.58, 157.32,
156.99, 140.29, 139.13, 132.51, 131.69, 131.06, 127.91, 127.53,
120.78, 119.67, 116.48, 113.69, 55.6.
(KBr, cmꢁ1):
1524 s, 1416 m,
m
(N(1)–H) 3268 s,
m(C@C) 1624 s, m(–C(8)@N(3))
m
(C(7)–S(1)) 741 s. 1H NMR (DMSO-d6, 400 MHz)
d: 9.25 (s, 1H, –C(7)–N(1)H), 8.27 (s, 1H, –N(3)@C(8)–H),
9.00–6.59 (m, 12H, C6H4), 3.70 (s, 3H, –C(4)–OCH3).

356
Saswati et al. / Polyhedron 50 (2013) 354–363
Table 1
Crystal and refinement data of complexes 1–3, 5 and 6.
Compound
1
2
3
5
6
Formula
M
Crystal system
Space group
Unit cell dimensions
a (Å)
C
32H25FN3NiOPS
C19H15FN4NiOS
425.12
monoclinic
P 21/c
C34H31BrN3NiO2PS2
747.33
C21H20N4NiO2S
451.18
C44H46N8Ni2O6S4
1028.55
monoclinic
P 21/n
608.29
triclinic
P 1
triclinic
triclinic
ꢀ
ꢀ
P1
P1
7.7728(11)
9.0984(13)
11.3329(16)
68.759(2)
82.879(2)
69.544(2)
699.91(17)
1
13.0818(8)
5.8005(3)
23.5843(15)
90
102.298(4)
90
1748.53(18)
4
1.615
14.536(6)
14.901(7)
16.450(7)
91.83(4)
98.69(3)
110.60(4)
3283.(2)
9.8581(7)
10.1348(8)
11.9150(8)
112.224(5)
98.817(5)
103.001(6)
1035.57(15)
2
9.1065(4)
22.9648(10)
11.5615(5)
90
111.3700(10)
90
2251.61(17)
2
1.517
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
4
Dcalc (g cmꢁ3
F (000)
)
1.443
314
0.863
1.512
1528
2.020
1.447
468
1.062
872
1.256
1068
1.080
l
(Mo K
a
) (mmꢁ1
)
Maximum/minimum trans.
0.9914/0.8743
26.00
0.9875/0.8953
30.5
0.9272/0.4359
27.71
1.000/0.919
25.63
0.9632/0.8566
29.51
2h (max) (o)
Reflections collected/unique
7228/5331
[Rint = 0.0176]
R1 = 0.0405,
wR2 = 0.0689
R1 = 0.0474,
wR2 = 0.0733
1.053
26906/5357
[Rint = 0.0808]
R1 = 0.0457,
wR2 = 0.0722
R1 = 0.1269,
wR2 = 0.0916
0.969
53431/15052
[Rint = 0.0713]
R1 = 0.0454,
wR2 = 0.1110
R1 = 0.1019,
wR2 = 0.1459
0.811
12009/3894
[Rint = 0.024]
R1 = 0.0239,
wR2 = 0.0564
R1 = 0.0239,
wR2 = 0.0581
1.01
40605/5975
[Rint = 0.0868]
R1 = 0.0413,
wR2 = 0.1106
R1 = 0.0753,
wR2 = 0.1354
0.844
R1 [I > 2r(I)]
wR2 [all data]
Goodness-of-fit (GOF) on S
Minimum/maximum res. (e Åꢁ3
)
0.468/ꢁ0.205
0.298/ꢁ0.398
0.546/ꢁ0.717
ꢁ0.23/0.23
0.377/ꢁ0.544
Table 2
Hydrogen bond distances (Å) and angles (o) for 1–3, 5 and 6.
D–H. . .A
D–H (Å)
Dꢀ ꢀ ꢀA (Å)
Hꢀ ꢀ ꢀA (Å)
<D–Hꢀ ꢀ ꢀA (°)
[Ni(L1)(PPh3)] (1)
C22–H22ꢀ ꢀ ꢀS1a
C30–H30ꢀ ꢀ ꢀF1b
C24–H24ꢀ ꢀ ꢀO1c
0.91(4)
0.93(1)
0.99(5)
3.707(6)
3.211(7)
3.428(7)
2.92(5)
2.50(1)
2.57(4)
144.8(31)
133.4(43)
145.9(35)
Symmetry transformations used to generate equivalent atoms:
(a) x, y, z; (b) x + 2, +y ꢁ 1, +z + 1; (c) x, +y + 1, +z
[Ni(L1)(Py)] (2)
C12–H12ꢀ ꢀ ꢀF1a
0.88(3)
0.77(3)
3.436(4)
3.584(3)
2.60(3)
2.84(3)
159.2(25)
162.6(24)
N1–H1ꢀ ꢀ ꢀS1b
Symmetry transformations used to generate equivalent atoms:
(a) ꢁx, +y + 1/2 + 1, ꢁz + 1/2; (b) ꢁx, ꢁy ꢁ 1, ꢁz + 1
Ni(L2)(PPh3)]ꢀDMSO (3)
N1A–H1Aꢀ ꢀ ꢀS2a
N1A–H1Aꢀ ꢀ ꢀO2a
N1–H1ꢀ ꢀ ꢀS2Ab
N1–H1ꢀ ꢀ ꢀO2Ab
0.88
0.88
0.88
0.88
3.769(4)
2.854(4)
3.829(4)
2.917(4)
2.90
2.01
3.01
2.04
169.0
161.5
155.0
171.7
Symmetry transformations used to generate equivalent atoms:
(a) ꢁx, ꢁy + 1, ꢁz + 1; (b)ꢁx + 1, ꢁy + 1, ꢁz + 1
Ni(L3)(4-Pic)] (5)
N1ꢀ ꢀ ꢀH1N. . .N2a
0.83(2)
0.98
2.14(2)
2.86
2.962(2)
3.764(2)
173(2)
154
C20ꢀ ꢀ ꢀH20B. . .S1b
Symmetry transformations used to generate equivalent atoms:
(a) ꢁx + 1, ꢁy + 1, ꢁz + 1; (b) ꢁx, ꢁy + 1, ꢁz
[{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6)
C15–H15ꢀ ꢀ ꢀO3a
0.93(4)
0.94(3)
0.93(4)
0.93(4)
0.97(3)
0.99(3)
0.92(3)
3.308(4)
3.359(3)
2.839(3)
3.807(2)
3.563(3)
3.332(4)
3.814(3)
2.55(4)
2.61(3)
1.91(4)
2.95(3)
2.61(3)
2.39(3)
2.97(4)
138.7(34)
136.7(26)
178.2(33)
153.0(29)
165.8(24)
159.2(27)
153.9(30)
C6–H6ꢀ ꢀ ꢀO3b
N1–H1ꢀ ꢀ ꢀO3b
N1–H1ꢀ ꢀ ꢀS2b
C8–H8ꢀ ꢀ ꢀO1c
C21–H21aꢀ ꢀ ꢀO2d
C21–H21cꢀ ꢀ ꢀS1e
Symmetry transformations used to generate equivalent atoms:
(a) x, y, z; (b) ꢁx + 1, ꢁy, ꢁz + 1; (c) x + 1/2, ꢁy + 1/2, +z + 1/2; (d) x, +y, +z ꢁ 1; (e) x + 1, +y, +z
fractometer (3 and 6) and Stoe Mark II-Image Plate diffractometer
(5) equipped with a graphite monochromator and a Mo K radiator
(k = 0.71073 Å). Crystallographic data and details of refinement are
given in Table 1. Details of the classical hydrogen bonding are gi-
ven in Table 2. The unit cell dimensions and intensity data were
a
2.5. Crystallography
Single crystals of the complexes were mounted on a Bruker
Smart Apex CCD diffractometer (1 and 2), Bruker Smart Apex II dif-

Saswati et al. / Polyhedron 50 (2013) 354–363
357
measured at 293 (2) K for 1 and 2, 100 (2) K for 3 and 6 and 173 K
Q = PPh3 (1, 3)
H2L1 (X = F)
Py (2)
for 5. The intensity data were corrected for Lorentz, polarization
and absorption effects. Absorption corrections were applied using
SADABS [45] and the structures were solved by direct methods using
the program SHELXS-97 [46] and refined using least squares with the
SHELXL-97 [46] software program. Hydrogens were either found or
placed in calculated positions and isotropically refined using a rid-
ing model. The non-hydrogen atoms were refined anisotropically.
H2L2 (X = Br)
H2L3 (X = OMe)
Imz (4)
4 -Pic (5)
12
O
11
Q
13
1
Ni
HC
10
N
9
14 O-
S
B (1-5)
N
HC8
C
N 3
N2
HN
1
2.6. Antibacterial activity
S-
X
7 C
HN1
2
X
The antibacterial activity of the compounds (ligands and com-
plexes) was studied against Escherichia coli (E. coli) and Bacillus
by the agar well diffusion technique. Mueller Hinton-agar (con-
taining 1% peptone, 0.6% yeast extract, 0.5% beef extract and 0.5%
NaCl, at pH 6.9–7.1) plates were prepared and 0.5 – McFarland cul-
ture (1.5 ꢂ 108 cells/mL) of the test organisms were swabbed onto
the agar plate (as per CLSI guidelines, 2006). The compounds were
dissolved in DMSO, varying their concentration from 1000–
1
3
NH
C
6
4
5
X
N
N
S
A (H2L1-3
)
CH
Ni
O
N
N
O
Ni
HC
1.95 lg/mL. Nine millimeter wide wells were dug on the agar plate
N
using a sterile cork borer. Hundred microgram per millimeter of
each compound from all dilutions were added into the wells using
a micropipette. These plates were incubated for 24 h at 35 2 °C.
The growth of the test organisms was inhibited by diffusion of
the compounds and then the inhibition zones developed on the
plates were measured [47,48]. The effectiveness of an antibacterial
agent in sensitivity is based on the diameter of the zones of inhibi-
tion, which was measured to the nearest millimeter (mm). The
standard drug Vancomycin was also tested for its antibacterial
activity at the same concentration and under similar conditions
to that of the compounds as a positive control. DMSO was used
as a negative control under the same conditions for each organism.
S
N
C
N
N = 4,4'-bipyridine
HN
C (6)
X
Scheme 1. Schematic representation of the ligands (A) and the synthesis of the
mixed-ligand Ni(II) complexes (B and C).
tridentate fashion (B, Scheme 1), forming a six- and a five-membered
chelate ring with O(1)–Ni(1)–N(3) and N(3)–Ni(1)–S(1) bite angles
of 94.4 (2) and 87.0(1)° (1), 95.3(8) and 87.3(6)° (2), 95.2(1) and
87.1(1)° (3) and 96.16(6) and 87.49(4)° (5), respectively. The
co-ligand {Q = triphenylphosphine (1 and 3), pyridine (2) and 4-
pic (5)} is coordinated to the metal center, and is trans to the nitro-
gen atom. The rather large Ni(1)–P(1)/N(4) distances are [2.224(1)
(1), 1.912(2) (2), 2.205(2) (3) and 1.921(16) Å (5)], which revealed
that the triphenylphosphine, pyridine or picoline moiety are rather
weakly coordinated to the Ni-centre [49]. The nickel centre in all
compounds is thus nested in a NOSN or NOSP core, which is
slightly distorted from an ideal square-planar geometry, as
reflected in the bond parameters around the metal center. The
Ni–N, Ni–O, Ni–P/N (co-ligand) and Ni–S distances are normal, as
observed in other structurally characterized complexes of nickel
containing these bonds [22,27,28]. Structural characterization of
complex 4 by X-ray crystallography has not been possible, as its
single crystals could not be grown. As all five complexes have been
synthesized similarly and display similar properties, the [Ni(L2)(Q)]
(Q = Imz) complex is assumed to have a similar structure to 1–3
and 5.
3. Results and discussion
3.1. Synthesis
In order to explore the possibility of forming monomeric com-
plexes by splitting the sulfur bridge in {M(L)}n type complexes,
the reaction of the thiosemicarbazones with Ni(OAc)2 has been car-
ried out with different monodentate ligands (Q), viz. triphenyl-
phosphine (PPh3), pyridine (Py), imidazole (Imz) and 4-picoline
(4-Pic), in refluxing methanol. From each of these reactions a
mixed-ligand monomeric complex of the type [Ni(L)(Q)]
(Q = PPh3, Py, Imz, 4-Pic) (1–5) has been obtained. The mixed-li-
gand dinuclear dinickel(II) complex [{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO
(6) was achieved by the reaction of the thiosemicarbazone (H2L3)
with Ni(OAc)2 using 4,40-bipyridine as an exo-bidentate ligand un-
der reflux conditions. The synthetic methods of all the complexes
are illustrated in Scheme 1.
All the molecules are found to show either inter (1, 2 and 5) or
intra (1 and 3) molecular hydrogen bonding. Complex 1 is found to
show both inter and intra molecular hydrogen bonding. [Ni(L1)(-
PPh3)] (1) molecules form a polymeric unit via a pair of hydrogen
bonds between the phenolic oxygen O(1) of one molecule and
the phenyl (PPh3) proton C(24)–H of another moiety (Supplemen-
tary Fig. SF 1) and between the fluorine F(1) of one molecule and
the phenyl (PPh3) proton C(30)-H of another moiety (Fig. 5), form-
ing intermolecular hydrogen bonding. Another hydrogen bonding
interaction between the thione sulfur S(1) and phenyl (PPh3)
hydrogen, C(22)–H, is also observed to constitute an intramolecu-
lar hydrogen bond (Supplementary Fig. 2) for 1. Complex 2 is found
to show only inter molecular hydrogen bonding. Two [Ni(L1)(Py)]
(2) molecules form a dimeric unit via a pair of reciprocal hydrogen
3.2. Structures
3.2.1. Description of the X-ray structures of complexes 1–3 and 5
The observed elemental (C, H, N) analytical data of all the com-
plexes are consistent with their compositions. It appears from the
formulation of the monomeric complexes that the thiosemicarba-
zones are serving as tridentate ligands. In order to authenticate
the coordination mode of the thiosemicarbazones in these com-
plexes, the structures of few members (1–3 and 5) of this family
of monomeric complexes have been determined by X-ray crystal-
lography. The atom numbering schemes for these complexes are
given in Figs. 1–4, respectively, with the relevant bond distances
and angles collected in Table 3. The structures show that the thio-
semicarbazone ligand (L2ꢁ) is coordinated to nickel in the expected

358
Saswati et al. / Polyhedron 50 (2013) 354–363
Fig. 1. ORTEP diagram of [Ni(L1)(PPh3)] (1) with the atom labelling scheme.
Fig. 2. ORTEP diagram of [Ni(L1)(Py)] (2) with the atom labelling scheme.
bonds between the N(1)–H proton of one molecule and the thione
sulfur S(1) of other moiety (Supplementary Fig. 3). Complex 2 is
also found to show a polymeric one-dimensional zig-zag chain
(Fig. 6) through inter molecular hydrogen bonding between the
fluorine F(1) of one molecule and the phenyl proton C(12)–H of an-
other moiety. For complex 3 there is only one possible hydrogen
bonding interaction found (Supplementary Fig. 4) between the
N(1)–H proton of the ligand and the O(2) and S(2) atoms of the sol-

Saswati et al. / Polyhedron 50 (2013) 354–363
359
Fig. 3. ORTEP diagram of [Ni(L2)(PPh3)]ꢀDMSO (3) with the atom labelling scheme.
Table 3
Selected bond distances (Å) and bond angles (°) for [Ni(L1)(PPh3)] (1), [Ni(L1)(Py)] (2),
[Ni(L2)(PPh3)]ꢀDMSO (3), Ni(L3)(4-Pic)] (5) and [{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6).
1
2
3
5
6
Bond distances
Ni(1)–O(1)
Ni(1)–N(3)
Ni(1)–S(1)
Ni(1)–P(1)
Ni(1)–N(4)
1.848(4)
1.882(3)
2.137(1)
2.224(1)
–
1.854(2)
1.849(2)
2.154(8)
–
1.838(3)
1.877(3)
2.146(1)
2.205(2)
–
1.846(11)
1.858(15)
2.148(5)
–
1.851(2)
1.856(2)
2.139(8)
–
1.912(2)
1.921(16)
1.920(2)
Bond angles
O(1)–Ni(1)–N(3)
O(1)–Ni(1)–S(1)
N(3)–Ni(1)–S(1)
O(1)–Ni(1)–P(1)
O(1)–Ni(1)–N(4)
N(3)–Ni(1)–P(1)
N(3)–Ni(1)–N(4)
S(1)–Ni(1)–P(1)
N(4)–Ni(1)–S(1)
94.4(2)
178.1(1)
87.0(1)
88.0(1)
–
177.5(1)
–
90.5(5)
–
95.3(8)
176.1(6)
87.3(6)
–
85.8(8)
–
177.9(9)
–
91.7(6)
95.2(1)
177.3(9)
87.1(1)
86.5(9)
–
173.1(1)
–
91.5(5)
–
96.16(6)
176.00(5)
87.49(4)
–
87.18(6)
–
176.60(6)
–
89.20(4)
96.1(9)
175.6(6)
87.1(7)
–
87.5(9)
–
176.3(1)
–
89.4(7)
0.056(2) Å for atom C(7)] of the ligand by 76.84(8)° (Supplemen-
tary Fig. 6). The same dihedral angle in compounds 1–3 varies be-
tween 15.74(10) and 25.70(17)°. Complex 5 is also found to show
inter molecular C–H. . .S hydrogen bonding between the thione sul-
fur S(1) of one molecule with a methoxy proton C(20)–H of a
neighboring molecule.
Fig. 4. ORTEP diagram of [Ni(L3)(4-Pic)] (5) with the atom labelling scheme.
vent (DMSO) molecule. Complex 5 is found to show only inter
molecular hydrogen bonding (Supplementary Fig. 5). In the crystal,
[Ni(L3)(4-Pic)] (5) molecules are linked to form inversion dimers
via a pair of N–H. . .N hydrogen bonds between the N(1)–H proton
of one molecule and the imine nitrogen N(2) of another molecule.
The consequence of this is that to minimize steric hindrance, the
ligand is no longer relatively planar, with the methoxybenzene ring
[(C(1)–C(6)] being inclined to the mean plane of the remaining het-
ero atoms [N(1)–N(3)/S(1)/O(1)/C(7)–C(14); maximum deviation
3.2.2. Description of the X-ray structure of complex 6
The molecular structure and atom-labelling scheme for
complex 6 are shown in Fig. 7. Selected bond distances and angles
are collected in Table 3. Complex 6 crystallizes in the monoclinic
space group P 21/n with the molecule sitting across a crystallo-
graphic center of inversion. Each half of the complex [{Ni(L3)}2
(
l
-4,40-byp)]ꢀ2DMSO closely resembles the structure of 2, which
essentially consists of the same donor atoms attached to its Ni(II)
center in the same geometric pattern with closely matching

360
Saswati et al. / Polyhedron 50 (2013) 354–363
Fig. 5. One-dimensional zig-zag chain through inter molecular hydrogen bonding in 1.
Fig. 6. One-dimensional zig-zag chain through inter molecular hydrogen bonding in 2.
Fig. 7. ORTEP diagram of [{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6) with the atom labelling scheme.

Saswati et al. / Polyhedron 50 (2013) 354–363
361
Table 4
Table 5
Electronic spectrala data for the studied complexes.
Cyclic voltammetrica results for the nickel(II) complexes at 298 K.
Complex
kmax/nm (
e
/dm3 molꢁ1 cm-1
)
Complex
Potentials (V) vs. Ag/AgCl
[Ni(L1)(PPh3)] (1)
[Ni(L1)(Py)] (2)
416 (7300), 372 (14100), 269 (22700)
420 (8400), 371 (13400), 262 (23300)
412 (5500), 368 (13510), 264 (19654)
422 (7600), 354 (13650), 256 (18968)
428 (8500), 335 (13480), 292 (20843)
404 (6700), 357 (13780), 280 (22156)
M(II)/M(III)
M(II)/M(I)
Ligand–centered
reduction
[Ni(L2)(PPh3)]ꢀDMSO (3)
[Ni(L1)(PPh3)] (1)
[Ni(L1)(Py)] (2)
[Ni(L2)(PPh3)]ꢀDMSO
(3)
1.023
1.029
0.998
ꢁ0.984
ꢁ0.886
ꢁ1.012
ꢁ1.684
ꢁ1.681
ꢁ1.774
[Ni(L2)(Imz)] (4)
[Ni(L3)(4-Pic)] (5)
[{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6)
[Ni(L2)(Imz)] (4)
[Ni(L3)(4-Pic)] (5)
0.921
0.894
ꢁ1.008
ꢁ1.093
ꢁ1.781
ꢁ1.793
a
In DMSO.
[{Ni(L3)}2(
l
-4,40-
0.674, 0.980 ꢁ1.096, ꢁ1.251 ꢁ1.803
byp)]ꢀ2DMSO (6)
dimensions. The only significant difference observed in the case
of 6 is that the Ni(1)–N(4) bond involving the nickel acceptor cen-
ter and the N(4) aromatic nitrogen atom of 4,40-byp is longer
(1.920(2) Å) than the corresponding Ni(1)–N(4) (pyridine) bond
in 2, which is 1.912(2) Å. This lengthening indicates compara-
tively weaker binding of the 4,40-byp nitrogen N(4) to the Ni(II)
center. This is quite usual for this type of bridging systems
[50,51]. The two pyridine rings of 4,40-byp lie in the same plane
and are perpendicular to the equatorial planes of the two halves
of the two [Ni(L)] units. The chelate bite angles for the five- and
six-membered rings have values within the expected ranges
[S(1)–Ni(1)–N(3), 87.1(7)°; O(1)–Ni(1)–N(3), 96.1(9)°] [52]. Com-
plex 6 is found to show both inter and intra molecular hydrogen
bonding. A selected hydrogen bonding diagram is shown in
Supplementary Fig. 7.
a
Solvent: CH3CN; working electrode: platinum; auxiliary electrode: platinum;
reference electrode: Ag/AgCl; supporting electrolyte: 0.1 M TEAP; scan rate:
100 mV/s.
3.3. Spectral characteristics
The infrared spectra of all the complexes are mostly similar. The
ligands exhibit bands due to
(–C(14)O(1)–H) moieties in the 3357–2994 cmꢁ1 region, however
the complexes do not exhibit (–C(7)N(2)–H) or (–C(14)O(1)–H)
m(–C(7)N(1)–H), m(–C(7)N(2)–H) and
m
m
m
bands. Thus it reveals that the ligands coordinate to the metal
centre in their anionic forms. The sharp band in the range
752–749 cmꢁ1 due to
m
(C(7)–S(1)) stretching in the ligand is low-
ered by 10–15 cmꢁ1, indicating participation of the thione sulfur in
Fig. 8. Cyclic voltammogram of complex 3.
coordination [53,54]. The characteristic m(P–C) bands at 1094 and
1098 cmꢁ1 in complexes 1 and 3, respectively attribute to the pres-
ence of PPh3 [27].
The electronic spectra of the complexes (Table 4) were recorded
using DMSO solutions. The main features of all the spectra are
quite similar. Three strong absorptions are observed in the wave-
length range 430–220 nm. The lower energy absorptions at around
404–428 nm are ascribable to ligand-to-metal charge transfer
transitions, whereas the higher energy absorptions are likely to
be due to ligand centered transitions [55].
the negative side. The two waves on the negative side of Ag/AgCl
at Epa values within the potential windows ꢁ0.886 to ꢁ1.093 V
and ꢁ1.681 to ꢁ1.793 V, are assigned to the reduction of the cen-
tral metal, Ni(II)/Ni(I), and ligand, respectively. The wave on the
positive side of Ag/AgCl at Epa values within the potential window
0.894 to 1.029 V is assigned to the oxidation of the metal, Ni(II)/
Ni(III). The dinuclear complex 6 exhibits three successive irrevers-
ible one-electron reductions within the potential window ꢁ1.096
to ꢁ1.251 V versus Ag/AgCl in acetonitrile which are assigned to
NiII–NiII/NiI–NiII and NiI–NiII/NiI–NiI processes and a ligand-cen-
tered reduction, respectively [51]. The dinickel(II) unit also shows
two irreversible oxidative responses [58] on the positive side of
Ag/AgCl, within the potential window 0.674–0.980 V, which are as-
signed to the oxidation of the metal, Ni(II)/Ni(III).
The potentials of both Ni(II)–Ni(III) oxidation and Ni(II)–Ni(I)
reduction in the complexes have been found to be dependent on
the nature of the substituent X in the phenyl fragment of 4-X-phe-
nylthiosemicarbazone, and this reflects the effect of the electronic
nature of the substituent. The potential increases with increasing
electron-withdrawing character of the substituent X. Both the
reduction and oxidation of the metal centre occur at the highest
potential for the most electron withdrawing substituent (X = F,
complexes 1 and 2), while for the most electron releasing substitu-
ent (X = OMe, complexes 5 and 6), it occurs at the lowest potential
[59–61].
The 1H NMR spectral data of the free ligands and their corre-
sponding nickel(II) complexes (1–6) were recorded using DMSO-
d6. The spectra of the free ligands exhibit two close but separate
singlets in the range 11.88–9.95 ppm due to OH (–C(14)–O(1)H)
and NH (–C(7)–N(2)H) groups, which are absent in the spectra of
the complexes, indicating coordination of these groups to the me-
tal centre. Signals for aromatic protons are found as multiplets in
the 9.00–6.34 ppm range [56]. Detailed NMR data have been in-
cluded in the Section 2.
3.4. Electrochemical properties
Electrochemical properties of the complexes (1–6) have been
studied by cyclic voltammetry in acetonitrile solution (0.1 M
TEAP). Voltammetric data are given in Table 5 and a selected vol-
tammogram is shown in Fig. 8. All the mononuclear complexes
(1–5) show one irreversible oxidative response [57] on the positive
side of Ag/AgCl and two irreversible reductive responses [57] on

362
Saswati et al. / Polyhedron 50 (2013) 354–363
3.5. Antimicrobial activity
in accordance with the reported values. However, the difference in
value may be attributed to the nature of compounds synthesized
with different ligands.
In the present study, the synthesized compounds (1–6) showed
potential antibacterial activity against the pathogens tested (E. coli
and Bacillus) by the agar well-diffusion method, and in some cases
they showed promising results by giving MIC values less than the
standard drug examined. The results (Table 6, Fig. 9) also indicate
that the corresponding nickel(II) complexes showed much better
antibacterial activity with respect to the individual ligands against
the same microorganism under identical experimental conditions,
which is in agreement with reported results [47,48,62–65]. A pos-
sible explanation is that, by coordination, the polarity of the ligand
and the central metal ion are reduced through the charge equili-
bration, which favors permeation of the complexes through the li-
pid layer of the bacterial cell membrane [47,48,62–65].
4. Conclusion
The study of six new Ni(II) complexes of 4-(p-X-phenyl)thio-
semicarbazones of salicylaldehyde reported in this paper reveals
that the structural parameters (e.g. Ni–N and Ni–P bond distances)
and the redox potentials of these complexes can be fine tuned by
changing the substituent on the 4-aryl (X) part. The complexes
have been screened for their antibacterial activity against E. coli
and Bacillus. The minimum inhibitory concentration of these com-
plexes and antibacterial activity indicates that compound 4 is the
potential lead molecule for drug designing.
From the zone of inhibition, it is observed that complex 4
showed the most promising results, as compared to the other com-
pounds of this study, and the difference in value may be attributed
to the nature of the compounds synthesized with imidazole as co-
ligands [66,67]. The antibacterial activity of a similar type of oxo-
metal complex has also been recently reported [68,69] using the
agar well diffusion technique against E. coli, Shigella, Pseudomonas,
Salmonella, Staphylococcus and Bacillus, and the present results are
Acknowledgements
The authors thank the reviewer for his comments and sugges-
tions, which were helpful in preparing the revised version of the
manuscript. R.A. thanks the Department of Science and Technol-
ogy, Govt. of India for Funds (Grant SR/FT/CS-010/2009) as SERC
Fast Track Scheme of Young Scientist. R.D. acknowledges the use
of the UV–Vis spectrophotometer purchased by the DST (India)
Grant No. SR/FT/CS-016/2008. Y.P. Patil gratefully acknowledges
the Council of Scientific and Industrial Research, New Delhi, India,
for the award of a research fellowship. The authors thank Dr. S.
Chattopadhyay, BESU for the help in the electrochemical study.
The authors would also like to thank Dr. Surajit Das, Department
of Life Science, NIT, Rourkela for the help given in obtaining biolog-
ical data.
Table 6
Minimum inhibitory concentration (MIC) value in
lg/mL of the Schiff base ligands
(H2L1ꢁ3), nickel(II) complexes and standard drugs against pathogenic strains.
E. coli
Bacillus
H2L1
500
125
62.5
125
31.2
15.6
125
31.2
62.5
30
250
125
125
250
125
15.6
250
31.2
125
30
[Ni(L1)(PPh3)] (1)
[Ni(L1)(Py)] (2)
H2L2
[Ni(L2)(PPh3)]ꢀDMSO (3)
[Ni(L2)(Imz)] (4)
H2L3
Appendix A. Supplementary material
CCDC 870156, 870155, 870154, 884956 and 873841 contain the
supplementary crystallographic data for complexes 1, 2, 3, 5 and 6
respectively. 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.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2012.11.031.
[Ni(L3)(4-Pic)] (5)
[{Ni(L3)}2(
l
-4,40-byp)]ꢀ2DMSO (6)
Vancomycin
500
400
300
200
100
0
E.Coli
Bacillus
References
[1] H.-J. Kruger, R.H. Holm, J. Am. Chem. Soc. 112 (1990) 2955.
[2] Z. Lu, C. White, A.L. Rheingold, R.H. Crabtree, Inorg. Chem. 32 (1993) 3991.
[3] S. Mandal, P.K. Bharadwaj, Z.-Yuan. Zhou, T.C.W. Mak, Polyhedron 14 (1995)
919.
[4] G.J. Colpas, M. Kumar, R.O. Day, M.J. Maroney, Inorg. Chem. 29 (1990) 4779.
[5] S.B. Choudhury, D. Ray, A. Chakravorty, Inorg. Chem. 29 (1990) 4603.
[6] S.W. Ragsdale, H.G. Wood, J.A. Morton, L.G. Ljungdahl, D.V. Dervartanian, in:
J.R. Lancaster Jr (Ed.), The Bioinorganic Chemistry of Nickel, VCH, New York,
1988. Chapter 14.
[7] M.J.M. Campbell, Coord. Chem. Rev. 15 (1975) 279.
[8] S.B. Padhye, G.B. Kauffman, Coord. Chem. Rev. 63 (1985) 127.
[9] D.X. West, A.E. Liberta, S.B. Padhye, R.C. Chikate, P.B. Sonawane, A.S. Kumbhar,
R.G. Yerande, Coord. Chem. Rev. 123 (1993) 49.
[10] D.L. Klayman, J.P. Scovill, J.F. Bartosevich, J. Bruce, J. Med. Chem. 26 (1983) 39.
[11] J.S. Casas, M.S. Garcia-Tasende, J. Sordo, Coord. Chem. Rev. 209 (2000) 197.
[12] D.R. Smith, Coord. Chem. Rev. 164 (1997) 575.
[13] E.W. Ainscough, A.M. Brodie, J.D. Ransford, J.M. Waters, J. Chem. Soc., Dalton
Trans. (1997) 1251.
[14] M.A. Ali, A.H. Mirza, A.M.S. Hossain, M. Nazimuddin, Polyhedron 20 (2001)
1045.
[15] M. Baldini, M.B. Ferrari, F. Bisceglie, G. Pelosi, S. Pinelli, P. Tarasconi, Inorg.
Chem. 42 (2003) 2049.
[16] M.B. Ferrari, F. Bisceglie, G. Pelosi, P. Tarasconi, R. Albertini, G.G. Fava, S. Pinelli,
J. Inorg. Biochem. 89 (2002) 36.
[17] M.B. Ferrari, F. Bisceglie, G. Pelosi, P. Albertini, P.P. Dall’Aglio, A. Bergamo, G.
Sava, S. Pinelli, J. Inorg. Biochem. 98 (2004) 301.
Fig. 9. Minimum inhibitory concentration (MIC) of the Schiff base ligands (H2L1ꢁ3),
their corresponding nickel(II) complexes (1–6) and standard drugs against patho-
genic strains.

Saswati et al. / Polyhedron 50 (2013) 354–363
363
[18] J. Garcia-Tojal, J.L. Pizarro, A. Garcia-Orad, A.R. Perez-Sanz, M. Ugalde, A.A.
Diaz, J.L. Serra, M.I. Arriortua, T. Rojo, J. Inorg. Biochem. 86 (2001) 627.
[19] M.B. Ferrari, F. Bisceglie, G. Pelosi, P. Tarasconi, R. Albertini, A. Bonati, P.
Lunghi, S. Pinelli, J. Inorg. Biochem. 83 (2001) 169.
[20] Z. Afrasiabi, E. Sinn, S. Padhye, S. Duttab, S. Padhye, C. Newton, C.E. Anson, A.K.
Powell, J. Inorg. Biochem. 95 (2003) 306.
[42] I.G. Santos, U. Abram, R. Alberto, E.V. Lopez, A. Sanchez, Inorg. Chem. 43 (2004)
1834.
[43] T.S. Lobana, G. Bhargava, V. Sharma, M. Kumar, Indian J. Chem., Sect. A: Inorg.,
Bio-inorg., Phys., Theor., Anal. Chem. 42A (2003) 309.
[44] Part 1: S. Ghosh, S. Purohit, Indian J. Chem., Sect. A: Inorg., Bio-inorg., Phys.,
Theor., Anal. Chem. 26A (1987) 131.
ˇ
[21] E. Bermejo, R. Carballo, A. Castineiras, R. Domínguez, A.E. Liberta, C. Maichle-
[45] Bruker, SADABS
2003.
, SAINT, SHELXTL and SMART, Bruker AXS Inc., Madison, Wisconsin, SA,
Mössmer, M.M. Salberg, D.X. West, Eur. J. Inorg. Chem. (1999) 965.
[22] S. Datta, D.K. Seth, R.J. Butcher, S. Bhattacharya, Inorg. Chim. Acta 377 (2011)
120.
[23] S. Priyarega, P. Kalaivani, R. Prabhakaran, T. Hashimoto, A. Endo, K. Natarajan, J.
Mol. Struct. 1002 (2011) 58.
[46] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[47] A.R. Yaul, V.V. Dhande, S.G. Bhadange, A.S. Aswar, Russ. J. Inorg. Chem. 56
(2011) 549.
[48] A.A. Abdel Aziz, J. Mol. Struct. 979 (2010) 77.
[24] D.X. West, G.A. Bain, R.J. Butcher, J.P. Jasinski, Y. Li, R.Y. Pozdniakiv, J. Valdes-
Martinez, R.A. Toscano, S. Hernandez-Ortega, Polyhedron 15 (1996) 665.
[25] J. Valdes-Martinez, S. Hernandez-Ortega, V.B. Jimenez, Acta Crystallogr., Sect.
E: Struct. Rep. Online 58 (2002) m710.
[26] J. Valdes-Martinez, S. Hernandez-Ortega, V.B. Jimenez, Acta Crystallogr., Sect.
E: Struct. Rep. Online 60 (2004) 42.
[27] T.S. Lobana, P. Kumari, G. Hundal, R.J. Butcher, Polyhedron 29 (2010) 1130.
[28] T.S. Lobana, P. Kumari, M. Zeller, R.J. Butcher, Inorg. Chem. Commun. 11 (2008)
972.
[49] S. Halder, R.J. Butcher, S. Bhattacharya, Polyhedron 26 (2007) 2741.
[50] R. Dinda, S. Ghosh, L.R. Falvello, M. Tomás, T.C.W. Mak, Polyhedron 25 (2006)
2375.
[51] S. Pasayat, S.P. Dash, Saswati, P.K. Majhi, Y.P. Patil, M. Nethaji, H.R. Dash, S.
Das, R. Dinda, Polyhedron 38 (2012) 198.
[52] M. Sutradhar, G. Mukherjee, M.G.B. Drew, S. Ghosh, Inorg. Chem. 45 (2006)
5150.
[53] S.K. Chattopadhyay, D. Chattopadhyay, T. Banerjee, R. Kuroda, S. Ghosh,
Polyhedron 16 (1997) 1925.
[29] R. Prabhakaran, R. Karvembu, T. Hashimoto, K. Shimizu, K. Natarajan, Inorg.
Chim. Acta 358 (2005) 2093.
[30] V.M. Leovac, A.F. Petrovic, E.Z. Ivegeš, S.R. Lukic, J. Therm. Anal. Calorim. 36
(1990) 2427.
[31] S. Purohit, A.P. Koley, L.S. Prasad, P.T. Manoharan, S. Ghosh, Inorg. Chem. 28
(1989) 3735.
[32] P. Sengupta, R. Dinda, S. Ghosh, Transition Met. Chem. 27 (2002) 665.
[33] V.V. Bon, S.I. Orysyk, V.I. Pekhnyo, S.V. Volkov, J. Mol. Struct. 984 (2010) 15.
[34] S. Lhuachan, S. Siripaisarnpipat, N. Chaichat, Eur. J. Inorg. Chem. (2003) 263.
[35] J.-M. Yang, W.-B. Ma, B.-H. Chen, G.-S. Huang, Y.-X. Ma, Acta Crystallogr., Sect.
E 60 (2004) m852.
[54] A. Pérez-Rebolledo, I.C. Mendes, N.L. Speziali, P. Bertani, J.M. Resende, A.F. de
Carvalho Alcôntara, H. Beraldo, Polyhedron 26 (2007) 1449.
[55] R. Dinda, P. Sengupta, S. Ghosh, T.C.W. Mak, Inorg. Chem. 41 (2002) 1684.
[56] S. Naskar, D. Mishra, R.J. Butcher, S.K. Chattopadhyay, Polyhedron 26 (2007)
3703.
[57] Ki-Y. Choi, S.M. Yang, K.C. Lee, H. Ryu, C.H. Lee, J. Seo, M. Suh, Transition Met.
Chem. 33 (2008) 99.
[58] A.H. Al-Kubaisi, Bull. Korean Chem. Soc. 25 (2004) 37.
[59] S. Halder, R. Acharyya, S.M. Peng, G.H. Lee, M.G.B. Drew, S. Bhattacharya, Inorg.
Chem. 45 (2006) 9654.
[60] A. Sarkar, S. Pal, Inorg. Chim. Acta 361 (2008) 2296.
[61] S.P. Dash, S. Pasayat, Saswati, H.R. Dash, S. Das, R.J. Butcher, R. Dinda,
Polyhedron 31 (2012) 524.
[36] D. Kovala-Demertzi, M.A. Demertzis, J.R. Miller, C.S. Prampton, J.P. Jasinski, D.X.
West, J. Inorg. Biochem. 92 (2002) 137.
[37] P.N. Yadav, M.A. Demertzis, D. Kovala-Demertzi, S. Skoulika, D.X. West, Inorg.
Chim. Acta 349 (2003) 30.
[62] A. Tarushi, E.K. Efthimiadou, P. Christofis, G. Psomas, Inorg. Chim. Acta 360
(2007) 3978.
[38] R. Carballo, J.S. Casas, E. Garcia-Martinez, G.P. Gabian, A. Sanchez, J. Sordo, E.M.
Vazquez-Lopez, J.C. Garcia-Monteagudo, U.J. Abram, J. Organomet. Chem. 656
(2002) 1.
[39] L.A. Ashfield, A.R. Cowley, J.R. Dilworth, P.S. Donnely, Inorg. Chem. 43 (2004)
4121.
[63] E.K. Efthimiadou, Y. Sanakis, N. Katsaros, A. Karaliota, G. Psomas, Polyhedron
26 (2007) 1148.
[64] A.M. Ramadan, J. Inorg. Biochem. 65 (1997) 183.
[65] P.G. Avaji, C.H.V. Kumar, S.A. Patil, K.N. Shivananda, C. Nagaraju, Eur. J. Med.
Chem. 44 (2009) 3552.
[40] I. Paul, F. Basuli, T.C.W. Mak, S. Bhattacharya, Angew. Chem., Int. Ed. 40 (2001)
2923.
[41] S.I. Orysyk, V.V. Bon, O.O. Obolentseva, Yu.L. Zborovskii, V.V. Orysyk, V.I.
Pekhnyo, V.I. Staninets, V.M. Vovk, Inorg. Chim. Acta 382 (2012) 127.
[66] E.B. Anderson, T.E. Long, Polymer 51 (2010) 2447.
[67] R. Dahiya, H. Gautam, Afr. J. Pharm. Pharacol. 5 (2011) 447.
[68] N. Sharma, M. Kumari, V. Kumar, J. Coord. Chem. 63 (2010) 1940.
[69] Z.H. Chohan, S.H. Sumrra, M.H. Youssoufi, Eur. J. Med. Chem. 45 (2010) 2739.