A new series of Ni(II), Cu(II), Co(II) and Pd(II) complexes with an ONS donor Schiff base: Synthesis, crystal structure, catalytic properties and bioactivities

Article abstract of DOI:10.1016/j.poly.2014.02.043

A new series of bichelated complexes of the formula M(L)₂ and M(L)Cl, where M = Ni(II), Cu(II), Co(II) and Pd(II) and L = a deprotonated Schiff base, were synthesized from the reaction of 5-bromo N-[(2-benzylthio)- phenyl] salicylaldimine (HL, 1), a new potential tridentate (O, N, S donor) Schiff base, with metal salts in methanol medium, and the complexes were characterized by a variety of physicochemical techniques, namely elemental analyses, FT-IR, ¹H NMR and UV-Vis spectroscopies, thermogravimetric analysis and conductivity studies. The coordination mode of the palladium complex was determined by single crystal X-ray diffraction studies and was found to possess a distorted square planar structure with the ligand coordinated as a uninegatively charged tridentate chelating agent via the hydroxyl oxygen, azomethine nitrogen and thioether sulfur atoms, and the remaining fourth coordinating site was filled by a chloride ion. The copper complex shows very good catalytic activities towards the oxidation of organic thioethers to the corresponding sulfoxide and sulfones using H₂O₂ as the oxidant. The ligand and complexes exhibited considerable antibacterial and antifungal activities against Klebsiella pneumoniae (ATCC 10536), Staphylococcus aureus (ATCC 11632) and Candida albicans.

Full text of DOI:10.1016/j.poly.2014.02.043

Polyhedron 74 (2014) 93–98
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
A new series of Ni(II), Cu(II), Co(II) and Pd(II) complexes with an ONS
donor Schiff base: Synthesis, crystal structure, catalytic properties
and bioactivities
b
c
c
Mukul Kalita a, Prasanta Gogoi a, Pranjit Barman a, , Bipul Sarma , Alok K. Buragohain , Ranjan D. Kalita
⇑
a Department of Chemistry, National Institute of Technology, Silchar 788010, Assam, India
b Department of Chemical Sciences, Tezpur University, Tezpur 784028, Assam, India
c Department of Molecular Biology and Biotechnology, Tezpur University, Tezpur 784028, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of bichelated complexes of the formula M(L)2 and M(L)Cl, where M = Ni(II), Cu(II), Co(II) and
Pd(II) and L = a deprotonated Schiff base, were synthesized from the reaction of 5-bromo N-[(2-benzyl-
thio)-phenyl] salicylaldimine (HL, 1), a new potential tridentate (O, N, S donor) Schiff base, with metal
salts in methanol medium, and the complexes were characterized by a variety of physicochemical tech-
niques, namely elemental analyses, FT-IR, 1H NMR and UV–Vis spectroscopies, thermogravimetric anal-
ysis and conductivity studies. The coordination mode of the palladium complex was determined by single
crystal X-ray diffraction studies and was found to possess a distorted square planar structure with the
ligand coordinated as a uninegatively charged tridentate chelating agent via the hydroxyl oxygen, azome-
thine nitrogen and thioether sulfur atoms, and the remaining fourth coordinating site was filled by a chlo-
ride ion. The copper complex shows very good catalytic activities towards the oxidation of organic
thioethers to the corresponding sulfoxide and sulfones using H2O2 as the oxidant. The ligand and com-
plexes exhibited considerable antibacterial and antifungal activities against Klebsiella pneumoniae (ATCC
10536), Staphylococcus aureus (ATCC 11632) and Candida albicans.
Received 30 November 2013
Accepted 17 February 2014
Available online 12 March 2014
Keywords:
ONS donor ligand
Schiff base
Crystal structure
Catalytic activities
Bioactivities
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
complexes appear to be due to the chelating behavior of the ligand,
with most of metal ions coordinated through N and S donor atoms
Schiff bases have a central role in coordination chemistry as
they form stable complexes with most of transition metals [1].
Schiff bases with both hard nitrogen and soft sulfur donor atoms
in the ligand have a tunable capability for coordinating with a wide
range of metal ions, to give stable and intensely colored metal
complexes [2]. Metal complexes with an ONS donor set have
engendered much research because of their potential applications
in fundamental and applied sciences due to their diverse roles in
metallo-enzymes [3,4]. S-ligated transition metal complexes may
mimic the ligation of certain biomolecules in proteins [5]. Chelat-
ing nitrogen-sulfur ligands are potential models for synthesizing
copper complexes as most copper metalloenzymes contain the N,
S donor set [6]. The antibacterial and antifungal activities of
[7]. They show anticancer, antifungal, antibacterial, antiviral and
antitumor activities, in particular for first row transition metal
complexes with such ligands [8]. Nickel complexes with tridentate
ONS donor Schiff bases are found to be good catalysts for the
Kumada–Tamao–Corriu coupling [9]. Copper complexes mediate
the activation of dioxygen, i.e. the binding of O2 to copper in chem-
ical systems that involve redox activity or oxidative transforma-
tions [10]. On the other hand, Schiff base palladium(II)
complexes are used as catalysts in the polymerization of ethylene,
epoxidation, allylic alkylation, the Heck reaction, Suzuki–Miyaura
coupling reactions etc. [9,11]. Schiff bases containing a thioether
donor site have been explored more than other congeners in form-
ing palladium complexes [12]. Generally, neutral tridentates show
octahedral complexes where two ligands encompass the metal ion
in an octahedral array.
The aim of the present work is to study the chelating behavior
of a thioether containing Schiff base ligand towards nickel(II), cop-
per(II), cobalt(II) and palladium(II) ions. The reactions afforded bin-
ary complexes, except for palladium(II). The structures of the
ligand and the complexes were characterized by elemental
⇑
Corresponding author. Tel.: +91 9435374128; fax: +91 3842 2247979.
E-mail addresses: mukulkalita88@gmail.com (M. Kalita), prasantagogoi799@
gmail.com (P. Gogoi), barmanpranjit@yahoo.co.in (P. Barman), bcsarma@tezu.
ernet.in (B. Sarma), alak@tezu.ernet.in (A.K. Buragohain), dkranjan@gmail.com
(R.D. Kalita).
http://dx.doi.org/10.1016/j.poly.2014.02.043
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

94
M. Kalita et al. / Polyhedron 74 (2014) 93–98
analysis, FT-IR, 1H NMR and UV–visible spectroscopies, thermo-
gravimetric analysis, conductivity as well as single crystal X-ray
diffraction analysis. The catalytic activities of the copper complex
for the oxidation of organic thioethers to the corresponding sulfox-
ide and sulfones using H2O2 as an oxidant were studied. Antibacte-
rial and antifungal activity of the ligand and the complexes were
studied by the agar disc diffusion method and showed
considerable inhibition activity against the Gram positive and
Gram negative bacterias Klebsiella pneumoniae (ATCC 10536) and
Staphylococcus aureus (ATCC 11632), respectively.
yellow microcrystalline product that formed was filtered off,
washed with 25% methanol–water solution several times to remove
impurities and dried under vacuum (10ꢀ2 torr) (purity was checked
by TLC). Yield: 69%; M.P.: 256 °C. IR (KBr, cmꢀ1): 3440 (s), 1604 (s),
1441 (s), 1157 (s), 749 (s), 634 (s), 546 (m). UV–Vis (DCM, kmax, nm):
464, 307, 255. Anal. Calc. for C40H30O2N2S2Br2Ni: C, 56.30; H, 3.52;
N, 3.28; S, 7.50. Found: C, 56.21; H, 3.42; N, 3.33; S, 7.48%.
2.1.3. Synthesis of the CuL2 complex (3)
The copper complex 3 was prepared in the same way as de-
scribed for the nickel complex 2, except copper nitrate trihydrate
(0.241 g 1 mmol) was used. The solution was kept undisturbed
for 2 days .The dark green microcrystalline product that formed
was filtered off, washed with 25% methanol–water solution several
times to remove impurities and dried under vacuum (10ꢀ2 torr)
(purity was checked by TLC). Yield: 73%; M.P.: 243 °C. IR (KBr,
cmꢀ1): 3057 (s), 1606 (s), 1452 (s), 1164 (s), 748 (s), 694 (s), 540
(m). UV–Vis (DCM, kmax, nm): 415, 294, 236. Anal. Calc. for C40H30-
O2N2S2Br2Cu: C, 55.98; H, 3.49; N, 3.26; S, 7.46. Found: C, 55.89; H,
3.41; N, 3.19; S, 7.42%.
2. Experimental
2.1. Material and methods
All starting chemicals were commercially available reagents
and were used without further purification. Nickel chloride hexa-
hydrate, copper nitrate trihydrate and cobaltous chloride hexahy-
drate were purchased from Merck India and 5-bromo 2-hydroxy
benzaldehyde and sodium tetrachloropalladate were purchased
from Alfa Aesar. 2-(Benzylthio) aniline was prepared according to
the literature method [13]. Elemental analyses were recorded on
a Perkin–Elmer Model 240C elemental analyzer. Infrared spectra
of the ligand and the complexes were recorded on an IR-affinity-I
FT-IR SHIMADZU spectrometer as KBr pellets. Electronic spectra
were measured on a Cary 100 Bio UV–visible spectrophotometer.
The 1H NMR spectra were recorded on a Bruker 400 DRX spectrom-
eter in CDCl3 cal conductivities were measured on a CM-180 con-
ductivity meter (Elico India). Thermogravimetric analyses were
performed on a TGA 4000 thermal analyzer (Perkin Elmer) with a
heating rate of 10 °C minꢀ1 under a nitrogen atmosphere. Melting
points were recorded on a Veego melting point apparatus and were
uncorrected. All other reagents and solvents, methanol, ethanol,
DCM (dichloromethane), DMF (dimethylformamide), DMSO (di-
methyl sulfoxide), chloroform, benzene and acetonitrile, used were
of commercial grade and employed as received or purified by stan-
dard methods prior to use. All reactions were carried out in the
open atmosphere.
2.1.4. Synthesis of the CoL2 complex (4)
The cobalt complex 4 was prepared in the same way as de-
scribed for complexes 2 and 3, except that cobalt sulfate heptahy-
drate (0.281 g 1 mmol) was used. The solution was kept
undisturbed for 3 days. The black micro crystalline product that
formed was filtered off, washed with a 25% methanol–water solu-
tion several times to remove impurities and dried under vacuum
(10ꢀ2 torr) (purity was checked by TLC). Yield: 65%; M.P.: 252 °C.
IR (KBr, cmꢀ1): 3440 (s), 1600 (s), 1440 (s), 1151 (s), 751 (s), 629
(s), 552 (m). UV–Vis (DCM, kmax, nm): 432, 271, 245. Anal. Calc.
for C40H30O2N2S2Br2Co: C, 56.29; H, 3.52; N, 3.28; S, 7.50. Found:
C, 56.32; H, 3.46; N, 3.25; S, 7.47%.
2.1.5. Synthesis of the PdLCl complex (5)
For the preparation of the palladium complex, the ligand, 1
(321 mg, 0.81 mmol) was dissolved in boiling ethanol (15 mL). A
solution of sodium tetrachloropalladate (250 mg, 0.85 mmol) in
15 ml ethanol was added drop by drop to the above solution. The
solution was stirred in a water bath at 90 °C for 1 h. The color of
the solution changed to bright orange yellow. The solution was
then kept undisturbed for 2 hrs. Orange red needle-like crystals,
suitable for X-ray diffraction, formed and were filtered off, washed
with a 25% ethanol–water solution several times to remove impu-
rities and dried under vacuum (10ꢀ2 torr) (purity was checked by
TLC). Yield: 88%; M.P.: 230 °C. IR (KBr, cmꢀ1): 1600 (s), 1439 (s),
752 (s), 560 (s). 1H NMR (CDCl3, 400 MHz) d: 8.25 (1H, s, CH@N),
2.1.1. Synthesis of bromo N-[2-(benzylthio)-phenyl] salicylaldimine,
HL (1)
To an ethanol solution of 2-(benzylthio) aniline (0.215 g,
1 mmol), an ethanolic solution of 5-bromo 2-hydroxy benzalde-
hyde (0.1 mL, 1 mmol) was added dropwise with continuous stir-
ring. The solution was then refluxed for 30 minutes and the color
of the solution changed to orange red. The solution was then kept
undisturbed for 6 hrs at room temperature. The yellow crystalline
product that formed was filtered off, washed several times with
ethanol and dried in a vacuum (10ꢀ2 torr) (purity was checked
by TLC). Yield: 90%; M.P.: 123 °C. IR (KBr pellet, cmꢀ1): 3440 (m),
1612 (s), 1467 (s), 1173 (s), 1064 (s), 750 (s). 1H NMR (CDCl3,
400 MHz) d: 11.40 (1H, s, OH), 8.41 (1H, s, CH@N), 6.91–7.42
(13H, m, Ar–H), 4.2 (2H, s, CH2). UV–Vis (DCM, kmax, nm): 271,
362. Anal. Calc. for C20H16ONSBr: C, 60.31; H, 4.02; N, 3.52; S,
8.04. Found: C, 59.92; H, 4.15; N, 4.02; S, 7.98%.
7.10–7.75 (13H, m, Ar–H), 4.45 (2H, s, CH2). UV–Vis (DCM, kmax
,
nm): 475, 325, 251. Anal. Calc. for C20H16ONSBrPdCl: C, 52.18; H,
3.47; N, 3.04; S, 6.75. Found: C, 52.23; H, 3.41; N, 3.16; S, 6.62%.
2.2. General procedure for the catalytic oxygenation of thioethers
Three catalytic reactions were performed by a similar proce-
dure. To a solution of the copper complex catalyst (0.0125 mmol)
in methanol–dichloromethane (1:9) mixed solvent, 2.8 mmol of
sulfide and 1 ml of 50% H2O2 were added at 0 °C. The reaction mix-
ture was stirred for 2 hrs. The solution was dried in a vacuum and
the products were separated and purified by preparative TLC using
benzene–acetonitrile (95:5) mixed solvent. The products were
characterized by FT-IR and 1H NMR spectroscopies.
2.1.2. Synthesis of the NiL2 complex (2)
For the preparation of the nickel complex 2, the ligand 1
(0.794 g, 2 mmol) was dissolved in boiling methanol (30 mL) fol-
lowed by addition of 2 mmol methanolic sodium hydroxide solu-
tion. A hot solution of nickel chloride hexahydrate (0.237 g,
1 mmol) dissolved in methanol (30 mL) was added drop by drop
to the above solution with continuous stirring. The solution was
stirred for 30 minutes. The color of the solution changed to
brown–black. It was then kept undisturbed for 24 h. The dark
2.3. Crystallography
Single-crystal X-ray diffraction data for compound 5 were col-
lected at 100 K with Mo Ka radiation (k = 0.71073 Å) using a Bruker

M. Kalita et al. / Polyhedron 74 (2014) 93–98
95
Smart Apex II CCD diffractometer equipped with a graphite mono-
chromator. The SMART [14] software was used for data collection
and also for indexing reflections and determining unit cell param-
eters. Collected data were integrated using SAINT [14] software. The
structure was solved by direct methods and refined by full-matrix
least-square calculations using SHELXTL [15] software. Absorption
corrections were done by the multi-scan method (SADABS) [14]. All
the non-H atoms were refined in an anisotropic approximation
against F2 of all reflections. The H-atoms were placed at their cal-
culated positions and refined in isotropic approximations. Crystal
data and structure refinements are given in Table 1.
For 1, the aromatic OH proton appears downfield compared to the
other peaks, as a singlet at 11.40 ppm. A singlet at 8.41 ppm is due
to the benzylimine proton (CH@N). The aromatic (Ar–H) and ben-
zylic protons (CH2) appear as a multiplet and singlet at 6.91–7.42
and 4.2 ppm respectively. In the case of the palladium complex 5,
the aromatic OH proton disappears due to deprotonation of the li-
gand. The singlet at 8.25 ppm is due to benzylimine proton
(CH@N). The aromatic (Ar–H) and benzylic protons (CH2) appear
as a multiplet and singlet at 7.10–7.75 and 4.45 ppm respectively.
The UV-visible spectrum of the ligand shows two bands at 271
and 362 nm in CH2Cl2, which may be assigned to the p–
p⁄ transi-
tion of the phenyl rings and n–p⁄ transition of the imine moiety,
respectively. All the complexes show bands in the range 241–
255 nm, which may be attributed to the
3. Results and discussion
p–
p⁄ transitions of the
phenyl rings. The bands in the region 271–325 nm have been as-
signed to the n–p⁄ transitions of the imine moiety. The bands in
the range 432–475 nm may be attributed to d–d transitions.
The FT-IR spectrum of the ligand exhibits a broad band at
3.1. Synthesis
The reactions of the ONS donor ligand with metal salts in a
methanol medium are shown in Scheme 1. All the complexes are
air stable, non-hygroscopic and soluble in DCM, chloroform, DMSO
and DMF. The Schiff base behaves as a monoionic tridentate ligand,
bonding through the phenolic oxygen, azomethine nitrogen and
thioether sulfur atoms to Ni(II), Cu(II), Co(II) and Pd(II). The Ni(II),
Cu(II) and Co(II) complexes are octahedral in nature. However, the
Pd(II) complex shows a slightly distorted square planar structure.
3440 cmꢀ1, which can be attributed to
m
(O–H), and a strong band
at 1612 cmꢀ1, which is associated with the (C@N) stretching vibra-
tion; other strong bands belonging to (C@C) and (C—S) are found
at 1467 and 750 cmꢀ1 respectively. The spectra of complexes exhi-
m
m
bit a band for m
(C@N) in the range 1600–1606 cmꢀ1, which shows a
shifting to lower frequencies by 12–6 cmꢀ1 compared to the ligand
(HL), which indicates the coordination of the ligand to the metal
atoms through the nitrogen atom. The disappearance of the band
3.2. Spectral characterization
for the m(OH) vibration in the spectra of the complexes indicates
the deprotanation of the phenolic proton, followed by coordination
of the phenolic oxygen with the metal atoms. Moreover, the phe-
The 1H NMR (400 MHz) spectra of the ligand 1 (HL) and the pal-
ladium complex 5 were recorded in CDCl3 in the range 0–15 ppm.
nolic
m(CO) stretching vibration in the ligand is observed at
1173 cmꢀ1, and this is shifted by 9–22 cmꢀ1 towards lower wave-
numbers in the complexes, suggesting coordination of the phenolic
oxygen to the metal ions [16]. Further, for the palladium complex a
band present at 468 cmꢀ1 confirms the imine nitrogen palladium
bond [17].
Table 1
Crystal structure and structure refinement details for complex 5.
Compound
Palladium complex 5
CCDC entry no.
Empirical formula
Formula weight
955390
C
20H15BrClNOPdS
3.3. Molar conductivity studies
539.15
296(2)
0.71073
T (K)
The molar conductivity of the nickel complex 2 is 20.5 s cm2 -
molꢀ1, for the copper complex 3 it is 21.5 s cm2 molꢀ1 and for
the cobalt complex 4 it is 32.1 s cm2 molꢀ1. The molar conductivity
values in the range 20.5–32.1 s cm2 molꢀ1 in acetonitrile reveal
that all the above complexes behaved as non-electrolytes [18].
However, the palladium complex, 5 shows a molar conductivity
of 64 s cm2 molꢀ1, which may be attributed to it acting as an elec-
trolyte [19].
0
k (AÅ)
Crystal system
Space group
triclinic
ꢀ
P1
Unit cell dimensions
0
9.2939(2)
11.8644(2)
18.1135(3)
a (AÅ)
0
b (AÅ)
0
c (AÅ)
a
(°)
95.6510(10)
98.3630(10)
102.9190(10)
1908.20(6)
b (°)
c
(°)
3.4. Thermal analysis
0
V (ÅA3)
Z
4
Typical thermograms of the complexes and the results are
shown in Fig. 1 and Table 2 respectively. The thermal decomposi-
tion of the Ni(II), Cu(II) and Co(II) metal complexes was studied as a
function temperature by TGA. They exhibit two decompositions.
The first decomposition takes place in the range 200–538 °C, due
to the cleavage of the C13H11NS moiety of the ligand. The second
decomposition takes place in the range 490–679 °C, and this is
attributed to the complete detachment of the ligand from the me-
tal atom. The remaining residue of 8.76–22.76% consists of the cor-
responding metal oxide [20].
Dcalc (Mg/m3)
1.877
3.325
1056
l
(mmꢀ1
)
F (000)
Crystal size (mm3)
h Range for data collection (°)
Index ranges
0.31 ꢁ 0.22 ꢁ 0.06
2.24–30.32
ꢀ13 6 h 6 13
ꢀ16 6 k 6 16
ꢀ25 6 l 6 25
30 637
Reflections collected (Rint
Independent reflections (Rint
Completeness (%)
Absorption correction
Maximum and minimum transmission
Refinement method
)
10 816 (0.0382)
93.00%
)
semi-empirical from equivalents
0.8254 and 0.4255
full-matrix least-squares on F2
11 632/0/469
1.077
3.5. X-ray crystallography
ꢀ
Data/restraints/parameters
Complex 5 crystallizes in the triclinic space group P1 with two
Goodness-of-fit on F2
R1 = 0.0331, wR2 = 0.0881
R1 = 0.0462, wR2 = 0.1076
molecules in the asymmetric unit. The structure of the complex
has been determined by single crystal X-ray diffraction analysis.
The molecular structure of the complex, along with the atomic
Final R indices [I > 2
R indices (all data)
r(I)]

96
M. Kalita et al. / Polyhedron 74 (2014) 93–98
Br
N
Br
N
M
N
OH
Methanol
MXn.n' H2O
O
S
S
O
+
NaOH
S
RT 30 Min
2-4
Br
HL
Where M=Ni2+, X=Cl-,n=2, n'=6
M=Cu2+,X=NO3- ,n=2, n'=3
M=Co2+,X=Cl-,n=2, n'=7
Scheme 1. Synthesis of metal complexes.
and chlorine atoms. Selected bond lengths and bond angles are gi-
ven in Table 3.
ꢁ1L/ꢂ
100
80
60
40
20
0
ꢁ&X/ꢂ
ꢁ&R/ꢂ
ꢁ3G/&O
3.6. Oxidation of thioether
The present work also describes the catalytic oxidation of sul-
fides to sulfoxides and sulfones by the synthesized copper(II) com-
plex in CH2Cl2 and methanol (9:1) in the presence of hydrogen
peroxide [10]. The complex showed a pronounced catalytic activity
toward H2O2 induced oxidation of sulfides under atmospheric con-
ditions, Eq. (1). The oxidation of the organic thioether did not occur
in the absence of catalyst. The sulfoxides and sulfones were sepa-
rated by preparative TLC and were characterized by their melting
points, FT-IR and 1H NMR spectra. The conversion was calculated
on the basis of the isolated yields, shown in Table 4.
O
S
O
O
H2O2
Cat.
0
100
200
300
400
500
600
S
ð1Þ
S
+
Temperature (oC)
R1
R2
R1
R2
R1 R2
Fig. 1. Thermogravimetric analyses of the metal complexes.
3.7. Antibacterial and antifungal activities of the ligand and its
complexes
numbering, is shown in Fig. 2. The palladium atom is coordinated
to the monoionic ONS donor ligand in a tridentate fashion and
the chlorine atom fulfils the slightly distorted square planar geom-
etry. The ONS donor set, palladium atom and the chloride ion al-
most reside in the same plane. The bite angles are S—Pd—Cl,
89.19(3), O—Pd—Cl, 89.44(6), N—Pd—O, 94.6(1), N—Pd—S,
87.33(8)°. Again, the angles N—Pd—Cl (173.76(8)°) and S—Pd—O
(173.35(7)°) confirm the distortion from the square planar geome-
try. The Pd—S and Pd—O bond distances match with regular Pd—S
and Pd—O bond distances [21]. The benzyl moiety of the ligand in
the complex is tilted to the outside of the basal plane, which may
be due to repulsion of the electronegative chloride ion with the
benzyl moiety. Moreover, from the Pd—O (1.992(2) Å), Pd—N
(2.001(2) Å), Pd—S (2.2225(8) Å) and Pd—Cl (2.3108(6) Å) bond
lengths we can conclude that the oxygen and nitrogen atoms are
more strongly coordinated to palladium, compared to the sulfur
In an antimicrobial study, the MIC values of the ligand and com-
plexes 2–4 were determined according to the literature method of
Rangasamy et al. [22]. The ligand and the complexes were tested
for their in vitro antibacterial activities against the Gram positive
and Gram negative bacteria S. aureus and K. pneumonia respec-
tively, using the agar well diffusion method and the MIC was deter-
mined by the serial dilutions in liquid broth method. The ligand
and the complexes exhibited activity against both S. aureus and
K. pneumonia. The negative control, DMF, did not exhibit any anti-
bacterial properties. The zones of inhibition of the compounds are
given in Table 5. It is observed that the copper complex 3, with the
lowest stock concentration, was active against both bacterial
strains. The cobalt complex 4 demonstrated the highest zone of
inhibition against K. pneumonia at 16 mm and ligand 1 was found
Table 2
Thermogravimetric analyses of the metal complexes.
Compound
First decomposition
Second decomposition
Temperature range (°C)
Weight loss (%)
Calc.
Temperature range (°C)
Weight loss (%)
Calc.
Found
Found
NiL2
200–490
195–523
245–537
186–331
49.97
49.68
49.95
23.52
50.52
49.46
49.64
23.70
491–638
524–670
538–679
532–570
91.24
90.73
91.22
77.24
91.15
90.51
90.83
77.07
CuL2
CoL2
PdLCl

M. Kalita et al. / Polyhedron 74 (2014) 93–98
97
Fig. 2. Molecular structure of the palladium complex 5 shown with 50% probability ellipsoids.
Table 3
Selected bond lengths (Å) and bond angles (°) for 5.
Table 5
The zones of inhibition of the ligand and complexes 2–4.
Bond lengths
Bond angles
Compound
Zone of inhibition (mm)
Pd—N(1)
Pd—O(1)
Pd—S(1)
Pd—Cl(1)
S—C(13)
2.001(2)
1.992(2)
2.2225(7)
2.3108(8)
1.776(3)
1.832(4)
1.301(4)
1.308(4)
1.433(4)
N(1)—Pd—O(1)
N(1)—Pd—S(1)
O(1)—Pd—S(1)
N(1)—Pd—Cl(1)
O(1)—Pd—Cl
94.6(1)
(K. pneumonia)
(S. aureus)
87.33(8)
173.36(6)
173.76(8)
89.44(6)
89.19(3)
1
2
3
4
14
12
13
16
37
0
23
22
21
21
35
0
S—C(14)
S(1)—Pd—Cl(1)
Gentamycin sulfate
Nystatin (antifungal)
DMF
O(1)—C(1)
N(1)—C(7)
N(1)—C(8)
0
0
Table 6
Table 4
MIC activity data of compounds:
Oxidation of sulfides, catalyzed by CuL2 in dichloromethane methanol (9:1) mixed
solvent.
Compound
K. pneumonia
S. aureus
MIC
MIC (mg/ml)
Entry
Equiv
Time Yield (%)
1
2
3
4
2.5
5
870
3.5
0
312
1.25
425
875
0
H2O2
(50%)
(h)
Sulfoxide Sulfone
5
2.5
25
40
NO2
DMF
S
against the bacterial strains. It has been observed that the activity
against the Gram positive bacteria S. aureus is greater compared to
K. pneumoniae, the Gram negative bacteria. Of all the compounds,
the ligand 1 and the copper complex 3 exhibited better antibacte-
rial properties, as is evident from the well diffusion and MIC assays.
5
5
2.5
2.5
20
20
45
40
S
S
Cl
Cl
4. Conclusion
to show the highest zone of inhibition against S. aureus. The MIC
assay showed that the compounds had antibacterial properties at
various concentrations. The results are shown in Table 6. The li-
gand exhibited the lowest MIC against S. aureus, with an activity
A new sterically and electronically tunable mixed hydroxyl-
imine-thioether tridentate ligand and its four mononuclear Ni(II),
Cu(II), Co(II) and Pd(II) complexes have been prepared. These were
characterized by physio-chemical analysis. Single crystal X-ray dif-
fraction data and an electronic spectrum revealed a slightly dis-
torted square planar complex for complex 5. The copper complex
of 312
MIC against K. pneumonia at 870
MIC studies show that the ligand and the complexes are active
lg/ml, while the copper complex 3 exhibited the lowest
l
g/ml. The antimicrobial and

98
M. Kalita et al. / Polyhedron 74 (2014) 93–98
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Acknowledgments
The authors thank IIT Bombay for spectral and analytical data.
The authors also thank the Director of NIT, Silchar for financial
assistance (M.K. & P.G.) and AICTE for financial support.
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Appendix A. Supplementary data
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CCDC 955390 contains the supplementary crystallographic data
for palladium complex. 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: de-
posit@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.2014.02.043.
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