Synthesis, characterization, X-ray crystallography, and antimicrobial activities of Ni(II) and Cu(II) complexes with a salicylaldehyde-based thiosemicarbazone ligand

Article abstract of DOI:10.1080/00958972.2014.880426

A new salicylaldehyde-based ONS tridentate salicylaldehyde-N(4)- diethylthiosemicarbazone (H₂SANEt₂) has been synthesized and characterized by elemental analyses mass, IR, and ¹H NMR spectral parameters. The coordination m

Full text of DOI:10.1080/00958972.2014.880426

Journal of Coordination Chemistry, 2014
Vol. 67, No. 2, 286–299, http://dx.doi.org/10.1080/00958972.2014.880426
Synthesis, characterization, X-ray crystallography, and
antimicrobial activities of Ni(II) and Cu(II) complexes with a
salicylaldehyde-based thiosemicarbazone ligand
NITIS CHANDRA SAHA*†, RAJESH PRADHAN†, MOUSUMI DAS‡, NASIMA
KHATUN‡, DEBMALYA MITRA‡, AMALESH SAMANTA‡, ALEXANDRA M.Z.
SLAWIN§, ATISH DIPANKAR JANA¶, JULIA KLANKE‖ and EVA RENTSCHLER‖
†Department of Chemistry, University of Kalyani, Nadia, India
‡Division of Microbiology, Department of Pharmaceutical Technology, Jadavpur University, Kolkata,
India
§
School of Chemistry, University of St Andrews, Fife, UK
Department of Physics, Behala College, Kolkata, India
Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University, Mainz, Germany
¶
‖
(Received 9 October 2013; accepted 5 December 2013)
A
new salicylaldehyde-based ‘ONS’ tridentate salicylaldehyde-N(4)-diethylthiosemicarbazone
1
(
H
2
SANEt
spectral parameters. The coordination mode of the synthesized ligand is reported by solid state isola-
tion and physico-chemical identification of Ni(II) and Cu(II) complexes, [Ni(SANEt )] (1) and [Cu
SANEt )] (2). Both complexes are neutral and oxygen-bridged dinuclear species. The ligand is
2
) has been synthesized and characterized by elemental analyses, mass, IR, and H NMR
2
2
(
2 2
bideprotonated ‘ONS’ tridentate in both complexes. IR spectral data indicate that coordination of
each metal of the two complexes occurs through phenolic oxygen, azomethine nitrogen, and thiolato
sulfur. X-ray crystallographic data of 1 and 2 (both monoclinic, P2 /c) show a MONSO (where
1
M=Ni and Cu) square-planar coordination around each metal. Magnetic studies of 2 show that
the two Cu(II) centers are strongly antiferromagnetically coupled via the bridging phenoxo O. All
the synthesized compounds were tested for their in vitro antimicrobial activities against pathogenic
bacteria. The inhibition power of the complexes was greater than the parent ligand.
Keywords: Thiosemicarbazone; Ni, Cu-complexes; Crystal structures; Magnetic property;
Antimicrobial activity
*
Corresponding author. Email: nitissaha@klyuniv.ac.in
2014 Taylor & Francis
©

Ni(II) and Cu(II) thiosemicarbazone complexes
287
1. Introduction
Thiosemicarbazones are an excellent class of nitrogen & sulfur containing ligands with
interesting bonding capabilities, biological and chemical properties [1]. Presence of sulfur
in these complexes often shows various pharmacological activities [2] including antitumoral
[
3–7], anticancer [8], antibacterial [9], antifungal [10], and antiHIV [11] activity. The chem-
ical nature of the moiety attached to the C=S carbon in thiosemicarbazone derivative is
responsible for various biological and medicinal properties. Derivatives of thiosemicarba-
zones inhibit the activities of ribonucleotide reductase [12]. Because of their biological
potency, there is interest in metal complexes of heterocyclic thiosemicarbazones as well as
salicylaldehyde-thiosemicarbazones. Deprotonation of phenoxy hydrogen and N3 hydrogen
of the ligand form dianionic compound that coordinates with various metal via phenoxy
oxygen, imine nitrogen, and thiolate sulfur [13]. Dinuclear copper(II) complexes of Schiff-
based ligands have interesting properties as well as applications in magnetism, catalysis,
biology, etc. Deprotonation of phenoxy and bridging oxygen with two metals makes the
salicylaldehyde-thiosemicarbazone
a
potential dinucleating ligand. Hydroxo-and
phenoxo-bridged metal complexes involving M O (M=Ni(II), Cu(II), etc.) bridging present
2
2
in various metallo-enzymes have importance in biochemistry [14].
As part of our efforts towards synthesis and characterization of new metal ion materials
containing bio-relevant thiosemicarbazones and in continuation of our earlier publication
[
15], this communication reports the synthesis, spectroscopic and structural characterization,
and antimicrobial activities of Ni(II) and Cu(II) complexes with H SANEt along with the
2
2
magnetic properties of the Cu(II) complex.
2
2
. Experimental setup
.1. Materials and measurements
Mueller-Hinton agar was purchased from Merck India Ltd. All other reagents were of AR
grade and obtained from commercial sources and used without purification. Spectrograde
solvents were used for spectral measurements. Elemental analyses (C, H, N, and S) were
done with a Perkin-Elmer 2400 CHNS/O analyzer. The nickel and copper contents of the
complexes were determined gravimetrically as anhydrous dimethylglyoximatonickel(II) and
iodometrically, respectively. Electronic spectra were recorded on a Shimadzu UV-2401PC
−
1
spectrophotometer. IR spectra were recorded (4000–450 cm ) on a Perkin-Elmer L120-
1
0
00A FT-IR spectrophotometer with KBr pellets. H NMR spectrum of the ligand was
recorded in DMSO-d with a Bruker AC 400 superconducting FT NMR. Mass spectroscopy
6
was performed with a Jeol JMS-D300 mass spectrometer. A Rigaku Mercury 70 diffractom-
eter was used to collect X-ray data of the complexes. Antiferromagnetism of the complex
was performed with SQUID magnetometer MPMS-7 Quantum Design.
2
2
.2. Synthesis
.2.1. Synthesis of H SANEt . Salicylaldehyde-N(4)-diethylthiosemicarbazone, H SA-
2
2
2
NEt , (figure 1) was synthesized by refluxing an equimolar mixture of S-methyldithiocar-
2
bazate [16] and salicylaldehyde in dry ethanol involving conversion of salicylaldehyde into

2
88
N.C. Saha et al.
2 2
Figure 1. Formulation of H SANEt .
its S-methyldithiocarbazate derivative, followed by transamination [17] of the derivative
with diethylamine. An orange microcrystalline solid (from ethanol) was obtained with a
yield of ca. 70–75% (m.p.: 103–104 °C). Anal. Calcd for C H N OS (%): C, 57.34; H,
1
2 17 3
6
.82; N, 16.70; S, 12.74. Found (%): C, 56.75; H, 5.93; N, 16.08; S, 12.21. m/z: 252.04
+
(M , 98%).
2
.2.2. Synthesis of [Ni(SANEt )] (1) and [Cu(SANEt )] (2). The Ni(II) and Cu(II)
2
2
2 2
complexes were prepared by refluxing ethanolic solutions of the ligand (1.05 mM) and Ni
OAc) or Cu(OAc) (1.05 mM) in a water bath for 2 h. Bright yellow ligand solution, in
(
2
2
both the cases, was changed to dark brown. On slow evaporation of the dark brown solu-
tions, the desired Ni(II) or Cu(II) complexes crystallized, and then were filtered off, washed
with cold ethanol, and were dried over anhydrous CaCl ; the yield varied between 70 and
2
7
7%. Dark brown needle-shaped single crystals, in both the cases, were obtained from pen-
tane/dichloromethane mixture suitable for X-ray diffraction. Anal. Calcd for
C H N Ni O S (%): C, 46.80; H, 4.91; N, 13.64; S, 10.40; Ni, 19.06. Found: C, 46.20;
2
4
30
6
2 2 2
+
H, 4.08; N, 12.98; S, 10.12; Ni, 18.80. m/z: 614.99 (M , 44%). Anal. Calcd for
C H N Cu O S (%): C, 46.05; H, 4.83; N, 13.43; S, 10.23; Cu, 20.32. Found: C, 45.80;
2
4
30
6
2 2 2
+
H, 4.08; N, 12.98; S, 10.01; Cu, 19.80. m/z: 624.90 (M , 56%).
2
.3. Single-crystal X-ray diffraction studies
X-ray diffraction data of [Ni(SANEt )] (1) and [Cu(SANEt )] (2) were collected on a
2
2
2 2
Rigaku Mercury 70 diffractometer. The radiation used was MoKα and the data were
corrected for Lorentz-polarization and absorption effects. The structures were solved by
Patterson Methods (DIRDIF99 PATTY) and refined using full-matrix least squares based on
2
/
Fobs/ [18]. The non-hydrogen atoms were refined anisotropically, while hydrogens, either
located from difference electron density maps or generated using idealized geometry, were
used in the structure factor calculations with isotropic thermal parameters using the “riding”
model. Neutral atom scattering factors [19] were used and anomalous dispersion effects
were included in FCalcd [20].
2
.4. DFT calculation
In order to obtain the optimized geometry of the complex species, a representative DFT
calculation was carried out taking the dinuclear Ni(II) complex, with B3LYP density
functional and 6-31G(d,p) basis set using GAMESS software package [21].

Ni(II) and Cu(II) thiosemicarbazone complexes
.5. Antimicrobial activity
289
2
The compounds were tested for their in vitro antimicrobial activities using 18 types of micro-
organisms, Escherichia coli 55/10HD, Micrococcus luteus 9341, Salmonella typhi 74,
Staphylococcus aureus ML191, Klebsiella pneumoniae 714, Pseudomonas AMRI 100,
Vibrio cholerae 1363175, Shigella sonnei BCH217, Proteus vulgaris 24, Streptococcus
faecalis 52, Shigella dysenteriae 1, Bacillus cereus 11778, Streptococcus epidermidis 12228
(both Gram-positive and negative), Pseudomonas aeruginosa 25619, Micrococcus sp.
1
0240, Bacillus subtilis 6633, Bacillus pumilus 14884, and Bacillus bronchiseptica 4617,
which were obtained from Division of Microbiology, Department of Pharmaceutical Tech-
nology, Jadavpur University. Clinically used antibacterial agent amoxicillin was employed as
the reference material [22]. These strains were grown in Mueller-Hinton agar at 37 °C for
2
4 h and the suspension was prepared by matching a 0.5 McFarland standard [23]. All the
tested compounds were dissolved in 4% DMSO solution along with sterile distilled water
making up the 2-mL volume and tested for screening using Agar Dilution [24]. Then,
Minimum Inhibitory Concentration was determined as per NCCLS protocol [25] and by INT
assay. The drug showing best result against a particular organism is selected from both the
sets of drugs, and effect on bacterial growth rate was observed. With same combination of
drug and organism from each set, scanning electron microscopy (model: Jeol Jsm-6360) was
done to find out the mode of action of drugs as well as to observe the morphological
alteration behind drug exposure.
3
3
. Results and discussion
.1. Crystal structures of [Ni(SANEt )] (1) and [Cu(SANEt )] (2)
2
2
2 2
X-ray crystallographic analyses reveal that both 1 and 2 are isomorphous dinuclear species
figures 2 and 3, respectively). In both complexes, the metal centers possess nearly
square-planar coordination with deviations of ‒0.044(1) Å, ‒0.037(1) Å, 0.089(1) Å, and
.103(1) Å for Ni1, Ni21, Cu1, and Cu21, respectively, from the ideal planes. S10 and O1
(
0
of a ligand bind trans to a metal center, with N8 of the same ligand and the phenoxo O21
of another ligand in the other two trans sites of the metal center. Phenoxo O1 and O21 are
shared by both coordination units. Coordination planes of the two metal units are joined
along the line connecting C1, O1, O21, and C21 and are twisted with respect to each other
having a torsion angle of 144.03° giving the whole unit an ‘X’ shape when viewed
edge-on. Crystallographic data and refinement parameters are given in table 1.
In 1, Ni‒O distances are 1.88(2)‒1.907(2) Å, with Ni1‒N8 and Ni2‒N28 distances
of 1.843(3) Å and 1.842(3) Å. Ni1‒S10 and Ni2‒S30 distances are 2.136(1) Å and
2
.133(1) Å, respectively. The bond angles show no unusual values (table 2).
In 2, Cu‒O distances are 1.936(3)‒1.981(3) Å, with Cu1‒N8 and Cu2‒N28 distances of
.917(4) Å and 1.934(4) Å, respectively. Cu1‒S10 and Cu22‒S30 distances are 2.205(1) Å
1
and 2.201(1) Å, respectively. The bond angles are usual for this type of complex (table 3).
In both complexes, all classical hydrogen bonds are intramolecular (table S1, see online
supplemental material at http://dx.doi.org/10.1080/00958972.2014.880426).
The supramolecular assemblies of dinuclear units are governed by π···π and CH···π
interactions. As depicted in figure 2, the six-member metal chelate rings R4 and R5 and the
phenyl rings R6 and R7 are responsible for π-stacking interactions between successive dinu-
clear units. These π-stacking interactions (table S2) lead to a 1-D chain of the dinuclear

2
90
N.C. Saha et al.
Figure 2. ORTEP diagram (30% ellipsoidal probability) with atom numbering scheme for 1.
Figure 3. ORTEP diagram (30% ellipsoidal probability) with atom numbering scheme for 2.
units along the crystallographic a-axis (figure 4). Five-member metal chelate rings involving
S and N (R2 and R3) are also involved in this interaction, forming tubular assembly along
the crystallographic a-axis through centrosymmetric arrangement of adjacent ‘X’-shaped

Ni(II) and Cu(II) thiosemicarbazone complexes
Table 1. Crystal data and refinement parameters.
291
Complex
1
2
Crystal data
Formula
Ni
2
C
24
H
30
N
6
O
2
S
2
2 24 30 6 2 2
Cu C H N O S
Formula weight
Crystal system
Space group
a, b, c [Å]
616.06
Monoclinic
P2 /c (No. 14)
625.75
Monoclinic
P2 /c (No. 14)
1
1
13.342(4), 12.347(3), 16.882(5)
13.432(4), 11.985(3), 17.140(5)
α, β, γ [°]
V [Å ]
90, 111.006(6), 90
2596.2(13)
90, 109.216(8), 90
2605.5(13)
3
Z
4
4
3
D(Calcd) [g/cm ]
μ(MoK ) [mm]
F (0 0 0)
1.576
1.646
1280
1.595
1.827
1288
α
Crystal size [mm]
Data collection
Temperature (K)
Radiation [Å]
0.10 × 0.10 × 0.10
0.03 × 0.10 × 0.10
93
93
MoK
α
0.71075
α
MoK 0.71075
Theta min-max [°]
Data set
Tot., uniq. data, R(int)
Observed data [I > 0.0 σ(I)]
Refinement
0.0, 25.4
0.0, 25.4
−16 : 13; −14 : 13; −15 : 20
15920, 4724, 0.054
3360
−15 : 16; −14 : 10; 20 : 18
15949, 4735, 0.054
3493
Nref, Npar
4724, 325
4735, 325
R, wR2, S
Max. and av. shift/error
Min. and max. resd. dens. [e/Å ]
0.0462, 0.1051, 1.00
0.01, 0.00
−0.44, 0.56
0.0504, 0.1355, 1.07
0.02, 0.00
−0.64, 1.51
3
Table 2. Selected bond distances and angles (Å, °) for 1.
Bond distances
Ni1‒S10
Ni1‒O1
Ni1‒O21
Ni1‒N8
2.1360(13)
1.881(2)
1.907(2)
1.843(3)
Ni2‒S30
Ni2‒O1
Ni2‒O21
Ni2‒N28
2.1325(12)
1.905(2)
1.890(2)
1.842(3)
Bond angles
S10‒Ni1‒O1
S10‒Ni1‒O21
S10‒Ni1‒N8
O1‒Ni1‒O21
O1‒Ni1‒N8
O21‒Ni1‒N8
Ni1‒S10‒C10
Ni1‒O1‒C1
Ni1‒O21‒C21
Ni1‒N8‒N9
Ni1‒N8‒C7
Ni1‒O1‒Ni21
174.78(8)
98.37(8)
87.60(10)
77.16(10)
96.76(12)
173.53(11)
95.81(15)
127.6(2)
130.4(2)
122.8(2)
123.7(3)
90.62(10)
S30‒Ni21‒O1
S30‒Ni21‒O21
S30‒Ni21‒N28
O1‒Ni21‒O21
O1‒Ni21‒N28
O21‒Ni21‒N28
Ni21‒S30‒C30
Ni21‒O1‒C1
Ni21‒O21‒C21
Ni21‒N28‒N29
Ni21‒N28‒C27
Ni1‒O21‒Ni21
98.04(8)
173.37(8)
87.83(10)
76.98(10)
174.13(12)
97.16(12)
95.26(16)
130.7(2)
126.6(2)
122.3(3)
123.7(3)
90.30(10)
molecular complexes (figure 4). Terminal –CH3 groups provide the site for CH···π
interactions (table S3), through which the tubular units are interconnected (figure 5).
3
.2. DFT structure of [Ni(SANEt )] (1)
2 2
A DFT optimization has been carried out for the Ni(II) complex (figure S1). The calculated
optimized geometry is nearly identical to the one observed in the crystal structure. Bond
distances are slightly higher in the calculated geometry, Ni‒O distances of 1.863 Å and

2
92
N.C. Saha et al.
Table 3. Selected bond distances and angles (Å, °) for 2.
Bond distances
Cu1‒S10
Cu1‒O1
Cu1‒O21
Cu1‒N8
2.2048(13)
1.939(3)
1.967(3)
1.917(4)
Cu2‒S30
Cu2‒O1
Cu2‒O21
Cu2‒N28
2.2005(13)
1.981(3)
1.936(3)
1.934(4)
Bond angles
S10‒Cu1‒O1
S10‒Cu1‒O21
S10‒Cu1‒N8
O1‒Cu1‒O21
O1‒Cu1‒N8
O21‒Cu1‒N8
Cu1‒S10‒C10
Cu1‒O1‒C1
Cu1‒O21‒C21
Cu1‒N8‒N9
Cu1‒N8‒C7
Cu1‒O21‒Cu2
171.92(11)
101.39(8)
87.74(10)
76.28(11)
94.28(13)
170.43(12)
93.49(17)
127.2(3)
132.1(3)
120.8(3)
125.3(3)
98.62(13)
S30‒Cu2‒O1
S30‒Cu2‒O21
S30‒Cu2‒N28
O1‒Cu2‒O21
O1‒Cu2‒N28
O21‒Cu2‒N28
Cu2‒S30‒C30
Cu2‒O1‒C1
102.16(9)
173.94(11)
87.48(10)
76.05(11)
168.48(12)
93.71(13)
94.25(17)
131.2(3)
Cu2‒O21‒C21
Cu2‒N28‒C27
127.1(3)
125.1(3)
Cu1‒O1‒Cu2
98.04(13)
Figure 4. The supramolecular 1-D chain of molecular complexes through π···π interaction that run along the
crystallographic a-axis (left) and the tubular view of this chain when seen along the a-axis (right). The tube has a
rhombic cross-section.
1.891 Å and Ni‒N distances 1.837 Å and 1.838 Å. Ni‒S distances are identical (2.162 Å).
The calculated torsion angle between the two metal coordination planes is 144.03°. The
HOMO and LUMO have a gap of 3.546 eV; these frontier orbitals are composed of both
metals and ligand orbitals (figure S2).
3
.3. IR spectral studies
IR spectra of H SANEt and its Ni(II) and Cu(II) complexes provide information about the
2
2
−
1
mode of ligand coordination. The band at 1616 cm in the ligand spectrum corresponds to

Ni(II) and Cu(II) thiosemicarbazone complexes
293
Figure 5. The packing of tubular units through CH···π interaction (shown as yellow dotted lines) in which the
terminal –CH groups play a prominent role (see http://dx.doi.org/10.1080/00958972.2014.880426 for color version).
3
−
1
−1
azomethine –CH=N stretch, shifted to 1596 cm for Ni(II) and 1593 cm for Cu(II) in the
metal complexes, indicating that azomethine N participates in bond formation. Another
−
1
peak at 3361 cm due to ‒NH group of the ligand disappeared in metal complexes, indicat-
ing a pi-bond in between the N–C for formation of M–S sigma bond by converting –C=S
‒
−1
into –C‒S . A strong peak at 765 cm (–C=S), in ligand, shifted lower in metal complexes
supporting this.
3
.4. UV–Vis spectra
UV–Visible spectra of ligand and complexes in DMSO and in the solid state show that all
compounds have same structure in solution and in the solid state. In 1, a broad absorbance at
−
1
1
1
2
2,000 cm is due to the A → A transition in a square-planar geometry [26]; absorption
g
2 g
−1
below 10,000 cm also indicates square-planar geometry [27]. Complex 2 showed bands at
−
1
−1
3
0,000 cm and 40,000 cm corresponding to n–π* and π–π* transitions, respectively [28].
−
1
The LMCT band, in 2, appeared around 20,000 cm due to Cu‒S bonding [29].

2
94
N.C. Saha et al.
1
3
.5. H NMR spectrum of H SANEt
2 2
1
The H NMR spectrum of the free ligand in DMSO-d gives singlets at δ 8.54 (1H) and
6
11.15 (1H) assigned to salicylaldehyde –CH and thiosemicarbazate –NH, respectively. One-
proton singlet at δ 8.54 ppm, ascribed as phenolic –OH proton, indicates the existence of
1
hydrogen-bonded stabilized form of the ligand. The H NMR spectrum shows a triplet at δ
6
.92 (2H) due to the aromatic protons; the two peaks, a quartet at δ 3.77(4H), and a triplet
at 1.19 (6H) are assigned to the two –CH – and two –CH groups of –NEt , respectively.
2
3
2
3
.6. Antimicrobial activity
The ligand and its complexes were active towards antimicrobial effect at MIC concentration
0–400 μg/mL. Ligand is the most active against V. cholerae 1363175 with lower MIC con-
1
centration 10 μg/mL, whereas 1 is more effective against S. typhi 74, V. cholerae 1363175,
and S. dysenteriae 1 at lowest MIC concentration of 10 μg/mL. Complex 2 was active
against S. typhi 74, S. dysenteriae 1, and S. epidermidis 12228 at MIC concentration 10 μg/
mL (table 4). The compounds are active toward a variety of micro-organisms at different
MIC values (table 5). The test drugs are broad spectrum, i.e. effective on both gram-positive
and gram-negative organisms, more effective on enteric organisms. As the cell wall archi-
tectures were different in the different micro-organisms, there might be a common target of
these drugs. By analyzing bacterial growth curve, we conclude that these compounds are
bacteriostatic agents. The details of the time-dependent in vitro growth curves of different
bacteria at MIC values against the complex species are shown in figure 6. The enhanced
antimicrobial activity of both complexes may be explained in terms of Overtone’s concept
of cell permeability [30] and Tweedy’s chelation theory [31]. Generally, antimicrobial effi-
ciency decreases in the order cationic > neutral > anionic complex [32], consistent with
greater activity of complex over the ligand. The actual process of destruction of bacterial
cell has been shown by treating Sh. sonnie BCH217 and Micrococcus 10240 with ligand
Table 4. Representation of MIC (µg/ml) values of synthetic drugs on tested organisms.
Organisms
Ligand
Complex 1
Complex 2
AM*
S. typhi 74
E. coli 55/10HD
M. luteus 9341
S. aureus ML191
K. pneumoniae 714
Pseudomonas AMRI 100
V. cholerae 1363175
Sh. sonnei BCH217
P. vulgaris 24
S. faecalis 52
S. dysenteriae 1
B. cereus 11778
P. aureginosa 25619
Micrococcus sp. 10240
B. subtilis 6633
B. pumilus 14884
B. bronchiseptica 4617
S. epidermidis 12228
–
–
–
–
400
–
10
200
400
400
200
400
400
400
–
10
50
400
50
50
400
10
400
–
–
10
50
–
50
100
100
100
50
10
–
–
25
25
–
10
–
25
1
5
5
100
100
25
50
256
5
–
–
10
400
–
100
–
–
–
10
1
25
100
25
25
50
50
5
400
100
–
AM* = amoxicillin, which is used as a standard drug.
–” represents no antimicrobial activity.
“

Ni(II) and Cu(II) thiosemicarbazone complexes
295
Table 5. Zone diameter of MIC (mm) values of synthetic drugs on tested organisms.
Organisms
Ligand
Complex 1
Complex 2
AM*
S. typhi 74
E. coli 55/10HD
M. luteus 9341
S. aureus ML191
K. pneumoniae 714
Pseudomonas AMRI 100
V. cholerae 1363175
Sh. sonnei BCH217
P. vulgaris 24
S. faecalis 52
S. dysenteriae 1
B. cereus 11778
P. aeruginosa 25619
Micrococcus sp. 10240
B. subtilis 6633
B. pumilus 14884
B. bronchiseptica 4617
S. epidermidis 12228
–
–
–
–
6.0 ± 0.2
8.0 ± 0.2
7.0 ± 0.7
7.2 ± 0.7
8.0 ± 0.2
–
7.0 ± 0.7
6.2 ± 0.1
–
8.0 ± 0.1
8.5 ± 0.5
13.3 ± 0.9
7.0 ± 0.2
15.5 ± 0.9
9.0 ± 0.9
9.0 ± 0.6
7.5 ± 0.5
8.6 ± 0.1
11 ± 4
9.2 ± 0.3
9.5 ± 0.5
12.0 ± 0.2
9.5 ± 0.6
7.8 ± 0.8
12.7 ± 0.2
11.6 ± 0.6
–
–
6.0 ± 0
8.0 ± 0.2
6.4 ± 0.1
–
–
7.0 ± 0.2
7.0 ± 0.1
7.5 ± 0.1
6.1 ± 0.1
6.0 ± 0.1
–
8.2 ± 0.2
6.1 ± 0.1
–
6.2 ± 0.1
–
–
–
–
7.2 ± 0.2
6.0 ± 0
–
8.0 ± 0.2
6.4 ± 0
7.1 ± 0.2
6.6 ± 0.1
6.5 ± 0
6.0 ± 0.2
6.0 ± 0
–
6.0 ± 0.2
–
–
–
7.0 ± 0.1
6.4 ± 0.1
–
6.5 ± 0.1
13.0 ± 0.4
AM* = amoxicillin, which is used as a standard drug.
–” represents no zone of inhibition of drugs.
“
and 1, respectively, as referenced under SEM. Ligand made the cell fragile and
subsequently made leakage of cytoplasm in Sh. sonnie BCH217 (figure 7); 1 caused swell-
ing of Micrococcus 10240 cell and deformation of structure by increasing cell permeability
(
figure 8).
3
.7. Magnetic property
The magnetic measurements of 2 were performed with a SQUID magnetometer (MPMS-7
Quantum Design) from 2 to 300 K with an applied field of 1 Tesla on a powdered micro-
crystalline sample. The magnetic susceptibility data of χT versus T (χ for two copper(II)
ions) of 2 are shown in figure 9 and the parameters are shown in table 6. All experimental
magnetic data were corrected for the underlying diamagnetism of the sample holder and of
the constituent atoms (Pascal’s tables). Magnetic susceptibility could be fitted by the least
square method with the classic Bleaney‒Bowers equation [33]. For the spin Hamiltonian
simulations of the data, the routine JulX was used. The simulation was obtained by using
the Hamilton:
X
H^ ¼ ꢀ2
^ ^
J S S
i; j i j
i\j
3
−1
The χT at room temperature is 0.15 cm K M , which lies far below the value of 0.75
3
−1
cm K M expected for two uncoupled spins with S = S = 0.5. The χT value decreases
1
2
3
−1
rapidly with decreasing temperature reaching a constant value close to 0 cm K M at
100 K and follows the Curie−Weiss law with Weiss constant θ = 0 K. This magnetic
~
behavior is generally observed for complexes that possess a strong intracomplex antiferro-
magnetic interaction [34, 35]. The antiferromagnetic coupling for the complex is J = ‒299
1
2
−
1
cm , g = g = 2.00 and a paramagnetic impurity of 2.2% with a spin of S (PI) = 1 and a
1
2

2
96
N.C. Saha et al.
Figure 6. Time-dependent in vitro growth curves at MIC values of (a) Sh. sonnei BCH217 against ligand; (b)
B. cereus 11778 against ligand; (c) V. cholerae 1363175 against complex 1; (d) S. typhi 74 against 1; (e)
K. pneumoniae 714 against complex 2; and (f) S. epidermidis 12228 against 2.
Figure 7. SEM micrographs of Sh. sonnei BCH217: before [figure 7(a)] and after [figure 7(b)] treating with
ligand.
Theta‒Weiss temperature of 0 K of the impurity. TIP is the temperature-independent
paramagnetism. Thus, the J value here shows a strong antiferromagnetic interaction
between two copper(II) ions. The dominant exchange pathway, through the two oxygen

Ni(II) and Cu(II) thiosemicarbazone complexes
297
Figure 8. Representative SEM micrographs of Micrococcus 10240: before [figure 8(a)] and after [figure 8(b)]
treating with 1.
Figure 9. The magnetic susceptibility data of χT vs. T plot of 2.
Table 6. Magnetic parameters for 2.
−
1
S
1
S
2
J
12/cm
g
1
g
2
TIP/1e-6emu
50
Imp/%
2.2
Spin of PI
1
Theta–Weiss PI/K
0.5
0.5
−299.233
2.0
2.0
1
bridges, involves interaction of two copper dx −y orbitals and an ‘s’ and a ‘p’ orbital on the
2
2
oxygen with predominantly σ overlap. Out of plane distortions at the copper centers of 2
may be due to some reduction of σ overlap and as well as exchange, but the effect on the
exchange is small. Because of the proximity of the two metal centers in the N S O frame-
2
2 2
work, this magnetic behavior may be assigned as an ‘intramolecular antiferromagnetic
exchange interaction’ propagated by the endogenous bridging oxygens [36].

2
98
. Conclusion
N.C. Saha et al.
4
The present communication provides a general and effective method for the synthesis of
salicylaldehyde-N(4)-diethylthiosemicarbazone (H SANEt ) and its Ni(II) and Cu(II)
2
2
complexes. The complexes are neutral, oxygen-bridged dinuclear species, and crystallize in
monoclinic crystal system with nearly square-planar geometries around the metal. All the
compounds show potential antimicrobial actions against pathogenic bacteria. The ligand is
active against V. cholerae 1363175, but coordination of the thiosemicarbazone to nickel(II)
resulted in enhancement of activity against S. typhi 74 and S. dysenteriae 1. Coordination
to copper(II) resulted in enhancement of activity against almost all the studied micro-organ-
isms. The compounds are effective against both gram-positive and gram-negative organ-
isms. Hence, complexation of the thiosemicarbazone ligand with the metal enhances the
antimicrobial activities, as observed in similar type of complexes [37, 38]. Complex 2
shows strong antiferromagnetic interaction between two Cu(II) centers coupled via the
bridging phenoxo O.
Supplementary material
Crystallographic data for the structures reported here have been deposited with the
Cambridge Crystallographic Data Center, CCDC Nos. 903324 and 903325. Copies of this
information may be obtained free of charge from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +44-1223-336-033); E-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk.
Acknowledgments
One of us (Rajesh Pradhan) is thankful to University of Kalyani for providing financial support
in the form of University Research fellowship. The financial support received from the
DST-PURSE program, University of Kalyani, is thankfully acknowledged.
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