Transition metal complexes of a new hexadentate macroacyclic N 2O4-donor Schiff base: Inhibitory activity against bacteria and fungi

Article abstract of DOI:10.1016/j.ejmech.2010.03.025

A new hexadentate macroacyclic N₂O₄ - donor ligand, glyoxal bis(N-nitroso phenylglycine) (gbnp), has been designed and structurally characterized. Manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes of gbnp have

Full text of DOI:10.1016/j.ejmech.2010.03.025

European Journal of Medicinal Chemistry 45 (2010) 2981e2986
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Transition metal complexes of a new hexadentate macroacyclic N2O4-donor
Schiff base: Inhibitory activity against bacteria and fungi
*
Manjula Patil, Rekha Hunoor, Kalagouda Gudasi
Department of Chemistry, Karnatak University, Dharwad 580 003, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new hexadentate macroacyclic N2O4 e donor ligand, glyoxal bis(N-nitroso phenylglycine) (gbnp), has
been designed and structurally characterized. Manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II)
complexes of gbnp have been prepared and characterized by elemental analyses, molar conductance
measurements, magnetic moment, spectral (IR, 1H NMR, electronic and FAB mass) and thermal studies.
The molecular dynamics of the ligand was studied by the variable temperature NMR studies, which
suggest the presence of two isomeric forms. The antimicrobial activity of all the compounds was studied
against Escherichia coli, Bacillus cirroflagellosus, Aspergillus niger and Candida albicans. Among the new
complexes, copper(II) complex has the highest potential against all the microorganisms tested.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Received 23 November 2009
Received in revised form
14 March 2010
Accepted 16 March 2010
Available online 25 March 2010
Keywords:
Amino acid Schiff base
Metal complex
N-Nitroso compound
Variable temperature NMR
Antimicrobial activity
1. Introduction
and have achieved recognition for their role in biological systems
such as mutagenesis and carcinogenesis [18e27]. In addition to the
The chemistry of nitroso compounds has been intensively
studied in the past decades, especially in the field of asymmetric
synthesis [1,2], nitroso DielseAlder reaction [3,4], N-nitroso aldol
reaction [5] and nitroso ene reaction [6]. In 1992, nitric oxide (NO)
was selected by Science magazine as the “Molecule of the Year” [7]
due to its participation in several biological functions [8]. In the
same year, a book dealing exclusively with metal nitrosyls (metal-
eNO compounds) was published [9]. NO binds to the metal centers
of hemecontaining biomolecules such as the enzyme guanylyl
cyclase forming FeeNO bonds [10,11]. These observations helped to
make the study of metaleNO compounds interdisciplinary in
nature, bridging traditional inorganic chemistry with biochemistry
and pharmacology.
biochemical research, Schiff bases and their metal complexes are
being used as analytical reagents also [28].
In continuation of our study on coordination chemistry of amino
acid Schiff bases [29,30], we thought it would be useful to synthetic
coordination compounds of a Schiff base containing prudent
N-nitroso moieties and to evaluate them for their antimicrobial and
anticancer activities. Here we report the synthesis and spectro-
scopic characterization of manganese(II), cobalt(II), nickel(II)
copper(II) and zinc(II) complexes of gbnp (Fig. 1). A comparative
antibacterial and antifungal activity of these compounds is
evaluated.
2. Experimental
Aim of the present work was to insert NO group in amino acid
Schiff bases. As we know amino acid Schiff bases readily form
complexes with metal ions which play an important role as the
basic compounds for modeling more complicated amino acid Schiff
bases [12e16]. They are key intermediates in a variety of metabolic
reactions involving amino acids [17]. The preparative accessibility,
diversity and structural variability make Schiff bases very attractive
2.1. Methods
2.1.1. Synthesis of the ligand [gbnp]
The preparation of glyoxal bis(N-nitroso phenylglycine) (gbnp)
involves the following steps as outlined in Scheme 1.
2.1.1.1. Synthesis of N-phenylglycine ester [pge]. It was prepared by
following the procedure as described in the literature [31].
* Corresponding author. Tel.: þ91 0836 2460129(Res), þ91 0836 2215286(Off);
fax: þ91 0836 2771275.
2.1.1.2. Synthesis of N-nitroso phenylglycine ester [npge]. A suspen-
sion of pge (1.79 g, 0.01 mol) in 20 ml of (1:1) aqueous acetic acid
E-mail address: kbgudasi@gmail.com (K. Gudasi).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.03.025

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M. Patil et al. / European Journal of Medicinal Chemistry 45 (2010) 2981e2986
washed with ethanol and recrystallized from hot ethanol. Yield:
87%. M.P.: 155 ꢀC.
N
N
NH
HN
2.1.1.5. Preparation of the complexes (1e5). The respective hydrated
metal chlorides [0.01 mol, M ¼ manganese(II), cobalt(II), nickel(II),
copper(II), zinc(II)] dissolved in 10 ml of ethanol was added to
ethanolic (20 ml) solution of gbnp (0.41 g, 0.01 mol) and refluxed
for 4e5 h. The colored complexes so obtained were filtered, washed
with ethanol and dried under vacuum over anhydrous CaCl2. Yield:
80e85%.
O
O
N
O
N
O
N
N
Fig. 1. Structure of the ligand.
3. Pharmacology
The in vitro antimicrobial activity of all the compounds was
studied against Gram negative (Escherichia coli) and Gram positive
(Bacillus cirroflagellosus) bacteria and fungi, Aspergillus niger and
Candida albicans by agar well diffusion method [32,33]. The
nutrient broth was prepared by dissolving peptone (0.5%), yeast
extract (0.15%), beef extract (0.15%), sodium chloride (0.36%) and
monopotassium phosphate (0.13%) in distilled water (100 ml). The
pH of the solution was adjusted to 7.2 by adding sodium hydroxide
solution (4%) and the resulting solution was autoclaved for 20 min
at 15 psi. Each test sample (5 mg) was dissolved in DMSO (1 ml) and
was taken and cooled to 0 ꢀC. A solution of sodium nitrite (0.79 g,
0.01 mol) in 8 ml water was added dropwise with stirring for
30 min, maintaining the temperature between 0e5 ꢀC. Further, the
reaction mixture was stirred for 2 h. Thick oil separated was
extracted with ether. Ether layer was washed with distilled water
several times. Ether was evaporated to get back the oil and dried
over anhydrous calcium chloride. The purity was confirmed by TLC
and 1H NMR analysis. Yield: 80%.
2.1.1.3. Synthesis of 2-[nitroso (phenyl) amino] acetohydrazide
(npah). The mixture of npge (2.08 g, 0.01 mol) and hydrazine
hydrate (0.49 ml, 0.01 mol) in 20 ml absolute ethanol was refluxed
at water bath temperature for 4e5 h. The solid separated was
filtered and washed with ethanol. The crude product was recrys-
tallized from hot ethanol and dried in vacuo. Yield: 82%. M.P.: 115 ꢀC.
0.1 ml of this solution (50
mg) was used for testing.
4. Results and discussions
The analytical data of the ligand and its metal complexes is
summarized in Table 1 and are in good agreement with those
2.1.1.4. Synthesis of glyoxal bis(N-nitroso phenylglycine) (gbnp). To
npah (1.94 g, 0.01 mol) in 20 ml absolute ethanol, glyoxal (0.58 g,
0.01 mol) was added and refluxed on a water bath for 4e5 h. The
reaction mixture was cooled. The solid separated was filtered,
required
by
the
general
formula
[M(gbnp)]Cl2$nH2O
[M¼manganese(II), cobalt(II), nickel(II), copper(II), zinc(II), n¼ 2, 3].
Attempts to crystallize the ligand and its complexes, suitable for
X-ray diffraction studies were unsuccessful. The obtained
O
NH2
N
H
N
N
NaNO2/CH3COOH
C2H5COOCH2Cl
+
0 - 5 o
C
COOC2H5
C2H5COO
npge
NH2-NH2
O
N
N
N
H
O
NH
O
O
N
HN
NH2
N
O
O
O
O
N
N
N
N
npah
gbnp
Scheme 1.
Table 1
Analytical data of gbnp and its complexes.
Compound Compound
code
Empirical
formula
Formula Found (calcd.) %
weight
Melt/dec. LM
(
Uꢁ1
pt. (ꢀC)
cm2 molꢁ1
)
C
H
N
M
Cl
e
1
2
3
4
5
gbnp
C
18H18N8O4
410.10
52.40 (52.70) 4.10 (4.42) 27.15 (27.30)
36.22 (36.61) 4.00 (4.06) 18.18 (18.90) 9.00 (9.30)
36.30 (36.80) 3.24 (3.81) 19.26 (19.44) 10.00 (10.22) 12.14 (12.32) 230
37.22 (37.51) 3.35 (3.82) 19.12 (19.45) 10.10 (10.17) 12.05 (12.33) 205
37.12 (37.20) 3.28 (3.78) 19.10 (19.29) 10.55 (10.93) 12.15 (12.22) 210
37.00 (37.08) 3.64 (3.77) 19.04 (19.23) 11.12 (11.21) 12.00 (12.10) 208
e
e
155
e
[Mn(gbnp)]Cl2 $3H2O C18H24Cl2MnN8O7 590.00
[Co(gbnp)]Cl2 $2H2O C18H22Cl2CoN8O6 576.00
[Ni(gbnp)]Cl2 $2H2O
[Cu(gbnp)]Cl2 $2H2O C18H22Cl2Cu N8O6 580.60
[Zn(gbnp)]Cl2 $2H2O C18H22Cl2ZnN8O6 582.40
11.95 (12.03) 220
76.21
78.20
74.50
79.67
73.48
C18H22Cl2NiN8O6
575.70

M. Patil et al. / European Journal of Medicinal Chemistry 45 (2010) 2981e2986
2983
Table 2
Thermogravimetric characteristics of the complexes under study.
Compound
Process
Temp ꢀC
Product (No. of moles)
Mass %
Calcd.
Residue %
Exptl.
Calcd.
12.00
Exptl.
1
2
3
4
5
Decomposition of coordination sphere
Decomposition of coordination sphere
Decomposition of coordination sphere
Decomposition of coordination sphere
Decomposition of coordination sphere
80e100
100e450
90e120
120e500
100e120
120e550
80e120
H2O (3)
9.15
81.35
6.25
83.33
6.25
83.38
6.20
82.67
6.18
9.00
81.00
6.00
83.20
6.12
83.10
6.00
82.40
6.10
11.50
12.68
12.45
13.22
13.80
L (1) þ Chloride (2)
H2O (2)
13.00
12.97
13.69
13.97
L (1) þ Chloride (2)
H2O (2)
L (1) þ Chloride (2)
H2O (2)
120e500
90e110
L (1) þ Chloride (2)
H2O (2)
110e450
L (1) þ Chloride (2)
82.42
82.25
Fig. 2. FAB mass spectrum of [Mn(gbnp)]Cl2$3H2O.
complexes are insoluble in water, methanol and ethanol but
soluble in DMF and DMSO. The molar conductance values fall in
the range of 74.50e79.67 Uꢁ1 cm2 molꢁ1, suggesting 1:2 electro-
lytic nature for the complexes [34]. All the complexes lost lattice
held water molecules in the 80e120 ꢀC temperature range (Table
2). The FAB mass spectrum (Fig. 2) of [Mn(gbnp)]Cl2$3H2O shows
the molecular ion peak at 590, which supplements the proposed
composition for the complex.
values for the complexes are lower than the free ion value, which is
an indication of orbital overlap and delocalisation of d-orbitals. The
b
values obtained are less than unity suggesting a considerable
amount of covalent character of the metaleligand bonds. The
value for the nickel(II) complex is less than the cobalt(II) complex,
b
indicating the greater covalent nature of the former.
The electronic spectrum of copper(II) complex exhibits a band at
16,778 cmꢁ1 which is assigned to the transition 2Eg
/
2T2g in an
IR spectral data of the ligand in comparison with those of the
complexes coordination of the ligand through carbonyl oxygens,
azomethine nitrogens and oxygens of nitroso groups. Table 3 lists
such selected vibration bands and the respective assignments.
The presence of new bands at 530e570 cmꢁ1 and
octahedral geometry [38]. The manganese(II) complex in DMSO
solution show one band in the 14,700e18,200 cmꢁ1 region prob-
ably due to metal-ligand charge transfer transition [39].
Magnetic moment values (Table 4) along with electronic spec-
tral data were used to determine the stereochemistry of the iso-
lated complexes. The room temperature magnetic moments of all
the complexes are in agreement with the spin free values. The
magnetic moment values for manganese(II), cobalt(II) and nickel(II)
indicate the high spin octahedral nature of the complexes.
410e430 cmꢁ1 in the spectra of the complexes correspond to
n
(MeN) and n(MeO) vibration bands [35,36].
The electronic spectral measurements were used for assigning
the stereochemistries of complexes based on the positions and
number of the ded transition peaks. The electronic spectrum of the
The 1H NMR spectra of gbnp at different temperatures are
depicted in Fig. 3. The spectrum at room temperature (30 ꢀC)
exhibited two signals for methylene groups (4.82, 5.15 ppm), -NH
protons (11.88, 12.01 ppm) and azomethine protons (7.72, 7.77 ppm)
indicating the existence of cis and trans isomeric forms [40]. It is
proposed that, in this compound, restricted rotation about the pC]N
linkage as well as the partial double bond character of the amide CeN
ligand shows three peaks at 27,855, 32,362 and 39,062 cmꢁ1
,
assigned to
p* ) n of C]N, N]O and C]O chromophores
respectively [37]. On complexation, these peaks have shifted to
higher wavelengths suggesting coordination of azomethine
nitrogen, nitroso oxygen and carbonyl oxygen. The cobalt(II)
complex exhibit two ded bands at 15,200 cmꢁ1 and 19,200 cmꢁ1
4
4
assigned to T1g
/ /
4A2g and T1g 4T2g, respectively, in an octa-
hedral geometry [32,38]. The spectrum of nickel(II) complex exhibit
Table 3
three bands at 11,148 cmꢁ1,17,667 cmꢁ1 and 26,737 cmꢁ1, which are
Diagnostic IR bands of gbnp and its complexes.
3
3
3
due to A2g
transitions respectively and suggest an octahedral geometry [38].
The n2 n1 values of 2.1 and 1.58 for cobalt(II) and nickel(II)
/ (n1), A2g / (n2) and A2g / (n3)
3T1g 3T1g 3T1g
Compounds
n
(OH)water
n
(C]O)
n(NeH) n(C]N) n(N]O) n(MeN) n(MeO)
gbnp
e
1678s 3197m 1585m 1478m
e
e
/
1
2
3
4
5
3438b
3369b
3375b
3430b
3497b
1603s 3051m 1511m 1404w 535w
1603s 3092m 1517m 1401w 534w
1605s 3110m 1519m 1452m 537w
1604s 3105m 1512m 1410w 570w
1612s 3085m 1512w 1437m 542w
412w
421w
428w
422w
419w
complexes also suggest octahedral geometry around the metal ions.
Ligand field parameters (Table 4) such as Racah interelectronic-
repulsion parameter (B0), ligand field splitting energy (Dq), cova-
lency factor (
b) and ligand field stabilization energy (LFSE) have
been calculated for cobalt(II) and nickel(II) complexes [38]. The B0
b ¼ broad, m ¼ medium, w ¼ weak.

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M. Patil et al. / European Journal of Medicinal Chemistry 45 (2010) 2981e2986
Table 4
Magnetic susceptibility and electronic spectral data of compounds.
Compounds
meff (B.M.)
ded bands (lmax in cmꢁ1
)
Dq (cmꢁ1
)
B0 (cmꢁ1
)
b
n2
/n1
LFSE (K cal molꢁ1
)
1
2
3
4
5
5.98
4.00
2.67
1.80
e
e
e
e
e
e
7,150a, 15,200, 19,200
805
1114.8
e
863
730
e
0.89
0.70
e
2.1
1.58
e
27.60
38.22
e
11,148, 17,667, 26,737
16,778
Diamagnetic.
e
e
e
e
e
e
a
Calcd. value.
bond led to the formation of isomers. To overcome the rotational
restriction and to find the coalescence temperature, the ligand, gbnp
was studied by variable temperature 1H NMR technique.
due to the tumbling motion of the molecules. The giso at 300 and
77 K are 2.1132 and 2.1182 respectively. Mononuclear nature of the
complex was also evident from the absence of a half field signal,
due to ms ꢂ2 transitions, ruling out any CueCu interaction [41].
From the in vitro antimicrobial screening results (Table 5 and
Fig. 6), it is observed that the ligand is moderately active against
bacteria, E. coli, B. cirroflagellosus and fungi, A. niger, C. albicans. All
the complexes have shown higher activity in comparison with the
ligand and metal salts against both bacteria and fungi used. The
activity of the ligand has enhanced on complexation. Among the
complexes, copper(II) complex has the highest potential against all
the microorganisms even more than the standard drugs used. Such
an enhanced activity of the complexes can be explained on the
basis of Overtone’s concept and Tweedy’s chelation theory [42].
According to Overtone’s concept of cell permeability, the lipid
membrane that surrounds the cell favors the passage of only lipid
soluble materials due to which liposolubility is an important factor
that controls antimicrobial activity. On chelation, the polarity of the
metal ion is reduced to a greater extent due to the overlap of the
ligand orbital and partial sharing of the positive charge of the metal
ion with donor groups. Further, it increases the delocalisation of
The ligand exist as Z/E geometrical isomers about the pC]N
bond of Schiff base moiety as well as cis/trans amide conformers
(Fig. 4). As the temperature was lowered below 30 ꢀC (at 20 ꢀC), the
two signals of methylene (Fig. 5a), azomethine and eNH group
became prominent indicating the presence of two isomers (ratio
1:3). When the temperature was raised to 41 ꢀC, one of the two
signals of each group started diminishing in the isomer ratio 1:4. At
still higher temperature (at 58 ꢀC), only one signal predominates in
the ratio 1:8 indicating a single amide conformer at and above
58 ꢀC. In this investigation it is observed that, during the conversion
of cis/trans amide conformers, the eNH proton (Fig. 5b) of
predominant form has shifted to the upfield region at elevated
temperatures whereas the position of methylene and azomethine
protons has remained the same.
The 1H NMR spectrum of zinc(II) complex recorded in DMSO-d6
solution state shows only one set of signals indicating the existence
of the molecule in only one isomeric form. On complexation, the
eNH proton has shifted downfield to 11.86 ppm due to the
involvement of adjacent amide pC]O group in coordination.
The signal due to azomethine proton observed at 7.71 ppm
exhibited a downfield shift (0.10 ppm) suggesting the involvement
of azomethine nitrogen in coordination. The methylene protons
and the aromatic protons have appeared at 5.04 and 7.44e7.68 ppm
respectively. Thus 1H NMR spectral observations supplement
infrared spectral assignments, for the ligating mode of the ligand.
The ESR spectra of the copper(II) complex at both 300 K and 77 K
show one intense absorption band at high field, which is isotropic
p-electrons over the whole chelate ring and enhances the lip-
ophilicity of the complexes. This increased lipophilicity enhances
the penetration of the complexes into lipid membranes and
blocking of metal binding sites on the enzymes of the microor-
ganisms. These complexes also disturb the respiration process of
the cell and thus block the synthesis of the proteins that restricts
further growth of the organism. The variation in the effectiveness of
the different compounds against different organisms depends on
the impermeability of the cells of microbes or difference in ribo-
some of the microbial cells [43].
O
O
R3
N
R2
N
N
H
N
H
R1
R1
R2
R3
trans E
trans Z
R1
R1
R2
N
N
R3
N
O
O
N
H
H
R3
R2
cis E
cis Z
H
N
N
R1
=
N
O
N
R3
=
N
N
O
R2 = H
O
Fig. 3. Variable-temperature 1H NMR spectrum of gbnp.
Fig. 4. cis/trans conformers.

M. Patil et al. / European Journal of Medicinal Chemistry 45 (2010) 2981e2986
2985
Fig. 5. Competition between isomers for stereointerconversion resulting in the formation of plateau and peak coalescence, a (eCH2 group) and b (eNH group).
5. Conclusion
Table 5
In vitro antimicrobial activity of gbnp and its metal complexes through agar well
diffusion method.
A newly synthesized macroacyclic ligand, glyoxal bis(N-nitroso
phenylglycine) (gbnp) has potential binding sites towards metal
ions. It acts as a hexadentate ligand by coordinating through two
azomethine nitrogens, two amide carbonyl oxygens and two
nitroso oxygens in N2O4 fashion. It forms octahedral complexes
with manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II)
ions. FAB mass spectral analysis reveals the existence of monomeric
complex and thermal studies support the presence of lattice held
water molecules. The antibacterial and antifungal screening of the
ligand and the complexes shows that the ligand is less active
compared to the complexes. Among the complexes, [Cu(gbnp)]
Cl2$2H2O has the highest potential against all the microorganisms.
The proposed structure of the complex is given in Fig. 7.
Compound
Zone of inhibition (mm)a (standard deviation)
Antibacterial
B. C.
Antifungal
A. N.
E. C.
C. A.
MnCl2$6H2O
CoCl2$4H2O
NiCl2$6H2O
CuCl2$2H2O
ZnCl2$2H2O
1
2
3
14.3(2.1)
26.7(1.5)
20.7(0.6)
19.7(0.6)
21.3(1.1)
21.7(1.1)
31.3(1.1)
21.7(2.1)
34.7(0.6)
23.3(0.6)
16.0(1.0)
28.3(0.6)
e
20.3(1.2)
27.3(1.2)
20.0(1.7)
19.0(1.0)
24.0(1.0)
21.3(1.5)
28.3(0.6)
22.0(1.7)
34.0(2.0)
21.3(0.6)
16.3(1.5)
28.3(1.2)
e
22. 7(2.3)
20. 7(1.1)
20. 7(1.1)
20. 3(1.1)
19.0(1.0)
27. 3(1.5)
21. 3(1.5)
23. 7(1.1)
32. 7(1.1)
22. 7(2.1)
16. 7(0.6)
e
21.3(1.5)
19.7(2.1)
19.7(2.1)
20.3(0.6)
19.7(0.6)
27.7(1.5)
21.3(1.5)
21.3(1.5)
31.3(1.5)
23.3(1.5)
19.3(0.6)
e
4
5
gbnp
Norfloxacin
Griseofulvin
6. Experimental protocols
29(1.0)
29.3(0.6)
E. C. ¼ Escherichia coli, B. C. ¼ Bacillus cirroflagellosus, A. N. ¼ Aspergillus niger,
C. A. ¼ Candida albicans.
6.1. Chemistry
Key to interpretation: less than 10 mm e inactive; 10e15 mm e weakly active;
15e20 mm e moderately active; More than 20 mm e highly active.
The carbon, hydrogen and nitrogen contents were determined
using Heraus C H N rapid analyzer. The chloride content of the
complexes was determined as AgCl gravimetrically [44]. Infrared
a
Average values of triplicates.
Fig. 6. Antimicrobial activities of metal salts, metal complexes (1e5), gbnp and the standards.

2986
M. Patil et al. / European Journal of Medicinal Chemistry 45 (2010) 2981e2986
Institute of Technology, Bombay for recording 1H NMR spectra
and ESR spectra. The authors also thank the Sophisticated
Analytical Instrument Facility, Central Drug Research Institute,
Lucknow for providing FAB mass spectra. The authors thank
Professor S. B. Padhye, University of Pune, India for magnetic
measurement facilities. Thanks are also due to the University
Sophisticated Instrumentation Center, Karnatak University,
Dharwad for carrying out elemental and electronic spectral
analyses.
N
N
NH
HN
N
O
M
O
N
O
O
N
N
Cl2.nH2O
References
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(1992) 5900.
Fig. 7. The proposed structure of the complexes.
spectra (in
a KBr matrix) were recorded in the region
4000e400 cmꢁ1 on a Thermo Nicolet 320 FT-IR spectrometer.
1H NMR spectra were recorded in DMSO-d6 as the solvent at
400 MHz on a BRUKER AMX 400 spectrometer using tetrame-
thylsilane (TMS) as an internal reference. Electronic spectra of the
complexes were recorded on a Cary-Bio-50 Varian in DMSO
solution (10ꢁ5 M for UV-region and 10ꢁ2 M for visible region). The
magnetic susceptibility measurements were carried out on
a Faraday balance using Hg[Co(NCS)4] as the calibrant and
diamagnetic corrections were made by direct weighing of the
ligand for diamagnetic pull. FAB mass spectrum of the complex
was recorded on a JEOL SX 102/DA-6000 mass spectrometer/data
system using Argon/Xenon (6 kV, 10ma) as the FAB gas. The
accelerating voltage was 10 kV and spectra were recorded at
room temperature. Conductance measurements were recorded in
DMSO (10ꢁ3 M) using Elico conductivity bridge type CM-82,
provided with a dip type conductivity cell fitted with platinum
electrodes. ESR spectra were recorded on Varian E-4 X-band
spectrometer using tetracyanoethylene (TCNE) as ‘g’ (g ¼ 2.0027)
marker at room temperature and also at liquid nitrogen
temperature. The thermal studies of the complexes were made
with Mettler Toledo TGA/SDTA851e with stare software, under
nitrogen atmosphere with a heating rate of 10 ꢀC/min in the
temperature range of 50e1000 ꢀC.
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were prepared in triplicate and allowed to stand for an hour in order
to facilitate the diffusion of the drug solution and then were incu-
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The authors are thankful to the Sophisticated Instrumenta-
tion Facility, Indian Institute of Science, Bangalore and Indian