Synthesis, characterization and biological evaluation of mononuclear Co(II), Ni(II), Cu(II) and Pd(II) complexes with new N2O2 schiff base ligands

Article abstract of DOI:10.1248/cpb.59.166

New tetradentate N₂O₂ donor Schiff bases and their mononuclear Co(II), Ni(II), Cu(II), and Pd(II) complexes were synthesized and characterized extensively by IR, ¹H-, ¹³C-NMR, mass, ESR, conductivity measurement

Full text of DOI:10.1248/cpb.59.166

166
Regular Article
Chem. Pharm. Bull. 59(2) 166—171 (2011)
Vol. 59, No. 2
Synthesis, Characterization and Biological Evaluation of Mononuclear
Co(II), Ni(II), Cu(II) and Pd(II) Complexes with New N2O2 Schiff Base
Ligands
Geeta BUDIGE,a Muralidhar Reddy PUCHAKAYALA,b Shobha Rani KONGARA,a Anren HU,*,c and
Ravinder VADDE*,a
a Department of Chemistry, Kakatiya University; Warangal–506 009, A.P., India: b Department of Chemistry, National
Dong Hwa University; Hualien–97441, Taiwan: and c Department of Laboratory Medicine and Biotechnology, Tzu Chi
University; Hualien–97004, Taiwan. Received July 26, 2010; accepted October 26, 2010
New tetradentate N2O2 donor Schiff bases and their mononuclear Co(II), Ni(II), Cu(II), and Pd(II) com-
1
plexes were synthesized and characterized extensively by IR, H-, 13C-NMR, mass, ESR, conductivity measure-
ments, elemental and thermal analysis. Specifically the magnetic and electronic spectral measurements demon-
strate the octahedral structures of cobalt(II), nickel(II) complexes and square planar geometries of copper(II),
palladium(II) complexes. All the ligands and complexes were screened for their in vitro antibacterial activity
against two Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus) and two Gram-negative bacteria
(Escherichia coli, Klebsiella pneumonia). In this study, Pd(II) complexes exhibited potent antibacterial activity
against B. subtilis, S. aureus whereas other metal complexes also exerted good activity towards all tested strains
even than standard drugs streptomycin and ampicillin.
Key words Schiff base; metal complex; antibacterial activity
Schiff bases have a variety of applications in biological,
In previous studies, we have described the synthesis, cat-
clinical, and pharmacological areas. The synthesis and appli- alytic and biological applications of Schiff bases and their
cation of Schiff bases and their coordination compounds metal complexes derived from o-phthalaldehyde (OPA) with
have been highly considered in inorganic, organic and bio- various amines.19—27) In this respect, we have also developed
logical fields, since their structural properties similar to some some useful macrocyclic Schiff bases and their metal com-
of the biological systems.1—6) Additionally, tetradentate plexes. Results from these studies have also shown that com-
Schiff bases composed of N2O2 donor atoms set have been plexation of metals with Schiff base ligands serves to im-
recognized as a kind of important chelating ligands for prove their antimicrobial activity. There are few other re-
designing medicinally and catalytically useful metal com- search groups also reported the importance of Schiff base
plexes.7—9) The flexible coordination behavior of these types chemistry of the combination of o-phthalaldehyde with
of chelating ligands could also be useful to generate interest- amines.28,29) However, a careful literature survey reveals that
ing dimeric and polymeric structures as synthones for Schiff bases from the combination of amino acids and o-ph-
supramolecular chemistry.10,11) Usually, the N, O donor het- thalaldehyde and their coordination behavior towards the
erodentate Schiff bases can be derived by condensing the transition elements have yet not been studied. The combina-
aldehydes/ketones with various amines or amino acids.12,13) tion of dialdehyde i.e. o-phthalaldehyde and aminoacids is
N2O2 Schiff base ligands derived from salicylald ehyde and expected to provide a new class of tetradentate N2O2 donor
diamine have been known.14,15) Dialdehydes and diketones ligands to design new coordination compounds with im-
with amines and amino acids have also been utilized to ob- proved catalytic and biological activities. The present manu-
tain a variety of N2O2 Schiff base ligands.16)
script describes the synthesis, characterization and antibac-
Amino acids plays an important role in many physiologi- terial activities of cobalt(II), nickel(II), copper(II), and palla-
cal activities of the human body and also helpful in under- dium(II) complexes with the tetradentate N2O2 Schiff bases
standing biological functions of macromolecules such as pro- derived using o-phthalaldehyde, aminoacids i.e., L-trypto-
teins.17) In particular, tryptophan (Trp)/histidine (His) ana- phan and L-histidine. The ligands synthesized in this work
logues as promising candidates for novel antimicrobial thera- can behave as dianionic tetra dentate donor groups. All the
peutics. In the recent years, a series of synthetic peptide ana- metal complexes have shown moderate to good antibacterial
logues based on Trp-His and His-Arg (antimicrobial pep- activity against Gram-positive and Gram-negative bacteria.
tides) structural frameworks have been prepared and found to
Experimental
be active against several Gram-positive and Gram-negative
bacterial strains as well as against fungal strains.18) Further-
All the chemicals used in this work were of analar grade. Solvents were
purified and dried before use according to the standard procedures. The
metal contents were determined by complexometric titration with ethylene-
diaminetetraacetic acid (EDTA) for cobalt. Nickel and palladium were deter-
more, it is well known that the human body contains essen-
tial metaloelements which play important roles and interact
with many biological molecules to fully understand the phys- mined by gravimetric procedure using dimethylglyoxime as precipitating
agent and copper was determined by iodometric procedure. Elemental analy-
sis (C, H, and N) was obtained using Perkin-Elmer elemental analyzer. The
iological functions by studying their chemistry coordination
and behavior.17,18) In the present studies we have introduced
infrared spectra were recorded in KBr/Nujol on Perkin- Elmer-283 spec-
an azomethine (Schiff base) linkage to tryptophan/histidine,
which may permit a variety in their coordination behaviour
and complexation role.
trophotometer in the range of 4000—200 cmꢀ1 and electronic spectra in
1
MeOH were obtained using Shimadzu UV-265 Spectrometer. H- and 13C-
NMR spectra in dimethyl sulfoxide (DMSO) were recorded on a Brucker
© 2011 Pharmaceutical Society of Japan
∗ To whom correspondence should be addressed. e-mail: anren@mail.tcu.edu.tw; ravichemku@rediffmail.com

February 2011
167
Table 1. Analytical and Physical Data of the Ligands and Complexes
Found (Calcd %)
mp (°C)/
Decomp.
Temp.
LMa
(BM)
Yield
(%)
S. No.
Complexes/Formulae
Color
meff
M
—
—
C
H
N
1
2
CEIMAP
C30H26N4O4
CIMPAP
C20H20N6O4
[Co(CEIMAP)(H2O)2]2H2O
C30H32N4O8Co
[Co(CIMPAP)(H2O)2]2H2O
C20H26N6O8Co
[Ni(CEIMAP)(H2O)2]2H2O
C30H32N4O8Ni
[Ni(CIMPAP)(H2O)2]2H2O
C20H26N6O8Ni
[Cu(CEIMAP)]2H2O
C30H30N4O6Cu
[Cu(CIMPAP)]2H2O
C20H22N6O6Cu
[Pd(CEIMAP)]
C30H24N4O4Pd
Pale
Yellow
Yellow
71.08
(71.12)
58.10
(58.12)
56.68
(56.70)
46.50
(46.56)
56.73
(56.70)
46.50
(46.56)
59.66
(59.64)
46.45
(46.48)
58.40
5.14
(5.17)
4.88
(4.94)
5.10
(5.08)
5.58
(5.68)
5.05
(5.08)
5.60
(5.68)
4.70
(4.67)
4.40
(4.38)
3.98
11.01
(11.06)
20.52
(20.58)
8.63
(8.82)
14.70
(14.81)
8.78
(8.82)
14.73
(14.84)
9.30
(9.27)
16.65
(16.61)
9.20
188—190
180—182
250—252
243—245
235—237
220—223
248—250
234—236
255—256
240—242
—
—
9
—
75
78
80
78
82
84
76
75
78
85
—
3
Pink
9.30
(9.27)
10.36
(10.39)
9.20
(9.27)
10.35
(10.39)
10.58
(10.52)
12.58
(12.56)
17.44
(17.42)
20.80
(20.75)
4.96
5.13
3.09
3.26
1.93
1.92
—
4
Pale
Pink
Light
Green
Green
12
15
17
10
14
13
17
5
8
7
Light
Green
Green
8
9
Reddish
Brown
Reddish
Brown
(58.92)
46.88
(46.84)
(3.96)
3.60
(3.54)
(9.17)
16.42
(16.39)
10
[Pd(CIMPAP]
C20H18N6O4Pd
—
WH 300 (200 MHz) and Varian Gemini (200 MHz) spectrometers using
tetramethylsilane (TMS) as an internal reference. An ion trap mass spec-
trometer (Agilent Series LC/MSD Trap SL) equipped with an electrospray
ionization (ESI) source was used for MS analyses (Agilent, Palo Alto, CA,
U.S.A.). Conductance measurements were carried out at room temperature
on freshly prepared 10ꢀ3 M EtOH solutions using a Coronation digital con-
ductivity meter. The magnetic studies were carried out at room temperature
on a Gouy balance calibrated with Hg [Co(SCN)4]. The ESR spectra of
Cu(II) complex are recorded at room temperature and liquid nitrogen tem-
perature (LNT). The thermogravimetric-differential thermogravimetric (TG-
DTG) thermograms of the complexes were recorded on Mettler Toledo star
system. The antibacterial activity of the compounds was determined by the
cup plate method and the minimum inhibitory concentration by liquid dilu-
tion method.
Synthesis of Schiff Bases. 2-{[(E)-1-[2-({[1-Carboxy-2-(1H-3-indolyl)
ethyl]imino}methyl)phenyl]methylidine}amino)-3-indolyl)propanoicacid
(CEIMAP) (L1) KOH (0.32 g) was dissolved in methanol and methanolic
solution of L-tryptophan (0.02 mol) was added to it. The mixture was stirred
magnetically at room temperature for 1 h. When the mixture became homo-
geneous, a solution of o-phthalaldehyde (0.01 mol, 1.32 g) in methanol
(20 ml) was added. After 2 h yellow crystals were appeared. The crystals
were filtered and washed with ethanol and recrystallized from hot methanol.
The crystals were suction filtered washed with diethyl ether and dried in vac-
uum. The product was found to be TLC pure in 7 : 3 mixtures of methanol
and chloroform.
Results and Discussion
The analytical data and the physical properties of the com-
plexes are listed in Table 1. The complexes can be repre-
sented by the formula [ML (H2O)2]2H2O where [MꢂCo(II),
Ni(II)], [ML]ꢃH2O where [MꢂCu(II) and Pd(II)] and
[LꢂL1, L2]. In addition, all these compounds (except Pd(II)
complex) showed a single peak in ESI-MS suggesting the pu-
rity of the ligands and their metal complexes. The MS data is
in good agreement with the proposed molecular formulae.
The low molar conductance values of all the complexes in
dichloromethane measured at 10ꢀ3 M concentration are in the
range of 9—17 indicate that all the complexes behave as
non-electrolytes.30) The general strategy for the synthesis of
Schiff base ligands and their metal complexes is illustrated in
Chart 1.
Infrared Spectra The infrared frequencies of the Schiff
base ligand and its Co(II), Ni(II),Cu(II) and Pd(II) complexes
are given in Table 2. All the complexes exhibit broad bands
in the 3440—3590 cmꢀ1 range and this may be attributed to
the presence of coordinated or lattice water molecules. A
strong IR absorption band observed in the free Schiff base
around 1615—1630 cmꢀ1, assignable to the n(CꢂN) stretch-
ing vibration, was shifted to lower wave numbers by 15—
20 cmꢀ1 upon coordination. This feature indicates that the
imino nitrogen is coordinated to the metal ion. Further, the
2-({(E)-1-[2-({[1-Carboxy-2-(1H-5-imidazolyl)(ethyl]imino}methyl)
phenyl]methylidine}amino)-3-1H-5-imidazolyl)propanoicacid
(CIM-
PAP) (L2) L(ꢁ) histidine (0.02 mol) dissolved in MeOH (10 ml) was
added slowly with constant stirring to an alcoholic solution (20 ml) contain-
ing KOH. The solution was stirred for 1 h and filtered. To the filtrate o-ph-
thalaldehyde (1.32 g, 0.01 mol) dissolved in MeOH (20 ml) was added drop
wise with constant stirring. The resulting yellowish solution was evaporated
under reduced pressure and kept at room temperature for 1 d. The yellow
precipitate was filtered, washed with cold alcohol and ether then crystallized
twice from methanol. The crystals were suction filtered, washed with diethyl
ether and dried in vacuum. The product was found to be TLC pure in 6 : 4
mixtures of ethyl acetate and n-hexane, tested in perpendicular directions.
General Procedure for Synthesis of Metal Complexes A solution of
cobalt(II) acetate, nickel(II) acetate, copper(II) acetate and palladium(II)
chloride (0.002—0.005 mol) in methanol (25 ml) was added drop wise to a
methanolic solution (30 ml) of Schiff base (0.002—0.005 mol) and stirred at
room temperature with constant stirring. The resulting mixture was allowed
to reflux on a water bath for 2 h until a solid is separated out. The precipi-
tates were suction filtered, purified by repeated washing with chloroform and
methanol and dried in vacuum desiccators (yieldꢂ75—85%).
n
asym(COOꢀ) absorption of ligands was shifted to higher fre-
quency in the 1575—1590 cmꢀ1 range and the nsym(COOꢀ)
was shifted to lower frequency in the 1340—1386 cmꢀ1
range in the respective spectra of complexes. The shift ob-
served for both nasym(COOꢀ) and nsym(COOꢀ) visualizes the
coordination of carboxyl oxygen to the metal ions along with
imino nitrogen atom.31) In the low frequency regions, bands
detected around 520—535 cmꢀ1 ranges are assigned to M–N
(imino nitrogen) and the bands at 420—460 cmꢀ1 ranges are
assigned to M–O (carboxylato oxygen atom).20—27,32)
1H-NMR Spectra The NMR spectra of the Schiff base
ligands and Pd(II) complexes were shown in Table 3. In the

168
Vol. 59, No. 2
free Schiff base spectra the signals were appeared in the
range of 8.18—8.20 ppm due to (HCꢂN) protons.24) How-
ever in the spectra of Pd(II) Schiff base complexes, the sig-
nals were observed in the up field regions of 8.28—8.30 ppm
supporting the coordination of imino nitrogen atom to
Pd(II).25) While the free ligands NMR spectra have a charac-
teristic NMR signal for carboxyl group proton in the 10.17—
1
10.88 ppm range, the disappearance of this signal in the H-
NMR spectra of Pd(II) complexes indicating the involvement
of carboxylate ion oxygen in chelation through deprotona-
tion. There is no appreciable change in the peak position cor-
responding to NH and aromatic protons.
13C-NMR Spectra The 13C-NMR signals for the Pd(II)
complexes are assigned by the comparison with the spectra
of corresponding free Schiff base ligands. A down field shift
of CHꢂN group in the range of 172.6—174.5 ppm and for
carboxyl carbon COOꢀ ion in the range of 192.6—
195.0 ppm in the complex NMR spectra indicates that the
ligand coordinates through both the nitrogen atom of CHꢂN
and the oxygen of COOꢀ ion.19—27)
Electronic Spectra The Co(II) complex exhibited well
resolved bands at 1040—1090, 518—540 nm and a strong
high energy band at 426—494 nm and are assigned to transi-
4
4
4
tions, T2g←4T1g(F) (n1), A2g←4T1g(F) (n2) and T1g(P)←
4T1g(F) (n3) for a high spin octahedral geometry.19) The mag-
netic susceptibility measurements for the solid Co(II) com-
plex is also indicative of four unpaired electrons per Co(II)
ion suggesting consistency with their octahedral environ-
ment. The Co(II) complexes exhibit magnetic moment values
of 4.96—5.12 which are well agree with the octahedral range
Chart 1. Synthetic Pathways of Schiff Base Ligands and Metal Complexes
Table 2. Infrared Spectral Data of the Ligands and Complexes (cmꢀ1
)
n(C–O)
n(COO–)
S. No.
Complexes
CEIMAP
n(CꢂN)
n(N–H)
n(M–H2O)
n(M–N)
n(M–O)
of COOH
asy/sym
1
2
3
4
5
6
7
8
9
1630
1618
1615
1600
1615
1600
1628
1618
1630
1618
3198
2919
3398
2919
3198
2915
3390
2910
3394
2916
1720
1710
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
CIMPAP
[Co(CEIMAP)(H2O)2]2H2O
[Co(CIMPAP)(H2O)2]2H2O
[Ni(CEIMAP)(H2O)2]2H2O
[Ni(CIMPAP)(H2O)2]2H2O
[Cu(CEIMAP)]2H2O
[Cu(CIMPAP)]2H2O
[Pd(CEIMAP)]
1590, 1376
1585, 1340
1584, 1376
1575, 1340
1590, 1376
1585, 1386
1590, 1376
1585, 1340
710
712
710
712
—
—
—
—
520
535
520
535
535
528
520
535
460
450
460
450
464
458
460
420
10
[Pd(CIMPAP]
—
Table 3. 1H- and 13C-NMR Spectral Data of the Ligands and Complexes
S.
No.
1H-NMR peak position
13C-NMR peak position
Complexes
CEIMAP
(d ppm)
(d ppm)
1
2
3
4
10.17 (2H, s, COOH), 9.80 (2H, s, NH), 8.18 (2H, s, CHꢂ
N),7.35—7.58 (12H, m,Ar-H), 3.49—3.65 (2H, d, CH),
2.18—2.20 (4H, d, CH2)
12.20 (2H, d, NH), 10.88 (2H, s, COOH), 8.20 (2H, s,
CHꢂN), 7.37—7.73 (4H, m, Ar-H), 6.98 (4H, s, CH),
3.79 (2H, t, CH), 3.18 (4H, s, CH2)
9.80 (2H, s, NH), 8.28 (2H, s, CHꢂN), 7.35—7.58 (12H,
m, Ar-H), 3.49—3.60 (2H, d,CH), 2.18—2.20
(4H, d, CH2)
11.98 (2H, d, NH), 8.28 (2H, s, CHꢂN), 7.37—7.73
(4H, m, Ar-H), 6.99 (4H, s, CH), 3.79 (2H, t, CH),
3.20 (4H, s, CH2)
18.8 (2C, CH2), 69.1 (2C, CH), 117.8, 121.6, 126.8,
130.9, 133.2, 135.6 (22C, Ar-C), 152.6 (2C, CHꢂN),
176.0 (2C, COOH)
19.6 (2C, CH2), 68.4 (2C, CH), 118.8, 131.4, 134.5,
136.3 (12C, Ar-C), 152.5 (2C, CHꢂN),
176.1 (2C, COOH)
19.6 (2C, CH2), 69.8 (2C, CH), 117.2, 121.3,
126.4, 131.2, 132.8, 135.7 (22C, Ar-C),
172.6 (2C, CHꢂN), 195.0 (2C, COOꢀ)
19.4 (2C, CH2), 68.2 (2C, CH), 119.0, 131.2, 134.4,
136.4 (12C, Ar-C), 174.5 (2C, CHꢂN),
192.6 (2C, COOꢀ)
CIMPAP
[Pd(CEIMAP)]
[Pd(CIMPAP]

February 2011
169
of 4.3—5.2 BM this further supports the electronic spectral sponds to the loss of water molecules in the temperature
results. range of 160—195 °C corresponding to the loss of coordi-
The electronic spectra of the Ni(II) complex showed d–d nated water molecules. The presence of endothermic peak at
bands in the regions 995—1072, 640—725 and 360— 175—200 °C in DSC curve of the complex also further con-
3
3
390 nm and are assigned to T2g(F)←3A2g(F) T1g(F)← firms the presence of coordinated water. The third stage
3A2g(F) and T1g(P)←3A2g(F) transitions respectively consis- weight loss show in the temperature range of 245—275 °C
3
tent with their octahedral configuration.21) Ni(II) complexes corresponds to the loss of organic moiety.34) The thermo-
showed the magnetic moment values of 3.09—3.26 within grams of Cu(II) complexes show only two stages of decom-
the range of 2.8—3.5 BM (octahedral range) suggesting con- position. The first stage of the thermogram corresponds to
sistency with their octahedral environment.
the dehydration of water molecules and the second stage for
The electronic spectra of the Cu(II) complexes showed an the loss of organic moiety.20) The thermal data of Pd(II) com-
intensive band at about 732—676 nm attributed to 2A1g←2B1g plexes indicate no coordinated water molecules. The sharp
transition and a broad band around 494—320 nm attributed decomposition corresponding to the loss of organic moiety in
2
to Eg←2B1g transition of square planar environment.20) The complexes can be seen in the differential thermal analysis
magnetic susceptibility measurements of Cu(II) complexes is (DTA) curves which contain one short exothermic peak
1.92—1.93 BM, which suggests the presence of one unpaired falling in the range of 258—286 °C.25) The final product of
electron with square-planar configuration. Furthermore, the decomposition of all the complexes above 680 °C corre-
electronic spectra of the Pd(II) complexes exhibit bands in sponds to metal oxide.
the regions of 690—600, 555—450 and 410—370 nm, but
ESR Spectra The trends of ESR spectra of Cu(II) com-
all these three were not observed in most of the complexes. plexes g^(2.215)ꢄg(2.044) observed for [Cu(CEIMAP)]
The Pd(II) complexes prepared have been found to show a 2H2O and g||(2.204)ꢄg^(2.038) observed for [Cu(CIM-
broad d–d transition band in the region of 480—465 nm as- PAP)]2H2O indicate a d(x2ꢀy2) ground state. The g||ꢄ2.3 is
signable to 1B1g←1A1g transition typical for the square planar characteristic of an ionic environment and g||ꢅ2.3 of a cova-
geometry.25,26) Magnetic susceptibility measurements show lent environment in M–L bonding. In the present complexes
these complexes to be diamagnetic, confirmed by sharp sig- g|| indicate a fair degree of covalent character in the Cu–L
nals in the 1H-NMR spectra.
bonding.35,36)
Thermal Analysis The thermograms of all the Co(II),
Antibacterial Activity Antibacterial activities of Co(II),
Ni(II) complexes show three stages of decomposition, the Ni(II), Cu(II) and Pd(II) complexes were studied along with
first two corresponding to loss of water molecules and the the metal salts (cobalt(II) acetate, nickel(II) acetate,
third corresponding to decomposition of the complex with copper(II) acetate, and palladium(II) chloride), metal free
the loss of organic moiety.19,21) The thermograms of ligands and two existing antibacterial drugs viz., strepto-
Co(II)/Ni(II) complexes show initial weight loss in the tem- mycin and ampicillin. Preliminary screening for all the metal
perature range of 90.4—104 °C also the differential scanning salts, metal free ligands and complexes were performed at
calorimetry (DSC) curve of these complexes show an en- the fixed concentration of 1000 mg/ml. Based on the obtained
dothermic peak in the above temperature range further giving values of the relative zone inhibition,37—43) of the two ligands
evidence for the presence of water molecules. The loss of such as CEIMAP and CIMPAP and their complexes were
water molecules in this temperature range indicates that they found to be very effective (Table 4) than ligand free metal ac-
are present as lattice-held water.33) The second stage corre- etates and chlorides. Inhibition was recorded by measuring
Table 4. Zones of Inhibitions of Ligands, Metal Salts, Complexes and Standard Drugs against Four Different Bacteria
Zones of inhibition (mm)
S. No.
Ligand/Complexes
Gramꢁve bacteria
Gramꢀve bacteria
a
b
c
d
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
CEIMAP
CIMPAP
Cobalt(II) acetate
10
12
05
24
27
04
30
34
06
36
37
08
38
40
10
11
12
14
04
22
23
04
32
34
05
35
36
08
38
39
12
13
08
11
02
18
23
02
28
32
04
36
38
05
40
44
06
08
09
10
03
20
20
03
25
30
04
32
35
06
37
36
06
07
[Co(CEIMAP)(H2O)2]2H2O
[Co(CIMPAP)(H2O)2]2H2O
Nickel(II) acetate
[Ni(CEIMAP)(H2O)2]2H2O
[Ni(CIMPAP)(H2O)2]2H2O
Copper(II) acetate
[Cu(CEIMAP)]2H2O
[Cu(CIMPAP)]2H2O
Palladium(II) chloride
[Pd(CEIMAP)]
[Pd(CIMPAP)]
Streptomycin
Ampicillin
a, Bacillus subtilis (MTCC 619); b, Staphylococcus aureus (MTCC 96); c, Escherichia coli (MTCC 722); d, Klebsiella pneumoniai (MTCC 109).

170
Vol. 59, No. 2
confirmed by electronic spectroscopic and magnetic meas-
urements data. ESR spectroscopic measurements were moni-
tored to explain the covalent nature of the complexes synthe-
sized. These complexes were found to be effective antibacter-
ial agents than commercial streptomycin and ampicillin
drugs. However, the method of action of these compounds is
unknown. We assumed yet the potent activity of ligands and
their complexes is may be due to the presence of indole and
imidazole moieties in them.
Acknowledgment The authors thank the University Grant Commission
(UGC, F. No. 34-363/2008(SR)), New Delhi, India, and National Science
Coouncil (NSC), Taiwan, for financially supporting this research.
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