Binuclear cobalt(II), nickel(II), copper(II) and palladium(II) complexes of a new Schiff-base as ligand: Synthesis, structural characterization, and antibacterial activity

Article abstract of DOI:10.1016/j.saa.2010.08.004

A binucleating new Schiff-base ligand with a phenylene spacer, afforded by the condensation of glycyl-glycine and o-phthalaldehyde has been served as an octadentate N₄O₄ ligand in designing some binuclear complexes of cobalt(II), nic

Full text of DOI:10.1016/j.saa.2010.08.004

Spectrochimica Acta Part A 77 (2010) 911–915
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Short communication
Binuclear cobalt(II), nickel(II), copper(II) and palladium(II) complexes of a new
Schiff-base as ligand: Synthesis, structural characterization, and
antibacterial activity
B. Geetaa, K. Shravankumara, P. Muralidhar Reddyb, E. Ravikrishnaa,
M. Sarangapania, K. Krishna Reddya, V. Ravindera,∗
a Department of Chemistry, Kakatiya University, Warangal, A.P. 506009, India
b Department of Chemistry, National Dong Hwa University, Hualien 97401, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
A binucleating new Schiff-base ligand with a phenylene spacer, afforded by the condensation of
glycyl–glycine and o-phthalaldehyde has been served as an octadentate N4O4 ligand in designing some
binuclear complexes of cobalt(II), nickel(II), copper(II), and palladium(II). The binding manner of the lig-
and to the metal and the composition and geometry of the metal complexes were examined by elemental
analysis, conductivity measurements, magnetic moments, IR, 1H, 13C NMR, ESR and electronic spectro-
scopies, and TGA measurements. There are two different coordination/chelation environments present
around two metal centers of each binuclear complex. The composition of the complexes in the coordi-
nation sphere was found to be [M2(L)(H2O)4] (where M = Co(II) and Ni(II)) and [M2(L)] (where M = Cu(II)
and Pd(II)). In the case of Cu(II) complexes, ESR spectra provided further information to confirm the bin-
uclear structure and the presence of magnetic interactions. All the above metal complexes have shown
moderate to good antibacterial activity against Gram-positive and Gram-negative bacteria.
© 2010 Elsevier B.V. All rights reserved.
Received 9 March 2010
Received in revised form 19 July 2010
Accepted 3 August 2010
Keywords:
Binuclear complexes
Schiff-base: synthesis, structural
characterization
Antibacterial activity
1. Introduction
this regard, there is much current interest in designing dinucleating
ligands and their transition metal complexes.
Transition metal complexes with Schiff-bases have expanded
enormously and embraced wide and diversified subjects com-
prising vast areas of organometallic compounds [1] and various
aspects of biocoordination chemistry [2]. The design and synthesis
of symmetrical Schiff-bases, derived from the 1:2 stepwise conden-
sation of carbonyl compounds, with alkyl or aryl diamines, and a
wide range of aldehyde or ketone functionalities, as well as their
metal(II) complexes have been of interest due to their preparative
accessibility, structural variability and tunable electronic proper-
ties allowing to carry out systematic reactivity studies based on
ancillary ligand modifications [3]. In recent years much effort has
been put in synthesis and characterization of mono- and bi-nuclear
transition–metal complexes. Schiff-base ligands that are able to
form binuclear transition metal complexes are useful to study
the relation between structures and magnetic exchange interac-
tions [4], and to mimic bimetallic biosites in various proteins and
enzymes [5]. The complexes thus play an important role in develop-
ing the coordination chemistry related to catalysis and enzymatic
reactions, magnetism and bioinorganic modeling studies [6,7]. In
Commonly, the multidenate binucleating Schiff-bases with in-
built spacers can take up two same or different metal ions. Various
mono- and dialdehyde/ketones have been employed to condense
with amines or aminoacids to explore multidentate binucleating
Schiff-bases to design a variety of binuclear transition metal com-
plexes [3–5,8–11]. Shakir and Varkey [12] have reported on the
synthesis, characterization of macrocyclic binuclear Cu(II), Ni(II),
Zn(II) complexes by template condensation of diethylenetrimine
with dicarboxylic acids. Similarly, the binuclear Ni(II) and Pd(II)
complexes have been prepared and characterized by Al-Kubaisi
[13]. Recently, the authors group developed various coordina-
tion compounds including Schiff-base macrocycles derived from
o-phthalaldehyde and different amines [14–24]. Further, we also
disclosed the excellent catalytic and antibacterial activity of the
macrocyclic Schiff-bases and their metal complexes in our recent
reports [14–24]. However, to our knowledge the combination of
o-phthalaldehyde and aminoacids has never been used to synthe-
size Schiff-base ligands. In the context of this background we are
now interested to explore some multidentate binucleating Schiff-
base ligands. Herein, we have noticed that glycyl–glycine with
several potential donor atoms could be a good choice to condense
with o-phthalaldehyde to develop binucleating Schiff-base ligands.
In this connection it was interesting to synthesize and study the
∗
Corresponding author. Tel.: +91 9390100594.
E-mail address: ravichemku@rediffmail.com (V. Ravinder).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.08.004

912
B. Geeta et al. / Spectrochimica Acta Part A 77 (2010) 911–915
Scheme 1. Synthetic route of binuclear Co(II), Ni(II), Cu(II) and Pd(II) complexes.
transition metal complexes with Schiff-base produced from con-
densation reaction of o-phthalaldehyde with glycyl–glycine (see
Scheme 1). A description on characterization data using analytical,
spectroscopic, thermal and magnetic data has been systematically
presented. Furthermore, the application of these metal complexes
as potential antibacterial agents has also been demonstrated.
balance calibrated with Hg [Co(SCN)4]. All the mass spectra were
recorded using MALDI Autoflex time-of-flight mass spectrometer.
The ESR spectra of Cu(II) complex are recorded at room tempera-
ture and liquid nitrogen temperature. The 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
dilution method [25–28].
2. Experimental
2.2. Synthesis of Schiff-base ligand (L)
2.1. Materials and methods
Glycyl–glycine (0.64 g, 0.02 mol) dissolved in methanol (10 mL)
was added slowly with constant stirring to KOH in methanol. The
solution was stirred for half an hour and then filtered. To the filtrate
o-phthalaldehyde (1.32 g, 0.01 mol) dissolved in MeOH (20 mL) was
added drop wise with constant stirring. The resulting solution was
evaporated under reduced pressure and kept at room temperature
for 2 h. The dirty white precipitate was washed with cold alcohol.
The crystals were suction filtered washed with diethyl ether and
dried in vacuum. The product was found to be TLC pure in 7:3 mix-
tures of methanol and chloroform (mobile phase). Our synthetic
route of Schiff-base ligand is shown in Scheme 1.
All the chemicals used were of analar grade. Solvents were
purified and dried before use according to the standard proce-
dures. The metal contents were determined by complexometric
titration with EDTA for cobalt. Nickel and palladium were deter-
mined by gravimetric procedure using dimethylglyoxime as
precipitating agent and copper was determined by iodometric
procedure. Elemental analysis (C, H, N) was obtained using Perkin-
Elmer elemental analyzer. The infrared spectra were recorded in
KBr/CsBr/Nujoll on Perkin-Elmer-283 spectrophotometer in the
range of 4000–200 cm−1 and electronic spectra in MeOH were
obtained using Shimadzu UV-265 Spectrometer. 1H and 13C NMR
spectra in CDCl3/DMSO were recorded on a Brucker WH 300
(200 MHz) and Varian Gemini (200 MHz) spectrometers using TMS
as an internal reference. Conductance measurements were car-
ried out at room temperature on freshly prepared 10−3 M EtOH
solutions using a coronation digital conductivity meter. The mag-
netic studies were carried out at room temperature on a Gouy
2.2.1. 2-(2-[((E)-1-2-[(2-[(carboxymethyl)amino]-2-
oxoethylimino)methyl]phenylmethylidene)amino]acetylamino)acetic
acid (L) (CMAIPA)
Yield 74%; mp 196–198 ◦C; IR 3318, 2918, 2842, 1720, 1643,
1632, 1570, 1128 cm−1 1H NMR (200 MHz, DMSO) ı in ppm 11.56
;

B. Geeta et al. / Spectrochimica Acta Part A 77 (2010) 911–915
913
Table 1
Analytical, spectral and physical data of the ligand and complexes.
Complexes/molecular formulae
ꢀmax (nm)
ꢁMa
Found (Calcd.) (%)
C
(ꢂ−1 cm2 mol−1
)
H
N
M
ꢃeff (BM)
CMAIPA C16H18N4O6
–
–
14
13
16
20
53.04 (54.84)
35.14 (35.15)
35.20 (35.17)
36.70 (36.69)
41.20 (41.17)
5.01 (4.94)
6.06 (6.05)
6.10 (6.06)
4.58 (4.53)
3.50 (3.46)
15.48 (15.46)
8.60 (8.63)
8.60 (8.63)
10.10 (10.07)
12.02 (12.00)
–
–
[Co2L(H2O)4]·3H2O C16H30N4O13Co2
[Ni2L(H2O)4]·3H2O C16H30N4O13Ni2
[Cu2L]·3H2O C16H24N4O9Cu2
[Pd2L] C16H16N4O6Pd2
622, 661
937, 591, 376
710, 543, 432
610, 520, 405
18.10 (18.15)
18.02 (18.09)
22.80 (22.84)
22.84 (22.80)
3.50
2.90
1.58
0.00
(s, 2H, COOH), 8.19 (s, 2H, CH N), 7.22–7.54 (m, 4H, Ar–H), 5.83 (s,
4H, CH2), 5.60 (s, 2H, NH), 4.25 (d, 4H, CH2); 13C NMR (67.93 MHz,
DMSO) ı 48.5 (2C, CH2), 58.3 (2C, CH2), 130.6, 132.3, 136.4 (6C,
Ar–C), 163.7(2C, CH N), 171.2 (2C, C O), 180.4 (2C, COOH); Anal.
Found: C, 53.04; H, 5.01; N, 15.48%. Calcd. for C16H18N4O6: C, 58.84;
H, 4.94; N, 15.46%. MS: [M]+ at m/z 362.
Co(II), Ni(II), Cu(II) and Pd(II) complexes using the coordination of
nitrogens from C N of Schiff-base and NH of amide group and the
oxygens from amide and carboxyl groups [17,18,30]. Further, the
bands in the range of 450–470 and 510–515 cm−1 assignable to
the ꢄ(M–O) and ꢄ(M–N) respectively are providing additional sup-
port to propose the M–L bonds through carboxyl oxygen and imino
nitrogen in all the complexes [14,15,17,18] (Table 2). The IR spec-
trum of [Pd2L] binuclear complex is shown in electronic supporting
information as Fig. S1.
2.3. Synthesis of complexes
A solution of cobalt(II) acetate, nickel(II) acetate and copper(II)
acetate (0.002–0.005 mol) in methanol (25 mL) and palladium(II)
chloride (1.062 g in 40 mL 0.1 M HCl and 40 mL methanol) was
added drop wise to a methanolic solution (30 mL) of Schiff-base
(0.002–0.005 mol) with constant stirring at room temperature. The
resulting mixture was allowed to reflux on a water bath for 2 h until
a solid is separated out. The precipitates were suction filtered, puri-
fied by repeated washing with chloroform and methanol and dried
in vacuum desiccators (Yield: 70–85%).
3.2. 1H NMR spectral analysis
In the 1H NMR spectra, the integral intensities of each signal
were found to agree with the number of different types of pro-
tons present in the complex. A signal appeared in the ligand 1H
NMR spectrum at 8.19 ı is due to CH N protons. However, in the
spectra of palladium complex the signal was moved down-field at
8.30 ı suggests the coordination of imino nitrogen to palladium
ion [22,23]. The carboxyl proton of the ligand was observed at
11.56 ppm. However, this was not present in the complex spectrum
due to the involvement of carboxyl oxygen in chelation through
deprotonation [31]. Further, a broad signal found in the complex
spectrum at 6.0 ppm corresponds to NH proton, which was shifted
from 5.60 ppm of ligand give evidence to the coordination of NH
group [5].
3. Results and discussion
All the complexes are soluble in methanol and water. The
elemental analysis data and the physical properties of the
complexes are listed in Table 1. The complexes can be repre-
sented as [M2L(H2O)4]·3H2O where (M = Co(II), Ni(II)) and [M2L]·
3H2O where (M = Cu(II))and [M2L] where (M = Pd(II)) and
(L = ligand). The low molar conductance values of all the complexes
in dichloromethane measured at 10−3 M concentration are in
the range of 13–20 indicate that all the complexes behave as
non-electrolytes [29].
3.3. 13C NMR spectral analysis
In the 13C spectra of Pd(II) complex, a down-field shift of CH
N
group was observed in at 175.4 ppm and for carboxyl carbon at
195.3 ppm. It signifies that the ligand coordinates through the nitro-
gen atom of CH N [22,23] and through the oxygen of carboxyl
group of the ligand [22,23,31]. Furthermore, the down-field of shift-
ing of amide adjacent carbonyl (C–O) describes the coordination of
this site to palladium ion. However, the enolic carbon peak shifted
to 108.0–115.3 ı suggesting that coordination of C–O group to the
metals by deprotonation. The 1H and 13C NMR spectrum of [Pd2L]
binuclear complex is given in Supplementary Figs. S2 and S3.
3.1. Infrared spectral analysis
The infrared (IR) spectra−o1f all the complexes show ꢄN–H broad
bands in the 3128–3260 cm range. This band was shifted towards
lower side about 90–110 cm−1 compared to the ligand spectrum
indicating the coordination of amino nitrogen to the metal ion [5]. A
medium intensity band due to ꢄC N appeared at 1620–1630 cm−1
was also found to be shifted towards lower side about 13–23 cm−1
compared to ligand spectrum and supports the coordination of
imino nitrogen (C N) of ligand to the metal ion [14,15,17,18].
In addition to this, the appearance of new band in the range of
1565–1570 cm−1 assignable to ꢄ(C–O) suggests the coordination of
carbonyl group of glycyl–glycine moiety in the enol form through
deprotonation. This situation specify the formation of binuclear
3.4. Electronic spectral analysis
The electronic spectrum of bimolecular Co(II) complex
with the ligand exhibit the d–d transition bands in the
4
4
regions 622 and 661 nm assigned to the A2g ← T1g(F)(ꢄ2) and
4
4T1g(P) ← T1g(F)(ꢄ3) transitions respectively [14]. This indicates
Table 2
Infrared spectral data of the ligand and complexes (cm−1).
Complexes
ꢄ(C N)
ꢄ(N–H)
ꢄ(C–O) of COOH
ꢄ(COO–) asy/sym
ꢄ(M–H2O)
ꢄ(M–N)
ꢄ(M–O)
CMAIPA
1643
1630
1628
1620
1620
3318
3228
3206
3128
3260
1720, 1632
1570
–
1583, 1383
1579, 1383
1583, 1383
1583, 1383
–
725
725
–
–
510
509
510
508
–
470
470
450
450
[Co2L(H2O)4]·3H2O
[Ni2L(H2O)4]·3H2O
[Cu2L]·3H2O
[Pd2L]
1565
1570
1570
–

914
B. Geeta et al. / Spectrochimica Acta Part A 77 (2010) 911–915
the octahedral geometry for Co(II) complex. Similarly, bimolecu-
lar Ni(II) complex electronic spectrum exhibits the d–d transition
bands in the regions 937, 591 and 376 nm signed to the T2g
molecules are not coordinated [15]. The thermal data of [Pd2L]
complexes indicate no coordinated water molecules [22,23]. The
sharp decomposition corresponding to the loss of organic moi-
ety in complexes can be seen in the DTA curves which contain
one short exothermic peak falling at 290 ◦C. The final product of
decomposition of the complex above 680 ◦C corresponds to metal
oxide. The analysis of the thermogram by the way of identifying
the final products offers further support to the composition of the
complexes proposed on the basis of elemental and spectral analy-
sis.
3
3
3
3
(F) ← A2g(F)(ꢄ1), 3T1g(F) ← A2g(F)(ꢄ2) and 3T1g(P) ← A2g(F)(ꢄ3)
transitions respectively [17,24]. This shows the octahedral geome-
try and was further confirmed by ꢄ2 to ꢄ1 ratio, which was in the
range of 1.50–1.63 [17,32]. The UV spectrum of the Cu(II) complex
recorded in DMF showed an intensive band at about 710, 543 and
2
2
2
432 nm bands could be assigned to A1g ← B1g
,
2B2g ← B1g and
2
2Eg ← B1g transitions respectively [33]. It indicates the square pla-
nar geometry for Cu(II) complexes. Further, Pd(II) complex shows
1
1
three bands at 610, 520 and 405 nm assignable to A2g ← A1g
,
3.7. ESR spectral analysis
1B1g ← A1g and 1Eg ← A1g transitions attributed to the square
planar geometry. From the electronic spectral data, diamagnetic
behavior and square planar geometry has been proposed to Pd(II)
complex [22,23].
1
1
The ESR spectrum of [Cu2L]·3H2O complex exhibits an axial sig-
nal, which can be interpreted in terms of tetrahedral species with
a strong signal in the low field region, corresponding to high g
value viz. 2.19, and a weak signal in the high field region due to
⊥
3.5. Magnetic properties
low g value viz. 2.06, while the gavg is 2.15. Splitting of the signal
ꢀ
in the high field region may be due to a difference in surroundings
between the two Cu(II) centers suggesting a binuclear structure
for this complex [35]. The g value is equal to 0.32, indicating that
anti-ferromagnetic interaction is taking place between the Cu(II)
The theoretical magnetic moments values of the cobalt(II),
nickel(II) and copper(II) complexes were 3.87, 2.83 and 1.73 B.M
respectively. Experimentally it has been found that mononuclear,
octahedral cobalt(II), nickel(II) and copper(II) complexes have mag-
netic moments in the range 4.3–5.2, 2.9–3.3 and 1.7–2.2 B.M.
However, in the present investigation, the magnetic moment
observed for the binuclear, octahedral Co(II) and Ni(II) complexes
were 3.50 and 2.90 B.M., respectively. These values are less than the
experimental values indicate the absence of metal–metal interac-
tion in the binuclear complex [34]. Further, the magnetic moment
of Cu(II) complex lies below the ‘spin only’ value, i.e. 1.58 B.M. The
lower value of magnetic moment at room temperature is consistent
with square planar geometry around the metal ions. In general, the
low magnetic moment values of binuclear copper complexes are
attributed to the anti-ferromagnetic moment interaction between
two central Cu(II) metal ions; this is an indication of the formation
of binuclear Cu(II) complex [34]. In addition, the magnetic suscep-
tibility measurements have also been carried out for Pd(II) complex
and was found to be diamagnetic, confirmed by sharp signals in the
1H NMR spectra.
ions [36]. The g > g > 2.0023 indicates that the unpaired electron
⊥
ꢀ
is present in the dxy ground state in a square planar geometry
[37,38].
3.8. Mass spectral data
The formation of binuclear Co(II), Ni(II), Cu(II) and Pd(II) com-
plexes further evidenced by mass spectral data. The proposed
molecular formula of binuclear Co(II), Ni(II), Cu(II) and Pd(II) com-
plexes was confirmed by the mass spectral analysis by comparing
its molecular formula weight with m/z value. The molecular ion
peaks and isotopic pattern of ligand and its binuclear Co(II), Ni(II),
Cu(II) and Pd(II) complexes shows different m/z values with dif-
ferent intensities. The mass spectra contain molecular ion peaks
at m/z (M+) 362 (ligand CMAIPA), 604 ([Co2L(H2O)4]·3H2O), 603.8
([Ni2L(H2O)4]·3H2O), 543 ([Cu2L]·3H2O) and 572 ([Pd2L]). This data
is in good agreement with the respective molecular formulae. Mass
spectrum of [Pd2L] is presented in Supplementary Fig. S4.
3.6. Thermal analysis
4. Antibacterial activity
Thermal behavior of the complexes has been studied using
TGA, and DTA analysis. Based on the thermograms, decomposi-
tion stages, temperature ranges, decomposition product as well
as weight loss percentages of the complexes were calculated. The
complexes [Co2L(H2O)4]·3H2O and [Ni2L(H2O)4]·3H2O undergo
decomposition mainly in three stages. In the first stage a peak
corresponding to the loss of the water molecule in the temper-
ature range of 70–110 ◦C was observed. The expulsion of water
molecules in this range indicates that they are lattice held. It is
further evidenced by an endothermic peak in the above tempera-
ture range in DTA curve, indicating that the water molecules are
of lattice type [14,17]. The second stage corresponds to the loss
of water molecules in the temperature range of 170–200 ◦C corre-
sponding to the loss of coordinated water molecules. The presence
of endothermic peak at 180–200 ◦C in DTA curve of the complex
also further confirms the presence of coordinated water. The third
stage corresponds to the loss of organic moiety. The final decompo-
sition of the complexes above 500 ◦C corresponds to metal oxide.
The thermogram of [Cu2L]·3H2O complex shows only two stages of
decomposition. The first stage corresponds to dehydration of water
molecules at 117 ◦C and second stage being the loss of organic moi-
ety. The presence of water molecules is further evidenced by DTA
curves. The expulsion of water molecules and the percentage of
loss of weight in the above temperature range indicate that water
Antibacterial activities of the ligand CMAIPA and its Co(II), Ni(II),
Cu(II), Pd(II) complexes against two Gram-positive (B. subtilis and
S. aureus) and two Gram-negative (E. coli and K. pneumonia)
bacteria were studied using three existing antibacterial drugs viz.,
streptomycin, ampicillin and rifampicin. Preliminary screening
for all the complexes was performed at the fixed concentration of
Table 3
Zone of inhibition of CMAIPA and its Co(II), Ni(II), Cu(II), Pd(II) complexes against
different bacteria.
Ligand/complexes
Zone of inhibition (mm)
(1000 ␮g/mL)
Gram-positive bacteria
Gram-negative bacteria
S. aureus
B. subtilis
E. coli
K. pneumonia
CMAIPA
11
10
21
16
19
42
10
11
51
08
14
24
15
35
06
08
48
08
19
20
25
40
06
07
45
[Co2L(H2O)4]·3H2O 15
[Ni2L(H2O)4]·3H2O
[Cu2L]·3H2O
[Pd2L]
Streptomycin
Ampicillin
12
28
45
12
13
49
Rifampicin

B. Geeta et al. / Spectrochimica Acta Part A 77 (2010) 911–915
915
Acknowledgment
The authors thank the University Grant Commission (UGC, F. No.
34-363/2008(SR)), New Delhi, India for financially supporting this
research.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.08.004.
References
Fig. 1. Comparison of MIC values (in ␮g/mL) of complexes and standard drugs
against different bacteria.
[1] S. Akine, S. Sunaga, T. Taniguchi, H. Miyazaki, T. Nabeshima, Inorg. Chem. 46
(2007) 2959–2961.
[2] J.R. Anacona, E. Bastardo, J. Camus, Transit. Met. Chem. 24 (1999) 478–480.
[3] A. Trujillo, S. Sinbandhit, L. Toupet, D. Carrillo, C. Manzur, J.R. Hamon, J. Inorg.
Organomet. Polym. 18 (2008) 81–99.
[4] V. Lozan, C. Loose, J. Kortus, B. Kersting, Coord. Chem. Rev. 253 (2009)
2244–2260.
[5] S.A. Sallam, Transit. Met. Chem. 31 (2006) 46–55.
[6] J. Costamagna, J. Vargas, R. Latorre, A. Alvarado, G. Mena, Coord. Chem. Rev. 119
(1992) 67–88.
[7] J.M. Bindlish, S.C. Bhatia, P.C. Jain, Indian J. Chem. 13 (1975) 81–82.
[8] M.A. Ali, A.H. Mirza, M. Nazimuddin, F. Karim, P.V. Bernhardt, Inorg. Chim. Acta
358 (2005) 4548–4554.
[9] B.J.A. Jeragh, A. El-Dissouky, J. Coord. Chem. 58 (2005) 1029–1038.
[10] P.A. Vigato, S. Tamburini, Coord. Chem. Rev. 248 (2004) 1717–2128.
[11] S.M.E. Khalil, K.A. Bashir, J. Coord. Chem. 55 (2002) 681–696.
[12] M. Shakir, S.P. Varkey, Transit. Met. Chem. 19 (1994) 606–610.
[13] A.H. Al-Kubaisi, Bull. Korean Chem. Soc. 25 (2004) 37–41.
[14] P.M. Reddy, A.V.S.S. Prasad, K. Shanker, V. Ravinder, Spectrochim. Acta A 68
(2007) 1000–1006.
[15] P.M. Reddy, A.V.S.S. Prasad, V. Ravinder, Transit. Met. Chem. 32 (2007) 507–513.
[16] P.M. Reddy, K. Shanker, R. Rohini, M. Sarangapani, V. Ravinder, Spectrochim.
Acta A 70 (2008) 1231–1237.
[17] P.M. Reddy, A.V.S.S. Prasad, R. Rohini, V. Ravinder, Spectrochim. Acta A 70
(2008) 704–712.
[18] P.M. Reddy, A.V.S.S. Prasad, Ch.K. Reddy, V. Ravinder, Transit. Met. Chem. 33
(2008) 251–258.
[19] M. Ashok, A.V.S.S. Prasad, P.M. Reddy, V. Ravinder, Spectrochim. Acta A 72
(2009) 204–208.
[20] K. Shanker, R. Rohini, V. Ravinder, P.M. Reddy, Y.P. Ho, Spectrochim. Acta A 73
(2009) 205–211.
[21] P.M. Reddy, Y.P. Ho, K. Shanker, R. Rohini, V. Ravinder, Eur. J. Med. Chem. 44
(2009) 2621–2625.
[22] K. Shanker, P.M. Reddy, R. Rohini, Y.P. Ho, V. Ravinder, J. Coord. Chem. 62 (2009)
3040–3049.
[23] K. Shanker, R. Rohini, K. Shravankumar, P.M. Reddy, Y.P. Ho, V. Ravinder, J. Ind.
Chem. Soc. 86 (2009) 153–161.
[24] A. Prasad, P.M. Reddy, K. Shanker, R. Rohini, V. Ravinder, Color. Technol. 125
(2009) 284–287.
1000 ␮g/mL. Inhibition was recorded by measuring the diameter
of the inhibition zone at the end of 24 h for bacteria. Among
the compounds tested the four metal complexes showed good
inhibition towards all tested strains (Table 3). The activity of
all these complexes were further confirmed by determining the
minimum inhibitory concentration [25,26,39] values by liquid
dilution method in which the effectiveness was observed at lower
concentrations. The comparison of the MICs (in ␮g/mL) of all
complexes and standard drugs against tested strains are presented
in Fig. 1 (Supplementary Table S1). It was found that Co(II), Ni(II),
Cu(II) complexes have good activity against all bacterial strains
with MIC value (15–35 ␮g/mL). In particular, Pd(II) complex
showed excellent activity (MIC range 5–10 ␮g/mL) against all
the bacterial strains even than standard drugs streptomycin
and ampicillin. The results from these studies have also shown
that complexation of metals to CMAIPA serves to improve the
antimicrobial of the ligand. This higher antibacterial activity of the
metal complexes compared to ligand is may be due to the change
in structure due to coordination and chelating tends to make
metal complexes act as more powerful and potent bactereostatic
agents, thus inhibiting the growth of the bacteria. Furthermore,
chelation reduces the polarity of the metal ion mainly due to the
partial sharing of its positive charge with the donor groups within
the chelate ring system. Such chelation increases the lipophilic
nature of the central metal atom, which favors its permeation
more efficiently through the lipid layer of the microorganism, thus
destroying them more forcefully [20,40–42]. Thus all complexes
showed more increased activity than the corresponding ligand
and the two antibacterial drugs. The activity of ligand, complexes
and standard drugs against different bacteria were found to be
CMAIPA(L) < streptomycin < [Ni2L(H2O)4]·3H2O = ampicillin < [Co2
L(H2O)4]·3H2O < [Cu2L]·3H2O < [Pd2L] < rifampicin for S. aureus,
CMAIPA(L) = streptomycin < ampicillin<[Ni2L(H2O)4]·3H2O<[Cu2L]·
3H2O < [Co2L(H2O)4]·3H2O < [Pd2L] < rifampicin for B. subtilis,
streptomycin<CMAIPA(L) =ampicillin<[Co2L(H2O)4]·3H2O < [Cu2L]·
3H2O [Ni2L(H2O)4]·3H2O<[Pd2L]<rifampicin for E. coli and strepto-
mycin < ampicillin<CMAIPA(L) < [Co2L(H2O)4]·3H2O<[Ni2L(H2O)4]·
3H2O < [Cu2L]·3H2O < [Pd2L] < rifampicin for K. pneumonia.
[25] R. Rohini, K. Shanker, P.M. Reddy, Y.-P. Ho, V. Ravinder, Eur. J. Med. Chem. 44
(2009) 3330–3339.
[26] R. Rohini, K. Shanker, P.M. Reddy, V.C. Sekhar, V. Ravinder, Arch. Pharm. 342
(2009) 533–540.
[27] R. Rohini, P.M. Reddy, K. Shanker, V. Ravinder, Acta Chim. Slov. 56 (2009)
900–907.
[28] R. Rohini, K. Shanker, P.M. Reddy, V. Ravinder, J. Braz. Chem. Soc. 21 (2010)
49–57.
[29] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122.
[30] W.R. Marson, H.B. Gray, J. Am. Chem. Soc. 90 (1968) 5721–5729.
[31] E. Keskioglu, A.B. Gunduzalp, S. C¸ ete, F. Hamurcu, B. Erk, Spectrochim. Acta A
70 (2008) 634–640.
[32] S. Chandra, R. Kumara, R. Singh, Spectrochim. Acta A 65 (2006) 215–220.
[33] J. Bjerrum, C.J. Ballhausen, C.K. Jorgensen, Acta Chem. Scand.
1275–1289.
8 (1954)
[34] R.L. Carlin, A.J. Vandryneveledt, Magnetic Properties of Transition Metal Com-
pounds, Springer-Verlag, New York, 1997.
5. Conclusions
[35] S.S. Tandon, L.C. Laurence, K. Thompson, S.P. Connors, J.N. Bridson, Inorg. Chem.
Acta 213 (1993) 289–300.
In this report the non-template synthesis of new binuclear
cobalt(II), nickel(II), copper(II), and palladium(II) complexes having
N4O4 Schiff-base ligand obtained by condensation of glycyl–glycine
with o-phthalaldehyde have been presented and all the synthesized
compounds were screened for their antibacterial activity against
two Gram-positive and two Gram-negative bacterial strains. In this
study the most potent activity was observed in Pd(II) complex
against all tested strains when compared to respective standard
drugs streptomycin and ampicillin.
[36] Z. Wang, Z. Wu, Z. Yen, Transit. Met. Chem. 19 (1994) 235–236.
[37] A.S. El Tabl, Polish J. Chem. 71 (1997) 1213–1222.
[38] B.A. Goodman, J.B. Raynor, Adv. Inorg. Chem. Radiochem. 13 (1970) 136–362.
[39] R. Rohini, P.M. Reddy, K. Shanker, A. Hu, V. Ravinder, Eur. J. Med. Chem. 45
(2010) 1200–1205.
[40] B.G. Tweedy, Phytopathology 55 (1964) 910–914.
[41] N.M.A. Atabay, B. Dulger, F. Gucin, Eur. J. Med. Chem. 40 (2005) 1096–1102.
[42] S.A. Patil, V.H. Naik, A.D. Kulkarni, P.S. Badami, Spectrochim. Acta A 75 (2010)
347–354.