Synthesis, characterization and biological activity of transition metal complexes with Schiff bases derived from 2-nitrobenzaldehyde with glycine and methionine

Article abstract of DOI:10.1016/j.saa.2012.03.077

Schiff bases derived from 2-nitrobenzaldehyde with amino acids (glycine, methionine) and their Co(II), Ni(II) and Cu(II) complexes have been synthesized and characterized by various physico-chemical techniques. From spectral studies, it has been concluded that the ligands acts as bidentate molecule, coordinates metal through azomethine nitrogen and carboxylate oxygen. Mass spectrum explains the successive degradation of the molecular species in solution and justifies ML₂ complexes. X-ray powder diffraction helps to determine the cell parameters of the complexes. Molecular structure of the complexes has been optimized by MM2 calculations and suggests a square planar geometry. The ligands and their metal complexes have been tested in vitro against Streptococcus, Staph, Staphylococcus aureus and Escherchia coli bacteria in order to assess their antibacterial potential. The results indicate that the biological activity increases on complexation.

Full text of DOI:10.1016/j.saa.2012.03.077

Spectrochimica Acta Part A 94 (2012) 143–151
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and biological activity of transition metal complexes
with Schiff bases derived from 2-nitrobenzaldehyde with glycine and methionine
Bibhesh K. Singha,∗, Hemant K. Rajourb, Anant Prakasha
a Inorganic & Bioinorganic Research Lab, Department of Chemistry, Govt. Post Graduate College, Ranikhet 263645 (Uttarakhand), India
b Department of Chemistry, Ramjas College, University of Delhi, Delhi 110007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Schiff bases derived from 2-nitrobenzaldehyde with amino acids (glycine, methionine) and their Co(II),
Ni(II) and Cu(II) complexes have been synthesized and characterized by various physico-chemical
techniques. From spectral studies, it has been concluded that the ligands acts as bidentate molecule,
coordinates metal through azomethine nitrogen and carboxylate oxygen. Mass spectrum explains the
successive degradation of the molecular species in solution and justifies ML2 complexes. X-ray powder
diffraction helps to determine the cell parameters of the complexes. Molecular structure of the complexes
has been optimized by MM2 calculations and suggests a square planar geometry. The ligands and their
metal complexes have been tested in vitro against Streptococcus, Staph, Staphylococcus aureus and Escher-
chia coli bacteria in order to assess their antibacterial potential. The results indicate that the biological
activity increases on complexation.
Received 23 December 2011
Received in revised form 15 March 2012
Accepted 26 March 2012
Keywords:
Antibacterial
Complexes
Molecular modeling
Powder XRD
Schiff base
© 2012 Elsevier B.V. All rights reserved.
Spectra
1. Introduction
complicated PLP-amino acid Schiff bases (PLP = pyridoxal-5ꢀ-
phosphate), as these are key interaction in a variety of metabolic
Presently, there is a growing interest in the coordination
chemistry of structurally modified bio-ligands. Transition metal
complexes with potential biological activity are the focus of exten-
sive investigations. Schiff bases have been often used as chelating
ligands in coordination chemistry [1], in catalysis, anti-oxidative
activity, medicine as antibiotics, anti-inflammatory agents and in
industry for anti-corrosion properties [2]. Amino acid-based Schiff
bases are very effective metal chelators and their metal complexes
are models for a number of important biological systems [3]. They
are key intermediates in a variety of metabolic reactions involving
amino acids such as: decarboxylation, transamination, recemiza-
tion and C C bond cleavage, which are catalyzed by enzymes [4].
The reduced Schiff base containing various amino acid derivatives
are excellent multidentate ligands for generating interesting multi-
dimensional network structures. The additional reactive functional
groups on the amino acid side chain of the ligands can lead to the
formation of unexpected and unusual structures [5,6].
reactions involving amino acids, which are catalyzed by enzymes
that requires PLP as a cofactor [7]. The preparation of Schiff bases
containing >C O and >C N groups with potential ligating ability
has drawn a lot of attention because of their use as chelating agents,
analytical reagents, metal indicators in complexometric titrations
and calorimetric reagents, in addition to biochemical research [8].
The behavior of the >C N bond is strongly dependent on the struc-
ture of the amine moiety, which in turn controls the efficiency of
the conjugation and may incorporate structural elements able to
modulate the steric crowding around the coordination [9].
The variety of possible Schiff-base metal complexes with wide
choice of ligands and coordination environments has prompted
us to undertake research in this area [10]. In this work, spectral
characterization serves as important tools for the interpreta-
tion of structures of bio-molecules. Powder diffraction data is
especially useful to deduce accurate cell parameters as well as
particle size. The fact that the three-dimensional reciprocal lat-
tice information is condensed on to a one-dimensional intensity
profile with respect to 2-theta in powder diffraction is the main
concern. This leads to overlapping of the diffraction peaks, consid-
erable and preferred orientation among the crystallites [11]. The
present works deals specially the coordination properties of 2-
nitrobenzaldehyde–glycine and 2-nitrobenzaldehyde–methionine
concerning its interactions with Co(II), Ni(II) and Cu(II). The
Metal Schiff-base complexes derived from amino acids play
an important role as the key compounds for modeling more
∗
Corresponding author. Tel.: +91 5966 220372; fax: +91 5966 220372.
E-mail address: bibheshksingh@yahoo.co.in (B.K. Singh).
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.03.077

144
B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
CH=N-CH2-COOH
CHO
Alc. KOH
+
H2N-CH2-COOH
NO2
NO2
CH2-CH2-S-CH3
CH=N-CH-COOH
CHO
CH2-CH2-S-CH3
Alc. KOH
+
H2N-CH-COOH
NO2
NO2
Scheme 1. Synthesis of ligands.
bio-efficacy of these complexes has also been examined against
the growth of bacteria in vitro to evaluate their anti-microbial
potential.
yellow crystalline product obtained was dried over fused calcium
chloride in desiccators. Yield: 89–90%. The synthesis of the ligands
is discussed in Scheme 1.
2.2.2. Synthesis of metal complexes
2. Experimental
The newly synthesized Schiff base (0.4 M) (Scheme 1) and appro-
priate metal nitrates (0.2 M) were dissolved separately in ethanol
(30 mL) and mixed with constant stirring. The mixture was stirred
magnetically for 5–8 h at 50 ◦C. On cooling to room tempera-
ture, solid product was obtained, filtered, washed with aqueous
ethanolic solution and finally dried over fused calcium chloride in
desiccators. Yield: 75–88%.
2.1. Material and methodology
All the chemicals used were of analytical grade and used as pro-
cured. The elemental analysis (C, H and N) of the complexes were
performed using Elementar vario EL III (Germany) model. Metal
contents were estimated on an AA-640-13 Shimadzu flame atomic
absorption spectrophotometer in solutions prepared by decompos-
ing the complex in hot concentrated HNO3. The molar conductance
at 10−3 M dilution was measured by Elico-Conductometer Bridge.
The IR spectra were recorded in the range of 4000–400 cm−1
and 400–100 cm−1 on Perkin-Elmer FTIR spectrophotometer in
KBr and polyethylene pellets respectively. The UV–visible spec-
tra were recorded in water on Beckman DU-64 spectrophotometer
with quartz cells of 1 cm path length and mass spectra (TOF-MS)
were recorded on Waters (USA) KC-455 model with ES+ mode in
DMSO. 1H NMR spectra were recorded in DMSO-d6 solvent on
a Bruker Advance 400 instrument. Magnetic susceptibility mea-
surements were carried out at room temperature in powder form
on a vibrating sample magnetometer PAR 155 with 5000G-field
strength, using Co[Hg(SCN)4] as the calibrate (magnetic suscep-
tibility ≈ 1.644 × 10−5 cm3 g−1). The XRD powder pattern were
recorded on a vertical type Philips 1130/00 diffractometer, oper-
ated at 40 kV and 50 Ma generator using the monochromatized Cu
2.3. Molecular modeling
Molecular modeling of the proposed structure of the com-
plexes was performed using HyperChem version 7.1 program
package. The correct stereochemistry was assured through the
manipulation and modification of the molecular coordinates to
obtain reasonable low energy molecular geometries. The poten-
tial energy of the molecule was the sum of the following terms
(E) = Estr + Eang + Etor + Evdw + Eoop + Eele, where all E’s represent the
energy values corresponding to the given types of interaction
(kcal/mol). The subscripts str, ang, tor, vdw, oop and ele denote
bond stretching, angle bonding, torsion deformation, vander-
waals interactions, out of plain bending and electronic interaction,
respectively. The molecular mechanics describe the application
of classical mechanics to determination of molecular equilibrium
structures. It enables the calculation of the total static energy
of a molecule in terms of deviations from reference unstrained
bond lengths, angles and torsions plus non-bonded interactions. On
account of non-bonded interactions and also the chemical sense of
each atom, treat the force field as a set of constants that have to
be fixed by appeal to experiment or more rigorous calculations. It
has been found that off-diagonal terms are usually largest when
neighboring atoms are involved, and so we have to take account
of non-bonded interactions, but only between next-nearest neigh-
bors.
˚
K␣ line at wavelength 1.54056 A as the radiation sources. Sample
was scanned between 10◦ and 70◦ (2ꢀ) at 25 ◦C. The crystallographic
data were analyzed by using the CRYSFIRE-2000 powder indexing
software package and the space group was found by GSAS program.
Debye Scherer relation in conjunction with estimation of 100% peak
width was used to estimate the particle size. The density was used
to estimate the particle size. The density was determined using
Archimedes method.
2.2. Synthesis of ligands and complexes
2.4. Biological activity
2.2.1. Synthesis of N-(2-nitrobenzaldehyde)glycine (NBG),
N-(2-nitrobenzaldehyde) methionine (NBM)
In vitro antibacterial activity of the synthesized compounds
against Streptococcus, Staph, Staphylococcus and Escherchia coli were
carried out using paper disc diffusion method [12]. The nutrient
agar medium (peptone, beef extract, NaCl and agar–agar) and 5 mm
diameter paper discs of Whatman No. 1 were used. The test com-
pound was dissolved in DMSO in 0.1–0.4% concentrations. The
paper discs were soaked in different solutions of the compound,
A homogeneous mixture (30 mL) of an aqueous solution of
glycine or methionine and ethanolic solution of KOH (0.02 mol) was
added with constant stirring to an ethanolic solution (30 mL) of 2-
nitrobenzaldehyde. Deprotonation of ligands becomes easier due to
addition of alcoholic KOH. The mixture was refluxed for 3 h. Excess
solvent was removed by slow evaporation and the cream/light

B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
145
dried and the placed in the petri plates (9 mm diameter) previously
seeded with the test organisms Streptococcus, Staph, Staphylococcus
aureus and E. coli. The plates were incubated for 24–30 h at 27 1 ◦C
and the inhibition zones (mm) were measured around each disc.
As the organism grows, it forms a turbid layer, except in the region
where the concentration of antibacterial agent is above the min-
imum inhibitory concentration, and a zone of inhibition is seen.
The size of the inhibition zone depends upon the culture medium,
incubation conditions, rate of diffusion and the concentration of the
antibacterial agent.
3. Results and discussion
All the complexes are coloured solids, air stable for an extended
period of time, but decomposing at higher temperature. They are
insoluble in common organic solvents and soluble in DMSO. The
molar conductance values at room temperature and 10−3 M dilu-
tion in DMSO were found in the range of 8–18 ohm−1 mol−1 cm2
indicating the non-ionic nature of all these complexes [13]. The
satisfactory results of analytical data (Table 1) revealed the ligands
and complexes were of good purity, forms ML2 complexes. Single
crystal of the compounds could not be isolated from any organic sol-
vents; thus Powder X-ray diffraction helps to predict crystal system.
However, the analytical and spectroscopic data enables us to pre-
dict possible structures. The magnetic moments of the complexes
were measured at room temperature and are listed in Table 1.
3.1. Spectroscopic studies
A mass spectrum is particularly useful when a poorly crystalline
nature of complexes prevents their X-ray characterization. Mass
spectrometry has been successfully used to investigate molecu-
lar species in solution [14]. The pattern of mass spectrum gives an
impression of the successive degradation of the target compound
with the series of peaks corresponding to the various fragments.
Their intensity gives an idea of stability of fragments. The mass
spectrum of ligands having molecular ion peaks at 208(90%, m/z)
and 282(74%, m/z) for NBG and NBM respectively, confirming purity
of the ligands. The recorded molecular ion peaks of the metal com-
plexes have been used to confirm the proposed formula. All the
synthesized complexes containing metal ion were confirmed by
good agreement between the observed and calculated molecular
formula [15]. Elemental analysis values are in close agreement
with the values calculated from molecular formulas assigned to
these complexes, which is further supported by the TOF-mass
studies. Some important fragments have been discussed in Fig. 1a
and b. The molecular ion fragments leading to the formation of
the species [M(L2)]+ which undergo demetallation to form the
species [bis(nitro phenyl)-ethylene]+ are usually present in the
mass spectra of these systems [16]. The last fragment at 209 and
283 respectively in complex III and VI are [LH]+ of the ligands peak
show similar pattern of degradation. The important mass peaks for
the complexes studied are given in Table 2.
The various IR spectral data are given in Table 3. The IR spec-
trum of the ligands show bands in the range of 1698–1695(s),
1630–1620(s) and 1400–1390(s) are assignable to ꢁ(COO) asym-
metric, ꢁ(C N) and ꢁ(COO) symmetric respectively [17]. The band
due to azomethine shifts in the complexes to lower wave num-
ber by ∼20 cm−1, indicating coordination of azomethine nitrogen
to metal ion. The C O and C O stretching frequency are assigned
to ꢁas(CO2) and ꢁs(CO2) modes of the carboxylate group and
these bands show considerable shift in all the complexes [17].
The separation between antisymmetric and symmetric stretch-
ing is ∼300 cm−1, indicating the covalent nature of metal oxygen
bond in complexes and monodenticity of carboxylate [18,19]. The

146
B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
Fig. 1. (a) Mass spectrum of complex III. (b) Mass spectrum of complex VI.
Schiff-base ligands are deprotonated, thus acting a uninegatively
charged bidentate ON chelate, coordinated to the metal ion via
one azomethine nitrogen atom and one deprotonated carboxy-
late oxygen atom (Fig. 2a and b). Non-ligand bands at 505–540(w)
and 490–470(m) cm−1 in spectra of all complexes are assignable to
ꢁ(M O) and ꢁ(M N) respectively [20].
complexes showed a singlet in the region ı 7.95–7.65 ppm, which
has been assigned to the azomethine proton ( HC N). The position
of the azomethine signal in the complexes is downfield in compar-
ison with the free ligand, suggesting deshielding of the azomethine
proton due to its coordination to metal ions through the azome-
thine nitrogen [21]. It was found that the COOH signal is found in
the region 9.95–9.90 ppm in the spectrum of ligand. This signal is
completely disappeared in the spectrum of the Ni(II) complex indi-
cating the involvement of the COOH group in chelation through
deprotonation of the COOH group [22]. A resonance at 2.52 ppm
The 1H NMR data (Table 3) for the free ligands and their nickel
complexes are in all cases consistent with the assigned struc-
tures. The spectrum of Schiff bases show a signal in the range
of 8.14–8.25 ppm for CH N azomethine. The spectrum of the

B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
147
Fig. 2. (a) IR spectrum of ligand NBG. (b) IR spectrum of the complex III.
Fig. 3. (a) 1H NMR spectrum of ligand NBG. (b) 1H NMR spectrum of complex II.

148
B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
Table 2
UV region, attributed to ligand transitions (n → ␲* and ␲ → ␲*),
and a characteristic broad bands in the region 656–660 nm and
Important mass peaks of the complexes studied.
2
2
2
2
507–510 nm assignable to B1g → Eg and B1g → A1g transitions
respectively in visible region, which indicates the possibility of
square planar geometry of Cu(II) complex. The Cu(II) complex has
magnetic moment 1.72–1.74 BM reveals square planar geometry
around the metal ion [26].
Complex
II
Mass assignments
[C18H14O8N4Ni]+
m/z
473
359
270
208
[C14
H
10O4N4Ni]+
[C14 H10O4N2]+
[LH]+
III
V
[C18H14O8N4Cu]+
[C14H10O4N4Cu]+
[C14H10O4N2]+
[LH]+
478
363
270
209
3.2. Powder X-ray diffraction
In the absence of single crystal, X-ray powder data are especially
useful to deduce accurate cell parameters. The diffraction pattern
reveals the crystalline nature of the complex. The indexing pro-
cedures were performed using (CCP4, UK) Crysfire program [29]
giving different crystal system with varying space group. The den-
sity and particle size of the metal complexes have been calculated.
The cell parameters of the complexes are shown in Table 4.
[C24
H
26O8N4 S2Ni]+
621
416
269
281
[C18H20O4N4 Ni]+
[C14 H10O4N2]+
[LH]+
VI
[C24H26O8N4 S2Cu]+
[C18H20O4N4 Cu]+
[C14 H10O4N2]+
[LH]+
626
420
270
282
3.3. Molecular modeling
Molecular mechanics attempts to reproduce molecular geome-
tries, energies and other features by adjusting bond length, bond
angles and torsion angles to equilibrium values that are dependent
on the hybridization of an atom and its bonding scheme. In order
to obtain estimates of structural details of these complexes, we
have optimized the molecular structure of complexes. Energy min-
imization was repeated several times to find the global minimum.
The energy minimization values for square planar and without
restricting the structure for the metal complexes are almost same.
The energy minimization value for complex II, and complex V are
53.80 kcal/mol (gradient 0.094046) and 64.94 kcal/mol (gradient
0.096531) respectively. On the basis of energy minimization, it have
been concluded that metal complexes of NBG are more stable than
corresponding metal complexes of the NBM. The optimized struc-
ture of the nickel complexes and their bond length in Å are shown
in Fig. 4a and b and their prominent bond angles are represented
in Tables 5a and 5b.
appears due to presence of CH2 group in nickel complex (Fig. 3a
and b) [23]. The peak at ı 4.95 ppm is assigned to CH group proton
which upfield at 5.20–5.26 ppm due to coordination of COO group
[24].
The electronic spectra of the ligands and their metal complexes
were recorded in DMSO at room temperature are given in Table 3.
The aromatic band of the ligands and complexes in the region
280–290 nm are attributed to a benzene ␲ → ␲* transitions. All
the complexes show an intense band at ca 384–397 nm which is
assigned to the n → ␲* transition of the non-bonding electrons
present on the nitrogen of the azomethine group in the Schiff bases
[25]. The electronic spectral data the Co(II) complexes show absorp-
tion bands in the region 520–545 nm and 410–435 nm assignable
4
4
to 2B2g → Eg(P) and 2B1g → A2g (P) transitions, respectively, sug-
gest square planar geometry of the complexes [26,27], which is also
corroborated by magnetic moment value given in Table 1. The rea-
son for the departure from the spin only value lies partly in the
existence of the second order Zeeman effect between the ground
and the higher ligand field terms [28]. However, it lies mainly in
the fact, that in the presence of spin-orbit coupling, the quenching
effect of the ligand field cannot be complete. Spectra of the nickel
complex shows an absorption band around 650 nm, assignable to a
3.4. Antibacterial activities
The free ligands and its respective metal complexes were
screened against Streptococcus, Staph, S. aureus and E. coli bacteria
to assess their potential antibacterial agents. The results are quite
promising. The bacterial screening results reveal that the free
ligand NBG showed the maximum activity against streproproteus
bacteria, where as the free ligand NBM showed the maximum activ-
ity against S. aureus bacteria. The cobalt(II) and nickel(II) complexes
of ligand NBG showed the maximum activity against streproproteus
bacteria whereas the copper(II) complex showed the maximum
activity against E. coli bacteria. The cobalt(II), nickel(II) and cop-
per(II) complexes of ligand NBM showed the consistent results,
1A1g → A2g transition and a shoulder in the region 552–560 nm
1
1
1
corresponding to a A1g → B1g transition which are consistent
with square planar stereochemistry about the nickel(II) ion. It can
be explained with the planar ligand set causes one of the d-orbitals
(dx2–y2) to be uniquely high in energy and the eight electrons can
occupy the other four d-orbitals but leave this strongly antibond-
ing one vacant. The diamagnetic nature of the Ni(II) complexes
further supports its square planar nature. The electronic spectrum
of the Cu(II) complex shows very intense absorption bands in the
Table 3
Infrared, electronic, 1H NMR spectra of ligands and their complexes.
S. no
Compd.
IR (cm−1
)
Electronic (nm)
1H NMR (ppm)
ꢁ(C N)
ꢁ(M O)
ꢁ(M N)
ꢁas(CO2)
ꢁS(CO2)
ı(CH N)
ı others
1
2
3
4
5
6
7
8
NBG
I
II
III
NBM
IV
1620(s)
1602(s)
1599(s)
1592(s)
1630(s)
1609(s)
1611(s)
1613(s)
–
–
1698(s)
1676(s)
1680(s)
1672(s)
1695(s)
1679(s)
1681(s)
1681(s)
1390(s)
1378(s)
1380(s)
1370(s)
1400(s)
1378(s)
1384(s)
1378(s)
287,390
8.14(singlet)
–
7.65(singlet)
–
8.25(singlet)
–
7.91(singlet)
–
9.90( COOH), 4.95( CH)
522(m)
517(w)
539(w)
–
516(m)
540(w)
532(m)
482(m)
486(m)
474(m)
–
478(w)
485(m)
490(m)
285,386, 387,520,435
284,391,650,560
281,384,507,656
290,396
280,397, 545,410
288,389,651,552
286,392, 510,660
5.20( CH)
9.95( COOH), 2.51 ( CH2 CH2−), 4.94 CH
2.52( CH2−CH2−) (5.26 CH)
V
VI
s, strong, m, medium, w, weak.

B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
149
Table 4
Crystallographic data of the complexes.
Complexes
Complex II
Complex III
Complex IV
Complex VI
Empirical formula
Formula weight
Temperature (K)
Wave length (Å)
Crystal system
Space group
C18H14N4O8Ni
473.03
298
1.54056
Triclinic
P1
10–70◦
C18H14N4O8Cu
477.87
298
C24 H26N4O8S2Co
621.54
298
C24 H26N4O8S2Cu
626.15
298
1.54056
1.54056
1.54056
Orthorhombic
Pmmm
10–70◦
Tetragonal
P4mm
10–70◦
Monoclinic
P2/m
10–70◦
2ꢀ range
a = 8.2975
b = 12.2013
c = 16.7121
˛ = 131.41
ˇ = 117.62◦
ꢂ = 61.97◦
1351.57
−3 ≤ h ≤ 3
−2 ≤ k ≤ 4
−1 ≤ l ≤ 8
1.17
a = 21.5886
b = 13.0975
c = 11.8673
˛ = ˇ = ꢂ = 90◦
a = 12.1359
b = 12.1359
c = 18.1998
˛ = ˇ = ꢂ = 90◦
a = 16.3123
b = 6.7698
c = 12.6179
˛ = ꢂ = 90◦
␤ = 106.65◦
Unit cell dimensions
(Å)
Volume (A3)
Limiting indices
3436.10
0 ≤ h ≤ 10
0 ≤ k ≤ 7
0 ≤ l ≤ 6
1.12
2682.12
0 ≤ h ≤ 7
0 ≤ k ≤ 6
0 ≤ l ≤ 9
1.18
1372.23
−8 ≤ h ≤ 8
−1 ≤ k ≤ 3
0 ≤ l ≤ 9
1.51
Density (g/cm3)
Z
2
5
3
2
Particle size (nm)
Avs. Eps
12.14
0.0000540
13.96
0.0000512
7.68
0.0000521
2.90
0.0000439
having maximum activity against S. aureus bacteria followed
by E. coli bacteria but their differences are small. On the basis of
antimicrobial results, it can be concluded that ligand NBM and its
metal complexes showed better activity than ligand NBG and its
metal complexes, may be due to the presence of methionine group.
In general, the activity was the least against Staph bacteria. The
antimicrobial data reveal that the complexes are more bioactive
than the free ligands (Fig. 5a and b). The enhanced activity of
the metal complexes may be ascribed to the increased lipophilic
nature of the complexes arising due to chelation. It was also noted
that the toxicity of the metal complexes increases on increasing
the metal ion concentration. It is probably due to faster diffusion
of the chelates as a whole through the cell membrane or due to the
chelation theory. The bounded metal may block enzymatic activity
of the cell or else it may catalyze toxic reactions among cellular
constituents.
Fig. 5. (a) Antibacterial screening of NBG and its metal complexes. (b) Antibacterial
Fig. 4. (a) Optimized structure of complex II. (b) Optimized structure of complex V.
screening of NBM and its metal complexes.

150
B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
CH 2-S-CH
3
NO2
O
CH 2
NO 2
C
O
C
CH=N
O
O
CH=N
CH=N
O
M
M
O
CH=N
C
O
NO 2
CH 2
C
O
NO2
CH 2-S-CH
3
M= Co(II), Ni(II), Cu(II),
Fig. 6. Proposed structure of complexes with ligand NBG and NBM.
Table 5a
The bond angle of complex II.
Acknowledgments
Authors thankfully acknowledge Council of Scientific and indus-
trial Research (CSIR) and University Grants Commission (UGC) New
Delhi, India for financial assistance.
Atom no.
Bond angle
O28 N26 O27
O30 N29 O31
O11 C10 O12
O18 C16 O15
O12 Ni13 N8
O15 Ni13 N14
C19 N14 Ni13
C7 N8 Ni13
C20 C19 N14
C6 C7 N8
120.35
119.94
119.67
119.51
96.08
References
96.24
121.07
130.44
133.03
133.59
119.95
113.15
[1] (a) K.R. Grunwald, G. Saischek, M. Volpe, F. Belaj, N.C. Mosch-Zanetti, Eur. J.
Inorg. Chem. 15 (2010) 2297–2305;
(b) M. Shebl, S.M.E. Khalil, S.A. Ahmed, H.A.A. Medien, J. Mol. Struct. 980 (1–3)
(2010) 39–50;
(c) Y. Scibuya, K. Nabari, M. Kondo, S. Yasue, K. Maeda, F. Uchida, H. Kawaguchi,
Chem. Lett. 37 (2008) 78–79.
O15 Ni13 N8
O12 Ni13 N14
[2] (a) N. Deligonul, M. Tumer, S. Serin, Trans. Met. Chem. 31 (2006) 920–929;
(b) Y.-h. Li, Z.-y. Yang, B.-d. Wang, Trans. Met. Chem. 31 (2006) 598;
(c) A. Bodakoti, M. Abid, A. Azam, Eur. J. Med. Chem. 41 (2006) 63–70;
(d) V.X. Jin, S.I. Tan, J.D. Ranford, Inorg. Chim. Acta 358 (2005) 677–686.
[3] (a) V.B. Badwaik, R.D. Deshmukh, A.S. Aswar, J. Coord. Chem. 62 (12) (2009)
2037–2047;
Table 5b
The bond angle of complex IV.
(b) R. Karamkar, C.R. Choudhary, S. Mitra, L. Dahlenburg, Struct. Chem. 16 (2005)
611.
Atom no.
Bond angle
[4] K.B. Hudasi, M.S. Patil, R.S. Vadavi, R.V. Shenoy, S.A. Patil, Trans. Met. Chem. 31
(2006) 580.
[5] (a) J.J. Vittal, in: J.J. Vittal, E.R.T. Tiekink (Eds.), Frontiers in Crystal Engineering,
vol. 297, Wiley, England, 2006;
(b) B. Sreenivasulu, M. Vetrichelvan, F. Zhao, S. Gas, J.J. Vittal, Eur. J. Inorg. Chem.
(2005) 4635.
[6] (a) X.B. Wang, J.D. Ranford, J.J. Vittal, J. Mol. Struct. 796 (1–3) (2006) 28–35;
(b) R. Ganguly, B. Sreenivasulu, J.J. Vittal, Coord. Chem. Rev. 252 (2008)
1027–1050.
[7] Y. Zou, W.-L. Liu, J.-L. Xie, C.-L. Ni, Z.-P. Ni, Y.-Z. Li, W.-J. Meng, Y.-G. Yao, J. Coord.
Chem. 57 (2004) 381–391.
[8] K. Dey, J. Sci. Ind. Res. 33 (1974) 76–94.
[9] J.M. Lassaletta, M. Alcarazo, R. Fernaandez, Chem. Commun. (2004) 298–299.
[10] (a) G.G. Mohamed, M.A. Zayed, S.M. Abdallah, J. Mol. Struct. 979 (1–3) (2010)
62–71;
O11 C10 O12
O18 C16 O15
O15 Ni13 N8
N14 Ni13 O12
N14 Ni13 O15
O12 Ni13 N8
C20 C19 N14
C6 C7 N8
119.07
119.41
117.86
116.45
96.10
96.21
134.79
138.28
131.19
131.54
119.49
119.97
97.93
97.69
107.35
109.66
C7 N8 C9
C19 N14 C17
O27 N26 O28
O31 N29 O30
C36 S35 C34
C39 S38 C37
C16 O15 Ni13
C10 O12 Ni13
(b) A.S. El-Tabl, F.A. El-Saied, W. Plass, A.N. Al-Hakimi, Spectrochim. Acta A 71
(2008) 90–99;
(c) H.F. Abd El-Halim, M.M. Omar, G.G. Mohamed, Spectrochim. Acta A 78 (2011)
36–44.
[11] B.K. Singh, P. Mishra, B.S. Garg, Spectrochim. Acta A 67 (2007) 719–729.
[12] C. Saxena, D.K. Sharma, R.V. Singh, Phosphorous Sulfur Silicon 85 (1993) 9.
[13] U.M. Rabie, J. Mol. Struct. 872 (2008) 113–122.
[14] (a) J. Sanmartin, F. Novio, A.M. Garcia-Deibe, M. Fondo, N. Bermejo, M.R.
Ocampo, Polyhedron 25 (2006) 1714–1722;
4. Conclusion
(b) I. Beloso, J. Castro, J.A. Garcia-Vazquez, P. Perez- Lourido, J. Romero, A. Sousa,
Polyhedron 22 (2003) 1099–1111;
Schiff base ligands derived from 2-nitrobenzaldehyde and
amino acids (glycine, methionine) acts as bidentate chelating
agents coordinates with transition metal ions to give square planar
environments, around the metal ion anchor. The complex crys-
tallizes in the triclinic/monoclinic/tetragonal/orthorhombic crystal
system. The metal chelates possess reasonable antimicrobial poten-
tial. The proposed structure of the complexes is given in Fig. 6.
(c) B.K. Singh, A. Prakash, D. Adhikari, Spectrochim. Acta
657–664.
A 74 (2009)
[15] S.J. Swamy, S. Pola, Spectrochim. Acta A 70 (2008) 929–933.
[16] N. Yoshida, K. Ichikawa, M.J. Shiro, Chem. Soc. Parkin. Trans. 2 (2000) 17–26.
[17] (a) K. Nokamoto, Infrared Spectra of Inorganic and Coordination Compounds,
Wiley Interscience, New York, 1975;
(b) L.J. Bellamy, The Infrared Spectra of Complex Molecules, 3rd ed., Chapman
and Hall, London, 1975.

B.K. Singh et al. / Spectrochimica Acta Part A 94 (2012) 143–151
151
[18] P.K. Shama, S.N. Dubey, Ind. J. Chem. 33(A) (1994) 1113.
[19] I. Sakiyan, N. Gunduz, T. Gunduz, Synth. React. Inorg. Met. Org. Chem. 31 (2001)
1175–1187.
[24] I.T. Ahmed, Trans. Met. Chem. 32 (2007) 674.
[25] J.C. Rasmussen, H. Toftlund, A.N. Nivorzhkin, J. Bourassa, P.C. Ford, Inorg. Chim.
Acta 251 (1996) 291–298.
[20] P.A. Vigato, S. Tamburini, Coord. Chem. Rev. 248 (2004) 1717.
[21] K. Shivakumar, Shashidhar, P. Vithal Ready, M.B. Halli, J. Coord. Chem. 61 (2008)
2274.
[26] K. Nakamoto, S.J. McCarthy, Spectroscopy & Structure of Metal Chelate Com-
pounds, John Wiley & Sons, USA, 1968.
[27] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1968.
[28] B.N. Figgis, Introduction to Ligand Fields, 1st ed., 1966, p. 263.
[29] R. Shirley, The CRYSFIRE system for Automatic Powder Indexing: Users Manual,
Lattice Press, 2002.
[22] G.G. Mohamed, M.M. Omar, M.M. Hindy, Spectrochim. Acta
1140–1150.
A 62 (2005)
[23] T. Ahamad, N. Nishat, S. Parveen, J. Coord. Chem. 61 (2008) 1963–1972.