Design, spectral characterization, DFT and biological studies of transition metal complexes of Schiff base derived from 2-aminobenzamide, pyrrole and furan aldehyde

Article abstract of DOI:10.1016/j.saa.2015.02.027

A series of two biologically active Schiff base ligands L¹, L² have been synthesized in equimolar reaction of 2-aminobenzamide with pyrrol-2-carboxaldehyde and furan-2-carboxaldehyde. The synthesized Schiff bases were used for complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar ratio of ligand: metal as 2:1. The characterization of newly formed complexes was done by ¹H NMR, UV-Vis, TGA, IR, mass spectrophotometry, EPR and molar conductivity studies. The thermal studies suggested that the complexes are more stable as compared to ligand. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies an octahedral geometry has been assigned for Co(II) and Ni(II) complexes and distorted octahedral geometry for Cu(II) complexes. All the synthesized compounds, were studied for their in vitro antimicrobial activities, against four bacterial strains and two fungal strains by using serial dilution method. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination.

Full text of DOI:10.1016/j.saa.2015.02.027

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Design, spectral characterization, DFT and biological studies of transition
metal complexes of Schiff base derived from 2-aminobenzamide, pyrrole
and furan aldehyde
b
c
Prateek Tyagi a, Sulekh Chandra a, , B.S. Saraswat , Deepansh Sharma
⇑
a Department of Chemistry, Zakir Husain Delhi College, University of Delhi, JLN-Marg, New Delhi 110002, India
b Department of Chemistry, School of Sciences, IGNOU, Maidan Garhi, New Delhi 110068, India
c Dairy Microbiology Division, National Dairy Research Institute, Karnal 132001, Haryana, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
TGA curve of ligand L1 and metal complexes 7–9.
ꢀ
Synthesis of 2-aminobenzamide
derived Schiff bases and their metal
complexes.
ꢀ
Characterization by physical, spectral
and analytical data.
ꢀ
ꢀ
DFT and TGA study.
L1, L2 coordinate in a tridentate
manner around M(II) ions.
In vitro antimicrobial and cytotoxicity
study of synthesized complexes.
ꢀ
a r t i c l e i n f o
a b s t r a c t
A series of two biologically active Schiff base ligands L1, L2 have been synthesized in equimolar reaction of
2-aminobenzamide with pyrrol-2-carboxaldehyde and furan-2-carboxaldehyde. The synthesized Schiff
bases were used for complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar
ratio of ligand: metal as 2:1. The characterization of newly formed complexes was done by 1H NMR, UV–
Vis, TGA, IR, mass spectrophotometry, EPR and molar conductivity studies. The thermal studies suggested
that the complexes are more stable as compared to ligand. In DFT studies the geometries of Schiff bases
and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On
the basis of the spectral studies an octahedral geometry has been assigned for Co(II) and Ni(II) complexes
and distorted octahedral geometry for Cu(II) complexes. All the synthesized compounds, were studied for
their in vitro antimicrobial activities, against four bacterial strains and two fungal strains by using serial
dilution method. The data also revealed that the metal complexes showed better activity than the ligands
due to chelation/coordination.
Article history:
Received 25 October 2014
Received in revised form 19 December 2014
Accepted 4 February 2015
Available online 13 February 2015
Keywords:
Schiff base
Ni(II)
Co(II) and Cu(II) complexes
Spectroscopic studies
Antimicrobial activity
DFT calculations
Ó 2015 Elsevier B.V. All rights reserved.
Introduction
possess diverse pharmacological properties, viz. antimicrobial,
analgesic, anti-inflammatory, anticancer, anticonvulsant, and anti-
In medicinal chemistry, benzamides derivatives are widely used
as antimicrobial agents. Benzamides derivatives are well known to
malarial to name a few [1–7]. The ambidentate nature of amide
group leads to the formation of regioisomers when forming a metal
complex, as it is possible to coordinate either through the nitrogen
or the oxygen atoms.
⇑
Corresponding author.
http://dx.doi.org/10.1016/j.saa.2015.02.027
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

2
P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
Heterocyclic compounds containing nitrogen, oxygen and sulfur
NH2
O
O
atoms constitute a class of compounds which shows momentous
biological activities [8]. Five membered heterocyclic compounds
in combination with aromatic moieties play a significant role in
designing a new class of molecules which shows significant biolo-
gical behavior and a different mechanism of action. Although a
large number of antibiotics are available, drug resistance against
various pathogens is the major cause of morbidity and mortality
throughout the world. The appearance of antibiotic resistant bacte-
rial strains makes it necessary that new class of antimicrobial
agent with substantial biological activity needs to be developed.
Schiff bases are potential antimicrobial agents and when
administered as their metal complexes, their antimicrobial activity
is further enhanced in comparison to the free ligand [9]. Metal
complexes containing amide functional groups confirm a wide
spectrum of biological activities [10–15] and are also used as drugs
in medicinal fields. Very limited research has been carried out on
the synthesis of transition metal complexes with oxygen and nitro-
gen donor Schiff base derivatives of 2-aminobenzamide. Therefore,
it is worthwhile to carry out the synthesis and study the spectral
properties of the Schiff bases derived from the reaction of
2-aminobenzamide with pyrrol-2-carboxaldehyde and furan-
2-carboxaldehyde. The goal of the study presented here is to
synthesize the Co(II, Ni(II) and Cu(II) metal complexes of Schiff
base produced from condensation of 2-aminobenzamide with
furan-2-carbaldehyde and pyrrol-2-carbaldehyde and to provide a
baseline of structural data using various spectroscopic techniques,
their thermal behavior, DFT studies and antimicrobial studies.
+
R
NH2
Reflux
Ethanol
NH2
O
N
R
,
L1 L2
N
O
N
N
NH2
NH2
M
O
X2
O
N
M
O
O
N
H2N
H2N
O
O
N
7-12
1-6
H
N
L1 R=
L2 R=
:
,
:
,
-1
-1
M = Co(II), Ni(II) and Cu(II), X =
Cl NO3
Scheme 1. Preparation of the ligands L1, L2 and their metal complexes 1–12.
(m, 1H, Ar AH), 7.68 (d, 1H, J = 7.96 Hz, Ar AH), 7.89 (d, 1H,
J = 4.8 Hz, furan AH), 8.09 (s, 2H, D2O exchangeable, ANH2),
8.19(d, 1H, J = 8 Hz, Ar AH), 8.97 (s, 1H, N@CH). Anal. Calcd. for
Experimental
Materials and methods
C
12H10N2O2 (214.22): C: 67.28; H: 4.71; N: 13.08; Found: C:
67.33%; H: 4.75%; N: 13.11%. Mass spectrum (ESI) [M]+ = 214.2.
All the chemicals were used of Anala R grade and received from
Sigma–Aldrich and Fluka. Metal salts were purchased from
E. Merck and used as received.
General procedure for the synthesis of metal complexes 1–12
General procedure for the synthesis of ligands L1–L2
Preparation of Co(II) complexes with (E)-2-(((1H-pyrrol-2-
yl)methylene)amino)benzamide L1 (1).
Ligand L1 was synthesized by adding ethanolic solution of pyr-
role-2-carbaldehyde (0.01 mol) to a magnetically stirred ethanolic
solution of 2-aminobenzamide (0.01 mol) and the mixture was
refluxed for 4 h through monitoring by TLC (Scheme 1). The reac-
tion mixture was cooled overnight, pale yellow product was pre-
cipitated out. It was filtered, washed and recrystallized with
ethanol. The same procedure was used for the synthesis of ligand
L2.
Hot ethanolic solution (15 mL) of CoCl2ꢂ6H2O (2 mmol) was
added drop wise to a magnetically stirred solution of (E)-2-(((1H-
pyrrol-2-yl)methylene)amino)benzamide L1 (4 mmol) in ethanol
(20 mL) (Scheme 1). The resultant mixture was refluxed for 10 h.
On keeping the resulting mixture overnight at 0 °C, the product
was separated out, which was filtered off, washed with cold etha-
nol, ether and dried under vacuum over P4O10. The same method
was used for the preparation of other metal complexes. Physical,
analytical and spectral data of ligand and metal complexes are
given in Table 1.
(E)-2-(((1H-pyrrol-2-yl)methylene)amino)benzamide L1
Yield: 82(%). Color (pale-yellow). M.p. 178–180 °C. IR (KBr,
cmꢁ1): 1612 (HC@N), 3240 (NH2), 3112 (NH), 1668 (amide CO).
1H NMR (DMSO-d6, d, ppm) 6.32–6.35 (m, 1H, pyrrole AH), 6.80
(d, 1H, J = 4.44 Hz, pyrrole AH), 7.14 (d, 1H, J = 4.48 Hz, pyrrole
AH), 7.30–7.33 (m, 1H, Ar AH), 7.52–7.55 (m, 1H, Ar AH), 7.82
(d, 1H, J = 7.2 Hz, Ar AH), 8.01 (s, 2H, D2O exchangeable, ANH2),
8.15 (d, 1H, J = 8.04 Hz, Ar AH), 8.93 (s, 1H, N@CH), 11.91 (s, 1H,
pyrrole ANH). Anal. Calcd. for C12H11N3O (213.24): C: 67.59; H:
5.20; N: 19.71; Found: C: 67.64%; H: 5.19%; N: 19.74%. Mass spec-
trum (ESI) [M]+ = 213.2.
Analysis
The carbon and hydrogen were analyzed on Carlo-Erba 1106
elemental analyzer. The nitrogen content of the complexes was
determined using Kjeldahl’s method. Molar conductance was mea-
sured on the ELICO (CM82T) conductivity bridge. ESI-MS spectra
were obtained using a VG Biotech Quattrro mass spectrometer
equipped with an elctrospray ionization source in the mass range
of m/z 100 to m/z 1000. IR spectra (CsBr) were recorded on FTIR
spectrum BX-II spectrophotometer. NMR spectra were recorded
with a model Bruker Advance DPX-300 spectrometer operating at
400 MHz using DMSO-d6 as a solvent and TMS as internal stan-
dard. The electronic spectra were recorded in DMSO on Shimadzu
UV mini-1240 spectrophotometer. Thermogravimetric analysis
(TGA) was carried out in dynamic nitrogen atmosphere
(E)-2-((furan-2-ylmethylene)amino)benzamides L2
Yield: 88(%). Color (light grey). M.p. 184–186 °C. IR (KBr, cmꢁ1):
1615 (HC@N), 3210 (NH2), 1022 (CAOAC), 1668 (amide CO). 1H
NMR (DMSO-d6, d, ppm) 6.61–6.64 (m, 1H, furan AH), 6.84 (d,
1H, J = 4.4 Hz, furan AH), 7.44–7.47 (m, 1H, Ar AH), 7.55–7.66

P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
3
Table 1
Physical measurements and analytical data of the ligand (L1, L2) and metal complexes (1–12).
No.
Molecular mass/molecular formula
m/z
MP (°C)
Yield (%)
Elemental analysis (%) found (calc.)
C
H
N
Ma
L1
L2
1
C12H11N3O [213.2]
C12H10N2O2 [214.2]
[Co(L1-H)2] [483.2]
213.21
214.24
483.32
178
184
230
82
77
69
67.45 (67.59)
67.24 (67.28)
59.60 (59.63)
5.17 (5.20)
4.73 (4.71)
4.15 (4.17)
19.76 (19.71)
13.11 (13.08)
17.35 (17.39)
–
–
12.17 (12.19)
C
24H20CoN6O2
[Ni(L1-H)2] [483.1]
24H20N6NiO2
[Cu(L1-H)2] [488.01]
24H20N6CuO2
[Co(L1-H)2] [483.2]
2
483.43
487.98
483.41
483.35
488.20
558.71
576.08
563.23
611.36
610.93
616.23
232
237
228
225
242
220
231
236
231
219
227
76
70
68
65
60
72
64
65
68
70
62
59.62 (59.66)
59.04 (59.07)
59.58 (59.63)
59.60 (59.66)
59.01 (59.07)
51.60 (51.63)
50.12 (50.04)
51.17 (51.21)
47.12 (47.15)
47.16 (47.17)
46.72 (46.80)
4.16 (4.17)
4.14 (4.13)
4.18 (4.17)
4.12 (4.17)
4.09 (4.13)
3.55 (3.61)
3.90 (3.85)
3.60 (3.58)
3.28 (3.30)
3.32 (3.30)
3.25 (3.27)
17.26 (17.39)
17.20 (17.22)
17.33 (17.39)
17.35 (17.39)
17.15 (17.22)
9.98 (10.04)
9.78 (9.73)
12.13 (12.15)
12.98 (13.01)
12.13 (12.19)
12.10 (12.15)
13.01 (13.02)
10.53 (10.56)
10.21 (10.19)
11.25 (11.29)
9.61 (9.64)
C
3
C
4
C
24H20CoN6O2
5
[Ni(L1-H)2] [483.1]
C24H20N6NiO2
6
[Cu(L1-H)2] [488.01]
C
24H20N6CuO2
7
[Co(L2)2]Cl2 [558.2]
C
24H20Cl2CoN4O4
8
[Ni(L2)2]Cl2.H2O [576.06]
C24H22Cl2N4NiO5
9
[Cu(L2)2]Cl2 [562.8]
9.91 (9.95)
C
24H20Cl2CuN4O4
[Co(L2)2](NO3)2 [611.4]
24H20CoN6O10
[Ni(L2)2](NO3)2 [611.1]
24H20N6NiO10
[Cu(L2)2](NO3)2 [616]
24H20CuN6O10
10
11
12
13.78 (13.75)
13.71 (13.75)
13.68 (13.64)
C
9.55 (9.60)
C
10.28 (10.32)
C
a
M = Co(II), Ni(II), Cu(II).
(30 ml/min) with a heating rate of 10 °C/min using a Schimadzu
TGA-50H thermal analyzer. EPR spectra of the Cu(II) complexes
were recorded as polycrystalline sample at room temperature on
E4-EPR spectrometer using the DPPH as the g-marker.
suspension. The working inoculums of aforementioned different
microorganisms containing 105 cfu/mL suspension was prepared
by diluting the 108 cfu/mL suspension, 103 times in Brain heart
infusion broth.
Preparation of antimicrobial suspension (1 mg/ml)
Dissolved 10 mg of each compound in 10 mL of dimethyl sul-
foxide to achieve 1 mg/mL concentration.
DFT calculations
The DFT calculations were performed using the B3LYP three
parameter density functional, which includes Becke’s gradient
exchange correction [16], the Lee, Yang, Parr correlation functional
[17] and the Vosko, Wilk, Nusair correlation functional [18]. The
gas phase geometries of Ligand L1, L2 and metal complexes (1–3)
were fully optimized with respect to the energy using the 6-
31+g(d,p) basis set using the Gaussian 09W suite [19]. Net atomic
charges had been obtained using natural bond orbital (NBO) analy-
sis of Weinhold and Carpenter [20].
Preparation of dilutions
In all, for ligands L1, L2, their metal complexes (1–12) and stan-
dard antimicrobial i.e., Ciprofloxacin for antibacterial and Flucona-
zole for antifungal, 28 tubes of 5 mL capacity were arranged in five
rows with each row containing 6 tubes. 1.9 mL of brain heart infu-
sion broth was added in the first tube in each row and then 1 mL in
the remaining tubes. Now, 100 lL of antimicrobial suspension dis-
solved in dimethyl sulfoxide was added to the first tube in each
row and then after mixing the content, 1 mL was serially trans-
ferred from these tubes to the second tube in each of the rows.
The contents of the second tube of each of the rows were mixed
and transferred to the third tube in each of the rows. This serial
dilution was repeated till the last tube in each of the rows. This
provided antimicrobial compounds concentrations of 50, 25, 12.5,
6.25, 3.125, 1.5625 mg/mL in the first to sixth tube separately in
each row. Finally, 1 mL of 105 cfu/mL of pathogenic strains suspen-
sion was added to the first, second, third, fourth and fifth rows of
tubes respectively. Additionally with the test samples and standard
drug (Ciprofloxacin/Fluconazole), the inoculum control (without
antimicrobials) and broth control (without antimicrobials and
inoculum) were also prepared. All the test tubes were then incu-
bated for 18 h at 37 °C.
Antimicrobial studies
The newly synthesized Schiff bases L1, L2 and their metal com-
plexes (1–12) were screened for their antimicrobial activity.
Antimicrobial study was assessed by Minimum Inhibitory Concen-
tration (MIC) by the serial dilution method [21]. For this, Pseu-
domonas aeruginosa ATCC 15442, Escherichia coli MTCC 143,
Salmonella typhi MTCC 733, Bacillus cereus ATCC 11770, Candida
albicans MTCC 183 and Aspergillus niger MTCC 972 microorganisms
were used to investigate the antimicrobial activity. Standard drugs
used for the antibacterial and antifungal activities were
Ciprofloxacin and Fluconazole respectively. Colonies of microor-
ganisms were picked off a fresh isolation plate and inoculated in
corresponding tubes containing 5 mL of brain heart infusion broth.
The broth was incubated for 6 h at 37 °C. The MC Farland No. 5
standard was prepared by adding 0.05 mL of 1% w/v BaCl2ꢂ2H2O
in Phosphate Buffered saline (PBS) to 9.95 mL of 1% v/v H2SO4 in
PBS. The growth of all the cultures was adjusted to Mc Farland
No. 5 turbidity standard using sterile PBS to achieve 108 cfu/mL
In vitro cytotoxicity
In vitro cytotoxic activity of synthesized ligands L1, L2 and their
metal complexes 1–12 were studied using the protocol of Meyer

4
P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
et al. Brine shrimp (Artemia salina leach) eggs were hatched in a
shallow rectangular plastic dish (22 ꢃ 32 cm), filled with artificial
seawater, which was prepared with commercial salt mixture and
double distilled water [22]. An unequal partition was made in
the plastic dish with the help of a perforated device. Approximately
50 mg of eggs were sprinkled into the large compartment, in dark
while the matter compartment was opened to ordinary light. After
2 days nauplii were collected by a pipette from the side in ordinary
light. A sample of the test compound was prepared by dissolving
20 mg of each compound in 2 mL of DMSO. From this stock solu-
1H NMR spectra
The 1H NMR spectra have been recorded for ligand L1 and L2.
The spectra of ligand L1 (Fig. 2) displayed azomethine (AHC@N)
proton as a singlet at 8.93 ppm. The pyrrole protons appeared as
a set of doublet and multiplet in the region 7.14–6.32 ppm.
Similarly, aromatic protons appears as a set of doublets and multi-
plets in the range 8.15–7.30 ppm. Pyrrole ANH proton appear as a
singlet in 11.91 ppm for the ligand L1. Similarly, in the spectra of
the ligand L2 the azomethine (AHC@N) proton appeared as a sin-
glet at 8.97. The appeared signals of all the protons of the ligand
L1, L2 were found as to be in their expected region.
tions 500, 50 and 5 lg/mL were transferred to 9 vials (three for
each dilutions were used for each test sample and Ld50 is the mean
of three values) and one vial was kept as control having 2 mL of
DMSO only for determine its any participating role. The solvent
was allowed to evaporate overnight. After 2 days, when shrimp lar-
vae were ready, sea water (1 mL) and 10 shrimps were added to
each vial (30 shrimps/dilution) and the volume was adjusted with
sea water to 5 mL per vial. After 24 h the number of survivors was
counted. Data were analyzed by Finney computer program to
determine the LD50 values.
IR spectra
The characteristic bands of IR spectra of ligands L1, L2 and their
metal(II) complexes are reported in order to confirm the binding
mode of the Schiff base ligands to the corresponding metal ion.
Both ligands possessed potential donor sites like azomethine link-
age (AC@N), amide group (ACONH2), furan (O) and pyrrole (ANH)
groups which have tendency to coordinate with metal ions
(Table 2). Peak corresponding to
was absent in IR spectra of L1 and, instead, a new band assigned
to azomethine
(HC@N) linkage appeared at 1612 cmꢁ1 confirming
the formation of Schiff base [24]. Similarly, the peak at 1615 cmꢁ1
in L2 corresponds to (HC@N) linkage. The IR spectrum of the L1, L2
shows peaks in range 3210–3240 due to the ANH2 vibrations [25].
The peak at 3112 cmꢁ1 in ligand L1 is assigned to (ANH) group of
pyrrole ring [26]. Similarly, the band at 1022 cmꢁ1 in ligand L2 cor-
m(C@O) stretching vibrations
Results and discussion
m
The Schiff base L1 (Scheme 1) was prepared by refluxing in etha-
nol (20–25 mL) an equimolar (0.01 mol) amount of 2-aminobenza-
mide and pyrrol-2-carboxaldehyde. The same method was used for
the preparation of the ligand L2. The structure of Schiff bases thus
formed was established by IR, 1H NMR, Mass spectrophotometry
and CHN analysis. The synthesized Schiff bases were soluble in
DMF, DMSO and in methanol, ethanol on heating only. The compo-
sition of the ligands was consistent with their NMR, IR, mass spec-
tral and CHN data.
m
responds m(CAOAC) stretching vibration of the furan ring [27]. The
comparison of the IR spectra of Schiff base ligands with corre-
sponding metal complexes gave clue of binding modes of the Schiff
base ligand to the corresponding metal ion. The IR band due to
azomethine AN shifts to lower frequency (14–22 cmꢁ1) 1590–
1601 cmꢁ1, representing the coordination of azomethine AN in
the complex formation [28]. This is also confirmed by the appear-
ance of new band in spectra of metal complexes in the range of
The synthesized Schiff bases was further used for the com-
plexation with Co(II), Ni(II) and Cu(II) metal ions, using the follow-
ing metal salt: CoCl2ꢂ6H2O for complexes 1 and 7, NiCl2ꢂ6H2O for
complexes 2 and 8, CuCl2 for complexes 3 and 9, Co(NO3)2ꢂ6H2O
for complexes 4 and 10, Ni(NO3)2ꢂ6H2O for complexes 5 and 11
and Cu(NO3)2ꢂ3H2O for complexes 6 and 12. The obtained com-
plexes are microcrystalline solids which are stable in air and
decompose above 219 °C (Table 1). They are insoluble in common
organic solvents such as acetone and chloroform, sparingly soluble
in ethanol, methanol and completely soluble in DMF and DMSO.
The molar conductance of the soluble complexes in DMF showed
468–492 cmꢁ1, which has been assigned to the
m(MAN) bond
[29]. The
m(C@O) stretching vibration of amide group at
1668–1670 cmꢁ1 in free ligands shifts to a lower side (1652–
1658 cmꢁ1) in all metal complexes, indicating the coordination of
H
N
H
N
values indicating that complexes 1–6 (11–14) ohmꢁ1 cm2 molꢁ1
)
N
N
are non-electrolytes and complexes 7–12 (98–114) ohmꢁ1 cm2
molꢁ1) are electrolytic in nature [23]. Physical measurements
and analytical data of the complexes 1–12 are given in Table 1.
m/z 92.10
m/z 106.13
O
N
O
N
Mass spectra
NH2
NH2
H
N
The ESI mass spectrum of ligand showed a molecular ion peak
at m/z = 231.2 amu corresponding to [M]+, which confirms the pro-
posed formula [C12H11N3O]+ and its base peak was observed at m/z
198. Similarly the molecular ion peak of ligand L2 shows a molecu-
lar ion peak at 214.1 and its base peak was observed at m/z 199.
Fragmentation pattern of ligand L1 is shown as Fig. 1. The mass
spectrum of the ligand L1 (Fig. 2) shows a series of peaks at
233.2, 214, 186, and 130 corresponding to various fragments. The
intensities of these peaks give the idea of the stability of the frag-
ments. The fragmentation pattern followed the cleavage of C@N,
CAN and CAC bonds. The mass spectrum of the metal complexes
1–12 showing the fragmentation model beside the m/z peak value
are given in Table 1.
m/z 148.16
m/z 213.24
m/z 52.08
O
H
N
H
N
N
N
m/z 170.22
m/z 198.23
Fig. 1. Mass fragmentation pattern of ligand L1.

P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
5
Fig. 2. (a) NMR spectra of L1 and (b) mass spectrum of ligand L1.
Table 2
indicates the non involvement of amido-N atom in complex
formation.
Important infrared spectral bands (cmꢁ1) and their assignments.
In complex 8, a broad band at 3430 cmꢁ1 and a band at
Compound
m(HC@N)
m
(CAOAC)
m
(C@O)
m(MAO)
m(MAN)
1632 cmꢁ1 corresponds to the stretching (
m-OH) and bending
L1
L2
1
2
3
4
5
6
7
8
9
10
11
12
1612
1615
1594
1597
1592
1590
1601
1597
1594
1599
1595
1593
1590
1598
–
1022
1668
1670
1656
1654
1652
1658
1652
1654
1655
1658
1653
1655
1658
1652
–
–
(d(H2O)) vibrations of uncoordinated water molecule. The appear-
ance of sharp band in range 1382–1388 cmꢁ1 in complexes 9–12,
confirms the uncoordinated behavior of the nitrate ion. The NAH
vibration band at 3112 cmꢁ1 in IR spectra of the ligand L1 disap-
peared in spectra of metal complexes 1–6 which indicates the
deprotonation of –NH moiety during complex formation. Also,
474
468
482
488
492
476
486
485
487
475
479
480
490
512
516
502
518
522
524
514
517
520
518
522
524
m
(CAOAC) ring vibration at 1022 cmꢁ1 in
1012
1008
1010
1014
1009
1008
the specific band of
ligand shifts to (1008–1014 cmꢁ1) in metal complexes 7–12 [27].
This is also supported by the appearance of new band in range of
502–524 cmꢁ1, which has been assigned to
m(MAO) bond [30].
Based on these observations it may be appreciated that the ligand
L1 coordinate uninegative tridentately around the Co(II), Ni(II) and
Cu(II) ion. However, ligand L2 coordinates neutral tridentately
around Co(II), Ni(II) and Cu(II) ion.
the ligands through the oxygen of amide group. The same is also
supported by the appearance of band in region of 502–524 cmꢁ1
which corresponds to (MAO) bond [30]. A noteworthy point in
the IR spectra of all metal complexes is the position of (NAH)
stretching vibration of NH2 of amide group. Sharp bands at
3210–3240 cmꢁ1 for all complexes have been found to be unal-
tered and are in the same position as in ligand L1 and L2 [25], which
,
Conductance and magnetic susceptibility measurements
m
m
The molar conductance values of metal complexes 1–12 were
obtained in DMF as a solvent at room temperature and their results
in (Oꢁ1 cm2 molꢁ1) are recorded as in Table 3. Generally, higher
molar conductance values are indicative of the electrolytic nature

6
P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
of the metal complexes and lower values shows their non-elec-
trolytic nature. The molar conductance of the metal complexes in
DMF showed values indicating that complexes 1–6 (11–14 ohmꢁ1
ranges and percentage mass losses of the decomposition reaction
are given in Table 4 together with evolved moiety and the theore-
tical percentage mass losses. The TG curve of ligand L1, refers to
two stages of mass losses at temperature ranges from 150 to
460 °C. These stages involved mass losses of 100.0% and mass loss-
es may be due to the successive losses of C12H11N3O at the given
temperature ranges [32]. All metal complexes undergo decomposi-
tion in two or three stages. In the first stage, a peak corresponding
to the loss of uncoordinated anion (chloride), followed with subse-
quent removal of the five membered heterocyclic ring in the sec-
cm2 molꢁ1
) are non-electrolytes and complexes 7–12 (98–
114.4 ohmꢁ1 cm2 molꢁ1) are electrolytic in nature. The determined
magnetic moment (BM) values of all the metal complexes, 1–12 at
room temperature were recorded in Table 3. The magnetic
moment values of Co(II) complexes were found in the range of
4.82–4.99 BM suggesting the Co(II) complexes as high-spin with
three unpaired electrons in an octahedral environment. The Ni(II)
complexes exhibited magnetic moment values in the range of
2.91–2.98 BM representative of two unpaired electrons per Ni(II)
ion suggesting these complexes to have octahedral geometry
[31]. The obtained magnetic moment values 1.93–1.96 BM for
Cu(II) complexes are indicative of one unpaired electron per Cu(II)
ion for d9-system suggesting spin-free distorted octahedral
geometry.
ond stage. In the third stage, there was
a loss in mass
corresponding to the decomposition of primary 2-aminobenza-
mide moiety and as a final stage; it left air stable metal oxide as
a residue.
EPR spectra
EPR spectra of Cu(II) complexes were recorded at room tem-
perature as polycrystalline sample, on X band at frequency of
9.1 GHz under the magnetic-field strength of 3000 G. The analysis
Electronic spectra
The electronic absorption spectra of the Co(II), Ni(II) and Cu(II)
complexes in DMSO were recorded at room temperature and the
band positions of the absorption maxima, band assignments and
the proposed geometry are listed in Table 3. The electronic spectra
of Co(II) complexes generally showed three absorption bands in
of Cu complexes gives g = 2.185–2.297, g\ = 2.052–2.098 and
k
G = 3.03–3.56 (Table 3). The observed g values for the complex
k
are less than 2.3 in agreement with the covalent character of the
metal ligand bond. The trend g > g\ > 2.0023 observed for the
k
complex indicates that unpaired electron is localized in dx2ꢁy2 orbi-
tal of the Cu(II) ion and the spectral features are a characteristic of
axial symmetry. Thus, a tetragonal geometry is confirmed for the
the region at 9786–9892, 17,334–17,759 and 29,726–
4
30,150 cmꢁ1 which assigned to transitions 4T1g ? 4T2g(F), T1g
?
4A2g(F) and 4T1g ? 4Tg(P), showing an octahedral geometry around
the Co(II) ion. The electronic spectral data of Ni(II) complexes
showed d–d bands in the region 10,785–11,580, 15,275–16,365
and 23,210–25,635 cmꢁ1 [25] respectively, to assigned the transi-
aforesaid complex [33]. G = (g ꢁ 2)/(g\ ꢁ 2), which measures the
k
exchange interaction between the metal centers in a polycrys-
talline solid, has been calculated. According to Hathaway, if G > 4,
the exchange interaction is negligible, but G < 4 indicates consider-
able exchange interaction in the solid complexes [34]. The ‘‘G’’
value for Cu complexes reported in this paper, is <4 indicating
the exchange interaction in solid complexes.
tions A2g(F) ? 3T2g(F), A2g(F) ? 3T1g(F) and A2g(F) ? 3T2g(F),
which are characteristic of Ni(II) in octahedral geometry. Electronic
spectra of Cu(II) complexes show the d–d transition bands in the
range 12,188–15,479, 18,621–19,132 and 24,402–27,322 cmꢁ1
[24].These bands correspond to 2B1g ? 2A1g (dx2ꢁy2 ? dz2),
3
3
3
Geometry optimization and NBO analysis
2B1g ? 2B2g (dx2ꢁy2 ? dxy) and 2 1g ? 2Eg (dx2ꢁy2 ? dxz, dyz) transi-
B
tions, respectively. On the basis of electronic transitions, a distort-
ed octahedral geometry is suggested for Cu(II) complexes.
Geometry optimization was done using B3LYP functional with
6-31+g(d,p) basis sets as incorporated in the Gaussian 09 W pro-
gramme in gas phase. The fully optimized geometries of the ligand
L1 and complexes 1–3 are shown in Fig. 4. The numbering scheme
for ligand L1, and complexes 1–3 are given in Scheme 2. The mole-
cular structure of complex 1 shows octahedral geometry around
the Co(II) center as revealed from the calculated bond lengths
and bond angles (Table 5). The C1AO1, C7AN1, N1AC8 and C9AN2
bond lengths become slightly longer in complexes as ligand L1
coordinates via azomethine nitrogen, oxygen of amide and by the
deprotonated nitrogen of pyrrole ring. The C1@O1 bond distance
in all complexes become longer due to the formation of MAO bond
which make the C1@O1 bond weaker. The pyrrole moiety is bent
Thermal analysis
Thermal behavior of the complexes has been studied using
Thermogravimetric analysis from ambient temperature to 800 °C
in nitrogen atmosphere. Based on the thermograms; decomposi-
tion stages, temperature ranges, decomposition product as well
as weight loss percentages of the complexes were calculated. The
TG curves were redrawn as% mass loss vs. temperature (TG) curves.
Typical TG curves for Co(II), Ni(II) and Cu(II) complexes (7–9) in
comparison to ligand L1 are presented in Fig. 3. The temperature
Table 3
Conductivity, magnetic, electronic spectra EPR spectra of metal complexes 1–12.
No.
OM (Oꢁ1 cm2 molꢁ1
)
BM (leff
)
kmax (cmꢁ1
)
g
g\
G
k
1
2
3
4
5
6
7
8
9
11.2
13.8
12.6
14.2
12.8
13.2
99.4
98
112.2
108.6
114.4
110.8
4.78
2.93
1.94
4.72
2.91
1.93
4.89
2.98
1.95
4.83
2.93
1.96
9870, 17,542, 29,918
10,870, 15,275, 25,635
14,792, 18,621, 25,712
9786, 17,559, 29,726
10,785, 15,718, 24,710
15,479, 18,998, 24,402
9892, 17,334, 30,150
11,340, 16,122, 23,210
12,188, 19,054, 25,178
9810, 17,612, 30,012
11,580, 16,365, 24,922
13,970, 19,132, 27,322
–
–
–
–
–
–
3.03
–
–
3.56
–
–
3.55
–
–
2.297
–
–
2.232
–
–
2.185
–
–
2.098
–
–
2.065
–
–
2.052
–
–
10
11
12
2.242
2.075
3.22

P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
7
Fig. 3. TGA curve of (a) ligand L1, (b) complex 7, (c) complex 8, and (d) complex 9.
Table 4
Thermal analysis data the ligand (L1) and metal complexes (7–9).
Comp. No.
Molecular formula
Stages
Temp (°C)
Decomposition species
Residual species
Mass loss (%)
Found
Calc.
100
L1
7
C12H11N3O
[Co(L2)2]Cl2
1st
2nd
1st
2nd
3rd
1st
2nd
3rd
1st
155–265
265–480
150–250
250–415
415–680
140–220
220–450
450–715
160–465
465–690
C4H4N
C8H7N2O
Cl2
–
100
CoO
13.46
13.04
14.22
13.42
12.96
14.13
C24H20Cl2CoN4O4
C8H8O2
C16H12N4O
HCl, 1/2 O2
C8H9O2
C16H12N4O
C10H8O2N2Cl2
C14H12N2O
8
9
[Ni(L2)2]Cl2ꢂH2O
NiO
CuO
C24H22Cl2N4NiO5
[Cu(L2)2]Cl2
24H20Cl2CuN4O4
C
2nd
0
out of the coordination plane and move far from Co(II) ion, which
results in the slight elongation of CoAN bond length. Similarly, the
C@O bond of the amide group moves out of the plane, which
results in increase of Co@O bond length. The CoAN and CoAO bond
lengths in complex 1 lies in the range of 2.012–2.014 and 2.122–
2.195 Å, respectively. This elongation in CoAN and CoAO bond
lengths caused a slight distortion from the regular octahedral
geometries. The bond angles in the coordination sphere of Co(II)
complexes are found approximately near to the perpendicular
value.
Similar bonding behavior is observed in case of complex 2 hav-
ing Ni(II) as metal center. All the bond lengths and bond angles
have very close values as compared to complex 1. However, com-
plex 3 having Cu(II) metal center shows a large degree of distortion
from the regular octahedral geometry. It is because of this
distortion that the axial CuAO1 and CuAO1 elongates to 2.456
0
and 2.584 Å, respectively. Also the CuAN1 and CuAN1 bond
lengths elongates to 2.364 and 23.93 Å, respectively. This elonga-
tion in bond lengths causes a change in the bond angle values of
coordination sphere. The bond angles N1ACuAN2 and N1 ACuAN2
reduces 69.23° and 72.12° respectively. The bond angle O1ACuAO1
is found to be 164.76°. The bond lengths and the bond angles with-
in the pyrrole and benzene ring do not change significantly on
coordination with metal ion.
Natural Bond Orbital analysis was done on complexes 1–3 and
the results revealed that the electronic configuration of Co(II) in
complex 1 is: [core]4s0.013d6.584p0.765s0.195p0.01, 18 core electrons,
7.55 valence electrons, and 0.023 Rydberg electrons with 25.573
electrons as a total electrons that is in agreement with the calculat-
ed natural charge (+01.421 e) on cobalt atom. Similarly, the elec-
0
0
0

8
P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
Fig. 4. Geometry optimized structures of (a) ligand L1, (b) complex 7, (c) complex 8, and (d) complex 9 (colour code: H = White, C = Grey, N = Blue, O = red, Co = Grey,
Ni = Silver Grey, Cu = Pink). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
C5
C10
C6
C7
C11
C8
C9
C4
C3
N1
C12
N2
C2
C5
C6
C7
C4
C3
C1
O1
C10
NH2
C8
M
H2N
O1'
C9
N2
C1'
C2'
N1
C11
C2
C12' N2'
C3'
C4'
N1'
C12
C1
C7'
C9'
C11
'
C8'
C10
'
H2N
H
C6'
O1
C5'
(a)
(b)
Scheme 2. Numbering scheme of the optimized structures (a) ligand L1 and (b) complexes 7–9.
tronic configuration of Ni(II) in complex 2 is [core]4s0.013d7.85
ꢁ0.2278 and 0.0034 hartree, respectively. The HOMO of the ligand
is concentrated on carbonyl oxygen of amide group, while LUMO is
concentrated on C1@O1 amide bond of 2-aminobenzamide.
The 0.020 hartree isovalue contours for the HOMO and LUMO are
displayed in Fig. 5. The lower HOMO energy values shows that
the molecule electron donating ability is weak. On contrary, the
4p0.725s0.015p0.02: 18 core electrons, 8.61 valence electrons (on
4s, 3d, 4p, 5s and 5p atomic orbitals), and 0.015 Rydberg electrons
with 26.625 as a total electrons and +1.375 e as a natural charge.
The electronic configuration of Cu(II) in complex 3 is [core]4s0.31
3d8.904p0.985p0.01: 18 core electrons, 10.2 valence electrons (on
4s, 3d, 4p and 5p atomic orbitals), and 0.017 Rydberg electrons
with 28.217 as a total electrons and +0.780 e as a natural charge.
We also calculated the energies for Highest occupied molecular
orbital (HOMO) and Lowest occupied molecular orbital (LUMO).
The calculated energies of the HOMO and LUMO for ligand are
higher HOMO energy implies that the molecule is
a good
electron donor. LUMO energy represent the ability of
a
molecule receiving electrons. On the basis of the above discussion
following (Fig. 6) structures can be proposed for the synthesized
complexes.

P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
9
Table 5
Antimicrobial study
Optimized geometry of the ligand and metal complexes (bond lengths in Angstroms;
bond angles in degrees).
After incubation, the tubes showing no visible growth were
measured to be demonstrating the minimum inhibitory concentra-
tion(MIC). Inoculum control showed growth, whereas the broth
control observed no growth. Among all the screened samples for
antimicrobial activity, 1, 6, 7, and 12 observed as significant
antimicrobial agents at quiet low concentration and could be con-
sidered as broad spectrum antimicrobial compounds (Table 6).
Whereas metal complexes 2–5 and 8–11 showed moderate activity
against all the tested pathogens. Whereas the standard drug was
effective against all the pathogens at the concentration of
1.5625–3.1250 mg/mL. The biological activity results showed that
majority of the Schiff base ligands possessed increased activity
upon coordination with different metal ions.
Parametersa
Ligand L1
Complex 1b
Complex 2c
Complex 3d
C1AC2
C1AN3
C1AO1
C2AC7
C7AN1
N1AC8
C8AC9
C9AN2
MAO1
MAN1
MAN2
1.510
1.376
1.245
1.419
1.381
1.291
1.434
1.391
–
–
–
–
–
–
–
–
–
–
–
–
–
1.452
1.360
1.299
1.431
1.397
1.341
1.397
1.412
2.012
2.122
2.195
2.014
2.127
2.193
85.45
82.54
88.87
82.52
84.19
84.64
177.16
1.453
1.364
1.301
1.428
1.399
1.343
1.395
1.420
2.237
2.167
2.210
2.234
2.198
2.234
82.76
83.24
85.43
81.29
85.14
82.23
172.35
1.451
1.368
1.300
1.432
1.403
1.349
1.398
1.422
2.456
2.364
2.243
2.584
2.393
2.297
87.45
69.23
84.32
72.12
78.74
81.34
164.76
0
MAO1
0
MAN1
0
MAN2
\N1MO1
\N1MN2
Cytotoxic bioassay
0
\O1MN2
The synthesized ligands L1, L2 and their metal complexes 1–12
were screened for their cytotoxicity (Brine Shrimp bioassay) using
the protocol of Meyer et al. [35]. The cytotoxic data recorded in
Table 7 revealed that all compounds were considered as almost
inactive in this assay. It was interesting to note that the metal com-
plexes showed potent cytotoxicity as compared to the ligands. This
activity relationship may serve as a basis for future development of
certain cytotoxic agents in clinical practices.
0
0
\N1 MN2
0
\N2MO1
0
\N1MO1
0
\O1MO1
a
b
c
Scheme 1 for numbering.
M@Co.
M@Ni.
M@Cu.
d
Fig. 5. Plot of HOMO (a) and LUMO (b) of ligand L1.
C5
C10
C6
C7
C5
C10
C6
C7
C11
C8
C9
C11
C4
C3
C8
C9
C4
C3
N1
C12
N1
N2
C12
C2
N2
C2
C1
O1
C1
O1
X2.nH2O
NH2
M
H2N
NH2
O1'
M
H2N
O1'
C1'
C2'
C1'
C2'
C12' N2'
C12' N2'
C3'
C4'
N1'
C3'
C4'
N1'
C7'
C9'
C11
'
C7'
C9'
C11
'
C8'
C8'
C10'
C10
'
C6'
C6'
C5'
C5'
7: X=Cl-1, n=1, 8-9; X=Cl-1, 10-12: X=NO3-1
M = Co, Ni, Cu
1-6
Fig. 6. Proposed structure of the newly obtained metal complexes.

10
P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
Table 6
MIC (minimum inhibitory concentration) values of L1, L2 and metal complexes 1–12 (mg/mL).
Compounds
Pathogenic strains
P. aeruginosa
E. coli
S. typhi
B. cereus
C. albicans
A. niger
Ciprofloxacina
Fluconazoleb
L1
L2
1
2
3
4
5
6
7
8
9
10
11
12
12.500
12.500
3.1250
6.2500
12.500
6.2500
6.2500
1.5625
3.1250
6.2500
3.1250
6.2500
12.500
3.1250
12.500
6.2500
1.5625
3.1250
6.2500
6.2500
0.1250
3.1250
3.1250
12.500
6.2500
1.5625
6.2500
1.5625
6.2500
6.2500
3.1250
6.2500
3.1250
3.1250
6.2500
3.1250
3.1250
6.2500
6.2500
3.1250
6.2500
3.1250
6.250
12.500
3.1250
1.5625
6.2500
3.1250
6.2500
3.1250
12.500
3.1250
1.5625
3.1250
6.2500
1.5625
12.250
12.250
12.500
12.500
6.2550
3.1250
6.2550
12.500
6.2550
6.2550
12.500
6.2550
12.500
6.2500
12.250
12.250
3.1250
6.2500
12.250
6.2500
3.1250
6.2500
6.2500
3.1250
12.250
6.2500
6.2500
3.1250
1.5625
3.1250
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
1.5625
6.2550
6.2550
6.2550
3.1250
3.1250
6.2550
6.2550
3.1250
3.1250
6.2550
3.1250
3.1250
6.2550
3.1250
a
Standard antibacterial drug.
Standard antifungal drug.
b
Table 7
Brine shrimp bioassay data of the ligands L1, L2 and their metal complexes 1–12.
References
[1] (a) V. Alexander, Chem. Rev. 95 (1995) 273;
Compounds
LD50 (M/mL)
Compounds
LD50 (M/mL)
(b) A.D. Granvoskii, A.L. Nivorozhkin, V.I. Minkin, Coord. Chem. Rev. 126
(1993) 1.
[2] D. Carbonnelle, F. Ebstein, C. Rabu, J.Y. Petit, M. Gregoire, F. Lang, Eur. J.
Immunol. 35 (2005) 546.
[3] K. Suzuki, H. Nagasawa, Y. Uto, Y. Sugimoto, K. Noguchi, M. Wakida, K.
Wierzba, T. Terada, T. Asao, Y. Yamada, K. Kitazato, H. Hori, Bioorg. Med. Chem.
13 (2005) 4014.
[4] M.V. Simonini, L.M. Camargo, E. Dong, E. Maloku, M. Veldic, E. Costa, A.
Guidotti, Proc. Natl. Acad. Sci. U.S.A. 103 (2006) 1587.
L1
L2
1
2
3
>2.16 ꢃ 10ꢁ3
>1.98 ꢃ 10ꢁ3
>2.94 ꢃ 10ꢁ4
>3.16 ꢃ 10ꢁ3
>2.99 ꢃ 10ꢁ4
>4.35 ꢃ 10ꢁ4
>3.23 ꢃ 10ꢁ4
6
7
8
9
10
11
12
>4.65 ꢃ 10ꢁ3
>4.12 ꢃ 10ꢁ4
>3.76 ꢃ 10ꢁ4
>2.78 ꢃ 10ꢁ4
>3.11 ꢃ 10ꢁ4
>3.23 ꢃ 10ꢁ4
>3.87 ꢃ 10ꢁ4
4
5
[5] E.A. Sener, K.K. Bingol, I. Oren, O.T. Arpaci, I. Yacin, N. Altanlar, Farmaco 55
(2000) 469.
[6] Y.F. Xiang, C.W. Qian, G.W. Xing, J. Hao, M. Xia, Y.F. Wang, Bioorg. Med. Chem.
Lett. 22 (2012) 4703.
[7] Y. Nagaoka, T. Maeda, Y. Kawai, D. Nakashima, T. Oikawa, K. Shimoke, T.
Ikeuchi, H. Kuwajima, S. Uesato, Eur. J. Med. Chem. 41 (2006) 697.
[8] D.W. Young, Heterocyclic Chemistry, 1st ed., Longman group Ltd., London,
1975.
[9] (a) E.M. Hodnett, W.J. Dunn, J. Med. Chem. 13 (1970) 768–770;
(b) D. Kessel, A.F.A. Sayyab, E.M.H. Jaffar, A.H.H.A. Lanil, Iraq. J. Sci. 22 (1981)
312;
(c) J. Chakraborty, R.N. Patel, J. Ind. Chem. Soc. 73 (1996) 191.
[10] A.P. Singh, N.K. Kaushik, A.K. Verma, R. Gupta, Ind. J. Chem. 50 (2011) 474.
[11] A.P. Singh, N.K. Kaushik, A.K. Verma, G. Hundal, R. Gupta, Eur. J. Med. Chem. 44
(2009) 1607.
[12] F. Lebon, M. Ledecq, Z. Benatallah, S. Sicsic, R. Lapouyade, O. Kahn, A. Garcon,
M.R. Ravaux, F. Durant, J. Chem. Soc. Perkin Trans. 2 (1999) 795.
[13] F. Lebon, M. Ledecq, M. Dieu, C. Demazy, J. Remacle, R. Lapouyade, O. Kahn, F.
Durant, J. Inorg. Biochem. 86 (2001) 547.
[14] F. Lebon, E. de Rosny, M. Reboud-Ravaux, F. Durant, Eur. J. Med. Chem. 33
(1998) 733.
[15] A. Mishra, N.K. Kaushik, A.K. Verma, R. Gupta, Eur. J. Med. Chem. 43 (2008)
2189–2196.
[16] M.A.D. Becke, Phys. Rev. A 38 (1988) 3098.
[17] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[18] S.H. Vosko, L. Wilk, M. Nusair, Can. J. Chem. 58 (1980) 1200.
[19] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery, Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian Inc., Wallingford, CT, 2009.
[20] F. Weinhold, J.E. Carpenter, The Structure of Small Molecules and Ions, Plenum,
New York, 1988. p. 227.
Conclusion
The newly synthesized Schiff bases ligands L1, L2 act as triden-
tate ligands, and all these are coordinated through the azomethine-
N, oxygen of amide and through nitrogen of pyrrole/oxygen of
furan to the metal ion. All the synthesized metal(II) complexes pos-
sessed an octahedral geometry except the Cu(II) complexes which
showed a distorted octahedral geometry. The reasonable agree-
ment between the theoretical and experimental data reflects to
the great extent the suitability of the applied basis set, 6-
31+g(d,p) for this type of work and confirms the suggested struc-
ture. The findings of antimicrobial studies indicated that the Schiff
base ligands possessed mostly moderate activity and metal(II)
complexes mostly possessed moderate to significant activities
against different bacterial and fungal strains which might be due
to azomethine (AHC@NA) linkage and/or heteroatoms present in
these compounds. The biological activity results showed that
majority of the Schiff base ligands possessed increased activity
upon coordination with different metal ions. The improvement in
biological activity upon coordination may be explained on the
basis of Overtone’s concept and chelation theory. The cytotoxicities
values indicates that metal complexes displayed significant cyto-
toxic activities, that might help in the development of potent
antimicrobial drugs. Further structural optimization studies might
thus represent a rationale for further investigation.
Acknowledgements
We thank the Principal, Zakir Husain Delhi College for providing
lab facilities, National Dairy Research Institute, Karnal for Antimi-
crobial activities. Authors are thankful to Defence Research &
Development Organisation, New Delhi, India, for financial
assistance.
[21] NCCLS, Method for Dilution Antimicrobial Susceptibility Test for Bacteria that
Grow Aerobically. Approved Standards, 5th ed., National Committee for
Clinical Standards, Villanova, PA, 2000.
[22] Y. Lu, N. Yeung, N. Sieracki, N.M. Marshall, Design of functional
metalloproteins, Nature (2009).
[23] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.

P. Tyagi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 143 (2015) 1–11
11
[24] M. Tyagi, S. Chandra, P. Tyagi, Spectrochim. Acta A 117 (2014) 1.
[25] P. Tyagi, S. Chandra, B.S. Saraswat, Spectrochim. Acta A 134 (2015) 200.
[26] M. Hanif, Z.H. Chohan, Spectrochim. Acta A 104 (2013) 468.
[27] B.K. Patel, S.C. Chaudhury, J. Ind. Chem. Soc. LXV (1988) 661.
[28] S. Chandra, S. Raizada, M. Tyagi, P. Sharma, Spectrochim. Acta A 69 (2008) 816.
[29] Z.H. Chohan, S.H. Sumrra, M.H. Youssoufi, T.B. Hadda, J. Coord. Chem. 63 (2010)
3981–3998.
[31] S. Chandra, Ruchi, K. Qanungo, S.K. Sharma, Spectrochim. Acta A 79 (2011)
1326.
[32] G.G. Mohamed, M.M. Omar, A.M.M. Hindy, Spectrochim. Acta Part A 62 (2005)
1140.
[33] S. Chandra, S. Bargujar, R. Nirwal, N. Yadav, Spectrochim. Acta A 106 (2013) 91.
[34] B.J. Hathaway, J.N. Bardley, R.D. Gillard (Eds.), Essays in Chemistry, Academic
Press, New York, NY, USA, 1971.
[30] M. Tyagi, S. Chandra, A. Akhtar, D. Chand, Spectrochim. Acta A 118 (2014)
1056.
[35] B.N. Meyer, N.R. Ferrigni, J.E. Putman, L.B. Jacobson, D.E. Nichols, J.L.
McLaughlin, Planta Med. 45 (1982) 31.