Associate Professor, B P Yadav

Research Scholar

Yogendra Sharma

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P: ISSN No. 2231-0045       RNI No. UPBIL/2012/55438    VOL.-III, ISSUE-II, November-2014                                                                                                                        
                                                                               Periodic Research 
65 
 
E: ISSN No. 2349-9435  
Complexes of The Schiff Base Derived 
from 4Aminophenyl Benzimidazole and 
4Methyl Benzaldehyde With Zn(II), 
Cd(II) And Hg(II) Halides 
 
 
 
 
Yogendra Sharma  
Research Scholar & Tutor, 
Deptt. of Chemistry, 
Meerut College Meerut  
 
 
 
 
 
Sandeep Kashyap 
Research Scholar, 
Department of Chemistry 
Meerut College Meerut, U.P 
 
 
 
 
 
B. P. Yadav 
Associate Professor, 
Deptt. of Chemistry,  
Meerut College Meerut  
 
 
 
 
Keywords: Schiff bases, 4Aminophenyl Benzimidazole, 4Methyl        
Benzaldehyde, biological activities. 
Chemistry 
 The sequence leading to the preparation of ligand and Schiff bases. 
4Aminophenyl 4methyl benzimidazole was prepared from 4methyl 
phenylenediamine and 4aminobenzoic acid. After that the preparation of 
the complexes have been studied. Than the proton NMR spectra and I.R-
spectra of the ligand and its complexes have been studied in the range 
4000400 cm1. Therefore the structure, molecular modeling and 
biological activities of complexes and its ligand have been studied 
Introduction 
Studies on metallo drugs acting as anticancer agents have gained 
momentum in recent times. Schiff bases are reported to show a variety of 
biological actions including antibacterial, antifungal, herbicidal, etc.
(1)
 It has 
been suggested that the azomethine linkage is responsible for the 
biological activities displayed by Schiff bases.
(2)
 
Benzimidazole and its derivatives have been shown to possess 
antibacterial and antimalarial activities. The benzimidazole moiety is 
reported to be toxic to fungi and a large number of benzimidazole 
derivatives have been synthesized and patented as fungicides
(3)
. The 
physiological activity and commercial application of 2amino benzimidazole 
have received much attention
(4)
. A number of aldehydes and ketones are 
found to react with 2amino benzimidazole derivatives leading to the 
formation of azomethines with a broad spectrum of biological activity.
(5,6)
 
In the present study, we have prepared 4aminophenyl 
benzimidazole (4apbi) and its Schiff bases with various aldehydes. We 
report herein the synthesis, characterization, molecular modeling studies 
and biological activity of complexes of zinc chloride and chlorides and 
bromides of cadmium(II) and mercury(II) with the Schiff base derived from 
4aminophenyl benzimidazole and 4methyl benzaldehyde (MBenz4apbi)  
Experimental: 
Preparation of the Ligand (M.Benz4apbi) 
 All the chemicals used were of high purity. 4Aminophenyl 
4methyl benzimidazole was prepared from 4methyl phenylenediamine 
and 4aminobenzoic acid by reported procedure
(5)
. The Schiff base was 
prepared by taking equimolar quantities of 4apbi (2.10 g) and 
4methylbenzaldehyde (1mL) in about 40mL of ethanol. The solution was 
refluxed for about 4h. The solvent was evaporated to dryness to obtain a 
buff coloured solid. It was recrystallised from ethanol and dried overnight at 
about 100C in vaccum for 4 h. The elemental analysis (Table 9.1) 
corresponds to the molecular formula (C22H19N3). 
Preparation of the Complexes 
 Each of the metal salts CdCl2, CdBr2, HgCl2, HgBr2 and ZnCl2 
(0.33 M) was refluxed separately with the ligand (0.66 M) in about 20 mL of 
Abstract 
          The study of complexes of the Schiff bases derived from 
4Aminophenyl Benzimidazole and 4Methyl Benzaldehyde with Zn(II), 
Cd(II) and Hg(II) halides. In present work the preparation of 
4Aminophenyl Benzimidazole (4apbi) and its Schiff bases have been 
studied with various aldehydes. Schiff bases and benzimidazole 
derivatives are reported to show biological activities like antibacterial, 
antifungal, and antimalarial. 
P: ISSN No. 2231-0045       RNI No. UPBIL/2012/55438    VOL.-III, ISSUE-II, November-2014                                                                                                                        
                                                                               Periodic Research 
66 
 
E: ISSN No. 2349-9435  
ethanol for 46 h. The reaction mixture was 
evaporated to minimum volume. About 10 mL of ether 
was then added to it and kept overnight in a 
refrigerator when the complex crystallized out. It was 
collected by filtration, washed with ether and dried 
under vacuum for 4h.Conductivity data were obtained 
using freshly prepared N,Ndimethylformamide 
solution of the complex (10.3 M) at 25C with a digital 
conductivity meter (modelCIS 13). Elemental 
analyses were carried out using a CarloErba 
Strumentazione (model 1106). The infrared spectra in 
the range 4000400 cm
1
 were recorded with KBr 
pellets using a Nicolet impact 400D spectrometer. The 
far infrared spectra in the range 400200 cm
1
 were 
recorded using Thermo Nicolet (model IR 100) 
spectrometer using high density polyethene. The 
proton NMR spectra were recorded using a 
Bruker400 instrument using DMSOD6 as the solvent 
and TMS as internal reference. Molecular modeling  
was carried out using the software. Molecular 
Modeling Pro Plus, designed by Chemsw Inc, USA. 
NH
N
N C
CH3
H CH3
(I)  
Table 9.1 
 Analytical Data of Complexes of Zn, Cd, Hg 
Halides with MBenz4Apbi (L) 
Comp. Found (Calc.) % mol S 
cm
2
/mol Carbon Nitrogen Hydrogen 
L(C22H19N3) 81.05 
(81.23) 
12.77 
(12.92) 
5.70 
(5.84) 
 
Zn2L2.Cl4 57.09 
(57.22) 
9.0 
(9.10) 
4.0 (4.11) 62 
Cd2L2.Cl4 51.77 
(51.92) 
8.12 
(8.26) 
3.60 
(3.73) 
59 
Cd2L2.Br4 44.02 
(44.,10) 
6.90 
(7.03) 
3.02 
(3.18) 
59 
Hg2L2.Cl4 44.12 
(44.25) 
6.87 
(7.04) 
3.02 
(3.18) 
67 
Hg2L2.Br4 38.40 
(38.50) 
5.93 
(6.12) 
2.70 
(2.77) 
68 
L(C22H19N3) 
 The biological screening was conducted by 
filter paper disc method. The nutrient agar was 
prepared separately for bacterial strains and fungus 
from the commercially available nutrients (Hi MEDIA). 
The test solutions consisting of 5 and 10 ppm of the 
metal ion were prepared by dissolving accurately 
weighed amounts of the complexes in DMF. 
Whatmann filter paper discs of about 6 mm were 
placed on the nutrient broth at appropriate spots, 
properly labeled, on the petriplates. The test solutions, 
ligand solution, DMF and phenol as control were 
inoculated into these different filter paper spots. The 
plates were then incubated at 37C for 24 h. The clear 
zones of inhibition of the respective test solutions and 
control were measured in mm using a scale and 
tabulated. 
Results and Discussion 
The analytical data of the complexes are 
given in Table 9.1. All the complexes are insoluble in 
common organic solvents except DMF and DMSO. 
The ligand and the complexes have melting point 
above 250C. The molar conductance of 103 M DMF 
solutions of the complexes calculated for the 
monomer was found to be in the range of about 
5968S cm2 mol1. The higher values of conductivity 
than those expected for nonelectrolytes indicate the 
solvation of the complexes resulting in the slight 
displacement of anion from the coordination sphere 
by the stronger donor DMF molecules. The 
complexes may hence be regarded as 
nonelectrolytes. 
(i)  NMR Spectra 
 The 1H NMR spectra of the ligand 
MBenz4apbi, shows the chemical shift for the NH 
proton at  12.43 ppm as a singlet and that of N=CH 
proton at 8.17 ppm as another singlet. The aromatic 
protons are observed in the region  6.67 to 7.83 
ppm. The protons of the benzlidene ring show 
chemical shifts at  3.22 ppm (m) and  3.43 ppm (m). 
 The proton NMR spectra of the complexes 
show a marginal or no shift in the chemical shifts of 
the aromatic benzlidene and N=CH protons. Only the 
signal corresponding to NH proton in the complexes 
show a large deviation and is not observed in the 
spectrum recorded up to  15 ppm. This indicates that 
the complexation of the ligand with the metal atom 
occurs through the imidazole nitrogen atom and 
suggests that the ligand is monodentate. The bond 
between the tertiary nitrogen and the metal deshields, 
inducing a major shift in the NH proton. 
 
IR Spectra 
The IR spectra of the ligand and the complexes were 
studied in the range 4000200 cm1. The absorption 
at 3359 cm1 is assigned to the stretching vibration of 
NH bond of the imidazole ring(7). It shows a 
considerable shift of 531 cm1 in the complexes. 
The absorptions at 1657 and 1616 cm1 due to 
N=CH and C=N stretching modes also show a shift of 
515 and 16 cm1 respectively in the complexes. 
These shifts indicate the bonding of imidazole 
nitrogen of benzimidazole to the metal atom(8). 
The bands due to the stretching vibrations of 
metalnitrogen bonds in all the complexes are 
observed in the region 286313 cm1 as reported in 
the literature(9). In the chloride complexes, the 
P: ISSN No. 2231-0045       RNI No. UPBIL/2012/55438    VOL.-III, ISSUE-II, November-2014                                                                                                                        
                                                                               Periodic Research 
67 
 
E: ISSN No. 2349-9435  
stretching modes of MCl (terminal) bonds are 
observed in the region 210350 cm1 as 
expected(10). The bands due to bridging chlorides in 
these complexes are observed below 200 cm1. The 
ratio of MCl(b), MCl(t) is 0.54 : 0.63 as expected. 
However, in the case of bromo complexes of 
cadmium(II) and mercury(II), the CdBr and HgBr 
stretching frequencies are probably near the limit of 
the spectrometer and hence were not observed. 
Similar results have been reported by Coates and 
Ridley(11) in their observations on low frequency 
infrared spectra of some complex halides of zinc(II), 
cadmium(II) and mercury(II). Considering that 
normally the complexes analyzing as MLX2 are 
dimeric with a halogen as bridge, we propose dimeric 
structure for all thecomplexes. 
 
Structure of the Complexes 
 Studies on Schiff base complexes derived 
from salicylidiene2amino benzimidazole with 
metals such as Fe(III), Cu(II), Zn(II), Cd(II) etc., have 
shown coordination of the ligand to the metal ions in a 
tridentate manner with donor sites O, N, N of the 
phenolicOH, benzimidazoleN3 and 
azomethineN
(12)
. 
 Salicylidiene2aminomethylbenzimidazole 
also acts as a tridentate ligand
(2)
. However, 
salicylidiene2(2aminophenyl) benzimidazole acts 
as a bidentate ligand bonding through the phenolic 
oxygen and the tertiary N of the imidazole ring of 
benzimidazole
(13)
. In certain cases as in the 
complexes of benzilidene2 (2aminophenyl) 
benzimidazole and salicylidiene2(2aminophenyl) 
benzimi dazole with Ti(IV), V(IV) and Sn(IV), the 
ligand acts as monodentate with imidazole nitrogen as 
the donor atom
(14)
. Our studies indicate that a related 
ligand Mbenz4apbi, also acts as monodentate with 
the azomethine nitrogen. This may be probably due to 
steric hindrance. The molecular modeling studies also 
indicate very high strain on the metal ion when the 
ligand coordinates as a bidentate. Hence, complexes 
with dimeric structure as shown in structure(II) is 
suggested, where the metal ion has a tetrahedral 
environment. 
Molecular Modeling Studies 
 Molecular modeling studies were carried out 
with an interactive graphics molecular modeling 
program Molecualr Modeling Pro Plus
(15)
. Energy 
minimization was repeated several times to find the 
global minimum. The JonesLeonard potential was 
applied on MN bonds to obtain a configuration with 
minimum repulsion and, hence, minimum steric strain. 
Representative structure of a chloride and a bromide 
complex with minimum global energy is shown in Figs 
1 and 2. The results show that the arrangement of the 
ligand around the metal atom, in space, varies in a 
chloride and a bromide complex due to the change in 
size of the halides. After the configuration with global 
minimum is attained, the total energy of the molecule 
and the percentage strain on the metal atom was 
computed. They are collected in Table 9.2. The total 
energy of these complexes varies between 696 and 
846 kJ/mol and the strain on the metal atom is 
3438%. From the results it is seen that the strain on 
the metal ion for the chloride complexes increases 
from Hg(II) to Cd(II) to Zn(II). The values of total 
energy do not show any specific trend. The molar 
volume of the complexes increases with the increase 
in the ionic radii of the metal ions in the order Zn(II), 
Cd(II) and Hg(II). 
L
M
X
X
X
M
X
L
(II)  
 The calculated metalnitrogen and 
metalhalide bond lengths and the relevant bond 
angles are given in Table 9.2. The ZnN bond lengths 
in dibromobis (nicotinamide)zinc(II) and 
dibromobis(benzimidazole)zinc(II) complexes are 
reported from single crystal xray studies to lie 
between 2.008 and 2.065 Å
(16,17)
. 
 The Zn ion has distorted tetrahedral 
geometry is these complexes. The ZnN bond lengths 
obtained in the present calculations are somewhat 
lower. It is suggested that this decrease in the bond 
length may be due to the bridging of the metal ions 
through the halide. 
 It is found that in the case of Cd(II) and Hg(II) 
complexes also, the MN bond length is lower than 
those reported in the literature
(18)
.  
 
 
 
P: ISSN No. 2231-0045       RNI No. UPBIL/2012/55438    VOL.-III, ISSUE-II, November-2014                                                                                                                        
                                                                               Periodic Research 
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E: ISSN No. 2349-9435  
 
  
Table 9.2 Molecular Modeling Data on Complexes Of Zn, Cd, Hg Halides With MBenz4apbi(L) 
Compound Total 
energy 
kJ/mol 
Strain 
on metal 
Molar vol. 
cm
3
/mol 
Bone length, Å Bond angle deg. 
MN MX1 MXb NMX1 MXbM XbMXb 
Zn2L2.Cl4 824 37.39 
38.37 
576.81 1.78 1.75 2.03 2.03 1.84 
1.93 
1.96 
1.96 
116 102 73 70 102 100 
Cd2L2.Cl4 846 37.38 
35.83 
580.33 1.65 1.78 2.22 2.14 2.08 
2.07 
2.07 
1.97 
106 114 73 73 93 100 
Cd2L2.Br4 696 34.11 
34.23 
594.10 1.89 1.93 2.37 2.37 2.25 
2.23 
2.24 
2.28 
115 113 83 82 93 92 
Hg2L2.Cl4 777 34.03 
32.59 
584.13 1.93 1.78 2.28 2.25 2.09 
2.14 
2.13 
2.13 
115 110 80 81 93 92 
Hg2L2.Br4 784 33.42 
35.45 
592.39 1.80 1.85 2.40 2.43 2.29 
2.23 
2.30 
2.26 
112 115 78 77 96 98 
L(C22H19
N3) 
136  247.41             
 
The metal halogen bond lengths are about 0.30.4Å 
shorter than those reported from the single crystal 
Xray studies of such complexes. The NMX bond 
angles show a small deviation from tetrahedral angle 
whereas the bond angles MXbM and XbMXb 
show large deviations. These deviations indicate the 
bridging through halogen and may arise from the 
bulky Schiff base ligand due to steric consideration
(19)
. 
(v)  Biological activity
(20)
 
 The ligand and its complexes were tested for 
their activity against a set of microorganisms. 
Representative bacterial strains from Grampositive 
bacteria (Bacillus subtilis and Staphylococcus aureus) 
and Gramnegative bacteria (Escherichia coli and 
Pseudomonas fluorescens) were tested. They were 
also investigated for antifungal activity against the 
fungus Fusarium. 
 All the complexes
(21,22)
 show moderately 
enhanced activity against the fungus Fusarium as 
compared to that for phenol as a standard and also 
for the free ligand at both 5 and 10 ppm 
concentrations. According to the chelation theory, the 
formation of a complex decreases the polarisability of 
the metal enhancing the lipophilicity of the complexes. 
It facilitates the interaction of the complexes with the 
amino acids of the microorganism. Therefore, a higher 
activity of the complexes as compared to that of the 
free ligand is expected. Studies indicate increased 
antibacterial activity of the complexes towards 
Pseudomonas fluorscens when compared to that of 
the free ligand.
(23,24) 
 
 
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P: ISSN No. 2231-0045       RNI No. UPBIL/2012/55438    VOL.-III, ISSUE-II, November-2014                                                                                                                        
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Complexes of The Schiff Base Derived from 4Aminophenyl Benzimidazole and 4Methyl Benzaldehyde With Zn(II), Cd(II) And Hg(II) Halides Sandeep Kashyap

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Complexes of The Schiff Base Derived from 4Aminophenyl Benzimidazole and 4Methyl Benzaldehyde With Zn(II), Cd(II) And Hg(II) Halides Sandeep Kashyap

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