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Archives of Applied Science Research, 2013, 5 (5):191-197
(http://scholarsresearchlibrary.com/archive.html)
ISSN 0975-508X
CODEN (USA) AASRC9
191
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Synthesis, characterization and molecular modeling of Ni(II) & Cu(II)
complexes with schiff base derived from 1H-benzo[d]imidazole-4-amine and
2-hydroxy benzaldehyde
Narendra Kumar Chaudhary* and Parashuram Mishra
Bio-inorganic and Materials Chemistry Research Laboratory, M. M. A. M. Campus (Tribhuvan
University), Biratnagar, Nepal
_____________________________________________________________________________________________
ABSTRACT
The purpose of this work is synthesis of novel Schiff base ligand, 2-((1H-benzo[d]imidazol-4-ylimino)methyl)phenol
and its metal complexes from 1H-benzo[d] imidazole-4-amine and 2-hydroxy benzaldehyde. Nickel and Copper
being essential trace elements have given considerable attention for the synthesis of metal complexes. They have
been characterized by elemental analysis and spectral techniques like IR,
1
HNMR and mass spectrometry. The
spectral studies of the complexes reveal that the ligand has coordination through the O and N atoms of the ligand.
Cell dimensions a(13.554540 Å), b(9.496137 Å), c(4.471746 Å), α(90.00
0
), β(90.00
0
) and γ(90.00
0
) for Nickel
complex and a(22.094890 Å), b(8.983012 Å), c(8.483077 Å), α(90.00
0
), β(90.00
0
) and γ(90.00
0
) for Copper complex
are in good agreement with Orthorhombic crystal systems for both. The molecular structure of the complexes has
been optimized by MM2 calculation and suggested tetrahedral geometry with sp
3
hybridisation of copper and
square planar geometry with dsp
2
hybridization of nickel complex respectively.
Keywords: Schiff base; Benzimidazole; Molecular modeling; MM2; Hybridization
_____________________________________________________________________________________________
INTRODUCTION
Coordination chemistry of Schiff bases has attracting considerable attentions of researchers in the field of chemical
science as well as in medical science for their immense biological activities and bears a curious history. Such ligands
and their complexes due to their biological activities provide a better understanding of metal- protein binding. Thus
Schiff bases containing these groups could act as a versatile model of metallic bio-sites. Transition metal complexes
of Schiff bases concerning interaction of metal ions with nitrogen and oxygen organic moieties have been of great
interest for many years since they are becoming an effective biochemical, analytical and antimicrobial reagents.
Many reports have shown that some drugs have greater activity when administered as metal complex as that as free
organic compounds [1-3]. Imidazole derivatives of Schiff bases have applications in the field of medical science due
to having their high chemoptherapeutic properties [4]. Nitrogen atom of Imidazole moiety bears interesting physical
and chemical properties that make different pharmacological activities of the compounds and its derivatives [5].
Literatures revealed that imidazole and its derivatives are reported to have, analgesic and anti-inflammatory activity,
cardiovascular activity, anti-neoplastic activity, anti- fungal activity, enzyme inhibition activity, antianthelmintic
activity, anti-filarial agent, anti- viral activity and anti- ulcer activity [6-8]. Aniline derivatives of Imidazole, also
called benzimidazole are reported to have parasitic and antiviral activities [9], so the Schiff base Ni(II) and Cu(II)
complexes of 1H-benzo[d]imidazole-4-amine and salicyldehyde, have been considered as a subject of great interest
for the present study, with a hope for future drug with high efficacy. More literature survey regarding the
benzimidazole derivatives focuses them as an important drug that selectively inhibits endothelial cell growth and
suppresses angiogenesis in vitro and in vivo [10]. 2-hydroxy benzaldehyde is taken as a second organic component
Narendra Kumar Chaudhary et al Arch. Appl. Sci. Res., 2013, 5 (5):191-197
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N
NH
N
O
N
HN
N
O
Ni
N
NH
N
O
N
HN
N
O
Cu
for the preparation of Schiff base that exhibit varieties of biological activities including antibacterial and antifungal.
The aim of present work is to carry out the synthesis, characterization and molecular modeling of Ni(II) & Cu(II)
complexes of Schiff bases derived from 1H-benzo[d]imidazole-4-amine and 2-hydroxy benzaldehyde. Nickel and
copper have been distinguished as an essential trace element for the life and play a multifunctional role in
association with organic molecules in the biological systems [11].
MATERIALS AND METHODS
All the chemicals and solvents used for the synthesis were of analytical grade and purchased from BDH and Merck
chemical co. They were used without further purification. The infrared spectra of the ligand and metal complexes
were run as KBr discs in the range 4000-400 cm
- 1
on a Shimadzu Infrared Spectrophotometer. Elemental analysis
(C, H, N) were performed by using a Flash EA 1112 Series elemental analyzer.
l
H NMR spectra were determined in
DMSO (internal standard TMS) on Bruker spectrometer. NiCl
2
.6H
2
O and CuCl
2
.2H
2
O salts were used for the
synthesis of metal complexes of Schiff base. Mass spectra were carried out, TOF-MS on water KC-455 model in
DMSO. The molecular structures of the complexes were optimized by CsChem 3D Utra-11 programme.
Synthesis of novel Schiff base ligand
The novel Schiff base ligand was prepared by condensation of 1H-benzo[d]imdazol-4-amine (1.3315 gm; 0.01mol)
with 2-hydroxy benzaldehyde (1.2212 gm; 0.01 mol) in 25 ml ethanol and the mixture was refluxed for 3 hrs at 45
0
C. The resulting solution was allowed to evaporate by slow diffusion process in air for a week. The crystals of novel
ligand were collected, washed several times with ethanol and recrystallized from hot ethanol and dried in vacuum
desiccators.
Figure 1. Structure of Novel Ligand [LH]
Synthesis of Metal complexes
The synthesized novel ligand was added to hot ethanolic solution of 0.2 mmol of metal chlorides drop wise and
refluxed for 5 hours and dried at room temperature. A good crystalline form of the complexes was obtained. All the
complexes were characterized by spectral techniques accordingly.
Figure 2. Structure of metal complexes [ML
2
]
Narendra Kumar Chaudhary et al Arch. Appl. Sci. Res., 2013, 5 (5):191-197
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RESULTS AND DISCUSSION
The synthesized compounds were crystalline, colored, nonhygroscopic, and soluble in water. Composition and
identity of the complexes were carried out by elemental analysis. The spectroscopic data for the newly synthesized
metal complexes are in good agreement with proposed molecular formula.
Elemental composition analysis
The elemental analysis (CHN) data for the novel ligand, and its metal complexes are summarized in the table below.
Table 1. Elemental analysis data of the complexes
Compound Empirical Formula Mol. Wt.
C
Found
(Calc.)
H
Found
(Calc.)
N
Found
(Calc.)
O
Found
(Calc.)
M
Found
(Calc.)
Novel Ligand C
14
H
11
N
3
O 237.26
70.23
70.87
4.92
4.67
17.87
17.71
6.80
6.74
-
Ni(II) Complex C
28
H
20
N
6
NiO
2
531.19
62.98
63.31
3.81
3.80
15.60
15.82
5.87
6.02
11.12
11.05
Cu(II) Complex C
28
H
20
CuN
6
O
2
536.04
62.75
62.74
3.76
3.75
15.69
15.68
5.96
5.97
11.81
11.85
Infrared spectral analysis
The comparison of IR spectra of novel ligand and metal complexes reveal the binding mode of ligands to metal ions
which is confirmed by a negative shift in the positions of absorption peaks. IR spectra of free ligand show a broad
band around 3350 cm
-1
which can be attributed to NH stretching vibration of benzimidazole moiety. One more
medium intensity band at the region of 3600-3640 cm
-1
is assignable to phenolic OH group whose negative shift in
metal complexes indicated metal coordination with phenolic oxygen. Medium intensity bands in the range of 1625
cm
-1
due to (C=N) in the novel ligand was shifted hypsochromically about 1025 cm
-1
which was in the range of
1607 - 1590 cm
-1
in metal complexes, indicating the imine nitrogen atom involvement in coordination to metal ions
[12-14]. This fact is further supported by the appearance of medium intensity band in the region below 500 cm
-1
assignable to
M-N
vibration. The appearance of one more medium intensity band in the region of 446 - 409 cm
-1
assignable due to
M-O
vibration, also indicated the metal oxygen binding mode in the complexes [15-16]. Thus from
the IR- spectral assignments it is clear that the compounds may be bonded to metal ions through the imine nitrogen.
1
H NMR spectral analysis
1
H NMR spectral comparison of novel ligand and metal complexes was made to confirm the binding nature of
ligand with metal ions viz. Ni (II) & Cu(II). The integral intensities of each signal in the
1
H NMR spectra of novel
ligand and its metal complexes were found to agree with the number of different types of protons present.
Figure 3.
1
HNMR spectra of Cu(II)-complex
Narendra Kumar
Chaudhary
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Compounds
(ppm)
C
14
H
11
N
3
O (Ligand) 5.0(s)
[OH
Ni-complex
9.00(s)
Cu-complex
9.00(s)
TOF-Mass spectral analysis
The proposed molecular formula of
comparing their formula weight with m/z values. The mass spectra contain molecular ion peak (M
for Ni(II) complex and 536.09 for Cu (II) complex. These data are in good agreement with the
formula.
Fragmentation of the complex as m/z: 530.10 (100.0%), 532.10 (39.6%), 531.10 (32.6%), 533.10 (13.6%),
534.09 (5.4%), 532.11 (4.5%), 534.10 (2.6%), 535.10 (1.8%), 536.09 (1.4%) for Ni complex and 535.09 (100.0%),
537.09 (45.3%
), 536.10 (30.6%), 538.10 (14.3%), 537.10 (4.9%), 536.09 (2.2%), 539.10 (2.2%)
X-ray powder diffraction study
X-
ray powder diffraction patterns of all ligands and their complexes were recorded between 9 and 80(2
of (2), interplanar spacing d (Å
) and the relative intensities (I/I0) of the compounds under study were recorded in
table 5.
Compounds
Formula
FW
Temp (K)
Wavelength
Crystal System
Space group
Unit cell dimension
a(Å)
b(Å)
c(Å)
α
β
γ
Volume (A
θ
range (0)
Limiting indices
Particle size(nm)
Intensity (%)
R indices
Density
Z
Chaudhary
et al
Arch. Appl. Sci. Res., 2013, 5 (
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Table 2.
1
H NMR spectral data
(ppm)
[OH
-Ar & NH imidazole]; 6.76-7.7 [CH-Ar]; 8.39(s) [CH
imine]; 8.1(s)
9.00(s)
[
1
H-ArH); 7.0-7.621 [8
1
H Ar-CH}
9.00(s)
[
1
H-ArH), 7.0-7.621 [8
1
H Ar-CH}
The proposed molecular formula of
metal complexes
was confirmed by the TOF mass spectral analysis by
comparing their formula weight with m/z values. The mass spectra contain molecular ion peak (M
for Ni(II) complex and 536.09 for Cu (II) complex. These data are in good agreement with the
Fragmentation of the complex as m/z: 530.10 (100.0%), 532.10 (39.6%), 531.10 (32.6%), 533.10 (13.6%),
534.09 (5.4%), 532.11 (4.5%), 534.10 (2.6%), 535.10 (1.8%), 536.09 (1.4%) for Ni complex and 535.09 (100.0%),
), 536.10 (30.6%), 538.10 (14.3%), 537.10 (4.9%), 536.09 (2.2%), 539.10 (2.2%)
ray powder diffraction patterns of all ligands and their complexes were recorded between 9 and 80(2
) and the relative intensities (I/I0) of the compounds under study were recorded in
Figure 4. XRD spectra of Copper complex
Table 3. Crystallographic data for complexes
Compounds
Complex 1 Complex 2 Ligand
Formula
C
28
H
20
N
6
NiO
2
C
28
H
20
N
6
CuO
2
C
14
H
11
N
3
O
531.19 535.09 237.26
Temp (K)
293 293 293
Wavelength
1.54056 1.54056 1.54056
Crystal System
Orthorhombic Orthorhombic Monoclinic
Space group
P N M A I M M A P2/m
Unit cell dimension
13.554540 22.094890 10.312
9.496137 8.983012 7.7972
4.471746 8.483077 8.9554
90.000 90.0000 90.00
90.000 90.000 120.00
90.000 90.000 90.00
Volume (A
3
) 575.58 1683.71 617.78
range (0)
19.0-70.0 7.0-30.0 12-67
Limiting indices
0
≤
h
≤
8
0 ≤ k ≤ 5
0 ≤ l ≤ 2
0
≤
h
≤
7
0 ≤ k ≤ 2
0 ≤ l ≤ 2
-1
≤
h
≤
2
-4 ≤ k ≤ 4
0 ≤ l ≤ 7
Particle size(nm)
49.123 50.341 11.92
Intensity (%)
7.2
−
100 5.9
−
100
3.4-100
R indices
0.0000106 0.000131 0.0000362
Density
1.405 1.343 1.151
1 2 1
Arch. Appl. Sci. Res., 2013, 5 (
5):191-197
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194
imine]; 8.1(s)
[CH imidazol]
was confirmed by the TOF mass spectral analysis by
comparing their formula weight with m/z values. The mass spectra contain molecular ion peak (M
+.
) at m/z 531.19
for Ni(II) complex and 536.09 for Cu (II) complex. These data are in good agreement with the
respective molecular
Fragmentation of the complex as m/z: 530.10 (100.0%), 532.10 (39.6%), 531.10 (32.6%), 533.10 (13.6%),
534.09 (5.4%), 532.11 (4.5%), 534.10 (2.6%), 535.10 (1.8%), 536.09 (1.4%) for Ni complex and 535.09 (100.0%),
), 536.10 (30.6%), 538.10 (14.3%), 537.10 (4.9%), 536.09 (2.2%), 539.10 (2.2%)
ray powder diffraction patterns of all ligands and their complexes were recorded between 9 and 80(2). The value
) and the relative intensities (I/I0) of the compounds under study were recorded in
Narendra Kumar Chaudhary et al Arch. Appl. Sci. Res., 2013, 5 (5):191-197
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Kinetics of thermal decomposition
Recently, there has been increasing interest in determining the rate- dependent parameters of solid-state non-
isothermal decomposition reactions by analysis of TG curves Thermogravimetric (TG) and differential thermo
gravimetric (DTA) analyses were carried out for different metal complexes in ambient conditions. The
thermogravimetric analysis revealed that the complexes of Cu & Ni loses mass between 65°C and 140°C,
corresponding to nearly 15 % of the total mass, followed by considerable decomposition up to 600°C, which
corresponds to the decomposition of the ligand molecule leaving metal oxide NiO and CuO as residue. On the basis
of thermal decomposition, the kinetic analysis parameters such as activation energy (E*), enthalpy of activation
(H*), entropy of activation (S*), free energy change of decomposition (G*) were evaluated graphically by
employing the Coats – Redfern relation.
Log [-Log (1- α) /T
2
] = log [AR/ E*(1-2RT/E*)]-E*/2.303RT .....................(1)
Where is the mass loss up to the temperature T, R is the gas constant, E*is the activation energy in J mole
-1
, is
the linear heating rate and the term (1-2RT/E*) ≅ 1. A straight line plot of left hand side of the equation (1) against
1/T gives the value of E* while its intercept corresponds to A (Arrhenius constant). The Coats and Redfern
linearization plots, confirms the first order kinetics for the decomposition process. The calculated values of
thermodynamic activation parameters for the decomposition steps of the metal complexes are reported in Table 4.
According to the kinetic data obtained from the TG curves, the activation energy relates the thermal stability of the
metal complexes. Among metal complexes, activation energy increases as complex 1 < complex 2. Same trends
happen with thermal stability of metal complexes. Both complexes have negative entropy, which indicates that the
complexes are formed spontaneously. The negative value of entropy also indicates a more ordered activated state
that may be possible through the chemisorptions of oxygen and other decomposition products. The negative values
of the entropies of activation are compensated by the values of the enthalpies of activation, leading to almost the
same values for the free energy of activation.
Table 4. Thermodynamic activation parameters of the metal complexes
Complex Order/n Steps E*/Jmol
-1
A/sec
-1
S*/
JK
-1
mol
-1
H*/
Jmol
-1
G*/ kJmol
-1
k×10
2
s
-1
C
28
H
20
N
6
NiO
2
1
I
II
57.66
65.804
1.125×10
5
1.256×10
5
-92.49
-110.175
112.745
96.114
61.228
89.18
1.72
1.02
C
28
H
20
CuN
6
O
2
1
I
II
59.066
7.178
6.27×10
5
1.16×10
5
-85.136
-109.603
74.10
125.89
55.29
93.104
3.27
1.79
Molecular Modeling
3D molecular modeling of the proposed structure of the complexes was performed using CsChem3D Ulta -11
program package. The correct stereochemistry was assured through the manipulation and modification of the
molecular coordinates to obtain reasonable low energy molecular geometries. The optimized structures of the
complexes were performed by MM2 programme contained CS chem. Office programme. The potential energy of the
molecule was the sum of the following terms: E = E
str
+ E
ang
+ E
tor
+ E
vdw
+ E
oop
+ E
ele
. Where all E’s represent the
energy values corresponding to the given types of interaction. The subscripts str, ang, tor, vdw, oop and ele denote
bond stretching, angle bonding, torsion deformation, van der waals interactions, out of plain bending and electronic
interaction, respectively. Molecular modeling showed square planar geometry for Ni(II) complex and tetrahedral
geometry for Cu(II) complex.