2
. The values of the electrical conductivity of the complexes were found in the range of 10
−11
to 10
−4
Ω
−1
cm
−1
and their conductivity increases with increase in temperature and decreases upon cooling over the studied temperature range indicating their semiconducting behavior.
28
The activation energy-temperature dependence follows the Arrhenius relation σ = σ
0
exp (−Ea/ kT), where σ
0
, Ea and k are conductivity constants,, the activation energy and the Boltzman constant, respectively. The plots of log σ
vs
. 1000/T (
. 4
) for all the compounds are found to be linear over the entire temperature range. The activation energy of the compounds lies in the range 0.43−0.75 eV.
DC electrical conductivity vs. 1000/T.
- Scanning Electron Micrographs
The morphology and particle size of the unsymmetrical Schiff base metal complexes have been illustrated by SEM.
. 6a
-
c
depict the SEM photograph of the synthesized Ni(II), Co(II) and Fe(III) complexes. The Scanning electron micrography (SEM) of metal complexes indicates the presence of well-defined crystals free from any shadow of the metal ion on their external surface. There is a uniform matrix of the synthesized complexes in the pictograph, which leads to dealing with homogeneous phase material. A single phase formation of Ni(II) complex having fiber morphologies in the form of a bundle with particle size 4-6 μm
29
and ~12 μm pore size is displayed in
. 5a
. Co(II) complex is granular shaped morphology with 2−3.5 μm particle size and ~4 μm pore size (
. 5b
). However Fe(III) complex is rock like shape morphology with 1.3−2.5 μm particle size and ~3 μm pore size (
. 5c
).
Scanning electron micrograph of complexes.
X-ray diffractogram of Ni (II) complex.
- X-ray Diffractogram
The powder X-ray diffraction spectrum of the Ni(II) complex is shown in
. 6
. The presence of sharp reflections in XRD pattern indicates the formation of single-phase compound. The XRD pattern shows ten reflections between 2θ range from 10.59−72.58° with maxima at 2θ = 10.59° corresponding to the value of d = 8.3458Å. All main peaks have been indexed by using appropriate methodology and use of computer program (PowdMult, Version 2.3). The indexing is confirmed on the basis of correction obtained between observed and calculated d and θ values based on characteristics of symmetry consideration.
30
The method also yielded hkl (miller indices) values. The 2θ values and relative intensities corresponding to the prominent peak have been listed in
4
. Assuming the Ni(II) complex as a tetragonal system, the unit cell lattice parameter are found to be a = b = 13.4176Å and c = 16.6916Å respectively, while the cell volume was 3005.01Å
3
. The particle size of the sample was calculated by using Scherrer formula t = 0.9λ/βcosθ. The other parameters such as particle size, radius of atom were calculated. All these values are tabulated in
5
.
The observed and calculated X-ray diffraction data of Ni(II) complex
The observed and calculated X-ray diffraction data of Ni(II) complex
X-ray parameters of Ni(II) complex
X-ray parameters of Ni(II) complex
- Antimicrobial Screening
The Schiff base and its metal complexes were evaluated for antimicrobial activity against two strain Gram +ve bacteria (
Staphalococcus aureus
,
Bacillus subtilis
), Gram –ve bacteria (
Salmonella typhimurium
,
Escherichia coli
) and fungus (
Aspergillus oryzae
,
Fusarium species
). The antimicrobial screening results are given in
6
. These observations show that the majority of the complexes are more active than their free ligand.
31
Chelation may enhance or suppress the biochemical potential of bioactive organic species. The antibacterial screening shows that compounds [NiL] and [CoL(H
2
O)
2
] exhibit the most activity.
32
The fungicidal screening shows that compounds [CuL(H
2
O)
2
] and [FeLCl(H
2
O)] are most effective against
Fusarium species
.
Antimicrobial activities of ligand and its complexes
Antimicrobial activities of ligand and its complexes
- Catalytic activity of Complexes
The catalytic oxidation of organic substrates by transition metal complexes is an area of current interest, in view of this in the present paper the catalytic activity of Ni(II) and Fe(III) complexes for epoxidation of styrene to corresponding styrene oxide were carried out using H
2
O
2
as an oxidant. These oxidation reaction yielded styrene oxide as a major product with minor amount of phenyl acetaldehyde as side product (
. 7
).
7
Epoxidation of styrene resulted 13.98 and 85.22% conversion and 100% Selectivity for both Ni(II) and Fe(III) complexes, respectively of styrene into styrene oxide (
. 8
). No significant side products were identified.
Oxidation of styrene.
Catalytic study of complexes.
CONCLUSIONS
Based on the physicochemical and spectral data discussed above square planer structure for Ni(II) complexes whereas octahedral geometry for Co(II), Mn(II), Cu(II), Cr(III) and Fe(III) complexes are proposed. It is assumed that the ligand behaves as dibasic ONNO tetradentate, coordinating via phenolic oxygen and azomethine nitrogen atoms. Thermal study revealed that complexes are thermally stable. The solid - state electrical conductivity of complexes increases with increase in temperature and suggested semiconducting behavior. An XRD study suggested the triclinic crystal system. The Catalytic conversions of styrene suggest that it increases with increase in amount of catalyst in presence of fixed amount of H
2
O
2
and styrene. The complexes are biologically active and showed enhanced antimicrobial activities compared to the free ligand. SEM images of the Ni(II), Co(II) and Fe(III) complexes shows the presence of well-defined crystals.
Acknowledgements
Publication cost of this paper was supported by the Korean Chemical Society.
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