1394 Shaikh et al.
Asian J. Chem.
cm-1 [14]. The participation of azomethine nitrogen is proved
by the shift of strong and sharp bands at 1613 and 1602 cm-1
for H2L1 and H2L2, respectively to a lower frequencies after compl-
exation [15]. All the complexes showed an additional non-
ligand bands in the regions 550-510 and 466-409 cm-1 assigned
to ν(M-O) and ν(M-N) stretching vibrations, respectively.
1H NMR spectra: 1H NMR spectra of Schiff base ligands
and their metal complexes were recorded in DMSO solvent.
The 1H NMR spectra of the parent ligands H2L1 and H2L2 exhibited
singlet signals at 12.89 and 12.94 ppm, respectively which was
attributed to phenolic -OH proton [16]. These OH signals disapp-
eared when 1H NMR spectra were performed in presence of
D2O. Also, the two ligands H2L1 and H2L2 showed singlets at
8.93 and 8.89 ppm, respectively, corresponding to -CH=N moiety.
On complexation the proton signals of azomethine carbon appe-
ared to be deshielded as they were shifted downfield compared
to the respective ligands indicating coordination through azome-
thine nitrogen atom [17]. The multiplets in the region 6.65-
7.90 ppm were assigned to aromatic ring protons (Table-2).
Electronic absorption spectra and magnetic suscepti-
bility: The electronic spectrum of Schiff base ligands and their
metal complexes were explored in DMSO solution (1 × 10-5 M).
The absorption spectra of the Schiff base ligands exhibited two
high intensity bands at around 270 and 330 nm (Table- 2) which
CHO
OH
+
2
NH2
H2N
C2H5OH
Reflux(3-4hrs)
H
H
N
C
N
C
OH
HO
X
X
H2L1 : X = -Cl;
H2L2 : X = -Br
Scheme-I: Structure of Schiff base
solution (0.001 mol). The solution was refluxed with continuous
stirring for about 4-5 h at 60 ºC. The precipitated complexes
were cooled and filtered, washed with cold methanol and dried
in vacuum.
Biological studies: The in vitro growth inhibition assay
of the compounds were tested for their antimicrobial activity
against the bacterial species Staphylococcus aureus, Escherichia
coli and fungi Aspergillus niger and Candida albicans by the
agar well diffusion method [11].
*
*
is attributed to benzene π→π transition and n→π transition
of non-bonding electrons present on azomethine nitrogen in
the Schiff bases, respectively. These two transitions were shifted
in the spectra of all the complexes with appropriate shifts. The
appearance of band around 480 nm in Ni(II) complexes is due
RESULTS AND DISCUSSION
1
to 1A1g→ B1g transition favouring a square planar geometry [18].
The crystalline solid complexes of Ni(II) and Pd(II) are
bright in colour, stable in air and decompose at higher temp-
erature (> 300 ºC). The complexes are insoluble in water and
other common organic solvents but soluble in DMF and DMSO.
The elemental analysis data confirmed 1:1 (metal:ligand)
stoichiometry for all the complexes (Table-1). The low values
of molar conductance in DMSO (10-3 M) solution at room temper-
ature indicate that these complexes are non-electrolytic in nature
[12].
IR spectra: The preliminary identification regarding the
formation of schiff bases and their complexes were obtained
from IR spectral data (Table-2).The IR spectra of free ligands
showed characteristic broad band of medium intensity in the
region 3677-3468 cm-1 assigned to intramolecular hydrogen
bonded ν(O-H) stretching vibration [13]. The disappearance
of this band in the corresponding metal complexes indicates
involvement of phenolic oxygen in coordination to the metal
after deprotonation. This is further confirmed by the shift in
the position of ν(C-O)) band to lower wave numbers by 20-30
The Pd(II) complexes display bands in the regions of 255-
259, 353-378 and 455-477 nm. The broad bands in the region
1
455-477 nm were considered due to d-d transition (1A1g→ B1g)
of square planar configuration [19]. Magnetic susceptibility
measurements supported the diamagnetic behaviour of all the
complexes.
Powder X-ray diffraction analysis: To understand the
crystal structure, X-ray diffractogram of complexes were obtained
in the range 5º to 70º (2θ) value and an independent indexing
for the X-ray powder diffraction data was done. The inter-planar
spacing (dhkl) were calculated by using Braggs equation for
the major refluxes. The preliminary data in the form of 1/d2
were fed to the computer and all the differences were calculated
as required for Hess and Lipson's method. The refluxes were
indexed and refined for obtaining the Miller indices h, k, l
using Back-cal program by computational method. The precise
lattice parameters and deviations were then obtained by using
program X-ray and program error matrix, respectively. There-
TABLE-1
ANALYTICAL AND PHYSICAL DATA OF THE LIGANDS AND THEIR METAL COMPLEXES
ΛM (S cm2
Microanalysis (%): Found (Calculated)
m.p.
(°C)
Compound
m.w. (Colour)
mol-1)
C
H
N
M
H2L1 [C20H14N2O2Cl2]
NiL1 [C20H12N2O2Cl2Ni]
PdL1 [C20H12N2O2Cl2Pd]
H2L2 [C20H14N2O2Br2]
NiL2 [C20H12N2O2Br2Ni]
PdL2 [C20H12N2O2Br2Pd]
385.00 (Bright orange)
441.71 (Brownish red)
489.42 (Yellow)
473.80 (Yellow)
530.51 (Brick red)
578.22 (Ochre yellow)
220
62.71 (62.32)
54.28 (54.33)
49.52 (49.04)
50.51 (50.65)
45.05 (45.23)
41.58 (41.50)
3.11 (3.64)
2.70 (2.77)
2.05 (2.45)
2.86 (3.98)
2.17 (2.26)
2.12 (2.07)
7.36 (7.27)
6.14 (6.33)
5.33 (5.72)
5.86 (5.91)
5.50 (5.28)
4. 78(2.84)
–
–
> 300
> 300
199
> 300
> 300
13.00 (13.29)
21.63 (21.74)
–
11.50 (11.07)
18.88 (18.40)
15.5
12.3
–
5.81
9.22
Shaikh, Julekha A.
