Vol. 30, No. 4 (2018) Synthesis and Biological Evaluation of Cu(II) Complexes with Schiff Bases Derived from 2-AminobenzoicAcid 915
to the metal ion. The phenolic ν(C-O) stretching frequency is
seen at 1394 cm–1. The new bands at 456 and 758 cm–1 which are
H
not present in the L1 spectrum corresponds to ν(Cu-N) and
ν(Cu-O).A broad band is obtained at 3200-3000 cm–1 indicates
N
O
the coordination of water molecules [9].
HO
OH
Electronic spectral and magnetic susceptibility: The
electronic spectra of ligand (L1) shows three bands at 276 nm
(36323 cm–1) corresponds to π→π*, while 315 nm (31746
cm–1) and 356 nm (280901 cm–1) corresponds to n→n* transi-
tion. Likely, the electronic spectra of ligand (L2) shows two
bands at 275 nm (36364 cm–1) may be assigned to π→π* and
another band at 331 nm (30211 cm–1) attributed to n→n* [10].
The electronic spectrum of hexa-coordinate complex of
Cu(II) with ligand L1, gives three absorption bands at 267.40
nm (37453 cm–1), 326.69 nm (30581 cm–1) and 419.20 nm
(23866 cm–1). The bands observed may be assigned to intra ligand
9.2 9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 6.8 6.6
ppm
Fig. 4. 1H NMR spectrum of ligand (L2) 2-[(2-hydroxybenzylidene)amino]-
benzoic acid
ppm corresponding to the hydroxyl proton of –COOH proton
[12], the peak at δ 10.27 ppm is attributed to phenolic –OH
proton [13], the signal at δ 8.86 ppm is assigned to (-CH=N-)
proton and the signals observed in the range δ = 7.02-7.81
ppm corresponds to eight protons of aromatic ring [16].
In 1H NMR spectrum of complexes of Cu(II), absence of
the peaks in the region δ 10.0 ppm and δ 11.0 ppm, indicates
the removal of protons from phenolic –OH group and carbo-
xylic –COOH group and the involvement in bonding. The peak
at δ 8.8 ppm in ligands is shifted to downfield, it outlines the
participation of this group in complexation. From the data, it
can be evident that bonding of Cu(II) with ligands L1 and L2
is through the phenolic oxygen, carboxylate oxygen and
azomethine group [14].
2
2
charge transfer, Cu→L charge transfer [11] and Eg→ T2g
transitions [12], respectively. The magnetic susceptibility value
lie at 1.48 BM, which is attributed to distorted octahedral
geometry of complex.
The magnetic susceptibility measurement of complex of
Cu(II) with L2 lie at 1.35 BM indicating a distorted octahedral
geometry. The electronic spectrum of this complex displays three
bands at 261.18 nm (38314 cm–1), 294.69 nm (33898 cm–1) and
411.80 nm (24272 cm–1). These bands are assigned intra ligand
2
charge transfer, Cu→L charge transfer and 2Eg→ T2g transitions
[13], respectively.
Cyclic voltammetry: In the cyclic voltammogram of complex
1, the peak to peak separation (∆Ep) is 250 mV and the ratio of
anodic to cathodic current (ipa/ipc) is less than unity which
confirmes the quasi reversible redox process. This complex also
shows one irreversible peak in the oxidative response with
Epa 0.10 V. For complex 2, the peak to peak separation (∆Ep)
is 100 mV and the ratio of anodic to cathodic current (ipa/ipc)
is 2.4 and the cathodic peak current is not equal to the anodic
peak current. This indicates the irreversible nature of the
electron transfer process [17].
1H NMR spectra: The 1H NMR spectrum of ligand (L1)
(Fig. 3), shows a signal at δ 3.95 ppm and a strong signal is
observed at δ 11.13 ppm corresponding to –OCH3 and hydroxyl
group of –COOH group [14], respectively, the peak at δ 9.92
ppm is attributed to phenolic –OH group present in ligand
[15], the signal at δ 8.85 ppm is assigned to (-CH=N-) proton
and the signals for the protons of the phenyl group attached to
ligand is observed are observed the range δ = 7.00-8.25 corres-
ponds to seven protons [16]. Likely, in the 1H NMR spectrum
of ligand (L2) (Fig. 4), a strong signal is observed at δ 11.13
EPR spectra: Both parallel and perpendicular features
of copper are resolved in the EPR spectra and were calculated
as 2.22 and 2.04, respectively. The g value of both Cu(II) comp-
lexes are found near to be 2.10, confirming the presence of
2
2
unpaired electrons in the dx -y orbital of Cu(II). The g value
suggest an octahedral arrangement around Cu(II) complexes.
The g value of these complexes were less than 2.3 and it indi-
cates the covalent nature of the M-L bond [10].
H
Based on the above spectral analysis, the structure of the
Schiff base copper(II) complexes are as follows:
N
O
HO
OH
OCH
3
H
N
H2O
H2O
Cu
H2O H2O
O
O
O
ppm
12 11 10
9
8
7
6
5
4
3
2
1
OCH3
Structure of complex 1 Cu(II) complex of L1
Fig. 3. 1H NMR spectrum of ligand (L1) 2-[(2-hydroxy-3-methoxybenzy-
lidene)amino]benzoic acid