Synthesis, spectral, redox, and antimicrobial activity of Schiff base transition metal(II) complexes derived from 4-aminoantipyrine and benzil

Article abstract of DOI:10.1081/SIM-120015081

A novel quadridentate, N₂O₂-type Schiff base, synthesised from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one (4-aminoantipyrine) and benzil, forms stable complexes with transition metal ions such as Cu(II), Ni(II), Co(II), Mn(II), Zn(II) and VO(IV) in ethanol. Microanalytical data, magnetic susceptibility, IR, UV-Vis., ¹H NMR, ESR and mass spectral techniques were used to confirm the structures. Electronic absorption and IR spectra of the complexes suggest an octahedral geometry around the central metal ion, except for the VO(IV)complex which has a square pyramidal geometry. The non-electrolytic behaviour of the chelates was assessed from the low conductance data, except for the vanadyl complex and the dipyridinyl adducts of the copper complexes which show a higher conductance, supporting an electrolytic nature of these complexes. The monomeric nature of the chelates was confirmed by their magnetic susceptibility values. Cyclic voltammograms of the [CuLCl₂] and [CuL(OAc)₂] complexes in DMSO solution at 300 K show a quasi-reversible peak for the Cu(II)/Cu(I) couple at Ep_a=-0.02 V and 0.54 V and Ep_c=-0.28 V and 0.23 V, respectively. The peak potentials were found to be solvent-dependent. The cyclic voltammogram of the [VOL]SO₄ complex in MeCN shows a quasi-reversible peak for the VO(IV)/VO(V) couple and another peak characteristic for the VO(IV)/VO(III) couple. The X-band ESR spectra of copper, manganese and vanadyl complexes in DMSO solution were recorded and their M.O. coefficients were also calculated. The in vitro antimicrobial activity of the investigated compounds and uncomplexed metal salts were tested against bacteria such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Salmonella typhi, Pseudomonous aeruginosa, Shigella flexneri and fungi such as Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates show higher antimicrobial activity for the above microorganisms than the free ligand and lower activity than the uncomplexed metal salts.

Full text of DOI:10.1081/SIM-120015081

This article was downloaded by: [Otterbein University]
On: 14 April 2013, At: 21:15
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt19
SYNTHESIS, SPECTRAL, REDOX, AND ANTIMICROBIAL
ACTIVITY OF SCHIFF BASE TRANSITION METAL(II)
COMPLEXES DERIVED FROM 4-AMINOANTIPYRINE AND
BENZIL
N. Raman a , A. Kulandaisamy a & K. Jeyasubramanian b
a Department of Chemistry, Virudhunagar Hindu Nadars' Senthikumara Nadar College,
Virudhunagar, 626 001, India
b Department of Chemistry, Mepco Schlenk Engineering College, Sivakasi, 626 005, India
Version of record first published: 15 Feb 2007.
To cite this article: N. Raman , A. Kulandaisamy & K. Jeyasubramanian (2002): SYNTHESIS, SPECTRAL, REDOX, AND
ANTIMICROBIAL ACTIVITY OF SCHIFF BASE TRANSITION METAL(II) COMPLEXES DERIVED FROM 4-AMINOANTIPYRINE AND BENZIL,
Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 32:9, 1583-1610
To link to this article: http://dx.doi.org/10.1081/SIM-120015081
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to
anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 32, No. 9, pp. 1583–1610, 2002
SYNTHESIS, SPECTRAL, REDOX, AND
ANTIMICROBIAL ACTIVITY OF SCHIFF
BASE TRANSITION METAL(II)
COMPLEXES DERIVED FROM 4-
AMINOANTIPYRINE AND BENZIL
N. Raman,1,* A. Kulandaisamy,1
and K. Jeyasubramanian2
1Department of Chemistry, Virudhunagar Hindu
Nadars’ Senthikumara Nadar College,
Virudhunagar 626 001, India
2Department of Chemistry, Mepco Schlenk Engineering
College, Sivakasi 626 005, India
ABSTRACT
A novel quadridentate, N2O2-type Schiff base, synthesised
from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one (4-ami-
noantipyrine) and benzil, forms stable complexes with tran-
sition metal ions such as Cu(II), Ni(II), Co(II), Mn(II), Zn(II)
and VO(IV) in ethanol. Microanalytical data, magnetic sus-
1
ceptibility, IR, UV-Vis., H NMR, ESR and mass spectral
techniques were used to confirm the structures. Electronic
absorption and IR spectra of the complexes suggest an
*Corresponding author. E-mail: drn_raman@yahoo.co.in
1583
DOI: 10.1081=SIM-120015081
Copyright # 2002 by Marcel Dekker, Inc.
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com

1584
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
octahedral geometry around the central metal ion, except for
the VO(IV)complex which has a square pyramidal geometry.
The non-electrolytic behaviour of the chelates was assessed
from the low conductance data, except for the vanadyl
complex and the dipyridinyl adducts of the copper complexes
which show a higher conductance, supporting an electrolytic
nature of these complexes. The monomeric nature of the
chelates was confirmed by their magnetic susceptibility va-
lues. Cyclic voltammograms of the [CuLCl2] and [Cu-
L(OAc)2] complexes in DMSO solution at 300 K show a
quasi-reversible peak for the Cu(II)=Cu(I) couple at
Epa ¼ ꢀ0.02 V and 0.54 V and Epc ¼ ꢀ0.28 V and 0.23 V,
respectively. The peak potentials were found to be solvent-
dependent. The cyclic voltammogram of the [VOL]SO4
complex in MeCN shows a quasi-reversible peak for the
VO(IV)=VO(V) couple and another peak characteristic for
the VO(IV)=VO(III) couple. The X-band ESR spectra of
copper, manganese and vanadyl complexes in DMSO solu-
tion were recorded and their M.O. coefficients were also
calculated. The in vitro antimicrobial activity of the in-
vestigated compounds and uncomplexed metal salts were
tested against bacteria such as Staphylococcus aureus, Bacillus
subtilis, Klebsiella pneumoniae, Salmonella typhi, Pseudomo-
nous aeruginosa, Shigella flexneri and fungi such as Aspergil-
lus niger and Rhizoctonia bataicola. Most of the metal chelates
show higher antimicrobial activity for the above micro-
organisms than the free ligand and lower activity than the
uncomplexed metal salts.
INTRODUCTION
Schiff bases derived from the condensation of 4-aminoantipyrine with
diketones represent an important class of chelating ligands and their metal
complexes are of great interest because of their importance in biological,
pharmacological, clinical and analytical applications.[176] Even though
4-aminoantipyrine itself exhibits some antimicrobial activity, its activity has
been markedly increased due to condensation with aldehydes, ketones, etc.
A literature search reveals that no work has been done on the Schiff base
derived from the condensation of 4-aminoantipyrine with benzil and its
transition metal complexes. As a part of our continuing efforts to investigate

SCHIFF BASE METAL(II) COMPLEXES
1585
Figure 1. Structure of the Schiff base.
transition metal chelates using 4-aminoantipyrine derivatives,[7] we describe
in this paper the synthesis, characterization, redox and biological activity of
transition metal complexes containing a new tetradentate N2O2 donor type
Schiff base derived from the condensation of 4-aminoantipyrine (1-phenyl-
2,3-dimethyl-4-aminopyrazol-5-one) with benzil. The structure of the Schiff
base is given in Fig. 1.
RESULTS AND DISCUSSION
The new Schiff base 1,2-(diimino-40-antipyrinyl)-1,2-diphenylethane
was synthesised by the condensation of 1-phenyl-2,3-dimethyl-4-amino-
pyrazol-5-one (4-aminoantipyrine) with benzil. The preparation of the
above Schiff base is described by the scheme in Fig. 2.
The metal chelates were prepared as follows:
Ethanol
VOSO4 ꢁH2O þ L
MCL2 ꢁxH2O þ L
½VOLꢂSO4 þ H2O
!
ð14Þ
Reflux
Ethanol
½MLCl2ꢂ þ xH2O
!
Reflux
M ¼ Cuð2Þ
M ¼ Nið6Þ
M ¼ Coð8Þ
M ¼ Mnð10Þ
M ¼ Znð12Þ
where M ¼ Cu(II), x ¼ 2; M ¼ Co(II), x ¼ 6; M ¼ Ni(II), x ¼ 6; M ¼ Mn(II),
x ¼ 4; M ¼ Zn(II), x ¼ 0

1586
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Ethanol
MðOAcÞ2 ꢁxH2O þ L
½MLðOAcÞ2ꢂ þ xH2O
!
Reflux
M ¼ Cuð3Þ
M ¼ Nið7Þ
M ¼ Coð9Þ
M ¼ Mnð11Þ
M ¼ Znð13Þ
where M ¼ Cu(II), x ¼ 1; M ¼ Co(II), x ¼ 0; M ¼ Ni(II), x ¼ 4; M ¼ Mn(II),
x ¼ 4; M ¼ Zn(II), x ¼ 2
The [CuL(Py)2]X2 complexes were synthesised by the following
equation:
Chloroform
½CuLX2ꢂ þ 2Py
½CuLðPyÞ2ꢂX2
!
Stirring
where X ¼ Cl (4) or OAc (5).
Microanalytical, molar conductance and magnetic susceptibility data
of the complexes are given in Table I. The analytical data of the complexes
agree very well with the general formulae [MLX2] or [VOL]SO4 (L ¼ 1,2-
(diimino-40-antipyrinyl)-1,2-diphenylethane, C36H32N6O2). The dipyridinyl
adduct of the [CuLX2] complexes corresponds to the general formula
[CuL(Py)2]X2 (X ¼ Cl or OAc). The monomeric nature of the complexes
was confirmed by their magnetic susceptibility data (Table I). The low
Figure 2. Scheme for the synthesis of the Schiff base.

SCHIFF BASE METAL(II) COMPLEXES
1587
conductance data of the Cu(II), Ni(II), Co(II), Mn(II) and Zn(II) chelates
confirm their non-electrolytic nature. However, the conductance of the
vanadyl complex and the dipyridinyl adducts of the copper complexes show
ten-fold higher conductance than that of other complexes, which suggest
that these complexes are eletrolytes. The structures of the [CuL(Py)2]X2
complexes are given in Fig. 3.
Infrared Spectra
In order to study the binding mode of the Schiff base to the metal in
the complexes, the IR spectrum of the free ligand was compared with the
spectra of the transition metal complexes. A strong band is observed in the
free ligand at 1650 cmꢀ1, characteristic of the cyclic keto group present in
the pyrazolone ring.[8710] This band is shifted to lower frequencies in all the
chelates upon coordination (Table II). Another band at 1630 cmꢀ1 in the
free ligand is due to the azomethine group. In the metal chelates, the band
characteristic of the azomethine group is shifted to 159071560 cmꢀ1 from
1630 cmꢀ1 in the ligand, suggesting coordination of the azomethine nitrogen
atom to the metal. All complexes, except the vanadyl complex, show
characteristic M-X frequencies (X ¼ Cl or OAc), indicating coordination of
the chloride or acetate groups.[11714] In addition, the vanadyl complex dis-
plays a band at 910 cmꢀ1 assignable to V¼O modes.[15] The [CuL(Py)2]X2
complexes (X ¼ Cl or OAc) show additional bands attributable to pyridine
ring vibrations at 1030 cmꢀ1 and 635 cmꢀ1, confirming the presence of
coordinated pyridine.[12]
1
FAB Mass and H NMR Spectra
The FAB mass spectra of the Schiff base and its copper complexes
were compared as regarding their stoichiometric composition. The Schiff
base shows a molecular ion peak Mþ at m=z ¼ 580 (28%). The molecular
ion peaks for [CuLCl2] and [CuL(OAc)2] complexes were observed at
m=z ¼712 (22%) and 763 (37%), respectively, which confirm the stoichio-
metry of metal chelates as MLX2.
1H NMR spectra of the ligand show the following signals: C6H5,
multiplet at 7.177.6 ppm, ¼C7CH3 at 2.3 ppm, 7N7CH3 at 3.373.4 ppm.
A slight downfield shift is observed for the [ZnL(OAc)2] complex. It also
exhibits a signal at 4.1 ppm assignable to 7CH3, present in the acetate
groups.

1588
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN

SCHIFF BASE METAL(II) COMPLEXES
1589

1590
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Figure 3. Suggested structures of the [CuL(Py)2]X2 complexes.
Electronic Absorption Spectra
The UV-Vis. spectral data of the Schiff base and its Cu(II), Ni(II),
Co(II) and VO(IV) complexes are given in Table III which includes the
solvents, absorption regions, band assignments, extinction coefficients and
the proposed geometry of the complexes. These values are comparable with
those of other reported similar type of complexes.[16719]
Table II. Important IR Spectral Data (cmꢀ1) of the Ligand and Its Complexes and
Their Assignments
No.
Compound
n(C¼O)
n(C¼N)
n(M7Cl)
n(M7OAc)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
L
[CuLCl2]
[CuL(OAc)2]
[CuL(Py)2]Cl2
[CuL(Py)2](OAc)2
[NiLCl2]
[NiL(OAc)2]
[CoLCl2]
[CoL(OAc)2]
[MnLCl2]
1650 s
1635 s
1630 s
1625 s
1620 s
1610 s
1615 s
1620 s
1615 s
1620 s
1600 s
1610 s
1625 s
1630 s
1630 s
1610 s
1600 s
1600 s
1580 s
1580 s
1590 s
1610 s
1600 s
1610 s
1580 s
1590 s
1610 s
1600 s
7
310 w
7
325 w
7
335 w
7
350 w
7
7
1320 m
7
1295 m
7
1360 m
7
(9)
7
1340 m
7
1320 m
7
1310 m
7
(10)
(11)
(12)
(13)
(14)
330 w
7
320 w
7
7
[MnL(OAc)2]
[ZnLCl2]
[ZnL(OAc)2]
[VOL]SO4

SCHIFF BASE METAL(II) COMPLEXES
1591
The [CuLCl2] and [CuL(OAc)2] complexes in DMSO solution show
bands at 14,085 cmꢀ1 and 12,033 cmꢀ1 respectively, which favour octahe-
dral geometry. These bands are shifted to 13,700 cmꢀ1 and 13,200 cmꢀ1
,
respectively, upon the coordination of pyridine. The electronic absorption
spectra of [CuL(OAc)2] and [CuL(Py)2](OAc)2 complexes are shown in
Fig. 4. This is also reflected in the cyclic voltammogram.
Redox Behaviour
Copper(II) Complexes
Cyclic voltammogram of the copper complexes in DMSO solution
show a quasi-reversible redox couple for Cu(II)=Cu(I) in the 1.0 V to ꢀ1.2
V range and the peak potentials of the complexes are given in Table IV.
With a view to examine the effect of the coordinating solvent on the redox
behaviour of the complexes, cyclic voltammograms of [CuL(Py)2]X2
complexes were recorded in DMSO solution and the data are reported in
Table IV. The cyclic voltammograms of [CuLCl2] and [CuL(Py)2]Cl2
complexes are shown in Fig. 5. In the [CuL(Py)2]X2 complexes, the redox
potentials for the Cu(II)=Cu(I) couple were slightly shifted to the
0.0270.09 V range (Table IV). Furthermore, the [CuL(Py)2]Cl2 complex
shows additional peaks for the copper(I)=copper(0) couple[20] at
Epc ¼ ꢀ0.77 V and Epa ¼ ꢀ0.62 V Such a large shift for the copper(-
I)=copper(0) couple may be due to the effect of coordinating ligands on the
copper(II) ion.
The cyclic voltammogram of the Schiff base in DMSO solution shows
an irreversible reduction peak at ꢀ1.52 V, which is beyond the range of
potentials studied for the complexes.
Oxovanadium(IV) Complexes
The cyclic voltammogram of the [VOL]SO4 complex in MeCN was
recorded at room temperature (Fig. 6). It shows a quasi-reversible peak for the
vanadium(IV)?vanadium(V) couple at Epa ¼ 0.60 V with the direct cathodic
peak for vanadium(V)?vanadium(IV) at Epc ¼ 0.51 V.[21] The complex also
shows another peak characteristic of vanadium(IV)? vanadium(III) at
Epc ¼ ꢀ0.92 V. In the anodic side, the peak at Epa ¼ ꢀ0.56 V is assigned to
the oxidation of vanadium(III)?vanadium(IV). The quasi-reversibility of the
VO(IV)=VO(V) couple was found to be unaffected by varying the scan rates
with peak potentials. The data are given in Table V.

1592
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN

SCHIFF BASE METAL(II) COMPLEXES
1593

1594
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Figure 4. The electronic absorption spectra of [CuL(OAc)2] (a) and [CuL-
(Py)2](OAc)2 (b) at 300 K in DMSO.
ESR Spectra
The ESR spectra of metal chelates provide information about hyper-
fine and superhyperfine structures which are of importance in studying the
metal ion environment in the complexes i.e., the geometry, nature of the
ligating sites of the Schiff base and the metal and the degree of covalency of
the metal-ligand bonds. The ESR spectra of the Cu(II) complexes were
recorded in DMSO at 300 and 77 K. A typical spectrum of the [CuLCl2]
complex is shown in Fig. 7. The spectra of the copper complexes at 300 K
show one intense absorption band in the high-field range, which are iso-
tropic due to the tumbling motion of the molecules. However, these com-
plexes in the frozen state show four well-resolved peaks with low intensities
in the low-field region and one intense peak in the high-field region. No
Table IV. Cyclic Voltammetric Data of Cu(II) Complexes in DMSO Solution
Containing 0.1 M TMAP at 300 K for the Cu(II)=Cu(I) Couple (Scan Rate
100 mVsꢀ1
)
No.
Complex
Epa (V)
Epc (V)
Ipa (mA)
Ipc (mA)
(2)
(3)
(4)
(5)
[CuLCl2]
ꢀ0.02
0.54
ꢀ0.28
0.23
ꢀ6.92
ꢀ10.25
ꢀ5.33
10.62
11.04
6.25
[CuL(OAc)2]
[CuL(Py)2]Cl2
[CuL(Py)2](OAc)2
ꢀ0.04
ꢀ0.19
0.45
0.17
ꢀ11.88
12.60

SCHIFF BASE METAL(II) COMPLEXES
1595
Figure 5. Cyclic voltammograms of [CuLCl2] (a) and [CuL(Py)2]Cl2 (b) at 300 K in
(0.1 M TMAP) DMSO. Scan rate 100 mVsꢀ1
.
band corresponding to the ms ¼ ꢄ2 transition was observed in the spectra,
ruling out any Cu-Cu interaction. The spin Hamiltonian parameters of the
complexes are reported in Table VI.
The copper complex parameters are consistent with tetragonally
elongated octahedral geometry (g >g >2.0) and the unpaired electron
k
?
occupies predominantly the dx2ꢀy2 orbital for the Cu(II) chelates.[22727] We
have used simplified M.O. theory[23] to calculate the bonding coefficients (in-
plane p-bonding b2 and in-plane s-bonding a2), summarised in Table VI.
These values indicate that there is a substantial interaction in the in-plane
s-bonding, whereas the in-plane p-bonding is almost ionic. The results are
anticipated because there are no appropriate ligand orbitals to combine with
the dxy orbital of copper(II) ion. The structures of the copper complexes are
given in Fig. 8.
The ESR spectra of the vanadyl complexes were recorded in DMSO
solution at 300 and 77 K and are shown in Fig. 9. The room temperature
spectra of the complexes are a typical eight-line pattern which shows that a
single vanadium is present in the molecule, i.e., it is monomer. In the frozen
state, the spectra show two types of resonance components, one set due to
the parallel features and the other set due to the perpendicular features,
which indicate axially symmetric anisotropy with well-resolved sixteen-line

1596
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Figure 6. Cyclic voltammogram of [VOL]SO4 at 300 K in MeCN (0.1 M TMAP).
Scan rate 100 mVsꢀ1
.
hyperfine splitting, characteristic of the interaction between the electron and
the vanadium nuclear spins. From Table VI, the observed order in the
parameters (A >A and g >g ) indicates that the unpaired electron is
k
?
?
k
present in the dxy orbital with square-pyramidal geometry around
the oxovanadium(IV) chelates.[28732] The vanadyl complex is shown in
Fig. 10.
Table V. Redox Potential for [VOL]SO4 (14) Complex in Acetonitrile Solution
Containing 0.1 M TMAP at 300 K for the VO(II)=VO(III) Couple
Scan rate mVsꢀ1
Epa (V)
Epc (V)
DEp
Ipa (mA)
Ipc (mA)
Ipc=Ipa
50
100
150
200
250
0.59
0.60
0.62
0.63
0.65
0.51
0.51
0.53
0.52
0.55
0.08
0.09
0.08
0.11
0.10
ꢀ17.74
ꢀ18.56
ꢀ19.38
ꢀ19.85
ꢀ20.49
15.29
15.80
16.53
17.21
17.84
0.86
0.85
0.85
0.87
0.87

SCHIFF BASE METAL(II) COMPLEXES
1597
Figure 7. The X-band ESR spectrum of [CuLCl2] in DMSO at 300 (a) and 77 K (b).
The molecular orbital coefficients viz. in-plane p-bonding (b2)and in-
plane s-bonding (a2) were calculated from the spin Hamiltonian parameters
of the complexes. The lower values of a2compared to b2 indicate that the
in-plane s-bonding is more covalent than the in-plane p-bonding. Fur-
thermore, the in-plane p-bonding coefficient value (b2) does not deviate
much from unity. For most of the complexes, the in-plane p-bonding
coefficient remains constant and spans the region 0.94 to 1.00. This is
consistent with Kivelson’s conclusion[31] that the dxy orbital is essentially
non-bonding while b2 remains constant.
The X-band ESR spectra of the manganese complexes were recorded
in DMSO solution at 300 K the typical spectrum of the [MnLCl2] complex

1598
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Table VI. The Spin Hamiltonian Parameters of the Copper, Vanadyl, and Man-
ganese Complexes in DMSO Solution
All
A
Hyperfine
Aiso
?
constants
610ꢀ4 cmꢀ1
No.
Complex
gll
g
giso
a2
b2
?
(2) [CuLCl2]
(3) [CuL(OAc)2]
(4) [CuL(Py)2]Cl2
143
137
156
33
27
43
32
7
7
76
87
81
78
73
92
94
122
2.36 2.08 2.13 0.86 0.89
2.33 2.07 2.15 0.73 0.82
2.34 2.07 2.16 0.79 0.91
2.37 2.04 2.17 0.75 0.86
(5) [CuL(Py)2](OAc)2 149
(10) [MnLCl2]
(11) [MnL(OAc)2]
(14) [VOL]SO4
7
7
196
7
7
7
7
2.02
1.99
7
7
7
7
1.92 1.96 1.91 0.75 0.92
is given in Fig. 11 and the parameters are summarised in Table VI. It shows
a six-line hyperfine structure due to manganese(II) (I ¼ 5=2). This is very
similar to those of mononuclear, hexa-coordinate manganese com-
6
plexes[34,35] with the ground state S5=2, indicating no significant magnetic
interaction between the manganese(II) ions. This fact is also supported by
the magnetic susceptibility data of the complexes. The proposed structures
for the manganese complexes are shown in Fig. 12.
Antimicrobial Activity
The in vitro biological screening effect of the investigated compounds
was tested against two Gram-positive bacteria: S. aureus and B. subtilis and
Figure 8. Suggested structures of the Cu(II) complexes.

SCHIFF BASE METAL(II) COMPLEXES
1599
Figure 9. The X-band ESR spectrum of [VOL]SO4 in DMSO at 300 (a) and 77 K (b).
Figure 10. Suggested structure of the [VOL]SO4 complex.

1600
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Figure 11. The X-band ESR Spectrum of [MnLCl2] in DMSO at 300 K.
five Gram-negative bacteria: K. pneumoniae, S. typhi, E. coli, P. aeruginosa
and S. flexneri. The inhibition zones were measured and are listed in
Table VII. The antifungal activity of the compounds were studied on A. niger
and R. bataicola and the zone of inhibition for the growth of fungi with
various concentration and the control is given in Table VIII. The biological
screening effect of the uncomplexed metal salts were tested against all
the bacteria (20 mg per test) and the fungi (100 mg per test). The zone of
Figure 12. Suggested structures of the Mn(II) complexes.

SCHIFF BASE METAL(II) COMPLEXES
1601

1602
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Table VIII. Antifungal Activity of the Compounds by the Well Diffusion Method
(Zone of Inhibition in mm)
Rhizoctonia bataicola
(mg)
Aspergillus niger (mg)
No.
Compound
100
200
300
100
200
300
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
L
[CuLCl2]
[CuL(OAc)2]
[CuL(Py)2]Cl2
[CuL(Py)2](OAc)2
[NiLCl2]
[NiL(OAc)2]
[CoLCl2]
[CoL(OAc)2]
[MnLCl2]
[MnL(OAc)2]
[ZnLCl2]
[ZnL(OAc)2]
[VOL]SO4
Controla
12
20
24
23
21
6
18
14
10
7
18
35
38
28
23
12
24
23
29
11
14
13
18
14
14
27
42
46
33
37
17
33
30
41
20
23
19
29
27
22
18
24
30
17
16
25
13
15
10
8
13
10
9
12
10
41
35
44
26
26
47
28
27
24
20
28
17
21
26
15
49
47
53
31
37
56
37
41
32
27
36
31
37
33
23
(9)
(10)
(11)
(12)
(13)
(14)
(15)
10
6
13
9
8
aAmphotericin.
inhibition for the growth of microorganisms is summarised in Table IX for
the sake of comparison.
From Tables VII and VIII, the observed values indicate that most of
the complexes have higher antimicrobial activity than the free ligand. Such
increased activity of the metal chelates can be explained on the basis of
Overtone’s concept[36] and the Tweedy’s chelation theory.[37] According to
Overtone’s concept of cell permeability, the lipid membrane that surrounds
the cell favours the passage of only lipid soluble materials, an increase in the
liposolubility is an important factor which controls the antimicrobial activ-
ity. The free ligand also has some lipophilicity, which has been further
improved by chelation with metal ion. On chelation, the polarity of the metal
ion will be reduced to a greater extent due to the overlap of the ligand orbital
and partial sharing of the positive charge of the metal ion with donor groups.
Further, it increases the delocalisation of p-electrons over the whole chelate
ring and enhances the lipophilicity of the complexes. This increased
lipophilicity enhances the penetration of the complexes into lipid
membranes and blocking of the metal binding sites in the enzymes of
microorganisms. These complexes also disturb the respiration process of

SCHIFF BASE METAL(II) COMPLEXES
1603

1604
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
the cell and thus block the synthesis of proteins, which restricts further
growth of the organism. Furthermore the mode of action of the compounds
may involve formation of a hydrogen bond through the azomethine group
with the active centres of cell constitutents, resulting in interference with the
normal cell process.[36739]
A comparative study of the Schiff base and its complexes with
uncomplexed metal salts (zone of inhibition) indicates that most of the
metal salts exhibit higher antimicrobial activity than the synthesised
compounds. The compound binds with organism to form the hypo-
thetical compound-organism complex. According to the Chelation Theory,
the compound-organism interaction visualised in the equilibria is given
below:[40]
*
L
þ
þ
R
LR
)
ðLigandÞ
½MLꢂ
ðOrganismÞ
ðLigand-organism complexÞ
RML
*
)
R
ðMetal chelateÞ ðOrganismÞ ðMetal bridged-ligand-organism complexÞ
*
)
MX2
þ
R
MRX2
ðMetal saltÞ
ðOrganismÞ
ðMetal-organism complexÞ
The above-mentioned equilibria suggest that the antimicrobial
activity of the compound depends on the ability of formation of a
compound-organism complex. The order of capability of forming the
compound-organism complex is in the following order:
Uncomplexed metal salt > Metal chelate > Free ligand
It clearly indicates that the uncomplexed metal salts have greater
ability to form the compound-organism complex. Hence, the metal salts
have higher antimicrobial activity.
EXPERIMENTAL
All the chemicals, such as the metal salts (CuCl2ꢁ2H2O, Cu(OAc)2ꢁ-
H2O, NiCl2ꢁ6H2O, Ni(OAc)2ꢁ4H2O, CoCl2ꢁ6H2O, Co(OAc)2, MnCl2ꢁ4H2O,
Mn(OAc)2ꢁ4H2O, ZnCl2, Zn(OAc)2ꢁ2H2O and VOSO4ꢁ2H2O) and solvents,
were Merck products and were used without purification. In the voltam-
metric experiments, Me4NClO4 (TMAP), used as the supporting electrolyte,

SCHIFF BASE METAL(II) COMPLEXES
1605
was purchased from Sigma. Elemental analyses,1H NMR and mass spectral
data of the samples were measured at the Regional Sophisticated Instru-
mentation Centre, Central Drug Research Institute, Lucknow, India. FAB
mass spectra were recorded on a JEOL SX 102=DA-6000 mass spectrometer
using m-nitrobenzyl alcohol as a matrix. The X-band ESR spectra of the
copper, mangenese and vanadyl complexes were recorded in DMSO solu-
tion on a Varian ESR spectrometer using diphenylpicrylhyrazyl (DPPH) as
internal standard at the Regional Sophisticated Instrumentation Centre,
Indian Institute Technology, Chennai. The IR spectra of the samples were
recorded on a Perkin-Elmer 783 spectrophotometer as KBr discs. The UV-
Vis spectra of the Schiff base and its Cu(II), Ni(II), Co(II) and VO(IV)
complexes were recorded on a Shimadzu UV-160 spectrophotometer. The
magnetic susceptibility measurements of the complexes were made on a
Guoy balance using CuSO4 as the calibrant. Cyclic voltammograms of the
[CuLCl2], [CuL(OAc)2] and [VOL]SO4 complexes (2 mmol) in DMSO
(10 mL at 300 K were recorded by using a BAS CV 50 electrochemical
analyser. The three-electrode cell contained a reference Ag=AgCl electrode,
Pt wire auxillary electrode and glassy carbon (0.07 cm2 dia) working elec-
trode. Unless stated otherwise, all of the potentials are referred to Ag=AgCl.
The molar conductances of the complexes in DMSO solution were measured
using a 305 Systronic conductivity bridge.
Synthesis of Schiff Base
An ethanolic solution (20 mL) of benzil (1.05 g, 5 mmol) and
4-aminoantipyrine (2.03 g, 10 mmol) was boiled under reflux for about 5 h.
On cooling, the yellow solid of 1,2-(diimino-4-antipyrinyl)-1,2-diphenyl-
ethane (L) formed which was filtered and recrystallized from ethanol. Yield:
3.48 g (60%).
Synthesis of Metal Complexes
The metal complexes of Cu(II), Ni(II), Co(II), Mn(II), VO(IV)
and Zn(II) were prepared by refluxing a mixture of MCl2, M(OAc)2
or VOSO4 (5 mmol) with 1,2-(diimino-40-antipyrinyl)-1,2-diphenylethane
(2.9 g, 5 mmol) in ethanol (50 mL) for about 6 h. Then the solution was
reduced to one-third on a waꢃter bath. To the resultant solution, was
added petroleum ether (60780 C b.p. range, 10 mL) with constant stir-
ring. The solid complex obtained was filtered, washed with EtOH and
dried in vacuo.

1606
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Synthesis of [CuL(Py)2]X2 Complexes (X ¼ Cl or OAc)
To a suspension of the solid [CuLCl2]=[CuL(OAc)2] complexes
(5 mmol) in CHCl3 (20 mL), was added pyridine (0.79 g, 10 mmol) with
constant stirring at 27 ꢃC for about 5 h. The solid product obtained
was filtered and washed thoroughly with CHCl3 and dried at room tem-
perature.
Antimicrobial Activity
The in vitro biological screening effects of the investigated compounds
were tested against two Gram-positive bacteria, S. aureus and B. subtilis and
four Gram-negative bacteria, K. pneumoniae, S. typhi, P. aeruginosa and S.
flexneri, by the well diffusion method[41] (Kirby-Bayer method) using agar
nutrient as the medium and gentamycin as control.
The antifungal activity of the compounds were evaluated by the well
diffusion method[41] against the fungi A. niger and R. bataicola cultured on
potato dextrose agar as medium. Acetonitrile was used as a solvent and
amphotericin as control. The stock solutions were prepared by dissolving
the compounds in acetonitrile. In a typical procedure, a well was made on
the agar medium inoculated with the microorganisms. The well was filled
with the test solution using a micropipette and the plate was incubated at
35 ꢃC for 24 h for the bacteria and 72 h for the fungi. During this period, the
test solution diffused and the growth of the inoculated microorganisms was
affected. The inhibition zone developed on the plate was measured. The
biological screening effects of uncomplexed metal salts were tested against
all the nine organisms by adopting the same procedure.
ACKNOWLEDGMENTS
The authors express their sincere thanks to the University Grants
Commission, New Delhi, for financial support and to Prof. P. R.
Athappan, School of Chemistry, Madurai Kamaraj University, for CV
facilities. The authors also thank the Managing Board, Principal and Head
of the Department of Chemistry of Virudhunagar Hindu Nadars’ Sen-
thikumara Nadar College for providing research facilities. K. J. thanks the
Management and Principal of Mepco Schlenk Engineering College for
their support. One of the authors (A. K.) thanks the Council of Scientific
and Industrial Research, New Delhi, for the award of a Senior Research
Fellowship.

SCHIFF BASE METAL(II) COMPLEXES
REFERENCES
1607
1. Ismail, K.Z.; El-Dissouky, A.; Shehada, A.Z. Spectroscopic and
Magnetic Studies on Some Copper(II) Complexes of Antipyrine Schiff
Base Derivatives. Polyhedron 1997, 16, 290972916.
2. Singh, L.; Sharma, A.; Sindhu, S.K. Structure and Bonding of Some
Newly Synthesized Complexes of Lanthanide(III) Complexes of
4[N-p-Dimethylaminobenzalidene)amino]antipyrine. Asian J. Chem.
1999, 11, 144571450.
3. Shankar, G.; Premkumer, R.R.; Ramalingam, S.K. 4-Aminoantipyrine
Schiff Base Complexes of Lanthanide and Uranyl Ions. Polyhedron
1986, 5, 991.
4. Chopra, J.R.; Uppal, D.; Arrora, U.S.; Gupta, S.K. Synthesis and
Spectral Studies of Cu(II) Complexes of 4[N-(2-Hydroxy-1-naphtha-
lidene)amino]antipyrine. Asian J. Chem. 2000, 12, 127771281.
5. Agarwal, R.K.; Garg, P.; Agarwal, H.; Chandra, J. Synthesis,
Magneto-Spectral and Thermal Studies of Co(II) and Ni(II) Com-
plexes of 4-[N-(N-(4-Dimethylaminobenzylidene)amino]antipyrine.
Synth. React. Inorg. Met.-Org. Chem. 1997, 27 (2), 2517268.
6. Singh, L.; Tyagi, N.; Dhaka, N.P.; Sindhu, S.K. Synthesis, Spectral
and Thermal Studies of Some Lanthanide(III) Complexes
of 4-[N-(Benzalidene)amino]antipyrine-thiosemicarbazone. Asian J.
Chem. 1999, 11, 5037508.
7. Raman, N.; Kulandaisamy, A.; Shunmugasundaram, A.; Jeyasubra-
manian, K. Synthesis, Spectral, Redox and Antimicrobial Activities of
Schiff Base Complexes Derived from 1-Phenyl-2,3-dimethyl-4-amino-
pyrazol-5-one and Acetoacetanilide. Transition Met. Chem. 2001, 26,
1317135.
8. Agarwal, R.K.; Singh, G. Preparation, Spectral and Thermal Studies
of Some Oxovanadium(IV) Complexes of 4-Aminoantipyrine. Synth.
React. Inorg. Met.-Org. Chem. 1986, 16 (8), 118371196.
9. Kuncheria, B.; Indrasenan, P. Thorium(IV) Nitrate Complexes with
Some Schiff Bases of 4-Aminoantipyrine and Certain Carbonyl
Compounds. Polyhedron 1988, 7, 1437146.
10. Donia, A.M.; El-Saled, F.A. Complexes of Mn(II) and Ni(II) with the
Keto Form of Some Antipyrine Schiff Base Derivatives. Polyhedron
1988, 7, 214972153.
11. Rao, M.S.; Reddy, K.H. Preferential Hexa-coordination of Cobalt(II)
Complexes with Hetaroaroyl-hydrazones. Indian J. Chem. 1999, 38A,
2627266.

1608
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
12. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Co-
ordination Compounds, 3rd Edn. Wiley Interscience: New York, 1977;
2967346.
13. Shakir, M.; Varkey, S.P.; Firdaws, F.; Hameed P.S. Template Synth-
esis of Iron(II), Cobalt(II), Copper(II) and Zinc(II) Complexes of
Diamidediimine Macrocycles. Polyhedron 1994, 13, 231972325.
14. Shakir, M.; Varkey, S.P.; Nasman, O.S. M. Transition Metal Com-
plexes of 20722-Membereed Octaaza Macrocycles: Synthesis and
Characterisation. Polyhedron 1995, 14, 128371288.
15. Zamian, J.R.; Dockal, E.R.; Castellano, G.; Oliva, G. Synthesis and
Characterisation of [N,N0-Ethylenebis(3-ethoxysalicylideneaminato]-
oxovanadium(IV). Polyhedron 1995, 14, 241172418.
16. Lever, A.B.P. Inorganic Electronic Spectroscopy, 2nd Edn. Elsevier:
New York, 1968; 2567265, 3177361.
17. Duta, R.L.; Syamal, A. Elements of Magnetochemistry, 2nd Edn. East-
West Press: New Delhi, 1992; 2067250.
18. Sharada, L.N.; Ganorkar, M.C. Synthesis and Structural Studies of
VO(IV), Mn(II), Co(II), Ni(II) & Cu(II) Complexes with New Tri-
dentate Schiff Bases Having ONO & ONN Donor Systems. Indian. J.
Chem. 1988, 27A, 6177621.
19. Former, R.L.; Urbach, F.L. Stereochemistry and Electronic Structure
of Oxovanadium(IV) Chelates with Tetradentate Schiff Base Ligands
Derived from 1,3-Diamines. Inorg. Chem. 1974, 13, 5877591.
20. Jeyasubramanian, K.; Samath, S.A.; Thambidurai, S.; Murugesan, R.;
Ramalingam, S.K. Cyclic Voltammetric and ESR Studies of a Tetra-
aza 14-Membered Macrocyclic Copper(II) Complex Derived from 3-
Salicylideneacetylacetone and o-Phenylenediamine; Stabilization and
Activation of Unusual Oxidation States. Transition Met. Chem. 1995,
20, 76780.
21. Dutton, K.G.; Fallon, D.; Murray, K.S. Synthesis, Structure, ESR
Spectra and Redox Properties of [N,N0-Ethylenebis(thiosalicylidene-
aminato)]oxovanadium(IV) and of Related {S,N} Chelates of Vana-
diium(IV). Inorg. Chem. 1988, 27, 34738.
22. Ray, R.K.; Kauffman, G.R. EPR Spectra and Covalency of
Bis(amidinourea=o-alkyl-1-amidinourea)copper(II) Complexes. Part
2ꢀ
II. Properties of the CuN4 Chromophore. Inorg. Chim. Acta 1990,
173, 2077214.
23. Boas, J.F.; Dunhill, R.H.; Pilbrow, J.R.; Srivastava, R.C.; Smith, T.D.
Electron Spin Resonance Studies of Copper(II) Hydroxycarboxylic
Acid Chelates in Aqueous and Non-aqueous Solutions. J. Chem. Soc.
(A) 1969, 947108.

SCHIFF BASE METAL(II) COMPLEXES
1609
24. Veeraraj, A.; Sami P.; Raman, N. Copper(II) Complexes of
3-Cinnamalideneacetylacetone: Synthesis and Characterisation. Proc.
Indian Acad. (Chem. Sci.) 2000, 112, 5157561.
25. Billing, D.E. Electron Spin Resonance Spectrum of the Copper(II) Ion
Incorporated into Barium Chloride Dihydrate. J. Chem. Soc. (A),
1970, 209972102.
26. Dudley, R.J.; Hathaway, B.J. Single-crystal Electronic and ESR
Spectra of Bis(aquo)monoacetylacetonatocopper(II) Picrate. J. Chem.
Soc. (A) 1970, 72571728.
27. Billing, D.E.; Hathaway, B.J.; Nicholls, P. The Single-crystal Elec-
tronic and Electtron Spin Resonance Spectra of Calcium Copper(II)
Acetate Hexahydrate. J. Chem. Soc. (A) 1970, 187771881.
28. Patel, K.S.; Kolawole, G.A. Magnetic and Spectral Properties of
VO(IV) Complexes of Quadridentate Naphthaldiamine Ligands. J.
Coord. Chem. 1982, 11, 2317237.
29. Boucher, L.J.; Tynan, E.C.; Yen, T.F. Spectral Properties of Ox-
ovanadium(IV) Complexes. I. b-Ketimines. Inorg. Chem. 1968, 7,
7317736.
30. Kadish, K.M.; Sazou, D.; Araullo, C.; Liu, Y.M.; Saoiabi, A.; Ferhat,
M.; Guilard, R. Electrochemical and Spectral Characterisation of
Copper, Zinc, and Vanadyl meso-Tetrakis(1-methylpyridinium-4-yl)-
porphyrin Complexes in Dimethyl Formamide. Inorg. Chem. 1988, 27,
231372320.
31. Yen, T.F. Electron Spin Resonance of Metal Complexes, 1st Edn.
Plenum Press: New York, 1969; 1117133.
32. Dodward, S.S.; Dhamnaskar, R.S.; Prabhu, P.S. Electron Spin Re-
sonance Spectral Studies of Vanadyl Complexes with Some Schiff
Bases. Polyhedron 1989, 8, 174871750.
33. Money, J.K.; Folting, K.; Huffman, J.C.; Collison, D.; Temperley, J.;
Mabbs, F.E.; Christou, G. Isolation and Structure of [V(OSiMe3)-
(edt)2]ꢀ (edt2ꢀ ¼ Ethane-1,2-dithiolate), an Intermediate in the
Conversion of [VO(Edt)2]2ꢀ to [Vs(edt)2]2ꢀ with (Me3Si)2S. EPR
Characteristion of the Series [VE(LL)2]2ꢀ (E ¼ O, S, OSiMe3,
LL ¼ edt; E ¼ O, LL ¼ pdt). Inorg. Chem. 1986, 26, 458374589.
34. Dowsing, R.D.; Gibson, J.F.; Goodgame, M.; Hayward, P.J. Electron
Spin Resonance Studies of Some Manganese(II) Complexes with
Heterocyclic Ligands. J. Chem. Soc. (A) 1969, 1877193.
35. Yang, G.; Zhu, H.G.; Chen, X.M. Synthesis, Crystal Structure and
EPR Spectra of One-dimensional Manganese(II) 3,5-Dinitrobenzoate
Dihydrate. Transition Met. Chem. 2001, 26, 4237425.
36. Anjaneyula, Y.; Rao, R.P. Preparation, Characterisation and Anti-
microbial Activity Studies on Some Ternary Complexes of Cu(II) with

1610
RAMAN, KULANDAISAMY, AND JEYASUBRAMANIAN
Acetylacetone and Various Salicylic Acids. Synth. React. Inorg. Met.-
Org. Chem. 1986, 16 (2), 2577272.
37. Dharmaraj, N.; Viswanathamurthi, P.; Natarajan, K. Ruthenium(II)
Complexes Containing Bidentate Schiff Bases and their Antifungal
Activity. Transition Met. Chem. 2001, 26, 1057109.
38. Malhota, R.; Kumar, S.; Dhindsa, K.S. Synthesis, Characterisation
and Microbiocidal Activity of Co(II), Ni(II), Cu(II) and Zn(II)
Complexes of Aryloxyacetic acid Hydrazides. Indian. J. Chem. 1993,
32A, 4577459.
39. Mishra, L.; Singh, V.K. Synthesis, Structural and Antifungal Studies
of Co(II), Ni(II), Cu(II) and Zn(II) Complexes with New Schiff Bases
Bearing Benzimidazoles. Indian J. Chem. 1993, 32A, 4467449.
40. Chakrawarti, P.B. Chelation and Antibiotic Activity. J. Indian Chem.
Soc. 2001, 78, 2737279.
41. Pelczar, M.J.; Chan, E.C.S.; Krieg, N.R. Microbiology, 5th Edn.
Blackwell Science: New York, 1998; 5357537.
Received September 27, 2001
Accepted June 21, 2002
Referee I: K. Moedritzer
Referee II: J. H. MacNeil