# Synthesis, Structural, and Biological Studies of  Some  Schiff Bases and Their Metal Complexes

Authors: A. P. Mishra; Monika Soni
Journal: Metal-Based Drugs
 (2008)

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## Abstract

New bidentate or tridentate Schiff bases and their
VO(II) and Co(II) complexes formed by the condensation of methyl
isobutyl ketone with nicotinamide (mna)/2-amino-4-chlorophenol
(map) and 2-hydroxy acetophenone with nicotinamide
(han)/isoniazide (hai). Physicochemical characterization has been
carried out to determine the structure of the complexes. The FAB
mass and thermal data show degradation pattern of the complexes.
XRD analysis reveals that all the studied complexes crystallize as
tetragonal crystal system. Some of the complexes have been
screened for their antimicrobial activity by the well diffusion
technique using DMSO as solvent on different species of pathogenic
bacteria/fungi, that is,E. coli, S. aureus, S. fecalis,
A. niger, T. polysporum, and their antimicrobial potency
have been discussed. It has been found that all the complexes are
antimicrobially active and show higher activity than the free
ligand. Metal chelation affects significantly the
antimicrobial/bioactive behavior of the organic ligands.


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## Body

## 1. Introduction

Research interest in V/O chemistry derives from its
utility in several biological and industrial processes [1]. The coordination chemistry of vanadium has acquired renewed interest since
the discovery of vanadium in organisms such as certain ascidians and Amanita
mushrooms and as a constituent of the cofactors in vanadate-dependent
haloperoxidases and vanadium nitroginase [2]. Recent advances in
catalytic and medicinal properties of vanadium complexes have stimulated their
design and synthesis. The biochemical aspects of vanadium complexes have
further promoted the coordination chemistry of vanadium [3]. Its
biological significance is further examplified by its incorporation in natural
products and enzyme in potent inhibitor of phosphoryl transfer. Vanadium-containing compounds have their utility as insulin mimetic and antiamoebic
agent. The potential of vanadium (V) complexes as antiamoebic agents has thus
far only been marginally explored [4]. It is also suggested that
vanadium could be considered as a representative of a new class of nonplatinum
metal antitumor agents.Schiff bases and their complexes have a variety of
applications in biological clinical and analytical fields [5].
Recently there has been a considerable interest in the chemistry of hydrazine
and hydrazone compounds because of their potential pharmacological applications [6].
The remarkable biological activity of acid hydrazides R–CO–NH–NH2,
their corresponding aryolhydrazones R–CO–NH–N=CHR, and also their mode of
chelation with transition metal ions has aroused interest in the past due to
possible biomimetic applications. The coordination compounds of aroylhydrazones
have been reported to act as enzyme inhibitors and are useful due to their
pharmacological applications [7]. In the present paper, we
describe the synthesis, characterization, and biological activity of some
oxovanadium (IV) and cobalt (II) complexes of Schiff bases, namely, mna,
map, han, and hai.


## 2. Experimental

### 2.1. Synthesis of Schiff Bases (Ligands) and Complexes

Schiff bases (mna, han, hai, map) have been synthesized
by condensing the methanolic solution of methyl isobutyl ketone (0.08 mol) to
the methanolic solution of nicotinamide/2-amino-4-chlorophenol (0.08 mol) and
the methanolic solution of 2-hydroxy acetophenon (0.08 mol) with the methanolic
solution of nicotinamide/isoniazid (0.08 mol) in equimolar ratio. The
condensation product was filtered, washed with ethanol and ether, recrystalised
with ethanol, and dried under reduced pressure over anhydrous CaCl2.
Purity of the compounds was monitored by TLC using silica gel G. Schiff bases
have been characterized by elemental and IR spectra.The VO(II) and
Co(II) complexes have been prepared by mixing the methanolic solution of VOSO4⋅5H2O/CoCl2⋅6H2O
(0.08 mol) to the methanolic solution of Schiff bases (mna, han, hai, map)
(0.016 mol) in 1 : 2 molar ratio. The resulting mixture was then refluxed on
water bath for 10–12 hours. The precipitated complexes were recrystallized
twice with ethanol, finally washed with petroleum ether (60–80°C), and dried
under reduced pressure over anhydrous CaCl2 in a dessicator.


### 2.2. Characterization of the Complexes

The microanalyses % C, N, and H are estimated (on Heraeus
elemental analyzer), and IR spectra were recorded (on Perkin Elmer RX-I
Spectrophotometer) from Lucknow. Room temperature molar conductance (on Elico-CM82 Conductivity Bridge) and electronic absorption measurements (on Perkin Elmer Lambda-2B spectrophotometer) have been done from Sagar. TGA (on mettler Toledo star e
system) has been
done from Chandigarh, X-ray from Nagpur, FAB mass (on JEOL SX102/DA-6000 mass
spectrometer/data system using argon/xenon (accelerating voltage 10 kV) from Lucknow. X-band EPR spectra were recorded at room
temperature on Varian E-112 spectrophotometer (TCNA (g=2.0027) as the standard)
from Mumbai.


## 2.1. Synthesis of Schiff Bases (Ligands) and Complexes

Schiff bases (mna, han, hai, map) have been synthesized
by condensing the methanolic solution of methyl isobutyl ketone (0.08 mol) to
the methanolic solution of nicotinamide/2-amino-4-chlorophenol (0.08 mol) and
the methanolic solution of 2-hydroxy acetophenon (0.08 mol) with the methanolic
solution of nicotinamide/isoniazid (0.08 mol) in equimolar ratio. The
condensation product was filtered, washed with ethanol and ether, recrystalised
with ethanol, and dried under reduced pressure over anhydrous CaCl2.
Purity of the compounds was monitored by TLC using silica gel G. Schiff bases
have been characterized by elemental and IR spectra.The VO(II) and
Co(II) complexes have been prepared by mixing the methanolic solution of VOSO4⋅5H2O/CoCl2⋅6H2O
(0.08 mol) to the methanolic solution of Schiff bases (mna, han, hai, map)
(0.016 mol) in 1 : 2 molar ratio. The resulting mixture was then refluxed on
water bath for 10–12 hours. The precipitated complexes were recrystallized
twice with ethanol, finally washed with petroleum ether (60–80°C), and dried
under reduced pressure over anhydrous CaCl2 in a dessicator.


## 2.2. Characterization of the Complexes

The microanalyses % C, N, and H are estimated (on Heraeus
elemental analyzer), and IR spectra were recorded (on Perkin Elmer RX-I
Spectrophotometer) from Lucknow. Room temperature molar conductance (on Elico-CM82 Conductivity Bridge) and electronic absorption measurements (on Perkin Elmer Lambda-2B spectrophotometer) have been done from Sagar. TGA (on mettler Toledo star e
system) has been
done from Chandigarh, X-ray from Nagpur, FAB mass (on JEOL SX102/DA-6000 mass
spectrometer/data system using argon/xenon (accelerating voltage 10 kV) from Lucknow. X-band EPR spectra were recorded at room
temperature on Varian E-112 spectrophotometer (TCNA (g=2.0027) as the standard)
from Mumbai.


## 3. Results and Discussion

The analytical and physical data of the metal complexes
are presented in Table1. Elemental analysis of the complexes indicates the
stoichiometry to be 1:2 metal: ligand (Schiff base). The molar conductance
values in methanol (10−3 M) are 124.5 and 53.8 S cm2 mol−1,
respectively, for Co(II) and VO(II) (mna) complexes which indicate the uni-bivalent
electrolytic nature of the complexes. The observed conductance values for
Co(II) and VO(II) (han), (hai), and (map) complexes fall in the range of 6.5–20.1 S cm2 mol−1 suggesting
the nonelectrolytic nature of the complexes.Table 1
Analytical and physical data of ligand and metal complexes.
Compound numberCompounds/Molecular FormulaeElemental analysis % found/(Cal.)Molecular wt/colourDec.temp./ M.Pt. (°C)C %H %N %Yield %μeff B.MCond. S cm2 mol−1(1)C11H14N2O (mna)120–12569.57.114.562.0——(Pinkish Cream)(69.4)(7.3)(14.7)(2)[VO(mna)2]SO4⋅2H2O230–23945.94.512.770.71.7653.8(Dark Green)(45.6)(4.8)(9.6)(3)[Co(mna)2(H2O)2] Cl2>30048.05.212.754.55.07124.5(Purple)(48.3)(5.1)(10.2)(4)C14H12N2O2(han)12370.15.211.991.2——(Cream)(70.0)(5.0)(11.6)(5)[VO(han)2] H2O205–20759.53.514.385.91.7820.1(Dark Green)(59.4)(3.8)(9.9)(6)[Co(han)2]276–27862.44.114.355.35.1216.9(Purple)(62.3)(4.0)(10.3)(7)C14H13N3O2(hai)24065.65.216.386.4——(Cream)(65.8)(5.0)(16.4)(8)[VO(hai)2]3H2O120–12553.43.513.154.21.797.1(Dark Brown)(53.2)(3.8)(13.3)(9)[Co(hai)2]2H2O>30055.73.713.173.45.1013.3(Light Brown)(55.5)(3.9)(13.8)(10)C11H14NOCl (map)14062.86.56.444.4——(Light Coffee)(62.5)(6.6)(6.6)(11)[VO(map)2]5H2O>30045.04.15.088.31.766.5(Black)(45.5)(4.4)(4.8)(12)[Co(map)2(H2O)2] 2H2O>30047.34.85.060.85.0818.8(Black)(47.6)(4.6)(5.0)Electronic spectra.Table 2
Electronic spectral data and ligand field parameters of metal complexes [8–11].
Compound numberComplexesTransitionsBands (cm−1)Parameters 10Dq,B, ß, ß%, ν1/ν2, LFSE, λGeometry of the complexes(2)VO(II)(mna)B22-E2(ν1)12722—Square pyramidal/trigonal
bipyramidalB22-B12(ν2)19567B22-A12(ν3)—(3)Co(II) (mna)T14g(F)-A24g(F)(ν2)124846935, 1029, 0.91,OctahedralT14g(F)-T14g(P)(ν3)196078.12, 2.2, 66.2, −525(5)VO(II) (han)B22-E2(ν1)12500—Square pyramidal/trigonal
bipyramidalB22-B12(ν2)22311B22-A12(ν3)—(6)Co(II) (han)T14g(F)-A24g(F)(ν2)123636868, 1003, 0.89,OctahedralT14g(F)-T14g(P)(ν3)1916810.4, 2.2, 65.6, −542(8)VO(II) (hai)B22-E2(ν1)13000—Square pyramidal/Trigonal
bipyramidalB22-B12(ν2)—B22-A12(ν3)24271(9)Co(II) (hai)T14g(F)-A24g(F)(ν2)165319183, 1004, 0.89,OctahedralT14g(F)-T14g(P)(ν3)2058410.3, 2.2, 87.7, −714(11)VO(II) (map)B22-E2(ν1)13200—Square pyramidal/Trigonal
bipyramidalB22-B12(ν2)—B22-A12(ν3)24218(12)Co(II) (map)T14g(F)-A24g(F)(ν2)168949385, 951, 0.84,OctahedralT14g(F)-T14g(P)(ν3)1991215.0, 2.2, 89.7, −717


## 4. Thermal Analysis

### 4.1. Thermal Decomposition of [VO(mna)2] SO4⋅2H2O
[2]

The TG curve of the
complex shows that the complex starts decomposing at 60°C. Elimination of
lattice water molecules has been observed on increasing the temperature up to
130°C (Re. wt%, obs./cal., 95/93.7). Above this
temperature a gradual (but slow) weight loss continues up to 450°C, which
corresponds to the decomposition of the Schiff base and sulphate moiety from
the metal chelate [12]. Almost horizontal thermal curve has been
observed after 450°C. The remaining weight (obs./cal. 29/24.6) corresponds to a mixture of metal
oxide in nitrogen atmosphere and some ashes as ultimate pyrolysis product.


## 4.1. Thermal Decomposition of [VO(mna)2] SO4⋅2H2O
[2]

The TG curve of the
complex shows that the complex starts decomposing at 60°C. Elimination of
lattice water molecules has been observed on increasing the temperature up to
130°C (Re. wt%, obs./cal., 95/93.7). Above this
temperature a gradual (but slow) weight loss continues up to 450°C, which
corresponds to the decomposition of the Schiff base and sulphate moiety from
the metal chelate [12]. Almost horizontal thermal curve has been
observed after 450°C. The remaining weight (obs./cal. 29/24.6) corresponds to a mixture of metal
oxide in nitrogen atmosphere and some ashes as ultimate pyrolysis product.


## 5. FAB Mass Spectra

The FAB mass spectrum of [Co(han)2]
[6]
shows a molecular ion peak (M+) at m/z 545 suggesting the complex to
be monomeric. The spectrum of complex also shows a series of peaks at m/z 513,
460, 391, 338, 276, 107 corresponding to various fragments [2, 13]. Their intensity
gives an idea about the abundance and stability of the fragments. On
the basis of the above spectral studies, the following molecular formula (see Table 1 [6])
may be suggested for this complex.The FAB mass spectrum of
[VO(map)2]⋅5H2O [14] shows a molecular ion peak (M+) at m/z 579, which suggests
the monomeric nature of the complex and confirms the proposed formula [14].
The peaks of appreciable intensity have been observed at m/z values 560, 519,
503, 487, 276, and 107, which indicate the fragmentation pattern. The m/z value
560 corresponds to [VO(map)2]⋅4H2O, 519 to [VO(map)2]2H2O,
503 to [VO(map)2]⋅H2O, 487 to [VO(map)2], 276
to [VO(map)]. The value 107 corresponds to VO with chelated O and N donor as
ligand moiety [2, 11, 13].


## 6. Infrared Spectra

### 6.1. Complexes of Oxovanadium (IV) and Cobalt (II) with Methyl Isobutyl Ketone
Nicotinamide (mna)

IR spectrum shows band at 1684 cm−1  ν(C=O); this has shifted to lower frequency region (1676 ± 10 cm−1)
in the complexes indicating the participation of amide (C=O) group in
chelation. The ligand band at 1620 cm−1 due to ν(C=N) azomethine
group has shifted to lower frequency (1590 ± 2 cm−1) in the complexes
indicating coordination through azomethine nitrogen. The appearance of broad
bands at 3350 and 3380 cm−1 in the spectra of complexes has been
assigned to associate water molecules [14, 15]. A medium intensity band at 655 cm−1 in Co(II)
complex is assignable to rocking mode due to coordinated water molecule. Some
new bands of weaker intensity at 520 ± 6 cm−1 and 469 ± 10 cm−1,
in both the complexes, give inferences about ν(M–O) and ν(M–N) bonding. The
characteristic band at 972 cm−1 in VO(II) complex has been assigned
to ν(V=O) vibrations [3]. The presence of an ionic sulphate
group in VO(II) complex has been confirmed by the appearance of the three bands [16, 17] at 1119(ν3) cm−1, 900(ν1), and 618(ν4)cm−1.


### 6.2. Complexes of Oxovanadium (IV) and Cobalt (II) with 2-Hydroxy
Acetopenone-Nicotinamide (han)

Schiff
base exhibits a strong intensity band at 1683 cm−1 due to C=O
(amide) and this has shifted to lower side (1675 cm−1) in Co(II)
complex, suggesting the chelation through carbonyl-oxygen atom of the free
base. A medium intensity band in ligand spectra at 1618 cm−1 is
attributed to ν(C=N) azomethine mode. In both complexes, this band has shifted
to higher frequency (1635 ± 6 cm−1), suggesting its involvement in
chelation [18]. Another important ligand band, occurring at
about 1350 cm−1 due to phenolic-OH, has been found absent in
complexes. This indicates the deprotonation of phenolic-OH on coordination with
metal. A band at 1202 cm−1 due to phenolic C–O shifts to higher side
(1220 ± 10 cm−1) in the complexes. This substantiates the same view.
The appearance of broad band
around 3410 cm−1 in the spectra of VO(II) complex has been assigned
to associated water molecule. The new weak bands at 420 ± 10 and 510 ± 2 cm−1 are due to the formation of ν(M–N) and ν(M–O) bands. In VO(II) complex, a
characteristic nonligand sharp band at 972 cm−1 is due to V=O
vibrations [10, 11, 16, 17].


### 6.3. Complexes of Oxovanadium (IV) and Cobalt (II) with 2-Hydroxy
Acetophenone-Isoniazide (hai)

IR spectrum exhibits a strong band at 1682 cm−1 due to (C=O) amide group. This has shifted down (1653 cm−1) in the
spectra of Co(II) complex indicating coordination through the carbonyl oxygen.
A band at 1607 cm−1 due to ν(C=N) azomethine group has shifted down
at 1593 ± 10 cm−1 in both complexes. This suggests the involvement of
the azomethine group in coordination. A band at 1373 cm−1 due to
phenolic-OH deformation has been found absent in complexes. This indicates the
deprotonation of phenolic-OH on coordination with metal ions [19–21].
A strong band at 1281 cm−1 in ligand spectrum due to C–O shifts to higher side (1325 ± 3 cm−1)
in complexes. This substantiates the same view [20]. The
appearance of broad band around 3310 ± 45 cm−1 in the spectra of
complexes has been assigned to associated water molecules. The new weaker bands
at 533 ± 8 and 420 ± 18 cm−1 in the metal complexes have been assigned
to ν(M–O) and ν(M–N) modes, respectively. A very sharp peak at 970 cm−1 suggests the presence of V=O bond in VO(II) complex [10, 11, 16, 17].


### 6.4. Complexes of Oxovanadium (IV) and Cobalt (II) with Methyl Isobutyl Ketone-2-Amino-4-Chloro Phenol (map)

The ligand spectrum exhibits
bands at 3380 cm−1 and 1386 cm−1 due to phenolic-OH.
These bands are absent in the spectra of the complexes, indicating the
deprotonation of phenolic-OH on coordination with metal ions. An intense ligand
band at 1278 cm−1 (phenolic-C–O) has shifted to higher frequency
side by 10–20 cm−1, in metal complexes. This further supports the
coordination of phenolic oxygen with metal ions. The ligand band at 1604 cm−1 (due to C=N) has shifted to lower frequency (1560 ± 6 cm−1) in the
complexes, indicating coordination through azomethine nitrogen [22, 23].
The appearance of broad band around 3186 ± 24 cm−1 in the spectra of
complexes has been assigned to associated water molecules. A medium intensity
band at 745 cm−1 in the spectrum of Co(II) complex is assignable to
rocking mode due to coordinated water molecule. Some new bands of weaker
intensity in complexes at 540 ± 5 cm−1 and 430 ± 5 cm−1 give
inference about ν(M–O) and ν(M–N) bonding. A nonligand sharp band at 983 cm−1 in the spectrum of VO(II) complex is assignable to νV=O [10, 11, 16, 17].


## 6.1. Complexes of Oxovanadium (IV) and Cobalt (II) with Methyl Isobutyl Ketone
Nicotinamide (mna)

IR spectrum shows band at 1684 cm−1  ν(C=O); this has shifted to lower frequency region (1676 ± 10 cm−1)
in the complexes indicating the participation of amide (C=O) group in
chelation. The ligand band at 1620 cm−1 due to ν(C=N) azomethine
group has shifted to lower frequency (1590 ± 2 cm−1) in the complexes
indicating coordination through azomethine nitrogen. The appearance of broad
bands at 3350 and 3380 cm−1 in the spectra of complexes has been
assigned to associate water molecules [14, 15]. A medium intensity band at 655 cm−1 in Co(II)
complex is assignable to rocking mode due to coordinated water molecule. Some
new bands of weaker intensity at 520 ± 6 cm−1 and 469 ± 10 cm−1,
in both the complexes, give inferences about ν(M–O) and ν(M–N) bonding. The
characteristic band at 972 cm−1 in VO(II) complex has been assigned
to ν(V=O) vibrations [3]. The presence of an ionic sulphate
group in VO(II) complex has been confirmed by the appearance of the three bands [16, 17] at 1119(ν3) cm−1, 900(ν1), and 618(ν4)cm−1.


## 6.2. Complexes of Oxovanadium (IV) and Cobalt (II) with 2-Hydroxy
Acetopenone-Nicotinamide (han)

Schiff
base exhibits a strong intensity band at 1683 cm−1 due to C=O
(amide) and this has shifted to lower side (1675 cm−1) in Co(II)
complex, suggesting the chelation through carbonyl-oxygen atom of the free
base. A medium intensity band in ligand spectra at 1618 cm−1 is
attributed to ν(C=N) azomethine mode. In both complexes, this band has shifted
to higher frequency (1635 ± 6 cm−1), suggesting its involvement in
chelation [18]. Another important ligand band, occurring at
about 1350 cm−1 due to phenolic-OH, has been found absent in
complexes. This indicates the deprotonation of phenolic-OH on coordination with
metal. A band at 1202 cm−1 due to phenolic C–O shifts to higher side
(1220 ± 10 cm−1) in the complexes. This substantiates the same view.
The appearance of broad band
around 3410 cm−1 in the spectra of VO(II) complex has been assigned
to associated water molecule. The new weak bands at 420 ± 10 and 510 ± 2 cm−1 are due to the formation of ν(M–N) and ν(M–O) bands. In VO(II) complex, a
characteristic nonligand sharp band at 972 cm−1 is due to V=O
vibrations [10, 11, 16, 17].


## 6.3. Complexes of Oxovanadium (IV) and Cobalt (II) with 2-Hydroxy
Acetophenone-Isoniazide (hai)

IR spectrum exhibits a strong band at 1682 cm−1 due to (C=O) amide group. This has shifted down (1653 cm−1) in the
spectra of Co(II) complex indicating coordination through the carbonyl oxygen.
A band at 1607 cm−1 due to ν(C=N) azomethine group has shifted down
at 1593 ± 10 cm−1 in both complexes. This suggests the involvement of
the azomethine group in coordination. A band at 1373 cm−1 due to
phenolic-OH deformation has been found absent in complexes. This indicates the
deprotonation of phenolic-OH on coordination with metal ions [19–21].
A strong band at 1281 cm−1 in ligand spectrum due to C–O shifts to higher side (1325 ± 3 cm−1)
in complexes. This substantiates the same view [20]. The
appearance of broad band around 3310 ± 45 cm−1 in the spectra of
complexes has been assigned to associated water molecules. The new weaker bands
at 533 ± 8 and 420 ± 18 cm−1 in the metal complexes have been assigned
to ν(M–O) and ν(M–N) modes, respectively. A very sharp peak at 970 cm−1 suggests the presence of V=O bond in VO(II) complex [10, 11, 16, 17].


## 6.4. Complexes of Oxovanadium (IV) and Cobalt (II) with Methyl Isobutyl Ketone-2-Amino-4-Chloro Phenol (map)

The ligand spectrum exhibits
bands at 3380 cm−1 and 1386 cm−1 due to phenolic-OH.
These bands are absent in the spectra of the complexes, indicating the
deprotonation of phenolic-OH on coordination with metal ions. An intense ligand
band at 1278 cm−1 (phenolic-C–O) has shifted to higher frequency
side by 10–20 cm−1, in metal complexes. This further supports the
coordination of phenolic oxygen with metal ions. The ligand band at 1604 cm−1 (due to C=N) has shifted to lower frequency (1560 ± 6 cm−1) in the
complexes, indicating coordination through azomethine nitrogen [22, 23].
The appearance of broad band around 3186 ± 24 cm−1 in the spectra of
complexes has been assigned to associated water molecules. A medium intensity
band at 745 cm−1 in the spectrum of Co(II) complex is assignable to
rocking mode due to coordinated water molecule. Some new bands of weaker
intensity in complexes at 540 ± 5 cm−1 and 430 ± 5 cm−1 give
inference about ν(M–O) and ν(M–N) bonding. A nonligand sharp band at 983 cm−1 in the spectrum of VO(II) complex is assignable to νV=O [10, 11, 16, 17].


## 7. ESR Spectra of the Oxovanadium (IV) Complexes

The X-band EPR spectra of oxovanadium (IV) (d1, 51V, I=7/2) complexes are not so resolved at room temperature to
exhibit all the eight-hyperfine lines. The calculated values of g||,g⊥,gav, and Δg for these two
complexes are given in Table 3.
Here, gav=1/3[2g⊥+g||]. The
values are typical of the spectra displayed by trigonal bipyramidal or square
pyramidal VO(II) complexes with one unpaired electron in an orbital of mostly dxy character. An anisotropic EPR spectrum is expected to exhibit two g values (gz=g||<g⊥=gx=gy) [2, 11, 20, 24, 25].Table 3
ESR parameters of the oxovanadium (IV) complexes.
Compound numberComplexesg||g⊥gavΔg(2)[VO(mna)2] SO4⋅2H2O1.90321.96641.94530.0632(8)[VO(hai)2]⋅3H2O1.94291.97241.96250.0295


## 8. X-Ray Studies

X-ray powder diffractogram of [Co(hai)2]⋅2H2O [13] and [VO(map)2]⋅5H2O [14] has been recorded using CuKα
as source in the range 5.50–80° (2θ). X-ray crystal system has been worked out
by trial and error methods, for finding the best fit between observed and calculated sin2θ
values [2]. Crystal parameters for [Co(hai)2]⋅2H2O [13] complex are as a=b=17.2238Å,c=30.4478Å,V=9032.62Å [3], Z=9, Dobs=1.000 g/cm3,
Dcal=1.030 g/cm3, particle size  =  21.87 nm, and crystal parameters
for [VO(map)2]⋅5H2O [14] complex are as a=b=11.2836Å,c=34.4447Å,V=4385.86Å [3], Z=7,Dobs=1.5367 g/cm3, Dcal=1.6951 g/cm3, particle size  =  12.01 nm. This reflects that these
complexes have crystallized in tetragonal system.


## 9. Biological Activity

The in vitro biological [26] screening results are given in
Tables 4 and 5.Table 4
Antibacterial screening data of Schiff bases and their metal
complexes. Standard  =  Gentamycin.
Compound numberDiameter of inhibition zone (mm) (concentrate in ppm)E.coliS. aureusS. fecalis2550100255010025501007(S.B)121216—1020———8(Complex)27313411121313131510(S.B)12131512121412—1311(complex)121316111215151415Standard202320101012182019DMSO—————————(—)  =  not measurable.Table 5
Antifungal screening data of Schiff bases and their
metal complexes. Standard  =  Nystatine.
Compound numberDiameter of inhibition zone (mm) (concentrate in ppm)A. nigerT. polysporum255010025501007(S.B)131315—15198(Complex)———11151710(S.B)———10191911(Complex)———121320Standard——————DMSO——————(—)  =  not measurable.These observations show that the majority
of the compounds are more active than their respective Schiff bases. In some
cases, Schiff bases and their complexes have similar activity against bacteria
and fungi. Chelation may enhance or suppress the biochemical potential of
bioactive organic species. The higher activity of the metal complexes may be
owing to the effect of metal ions on the normal cell membrane. Metal chelates
bear polar and nonpolar properties together; this makes them suitable for
permeation to the cells and tissues. Changing hydrophilicity and lipophilicity
probably leads to bring down the solubility and permeability barriers of cell,
which in turn enhances the bioavailability of chemotherapeutics on one hand and
potentiality at another [27].Structures of the Schiff base (Ligands).Proposed structures of the metal complexes.
(a)
(I) Oxovanadium(IV) and cobalt(II) complexes of Schiff base (mna). (II) Oxovanadium(IV) and cobalt(II) complexes of Schiff base (han)(b)
(III) Oxovanadium(IV) and cobalt(II) complexes of Schiff base (hai). (IV) Oxovanadium(IV) and cobalt(II) complexes of Schiff base (map)



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*Source: 875410-2008-07-27.xml*