Synthesis, complexation and biological activity of new Isatin Schiff-bases

Article abstract of DOI:10.4067/S0717-97072012000400030

Some new Schiff-bases derived from condensation of 3-hydrazono-2-oxo-2,3- dihydroindol-1-yl)-acetic acid hydrazide (3) with benzaldehyde, p-methoxy-benzaldehyde and p-chlorobenzaldehyde have been synthesized in high yields via refluxing in EtOH in the pre

Full text of DOI:10.4067/S0717-97072012000400030

J. Chil. Chem. Soc., 57, Nº 4 (2012)
SYNTHESIS, COMPLEXATION AND BIOLOGICAL ACTIVITY OF NEW ISATIN SCHIFF_BASES
S.A. SALLAM*, E.S.I. IBRAHIM AND M.I. ANWAR
Chemistry Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
(Received: August 5, 011 - Accepted: January 23, 2012)
ABSTRACT
Some new Schiff-bases derived from condensation of 3-hydrazono-2-oxo-2,3-dihydroindol-1-yl)-acetic acid hydrazide (3) with benzaldehyde, p-methoxy-
benzaldehyde and p-chlorobenzaldehyde have been synthesized in high yields via refluxing in EtOH in the presence of catalytic amount of acetic acid. The
I
synthesized compounds have been characterized by elemental analysis, IR, H-NMR and mass spectra. Cu(II), Zn(II), Mn(II) and Fe(III) complexes of the
synthesized compounds were prepared and characterized by elemental analysis, conductivity measurements, IR, UV-Vis. spectra and magnetic moment
measurements. TGA and DTA confirm the chemical formulation of the complexes and their thermal decomposition were evaluated. Antimicrobial activity of the
synthesized compounds have been screened using the desk diffusion method with different strains of bacteria: Staphylococcus aureus, Klebsiella pneumoniae,
Escherichia coli and Proteus volgaris were used.
Keywords: Isatin Schiff-bases; Cu(II), Zn(II), Mn(II) complexes; spectral, thermal properties and biological activity.
was filtered. The filtrate is concentrated under reduced pressure, the resulting
white crystalline precipitate was collected and crystallized from acetone-
hexane mixture. Yield: 1.1 g (69.6%), m.p. 139-140°C. Anal.: Calcd. (%) for
C12H11NO4 : C, 61.80; H, 4.75; N, 6.01. Found (%) : C, 61.79; H, 4.77; N, 5.87;
IR: ν(cm-1): 1696, 1675, 1653 (C=O); MS: M+ (%) = 233 (0.08), 205 (24), 172
(6), 162 (53), 160 (36), 148 (49.9), 120 (54), 119 (100), 91 (20).
(3-Hydrazono-2-oxo-2,3-dihydro-indol-1-yl)-acetic acid hydrazide: (3)
80% Hydrazine hydrate (4 ml , 80 mmol) was added to a solution
of (2) (1 g, 4.3 mmol) in EtOH (15 ml) and the mixture was stirred for 4 h
at room temperature and concentrated under reduced pressure. The resulting
solid white crystals was filtered off , crystallized from ethyl acetate to give
(3). Yield: 0.7 g (70 %); m.p. 183-186˚C. Anal.: calcd. (%) for C10H11N5O2 : C,
51.50, H, 4.75, N, 30.03; found (%): C, 51.48; H, 4.81; N, 29.98. IR: ν(cm-1):
3525(OH), 3433, 3337(NH), 1669(C=O), 1612(C=N); MS: (M+NHNH2) (%)
= 202 (9.16), 201 (72), 170 (100), 140 (20), 101 (38.5); 1H-NMR (CDCl3) δ
(ppm): 8.02 (d, 1H, H7), 7.88 (d, 1H, H6), 7.6 (m, 1H,H5), 7.5 (m, 1H, H8),
3.54 (s, 5H, 2NH2, OH), 2.6 (s, 2H, CH2).
INTRODUCTION
Isatin Schiff-bases are known to possess a wide range of pharmacological
properties
including
antibacterial1-3
,
anticonvulsant4-5
,
anti-HIV6-9
,
antifungal10-13 and antiviral activity14. Isatin bis-Schiff bases are characterized
by their capacity to co-ordinate to metal ions forming chelate rings15, act as
inhibitors of human α-thrombin16 and its copper(II) complex catalyzed the
oxidation of carbohydrates17. Recently it has been reported that isatin bis-imine
has antimicrobial properties18 and affects cell viability19.
We report here the synthesis and characterization of some new Schiff-
bases derived from the condensation of 3-hydrazono-2-oxo-2,3-dihydro-
indol-1-yl-acetic acid hydrazide with benzaldehyde, p-methoxybenzaldehyde
and p-chlorobenzaldehyde and also their Cu(II), Zn(II), Mn(II), and Fe(III)
complexes. Biological activity of the new compounds against strains of
bacteria [Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli and
Proteus vulgaris] was also tested.
(3-(Benzylidene-hydrazono)-2-oxo-2,3-dihydro-indol-1-yl)-acetic
benzylidene-hydrazide derivatives: (4-6)
acid
EXPERIMENTAL
Benzaldehyde or its derivative (20.0 mmol) was added to an acidified
(few drops of CH3COOH) stirred solution of (3) ( 2.3 g, 10.0 mmol) in
EtOH (20 ml) . The mixture was heated on a water bath for 2h, the precipitate
was filtered, washed with EtOH and crystallized from methanol to give the
following compounds:
Materials and methods
All used solvents and metal salts were of A.R. grade. They were supplied
by Merck and BDH and were used as received. All melting points measured
on a MEL-TempII melting point apparatus were uncorrected. Thin layer
chromatography (TLC) was carried out on aluminum sheets precoated with
silica gel mesh 60F 254 of 0.2 mm thick. Elemental analyses were carried out
using a Heraus CHN-rapid analyzer. Infrared spectra were recorded (KBr disc)
(3-Hydrazono-2-oxo-2,3-dihydro-indol-1-yl)-acetic acid benzylidene-
hydrazide: (HL1)
Yield: 85.3%; m.p. 196-198˚C. Anal. : calcd. (%) for C17H15N5O2: C,
63.54; H, 4.71; N, 21.79; found (%): C, 63.32 H, 4.77; N, 21.69. IR ν(cm-1):
3478 (OH), 3351 (NH), 1657(C=O), 1596, 1565 (C=N) ; MS: M+ (%) = 321
(0.03), 305 (0.05), 291(0.17), 187 (13.75), 186 (95.36), 170 (87.18); 142 (100);
1H-NMR δ (ppm): 12.1 (s, 1H, NH), 8.3 (s, 1H, CH), 8.0 - 7.2 ( m, 11 H, 9 Ar-
H, NH ), 2.7 (s, 2H, CH2).
in the 400-4000 cm-1 range on Bruker Vector22 spectrophotometer. H-NMR
1
measurements were carried out on a Bruker ARX (300 MHz) using d6-DMSO
as a solvent and TMS as internal standard. Mass spectral data are measured
on Varian MAT-711 mass spectrometer. GC-MS were obtained with model
5988A Hewlet-Packard 5890 spectrometer. Electronic absorption spectra
were obtained using 10-3 M DMF solutions in 1cm quartz cell on UV-1601PC
Shimadzu spectrophotometer. Magnetic susceptibility measurements were
carried out using the modified Gouy method20 on MSB-MK1 balance at room
temperature using [HgCo(SCN) ] as standard. The effective magnetic moment,
(3-2Hydrazono-2-oxo-2,3-dihydro-indol-1-yl)-acetic acid (4-methoxy-
benzylidene)-hydrazide: (HL2)
Yield 57%; m.p. 211-213˚C. Anal.: calcd.(%) for C18H17N5O3: C, 61.53; H,
4.88; N, 19.93; found (%): C, 61.51; H, 4.75; N, 19.89. IR ν(cm-1): 3447 (OH),
3293 (NH), 1650 (C=O), 1605, 1542 (C=N); MS: (M+-OCH3) (%) = 321 (0.7),
320 (5.72), 319 (24.1), 186 (95.25), 170 (82), 142 (100), 134 (23); 1H-NMR δ
(ppm): 12.01 (s, 1H, NH), 8.26 (s, 1H, CH), 8.11-6.81 ( m, 10H, 8Ar-H, NH2),
3.81 (s, 3H, OCH3), 2.71 (s, 2H, CH ).
μeff, per metal atom was calculat4e from the expression μeff = 2.83
B.M.,
χ.T
χ
where
is the molar susceptibility corrected using Pascal’s constant for
the diamagnetism of all atoms in the complexes. TGA, DTG and DTA were
recorded on Shimadzu-60 thermal analyzer under a dynamic flow of nitrogen
(30ml/min.) and heating rate 10˚C/min. Electrical conductivity measurements
were carried out at room temperature on freshly prepared 10-3M DMF solutions
using WTW conductivity meter fitted with L100 conductivity cell.
(3-Hydrazono-2-oxo-2,3-dihydr2o-indol-1-yl)-acetic
acid
(4-chloro-
benzylidene)-hydrazide: (HL3)
Yield 75.5%; m.p. 197-200˚C. Anal.: calcd.(%) for C17H14ClN5O2: C,
57.39; H, 3.97; N, 19.68; found (%): C, 57.37; H, 3.99; N, 19.71. IR ν(cm-
1): 3443 (OH), 3315 (NH), 1669 (C=O), 1594, 1559 (C=N), MS: (M+2)+ (%)
= 357.15 (0.07), M+ (%) = 355.5 (0.25), 325 (2.7), 186 (85), 170 (100), 142
Synthesis
(2,3-Dioxo-2,3-dihydro-indol-1-yl)acetic acid ethyl ester: (2)
To a stirred solution of isatin (1) ( 1.5 g, 10.18 mmol) in acetone (35 ml),
K2CO3 (1.4 g, 10.18 mmol) was added and the mixture was stirred for 1 h. A
solution of ethylchloroacetate (1 ml, 10.18 mmol) in acetone (15 ml) was added
dropwise with stirring for 5 h at room temperature after which the mixture
1
(84.6), 101 (27.6); H-NMR δ (ppm): 12.16 (s, 1H, NH), 8.35 (s, 1H, CH),
8.14-7.1 ( m, 10H (8Ar-H, NH2), 2.72 (s, 2H, CH2).
Synthesis of the complexes
To a solution of the Schiff-base (2 mmol) in EtOH (10 ml), a solution of
e-mail: shehabsallam@yahoo.com
1482

J. Chil. Chem. Soc., 57, Nº 4 (2012)
the metal salt (1 mmol) in ethanol (10 ml) was added dropwise with stirring.
The pH of the mixture was increased to 7–7.5 by addition of dilute KOH
solution. The whole mixture is refluxed with stirring for 2 hours. The formed
precipitate was filtered, washed with hot EtOH and dried under vacuum over
anhydrous CaCl2. Since the complexes were insoluble and non crystallizable in
common organic solvents, they were purified by washing thoroughly with hot
ethanol to remove unreacted metal salts.
group and disappearance of (NH) and amide (C=O) bands due to enolization.
These considerations suggest that the ligand has keto-enol tautomerism and
exist primarily in the enol form. The spectra exhibit a characteristic splitted
band in the 3266-3351 cm-1 range which is assigned to ν(NH2) in addition
to strong intensity band in the 750-765cm-1 range due to wagging vibration.
A strong band appeared at 1669-1650 cm-1 range is due to the isatin υ(C=O)
group. Two bands are shown in the 1605-1594 and 1565-1542 cm-1 range
which have been assigned as υ(C=N) of ketimine and aldimine moieties.
1H-NMR spectra showed signals attributed to the CH2, Ar-H, NH2, CH, and the
NH. 1H-NMR of compound (5) showed in addition to the previous signals a
new singlet at δ 3.81 ppm assigned to the OCH3 protons . Mass spectra confirm
the proposed structures of compounds (4-6).
Growth media
Nutrient agar medium of the following composition peptone 5.0 g, beef
extract 3.0 g, NaCl 5.0 g, agar 18.0 g and 1000 ml water has been used for
growing test organisms. The prepared media was poured into 9 cm plates
and allowed to solidify. Spore suspensions from actively growing cultures
were prepared using sterile distilled water. One ml of spore suspension was
transferred to these plates and incubated at 37˚C for appropriate growth periods
(1-3 days). 100 ppm of the tested compound was dissolved in DMF, while DMF
itself was used as control for comparison. The diameters of cleaning zones (in
mm) have been used as a parameter for antibacterial activity. Accordingly, the
resulting effects have been tentatively classified as follows: slightly active (1-
10 mm); moderately active (11-20 mm); highly active (20-30 mm) and very
highly active ( >30 mm).. Streptomycin was used as standard.
Metal complexes
All the complexes are stable at room temperature and non-hygroscopic
in nature. The stoichiometric ratios of the complexes have been calculated
from their elemental analysis. The complexes are insoluble in water and
common organic solvents (methanol, ethanol, benzene, chloroform, acetone,
dichloroethane and diethyl ether) but soluble in DMSO and DMF. The
analytical data (Table 1) show the following formulae for the complexes:
[Cu(HL1-3)2].(NO3)2.nH2O where n=5 , 1½ , 0 ; [Fe2(L1-3)(NO3)x(H2O)2]. (NO3)
z.nH2O where x=5, 5, 3; z=0, 0, 2; n=4, 1, 2 and [M2(L1-3)(H2O)4]. (NO3)3.nH2O
where M=Zn(II) and Mn(II) and n=1,1 ; ½, 1½; 1, 3. The molar conductance
values in DMF show that the Cu(II) complexes are 1:2 electrolytes, the Fe(III)
complexes are none-electrolytes except [Fe2(L3)(NO3)3(H2O)2].(NO3)2.2H2O
which is 1:2 electrolyte, the Zn(II) and Mn(II) complexes are 1:3 electrolytes.21
RESULTS AND DISCUSSION
Characterization of the Schiff-bases
Reaction of isatin (1) with ethyl chloroacetate afforded 2,3-dioxo-2,3-
dihydroindol-1-yl acetic acid ethyl ester (2) which upon reaction with hydrazine
hydrate in presence of acetic acid gave 3-hydrazono-2-oxo-2,3-dihydroindole-
1-ylacetic acid hydrazide (3). On heating (3) with each of benzaldehyde,
anisaldehyde and p-chlorobenzaldehyde in ethanol containing few drops of
acetic acid afforded the Schiff-bases HL1-HL3 respectively (Scheme 1)
IR Spectra
Some structurally significant IR bands of the free Schiff-bases and their
transition metal complexes are set out in Table 2.
The IR spectra of the Cu(II), Fe(III), Zn(II) and Mn(II) complexes show
the absence of υ(NH2) band due to overlapping with crystallization water band
while the band due to wagging vibration is shifted to lower frequency indicating
coordination through the amino nitrogen atom. A slight shift with decreasing
intensity of isatin υ(C=O) band confirms involvement of the carbonyl oxygen
in complexation. The disappearance of υ(OH) band in the spectra of the
complexes indicates deprotonation and participation in coordination with metal
ions. On the other hand, for the Cu(II) complexes the (OH) band is disappeared
due to overlapping with hydrated water band, and the deformation band δ(OH)
at 1250cm-1 almost has the same frequency as in the free ligand indicating non-
involvement of the OH group in coordination. The shifting in υ(C=N) band of
the aldimine moiety can be attributed to involvement in bonding while υ(C=N)
of the ketimine moiety appeared nearly at the same frequency as the parent
ligand indicating non-participating in bonding. The presence of coordinated
nitrate ions are indicated by two medium intensity bands at 1450, 1358 and
1432, 1302 cm-1 in the [Fe L1(NO )5(H2O)2].4H O and [Fe2L2(NO3)5(H2O)2].
H2O complexes due to υ4 an2d υ1 vib3rations of the 2nitrate ion of C2v Symmetry22.
Since (υ4-υ1) = 92 and 130 cm-1, the nitrate ions are coordinated as unidentate
group. These two complexes also exhibit bands due to bidentate nitrate groups
which show bands at 1506, 1292 and 1501, 1285 cm-1 with (υ4-υ ) =214 and
216 cm-1 .This is emphasized by the molar conductance of the1 complexes
which have values of 40 and 45 ohm −1 .cm2.mol −1 of 10-3M DMF solution,
indicating its non-electrolytic nature and hence the nitrate ions are coordinated
to the metal center. The IR spectrum of [Fe2L3(NO3)3(H2O)2].(NO3)2.2H2O
shows bands due to bidentate nitrate groups at 1500 and 1281cm-1 where (υ4-
υ1)=219 cm-1 together with strong and a medium intensity bands at 1381 and
855 cm-1 due to the υ3 and υ2 vibrations of the ionic nitrate (D3h)22. The Cu(II),
Zn(II) and Mn(II) complexes show strong bands in the 1367-1384 cm-1 range
and medium intensity bands in the 837-863 cm-1 range, due to the υ3 and υ2
vibrations of the ionic nitrate (D3h)23. A non ligand bands appear in the 515-612
and 413-515 cm-1 range in all the complexes have been assigned to υ(M-O)
and υ(M-N)24. Water of crystallization is shown by a medium intensity broad
band in the 3373-3525 cm-1 range in the spectra of the complexes.
Compound (3) shows three absorption bands at 3525, 3433 and 3337 cm-1
due to the hydrazide and hydrazone groups. This structure was also confirmed
by the 1H-NMR spectra which showed the presence of a broad singlet at δ 3.54
ppm assigned to the hydrazide and hydrazone groups together with two duplets
and three triplets in the δ 8.03-7.41 ppm range attributed to the four aromatic
protons besides a singlet at δ 2.6 ppm due to the methylene protons. Mass
spectrum of compound (3) shows that it losses a hydrazine molecule to give the
ketene radical cation with m/z = 201.IR spectrum of (2) shows three absorption
bands at 1696, 1675 and 1653 cm-1 assigned to the frequency of the carbonyl
groups. Mass spectrum of compound (2) showed the expected m/z = 233 which
losses the ethyl radical to give the cation with m/z = 205.
Magnetic and spectral studies
Magnetic moments and visible spectra of the complexes were used to
study the geometrical configuration of the metal complexes.
The magnetic moment values for the zinc(II) complexes are zero consistent
with its d10 configuration. Copper(II) complexes show magnetic moment values
in the 2.0-1.97 B.M. range which are close to spin only value. This range
indicates the absence of any appreciable spin-spin coupling between unpaired
electrons belonging to different molecules. According to Figgis25, a magnetic
moment value greater than 1.9 B.M. indicates tetrahedral or octahedral
IR spectra of the Schiff-bases HL1-HL3 showed a sharp medium intensity
band in the 3443-3478 cm-1 range assigned to stretching vibration of the (OH)
1483

J. Chil. Chem. Soc., 57, Nº 4 (2012)
stereochemistry, while magnetic moment value less than 1.9 B.M. is indicative
of square planer as well as tetrahedral stereochemistry. This shows that the
magnetic moment of the Cu(II) complexes is not of much use in deciding on
the stereochemistry of copper(II) complex.
The magnetic moments reported for the Fe(III) and Mn(II) complexes are
lower than the spin only values. The subnormal magnetic moments observed
for the complexes may be accounted for by the following:
Electronic spectra of the Schiff-bases and their complexes are recorded
in DMF. The copper(II) complexes show a broad band in the 625-665 range
which can be assigned to 2Eg→ 2T2g transition of copper(II) ion with octahedral
geometry29. The spectra of the Fe(III) complexes exhibit a band in the 516-485
nm range corresponding to A1g→ T1g transition consistent with octahedral
Fe(III) complexes29,30. The electronic spectra of the low-spin manganese
complex is dominated by strong charge-transfer bands. Any d-d band occurring
in the visible region is masked by strong charge-transfer bands.
Thermal Decomposition
6
4
a- Antiferromagnetic exchange interaction between the metal ions,
suggesting the possibility of spin-spin coupling26, 27
.
b- The possibility that the reduced moment represent a solid state
intermolecular interaction rather than an intramolecular coupling.
These considerations confirm the binuclear structure of the complexes.
Such lowering of the magnetic moment has been observed with other
polynuclear complexes28.
Thermal decomposition of the complexes studied in these work represents
characteristic pathways depending on the metal used as can be seen from the
TGA/DTG and DTA curves shown in Figures 1 and 2. The decomposition
stages, temperature ranges, decomposition products, as well as the found and
calculated weight loss are given in Tables 3 and 4.
Table 1: Analytical data, conductivity values and magnetic moments of the Schiff-bases and their complexes.
Elemental analysis
Found
Calcd. %
M.p.
°C.
Yield
%
* ΛM
DMF
**
Comopound
M.wt.
Color
μ /M
eff
C
H
N
M
63.49
63.58
4.51
4.67
21.91
21.81
HL1
320.82
918.48
849.35
726.51
705.60
350.82
916.12
825.35
747.51
744.6
yellow
green
198
>380
>380
>380
>380
213
85.3
72.3
—
—
130
40
—
2.0
1
L2
44.31
44.36
4.09
4.34
18.31
18.27
7.35
6.91
[Cu(H
)].(NO3)2 .5H2O
24.23
24.01
3.44
3.17
16.53
16.48
13.51
13.14
[Fe2L1(NO3)5(H2O)2].4H2O
[Zn2L1(H2O)4].(NO3)3.H2O
[Mn2L1(H2O)4].(NO3)3.H2O
HL2
brown
yellow
brown
white
63.2
2.72
Dia.
3.09
—
27.93
28.07
3.55
3.44
15.76
15.41
18.43
18.00
51.66
52.55
57
207
220
—
28.87
28.91
3.63
3.54
15.92
15.87
15.48
15.57
61.49
61.56
4.77
4.84
19.91
19.95
—
47.21
47.13
4.12
4.03
18.11
18.33
7.42
6.93
[Cu(H L2 )].(NO3)2.1½H2O
green
196
79.65
64.22
52.65
51.32
75.5
140
45
1.97
1.69
Dia.
2.11
—
2
26.36
26.17
2.69
2.78
16.73
16.96
13.53
13.95
[Fe2L2(NO3)5(H2O)2].H2O
brown
yellow
brown
white
220
[Zn2L2(H2O)4].(NO3)3.½H2O
28.83
28.89
3.11
3.47
14.61
14.98
17.81
17.49
296
220
225
—
[Mn2L2(H2O)4].(NO3)3.1½H2O
29.11
29.00
3.63
3.75
15.31
15.04
14.91
14.75
>380
200
57.48
57.40
3.81
3.93
19.67
19.7
HL3
355.32
897.48
847.85
761.01
—
[Cu(H L3 )].(NO3)2
44.47
44.51
3.31
3.27
18.01
18.33
6.8
7.07
green
245
78.32
68.26
53.22
56.21
115
145
207
205
1.97
1.66
Dia.
3.17
2
[Fe2L3(NO )3(H2O)2].(NO3)2.
24.23
24.06
2.38
2.59
16.86
16.51
13.45
13.17
32H2O
brown
yellow
brown
305
26.92
26.80
2.98
3.15
14.83
14.71
17.23
17.18
[Zn2L3(H2O)4].(NO3)3.H2O
[Mn2L3(H2O)4].(NO3)3.3H2O
>380
>380
26.35
26.28
3.73
3.60
14.52
14.43
13.97
14.15
776.10
−1
2
−1
* Conductance of 10-3M (ohm .cm .mol
** μeff at T=298°K B.M.
)
1484

J. Chil. Chem. Soc., 57, Nº 4 (2012)
Table 2: IR spectral data of the Schiff-bases and its complexes.
ν H2O
Compound
HL1
ν OH
ν NH2
ν(C=O)
ν(C=N)
ν(NO3)
ν(M-O)
ν(M-N)
─
3478s.
3351 s.
3266
1596s.
1565s.
1657s.
1645m.
1647m.
─
─
─
1596s.
1539s.
1383s.
863m.
1
3423br.
532m.
612m.
500m.
479m.
[Cu(H L2 )].(NO3)2 .5H2O
1506m.
1450m.
1358m.
1292m.
1603s.
1550m.
[Fe2L1(NO3)5(H2O)2].4H2O
3373br.
1595s.
1574m.
1380s.
837m.
[Zn2L1(H2O)4].(NO3)3.H2O
[Mn2L1(H2O)4].(NO3)3.H2O
3423br.
3422br.
1638m.
1641m.
602m.
518m.
474br.
429m.
1596s.
1549m.
1382s.
860m.
─
3447br.
3293 s.
3200
1605s.
1542m.
HL2
1650s.
1662m.
1668m.
─
─
─
3525br.
3445br
1600s.
1530m.
1383s.
863m..
[Cu(H L2 )].(NO3)2.1½H2O
550m.
526m.
505m.
481m.
2
1501m.
1432m.
1302m.
1285m.
1600m.
1529m.
[Fe2L2(NO3)5(H2O)2].H2O
3418br.
1601m.
1521m.
1383s.
845m.
[Zn2L2(H2O)4].(NO3)3.½H2O
[Mn2L2(H2O)4].(NO3)3.1½H2O
3428br.
3423br.
1670m.
1633m.
522m.
519br.
462br.
515br.
1601m.
1522m.
1382s.
860m.
─
3443s.
3315 s.
3283
1594s.
1559s.
HL3
1669s.
1654m.
1652m.
─
─
─
─
1592m.
1540s.
1384s.
860
[Cu(H L3 )].(NO3)2
533m.
515m.
413m.
467m.
3440br.
2
1500m.
1381s.
1281m.
855m.
1592m.
1541m.
[Fe2L3(NO3)3(H2O)2].(NO3).2H2O
3439br.
1600s.
1543m.
1367s.
837m.
[Zn2L3(H2O)4].(NO3)3.H2O
[Mn2L3(H2O)4].(NO3)3.3H2O
3428br.
3419br.
1650s.
533m.
526m.
467m.
450m.
1599m.
1538m.
1383s.
855m.
1650m.
m=medium, s=strong, br=broad
HL1 decomposes in three steps. The first step takes place in the 95-140˚c
range with DTG maximum at 124˚C associated with weight loss of 5.25%
(calcd. 4.98%), which represents the elimination of NH3 molecule. This step is
confirmed by endothermic DTA change in the 100-140˚C range with maximum
at 124˚C. Melting of this Schiff-base is shown by a sharp endothermic peak
at 203˚C. In the second step the ligand continue decomposition to lose
CH2CONHNCHC H5 fragment that appears in the 233-364˚C range with
DTG maximum a6t 329˚C. DTA confirms this step by appearing of a sharp
exothermic change in the 221-345˚C range with maximum at 271˚C indicating
decomposition of the ligand. Final decomposition of the ligand takes place in
the 435-597˚C range with DTG maximum at 490˚C and weight loss of 42.85%
(calcd. 43.0%). This step is confirmed by two successive exothermic changes
in the 435-505˚C and 506-595˚C range with DTA maxima at 465 and 543˚C.
The ligand has no plateau at 700 C
decomposed.
Copper(II) complexes decompose in four steps for [Cu(HL
ْ
which indicates that it is not completely
1
2
2
)].(NO3)2.5H2O and [Cu(HL )].(NO3)2.1½H2O and three steps for [Cu(HL
2
3
2
)].(NO )2. The dehydration process takes place in the first two steps for
[Cu(HL 3 )].(NO3)2.5H2O complex in the 25-90 and 145-187˚C range with
1
2
TGA maxima at 55 and 166˚C. This process is associated with mass loss of
3.9 and 5.86 % (calcd. 3.9 and 5.5%) representing the elimination of two and
three molecules of crystallization water accompanied with DTA change in
the 32-92 and 150-187˚C range with endothermic and exothermic peaks at
62˚C and 163˚C. This indicates that the complex has two different types of
hydrated water, loosely and strongly bound water. The dehydration process of
2
2
[Cu(HL )].(NO3)2.1½H2O complex takes place in the first step in the 30-72˚C
1485

J. Chil. Chem. Soc., 57, Nº 4 (2012)
range with DTG maximum at 56˚C with mass loss of 2.97% (calcd. 2.94%)
indicating dehydration of 1½ molecule of hydrated water. DTA confirms this
step by endothermic change in the 32-72˚C range with maximum at 53˚C.
the ligand decomposes in the 280-342˚C range with DTG maximum at 305˚C
and mass loss of 23.0% (calcd. 23.13%). This complex has no plateau at
2
2
700 C indicating incomplete decomposition. In the [Cu(HL )].(NO3)2.1½H2O
Evaporation of the nitrate ions and partial decomposition of the ligand start
complex 44% of the ligand decomposes in the 207-347˚C range with two
DTG maxima at 260˚C and 311˚C accompanied with mass loss of 33.37%
(calcd. 33.69%) and endothermic DTA change in the 262-340˚C range with
maximum at 302˚C. The complex reaches final decomposition with formation
of CuO in the 430-582˚C range with DTG maximum at 487˚C and mass loss
1
2
in the third step for the [Cu(HL )].(NO3)2.5H2O in the 190-270˚C range with
DTG maximum at 245˚C associated with mass loss of 20.0% (calcd. 20.17%).
This step is confirmed by appearance of exothermic change in the 202-282˚C
range with DTA maximum at 247˚C. This process takes place in the second step
2
2
for [Cu(HL )].(NO3)2.1½H2O in the 170-207˚C range with DTG maximum at
of 39.56% (calcd. 39.82%). DTA confirms this step by exothermic change at
3
2
194˚C and mass loss of 15.6% (calcd. 15.5% ). DTA confirms this step by
481˚C. The ligand in [Cu(HL )].(NO3)2 decomposes in the 320-390˚C and
sharp exothermic change in the 178-220˚C with maximum at 196˚C related to
510-570˚C range with DTG maxima at 303, 346, 373 and 537˚C, and mass loss
of 58.52 and 6.4 % (calcd. 58.59 and 5.91%), respectively. DTA confirms this
decomposition by exothermic changes in the 280-511 and 512-578˚C range
with maxima at 308, 349, 380 and 548˚C, respectively. The complex has no
plateau at 700 C indicating incomplete decomposition.
3
2
the melting process of the complex. [Cu(HL )].(NO3)2 loses its nitrate ions as
nitric acid in the first step in the 240-275˚C range with DTG maximum at 260˚C
accompanied with mass loss of 14.0% (calcd. 14.03%). This step is shown by
exothermic DTA change in the 252-275˚C range with maximum at 259˚C. The
1
2
ligand continues decomposition in [Cu(HL )].(NO3)2.5H2O where 33% of
Table 3: TGA. and DTG data of the HL1, HL2 and HL3 Schiff-bases and their complexes.
Residue%
and type
Mass loss%
Temp.
range °C
DTG
°C
Compound
HL1
Process
Product
Found
Calcd.
Found(Calcd.)
95-140
233-364
435-597
124
329
490
5.25
50.0
42.85
4.98
50.18
43.0
Partial decomposition
Decomposition
Final decomposition
NH3
CH2CONHNCHC6H5
0.43 L
Not complete
25-90
55
3.9
3.9
5.5
20.17
23.13
Dehydration
Dehydration
Partial decomposition
Decomposition
2H O
3H22O
2HNO3+0.09 L
0.33 L
145-187
190-270
280-342
166
245
305
5.86
20.0
23.0
Not complete
Not complete
1
[Cu(H L2 )].(NO3)2 .5H2O
59
19-124
8.28
8.47
Dehydration
4H2O
107
219
374
427
[Fe2L1(NO3)5(H2O)2].4H2O
182-245
312-488
15.06
31.44
14.82
31.39
Coordination sphere
Coordination sphere
2HNO3
3HNO3+2H2O+0.13L
20-130
194-335
345-447
93
254
407
2.88
9.60
8.26
2.48
9.91
8.52
Dehydration
Coordinated water
Ionization sphere
H2O
4H2O
HNO3
[Zn2L1(H2O)4].(NO3)3.H2O
[Mn2L1(H2O)4].(NO3)3..H2O
Not complete
Not complete
30-132
133-192
252-392
53
154
296
2.8
4.88
4.73
2.55
5.10
5.10
Dehydration
Coordinated water
Coordinated water
H2O
2H O
2H22O
26-62
170-207
207-347
46
2.97
15.60
33.37
2.94
15.38
33.69
Dehydration
Ionization sphere
Partial decomposition
1.5H2O
2HNO3 + CH3
0.44L
194
260
311
487
8.52 (8.68)
CuO
[Cu(HL22 )].(NO ) .1½H O
3
2
2
430-582
39.56
39.82
Final Decomposition
0.52L
22-63
205-302
47
2.21
27.15
2.18
27.25
Dehydration
Coordination sphere
H O
238
267
358
443
522
3HNO32+2H2O
Fe3O4
21.0 (18.7)
[Fe2L2(NO3)5(H2O)2].H2O
330-367
418-455
456-563
15.5
5.5
28.11
15.25
5.52
28.49
Coordination sphere
Partial decomposition
Final decomposition
2HNO
0.13L3
0.67L
1486

J. Chil. Chem. Soc., 57, Nº 4 (2012)
Table (3): Continued
1.20
[Zn2L2(H O)4].
19-80
219-315
355-448
56
287
386
1.34
9.51
11.76
Dehydration
0.5H2O
4H2O
HNO3 + 0.07L
(NO3)3.½2H2O
9.63
Coordinated water
Not complete
Not complete
11.71
Partial decomposition
26-100
105-200
67
31
187
294
332
3.96
9.42
3.62
9.66
Dehydration
Coordinated water
1.5H2O
4H2O
[Mn2L2(H O) ].
(NO3)3.1½2H24O
201-437
34.97
35.26
Partial decomposition
3HNO3 + 0.21L
240-275
320-390
260
303
346
373
537
27.35
58.52
27.57
58.59
Ionization sphere
Decomposition
2HNO
0.74L3
Not complete
Not complete
[Cu(H L3 )].(NO3)2
2
510-570
6.4
5.91
Ligand decomposition
0.07L
28-110
182-298
312-400
63
3.90
14.67
26.21
4.24
14.85
26.52
Dehydration
Ionization sphere
Coordination sphere
2H2O
2HNO3
3HNO3+2H2O
[Fe2L3(NO3)3(H2O)2].(NO3)
230
350
379
2.2H2O
158-231
232-395
213
299
2.75
25.87
3.33
26.01
Dehydration
H O
Ionization sphere +
coordinated water
Ionization sphere.
Final decomposition
4H2O +22HNO3
25.71/21.39
ZnO
[Zn2L3(H2O)4].(NO3)3.H2O
406-453
477-657
436
564
8.0
37.12
8.27
37.35
HNO
0.8L3
13-93
237-320
377-547
53
288
409
Dehydration
7.35
19.68
16.95
6.95
19.43
17.39
3H2O
[Mn2L3(H2O)4].
(NO3)3.3H2O
Partial decomposition
Ionization sphere +
coordinated water
2HNO + 0.07L
Not complete
HNO33+ 4H2O
Table 4: DTA data of the HL1, HL2 and HL3 Schiff-bases and their complexes.
Temp.
Compounds
rang.ºC
DTA peak ºC
ΔH J/g
Process
100-140
195-220
221-345
435-505
506-595
124 endo.
203 endo.
271 exo.
465 exo.
543 exo.
314
429
-300
-461
-1120
Partial decomposition
Melting
Decomposition
Decomposition
Final decomposition
HL1
32-92
150-187
202-282
62
endo.
132
-19
-337
Dehydration
Dehydration
Ionization sphere
163 exo.
247 exo.
1
[Cu(H L2 )].(NO3)2 .5H2O
64
endo.
109
30-124
70
36
58
Dehydration
[Fe2L1(NO3)5(H2O)2].4H2O
219 endo.
379 exo.
427 exo.
184-206
279-494
Coordination sphere
Coordination sphere
-6430
120-140
313-329
357-442
132 endo.
317 endo.
404 exo.
30
34
238
Dehydration
Coordinated water
Ionization sphere
[Zn2L1(H2O)4].(NO3)3.H2O
[Mn2L1(H2O)4].(NO3)3.H2O
30-85
128-150
277-330
62
endo.
22
31
-69
Dehydration
Coordinated water
Coordinated water
132 endo.
303 exo.
32-72
51
endo.
91
-174
142
Dehydration
Melting
Partial decomposition
Final decomposition
178-220
262-340
415-598
196 exo.
302 endo.
481 exo.
[Cu(H L2 )].(NO3)2.1½H2O
2
-7950
1487

J. Chil. Chem. Soc., 57, Nº 4 (2012)
Table 4. Continued
32-82 58
endo.
25
174
-272
-651
-240
-5150
Dehydration
Melting
Coordination sphere
Coordination sphere
Partial decomposition
Final decomposition
206-221
221-261
300-405
406-455
456-580
220 endo.
236 exo.
363 exo.
443 exo.
535 exo.
[Fe2L2(NO3)5(H2O)2].H2O
64-132
298-315
316-427
97
endo.
10
62
-1100
Dehydration
Melting
Partial decomposition
[Zn2L2(H2O)4].(NO3)3.½H2O
[Mn2L2(H2O)4].(NO3)3.1½H2O
303 endo.
391 exo.
26-61
43
endo.
34
59
141
- 399
Dehydration
118-150
151-239
240-335
137 endo.
203 endo.
299 exo
Coordinated water
Partial decomposition
Partial decomposition
252-275
280-511
259 exo.
308
349 exo.
380
-308
-1071
-289
Partial decomposition
Ligand decomposition
[Cu(H L3 )].(NO3)2
2
512-578
548 exo.
Final decomposition
66
endo.
33-88
298-309
310-448
106
205
-2190
Dehydration
Melting
Coordination sphere
303 endo.
352 exo.
382
[Fe2L3(NO3)3(H2O)2].(NO3)2.2H2O
166-227
350-388
210 endo.
367 endo.
190
61
Dehydration
Ionization sphere+
coordinated water
Ionization sphere.
Final decomposition
[Zn2L3(H2O)4].(NO3)3.H2O
[Mn2L3(H2O)4].(NO3)3.3H2O
427-453
474-657
443 exo.
569 exo.
- 31
- 5600
Dehydration
Partial decomposition
27-100
222-322
60 endo.
290 exo.
782
- 2870
Thermal decomposition of the iron(III) complexes takes place in three
steps for [Fe2L1(NO3)5(H2O)2].4H2O and [Fe2L3(NO3)3(H2O)2]. (NO3)2.2H2O
and five steps for [Fe2L2(NO3)5(H O) ].H2O. Dehydration process takes place
in the first stage in the 30-124, 302-632and 28-110˚C range with DTG maxima
at 59, 107; 52 and 63˚C for [Fe2L1(NO3)5(H2O)2].4H2O, [Fe2L2(NO3)5(H2O)2].
H O and [Fe L3(NO3) (H2O)2].(NO3)2.2H2O. This step is correlated with
m2ass loss of 8.228, 2.21 3and 3.9 % (calcd. 8.47, 2.18 and 4.24 %) indicating
the dehydration of four, one and two water molecules, respectively. DTA
confirms this step by endothermic changes at 64, 109; 58 and 66˚C. It is
noted that [Fe2L1(NO3)5(H2O)2].4H2O dehydrate in two steps which indicates
the presence of two types of crystallization water. [Fe L1(NO3)5(H2O) ].4H2O
and [Fe2L3(NO )3(H2O)2].(NO ) .2H2O complexes sho2 w elimination2of two
coordinated nit3rate ions as ni3tr2ic acid in the 182-245 and 182-198˚C range
with DTG maximum at 219 and 230˚C and mass loss of 15.06 and 14.67%
(calcd. 14.82 and 14.85%). In the next step, elimination of three coordinated
nitrate ions, two molecules of coordinated water and partial decomposition of
the ligand take place in the 312-488 and 312-400˚C range with DTG maxima
at 374, 427˚C and 350, 379˚C associated with mass loss of 31.44 and 26.21%
(calcd. 31.39 and 26.52%). This step is confirmed by a broad exothermic change
in the 279-494 and 310-448˚C range with maxima at 379, 427 and 352, 382˚C
for the two complexes. Sharp endothermic peak in the 298-309˚C range with
maximum at 303˚C is related to the melting process for [Fe L3(NO )3(H2O) ].
(NO3)2.2H2O. Both complexes have no plateau at 700C2 which3 indicat2es
incomplete decomposition. In the complex [Fe L2(NO3)5(H2O)2].H2O, three
coordinated nitrate ions and coordinated water are2eliminated in the second step
while two nitrate ions are lost in the third step which is contrary to the other
Fe(III) complexes. This happens in the 205-302 and 330-367˚C range with
DTG maxima at 238, 267 and 358˚C correlated with mass loss of 27.15 and
15.5% (calcd. 27.25 and 15.25%). Sharp endothermic peak at 220˚C indicates
melting of the complex followed by decomposition at 236 and 363˚C in the
221-261 and 300-405˚C range. Partial decomposition of the ligand starts in the
fourth step in the 418-455˚C range with DTG maximum at 443˚C associated
with mass loss of 5.5% (calcd. 5.52%) and exothermic DTA change in the 406-
455˚C range with maximum at 443˚C. Final decomposition with the formation
of Fe3O4 takes place in the 456-563˚C range with DTG maximum at 522˚C
and mass loss of 28.11% (calcd. 28.49%). DTA confirms this step by a broad
exothermic change in the 456-580˚C range with maximum at 535˚C.
Thermal decomposition of the Zinc(II) complexes takes place in three steps
for [Zn2L1(H2O)4].(NO3)3.H2O and [Zn2L2(H2O)4].(NO3)3.½H2O complexes
and four steps for [Zn2L3(H2O)4].(NO3)3.H2O complex. The dehydration process
takes place in the 30-130, 30-80 and 158-231˚C range with DTG maxima at 93,
56 and 213˚C associated with mass loss of 2.88, 1.34 and 2.75 (calcd. 2.48,
1.20 and 3.33 %), respectively. This step was also shown by endothermic peaks
at 132, 97˚C and 210˚C, respectively. In [Zn L1(H2O)4].(NO3) .H2O, the second
step is correlated with the elimination of fo2ur coordinated w3ater molecules in
the 194-335˚C range with DTG maximum at 254˚C and mass loss of 9.6%
(calcd. 9.91%) and also accompanied with endothermic DTA peak at 317˚C.
Elimination of the nitrate ions as nitric acid starts in the third step in the 345-
447˚C range with DTG maximum at 407˚C and mass loss of 8.26% (calcd.
8.52%). This step is confirmed by exothermic change in the 357-442˚C range
with DTA maximum at 404˚C. This complex shows high thermal stability as
only 26% of the complex decomposes in the temperature range of 30-700˚C
and so there is no plateau at 700 ْC indicating incomplete decomposition. In
the [Zn2L2(H2O)4].(NO )3.½H O complex, the coordinated water is eliminated
also in the second step3in the2219-315˚C range with DTG maximum at 287˚C
accompanied with weight loss of 9.51% (calcd. 9.63%). This complex melts
as shown by a sharp endothermic change in the 298-315˚C range with DTA
maximum at 303˚C. Exothermic change in the 316-427˚C range with maximum
at 391˚C indicates partial decomposition of the complex which appeared in the
TGA/DTG curve in the 355-448˚C range with maximum at 386˚C and mass
loss of 11.76% (calcd. 11.71%). The complex has no plateau at 700 Cْ which
indicate that it is not completely decomposed. In the [Zn2L3(H2O)4].(NO3)3.
H O complex, four coordinated water molecules together with two nitrate ions
ar2e eliminated in the second step in the 232-395˚C range with DTG maximum
at 299˚C and mass loss of 25.87% (calcd. 26.01%). DTA confirms this stage
by endothermic peak at 367˚C. In the third step a nitrate ion is eliminated as
nitric acid in the 406-453˚C range with maximum at 436˚C and mass loss
of 8.0% (calcd. 8.27%). This process is accompanied with exothermic DTA
change in the 427-453˚C range with maximum at 443˚C. Final decomposition
and formation of ZnO takes place in the last stage in the 477-657˚C range with
maximum at 564˚C and mass loss of 37.12% (calcd. 37.35%). DTA calorigram
shows this stage as exothermic change with maximum at 569˚C.
1488

J. Chil. Chem. Soc., 57, Nº 4 (2012)
Table 5: Antibacterial screening data of the Schiff-bases and their complexes.
Zone of Inhibition (mm)
Gram negative
E. c.
Compound
Gram positive
S. a.
K. p.
P. v.
DMF(Control)
HL1
-
-
-
-
-
-
8
7
1
15
8
7
16
-
9
6
-
-
-
[Cu(H L2 )].(NO3)2 .5H2O
[Fe2L1(NO3)5(H2O)2].4H2O
[Zn2L1(H2O)4].(NO3)3.H2O
[Mn2L1(H2O)4].(NO3)3.H2O
HL2
-
-
7
9
6
7
9
8
-
-
5
8
-
[Cu(H L2 )].(NO3)2.1½H2O
16
15
-
7
-
2
[Fe2L2(NO3)5(H2O)2].H2O
[Zn2L2(H2O)4].(NO3)3.½H2O
[Mn2L2(H2O)4].(NO3)3.1½H2O
HL3
6
-
-
-
7
9
5
7
6
7
7
8
20
-
6
8
-
[Cu(H L3 )].(NO3)2
17
5
8
-
2
[Fe2L3(NO3)3(H2O)2].(NO3)2. H2O
[Zn2L3(H2O)4].(NO3)3.H2O
[Mn2L3(H2O)4].(NO3)3.3H2O
Streptomycin
7
-
16
5
6
-
18
23
-
22
23
S. a.= Staphylococcus aureus.
K .p= Klebsiella pneumoniae.
E. c= Escherichia coli.
P. v= Proteus vulgaris.
The complexes [Mn2L1(H2O)4].(NO3)3.H2O, [Mn2L2(H2O)4].(NO3)3.1½H2O
and [Mn L3(H2O)4].(NO3)3.3H O show three decomposition steps. In the first
step, the2dehydration process 2takes place in the 30-132, 26-100 and 23-93˚C
range with DTG maxima at 53, 67 and 55˚C with mass loss of 2.8, 3.96 and
7.35% (calcd. 2.55, 3.62 and 6.95%), respectively. DTA confirms this step
by endothermic changes at 62, 63 and 60˚C, respectively. In the complex
[Mn2HL1(H O) ].(NO3)3.H2O, elimination of four coordinated water molecules
takes place 2in t4he 133-192˚C and 252-392˚C range with TGA maxima at 154
and 296˚C associated with mass loss of 4.88 and 4.73% (calcd. 5.10). DTA
shows this step by endothermic and exothermic changes at 132 and 303˚C.
This indicates the non-equivalent bonding of the coordinated water. In the
complex [Mn HL2(H O)4].(NO3) .1½H O, the coordinated water molecules
are eliminated2in the 2second ste3p in t2he 105-200˚C range with two DTG
maxima at 131 and 187˚C associated with mass loss of 9.42% (calcd. 9.66%).
This is shown by endothermic changes in the 118-150 and 151-239˚C range
with DTA maximum at 137 and 203˚C. Partial decomposition of the ligand
and elimination of the nitrate ions as nitric acid begin in the third step in
the 201-437˚C range with two DTG maxima at 294 and 332˚C. This step is
accompanied with mass loss of 34.97˚C (calcd. 35.26) and is confirmed by the
appearing of exothermic change in the 240-335˚C range with DTA maximum
completely decomposed. The complex [Mn2L3(H2O)4].(NO3)3.3H2O shows
the elimination of two nitrate ions as nitric acid and partial decomposition of
the ligand in the second step in the 237-320˚C rang, with maximum at 288˚C
and mass loss of 19.68% (calcd. 19.43%). DTA confirms this step by sharp
exothermic change with maximum at 290˚C. In the third step elimination of
the coordinated water molecules and a nitrate ion takes place. This process is
accompanied with mass loss of 16.95% (calcd. 17.39%). The complex has no
plateau at 700 C indicating uncompleted decomposition.
Based on the above analytical data and physicochemical properties, the
following structures are proposed in which the Cu(II) ions were coordinated
through the carbonyl groups (C=O) of isatin, the amino groups and the two
azomethine nitrogen C=N of the aldimine moiety. The Fe(III), Zn(II) and
Mn(II) ions were bonded by the carbonyl groups (C=O) of isatin, the amino
groups, C=O or the enolized carbonyl group (C–OH) of the amide, the
azomethine nitrogen C=N of the aldimine moiety and the coordinated nitrate
or water molecules.
at 299˚C. The complex has no plateau at 700 Cْ which indicates that it is not
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J. Chil. Chem. Soc., 57, Nº 4 (2012)
Figure 1. TGA, DTG and DTA of the [CuL2].(NO3)2.5H2O complex.
Figure 2. TGA, DTG and DTA of [Fe2HL2(NO3)5(H2O)2].H2O complex.
Antibacterial activity
Antibacterial activity of the synthesized compounds has been screened
using different strains of bacteria [Staphylococcus aureus, Klebsiella
pneumoniae, Escherichia coli, Proteus vulgaris]. The desk diffusion method
has been adapted for antibacterial activity31. The results are shown in
Table 5.
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J. Chil. Chem. Soc., 57, Nº 4 (2012)
It seems that all the synthesized compounds are devoted of activity against
Protus vulgaries while all the compounds are slightly active against Klebsiella
pneumoniae and Escherichia coli. (Cu(HL2].(NO3)2.1½H2O and [Cu(HL2].
(NO3)2 complexes are moderately active against Staphylococcus aureus.
[Zn2HL1(H2O)4].(NO3)3.H2O and [Zn2HL2(H2O)4].(NO3)3.½H2O complexes
are inactive against all the studied bacteria while [Zn2HL3(H2O)4].(NO3)3.H2O
complex is moderately active towards Staphylococcus aureus. [Mn HL3(H2O)4].
(NO3)3.3H2O complex has moderate activity against Klebsiella2pneumoniae
while [Mn2HL1(H2O)4].(NO3)3.H2O and [Mn2HL2(H2O)4].(NO3)3.1½H2O are
slightly active against Staphylococcus aureus. [Fe2HL1(NO3) (H O)2].4H2O
and [Fe2HL2(NO3)5(H2O)2].H2O are moderately active agai5nst 2 Klebsiella
pneumoniae and Staphylococcus aureus.
The increased activity of the complexes compared to the free ligands can
be explained on the bases of chelation theory32. Chelation reduces the polarity
of the metal ion; mainly because of the partial sharing of its positive charge
with donor groups and the possible π-electron delocalization over the whole
chelate ring. Chelation not only reduces the polarity of metal ion, but also
increases the lipophilic character of the chelate. As a result of this, interaction
between metal ion and the cell walls is favored resulting in interference with
normal cell processes. If the geometry and charge distribution around the
molecule are incompatible with the geometry and charge distribution around
the pores of the bacterial cell wall, penetration through the wall by the toxic
agent cannot take place33.
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