Preparation and characterization of sulfadiazine Schiff base complexes of Co(II), Ni(II), Cu(II), and Mn(II)

Article abstract of DOI:10.1007/s00706-004-0257-8

Complexes of Co(II), Ni(II), Cu(II), and Mn(II) containing Schiff base NOS donor ligands have been synthesised via chemical and electrochemical techniques. The structure of the complexes has been elucidated by elemental analysis, conductance, magnetic sus

Full text of DOI:10.1007/s00706-004-0257-8

Monatshefte f €u r Chemie 136, 1139–1155 (2005)
DOI 10.1007/s00706-004-0257-8
Preparation and Characterization
of Sulfadiazine Schiff Base Complexes
of Co(II), Ni(II), Cu(II), and Mn(II)
Kamal Y. El-Baradieꢀ
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
Received August 16, 2004; accepted (revised) September 15, 2004
Published online March 18, 2005 # Springer-Verlag 2005
Summary. Complexes of Co(II), Ni(II), Cu(II), and Mn(II) containing Schiff base NOS donor ligands
have been synthesised via chemical and electrochemical techniques. The structure of the complexes has
been elucidated by elemental analysis, conductance, magnetic susceptibility measurements, IR, ESR,
electronic spectral studies and thermal techniques (TGA and DTA). The electrochemical behaviour
of the metal complexes was studied using DC polarography and cyclic voltammetry. Antimicrobial
activity of the title Schiff base and its complexes has been tested against different microorganisms.
Keywords. Sulfadiazine; Schiff base; Complexes, Co(II), Ni(II), Cu(II), Mn(II); Biological activity.
Introduction
Schiff bases have played an important role in the development of coordination
chemistry as they readily form stable complexes with most transition metals. Schiff
bases and their metal complexes are becoming increasingly important as biochem-
ical [1], analytical [2, 3], industrial [4] reagents and redox catalysts [5–8] as well as
pigment dyes [9, 10]. What appears more important, is that Schiff bases and their
metal complexes are useful in biological and pharmaceutical applications [11–13].
In recent years, there has been considerable interest in the chemistry of sulfadrugs
and their metal complexes [14, 15]. However, the literature on the chemistry of
Schiff base complexes derived from sulfadrugs, especially their structure character-
istics, is rather incomplete.
Schiff bases and its metal complexes display obvious inhibitor effects against
Gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) and Gram
negative bacteria (Escherichia coli and Pseudomonos aeruginosa). These studies
reported the minimum inhibitor concentration of the used Schiff base and its metal
complexes on these microorganism [16].
ꢀ E-mail: kyelbaradie@hotmail.com

1
140
K. Y. El-Baradie
Fig. 1. Structure of Schiff base
The present paper deals with the chemical and electrochemical synthesis and
structural studies of Co(II), Ni(II), Cu(II), and Mn(II) complexes with a Schiff base
derived from sulfadiazine and salicylaldehyde (Fig. 1).
Results and Discussion
The analytical and physical data of the metal complexes are represented in Table 1.
The complexes are air stable for a long time, insoluble in different organic solvents
but soluble in DMF. The analytical data of the metal complexes indicate that the
complexes have 2:1 and 1:2 metal-ligand stoichiometry for chemical and electro-
chemical methods of preparation, respectively. The values of the molar con-
ꢁ
3
ꢁ1
2
ꢁ1
ductance (10 M solutions in DMF) are in the range 10.1–19.3 ꢀ cm mol
Table 1. Analytical and physical data of Schiff base complexes
L
ꢀeff
geff (ESR)
No.
Formula of complex (mol. wt)
ꢁ
1
2
cm mol
ꢁ1
ꢀ
BM
[
CoL (H O) ]H O
2 2 2 2
1
2
3
4
5
6
7
8
C H N O S Co
34 32 8 9 2
10.9
19.3
9.9
5.1
2.0165
2.0062
ꢁ
(
818.93)
Co L(AcO) (H O) ]3H O
[
2
2
2
4
2
C H N O SCo
2
4.9
2
1
32
4
14
(
713.86)
NiL (H O) ]H O
[
2
2
2
2
C H N O S Ni
34 32 8 9 2
3.1
(
818.7)
Ni L(AcO) (H O) ]2H O
[
2
2
2
4
2
C H N O SNi
13
18.9
10.1
17.9
12.5
16.4
2.95
1.82
1.79
5.56
4.92
ꢁ
2
1
30
4
2
(
695.4)
[
CuL ]2H O
2
2
C H N O S Cu
34 30 8 8 2
2.1587
2.0086
2.0123
2.0072
(
805.54)
Cu L(AcO) (H O) ]2H O
[
2
2
2
2
2
C H N O SCu
2
2
1
26
4
11
(
669.08)
MnL (H O) ]2H O
[
2
2
2
2
C H N O S Mn
34 34 8 10 2
(
832.93)
Mn L(AcO) (H O) ]2H O
[
2
2
2
4
2
C H N O SMn
2
2
1
30
4
13
(
687.86)

Sulfadiazine Schiff Base Complexes
1141
Table 2. Results of thermogravimetric analysis of mononuclear Co(II) and Mn(II) complexes
Mass loss=%
Found Calc.
Complex
mol. wt)
Temp.
ꢂ
Comp. no
Process
(
range= C
[
CoL (H O) ]H O
2
a) Loss of lattice
water molecule
2
2
2
3
0–105
2.5
4.6
2.2
4.4
(
818.93)
[
CoL (H O) ]
2
b) Loss of
2
2
105–255
255–390
390–585
(
(
(
800.93)
CoL2]
764.93)
CoL2]
574.93)
coordinated water
1
[
c) Loss of 2-imino-
pyrimidine
23.6
34.3
23.2
[
d) Loss of 2SO þ 2
2
34.6
benzene rings
ꢂ
Degradation of whole molecule and formation of CoO as a final product (585–760 C)
[
MnL (H O) ]2H O
2
a) Loss of lattice
water molecules
2
2
2
3
0–115
4.1
4.4
4.3
4.3
(
832.93)
[
MnL (H O) ]
2
b) Loss of coordinated
water
2
2
115–230
230–410
410–565
(
(
796.93)
7
[
MnL2]
c) Loss of 2-imino-
pyrimidine
21.9
34.5
22.8
760.93)
[
MnL2]
70.93
d) Loss of 2SO þ 2
2
34.1
5
benzene rings
ꢂ
Degradation of whole molecule and formation of MnO as a final product (565–785 C)
2
indicating a non-electrolytic nature of these complexes [17]. This reveals the in-
volvement of the acetate ion in the coordination sphere of the metal ions in the
binuclear complexes 2, 4, 6, and 8. The mononuclear complexes 1, 3, 5, and 7 are
deprived of anions.
Thermal Analysis
The results of thermogravimetric analysis of mononuclear and binuclear Co(II) and
Mn(II) complexes 1, 2, 7, and 8 are collected in Tables 2 and 3.
The thermograms of mononuclear Co(II) and Mn(II) complexes 1 and 7 show
ꢂ
that the weight losses in temperature ranges 30–105 and 30–115 C are attributed to
removal of one and two lattice water molecules associated with endothermic peaks
ꢂ
at 72 and 95 C in the DTA thermogram for complexes 1 and 7, respectively. The
ꢂ
weight losses in the temperature ranges at 105–255 and 115–230 C are attributed to
the elimination of the two coordinated water molecules with endothermic peaks at
ꢂ
139 and 176 C for both complexes. The removal of 2-iminopyrimidine takes place
within the temperature ranges 255–390 and 230–410 C with exothermic peaks at
ꢂ
ꢂ
352 and 372 C in the DTA thermogram followed by loss of two SO molecules and
two benzene rings within the temperature ranges 390–585 and 410–565 C asso-
2
ꢂ
ꢂ
ciated with exothermic peaks at 557 and 532 C for complexes 1 and 7, respectively.
ꢂ
The decomposition steps within the temperature ranges 585–760 and 565–785 C

1
142
K. Y. El-Baradie
Table 3. Results of thermogravimetric analysis of binuclear Co(II) and Mn(II) complexes
Mass loss=%
Complex
mol. wt)
Temp.
ꢂ
Comp. no
Process
(
range= C
Found
7.7
Calc.
[
Co L(AcO) (H O) ]3H O
2
a) Loss of lattice
water molecule
2
2
2
4
3
0–130
7.6
10.0
16.8
(
713.86)
[
Co L(AcO) (H O) ]
4
b) Loss of
2
2
2
1
30–240
9.8
(
659.86)
coordinated water
2
c) Loss of
[
CoL(AcO)2] (587.85)
CoL] (467.86)
240–430
430–590
17.4
10.8
2
acetic acid
d) Loss of
[
10.6
benzene ring
ꢂ
Degradation of whole molecule and formation of Co O as a final product (590–765 C)
2
3
[
Mn L(AcO) (H O) ]2H O
2
a) Loss of lattice
water molecules
2
2
4
2
3
0–120
5.2
10.3
17.1
11.6
5.2
10.5
17.4
(
687.86)
[
Mn L(AcO) (H O) ]
2
b) Loss of
2
2
4
1
20–265
(
655.86)
coordinated water
8
c) Loss of 2
acetic acid
[
Mn2L(AcO)2] (583.86)
Mn2L] (463.86)
265–455
455–610
d) Loss of
[
11.3
benzene ring
ꢂ
Degradation of whole molecule and formation of MnO as a final product (610–790 C)
2
ꢂ
with broad exothermic peaks at 628 and 642 C are due to decomposition of the
remainder ligand molecule leading to CoO and MnO as final products.
2
The binuclear Co(II) and Mn(II) complexes 2 and 8 were thermally decomposed
in several steps supported by DTA data. The thermograms of complexes 2 and 8 show
that the three lattice water molecules for complex 2 and two lattice water molecules
ꢂ
for complex 8 are eliminated at the temperature ranges 30–130 and 30–120 C with
ꢂ
endothermic peaks at 77 and 97 C. The four coordinated water molecules are elimi-
nated for both complexes 2 and 8 within the temperature ranges 130–240 and 120–
ꢂ
ꢂ
265 C with endothermic peaks at 180 and 198 C for complexes 2 and 8. The losses in
weight within the temperature ranges 240–430 and 265–455 C are due to removal of
ꢂ
ꢂ
two acetate groups with strong exothermic peaks at 400 and 392 C for complexes 2
ꢂ
and 8. The decrease in weight in the temperature ranges 430–590 and 455–610 C are
due to the elimination of a benzene ring. This step is confirmed by strong exothermic
ꢂ
peaks at 575 and 560 C for complexes 2 and 8, respectively. The last step of decom-
ꢂ
position lies within the temperature ranges 590–765 and 610–790 C associated with
ꢂ
broad exothermic peaks at 615 and 645 C, corresponding to the decomposition of the
ligand leading to Co O and MnO for complexes 2 and 8.
2
3
2
ꢀ
The order, n and activation energy, E , of the decomposition steps were deter-
mined using the Coats-Redfern equation [18] as given in Eqs. (1) and (2).
"
ꢁn#
1
1
ꢁ ð1 ꢁ ꢁÞ
2
ln
¼ M=T þ B for n
6
ð1Þ
ð1 ꢁ nÞT

Sulfadiazine Schiff Base Complexes
1143
Fig. 2. Coats-Redfern plots for complex 1
Fig. 3. Coats-Redfern plots for complex 2
ꢀꢁ
ꢁ
lnð1 ꢁ ꢁÞ
ln
¼ M=T þ B for n ¼ 1
ð2Þ
2
T
ꢀ
ꢀ
ꢀ
Where M ¼ ꢁE =R and B ¼ ln AR=FE and E , R, A, and F are the activation
energy, gas constant, pre-exponential factor, and heating rate, respectively.
The correlation coefficient, r, is calculated using the least squares method
1
ꢁn
2
for different values of n. The value of ln½ð1 ꢁ ð1 ꢁ ꢁÞ Þ=ð1 ꢁ nÞT ꢃ or
2
ln½ꢁlnð1 ꢁ ꢁÞ=T ꢃ from Coats-Redfern equation is plotted against 1000=T (see
ꢀ
Figs. 2 and 3). From the intercept and slope of such linear stage, the A and E
ꢀ
ꢀ
values were determined, respectively. The other kinetic parameters (DH , DS , and
DG ) were calculated using the relationships given in Eqs. (3)–(5).
ꢀ
ꢀ
ꢀ
DH ¼ E ꢁ RT
ð3Þ

1
144
K. Y. El-Baradie
Table 4. Values of correlation coefficient, slope, and intercept of the thermal decomposition and activation
parameters of complex 1
Coats-Redfern equation
Slope Intercept
Eꢀ
kJ mol
DHꢀ
kJ mol
ꢀ
DS
kJ K mol
DGꢀ
T
A
Step
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
kJ mol
ꢁ
1
K
kJ mol
n
r
0
0:9962 ꢁ3.6585 ꢁ2.0828
1
2
3
4
0.5 0.9956 ꢁ4.4210
0.2704 345
3.0072
44.1
36.7
42.6
35.3
41.27
20529.1
73.7
ꢁ0.164
97.85
1
0
0.9923 ꢁ5.3112
0.9915 ꢁ5.6126 ꢁ2.4722
0.5 0.9924 ꢁ4.9691 ꢁ0.9739 412
33.27
37.45
28.38
ꢁ0.212
ꢁ0.232
ꢁ0.242
120.5
182.2
229.4
1
0
0:9934 ꢁ4.4144
0.64755
0.9985 ꢁ4.8198 ꢁ5.3121
0.5 0.9986 ꢁ5.2971 ꢁ4.3703 625
10.3
1
0:9987 ꢁ5.8048 ꢁ3.3709
0.9937 ꢁ3.0523 ꢁ10.2139
0
0.5 0.9952 ꢁ3.6245 ꢁ9.3451 830
3.86
1
0:9962 ꢁ4.2462 ꢁ8.4054
Table 5. Values of correlation coefficient, slope and intercept of the thermal decomposition and activation parameters
of complex 2
Coats-Redfern equation
Eꢀ
kJ mol
DHꢀ
kJ mol
ꢀ
DS
kJ K mol
DGꢀ
T
A
Step
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
kJ mol
ꢁ
1
K
kJ mol
n
r
Slope
Intercept
0
0.9542
ꢁ1.6753 ꢁ7.6151
1
2
3
4
0.5 0.9817
ꢁ2.4127 ꢁ5.3116 350
27.34
68.79
35.83
86.41
25.02
65.12
4.3ꢄ10
0.88
ꢁ0.212
99.06
1
0
0:9938
ꢁ3.3603 ꢁ2.3828
0.9909
ꢁ6.4174
ꢁ7.7798
ꢁ9.4183
1.2360
5
0.5 0.9948
4.4611 453
8.3275
65.01
30.21
79.33
ꢁ0.141
0.253
128.7
200.3
257.4
1
0
0:9950
0:9899
ꢁ3.3148 ꢁ8.8645
0.5 0.9978
ꢁ4.0397 ꢁ7.5533 673
ꢁ4.9489 ꢁ5.9222
1
0.9956
0
0.9974
ꢁ7.9474 ꢁ5.3265
0.5 0.9983
1
ꢁ9.1217 ꢁ3.8583 848
212.7
ꢁ0.21
0:9987 ꢁ10.392
ꢁ2.2739
ꢀ
DS ¼ R½lnðAh=kTÞ ꢁ 1ꢃ
ð4Þ
ð5Þ
ꢀ
ꢀ
ꢀ
DG ¼ DH ꢁ TDS
Where k is Boltzmann’s constant and h is Planck’s constant. The order and kinetic
ꢀ
be negative which indicated that the activated complex is more ordered than the
parameters of complexes are listed in Tables 4 and 5. The DS values were found to
reactant and=or the thermal decomposition reaction is slower than normal. DGꢀ

Sulfadiazine Schiff Base Complexes
1145
values increase with increasing the order of the decomposition stages which indi-
cates that at high temperatures the ligand decomposes and require more energy for
its rearrangement in the activated state.
Scheme 1

1
146
K. Y. El-Baradie
Scheme 2
Based on the data of thermal analysis, the decomposition of mononuclear and
binuclear complexes can be represented as shown in Schemes 1 and 2.
IR Spectra
The most important IR assignments in the spectrum of the free Schiff base as well
as the bonding sites have been determined by a careful comparison of the spectrum
of the ligand and its metal complexes (Table 6). The IR spectrum of Schiff base
ꢁ
1
ꢁ1
shows broad bands at 3458 cm (ꢂOH) and 3100 cm (ꢂNH). The strong bands at

Sulfadiazine Schiff Base Complexes
1147
Table 6. IR and electronic spectra of complexes 1–8
IR spectra
Electronic spectra
No.
ꢂOH
cm 1
ꢁ
ꢂC¼N
ꢁ1
ꢂC¼N
ꢁ1
ꢂMꢁN
ꢁ1
ꢂMꢁN
ꢁ1
ꢂMꢁO
ꢁ1
ꢂ
Dq
B
ꢃ
ꢁ1
cm
cm
cm
cm
cm
cm
ꢁ1
ꢁ1
cm
cm
1
2
3
4
5
6
7
8
3468
1600
1605
1581
1602
1588
1607
1585
1605
1556
1583
1550
1584
1546
1584
1550
1538
445
362
572
15740
840
934
921
1011
–
839
897
723
754
–
0.86
1
8860
17668
0790
14700
3800
16000
5641
14280
8860
15385
0408
15490
1277
18780
3150
3430
3436
3360
3433
3436
3380
3420
450
447
467
445
457
450
465
377
386
366
360
332
365
380
560
575
572
579
574
560
572
0.92
0.69
0.72
–
2
2
2
1
–
–
–
2
–
–
–
2
–
–
–
2
ꢁ
1
1618 and 1582 cm are attributed to the ꢂ
pyrimidine ring. The Schiff base exhibits a medium intensity band at 2599 cm
vibration of the azomethine and
ꢁ
C¼N
1
which is assigned to the intramolecular H-bonding vibration (O–H–N). This situa-
tion is common for aromatic azomethine compounds containing an OH group in
ortho position to a C¼N group [19]. In the metal complexes, this band disappeared
ꢁ
1
completely. The two bands at 1339 and 1166 cm are assigned to the v and v
asy
sym
of the SO group.
2
The IR spectra of the binuclear metal complexes 2, 4, 6, and 8 show that the
Schiff base behaves as dibasic tetradentate ligand whereas for the mononuclear
complexes 1, 3, 5, and 7 the Schiff base is monobasic bidentate. The mode of
chelation is elucidated from the following evidences:
1
) The disappearance of vOH bands in the complexes reveals the deprotonation of
the enolic and phenolic OH groups indicating that the proton of the OH group is
displaced by the metal ions on complex formation.
2
) The IR spectra of complexes 2, 4, 6, and 8 showed shift to lower wavenumbers
in v
of both the azomethine and pyrimidine moieties by 10–30 and 26–
C¼N
ꢁ
1
3
6 cm , respectively. These data suggest that both the azomethine and one
nitrogen atom of the pyrimidine ring are involved in coordination to the metal
ions. For mononuclear complexes 1, 3, 5, and 7, the v band of the pyrimidine
C¼N
ꢁ
1
ring in the range 1584–1546 cm is unaffected by complexation indicating that
the N-atoms of the pyrimidine ring are not involved in complex formation.
) For the acetate complexes, the bands due to ꢂ and ꢂsym of the acetate group
3
asy
ꢁ
1
are observed at 1444 and 1344 cm for Co(II) complex 2, and at 1446 and

1
148
K. Y. El-Baradie
ꢁ ꢁ1
1
1
386 cm for Ni(II) complex 4. The ꢁv values in cm for complexes 2 and 4
ꢁ
1
are 100 and 60 cm which can be taken as evidence for the existence of
bidentate acetate groups [20, 21]. The Cu(II) complex 6 and Mn(II) complex
8
show two bands due to v and v
asy
of the acetate group at 1615 and
sym
ꢁ ꢁ1
1
1386 cm , and 1610 and 1400 cm , respectively. The ꢁv values between
vasy and vsym are 229 and 210 cm for complexes 6 and 8, respectively. These
values are higher than 200 cm which support the presence of monodentate
acetate groups [20, 21].
) The presence of water molecules in the complexes leads to the broad bands at
ꢁ
1
1
ꢁ
4
ꢁ
1
ꢁ1
3468–3410 cm (vH2O) and 1610–1595 cm (ꢄH2O) for both lattice and coor-
dinated water molecules. The coordinated water molecules give also bands at
ꢁ
1
ꢁ1
9
40–920 cm (ꢅH2O), 874–846 cm (!H2O). The latter bands (ꢅH2O þ !H2O)
are absent in the spectra of complex 5 which contains only lattice water [22].
The IR bands of the lattice water molecules are absent in the spectrum of
ꢂ
complex 5 heated at 150 C for 2 hours, whereas that of complex 7 heated at
ꢂ
150 C showed an obvious decrease in the intensity of the v
and ꢄH2O bands.
H2O
ꢂ
When complex 7 was heated to 250 C for 2 hours, bands due to the various
types of vibrations of the coordinated water molecules disappeared. However it
is worthy to mention that the IR spectrum in the latter case was found to suffer
some alteration presumably due to the occurrence of some decomposition in the
anhydrous complex.
5
) A shift of the v
ꢁ
band is observed in the IR spectra of the complexes, 943–
ꢁ1
SꢁN
35 cm , with respect to that of the ligand, 913 cm . This could be attributed
1
9
to deprotonation of the sulfonamido group and consequently the shortening of
the S–N bond distance.
ꢁ
1
6
7
) The appearance of new bands in the region 579–560 and 386–332 cm assign-
able to v and v , respectively [23], reflects the bonding of the metal ions
to oxygen and nitrogen atoms.
MꢁO
MꢁN
) The spectra of complexes 2, 4, 6, and 8 do not show characteristic sulfonamide
(
–SO NH–) group frequencies [v
2
and v
] and NH vibrations. This
SO2 ðasyÞ
SO2 ðsymÞ
commensurates that in these complexes, the oxygen of the sulfonamide group
coordinates in the enolic form through deprotonation [24]. The appearance of
new bands characteristic of ꢄNSO in the ranges 1448–1410 and 1354–1340 cm
further confirm enolisation of the Schiff base [25].
ꢁ
1
Magnetic Moments and Electronic Spectra
The room temperature magnetic moment (Table 1) for the Co(II) complexes 1 and
are 5.1 and 4.9 BM, respectively, which confirm the octahedral structure of these
2
complexes [23].
The electronic spectra of Co(II) complexes 1 and 2 recorded as Nujol mull
ꢁ
1
(
Table 6) display two bands at 15740, 18860 and 17668, 20790 cm , respectively.
4
4
4
4
These bands are assigned to T ! T (v ) and T ! T (p) (v ) [26]. Also,
1
g
2g
2
1g
2g
3
the ligand field parameters (Table 6) are additional evidence for the octahedral
structure [27].
The Ni(II) complexes 3 and 4 show magnetic moment values of 3.1 and
2.95 BM, respectively, expected for spin free octahedral Ni(II) complexes [28].

Sulfadiazine Schiff Base Complexes
1149
The Nujol mull electronic spectra of Ni(II) complexes 3 and 4 show two bands at
ꢁ
1
1
4700, 23800 and 16000, 25641 cm , respectively, which can be assigned to the
3
3
3
3
A ! T (F) (v ) and A ! T (p) (v ) transitions [26]. The calculated D ,
2
g
1g
2
2g
1g
3
q
B, and ꢃ values lie in the range reported for an octahedral environment around a
Ni(II) ion [29]. The ꢃ values obtained are less than unity suggesting considerable
amount of covalent character of the metal ligand bonds. Also, the ꢃ values for the
complexes are lower than the free ion’s value, thereby indicating orbital overlap
and delocalization of d-orbitals.
The magnetic moment values for Cu(II) complexes 5 and 6 are 1.82 and 1.79 BM.
These values indicate the absence of any appreciable spin coupling between unpaired
electrons belonging to different copper atoms. The electronic spectral bands appeared
ꢁ
1
at 14280, 18860 and 15385, 20408 cm for Cu(II) complexes 5 and 6, respectively.
2
2
2
2
These bands are assignable to transitions B ! A and B ! E of a square
1g
1g
1g
g
planar geometry [30]. The magnetic moment values for Mn(II) complexes 7 and 8 are
.56 and 4.92 BM, respectively which confirm the octahedral structure of these com-
plexes. The lower value for complex 8 can be attributed to antiferromagnetic inter-
5
action between adjacent Mn(II) ions [31]. The electronic absorption spectra of Mn(II)
ꢁ
1
complexes 7 and 8 display two bands at 15490, 21277 and 18780, 23150 cm ,
respectively, which correspond to the octahedral configuration. These bands are
6
4
6
4
assigned to A ! T (4G) and A ! E (G) transitions [32].
1
g
1g
1g
g
ESR Spectra
The geff values of mononuclear and binuclear complexes under investigation were
calculated and collected in Table 1.
The X-band ESR spectra of Co(II) complexes 1 and 2 at room temperature
show an intense broad signal with no hyperfine structure with geff values 2.0165
and 2.0062 which are characteristic of Co(II) octahedral structure [33]. The ESR
spectra of Cu(II) complexes 5 and 6 give a broad signal with no hyperfine structure
with geff values 2.1587 and 2.0086 which indicate that Cu(II) complexes have
square planar geometry. The ESR spectra of Mn(II) complexes 7 and 8 show broad
signals with g ¼ 2.0123 and 2.0072, which suggest the existence of octahedral
eff
high spin Mn(II) complexes [34].
The more positive contribution in the geff values of the mononuclear and bi-
nuclear complexes compared to the value of a free electron, 2.0023, indicates an
increase in the covalent nature of the bonding between the metal ion and the ligand
molecule [35].
Electrochemical Studies
The electroreduction of the ligand and its metal complexes was studied using DC
polarography at the dropping mercury electrode and cyclic voltammetry on a hang-
ing mercury drop in a medium 0.1 M KCl containing 50% v=v DMF.
The DC polarogram of the ligand displays a single wave with E1=2 ¼ ꢁ0:17 V
vs. SCE representing the reduction of the azomethine group. The reduction process
was found to be irreversible as gathered from the analysis of the wave using the
fundamental equation [36]. The ꢁn value amounted to 1.4, hence the most prob-
a

1
150
K. Y. El-Baradie
ꢂ
Table 7. Polarographic data obtained for some complexes in 0.1 M KCl at 25 C; values of ꢁn and ꢁ
a
were calculated from reciprocal slope (S ) of the log (i=i ) ꢁE plots
1
d
SlopeðS1Þ
id ꢀA
ꢁE1=2=V
ꢁna
ꢁ for n ¼ 2
a
mV
No.
(
a)
(b)
(a)
(b)
(a)
(b)
(a)
(b)
(a)
(b)
Ligand
2.12
1.5
0.63
0.92
–
0.17
0.24
0.13
0.13
0.33
1.33
1.1
–
42.0
33.5
27.4
25.1
51.7
14.5
22.1
–
1.4
4.06
2.67
–
0.7
2.03
1.335
–
Complex 1
Complex 2
Complex 3
Complex 5
1.76
2.15
2.35
1.14
0.88
2.75
2.32
1.97
1.075
1.175
0.57
1.17
0.4
1.5
1.2
35.9
30.1
1.64
1.96
0.82
0.98
(a) First wave; (b) second wave
able ꢁ value would be obtained for n ¼ 2, and the rate determining step in the
a
electrode process would involve two electrons. The total number of electrons
involved in the electrode process can be calculated from the i value making use
d
of the Ilkovic equation. The value thus determined amounts to ꢅ3.5 ꢀA denoting
that four electrons are consumed in the reduction reaction according to Eq. (6).
þ
ꢁ
ArꢁCH¼NꢁAr þ 4e þ 4H ꢁ! ArꢁCH þ H NꢁAr
ð6Þ
3
2
For the metal complexes 1, 2, 3, and 5 the DC polarogram of each comprises
two waves, the first one is due to the reduction of the azomethine center, whereas
the more negative one represents the reduction of the metal ion. The relative wave
heights of these waves is 2:1 denoting that the number of electrons involved in the
wave of the azomethine center is almost double as that of the metal ions. Since the
reduction of the metal ion involves two electrons, then the reduction of the azo-
methine group involves four electrons.
Analysis of the waves due to the reduction of the metal ions and the ligand
revealed that the electrode reaction proceeds in an irreversible manner. The most
probable ꢁ and n values are given in Table 7.
a
It is worthy to mention that the bonding of metal ions to the ligand causes an
obvious shift of E1=2 of the azomethine wave to more negative potentials. This can
be explained on the basis that the bonding of the metal ions to the ligand, which
takes place through proton displacement from the OH group, is more ionic than for
hydrogen ions. This increases the denoting character of the substituents which in
turn increases the charge migration to the CH¼N group, hence the aquisitation of
the electrons by the azomethine group would require a higher energy.
The CV curve for the ligand exhibits one cathodic peak at E ¼ 1:24 V but no
p
obvious anodic peaks. This behaviour is in favour of the 4 electron reduction of the
azomethine group since the 2 electron process leading to the hydrazo stage must
display an anodic peak [37]. For the metal complexes, the CV curves display two
cathodic peaks, the less negative one represents the reduction of the azomethine
group whereas the more negative one is due to the reduction of the metal ions
(
Fig. 4).
The peak potentials E shift to more negative values on increasing the scan rate
which denotes the irreversible nature of the electrode reactions [38]. The plot of E
p
p
1
=2
as a function of v (scan rate) is a linear relation with positive slope supporting

Sulfadiazine Schiff Base Complexes
1151
Fig. 4. Cyclic voltammograms of complex 1 at different scan rates
the irreversible electrode process. Further support for the irreversible reactions is
gathered from the absence of anodic peaks. Also the i vs. v plot, is a linear relation
p
with positive slope denoting that the electrode reaction is mainly governed by
diffusion. The data are collected in Table 7.
Biological Effects
A primary study of the Minimum Inhibitor Concentrations (MIC) of Schiff base and
its complexes on Gram positive bacteria (Staphylococcus aureus and Bacillus
subtilis) and Gram negative bacteria (Escherichia coli and Pseudo-monos aerugi-
nosa) are recorded in Table 8.
From Table 8, it is clear that the inhibition is much larger for most metal
complexes than the Schiff base on Gram positive and Gram negative bacteria.
The Cu(II) complexes 5 and 6 have the best inhibitor effect on Gram negative
and Gram positive bacteria compared to the other metal complexes. The binuclear
Ni(II) complex 4 has also an inhibitor effect on both Gram positive and Gram
negative bacteria but it is less effective than complex 5 on Staphylococcus aureus.
The antibiotic effect of binuclear Cu(II) complex 6 on Gram negative and Gram
positive bacteria is relatively stronger than that of complex 5. As gathered from

1
152
K. Y. El-Baradie
Table 8. Minimum inhibitor concentration of Schiff base and complexes against Gram negative and
Gram positive bacteria
Bacteria
Organism
Gram negative
Gram positive
Compound
Ligand
E coli
Ps aur
150
100
100
3.1
B sub
100
3.1
St aur
250
100
50
250
100
50
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
100
100
100
50
50
3.1
50
50
3.1
50
3.1
3.1
data given in Table 8, the order of inhibition of all complexes in the activity of the
bacteria studied can be arranged as follows. For Escherichia coli 5 > 3, 4, 6 > 2 >
ligand, for Pseudomonos aeruginosa 4, 6 > 5 > 2, 3 > ligand, for Bacillus subtilis
2, 6 > 3, 4, 5, ligand, and for Staphylococcus aureus 5 > 3, 4, 6 > 2 > ligand.
Such increased activity of the metal chelates can be explained on the basis of
chelation theory [39]. On chelation, the polarity of the metal ion will be reduced to
a great extent due to the overlap with the ligand orbital. Further, it increases the
Scheme 3

Sulfadiazine Schiff Base Complexes
1153
delocalisation of ꢆ-electrons over the whole chelate ring and enhances the lipophi-
licity of the complexes [40].
Based on the information gained in the present study, the bonding of the metal
ions to the ligand can be represented as shown in Scheme 3.
Experimental
Physical Measurements
All reagents were of the highest grade available from BDH and used without further purification. The
equipments and the methods employed in the present work were the same as reported earlier [41, 42].
Elemental analysis (C, H, N) was done at the micro analytical laboratory of Cairo University.
IR spectra were recorded on a Perkin Elmer 1430 spectrometer as KBr discs. Electronic spectra were
registered on a Shimadzu 240 UV-Vis spectrophotometer using Nujol mull technique. Magnetic
ꢂ
susceptibility measurements at room temperature (25 C) were determined on a Johnson Matthey
magnetic susceptibility balance using Hg[(Co(SCN) ] as calibrant; diamagnetic corrections were
4
calculated from Pascal’s constants. Conductance measurements were carried out by means of a YSI
ꢁ
3
model 32 conductance meter in DMF (10 M). The thermal studies, TGA and DTA, were achieved
using a Shimadzu TG 5O thermal analyzer. The ESR spectra were recorded on a Joel model JES FE2
XG spectrometer provided with an E 101 microwave bridge.
The pen recording polarograph Sargent-Welch model 4001 was used for studying the polarographic
behavior of the complexes under investigation. The cell described by Meites [43] was used for
recording the polargramms at a dropping mercury electrode (DME) (m ¼ 1.03mgsꢁ , t ¼ 3.3s at mer-
cury height h ¼ 60 cm) and a saturated calome electrode (SCE) as a reference electrode, supplied by
Sargent-Welch.
1
The cyclic voltammogramms of the complexes under investigation were recorded using a poten-
tiostate model 264 A (PAR-from EG&G). The 303 A electrode assembly, supplied by EG&G, with a
ꢁ
2
2
hanging mercury drop electrode (area ¼ 2.6ꢄ10 cm ) as a working electrode, a Pt wire as a counter
electrode, and Ag=AgCl=KCl as reference electrode.
s
3
The nutrient agar solid medium contained per 1000 cm (pH ¼ 7.2): beef extract 3 g, peptone 5 g,
Nail 5 g, and agar 20 g. It was sterilized under high pressure steam for 30min, serial dilutions of the
3
3
Schiff base and its complexes were prepared containing 250 ꢀg=cm down to 3 ꢀg=cm . The bacteria
used for testing the biological activity of the ligands and their complexes were Gram positive bacteria
(Staphylococcus aures and Bacillus subtilis) and Gram negative bacteria (Escherichia coli and
Pseudomonos aeruginosa) provided by the biology department. The bacteria chosen were found to
be sensitive towards metal complexes.
Preparation of Schiff Base
The Schiff base was prepared by refluxing a mixture of an ethanol solution of sulfadiazine (1mmol in
3
0cm ) and an ethanol solution of salicylaldehyde (1mmol in 20cm ) for 3 h. On cooling the reaction
3
3
mixture, the product formed was filtered off, recrystallized from ethanol, washed with diethyl ether,
and dried in a vacuum desiccator over silica gel.
Preparation of Complexes
The metal complexes of the sulfadiazine Schiff base with Co(II), Ni(II), Cu(II), and Mn(II) ions were
prepared by chemical and electrochemical techniques. In the chemical methods, the metal complexes
3
were prepared by refluxing ethanolic solutions of both the Schiff base (1mmol in 30cm ) and each of

1
154
K. Y. El-Baradie
3
3
the metal acetates (2mmol in 20 cm ) and sodium acetate solution (0.5g in 5 cm ) as buffering agent
for 3 h. After cooling the reaction mixture, the separated solids were filtered off, washed with ethanol
and diethyl ether and dried over silica gel. The analytical data and physical measurements are listed in
Table 1.
The electrochemical technique used was essentially the same as reported previously [44, 45] in
which the respective pure metal was used as the anode and Pt as the cathode and the electrolyte was the
3
Schiff base (1.9mmol), dissolved in a mixture of acetone (20 cm ) and ethanol (20 cm ) containing
3
2
5mg of Et NClO .
4 4
The anodic dissolution of the metal (Co, Ni, Cu, or Mn) in the electrolyte amounted to
8–64 mg within 2.5–5 h electrolysis at 10V and 20mA. The solid complexes formed were col-
5
lected, washed successively with acetone, ethanol, and diethyl ether, and then dried in a vacuum
desiccator.
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