Metal complexes of a novel Schiff base derived from sulphametrole and varelaldehyde. Synthesis, spectral, thermal characterization and biological activity

Article abstract of DOI:10.1016/j.molstruc.2010.06.002

Metal complexes of a novel Schiff base (HL = 3-(4′- ethylazomethinobenzene sulphonamide)-4-methoxy-1,2,5-thiadiazole) derived from condensation of sulphametrole and varelaldehyde are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, and thermal analysis (TG). From the elemental analyses data, 1:1 metal complexes are formed having the general formulae [MCl₃(HL) (H₂O)]·3H₂O (M = Cr(III), Fe(III)) and [MCl ₂(HL)(H₂O)₂]·yH₂O (where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II), y = 0-3). The important infrared (IR) spectral bands corresponding to the active groups in the ligand and the solid complexes under investigation were studied. IR spectra show that HL is coordinated to the metal ions in a neutral bidentate manner with ON donor sites of the enolic sulphonamide-OH and thiodiaza-N. The solid complexes have been synthesized and studied by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats-Redfern equation. All the metal chelates are found to be non-electrolytes. From the magnetic and solid reflectance spectra, the complexes have octahedral structures. The antibacterial and antifungal activities of the synthesized ligand and its metal complexes were screened against bacterial species (Escherichia coli and Staphylococcus aureus) and fungi (Candida and Aspergillus flavus). The activity data show that the metal complexes have a promising biological activity comparable with the parent Schiff base ligand against bacterial and fungal species.

Full text of DOI:10.1016/j.molstruc.2010.06.002

Journal of Molecular Structure 979 (2010) 62–71
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Metal complexes of a novel Schiff base derived from sulphametrole
and varelaldehyde. Synthesis, spectral, thermal characterization
and biological activity
b
Gehad G. Mohamed a, M.A. Zayed a, , S.M. Abdallah
*
a Chemistry Department, Faculty of Science, Cairo University, Giza 12613, Egypt
b Workers University, Aswan 10, Egypt
a r t i c l e i n f o
a b s t r a c t
Metal complexes of a novel Schiff base (HL = 3-(40-ethylazomethinobenzene sulphonamide)-4-methoxy-
1,2,5-thiadiazole) derived from condensation of sulphametrole and varelaldehyde are reported and char-
acterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, and
thermal analysis (TG). From the elemental analyses data, 1:1 metal complexes are formed having the gen-
eral formulae [MCl3(HL)(H2O)]ꢀ3H2O (M = Cr(III), Fe(III)) and [MCl2(HL)(H2O)2]ꢀyH2O (where M = Mn(II),
Fe(II), Co(II), Ni(II), Cu(II) and Zn(II), y = 0–3). The important infrared (IR) spectral bands corresponding
to the active groups in the ligand and the solid complexes under investigation were studied. IR spectra
show that HL is coordinated to the metal ions in a neutral bidentate manner with ON donor sites of
the enolic sulphonamide-OH and thiodiaza-N. The solid complexes have been synthesized and studied
by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were
studied kinetically using the integral method applying the Coats–Redfern equation. All the metal chelates
are found to be non-electrolytes. From the magnetic and solid reflectance spectra, the complexes have
octahedral structures. The antibacterial and antifungal activities of the synthesized ligand and its metal
complexes were screened against bacterial species (Escherichia coli and Staphylococcus aureus) and fungi
(Candida and Aspergillus flavus). The activity data show that the metal complexes have a promising bio-
logical activity comparable with the parent Schiff base ligand against bacterial and fungal species.
Ó 2010 Elsevier B.V. All rights reserved.
Article history:
Received 23 April 2010
Received in revised form 30 May 2010
Accepted 1 June 2010
Available online 8 June 2010
Keywords:
Novel Schiff base
Transition metal complexes
Spectroscopy
Thermal analysis
Biological activity
1. Introduction
and electrochemistry [22]. The complexes make these compounds
effective and stereospecific catalysts for oxidation, reduction and
Schiff bases play an important role in inorganic chemistry as
they easily form stable complexes with most transition metal ions.
The development in the field of bioinorganic chemistry has in-
creased the interest in Schiff base complexes, since it has been rec-
ognized that many of these complexes may serve as models for
biologically important species [1–5]. Schiff base ligands are consid-
ered ‘‘privileged ligands” because they are easily prepared by the
condensation between aldehydes and imines. Schiff base ligands
are able to coordinate many different metals [6–10], and to stabi-
lize them in various oxidation states. The Schiff base complexes
have been used in catalytic reactions [11] and as models for biolog-
ical systems [12,13]. During the past two decades, considerable
attention has been paid to the chemistry of the metal complexes
of Schiff bases containing nitrogen and other donors [14–19]. This
may be attributed to their stability, biological activity [20] and po-
tential applications in many fields such as oxidation catalysis [21],
hydrolysis and they show biological activity, and other transforma-
tions of organic and inorganic chemistry [23]. It is well known that
some drugs have higher activity when administered as metal com-
plexes than as free ligands [23].
Sulphametrole (SMR) was designated by chemical abstracts as
N1-(4-methoxy-1,2,5-thiadiazol-3-yl)sulphanilamide. It had the
molecular formula C9H10 N4O3S2 (F.W = 286.33 g/mole). Sulfamet-
role is a sulphonamide antibacterial drug. Synthesis, spectroscopic,
thermal and antimicrobial studies of some metal complexes of Schiff
base derived from and 2-thiophene carboxaldehyde [24] and o-vani-
lin [25] were reported. The present study deals with the preparation
of novel Schiff base ligand and its chelates with some transition met-
als, e.g. Cr(III), Mn(II), Fe(III), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II). The
solid complexes have been synthesized and studied by elemental
analyses, molar conductance, solid reflectance, IR and thermogravi-
metric analysis (TG). The thermal dehydration and decomposition of
these complexes were studied kinetically using the integral method
applying the Coats–Redfern. The biological activity of the parent
Schiff base and its complexes was studied.
* Corresponding author. Tel.: +20 2 22728437, +20 105776675.
E-mail address: mazayed429@yahoo.com (M.A. Zayed).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.06.002

G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
63
2.5. Biological activity
2. Experimental
Antimicrobial activity of the tested samples was determined
using a modified Kirby-Bauer disc diffusion method [26]. One hun-
dred microliters of the tested bacteria or fungi were grown in
10 mL of fresh media until they reached account of approximately
108 cells/mL for bacteria and 105 cells/mL for fungi [27]. One hun-
dred microliters of microbial suspension was spread onto agar
plates corresponding to the broth in which they were maintained.
Isolated colonies of each organism that might be playing a patho-
genic role should be selected from primary agar plates and tested
for susceptibility by disc diffusion method [28]. Of the many media
available, NCCLS recommends Mueller–Hinton agar due to its re-
sults in good batch-to-batch reproducibility. Disc diffusion method
for filamentous fungi tested by using approved standard method
(M38-A) developed [28]. For evaluating the susceptibilities of fila-
mentous fungi to antifungal agent, the disc diffusion method was
applied for yeast developed by using approved standard method
(M44-P) [28]. Plates inoculated with filamentous fungi as Asprgillus
flavus at 25 °C for 48 h; Gram (+) bacteria as Staphylococcus aureus;
Gram (ꢁ) bacteria as Escherichia coli, they were incubated at 35–
37 °C for 24–28 h and yeast as Candida albicans incubated at
30 °C for 24–28 h and, then the diameters of the inhibition zones
were measured in millimeters [28]. Standard discs of tetracycline
(antibacterial agent), and amphotericin B (antifungal agent) served
as positive controls for antimicrobial activity but filter discs
2.1. Materials and reagents
All chemicals used were of the analytical reagent grade (AR),
and of highest purity available. Sulphametrole, varelaldehyde and
ferrous chloride were purchased from Sigma. Copper (II) chloride
dihydrate, ferric and chromium chlorides hexahydrates were ob-
tained from Prolabo. Manganese (II), cobalt (II) and nickel (II) chlo-
rides hexahydrate and the organic solvents (ethyl alcohol,
diethylether, and dimethylformamide (DMF)), were purchased
from BDH. Zinc chloride dihydrate was obtained from Ubichem.
They included also Zinc oxide, disodium salt of EDTA (Analar),
ammonia solution (33% v/v) and ammonium chloride (El-Nasr
pharm. Chem. Co., Egypt). Hydrochloric and nitric acids from
Merck were used. De-ionized water collected from all glass equip-
ments was usually used in all preparations.
2.2. Instruments
The molar conductance of solid complexes in DMF was mea-
sured using Sybron-Barnstead conductometer (Meter-PM.6,
E = 3406). Elemental microanalyses of the separated solid chelates
for C, H, N and S were performed at the Microanalytical Center,
Cairo University. The analyses were repeated twice to check the
accuracy of the data. Infrared spectra were recorded, as KBr pellets,
on a Perkin–Elmer FT-IR type 1650 spectrophotometer in wave
number region 4000–400 cmꢁ1. The solid reflectance spectra were
measured on a Shimadzu 3101pc spectrophotometer. The molar
magnetic susceptibility was measured on powdered samples using
the Faraday method. The diamagnetic corrections were made by
Pascal’s constant and Hg[Co(SCN)4] was used as a calibrant. The
thermogravimetric analysis (TG) was carried out in dynamic nitro-
gen atmosphere (10 mL minꢁ1) with a heating rate of 10 °C minꢁ1
using Shimadzu TG-60H thermal analyzer. The 1H NMR spectra
were recorded using 300 MHz Varian-Oxford Mercury. The biolog-
ical activity was carried out at the Microanalytical Center, Cairo
University.
impregnated with 10 lL of solvent (distilled water, chloroform,
DMSO) were used as a negative control. The agar used is Muel-
ler–Hinton agar that is rigorously tested for composition and pH.
Further the depth of the agar in the plate is a factor to be consid-
ered in the disc diffusion method. This method is well documented
and standard zones of inhibition have been determined for suscep-
tible and resistant values. Blank paper discs (Schleicher and Schu-
ell, Spain) with a diameter of 8.0 mm were impregnated with 10 lL
of tested concentration of the stock solutions. When a filter paper
disc impregnated with a tested chemical is placed on agar, the
chemical will diffuse from the disc into the agar. This diffusion will
place the chemical in the agar only around the disc. The solubility
of the chemical and its molecular size will determine the size of the
area of chemical infiltration around the disc. If an organism is
placed on the agar, it will not grow in the area around the disc if
it is susceptible to the chemical. This area of no growth around
the disc is known as zone of inhibition or clear zone. For the disc
diffusion, the zone diameters were measured with slipping calipers
of the national committee for clinical laboratory standards [28].
Agar based methods such Etest and disc diffusion can be good
alternatives because they are simpler and faster than broth-based
methods [29].
2.3. Synthesis of Schiff base (HL)
Ethanolic hot solution (60 °C) of varelaldehyde (0.58 g,
10 mmol) was mixed with ethanolic hot solution (60 °C) of sulph-
ametrole (2.54 g, 10 mmol) in 50 mL quickfit flask. The resulting
mixture was left under reflux for 3 h and the formed solid product
was separated by filtration, purified by crystallization from etha-
nol, washed with diethyl ether and dried in a vacuum over anhy-
drous calcium chloride. The yellow product is produced in 90%
yield.
3. Results and discussion
3.1. Schiff base characterization
2.4. Synthesis of metal complexes
The new prepared Schiff base (HL = 3-(40-ethylazomethinoben-
zene sulphonamide)-4-methoxy-1,2,5-thiodiazole) is subjected to
elemental analyses, IR and 1H NMR spectral studies. The results
of elemental analyses (C, H, N, S) with molecular formula and the
melting point are presented in Table 1. The results obtained are
in good agreement with those calculated for the suggested formula
and the melting point is sharp indicating the purity of the prepared
Schiff base. The structure of the Schiff base under study is given be-
low in Fig. 1. The IR spectral data of HL Schiff base is listed in Table
The following detailed preparation is given as an example and
the other complexes were obtained similarly. The Cu(II) complex
was prepared by the addition of hot solution (60 °C) of the Cu(II)
chloride (0.17 g, 1 mmol) in an ethanol–water mixture (1:1,
25 mL) to the hot solution (60 °C) of the Schiff base (0.294 g,
1 mmol) in the same solvent mixture (25 mL). The resulting mix-
ture was stirred under reflux for one hour whereupon the complex
precipitated. It was collected by filtration, washed with a 1:1 eth-
anol: water mixture and diethyl ether.
2. It was found that the
m(C@N) of the azomethine group and
m
(C@N) of the thiadiazole moiety occur at 1597 and 1650 cmꢁ1
,

64
G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
Table 1
Analytical and physical data of HL ligand and its metal complexes.
Compound
m.p.
(°C)
Colour (% yield)
% Found (calcd.)
leff.
Km
(B.M.) Xꢁ1 molꢁ1 cm2
C
H
N
S
M
–
HL, C12H14N4O3S; 294 g/mol
205
Yellow
(90)
Green
48.70
4.41
18.93
(19.05)
10.42
(10.68)
11.63
(11.81)
10.10
(10.60)
11.10
(11.36)
10.95
(10.89)
10.48
(10.89)
10.12
10.62
(10.88)
6.23
(6.10)
7.03
(6.75)
5.73
(6.05)
6.10
(6.49)
6.18
(6.23)
6.03
(6.23)
5.78
(5.96)
6.65
–
–
(48.98)
27.52
(4.76)
4.46
[CrCl3(HL)(H2O)]ꢀ3H2O, C12H22Cl3CrN4O7S; 524.5 g/mol
[MnCl2(HL)(H2O)2]ꢀH2O, C12H20Cl2MnN4O8S; 473 g/mol
[FeCl3(HL)(H2O)]ꢀ3H2O, C12H22Cl3FeN4O7S; 528.5 g/mol
[FeCl2(HL)(H2O)2]ꢀ2H2O, C12H22Cl2FeN4O7S; 493 g/mol
[CoCl2(HL)(H2O)2]ꢀ3H2O, C12H24Cl2CoN4O8S; 514 g/mol
[NiCl2(HL)(H2O)2]ꢀ3H2O, C12H24Cl3NiN4O8S; 514 g/mol
[CuCl2(HL)(H2O)2]ꢀ2H2O, C12H26Cl2CuN4O9S; 500.5 g/mol
[ZnCl2(HL)(H2O)2], C12H18Cl2N4O5SZn; 466 g/mol
>300
>300
>300
>300
>300
>300
>300
>300
10.05
(9.91)
11.28
(11.60)
10.3
(10.60)
11.02
(11.36)
11.52
(11.48)
11.66
(11.48)
12.03
(11.84)
14.07
5.52
5.42
5.69
5.15
5.06
3.87
2.07
diam.
13.56
17.82
19.28
10.96
17.30
11.92
9.18
(66)
(27.45)
30.42
(4.19)
4.08
Yellowish brown
(69)
Brownish Black
(71)
Yellow
(63)
Green
(30.38)
27.54
(4.22)
4.05
(27.25)
29.15
(4.16)
4.34
(29.21)
28.25
(4.46)
4.31
(65)
(28.02)
27.85
(4.67)
4.76
Yellowish Brown
(70)
Green
(70)
White
(28.02)
26.74
(4.67)
5.06
(26.84)
31.11
(4.85)
3.60
(10.44)
11.86
23.83
(62)
(30.90)
(3.86)
(12.02)
(6.87)
(13.95)
O
S
N
NH
OCH3
O
H3C
N
N
S
O
S
N
N
OCH3
OH
H3C
N
S
N
Fig. 1. Structure of Schiff base ligand (HL).
Table 2
IR spectra (4000–400 cmꢁ1) of the HL ligand and its metal complexes.
Compound
m(NH)
m(OH) enolic
m(SO2) (asym) v(SO2) (sym.)
m(CH@N) azomethine
m
(C@N) thiodiaza V(H2O) (coord.)
m(MAO)
m(MAN)
HL
3381br
–
–
1321sh
1308sh
1158sh
1174m
1597sh
1594br
1650sh
1645sh
–
–
–
[CrCl3(HL)(H2O)]ꢀ3H2O
3178s
830m
782m
820s
550w
420w
[MnCl2(HL)(H2O)2]ꢀH2O
[FeCl3(HL)(H2O)]ꢀ3H2O
[FeCl2(HL)(H2O)2]ꢀ2H2O
[CoCl2(HL)(H2O)2]ꢀ3H2O
[NiCl2(HL)(H2O)2]ꢀ3H2O
[CuCl2(HL)(H2O)2]ꢀ2H2O
[ZnCl2(HL)(H2O)2]
–
–
–
–
–
–
–
3100br
3150br
3230w
3150br
3250br
3168br
3170br
1321m
1321w
1323m
1322m
1320sh
1320m
1324m
1145m
1160m
1155m
1155w
1154m
1147m
1135m
1598m
1595m
1598sh
1597m
1597m
1596sh
1596m
1628sh
1622sh
1631m
1625m
1628m
1625sh
1620sh
554w
520s
440w
430w
434w
430w
466w
441w
432w
782s
836m
742m
887m
742m
834m
774m
834m
774m
822m
752m
845m
725m
520m
522w
586m
532m
525m
sh = sharp, m = medium, s = small, w = weak, br = broad.
respectively. In addition, the ligand exhibits two bands at 1321 and
1158 cmꢁ1 which is attributed to
asym(SO2) and sym(SO2) stretch-
ing vibrations, respectively [24,25]. Also, it has band at
3412 cmꢁ1 which attributed to (NH). The 1H NMR data for HL li-
m
gand (Fig. 2A), recorded in DMSO-d6, show a sharp signals at
9.80 and 3.986 ppm which may be assigned to the azomethine (s,
m
m
a

G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
65
Fig. 2. 1H NMR spectra of (A) HL and (B) Zn complex.
ACH@N, 1H) and methoxy (s, AOCH3; 3H) protons, respectively. A
multiple observed in the region 0.858 and 1.267 ppm for HL corre-
sponds to the methyl protons (m, CH3ACH2ACH@N; 3H) and (m,
CH3ACH2ACH@N; 2H), respectively. Another doublet–doublet
bands at 6.60 and 7.577 and 6.70 and 7.70 ppm for HL may reason-
ably be assigned to phenyl protons (d,d, C6H4; 4H; J = 8.65 Hz). A
broad band observed at 11.04 ppm may be attributed to the sec-
ondary amine proton (ASO2ANH; 1H).
complexation suggesting the coordination via thiadiazole nitrogen
(N ? M). In addition, the ligand exhibits two bands at 1321 and
1158 cmꢁ1 due to
m
asym(SO2) and
respectively [24,25]. Also, it has a band at 3412 cmꢁ1 which attrib-
uted to (NH). The bands due to asymmetric and symmetric SO2
group are shifted to lower frequencies (Table 2) upon complexa-
msym(SO2) stretching vibrations,
m
tion. While the m(NH) is disappeared or hidden under the broad
bands at 3450–3100 cmꢁ1 in the spectra of the complexes as the
result of the presence of coordinated water molecules which in
turns make it difficult to confirm the enolization of the sulphona-
mide group. The blue shift of the SO2 stretching vibration to lower
frequencies and the appearance of new absorption band for enol
3.2. Composition and structures of Schiff base complexes
The isolated solid complexes of Cr(III), Mn(II), Fe(III), Fe(II),
Co(II), Ni(II), Cu(II) and Zn(II) ions with the Schiff base ligand were
subjected to elemental analyses (C, H, N, S and metal content), IR,
1H NMR, magnetic studies, molar conductance, and thermal analy-
sis (TG), to identify their tentative formulae in a trial to elucidate
their molecular structures. The results of elemental analyses, Table
1, are in good agreement with those required by the proposed for-
mulae. The complexes are insoluble in water and most organic sol-
vents and soluble in DMF and DMSO solvents.
m
(OH) stretching mode at 3150–3250 cmꢁ1, confirm the tautomer-
ization (ASO(OH)@N) as a result of complex formation to give
more stable six-membered ring [24,25,30]. The IR bands of
m
(H2O) of coordinated water appeared at 820–887 and 725–
782 cmꢁ1, indicating the binding of water molecules to the metal
ions. In the far IR spectra of all the complexes, the non-ligand
bands observed at 520–586 and 420–466 cmꢁ1 regions can be as-
signed to
m(MAO) and m(MAN), respectively [31,32]. Therefore,
the IR spectra reveal that HL coordinated to the metal ions via eno-
lic AOH of sulphonamide group and thiadiazole-N.
3.3. Molar conductivity measurements
3.5. 1H NMR spectra
The chelates were dissolved in DMF and the molar conductivi-
ties of their solutions (10ꢁ3 M) at 25 2 °C were measured. It is
concluded from the results reported in Table 1 that the chelates
The 1H NMR data for HL ligand (Fig. 2A) and its Zn(II) complex
(Fig. 2B), recorded in DMSO-d6, show a sharp signal at 9.80 and
9.90 ppm which may be assigned to the azomethine protons
(ACH@N, 1H), respectively. However, a singlet at 3.986 and
4.08 ppm may be attributed to the methoxy protons (AOCH3;
3H). A multiple observed in the region 0.858 and 1.267 and 1.10
and 1.30 ppm for HL and Zn(II) complex corresponds to the methyl
protons (CH3ACH2ACH@N; 3H) and (CH3ACH2ACH@N; 2H),
respectively. Another doublet–doublet bands at 6.60 and 7.577
and 6.70 and 7.70 ppm for HL and Zn(II) complex, respectively,
may reasonably be assigned to phenyl protons (C6H4; 4H;
J = 8.65 Hz). A broad band observed at 11.04 ppm may be attrib-
uted to the secondary amine proton (ASO2ANH; 1H). It is found
that the enolic S(O)OH signal, appeared in the spectrum of Zn(II)
complex at 6.10 ppm indicating that ASO2ANH is enolized to the
AS(O)OH@NA and participation in the chelation with Zn(II) ion
[24,25]. The signal observed at 3.40 ppm with an integration corre-
sponding to four protons in Zn(II) complex is assigned to two water
molecules [24,25]. However, the resonance signals obtained for
have molar conductance values of 9.18–23.83
X
ꢁ1 molꢁ1 cm2
indicating that these chelates are non-electrolytes. It also indi-
cates the bonding of the chloride anions to the metal ions. The
relative high values obtained may be attributed to the replace-
ment of the coordinated chloride ions by solvent molecules, a
phenomenon usually encountered in complexes containing
chloride ions.
3.4. IR spectral studies
The IR spectral data of HL Schiff base and its complexes are
listed in Table 2. It was found that the m(C@N) of the azomethine
group occurs at 1597 cmꢁ1 in the free HL ligand; after complexa-
tion, this band is slightly shifted to lower wavenumbers (1594–
1598 cmꢁ1) indicating the non-involvement of the azomethine
nitrogen in chelate formation. However, the band due to the thia-
diazole moiety;
m
(C@N), in the free ligand is observed at 1650 cmꢁ1
and shifted to lower frequency values at (1620–1645 cmꢁ1) upon

66
G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
Zn(II) complex shows downfield shift as compared to the corre-
sponding ligand indicating the coordination of ligand to Zn(II) ion.
to the 6A1g ? T2g (G) transition in octahedral geometry of the com-
plexes [33]. The observed magnetic moment of Fe(III) complex is
5.69 B.M. Thus, the complex formed has the octahedral geometry
[25,33]. The spectrum shows also a band at 27,995 cmꢁ1 which
may attribute to ligand to metal charge transfer. The diffused
reflectance spectrum of the Mn(II) complex (Fig. 3) shows three
bands at 15,579, 22,145 and 26,977 cmꢁ1 assignable to
3.6. Magnetic susceptibility and electronic spectra measurements
From the diffused reflectance spectrum, the Fe(III) chelate
(Fig. 3) exhibits a band at 22,010 cmꢁ1, which may be assigned
Fig. 3. Diffused reflectance spectra of (A) Mn(II), (B) Co(II), (C) Fe(III) and (D) Cu(II) complexes.

G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
67
6A1g ? 4T1g
,
6A1g ? 4T2g(G) and 6A1g ? 4T1g(D) transitions, respec-
tion energies reflect the thermal stability of the complexes. The en-
tropy of activation is found to have negative values in all the
complexes which indicate that the decomposition reactions pro-
ceed spontaneously.
tively [34]. The magnetic moment value is 5.42 B.M. which indi-
cates the presence of Mn(II) complex in octahedral structure.
The electronic spectrum of the Fe(II) complex displays two
absorption bands at 14,880 and 18,036 cmꢁ1 which are assigned
to 5T2g ? 5Eg transitions [33]. Also the band at 25,655 cmꢁ1 is as-
signed to L ? M charge transfer. The observed magnetic moment
of 5.15 B.M. is consistent with an octahedral geometry [33]. The
electronic spectrum of the Co(II) complex (Fig. 3) gives three bands
at 15,289, 18,407 and 22,360 cmꢁ1. The bands observed are as-
The thermogram of [CrCl3(HL)(H2O)]ꢀ3H2O and [CuCl2(HL)(-
H2O)]ꢀ2H2O chelates show five decomposition steps within the
temperature range 30–900 and 50–950 °C, respectively. The first
two steps of decomposition within the temperature range 30–
250 and 50–230 °C correspond to the loss of three water molecules
of hydration, Cl2, one coordinated water molecule and C4H9ClNO
(in case of Cr(III) complex, mass loss = 51.32% (calcd. 50.62%))
and loss of two water molecules of hydration and coordination
and Cl2.(in case of Cu(II) complex, mass loss of 29.37% (calcd.
28.57%)). The energy of activation was found to be 44.40 and
78.24 (in case of Cr(III) complex) and 36.52 and 53.78 kJ molꢁ1
(in case of Cu(II) complex) for the first and second steps, respec-
tively. The subsequent steps (230–950 °C) correspond to the re-
moval of the organic part of the ligand leaving metal oxide as a
residue. The overall weight loss amounts to 86.02% (calcd.
85.51%) and 84.26 (calcd. 84.11%) for Cr(III) and Cu(II) complexes,
respectively.
The TG curves of the Mn(II), Fe(II), Co(II) and Ni(II) chelates
show four stages of decomposition within the temperature range
of 30–950 °C. The first step at 30–130 °C corresponds to the loss
of water molecules of hydration except Fe(II) complex, it corre-
sponds to the loss of hydrated and coordinated water molecules
(30–200 °C). The subsequent three steps (2nd, 3rd and 4th) involve
the loss of Cl2 and ligand molecule. The overall weight loss
amounts to 84.17% (calcd. 85.02%), 85.59% (calcd. 85.39%), 85.92%
(calcd. 85.60%) and 84.97% (calcd. 85.42%) and the activation ener-
gies are 82.37–176.9, 75.98–184.2, 145.6–165.7 and 102.4–243.4
for Mn(II), Fe(II), Co(II) and Ni(II) chelates, respectively.
signed to the transitions T1g (F) ? 4T2g (F) (
m
1), T1g (F) ? 4A2g
4
4
(F) ( 3), respectively, suggesting an octa-
m
2) and 4T1g (F) ? 4T2g (P) (
m
hedral geometry around Co(II) ion [32,40,42]. The magnetic sus-
ceptibility is found to be 5.06 B.M. indicating an octahedral
geometry [25]. The region at 25,790 cmꢁ1 refers to the charge
transfer band.
The Ni(II) complex is found to has a room temperature magnetic
moment value of 3.87 B.M.; which is in the normal range observed
for octahedral Ni(II) complexes [25,33,35]. The electronic spectrum
displays three bands in the solid reflectance spectrum at m1
:
14,968 cmꢁ1
21,347 cmꢁ1
:
:
3A2g ? 3T2g 2: 17,788 cmꢁ1 3A2g ? 3T1g(F) and m3
; m :
:
3A2g ? 3T1g(P). The spectrum shows also a band at
24,565 cmꢁ1 which may attributed to ligand to metal charge trans-
fer. The reflectance spectrum of Cu(II) chelat (Fig. 3) consists of a
shoulder band centered at 17,045 and 18,167–22,682 cmꢁ1. The
magnetic moment of 2.07 B.M. falls within the range normally ob-
served for octahedral Cu(II) complexes [25,33]. A moderately in-
tense peak observed at 24,664 cmꢁ1 is due to ligand–metal charge
transfer transition. The Zn(II) complex is diamagnetic and according
to the empirical formula, an octahedral geometry is proposed for
this complex.
Based on analyses and spectral studies, tentative proposed
structures of the complexes are shown in Fig. 5.
3.7. Thermal analysis (TG)
The TG data of the thermal decomposition of the complexes are
shown in Table 3, Fig. 4 and Scheme 1. The thermodynamic activa-
tion parameters of decomposition processes of dehydrated com-
3.8. Biological activity
plexes namely activation energy (E*), enthalpy (
D
H*), entropy
G*)
are evaluated graphically by employing the Coats–Redfern relation
[36]. The entropy of activation (
S*), enthalpy of activation ( H*)
and the free energy change of activation (
G*) were calculated.
In testing the antibacterial activity of these compounds we used
more than one test organism to increase the chance of detecting
antibiotic principles in tested materials. The sensitivity of a micro-
organism to antibiotics and other antimicrobial agents was deter-
mined by the assay plates which incubated at 28 °C for 2 days
for yeasts and at 37 °C for 1 day for bacteria. All of the tested com-
(D D
S*) and Gibbs free energy change of the decomposition (
D
D
D
The data are summarized in Table 4. The high values of the activa-
Table 3
Thermogravimetric data of HL metal complexes.
Complex
TG range (°C)
DTGmax (°C)
n#
Mass loss Total mass loss % Found (calcd.)
Assignment
Metallic residue
½Cr2O3
[CrCl3(HL)(H2O)]ꢀ3H2O
30–130
130–250
250–900
85
219
295, 484, 648
1
1
3
10.42 (10.30)
40.90 (40.32)
34.70 (34.89) 86.02 (85.51)
Loss of 3H2O
Loss of H2O, Cl2 and C4H9ClNO
Loss of C8H5N3O0.5
S
[MnCl2(HL)(H2O)2]ꢀH2O
[FeCl2(HL)(H2O)2]ꢀ2H2O
[CoCl2(HL)(H2O)2]ꢀ3H2O
[NiCl2(HL)(H2O)2]ꢀ3H2O
[CuCl2(HL)(H2O)2]ꢀ2H2O
30–100
100–280
280–950
94
252
500, 857
1
1
2
3.54 (3.80)
22.78 (22.57)
57.85 (58.65) 84.17 (85.02)
Loss of H2O
Loss of 2H2O and Cl2
Loss of C12H14N4O2S
MnO
FeO
CoO
NiO
CuO
30–200
200–370
370–950
63
272
504, 700
1
1
2
14.81 (14.60)
32.27 (32.05)
38.51 (38.74) 85.59 (85.39)
Loss of 4H2O
Loss of Cl2 and C4H9NO
Loss of C8H5N3OS
30–120
120–320
320–950
55
275
400, 690
1
1
2
11.29 (10.69)
20.92 (20.82)
53.71 (54.09) 85.92 (85.60)
Loss of 2H2O
Loss of 2H2O and Cl2
Loss of C12H14N4O2S
30–130
130–260
260–900
77
210
386, 552
1
1
2
10.69 (10.51)
20.39 (20.82)
53.89 (54.09) 84.97 (85.42)
Loss of 3H2O
Loss of 2H2O and Cl2
Loss of C12H14N4O2S
50–130
130–230
230–950
70
185
365, 556, 764
1
1
3
7.45 (7.19)
21.92 (21.38)
54.89 (55.54) 84.26 (84.11)
Loss of 2H2O
Loss of 2H2O and Cl2
Loss of C12H14N4O2S

68
G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
Fig. 4. Thermal analysis (TG) of (A) Mn(II), (B) Ni(II), (C) Fe(III) and (D) Co(II) complexes.
pounds showed a remarkable biological activity against different
types of Gram-positive and Gram-negative bacteria and against
fungi species. The data are listed in Table 5. On comparing the bio-
logical activity of the Schiff base and its metal complexes with the
standard (Tetracycline, Antibacterial agent) and (Amphotricine B,
Antifungal agent), it is seen that the biological activity follows
the order:
For Aspergillus flavus (Fungus): HL > amphotricine B > Cu(II) > -
Cr(III) > Fe(II) > Zn(II). Fe(III), Mn(II), Co(II) and Ni(II) complexes
have no antifungal activity.
For C. albicans (Fungus): amphotricine B > Cu(II) > Cr(III) = -
Co(III) > Ni(II) > Fe(II) = Mn(II) > HL > Zn(II). Fe(III) complex has
no antifungal activity.
It was demonstrated that the newly prepared Schiff base and its
metal complexes showed a higher effect on E. coli (Gram-negative
bacteria) and S. aureus (Gram-positive bacteria). It is known that
the membrane of Gram-negative bacteria is surrounded by an outer
membrane containing lipopolysaccharides. The newly synthesized
For Gꢁ bacteria HL > Fe(II) > Ni(II) > Cu(II) > tetracycline >
Mn(II) > Co(II) > Cr(III) > Zn(II) > Fe(III).
For G+ bacteria HL > Cu(II) > Fe(II) = Ni(II) > Mn(II) > tetracy-
cline > Co(II) > Cr(II) > Fe(III) > Zn(II).

G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
69
Scheme 1. Thermal decomposition scheme of metal complexes.
Table 4
Thermodynamic data of the thermal decomposition of H2L metal complexes.
*
Complex
Decomp. Temp. (°C)
E* (kJ molꢁ1
)
A (sꢁ1
)
D
S
(JKꢁ1molꢁ1
)
D
H* (kJ molꢁ1
)
D )
G* (kJ molꢁ1
[CrCl3(HL)(H2O)]ꢀ3H2O
30–100
44.40
78.24
119.6
182.7
223.5
53.25
82.37
132.4
176.9
22.95
75.98
137.4
184.2
63.85
145.6
187.9
165.7
51.18
102.4
182.9
243.4
36.52
53.78
79.54
123.2
189.6
3.67 ꢂ 108
4.09 ꢂ 1012
5.89 ꢂ 1010
2.99 ꢂ 109
4.05 ꢂ 107
2.87 ꢂ 108
4.55 ꢂ 1012
6.08 ꢂ 105
9.34 ꢂ 107
5.09 ꢂ 109
4.68 ꢂ 106
8.44 ꢂ 1010
1.65 ꢂ 1011
6.53 ꢂ 1012
3.76 ꢂ 1010
7.02 ꢂ 108
1.98 ꢂ 109
4.45 ꢂ 107
3.19 ꢂ 1012
4.56 ꢂ 1011
7.21 ꢂ 107
1.73 ꢂ 1010
4.26 ꢂ 1012
5.72 ꢂ 107
3.28 ꢂ 1010
4.66 ꢂ 108
ꢁ49.15
ꢁ85.76
ꢁ112.3
ꢁ165.9
ꢁ198.7
ꢁ34.65
ꢁ62.66
ꢁ106.6
ꢁ185.7
ꢁ63.88
ꢁ108.2
ꢁ162.7
ꢁ215.4
ꢁ43.76
ꢁ89.77
ꢁ152.4
ꢁ168.7
ꢁ56.14
ꢁ95.28
ꢁ166.7
ꢁ203.2
ꢁ36.84
ꢁ65.48
ꢁ106.9
ꢁ135.2
ꢁ186.4
62.18
59.86
122.3
196.8
242.3
45.65
97.16
125.3
161.5
60.52
96.74
166.3
241.3
67.32
106.1
166.8
225.4
50.46
99.43
128.4
195.8
61.52
102.3
158.6
190.7
215.6
64.57
88.98
142.1
205.7
260.4
37.22
76.42
109.5
183.4
48.89
141.2
186.9
266.8
68.66
111.3
152.6
183.7
50.66
91.86
152.3
192.6
76.36
129.7
172.7
202.2
246.3
130–230
230–320
400–550
550–800
30–110
140–230
240–330
550–700
30–140
200–310
450–620
620–850
30–110
150–270
300–460
500–720
30–110
120–280
300–520
560–720
50–130
130–230
230–420
420–660
660–950
[MnCl2(HL)(H2O)2]ꢀH2O
[FeCl2(HL)(H2O)2]ꢀ2H2O
[CoCl2(HL)(H2O)2]ꢀ3H2O
[NiCl2(HL)(H2O)2]ꢀ3H2O
[CuCl2(HL)(H2O)2]ꢀ2H2O
Schiff base and its metal complexes seem to be able to combine with
the lipophilic layer in order to enhance the membrane permeability
of the Gram-negative bacteria. The lipid membrane surrounding the
cell favours the passage of only lipidsoluble materials; thus the lipo-
philicity is an important factor that controls the antimicrobial activ-
ity. Also the increase in lipophilicity enhances the penetration of

70
G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
CH3
CH3
O
S
O
O
O
N
N
H
3C
S
H3C
S
N
N
OH
N
OH
N
S
N
N
.yH2O
M
H
2O
.3H2O
M
Cl
Cl
Cl
Cl
Cl
O
H2
H2O
M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II);
M = Cr(III) and Fe(III)
Fig. 5. The proposed structural formulae of metal complexes.
phonamide group and thiadiazole-N. The chelates are non-electro-
Table 5
lytes. All metal cations have octahedral geometry. The thermal
decomposition of the complexes as well as the thermodynamic
parameters is studied. The biological activities of the Schiff base
under investigation and its complexes against bacterial and fungal
organisms are promising which need further and deep studies on
animals and humans.
The antibacterial and antifungal activity of HL and its metal complexes.
Sample
Inhibition zone diameter (mm/mg sample)a
Escherichia Staphylococcus Aspergillus Candida
coli (Gꢁ)
aureus (G+)
flavus
albicans
(Fungus)
(yeast)
HL
41
17
28
14
42
18
36
15
40
27
40
41
13
34
23
14
0.0
0.0
14
0.0
0.0
16
12
0.0
13
16
14
0.0
14
16
15
18
12
0.0
[CrCl3(HL)(H2O)]ꢀ3H2O
[MnCl2(HL)(H2O)2]ꢀH2O
[FeCl3(HL)(H2O)]ꢀ3H2O
References
[1] Z.H. Chohan, S.K.A. Sheazi, Syn. React. Inorg. Met. Org. Chem. 29 (1999) 105.
[2] C. Jayabalakrishnan, K. Natarajan, Syn. React. Inorg. Met. Org. Chem. 31 (2001)
983.
[3] T. Jeeworth, H.L.K. Wah, M.G. Bhowon, D. Ghoorhoo, K. Babooram, Syn. React.
Inorg. Met. Org. Chem. 30 (2000) 1023.
[FeCl2(HL)(H2O)2]ꢀ2H2O 38
[CoCl2(HL)(H2O)2]ꢀ3H2O 25
[NiCl2(HL)(H2O)2]ꢀ3H2O 37
[CuCl2(HL)(H2O)2]ꢀ2H2O 35
[ZnCl2(HL)(H2O)2]
Tetracycline
15
32
[4] N. Dharmaraj, P. Viswanalhamurthi, K. Natarajan, Transit. Met. Chem. 26
(2001) 105.
[5] C.H. Colins, P.M. Lyne, Microhiul Methods, University Park Press, Baltimore,
1970. p. 422.
(Antibacterial agent)
Amphotricine B
(Antifungal agent)
0.0
0.0
17
21
[6] S.M.E. Khalil, Chem. Papers 54 (2000) 12.
[7] A.H. Osman, Transit. Met. Chem. 31 (2006) 35.
[8] S.A. Sallam, Transit. Met. Chem. 31 (2006) 46.
+++ = Inhibition values = 16–22 mm beyond control;
++++ = Inhibition values more than 23 mm beyond control.
´
ˇ
[9] M. Cindric, N. Strukan, V. Vrdoljak, T. Kajfez, B. Kamenar, Croati. Chim. Acta 76
(2003) 57.
a
+ = Inhibition values up to 10 mm beyond control; ++ = inhibition values = 11–
15 mm beyond control.
[10] C. Sousa, C. Freire, B. de Castro, Molecules 8 (2003) 894.
[11] D.E. Hamilton, R.S. Drago, A. Zombeck, J. Am. Chem. Soc. 109 (1987) 374.
[12] D. Chen, A.E. Martel, Inorg. Chem. 26 (1987) 1026.
Schiff base and its metal complexes into the lipid membranes and
thus restricts further growth of the organism [37–39]. This could
be explained by the charge transfer interaction between the studied
molecules and the lipopolysaccharide molecules which lead to the
loss of permeability barrier activity of the membrane. The Schiff base
and its metal complexes could enhance the antimicrobial effect on
both strains probably by the sulphonic hydroxyl group [40]. The
Schiff base and its metal complexes are more toxic on S. aureus than
on E. coli, probably due to the sulphonic OH, OCH3, S and CH3CH2CH
groups, which might interact with the double membrane. This activ-
ity is related to the nature and structure of the complexes. The Cu(II),
Fe(II), Ni(II), Mn(II) complexes were almost the most promising
broad spectrum antimicrobial agents due to the presence of coordi-
nated anion and OAH with higher antimicrobial activity than the
other complexes [39]. From the data the inhibition zone of the metal
chelates is higher than that of the ligand. Such increased activity of
the metal chelates is due to the lipophilic nature of the metal ion
in complexes. Furthermore, the mode of action of Schiff bases of
the compounds may involve the formation of a hydrogen bond
through the azomethine nitrogen atom with the active canters of
all the constituents, resulting in interference with normal cell pro-
cess [39,41,42].
[13] J. Costamagna, J. Vargas, R. Latorre, A. Alvarado, G. Mena, Coord. Chem. Rev.
119 (1992) 67.
[14] S.S. Djebbar, B.O. Benali, J.P. Deloume, Polyhedron 16 (1997) 2175.
[15] P. Bhattacharyya, J. Parr, A.T. Ross, J. Chem. Soc. Dalton Trans. 3149 (1998).
[16] L. He, S.H. Gou, Q.F. Shi, J. Chem. Crystallogr. 29 (1999) 207.
[17] J.C. Wu, N. Tang, W.S. Liu, M.Y. Tan, A.S.C. Chan, Chin. Chem. Lett. 12 (2001)
757.
[18] D. Chatterjee, A. Mitra, J. Coord. Chem. 57 (2004) 175.
[19] G. Minu, H. Bhowon, A.L.K. Wah, M.O.D. Ridana, D.R. Lacour, Syn. React. Inorg
Met. Org. Chem. 34 (2004) 1.
[20] C.M. Liu, R.G. Xiong, X.Z. You, Y.J. Liu, K.K. Cheung, Polyhedron 15 (1996) 4565.
[21] S.S. Djebbar, B.O. Benali, J.P. Deloume, Transit. Met. Chem. 23 (1998) 443.
[22] Y.J. Hamada, IEEE Trans. Electron Dev. 44 (1997) 1208.
[23] R. Ramesh, M. Sivagamasundari, Syn. React. Inorg. Met. Org. Chem. 33 (2003)
899.
[24] C.M. Sharaby, Spectrochim., Acta Part A 66 (2007) 1271.
[25] Gehad G. Mohamed, C.M. Sharaby, Spectrochim. Acta, Part A 66 (2007) 949.
[26] A.W. Bauer, W.M. Kirby, C. Sherris, M. Turck, Am. J. Clin. Pathol. 45 (1966) 493.
[27] M.A. Pfaller, L. Burmeister, M.A. Bartlett, M.G. Rinaldi, J. Clin. Microbiol. 26
(1988) 1437.
[28] (a) National Committee for Clinical Laboratory Standards, Performance 41
(1997);
(b) National Committee for Clinical Laboratory Standards. Methods for
Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow
Aerobically, Approved Standard M7-A3, Villanova, PA, 1993.;
(c) National Committee for Clinical Laboratory Standards. Reference Method
for Broth Dilution Antifungal Susceptibility Testing of Conidium-forming
Filamentous: Proposed Standard M38-A, Wayne, PA, USA, 2002.;
(d) National Committee for Clinical Laboratory Standards. Method for
Antifungal Disc Diffusion Susceptibility Testing of Yeast: Proposed Guideline
M44-P, Wayne, PA, USA, 2003.
4. Conclusion
[29] (a) L.D. Liebowitz, H.R. Ashbee, E.G.V. Evans, Y. Chong, N. Mallatova, M. Zaidi,
D. GibbsGlobal Surveillance Group, Diagn. Microbiol. Infect. Dis. 4 (2001) 27;
(b) M.J. Matar, L.O. Zeichner, V.L. Paetznick, J.R. Rodriguez, E. Chen, J.H. Rex,
Agents Chemother. 47 (2003) 1647.
[30] C.M. Sharaby, Syn React. Inorg. Met. Org. Nano-Met. Chem. 35 (2005) 133.
[31] J.R. Ferraro, Low Frequency Vibrations of Inorganic and Coordination
Compounds, first ed., Plenum Press, New York, 1971. pp. 168–196.
The results of this investigation support the suggested struc-
tures of the metal complexes. It is obvious from this study that
only mononuclear complexes are obtained. The IR spectral studies
reveal that HL coordinated to the metal ions via enolic AOH of sul-

G.G. Mohamed et al. / Journal of Molecular Structure 979 (2010) 62–71
71
[32] G.G. Mohamed, S.M. Khalil, Coord. Chem. 62 (2009) 645.
[36] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68.
[33] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic
Chemistry, sixth ed., Wiley, New York, 1999.
[34] G.M. Abu El-Reash, K.M. Ibrahim, M.M. Bekheit, Bull. Chem. Soc., France 128
(1991) 149.
[35] A.D. Garnovskii, I.S. Vasilchenko, D.A. Garnovskii, B.I. Kharisov, J. Coord. Chem.
62 (2009) 151.
[37] M. Tumer, H. Koksal, M.K. Sener, Trans. Met. Chem. 24 (1999) 414.
[38] M. Imran, J. Iqbal, S. Iqbal, N. Ijaz, Turk. J. Biol. 31 (2007) 67.
[39] N. Raman, S.J. Raja, A. Sakthivel, J. Coord. Chem. 62 (2009) 691.
[40] F. Azam, S. Singh, S.L. Khokhra, O. Prakash, J. Zhejiang Univ. Sci. B 8 (2007) 446.
[41] S.P. Xu, L. Shi, P.C. Lv, X.L. Li, H.L. Zhu, J. Coord. Chem. 62 (2009) 3198.
[42] S.P. Xu, L. Shi, P.C. Lv, R.Q. Fang, H.L. Zhu, J. Coord. Chem. 62 (2009) 2048.