Bivalent transition metal complexes of coumarin-3-yl thiosemicarbazone derivatives: Spectroscopic, antibacterial activity and thermogravimetric studies

Article abstract of DOI:10.1016/j.molstruc.2008.10.059

Schiff base complexes of Cu(II), Co(II) and Ni(II) with two coumarin-3-yl thiosemicarbazone derivatives (1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (OCET) and (1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (BOCET)

Full text of DOI:10.1016/j.molstruc.2008.10.059

Journal of Molecular Structure 920 (2009) 149–162
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Bivalent transition metal complexes of coumarin-3-yl thiosemicarbazone
derivatives: Spectroscopic, antibacterial activity and thermogravimetric studies
a
b
a
Moamen S. Refat a, , Ibrahim M. El-Deen , Zeinab M. Anwer , Samir El-Ghol
*
a Department of Chemistry, Faculty of Science – Port Said, Suez canal University, Port Said, Egypt
b Department of Chemistry, Faculty of Science – Ismalia, Suez canal University, Ismalia, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2008
Received in revised form 25 October 2008
Accepted 27 October 2008
Available online 12 November 2008
Schiff base complexes of Cu(II), Co(II) and Ni(II) with two coumarin-3-yl thiosemicarbazone derivatives
(1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (OCET) and (1E)-1-(1-(6-bromo-2-
oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (BOCET) were synthesized by the reaction of Cu(II),
Co(II) and Ni(II) chlorides with each mentioned ligand with molar ratio 1:2 metal-to-ligand. Both ligands
and their metal complexes were characterized by different physicochemical methods, elemental analysis,
molar conductivity, (UV–vis, Mass, Infrared, 1H NMR spectra) and also thermal analysis (TG and DTG)
techniques. The discussion of the outcome data of the prepared complexes indicate that the coumarin-
3-yl thiosemicarbazone derivatives ligands behave as a bidentate ligand through both thione sulphur
and azomethine nitrogen with 1:2 (metal:ligand) stoichiometry for all complexes. The molar conduc-
tance measurements proved that the complexes are electrolytes. The kinetic thermodynamic parameters
Keywords:
Coumarin
Thiosemicarbazide
Complexes
Kinetic thermodynamic parameters
Transition metals
such as: E*,
D D D
H*, S*and G*are calculated from the DTG curves, all complexes are more ordered except
Ni(II) complexes. The antibacterial activity of the coumarin-3-yl thiosemicarbazone derivatives and their
metal complexes was evaluated against some kinds of Gram positive and Gram negative bacteria.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Transition metal complexes of bis(thiosemicarbazone) ligands
have been studied and attract attention against the antitumor activ-
Coumarins comprise a very large class of compounds found
throughout the plant kingdom [1,2]. The coumarin derivatives
are known to have diverse applications as anticoagulants, spasmo-
lytics, anticancer drugs or as plant growth regulating agents [3,4].
Biological activity of coumarin nucleus and related derivatives
[5,6] has a great important effects like antibacterial [7], antithrom-
botic and vasodilatory [8], antimutagenic [9], lipoxygenase and
cyclooxygenase inhibition [10,11], scavenging of reactive oxygen
species, and ntiumourigenic [12,13].
Several reviews summarize advances in various medicinal
applications of metal complexes of coumarins [14,15]. As it was al-
ready reported in the literature the biological activity of some cou-
marin derivatives significantly enhances by binding to metal ions
[16,17]. Generally, the increasing activities of the complexes are
attributed to the synergistic effect that increases their lipophilicity
[18]. A broad array of medicinal applications of metal complexes of
coumarins has been investigated. It was found that in some cases
the metal complexes obtained revealed higher biological activity
than their ligands [19,20].
ity [21,22]. In particular bis(thiosemicarbazone) complexes of cop-
per(II) have been known for some time to be antitumor agents
[23,24]. Because of their biological activity and analytical applica-
tion, thiosemicarbazides and thiosemicarbazones, as well as their
metal complexes have been the subject of many studies [25,26].
In this paper we are reported an efficient route for the synthesis
of new Cu(II), Co(II) and Ni(II) complexes obtained from 3-(ethyli-
dene thiosemicarbazide) coumarin and 6-bromo-3-(ethylidene thi-
osemicarbazide) coumarin. The thermal decomposition of their
complexes is also used to infer the structure and the different ther-
modynamic activation parameters are calculated. The biological
activity of these ligands and their metal complexes are evaluated.
2. Experimental
CuCl2ꢀ4H2O, CoCl2ꢀ6H2O and NiCl2ꢀ6H2O and other chemicals
were purchased from Fluka and Merck companies, and were used
without further purification as received.
2.1. Synthesis of the Schiff base ligands
The coumarin thiosemicarbazone Schiff base ligands (Fig. 1)
were synthesized according to the known condensation method
[27]. The methanol solution (50 ml) of thiosemicarbazide was
* Corresponding author. Present address: Department of Chemistry, Faculty of
Science – Taif, Taif University, King Saudi Arabia.
E-mail address: msrefat@yahoo.com (M.S. Refat).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.10.059

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M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
NH2
CH3
HN
C
N
S
O
O
(1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide
OCET
NH2
CH3
HN
C
Br
N
S
O
O
(1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide
BOCET
Fig. 1. Structures of Schiff base OCET and BOCET ligands.
mixed with a solution of 3-acetyl coumarin or 6-bromo-(3-acetyl
coumarin). The mixture was refluxed and stir magnetically for
4 h at 80 °C on a hot plate. After cooling, the solid Schiff base li-
gands were filtered, and the solid products were washed several
times using methanol solvent. All organic impurities were removed
by washing the products with small portions of diethyl ether. The
ligands were recrystallized several times from ethyl alcohol and
were dried in vacuo over calcium chloride. The purity of the ligands
was evaluated by thin layer chromatography. Elemental analysis
CHN, Mwt, color, m.p., yield and conductivity of Schiff base ligands
were given in Table 1.
2.2. Synthesis of metal complexes
All of Cu(II), Co(II) and Ni(II) complexes were synthesized by
adding of the appropriate metal chlorides (1.0 mmol, in 20 ml ethyl
alcohol/water (50:50) volume to a hot solution of each thiosemi-
carbazone ligand (2.0 mmol, in 30 ml ethyl alcohol (95%)). The re-
sulted color solutions were stirred and refluxed on a hot plate at
80 °C for 1 h. The volume of the resulted solution was reduced to
half volume by evaporation. One day later, the colored solid com-
plexes formed, were filtered, the solids washed with ethanol and
diethyl ether and finally dried under vacuum. All complexes were
prepared and isolated in amorphous shape.
2.3. Analyses
Elemental analyses (C, H, and N) were performed using a Per-
kin-Elmer CHN 2400 elemental analyzer. The content of metal ions
was calculated gravimetrically as metal oxides. Molar conductance
measurements of the OCET and BOCET ligands and their complexes
with 1.0 ꢁ 10ꢂ3 mol/l in DMSO were carried out using Jenway 4010
conductivity meter. Magnetic measurements were carried out on a
Sherwood Scientific magnetic balance using Gouy method. 1H NMR
Varian 200 MHz spectrometer using DMSO as solvent, chemical
shift are given in ppm relative to tetramethylsilane. Electron im-
pact mass spectra were recorded on a Jeol, JMS, DX-303 mass spec-
trometer. The UV/vis, Spectra were obtained in DMSO solution
(1.0 ꢁ 10ꢂ3 M) for the ligands OCET and BOCET and their six com-
plexes with a Jenway 6405 Spectrophotometer using 1 cm quartz
cell, in the range 200–600 nm. IR spectra (4000–400 cmꢂ1) were
recorded as KBr pellets on Bruker FT-IR Spectrophotometer. Ther-

M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
151
mogravimetric analyses (TG/DTG) were carried out in the temper-
ature range from 25 to 800 °C in a steam of nitrogen atmosphere
using Shimadzu TGA 50H thermal analysis. The experimental con-
ditions were: platinum crucible, nitrogen atmosphere with a
30 ml/min flow rate and a heating rate 10 °C/min.
against Escherichia coli, Pseudomonas aeruginosa as Gram negative,
Bacillus subtilis and Staphylococcus aureus as Gram positive. The
concentration of each solution was 1.0 ꢁ 10ꢂ3 mol dm3. Commer-
cial DMSO was employed to dissolve the tested samples.
3. Results and discussion
2.4. Microbiological investigations
All the coumarin-3-yl thiosemicarbazone complexes show 1:2
metal:ligand stoichiometry ratio. The analytical data of the ligands
and their metal complexes with the stoichiometries proposed are
summarized in Table 1. The isolated solid complexes are stable
in air and are insoluble in water and common organic solvents
but soluble in DMF and DMSO. The molar conductance indicates
that all the complexes are electrolytic in nature. The metal com-
plexes are decomposed at different temperatures above 200 °C.
Elemental analyses data were in a good agreement with those re-
quired for the suggested formula.
For these investigations the filter paper disc method was ap-
plied according to Gupta et al. [28]. The investigated isolates of
bacteria were seeded in tubes with nutrient broth (NB). The seeded
NB (1 cm3) was homogenized in the tubes with 9 cm3 of melted
(45 °C) nutrient agar (NA). The homogeneous suspensions were
poured into Petri dishes. The discs of filter paper (diameter
4 mm) were ranged on the cool medium. After cooling on the
formed solid medium, 2 ꢁ 10ꢂ5 dm3 of the investigated com-
pounds were applied using a micropipette. After incubation for
24 h in a thermostat at 25–27 °C, the inhibition (sterile) zone diam-
eters (including disc) were measured and expressed in mm. An
inhibition zone diameter over 7 mm indicates that the tested com-
pound is active against the bacteria under investigation. The anti-
bacterial activities of the investigated compounds were tested
3.1. Molar conductivity of metal chelates
The molar conductivity values of the metal complexes in DMSO
solvent (10ꢂ3 mol) were in the range (98–232
X
ꢂ1 cm2 molꢂ1).
Fig. 2. Infrared spectra of: A = OCET; B = [Cu(OCET)2]Cl2ꢀH2O; C = [Co(O-
CET)2ꢀ2H2O]Cl2ꢀ2H2O; D = [Ni(OCET)2ꢀ2H2O]Cl2ꢀ2H2O.
Fig. 3. Infrared spectra of: E = BOCET; F = [Cu(BOCET)2ꢀ2H2O]Cl2ꢀH2O; G = [Co(BO-
CET)2ꢀ2H2O]Cl2ꢀ2H2O; H = [Ni(BOCET)2ꢀ2H2O]Cl2ꢀ2H2O.

152
M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
Conductivity measurements have frequently been used in struc-
tural characterization of metal chelates (mode of coordination)
within the limits of their solubility. These measurements were pro-
vided a method for testing the degree of ionization of the com-
plexes. In case of the presence of anions outside the coordination
sphere, the higher values of molar conductivity will be detected
Table 2
Infrared spectral data for OCET, BOCET ligands and their complexes (cmꢂ1).
Compounds
m
(OH) hydrated
m
(N–H) NH2
m(N–H) NH
m
s(C@O)
ms(C@N)
m
as(C@N)
m(OH) coordinated
ms(C@S)
m
(M–N)
m(M–S)
H2O
H2O
OCET
–
3388
3384
3387
3386
3408
3407
3409
3408
3235
3234
3234
3233
2228
2227
2227
2228
1718(s)
1717(s)
1716(s)
1716(s)
1723(s)
1722(m)
1722(m)
1720(m)
1602(s)
1566(s)
1557(s)
1559(s)
1590(s)
1557(s)
1557(s)
1540(s)
1556(s)
1523(s)
1539(s)
1541(s)
1546(s)
1521(s)
1507(s)
1507(s)
–
762(s)
747(s)
750(s)
751(s)
829(s)
819(s)
817(s)
817(s)
–
–
[Cu(OCET)2]Cl2ꢀH2O
[Co(OCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(OCET)2(H2O)2]Cl2ꢀ2H2O
BOCET
[Cu(BOCET)2]Cl2ꢀH2O
[Co(BOCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O
3465(br)
3471(br)
3346(br)
–
3466(br)
3465(br)
3466(br)
860(m)
816(m)
862(m)
–
770(m)
770(m)
773(m)
431(w)
432(w)
431(w)
–
458(w)
457(w)
455(w)
382(w)
380(w)
380(w)
–
390(w)
392(w)
391(w)
Fig. 4. HNMR spectra of OCET ligand.
Fig. 5. Mass spectra of OCET ligand.
Fig. 6. Mass spectra of BOCET ligand.

M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
153
and vice versa [29]. It is clear from the conductivity data that the
complexes present seem to be electrolytes, also the molar conduc-
tance values indicates that the anions were existed outside the
coordination sphere.
complexes are presented in Table 2 along within their tentative
assignment. The position of these bands are helpful to detected
the bonding sites of both ligand molecules interacted with Cu(II),
Co(II) and Ni(II). In principle, the ligand can exhibit thione-thiol
tautomerism since it contains a thioamide NH–C@S functional
3.2. Magnetic moments
group. The m
(S–H) band at 2556 cmꢂ1 is absent from the IR spectra
of the Schiff base ligands. At the same time the m(N–H) [31] band at
Octahedral, d2sp3, Co(II) complexes are expected to have effec-
tive magnetic moment in the range 1.70–1.90 B.M. The cobalt com-
plexes resulted have magnetic moment at 1.80 B.M.; thus the Co(II)
complex is octahedral fashion. Ni(II) complexes gave a moment of
3.10 B.M. and hence assigned as octahedral, because of the square
planar complexes of Ni(II) are a diamagnetic while tetrahedral
complexes have moments in the range 3.20–4.10 B.M. [30]. For
the Cu(II) in copper(II)/OCET complex the situation is detected at
magnetic moment 1.82 B.M., thus the Cu(II) complex is square pla-
nar. But in case of Cu(II)/BOCET the magnetic moment is equal to
1.97 B.M. which assigned to octahedral geometry.
3235 cmꢂ1 is present, indicating that, in the solid state the ligands
remain as the thione tautomer.
Infrared spectra of the ligands show strong bands in the region
1590–1602 cmꢂ1 and 1546–1565 cmꢂ1 which may be assigned to
the symmetric and asymmetric m(C@N) [32] vibrations for OCET
and BOCET ligands, respectively. These frequencies are shifted to-
wards lower wavenumber by ca. 33–50 cmꢂ1 in spectra of all me-
tal complexes, suggesting the coordination of nitrogen of the
azomethine group to the central metal atom in these complexes.
The metal–nitrogen bond [33,34] was detected by appearing fre-
quencies in the region 431–458 cmꢂ1 from the IR data. Further-
more in the spectra of both ligands, the strong band observed
at 762–829 cmꢂ1 was shifted to lower wavenumber by ca. 10–
15 cmꢂ1 in all metal complexes, indicating that thione sulphur
participate as a coordinating site. This prediction was confirmed
by the presence of new band at 380–395 cmꢂ1 which can be as-
3.3. Infrared spectra
The most important bands in the infrared spectra (Figs. 2 and 3)
of the both coumarin thiosemicarbazone ligands and their metal
signed to m(M–S) [35].
The spectra of the complexes exhibited a broad band’s at
ꢃ3460 cmꢂ1 that are attributed to OH of crystal water molecules,
while the bands observed at 770 and 860 cmꢂ1 for the complexes
of OCET and BOCET ligands, respectively, are assigned to coordi-
NH
2
H C
3
HN
S
N
NH2
O
O
H3C
HN
m/z 261
-NHCSNH2
S
Br
N
H C
3
N
O
O
m/z 340
-NHCSNH2
O
O
H3C
m/z 186
-CO
Br
N
H C
3
N
O
O
m/z 264
-Br
O
m/z 158
-CHCN
H3C
H3C
-CO
CH
3
N
N
N
-CO
O
O
O
m/z 186
m/z 158
-CO
m/z 132
CH3
m/z 91 (100%)
-CH=CH
N
-CHCN
m/z 65
m/z 132
m/z 91 (100%)
Scheme 2. Main fragments of BOCET ligand.
Scheme 1. Main fragments of OCET ligand.

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M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
Fig. 7. UV–vis spectra of OCET and BOCET and their complexes.

M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
155
nated water molecule [36]. From the IR data, it can be inferred that
the OCET and BOCET ligands involved in the complexation as a
bidentate ligands which coordinated with metal ions through their
thione sulphur and azomethine N atom.
are listed in Table 3. The bands in the range 200–450 nm can be as-
signed to
p* and/or n–p* interaligand transition. There are two
detected absorption bands at around 260 and 340 nm assigned to
p* and n–p* interaligand transition, respectively, in the elec-
p–
p–
tronic spectra of both ligand. These transition also found in the
spectra of the resulted complexes with small shifted and hyper-
chromically effect.
3.4. HNMR spectra
1H NMR spectra of both coumarin-3-yl thiosemicarbazone
Schiff base ligands were performed in DMSO and the chemical
shifts in ppm were recorded as follows:
3.7. Thermogravimetric analysis (TGA)
Ligand((1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thio-
semicarbazide (OCET)): d = 1.87 ppm (s, 3H, CH3–C@N),
d = 8.58 ppm (s, 1H, NH–C@S), d = 3.65 ppm (s, 2H, NH2–C@S),
The TGA curves of the Schiff base complexes (Fig. 8) were car-
ried out within a temperature range from room temperature up
to 800 °C. The thermal decomposition data of both ligands and
their metal complexes are listed in Table 4. The data from thermo-
gravimetric analysis clearly indicated that the decomposition of
the complexes proceeds in several steps. Hydration water mole-
cules were lost in between 30 °C and 150 °C. The coordinated water
molecules and chlorides ions were liberated in between 250 °C and
350 °C, finally the metal oxides were formed above 600 °C for
Cu(II), Co(II) and Ni(II) complexes. The decomposition was com-
plete at P600 °C for all complexes. The degradation pathway for
all complexes may be represented as follows.
d = 7.25 ppm (m, 2H, Ar–H6,7), d = 7.34 ppm (m, 3H, Ar–H4,5,8
)
(Fig. 4) and ligand((1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-
yl)ethylidene)thiosemicarbazide (BOCET)): d = 1.96 ppm (s, 3H,
CH3–C@N), d = 8.66 ppm (s, 1H, NH–C@S), d = 3.84 ppm (s, 2H,
NH2–C@S), d = 8.22 ppm (m, 1H, Ar–H5), d = 8.31 ppm (m, 1H, Ar–
H7), d = 8.11 ppm (t, 1H, Ar–H8), d = 8.04 ppm (s, 1H, Ar–H4).
By comparison between the free Schiff base ligands and their
metal complexes, found that, the 1H NMR signals of metal com-
plexes located in the same places of their free ligands with decreas-
ing in the intensity. This result proved that the absence of the
participation of NH group in the complexation and also existed
the C@S in thione feature.
30—150 ꢅC
½MðLÞ ðH OÞ ꢄ ꢀ Cl ꢀ nH O
½MðLÞ ðH OÞ ꢄ ꢀ CL þ nH O
ꢀꢀꢀꢀꢀꢀ!
2
2
2
2
2
2
2
2
2
2
ꢅ
150—600
½MðLÞ ðH2OÞ ꢄ ꢀ CL2
2H O þ CL þ MO or M O
ꢀꢀꢀꢀꢀꢀ!
2
2
2
3
2
2
where M = Cu, Co or Ni; n = 1 or 2).
3.5. Mass spectra
3.7.1. OCET and BOCET ligands
Mass spectra of the (1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethyli-
dene)thiosemicarbazide (OCET) (Fig. 5) and (1E)-1-(1-(6-bromo-
2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (BOCET)
ligands (Fig. 6) confirm the proposed formula by detected the fol-
lowing peaks:
Ligand (OCET): appearance of the final peak at 261 amu
(C12H11O2N3S, calculated atomic mass 261 amu) and other peaks
at 43, 75, 91, 132, 158 and 186 amu due to different fragment
steps. The intensity of these peaks gives an idea about the stability
of these fragments. Ligand(BOCET) has a molecular ion peak at
340 amu (C12H10O2N3SBr, calculated atomic mass 340 amu) and
other peaks at 65, 77, 91, 132, 186 and 264 amu assigned to the
various fragments as discussed in Schemes 1 and 2.
The (1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemi-
carbazide (OCET) melts at 250 °C with simultaneous decomposi-
tion. The two main degradation peaks were observed at 304 and
560 °C in the TG profile. The decomposition occurs with a mass loss
of 39.11% and its calculated value is 40.0% for the first step and
61.20% and its calculated value 60.38% for second step.
The (1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)-
thiosemicarbazide (BOCET) melts at 234 °C with simultaneous
decomposition. The two main degradation peaks were observed
at 300 and 560 °C in the TG profile. The decomposition occurs with
a mass loss of 31.24% and its calculated value is 30.67% for the first
step and 68.80% and its calculated value 69.32% for second step.
3.7.2. [Cu(OCET)2]Cl2ꢀH2O and [Cu(BOCET)2(H2O)2]Cl2ꢀH2O
3.6. Electronic spectra
Thermal analysis curves of Cu(II) complex show that decompo-
sition take places in three stages in temperature range 35–800 °C
(DTGmax 100, 280 and 604 °C) and (75, 240 and 510) for OCET and
BOCET ligands, respectively. The TG curve of the Cu(II) complex of
OCET ligand show a weight loss (found: 2.53%, calcd: 2.66%) be-
tween 35 and 175 °C corresponding to the loss of one crystal water
molecule. The second stage show a weight loss (found: 29.33%,
calcd: 28.27%) between 175 and 510 °C corresponding to the loss
two chloride ion and organic moiety (C4H4N4S2). The final product
formed at 800 °C, consist of copper oxide and two carbon atoms,
interpretive for no sufficiently of oxygen atoms encouraged the lib-
erated carbon as monoxide or dioxide.
The TG curve of the Cu(II) complex of BOCET ligand show a
weight loss (found: 2.22%, calcd: 2.07%) between 25 and 120 °C
corresponding to the loss of one crystal water molecule. The sec-
ond stage show a weight loss (found: 32.42%, calcd: 32.09%) be-
tween 120 and 350 °C corresponding to the loss two coordinate
water molecules, two chloride ion and organic moiety
(C4H4N4S2). The third stage show a weight loss (found: 55.84%,
calcd: 56.50%) between 350 and 550 °C corresponding to the loss
two bromide ion and organic moiety (C20H16O3N2). The final prod-
uct formed at 800 °C, consist of copper oxide (found: 9.52%, calcd:
9.09%).
The electronic spectra of OCET and BOCET ligands and their me-
tal complexes in DMSO are shown in Fig. 7 and the spectral data
Table 3
Electronic spectra of OCET, BOCET ligands and their metal complexes.
Compounds
OCET
kmax (nm)
e
(molꢂ1 cmꢂ1
)
Assignment
260
335
1330
1100
p–
p*
n–p*
[Cu(OCET)2]Cl2ꢀH2O
[Co(OCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(OCET)2(H2O)2]Cl2ꢀ2H2O
BOCET
265
330
2250
1810
p
–
p*
n–p*
p*
265
330
1130
600
p
–
n–p*
250
335
2720
2260
p
–
p*
n–p*
260
340
2650
2220
p
–
p*
n–p*
[Cu(BOCET)2(H2O)2]Cl2ꢀH2O
[Co(BOCET)2(H2O)2]Cl2ꢀ2H2O
255
2710
p
–
–
p*
p*
245
350
2230
810
p
n–p*
[Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O
245
375
1150
320
p
–
p*
n–p*

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M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
Fig. 8. TGA diagram of OCET, BOCET ligand and their metal complexes.
3.7.3. [Co(OCET)2(H2O)2]Cl2ꢀ2H2O and [Co(BOCET)2(H2O)2]Cl2ꢀ2H2O
The diagrams of Co(OCET)2(H2O)2]Cl2ꢀ2H2O and [Co(BOCET)2
(H2O)2]Cl2ꢀ2H2O reveals mass loss in temperature range 30–800 °C;
three or four stages are shown in the pyrolysis curve at (DTGmax
100, 280 and 604 °C) and (DTGmax 75, 250, 430 and 645 °C) for [Co
(OCET)2(H2O)2]Cl2ꢀ2H2O and [Co(BOCET)2(H2O)2]Cl2ꢀ2H2O, respectively.

M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
157
Table 4
Thermal decomposition of the OCET, BOCET ligands and their metal complexes.
Compounds
OCET
Steps
Temperature range
DTG peaks
Weight loss (calc.) found %
Assignment
1st
2nd
189–325
325–600
304
560
(40.00)39.11
(60.38)61.20
C2H6N3S
C10H5O2
[Cu(OCET)2]Cl2ꢀH2O
1st
2nd
3rd
35–175
175–510
510–657
75
230
502
(2.66)2.53
(28.27)29.33
(53.03)52.63
(15.24)15.51
H2O
2Cl + H4N4S2
C22H18N2O3
CuO + 2C
[Co(OCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(OCET)2(H2O)2]Cl2ꢀ2H2O
1st
2nd
3rd
35–175
175–510
510–657
100
280
604
(4.96)5.19
(38.51)38.0
(45.02)45.98
(11.20)10.83
2H2O
2Cl + 2H2O + C4H4N4S2
C20H18N2O2.5
1/2Co2O3
1st
30–120
120–260
260–460
460–560
75
234
417
507
(4.97)4.94
(14.78)15.17
(31.23)30.68
(38.69)38.17
(10.36)11.04
2H2O
2nd
3rd
4th
2H2O + 2Cl
C6H6N6S2
C18H16O3
NiO
BOCET
1st
2nd
220–350
350–600
300
560
(30.67)31.24
(69.32)68.80
C2H6N3S
C10H4O2Br
[Cu(BOCET)2(H2O)2]Cl2ꢀH2O
1st
2nd
3rd
25–120
120–350
350–550
75
240
510
(2.07)2.22
(32.09)32.42
(56.50)55.84
(9.09)9.52
H2O
2Cl + 2H2O + C4H4N4S2
2Br + C20H16O3N2
CuO
[Co(BOCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O
1st
30–120
120–350
350–500
500–710
75
250
430
645
(4.08)4.32
(12.13)12.64
(17.02)17.86
(57.20)56.79
(9.42)8.39
2H2O
2Cl + 2H2O
C2H6N4S2
2Br + C22H14N2O2.5
1/2Co2O3
2nd
3rd
4th
1st
2nd
3rd
30–160
160–500
500–680
75
195
658
(4.09)4.60
(35.82)35.22
(51.64)50.99
(8.53)9.19
2H2O
2Cl + 2H2O + C4H12N6S2
C20H8O3Br2
NiO
For [Co(OCET)2(H2O)2]Cl2ꢀ2H2O, the first stage corresponding to
the dehydration of two water molecules (found: 5.19%, calcd:
4.96%). The second stage was discussed concerning to the loss of
two uncoordinated chloride ions, two coordinated water molecules
and organic moiety (C4H4N4S2) weight loss (found: 15.17%, calcd:
14.78%).
the loss of two uncoordinated chloride ions, two coordinated
water molecules and organic moiety (C4H12N6S2). The final
products, formed at 800 °C, consist of nickel oxide a weight loss
(found: 11.04%, calcd: 10.36%) and (found: 9.19%, calcd: 8.53%)
for [Ni(OCET)2(H2O)2]Cl2ꢀ2H2O and [Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O,
respectively.
In case of [Co(BOCET)2(H2O)2]Cl2ꢀ2H2O, the first stage corre-
sponding to the dehydration of two water molecules (found:
4.32%, calcd: 4.08%). The second stage show weight loss (found:
12.64%, calcd: 12.13%) corresponding to the loss of two uncoordi-
nated chloride ions and two coordinated water molecules. The fi-
nal decomposition product is 1/2Co2O3, the overall weight loss
(found: 11.04%, calcd: 10.36%) and (found: 8.39%, calcd: 9.42%)
for [Co(OCET)2(H2O)2]Cl2ꢀ2H2O and [Co(BOCET)2(H2O)2]Cl2ꢀ2H2O,
respectively.
3.8. Kinetic studies
Several equations [37–44] have been proposed as means of ana-
lyzing a TG curve and obtaining values for kinetic parameters.
Many authors [37–43] have discussed the advantages of this meth-
od over the conventional isothermal method. The rate of a decom-
position process can be described as the product of two separate
functions of temperature and conversion [44], using
3.7.4. [Ni(OCET)2(H2O)2]Cl2ꢀ2H2O and [Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O
Thermal decomposition of [Ni(OCET)2ꢀ2H2O]Cl2ꢀ2H2O and
[Ni(OCET)2(H2O)2]Cl2ꢀ2H2O and [Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O pro-
ceeds in three or four ranged main stages in temperature range
30–800 °C (DTGmax 75, 234, 417 and 507 °C) and (DTGmax 75, 195
and 658 °C) for [Ni(OCET)2(H2O)2]Cl2ꢀ2H2O and [Ni(BO-
CET)2(H2O)2]Cl2ꢀ2H2O, respectively.
d
dt
a
¼ kðTÞfð
a
Þ
ð1Þ
where
a is the fraction decomposed at time t, k(T) is the tempera-
ture dependent function and f(a) is the conversion function depen-
dent on the mechanism of decomposition. It has been established
that the temperature dependent function k(T) is of the Arrhenius
type and can be considered as the rate constant k
ꢆ
For [Ni(OCET)2(H2O)2]Cl2ꢀ2H2O, the first stage show a weight
loss (found: 4.94%, calcd: 4.97%), corresponding to the loss of
two crystal water molecules. The second stage show a weight
loss (found: 15.17%, calcd: 14.78%), corresponding to the loss
of two uncoordinated chloride ions and two coordinated water
molecules.
k ¼ AeꢂE =RT
ð2Þ
where R is the gas constant in (J molꢂ1 Kꢂ1). Substituting Eq. (2) into
ꢁ
ꢂ
d
a
Aꢆ
=RT
eꢂE
Eq. (1), we get
¼
f(a) where / is the linear heating rate
dt
dT/dt. On integrationuand approximation, this equation can be ob-
tained in the following form
For [Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O, the first stage show
a
weight loss (found: 4.60%, calcd: 4.09%), corresponding to the
loss of two crystal water molecules. The second stage show a
weight loss (found: 35.22%, calcd: 35.82%), corresponding to
ꢃ
ꢄ
Eꢆ
RT
AR
ln gðaÞ ¼ ꢂ
þ ln
u
Eꢆ

158
M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
Fig. 9. Horowtiz–Metzger (HM) and Coats–Redfern (CR) of OCET, BOCET and their metal complexes.

M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
159
Fig. 9 (continued)

160
M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
where g(
a
) is a function of
a
dependent on the mechanism of the
when n = 1, the LHS of Eq. (4) would be log[ꢂlog(1 ꢂ
a)]. For a first-
reaction. The integral on the right-hand side is known as tempera-
ture integral and has no closed for solution. So, several techniques
have been used for the evaluation of temperature integral. Most
commonly used methods for this purpose are the differential meth-
od of Freeman and Carroll [37] integral method of Coat and Redfern
[40], the approximation method of Horowitz and Metzger [42]. In
the present investigation, the general thermal behaviors of the pre-
pared complexes in terms of stability ranges, peak temperatures
and values of kinetic parameters, are shown in Fig. 9 and Table 5.
The kinetic parameters have been evaluated using the following
methods and the results obtained by these methods are well agree-
ment with each other. The following two methods are discussed in
brief.
order kinetic process the Horowitz–Metzger equation may be writ-
ten in the form:
ꢃ
ꢅ
ꢆꢄ
wa
wc
Eꢆh
2:303RT2S
log log
¼
ꢂ log 2:303
where h = T ꢂ TS, w = w ꢂ w, w = mass loss at the completion of
c
a
a
the reaction; w = mass loss up to time t. The plot of log[log(wa/
wc)] versus h was drawn and found to be linear from the slope of
which E* was calculated. The pre-exponential factor, A, was calcu-
lated from the equation:
Eꢆ
RT2S
A
¼
½
u
expðꢂEꢆ=RTSÞꢄ
3.8.1. Coats–Redfern equation
The Coats–Redfern equation, which is a typical integral method,
can be represented as:
The entropy of activation,
D
S*, was calculated from Eq. (3). The en-
thalpy activation,
D D
H*, and Gibbs free energy,
G*, were calculated
S*, respectively.
H* and G* for the decom-
from;
D
H* = E* ꢂ RT and
D
G* =
D
H* ꢂ T
D
D
ꢅ
ꢆ
The calculated values of E*, A,
D
S*,
D
Z
Z
a
T2
d
a
a
A
a
ꢂEꢆ
¼
exp
dt
position steps are given in Table 5. According to the kinetic data
obtained from DTG curves, all the complexes have ꢂve entropy ex-
cept Ni(II) complexes of OCET and BOCET ligands. Which indicates
that activated complexes have more order systems than reactants
except Ni(II) complexes. Based on the activation energy values,
Co(II) and Ni(II) complexes have nearly the same thermal stability
due to they are isostructural.
n
RT
ð1 ꢂ Þ
0
T1
For convenience of integration the lower limit T1 is usually taken as
zero. This equation on integration gives.
ln½ꢂlnð1 ꢂ
a
Þ=T2ꢄ ¼ ꢂEꢆ=RT þ ln½AR=
u
Eꢆꢄ
A plot of left-hand side (LHS) against 1/T was drawn. E* is the
energyꢂo1f activation in J molꢂ1 and calculated from the slop and
A in (S ) from the intercept value. The entropy of activation in
(J Kꢂ1 molꢂ1) was calculated by using the equation:
Table 6
ꢅ
ꢆ
Ah
KBTS
Antibacterial activity data of OCET, BOCET ligands and their metal complexes,
inhibition zone (mm).
D
Sꢆ ¼ R ln
ð3Þ
Compound
Bacillus Staphylococcus Escherichia Pseudomonas
where kB is the Boltzmann constant, h is the Plank’s constant and TS
is the DTG peak temperature [45].
subtili
G+
aureus G+
coli Gꢂ
aeruginosa
Gꢂ
OCET
13
13
18
17
17
14
17
12
18
16
17
15
18
15
16
13
17
15
17
17
18
15
14
13
18
17
18
15
17
17
[Cu(OCET)2]Cl2ꢀH2O
[Co(OCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(OCET)2(H2O)2]Cl2ꢀ2H2O
BOCET
3.8.2. Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the approx-
imation methods. These authors derived the relation:
[Cu(BOCET)2(H2O)2]Cl2ꢀH2O
n
o
2
3
1ꢂn
[Co(BOCET)2(H2O)2]Cl2ꢀ2H2O 16
[Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O 18
Eꢆh
2:303RT2S
1 ꢂ ð1 ꢂ
a
Þ
4
5
log
¼
for n–1
ð4Þ
ð1 ꢂ nÞ
Table 5
Thermodynamic data of the thermal decomposition of OCET, BOCET ligands and their complexes.
Complexes
Stage
Method
Parameter
r
E (J molꢂ1
)
A (sꢂ1
)
D
S (J molꢂ1 Kꢂ1
)
D
H (J molꢂ1
)
D
G (J molꢂ1
)
OCET
2nd
2nd
2nd
2nd
2nd
2nd
2nd
2nd
CR
HM
2.41 ꢁ 105
1.55 ꢁ 1013
ꢂ96.7
ꢂ28.2
ꢂ176
ꢂ150
ꢂ69.4
ꢂ50.3
91.8
105
2.34 ꢁ 105
2.35 ꢁ 105
0.99354
0.99651
2.40 ꢁ 105
1.24 ꢁ 1013
2.34 ꢁ 105
2.36 ꢁ 105
[Cu(OCET)2]Cl2ꢀH2O
[Co(OCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(OCET)2(H2O)2]Cl2ꢀ2H2O
BOCET
CR
HM
9.98 ꢁ 104
1.13 ꢁ 102
1.08 ꢁ 104
2.24 ꢁ 105
9.33 ꢁ 104
1.06 ꢁ 105
2.30 ꢁ 105
2.23 ꢁ 105
0.99647
0.99994
CR
HM
1.99 ꢁ 105
4.32 ꢁ 109
1.92 ꢁ 105
2.53 ꢁ 105
0.99809
0.99937
2.13 ꢁ 105
4.30 ꢁ 1010
2.06 ꢁ 105
2.50 ꢁ 105
CR
HM
3.04 ꢁ 105
3.07 ꢁ 105
1.01 ꢁ 1018
5.13 ꢁ 1018
2.98 ꢁ 105
3.0 ꢁ 105
2.26 ꢁ 105
2.18 ꢁ 105
0.99647
0.99783
CR
HM
3.35 ꢁ 105
2.30 ꢁ 1019
117
99.4
3.28 ꢁ 105
2.30 ꢁ 105
0.99562
0.99759
3.24 ꢁ 105
2.72 ꢁ 1018
3.17 ꢁ 105
2.34 ꢁ 105
[Cu(BOCET)2(H2O)2]Cl2ꢀH2O
[Co(BOCET)2(H2O)2]Cl2ꢀ2H2O
[Ni(BOCET)2(H2O)2]Cl2ꢀ2H2O
CR
HM
1.19 ꢁ 105
1.40 ꢁ 105
4.30 ꢁ 105
1.52 ꢁ 107
ꢂ145
ꢂ115
ꢂ91.4
ꢂ73.9
149
131
1.12 ꢁ 105
1.34 ꢁ 105
2.26 ꢁ 105
2.24 ꢁ 105
0.99487
0.99951
CR
HM
1.88 ꢁ 105
3.22 ꢁ 108
1.80 ꢁ 105
2.64 ꢁ 105
0.99505
0.99822
2.03 ꢁ 105
2.64 ꢁ 109
1.96 ꢁ 105
2.63 ꢁ 105
CR
HM
4.05 ꢁ 105
3.92 ꢁ 105
1.13 ꢁ 1021
1.41 ꢁ 1020
3.97 ꢁ 105
3.85 ꢁ 105
2.58 ꢁ 105
2.62 ꢁ 105
0.99656
0.99808

M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
161
Fig. 10. The inhibition zone of OCET, BOCET ligands and their Cu(II), Co(II) and Ni(II) complexes on some kinds of bacterial.
3.9. Microbiological investigation
terial on Gram positive (Bacillussubtili, S. aureus) also toward Gram
negative (E. coli, P. aeruginosa), but the activity on Gram negative
more than Gram positive.
The results of antibacterial actives in vitro of the ligand and all
their complexes are shown in Table 6 and Fig. 10. From the results
we can see that all the test compounds have high activity antibac-
3.10. Structure of the complexes
Finally, it is concluded that from elemental analysis, IR and 1H
NMR spectra, the Schiff base ligands behave as a bidentate ligand
coordinated to the metal ions Cu(II), Co(II) and Ni(II) through the
thione CS group and azomethine group (Fig. 11).
NH2
NH
C
H3C
O
S
O
N
H2O
4. Conclusions
.nH2O.mCl
M
OH2
S
N
The structures of the complexes of Schiff bases OCET and
BOCET, with Cu(II), Co(II) and Ni(II) ions were interpretive by ele-
mental analyses, IR, NMR, molar conductance, magnetic, UV–vis,
mass, and thermal analysis data. Therefore, from the IR spectra, it
is concluded that OCET and BOCET behaves as a neutral bidentate
ligand, coordinated to the metal ions via azomethine N and thione
S. From the molar conductance data, it was found that all the M(II)
O
O
CH3
C
NH
H2N
Where n =1 or 2; m=2
Fig. 11. Suggested structure of the Schiff base complexes.

162
M.S. Refat et al. / Journal of Molecular Structure 920 (2009) 149–162
chelates are considered as 1:2 electrolytes. The 1H NMR spectra of
the free ligands show that the SH signal is absence in the spectra of
OCET and BOCET ligands this indicating that the SH proton not
exist and both ligands located as thione feature. On the basis of
the magnetic measurements octahedral geometry are suggested
for all investigated complexes except for Cu(II)/OCET complex is
a square planner. The synthesized ligands in comparison to their
metal complexes, were also screened for their antibacterial activity
against bacterial species, E. coli, P. aeruginosa as Gram negative, B.
subtilis and S. aureus as Gram positive. The activity data show the
metal complexes to be more potent antibacterials than the parent
Schiff base ligands against one or more bacterial species.
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