Synthesis, spectroscopic, and thermal characterization of Thiazole metal complexes: Biological activity studies

Article abstract of DOI:10.1080/15533174.2010.509300

Metal complexes of the organic ligand with N azomethine and N thiazole donation sites, derived from 3-(2-(2-(2,6-dichlorobenzylidene)hydrazinyl)-4-oxo- 4,5-dihydrothiazol-5-yl) acetic acid (H₂L), with some transition metal ions, namely Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II), are reported. They are characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, and molar conductance. The ionization constants are found to be 5.57 and 11.50, which can be attributed to loss of the hydrazo and the carboxylic acid protons, respectively. The stability constants of metal chelates, is calculated spectrophotometrically at 25C, and the order of stability follows the Irving and Williams order. The chelates are found to have octahedral geometrical structures. The ligand (H₂L) and its binary chelates are subjected to thermal analyses, and the different activation thermodynamic parameters are calculated using Coats-Redfern equation. The ligand and its metal complexes show a remarkable biological activity against the desert locust Schistocerca gregaria (Forsk) (Orthoptera - Acrididae) and its adult longevities. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2010.509300

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:621–632, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.509300
Synthesis, Spectroscopic, and Thermal Characterization of
Thiazole Metal Complexes: Biological Activity Studies
M. M. Omar,1 G. G. Mohamed,1 M. A. Badawy,1 M. M. Nassar,2 and A. B. Kamel1
1Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
2Insecticides Department, Faculty of Science, Cairo University, Giza, Egypt
found a wide range of applications. Thiazoles represent a very
interesting class of compounds because of their wide applica-
tions in pharmaceutical, phytosanitary, analytical and industrial
aspects,[6,7] and have biological activities.[8,9] In recent years,
thiazole-based chemisensors have also been investigated and
shown to be successfully applicable in biological systems.[10] It
is known that 2-aminothiazole is a biologically active compound
with a broad range of activity, and it is also an intermediate in the
synthesis of antibiotics and dyes. Numerous thiazole derivative
organic ligands and their transition metal complexes have been
investigated by various techniques.[11−18] From these points of
view, it is interesting to study different types of transition metal
complexes of this biologically active ligand.
In this article, the synthesis and characterization of the
first row transition metal complexes with the formulae
[M(H2L)2Cl].xH2O (where M is Mn(II), Co(II), Ni(II), Cu(II),
and Zn(II); x = 0–4) and [Fe(H2L)Cl2]Cl, and H2L is a pro-
tonated ligand, (2-(2-(2,6-dichlorobenzylidene)hydrazinyl)-4-
oxo-4,5-dihydrothiazol-5-yl) acetic acid, have been studied. The
N of azomethine and N thiazole coordination sites are helpful as
they will do a cavity around the metal ions and hence they can be
used as analytical reagents for determination of metal ions. The
structure of the studied complexes is elucidated using elemen-
tal analyses, IR, 1H NMR, solid reflectance, magnetic moment,
molar conductance, and thermal analysis measurements. The bi-
ological activity of the parent organic ligand and its metal com-
plexes are reported. The structure of ligand is given in Figure 1.
Metal complexes of the organic ligand with N azomethine
and thiazole donation sites, derived from 3-(2-(2-(2,6-
N
dichlorobenzylidene)hydrazinyl)-4-oxo-4,5-dihydrothiazol-5-yl)
acetic acid (H2L), with some transition metal ions, namely Mn(II),
Fe(III), Co(II), Ni(II), Cu(II), and Zn(II), are reported. They
are characterized based on elemental analyses, IR, 1H NMR,
solid reflectance, magnetic moment, and molar conductance.
The ionization constants are found to be 5.57 and 11.50, which
can be attributed to loss of the hydrazo and the carboxylic acid
protons, respectively. The stability constants of metal chelates,
is calculated spectrophotometrically at 25◦C, and the order of
stability follows the Irving and Williams order. The chelates are
found to have octahedral geometrical structures. The ligand (H2L)
and its binary chelates are subjected to thermal analyses, and the
different activation thermodynamic parameters are calculated
using Coats-Redfern equation. The ligand and its metal complexes
show a remarkable biological activity against the desert locust
Schistocerca gregaria (Forsk) (Orthoptera – Acrididae) and its
adult longevities.
Keywords biological activity, thermal analyses, thiazole ligand, tran-
sition metal complexes, spectroscopy
INTRODUCTION
It has long been known that metal ions are involved in the
biological processes of life and have been a subject of interest.
The modes of action of these metal ions are often complex,
but are believed to involve bonding to the hetero-atoms of the
heterocyclic residues of biological molecules, i.e., proteins, en-
zymes, nucleic acids, etc.[1] Organic ligands and their metal
complexes played an important role in the development of coor-
dination chemistry, resulting in an enormous number of publica-
tions, ranging from pure synthetic work to physicochemical [2]
and biochemically relevant studies of metal complexes,[3–5] and
EXPERIMENTAL
Materials and Reagents
The chemicals used included CuCl2.2H2O (Sigma),
CoCl2.6H2O and NiCl2.6H2O (BDH); MnCl2 (sigma),
ZnCl2.2H2O (Ubichem), and FeCl3.6H2O (Prolabo), thiosemi-
carbazide and maleic anhydride (Merck). Organic solvents
(spectroscopic pure from BDH) used included absolute ethyl al-
cohol, diethylether and dimethylformamide (DMF). Hydrogen
peroxide and chloride, carbonate and hydroxide salts of sodium
(A.R.) were used. Hydrochloric and nitric acids (Merck) were
used.
Received 18 February 2010; accepted 7 July 2010.
Address correspondence to G. G. Mohamed, Chemistry Depart-
ment, Faculty of Science, Cairo University 12613, Giza, Egypt. E-mail:
ggenidy@hotmail.com
621

622
M. M. OMAR ET AL.
Biological Activity
Cl
H
The susceptible strain of locust, Schistocerca gregaria was
obtained from Locust Research laboratory, Entomology Depart-
ment, Faculty of Science, Cairo University. A stock colony was
reared in cages 40x50x65 cm. Except for the front side, which
was made of glass; all the other three sides of the cages were
made of wood, with a small window closed by wire gauze for
ventilation. Each cage was supplied every morning with a suit-
able amount of fresh food, consisting of clover or maize leaves.
The cages were provided with pots of moistened, sieved sand
to serve as ovipositional sites. The locust culture and the exper-
imental tests, unless otherwise mentioned, were kept in a dark
room covered with thick black curtains. Light was provided by
a set of 60-watt electric bulbs. A bulb was hung in front of the
glass side of each cage. All bulbs were connected to a time
switch (a 24 hour automatic program timer) that would turn
the lights on at 4.00 a.m. and off at 6.00 p.m., approximately
corresponding to the times of sunrise and sunset in Egypt. Tem-
perature in the cages was recorded to range between 30 and
35◦C, while the relative humidity fluctuated between 60 and
80%.
Susceptible strain of Schistocerca gregaria was reared away
from any insecticidal contamination. 5th Nymphal instars of
Sch. gregaria nymphs, were treated with the novel chemicals
of thiazole derivatives using topical treatment techniques ac-
cording to method of Nassar.[34] After preliminary test, three
groups of 5th nymphal instars (5 insects of each group) were
received 2µg/insect of all tested compounds. Treatment was
replicated three times, and not less than 15 insects were treated
with each tested compound. Starting with the day after treat-
ment, all mortalities, malformation and adult longevities were
recorded. Mortality % was calculated for the next instars con-
sidering the initial number of treated hoppers, irrespective of the
instars under test. All experiments were performed as triplicate
and data plotted were the mean value.
S
O
H
N
N
C
N
O
Cl
O
FIG. 1. Structure of H2L ligand.
Solutions
Fresh stock solution of 5 × 10−4 M ligand; H2L, was pre-
pared by dissolving the accurately weighed amount (0.173 g/L)
in the appropriate volume of absolute ethanol. 5×10−4 M Stock
solution of the metal salts was prepared by dissolving the ac-
curately weighed amounts of the metal salts in the appropriate
volume of de-ionized water. The metal salt solutions were stan-
dardized by the recommended procedures.[32] Dilute solutions
of the metal ions and organic ligand under study were prepared
by accurate dilution. 1.0 N Stock sodium hydroxide solution
was prepared by accurate dilution and used for pH adjustment.
Mixture of 0.04 M phosphoric, acetic and boric acids was pre-
pared to obtain universal buffer solutions of the required pH
values from 2–13. The pH was adjusted by adding 0.2 N NaOH
solution to 100 mL of the acid mixture.[33]
Instruments
The molar conductance of solid chelates in DMF was mea-
sured using Sybron-Barnstead conductometer (Meter-PM.6, E
= 3406). Infrared spectra were recorded on a Perkin-Elmer FT-
IR type 1650 spectrophotometer in wavenumber region 4000–
400 cm−1. The spectra were recorded as KBr pellets. The solid
reflectance spectra were measured on a Shimadzu 3101pc spec-
trophotometer. The molar magnetic susceptibility was mea-
sured 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 mass spectrum was recorded by the EI (Electron Ion-
ization) technique at 70 eV using MS-5988 GS-MS Hewlett-
Packard instrument. The 1H NMR spectra were recorded using
300 MHz Varian-Oxford Mercury. The deuterated solvent used
was dimethylsulphoxide (DMSO) and the spectra extended from
0 to 15 ppm. The thermal analyses (TG, DTG and DTA) were
carried out in dynamic nitrogen atmosphere (20 mL.min−1) with
a heating rate of 10◦C min−1 using Shimadzu TG-60H and DTA-
60H thermal analyzers.
RESULTS AND DISCUSSION
Synthesis of Organic Ligand (H2L)
A mixture of 2,6-dichlorobenzaldehyde and thiosemicar-
bazide (0.005 mol) and maleic anhydride (0.0055 mol) in anisole
(3 mL) was refluxed for 15 min. After cooling, ethanol (10 mL)
was added and the solid precipitate was collected and recrystal-
lized from DMF/H2O mixture.
Cl
O
S
Cl
H
reflux,15 min.
S
N
O
H
+
NH
O
N
N
CH
NH2
N
O
Cl
O
Cl
O
(H2L)

CHARACTERIZATION OF NEW THIAZOLE METAL COMPLEXES
623
and Williams order[21] for divalent metal ions of the 3d series.
Synthesis of Metal Complexes
The metal complexes were prepared by the addition of hot It is clear from Table 1 that the stability of Cu(II) complex is
ethanolic solution (60◦C, 10 mL) of the appropriate metal chlo- considerably larger as compared to other metals of the 3d se-
ride (1 mmol) to the hot ethanolic solution (60◦C, 10 mL) of the ries. Under the influence of the ligand field, Cu(II) (3d9) will
organic ligand (0.173 g H2L, 1 mmol). The resulting mixture receive some extra stabilization[22] due to tetragonal distortion
was stirred whereupon the complexes precipitated. They were of octahedral symmetry in its complexes. The Cu(II) complexes
collected by filtration, washed several times with ethanol and will be further stabilized due to the Jahn-Tellar effect.[23] The
diethyl ether for further purification and dried under vaccum.
free energy of formation, ꢁGo, accompanying the complexa-
tion reaction has been determined at 25◦C (Table 1). From this
table, it is apparent that the negative values of ꢁGo show that
the complexation reaction proceeds spontaneously.
Characterization of Organic Ligand
The organic ligand is prepared and subjected to elemental
1
analyses, mass, H NMR, and IR spectral analyses. The re-
Elemental Analyses of the Complexes
The results of elemental analyses are in good agreement with
those required by the proposed formulae given in Table 1.
sults of elemental analyses 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 organic ligand.
Molar Conductance Measurements
Table 1 shows the molar conductance values of the 10−3M
concentration complexes in DMF solvent at 25 2◦C. It is con-
cluded from the results that the Mn(II), Co(II), Ni(II), Cu(II),
and Zn(II) complexes have a molar conductivity values in the
range 17.60–31.40 ꢂ−1 mol−1 cm2, which indicates the non-
ionic nature of these complexes, and they are considered as
non-electrolytes. Fe(III) complex is found to has molar conduc-
tance value of 79.50 ꢂ−1 mol−1 cm2, indicating that it is 1:1
electrolyte.
Mass spectrum of the organic ligand
The important peaks and its relative intensities for the molec-
ular ions are shown in Scheme 1. Mass spectrum of the studied
organic ligand is characterized by moderate to high relative in-
tensity molecular and fragment ion peaks. Scheme 1 shows a
well-defined parent peak of H2L at m/z = 346 (R.I. = 2%).
Fragment at m/z = 58 (R.I. = 100%, base peak) is attributed to
C2H2S ion as shown in the mass spectrum of H2L.
Absorption Spectra of the Organic Ligand
IR Spectral Studies
The absorption spectrum of 1 × 10−4 M solution of H2L
ligand under investigation in buffer solutions of varying pH
values from 2–13 are scanned in the wavelength range from 200
to 700 nm, against the same solvent as a blank. The absorption
spectrum of H2L ligand shows sharp bands at 290 (ꢀ = 1970
L.mol−1cm−1) and 310 (ꢀ = 2098 L.mol−1cm2). These bands
can be attributed to π − π* transitions within the azomethine
group of the organic ligand molecule.
The IR spectral data of the organic ligand and its com-
plexes are listed in Table 2. The IR spectra of the complexes
are compared with the free ligand in order to determine the co-
ordination sites that may involved in chelation. Upon compari-
son, it is found that the υ(C=N)azomethine and the υ(C=N)thiazole
stretching vibrations are found in the free H2L ligand at 1623
and 1583 cm−1, respectively. However, the participation of the
(C=N)azomethine and υ(C=N)thiazole groups in chelation are ascer-
tained from the shift of the bands to higher wavenumbers in the
spectra of the complexes to 1625–1654 and 1590–1586 cm−1
,
Ligands dissociation and metal-ligand stability constants
The ligand dissociation constant was calculated using the half
height method.[19] H2L ligand is found to have two pKa values
of 5.57 and 11.50, which can be attributed to loss of the hydrazo
group and the carboxylic acid protons, respectively. The free
energy change, ꢁGo, was also calculated and found to be 356.4
and 506.9 kJ mol−1 for the first and second ionizations, respec-
tively. The positive values indicate the spontaneous character of
dissociation reaction.
respectively, indicating the participation of the azomethine and
thiazole nitrogen in coordination (M—N) ).[24]
The υ(C=O),υasym(COO) and υsym(COO) stretching vibra-
tions are observed at 1731, 1409, and 1094 cm−1 for H2L ligand,
respectively. These stretching vibrations are shifted to higher or
lower frequencies in the region 1721–1733, 1402–1430, and
1059–1097 cm−1 in the complexes, respectively. Although,
the carboxylate O atom not involvement in the complexes
formation,[25] the shift in position of the υ(C=O), υasym(COO)
and υsym(COO) stretching vibrations may be due to hydrogen
bond formation and formation of stable six membered ring. The
IR spectrum of the H2L ligand shows a broad band at 3445
cm−1, which can be attributed to the carboxylic OH group. This
band is still broad in all complexes (Table 2), and the shift in
position of this band can support the hydrogen bond formation.
The stability constants of Mn(II), Fe(III), Co(II), Ni(II),
Cu(II), and Zn(II) complexes are determined spectrophotomet-
rically using Taneja method.[20] The mean logβ1 and logβ2
values are listed in Table 1. The complex-forming abilities of
the transition metal ions are frequently characterized by stability
orders. The order of stability constants is found to be Mn2+
Co2+ < Ni2+ < Cu2+ > Zn2+ in accordance with the Irving
<

624

CHARACTERIZATION OF NEW THIAZOLE METAL COMPLEXES
625
TABLE 2
IR spectral data (4000–400 cm−1) of H2L ligand and its metal complexes
υ(OH)
υ(C=O) υ(C=O) υ(C=N) υ(C=N) υ(COO) υ(COO)
Compound
carboxylic υ(NH) carboxylic carbonyl azomethine thiazole υ(asym.) (sym.) υ(M-N) υ(M-O)
H2L
3445br 3086br 1731sh
3471br 3058s 1725sh
3396br 3069br 1732m
1699sh
1701s
1700s
1704s
1700s
1700s
1695s
1623sh
1640sh
1648sh
1625m
1651sh
1637sh
1654m
1583sh 1409sh 1094m
1588m 1428m 1060m
—–
544s
578s
540w
—–
442s
409m
451w
447s
448s
445s
[Mn(H2L)2Cl2]
[Fe(H2L)2Cl2]Cl
[Co(H2L)2Cl2]
[Ni(H2L)2Cl2].4H2O 3355br
[Cu(H2L)2Cl2]
[Zn(H2L)2Cl2]
1586s
1589m
1588s
1430m
1402s
1430m 1059m 544w
1060s
1097s
3411br
Dis.
Dis.
1721m
1724m
3393br 3016br 1726sh
3448br 3077s 1733sh
1588sh 1402m 1095m
1590m 1424m 1090s
542s
538s
sh = sharp, m = medium, br = broad, s = small, w = weak.
involving d2sp3 hybridization in Fe(III) ion.[37] The spectrum
shows also a band at 25,420 cm−1 which may be attributed to
ligand to metal charge transfer.
The studied Ni(II) complex is high spin with a room tem-
perature magnetic moment value of 3.28 B.M., which indicates
octahedral geometry.[37] Three bands, in the solid reflectance
Therefore, from the IR spectra, it is concluded that H2L
behaves as neutral bidentate ligand in all the complexes coordi-
nating to the metal ions via azomethine N and thiazole N atoms.
1H NMR Spectral
3
3
spectrum at ν1: 13,257 cm−1: A2g → T2g, ν2: 14,780 cm−1
:
1
The H NMR data for H2L ligand and its Zn(II) complex,
3A2g → T1g(F) and ν3: 22,444 cm−1: A2g → T1g (P) are
displayed. The spectrum shows also a band at 25,333 cm−1
which may be attributed to ligand to metal charge transfer. The
electronic spectrum of the Co(II) complex gives three bands
at 12,870, 15,974, and 21,208 cm−1. The region at 25,445
cm−1 refers to the charge transfer band. The bands observed
3
3
3
recorded in DMSO-d6, show a sharp signal at 8.547 and 8.537
ppm, which may be assigned to the azomethine protons (–
CH=N, 1H), respectively. However, a multiple at 7.589–7.426
and 7.576–7.444 ppm may be attributed to the phenyl protons
(4H, 3Ar-H, 1 thiazolyl-H) and (8H, 6Ar-H, 2 thiazolyl-H) for
H2L ligand and its Zn(II) complex, respectively. Another multi-
ple observed at 3.048–2.851 and 3.017–2.858 ppm for H2L and
Zn(II) complex, corresponds to the methylene protons (-CH2;
2H) and (CH2; 4H), respectively. A multiple bands at 4.398–
4.356 (NH, 1H) and 4.470–4.444 ppm (NH, 2H) for HL and
Zn(II) complex, respectively, may reasonably be assigned to
secondary amine protons. A broad band observed at 12.00 ppm
may be attributed to the COOH proton (-COOH; 1H). This sig-
nal is found at 11.797 ppm in Zn(II) complex. This indicates the
non-involvement of the COOH group in chelation and this shift
can be assigned to hydrogen bond and formation of stable six
membered ring.
4
4
4
are assigned to the transitions T1g(F) → T2g(F) (ν1), T1g(F)
4
4
4
→ A2g(F) (ν2) and T1g(F) → T2g(P) (ν3), respectively, sug-
gesting an octahedral geometry around Co(II) ion.[38] The mag-
netic moment value is found to be 4.94 B.M. indicating of
octahedral geometry.[37] The reflectance spectrum of the Cu(II)
chelate consists of a broad band centered at 15,575 and 17,640
cm−1. The Eg and T2g states of the octahedral Cu(II) ion
(d9) split under the influence of the tetragonal distortion and
the distortion can be such as to cause the three transitions
2
2
2B1g → B2g; 2B1g → Egand 2B1g → A1g to remain unresolved
in the spectrum.[39] The magnetic moment of 1.97 B.M. falls
within the range normally observed for octahedral geometry.[39]
A moderately intense peak observed at 21,750 cm−1 is due to
ligand to metal charge transfer transition.[40] The Zn(II) com-
plex is diamagnetic and according to the empirical formula, an
octahedral geometry is proposed.
2
2
2
Magnetic Susceptibility and Electronic Spectral Studies
The diffused reflectance spectrum of the Mn(II) com-
plex shows three bands at 16.350, 22.080, and 27.390 cm−1
6
6
6
assignable to 4T1g → A1g, 4T2g(G) → A1g and 4T1g(D) → A1g
transitions, respectively.[36,37] The magnetic moment value 5.24
B.M. indicates the presence of Mn(II) complex in octahedral
structure. From the diffused reflectance spectrum, it is observed
that the Fe(III) chelate exhibits a band at 21,340 cm−1, which
may be assigned to the 6A1g →T2g(G) transition in octahedral
Thermal Analyses (TG, DTG and DTA) Studies
The TG curve of H2L ligand (Figure 2a) exhibits a first
estimated mass loss of 51.68% (calcd.51.73%) at 200–390◦C,
which may be attributed to the liberation of 3NO, 2HCl and
CH4 molecules as gases. In the 2nd stage within the temperature
range from 390–750◦C, the remaining organic part (C11H3S) is
lost with an estimated mass loss of 48.32% (calcd. 48.27%).
The loss of C11H3S molecule can also be estimated in the
geometry of the complex.[37] The A1g → T1g transition ap-
pears to be split into two bands at 17,460 cm−1 and 13,220
cm−1. The observed magnetic moment value of Fe(III) com-
plex is found to be 5.87 B.M., indicating octahedral geometry
6
5

626
M. M. OMAR ET AL.
Cl
Cl
H
H
S
O
H
N
N
CH
S
CH3
N
N
CH
N
O
N
Cl
O
Cl
O
m/z = 301(f = 300, R.I = 6%)
m/z = 346 (f = 346, R.I. = 2%)
H
H
S
S
CH3
CH3
N
N
N
N
CH
CH
2
N
N
O
O
m/z = 156 (f =153, R.I. = 19%)
m/z = 232 (f = 233, R.I. =
N
S
NH
H
S
N
N
N
CH
2
O
N
O
m/z =129 (f =125, R.I. = 25%)
m/z =143 (f =146, R.I. = 6%)
S
N
H
S
S
N
N
N
O
O
m/z =115 (f =115, R.I. = 6%)
m/z =101 (f =100, R.I. = 20%)
m/z = 85 (f = 87, R.I. = 38%)
H
H
S
S
S
H2C
H
H
m/z = 58 (f = 55, R.I. = 100%)m/z = 46 (f = 50, R.I.= 11%)
m/z =72 (f = 73, R.I. = 26%)
SCH. 1. Mass fragmentation pattern of H2L ligand.
mass spectrum of the ligand at m/z =165 (f. =167, R.I. = the remaining ligand as gases. The overall weight loss amounts
2%) is observed. This fragment ion, C11H3S, is fragmented to to 90.43% (calcd. 90.64%). Figure (2b) shows the DTA curve
give different fragment ions (see scheme 1), which is observed which shows six exothermic peaks at (81, 238, 333, 477, 632,
as single decomposition step in the TG curve. The TG curve and 733◦C) and one endothermic peak at (200◦C). The appear-
of the [Fe(H2L)2Cl2]Cl chelate represents four decomposition ance of many exothermic and endothermic peaks are due to the
steps as illustrated in Figure 2b and Table 3. The first step removal of the anions and ligand molecules as gases. The TG
of decomposition within the temperature range 30–85◦C corre- curve of the Co(II) chelate is shown in Figure 2c. It decomposes
sponds to the loss of 3HCl molecules with a mass loss of 12.28% in five steps in the temperature range 30–950◦C. The first step
(calcd. 12.81%). The remaining steps of decomposition within is accounted to the loss of 3HCl molcules with a mass loss of
the temperature range 85–720◦C correspond to the removal of 13.54% (calcd. 13.32%). The mass losses of the remaining steps

CHARACTERIZATION OF NEW THIAZOLE METAL COMPLEXES
627
TGA
%
DTA
uV
DrTGA
mg/min
DrTGA
mg/min
TGA
%
DTA
uV
DTA
TGA
DrTGA
0.10
300.tadDTA
300.tadTGA
300.tadDrTGA
100.00
50.00
0.00
100.00
50.00
0.00
Detector:
DTG-60H
Sample Name: 304
Sample Weight:4.894[mg
0.00
40.00
0.00
-0.50
-1.00
-1.50
a
Detector:
DTG-60H
0.00
Sample Name:300
-10.00
-20.00
-30.00
b
Sample Weight6:.270[mg
20.00
0.0 0
-0.10
-20.00
-0.20
0.00
200.00
400.00
600.00
Tem p [C]
800.00
1000.00
0.00
200.00
400.00
600.00
Tem p [C]
800.00
1000.00
DrTGA
mg/min
TGA
%
DTA
uV
DrTGA
mg/min
0.20
TGA
%
DTA
uV
DTA
100.00
80.00
60.00
40.00
20.00
100.00
50.00
0.00
302.tad DTA
302.tad TGA
302.tad DrTGA
TGA
DrTGA
10.00
Detector:
DTG-60H
Sample Name: 303
Sample Weight:9.779[mg
Detector:
DTG-60H
Sample Name: 302
50.00
0.10
0.00
d
Sample Weight:3.890[mg]
0.00
c
0.00
-10.00
-20.00
0.00
-0.50
-0.10
-0.20
0.00
200.00
400.00
600.00
Tem p [C]
800.00
1000.00
0.00
200.00
400.00
600.00
Tem p [C]
800.00
1000.00
FIG. 2. Thermal analyses (TG, DTG and DTA) of H2L and its complexes. Where (a) H2L ligand, (b) Fe(III), (c) Co(II), and (d) Ni(II) complexes.
(T = 100–950◦C) correspond to the removal of C24H12N6O6S2 ergy (E∗), enthalpy (ꢁH∗), entropy (ꢁS∗) and Gibbs free en-
and 3HCl molecules as gases (estimated mass loss = 78.10%; ergy change of the decomposition (ꢁG∗) are evaluated graph-
calcd. = 77.55%). These steps are accompanied by exothermic ically by employing the Coats-Redfern relation.[30] The acti-
peaks (298 and 568◦C) and endothermic peaks (54, 137, and vation energies of decomposition are found to be in the range
875◦C). On the other hand, [Ni(H2L)2Cl2].4H2O chelate ex- 61.42–264.9 kJmol−1 and the data is summarized in Table 4
hibits three decomposition steps (Figure 1d) within the temper- and Figures 3 and 4. The high values of the activation en-
ature range from 30–650◦C. The estimated mass loss = 20.71% ergies calculated from the thermal decomposition reflect the
(calcd. 20.36%) of the first step within the temperature range thermal stability of the complexes. The entropy of activa-
from 30–175◦C can be attributed to the loss of 4HCl and 2H2O tion is found to have negative values in all the complexes
molecules. According to the data listed in Table 5, the total mass that indicate that the decomposition reactions proceed spon-
loss of the decomposition steps are found to be 91.64% (calcd. taneously.
91.60%) and NiO is suggested as a residue. The DTA data are
listed in Table 3 and represented graphically in Figure 2d. It is
clear from these data that these mass losses have two exothermic
(262 and 572◦C) and two endothermic (76 and 465◦C) peaks.
2.10. Structural Interpretation
On the basis of the above observations and from the magnetic
and solid reflectance measurements, octahedral and tetrahedral
Calculation of Activation Thermodynamic Parameters
The thermodynamic activation parameters of decomposi- geometry is suggested for the investigated complexes. The struc-
tion processes of dehydrated complexes namely activation en- tures of the complexes are shown in Figure 5.

628
M. M. OMAR ET AL.
2.15
2.25
2.78
2.98
-6.355
y = -0.7028x - 4.8602
R2 = 0.9964
y = -0.9111x - 4.367
R2 = 0.9991
-6.95
-6.04
-6.455
1.68
1.72
1.07
1.09
-5.86
y = -0.7334x - 4.8099
R2 = 0.9944
y = -3.2058x - 2.3997
R2 = 0.9977
-6.08
-5.92
1000/T
FIG. 3. Coats-Redfern plot of the decomposition steps of Fe(III)-H2L complex.
here on the basic idea of applying any chemotherapeutic agent
that depends essentially on the specific control of only one bio-
logical function and not multiple ones. The biological activities
of H2L and its metal complexes are studied against the different
Biological Activity
The main aim of the production and synthesis of any antimi-
crobial compound is to inhibit the causal microbe without any
side effects on the patients. In addition, it is worthy to stress
-6.6
-6.18
3.25
3.35
2.44
2.49
-7.2
y = -0.4285x - 5.1469
R2 = 0.9981
y = -5.4872x + 10.767
R2 = 0.9979
-6.23
-7.8
-5.958
0.96
1
1.2
1.22
-5.933
-5.967
-5.976
-5.985
y = -0.6803x - 5.1488
R2 = 0.9831
y = 0.3775x - 6.3181
R2 = 0.9875
-5.953 1000/T
FIG. 4. Coats-Redfern plot of the decomposition steps of Co(II)-H2L complex.

629

630
M. M. OMAR ET AL.
Cl
Cl
N
N
N
N
M
Fe
.Cl
N
N
N
N
Cl
Cl
M=Mn(II), Co(II), Cu(II), and Zn(II).
Cl
N
N
Ni
.4H2O
N
N
Cl
FIG. 5. Structure of metal complexes.
5th instar nymphs with the complexes is found to cause differ-
ent mortality after 24 hr post treatment. A dose (2 µg/insect)
mortality of complexes can be easily observed in Table 5.
Thus the highest mortality is found to be 100%, which is ob-
tained after nymphal treatment with [Cu(H2L)2Cl2] complex.
Meanwhile, 80% mortality is recorded after nymph treatment
with the [Fe(H2L)2Cl2]Cl, [Co(H2L)2Cl2] and [Zn(H2L)2Cl2]
complexes. On the other hand, different nymphal deformation
is obtained due to the effect of thiazole complexes against
Schistocerca gregaria nymphs. The lowest deformation is 20%
when nymph is treated with [Ni(H2L)2Cl2].4H2O complex. The
developmental stages of the desert locust Schistocerca gregaria
Forsk. The data are listed in Table 5. On comparing the biolog-
ical activity of the organic ligand and its metal complexes with
specific control of only one biological function and not multiple
ones, the following results are obtained:
I-Effect of H2L Ligand and its Metal Complexes on the 5th
Nymphal Instars of Schistocerca gregaria
The results of the effect of novel benzylidene complexes on
5th instars nymph of Schistocerca gregaria is recorded in Table
5. It is observed from this table that treatment of newly ecdysed
TABLE 4
Thermodynamic data of the thermal decomposition of H2L and its metal complexes
Complex
H2L
Decomp. Temp. îC
E∗ kJmol−1
A s−1
ꢁS∗ kJmol−1
ꢁH∗ kJmol−1
ꢁG∗ kJmol−1
25-390
390-650
25-85
78.37
121.8
134.6
174.5
140.5
61.42
104.0
82.10
63.19
117.5
74.71
264.9
217.6
220.4
1.1 × 106
4.8 × 106
1.1 × 108
4.8 × 107
1.0 × 108
1.8 × 107
4.7 × 1014
1.3 × 108
2.3 × 108
2.3 × 108
1.9 × 1010
8.4 × 105
2.4 × 106
2.4 × 1013
−130.7
−121.9
−56.10
−75.40
−72.40
−112.0
−70.40
−63.20
−65.00
−70.80
−57.10
−100.0
−83.30
−76.20
75.29
117.3
130.6
157.6
114.1
56.16
103.6
71.03
39.64
70.00
123.6
259.4
195.8
215.7
123.6
183.9
157.6
311.4
343.7
127.0
100.2
155.1
223.5
47.48
50.58
32.64
41.42
212.2
[Fe(H2L)2Cl2]Cl
85-248
248-386
520-716
22-100
100-200
200-425
425-625
625-1000
22-176
[Co(H2L)2Cl2]
[Ni(H2L)2Cl2].4H2O
176-320
472-620

CHARACTERIZATION OF NEW THIAZOLE METAL COMPLEXES
631
TABLE 5
Biological effect of H2L and its metal complexes on the desert locust Schistocerca gregaria and adult longevities of Schistocerca
gregaria (Forsk) (Orthoptera – Acrididae)
Desert locust Schistocerca gregaria
% Nymphal instar % Adult stage
Dose of the complexes Nymph Deformed
adult longevities of Schistocerca gregaria
Adult longevities (Days S.E)
2µg/insect
mortality nymphs % Emerged % Deformed % normal
Male
Female
(H2L)
40
40
80
80
20
100
80
00
34
19
15
6
22
00
00
00
26
41
5
14
58
00
20
00
15
22
00
00
32
00
6
11
19
00
00
26
00
14
98.8
86 4.3∗
92 4.4∗
00
79 2.7∗
88 4.2∗
00
[Mn(H2L)2Cl2]
[Fe(H2L)2Cl2]Cl
[Co(H2L)2Cl2]
[Ni(H2L)2Cl2].4H2O
[Cu(H2L)2Cl2]
[Zn(H2L)2Cl2]
control
00
00
89 4.3∗
00
87 5.1∗
00
76 5.2∗
129.2+5.2
72 4.2∗
120.7+4.5
00
∗: Significance at P < 0.05
(NS): Nonsignificance at P < 0.05
mortalities obtained reveal that many of adult deformations are plication of different chemicals against locusts Schistocerca
inversely proportional with normal adults. [Zn(H2L)2Cl2] com- Gregaria.[31]
plex is found to produce 14% deformation of normal adult,
while the adult malformation is 6%. In conclusion, the data
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