Synthesis, characterization and thermal studies on metal complexes of new azo compounds derived from sulfa drugs

Article abstract of DOI:10.1016/j.saa.2007.01.034

Four new azo ligands, L1 and HL2-4, of sulfa drugs have been prepared and characterized. [MX₂(L1)(H₂O)_m]·nH₂O; [(MX₂)₂(HL2 or HL3)(H₂O)_m]·nH₂O and [M₂X₃(L4)(H₂O)]·nH₂O; M = Co(II), Ni(II) and Cu(II) (X = Cl) and Zn(II) (X = AcO); m = 0-4 and n = 0-3, complexes were prepared. Elemental and thermal analyses (TGA and DTA), IR, solid reflectance spectra, magnetic moment and molar conductance measurements have accomplished characterization of the complexes. The IR data reveal that HL1 and HL2-3 ligands behave as a bidentate neutral ligands while HL4 ligand behaves as a bidentate monoionic ligand. They coordinated to the metal ions via the carbonyl O, enolic sulfonamide {single bond}S(O)OH, pyrazole or thiazole N and azo N groups. The molar conductance data reveal that the chelates are non-electrolytes. From the solid reflectance spectra and magnetic moment data, the complexes were found to have octahedral, tetrahedral and square planar geometrical structures. The thermal behaviour of these chelates shows that the water molecules (hydrated and coordinated) and the anions are removed in a successive two steps followed immediately by decomposition of the ligand in the subsequent steps. The activation thermodynamic parameters, such as, E^*, ΔH^*, ΔS^* and ΔG^* are calculated from the TG curves applying Coats-Redfern method.

Full text of DOI:10.1016/j.saa.2007.01.034

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 68 (2007) 1382–1387
Synthesis, characterization and thermal studies on metal complexes
of new azo compounds derived from sulfa drugs
Gehad G. Mohameda,∗, Mohamed A.M. Gad-Elkareemb
a Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
b Chemistry Department, Faculty of Science, Al-Azhar University, Assiut, Egypt
Received 14 October 2006; accepted 12 January 2007
Abstract
Four new azo ligands, L1 and HL2–4, of sulfa drugs have been prepared and characterized. [MX2(L1)(H2O)m]·nH2O; [(MX2)2(HL2 or
HL3)(H2O)m]·nH2O and [M2X3(L4)(H2O)]·nH2O; M = Co(II), Ni(II) and Cu(II) (X = Cl) and Zn(II) (X = AcO); m = 0–4 and n = 0–3, complexes
were prepared. Elemental and thermal analyses (TGA and DTA), IR, solid reflectance spectra, magnetic moment and molar conductance mea-
surements have accomplished characterization of the complexes. The IR data reveal that HL1 and HL2–3 ligands behave as a bidentate neutral
ligands while HL4 ligand behaves as a bidentate monoionic ligand. They coordinated to the metal ions via the carbonyl O, enolic sulfonamide
S(O)OH, pyrazole or thiazole N and azo N groups. The molar conductance data reveal that the chelates are non-electrolytes. From the solid
reflectance spectra and magnetic moment data, the complexes were found to have octahedral, tetrahedral and square planar geometrical structures.
The thermal behaviour of these chelates shows that the water molecules (hydrated and coordinated) and the anions are removed in a successive
two steps followed immediately by decomposition of the ligand in the subsequent steps. The activation thermodynamic parameters, such as, E*,
ꢀH*, ꢀS* and ꢀG* are calculated from the TG curves applying Coats–Redfern method.
© 2007 Published by Elsevier B.V.
Keywords: Sulfa drugs; Metal complexes; IR; Conductance; Solid reflectance; Magnetic moment; Thermal analysis
1. Introduction
bound [14]. Certain theories had been advanced advocating that
a major portion of drug action occurred through complexation
[15].
Aromatic sulfonamide derivatives exhibit a range of bioac-
tivities, including anti-angiogenic [1,2], anti-tumor [2,3],
anti-inflammatory and anti-analgesic [4], anti-tubercular [5],
anti-glaucoma [6], anti-HIV [7], cytotoxic [8], anti-microbial
[9] and anti-malarial [10] agents. The synthesis of metal sul-
fanildie compounds had received much attention due to the
fact that sulfanilamides were the first effective chemothera-
peutic agents to be employed for the prevention and cure of
bacterial infections in humans. The pharmacological activity of
these types of molecules is often enhanced by complexation
with metal ions [11,12]. The anti-bacterial activity of sulfon-
amides is confined only to microorganisms which synthesize
their own folic acid [13]. The effectiveness of burn treatment
seemed to depend not only in the presence of metal ion but also
crucially on the nature of the material to which the metal ion is
The importance of metal ions in biological systems is well
known. One of the very interesting features of metal coordi-
nated systems is the concerted spatial arrangement of the ligands
around the metal ions. Among metal ions of biological impor-
tance, the Cu(II) ion presents a high number of complexes with
distortion [16]. Metal complexes of sulfonamide ligands incor-
porating additional donor atoms from iminomethyl and phenol
groups[17], iminomethylandthiophenolgroups [18]orpyridine
groups [19,20] had been investigated recently.
In continuation to our work on sulfa drugs [21–23], this arti-
cle involves the synthesis and characterization of Co(II), Ni(II),
Cu(II) and Zn(II) complexes with four new azo sulfa drugs had
been described. The solid products were characterized by ele-
mental and thermal analyses, IR, molar conductance, magnetic
moment and solid reflectance spectra measurements. The ther-
mal decomposition of the complexes is also used to infer the
structure and the different thermodynamic activation parameters
are calculated.
∗
Corresponding author.
E-mail address: ggenidy@yahoo.com (G.G. Mohamed).
1386-1425/$ – see front matter © 2007 Published by Elsevier B.V.
doi:10.1016/j.saa.2007.01.034

G.G. Mohamed, M.A.M. Gad-Elkareem / Spectrochimica Acta Part A 68 (2007) 1382–1387
1383
2. Experimental
hydrazino]-N-1,3-thiazol-2-yl-benzenesulfonamide (HL2), 4-
[2-(5-oxo-1,3-diphenyl-1,5-dihydro-4H-pyrazol-4-yl-idene)-
hydrazino]-N-pyrimidin-2-ylbenzenesulfonamide (HL3) and N-
[amino(imino)methyl]-4-[2-(5-oxo-1,3-diphenyl-1,5-dihydro-
4H-pyrazol-4-ylidene)-hydrazino]benzenesulfonamide (HL4),
respectively.
All chemicals used in the preparation of the com-
plexes and in solution studies were of the highest purity
available. They included 4-aminobenzenesulfonamide (1a),
4-amino-N-1,3-thiazol-2-ylbenzenesulfonamide (1b), 4-amino-
N-pyrimidin-2-ylbenzenesulfonamide (1c) and 4-amino-N-
[amino(imino)methyl]benzenesulfonamide (1d) supplied from
Sigma. Cobalt acetate tetrahydrate (BDH), copper and zinc
acetate dihydrate (Prolab), and nickel chloride hexahydrate
(BDH). Ethylenediaminetetracetic acid (EDTA) disodium salt,
zinc oxide (Analar), and ammonium chloride and hydroxide
(Merck) were used as received. The organic solvents used
included absolute ethyl alcohol (BDH) and diethyl ether and
dioxane (Aldrich).
Elemental analyses (C, H, N, S and M) were performed in the
Microanalytical Center at Cairo University. The analyses were
repeated twice. 1H NMR spectra were carried out in DMSO-d6
at 300 MHz on Varian Mercury VX spectrometer using TMS as
an internal standard. The IR spectra were recorded using 1430
Perkin-Elmer FT-IR spectrometer and in wave number region
4000–400 cm−1. The spectra were recorded as KBr disks. The
molar magnetic susceptibilities of the powdered samples were
measured using the Faraday method (magnetic susceptibility
balance–Sherwood were made by Pascal’s constant using Hg[Co
(SCN)4] calibrant. The diffuse reflectance spectra were recorded
using Shimadzu 3101pc spectrophotometer. The spectra were
recorded as BaSO4 disks. The molar conductance measurements
of the complexes were carried out in DMF using a Genway
4200 conductivity meter. pH measurements were carried out
using GENWAY 3020 pH meter. Thermal analyses (TGA and
DTA) of the complexes were carried out in dynamic nitrogen
atmosphere (20 mL min−1) with a heating rate of 10 ◦C min−1
using Shimadzu TGA-50 H and DTA-50 Hz. The percent weight
loss was measured from the ambient temperature up to 1000 ◦C.
Highly sintered ␣-Al2O3 was used as a reference. Metal contents
of the complexes were determined by titration against standard
EDTA after complete decomposition of the complexes with aqua
regia in a 50 mL digestion flasks.
2.2. Preparation of solid complexes
Metal complexes were synthesized by the addition of a hot
ethanolic solution (60 ◦C) of the appropriate metal chloride
or acetate (25 mL, 0.1 mmol) to a hot ammoniacal ethanolic
solution (25 mL) of azo ligands (25 mL, 0.05 mmol). The result-
ing mixture was stirred under reflux for 2 h and left to cool
whereby the complexes were precipitated. The solid complexes
were filtered, washed firstly by ethanol and then by diethyl
ether and dried in vacuum desiccator over anhydrous calcium
chloride.
3. Results and discussion
3.1. Preparation and characterization of the ligands
It has been found that the reaction of 4-aminobenzene-
sulfonamide (1a) with nitrous acid (NaNO2/HCl) afforded the
diazonium salt 2a, which underwent coupling reaction with
2,5-diphenyl-2,4-dihydro-3H-pyrazol-3-one (3) to yield the azo
coupling product L1. The structure of L1 was elucidated based
on elemental (Tables 1S and 2S in supplementary data) and
spectral data. The 1H NMR spectrum of L1 (Table 3S in supple-
mentary data) indicated the signals of 4H-pyrazole and NH at
δ = 3.49 and 13.62 ppm, respectively, indicated that the structure
of L1 is present in a mixture of the two toutomeric forms the azo
and the hydrazo form. Its IR spectra (Tables 4S and 5S in supple-
mentary data) showed the absorption bands of NH2, C O and
N N at 3356, 3264, 1656 and 1547 cm−1, respectively. In the
same way, 1b–d underwent diazotization and coupling with 3 to
give HL2–4, as shown in Scheme 1. Compounds L1 and HL2–4
are separated in high yield (80–85%).
The aim of this study is to investigate the chelating properties
of different new azo ligands towards some biologically impor-
tant metals like Co(II), Ni(II), Cu(II) and Zn(II) and assign the
possible structures of these complexes. The results of the ele-
mental analyses (C, H, N, S and metal content) with the proposed
molecular formulae are presented in Tables 1S and 2S in sup-
plementary data. The results obtained are in good agreement
with those calculated for the suggested formulae. 2:1 (M: L2
or L3 or L4) solid chelates are isolated and found to have
the general formulae [(MX2)2(HL2 or HL3)(H2O)m]·nH2O and
[M2X3(L4)(H2O)]·nH2O; M = Co(II), Ni(II) and Cu(II) (X = Cl)
and Zn(II) (X = AcO); m = 4 and n = 0–3. While L1 form 1:1
(M:L1) complexes with the formula [MX2(L1)(H2O)m]·nH2O;
M = Co(II), Ni(II) and Cu(II) (X = Cl) and Zn(II) (X = AcO);
m = 0–2 and n = 0–2. The solid complexes are prepared and
characterized by different tools of analyses like IR, molar
conductance, magnetic moment, solid reflectance and thermal
analyses (TGA and DTA) to through more light on the coor-
2.1. Preparation of the azo ligands (L1 and HL2–4)
A solution of the appropriate 4-aminobenzenesulfonamide
(1a), 4-amino-N-1,3-thiazol-2-ylbenzenesulfonamide (1b), 4-
amino-N-pyrimidin-2-ylbenzenesulfonamide (1c) and 4-amino-
N-[amino(imino)methyl]benzenesulfonamide (1d) (0.01 mol)
in 30 mL hydrochloric acid (30%, v/v) was treated with a
cold saturated solution of sodium nitrite (0.013 mol), with
stirring in ice-bath for 15 min, after that the cold solutions
were added to a cold solution of 2,5-diphenyl-2,4-dihydro-3H-
pyrazol-3-one (3) (0.01 mol) in ethanol (30 mL) containing
2.0 g of sodium acetate. The reaction mixtures were stirred in
ice-bath for 1 h. The solid products that formed were filtered
off, washed with cold water, dried and crystallized from the
proper solvent to give 4-[2-(5-oxo-1,3-diphenyl-1,5-dihydro-
4H-pyrazol-4-ylidene)-hydrazino]benzenesulfonamide (L1),
4-[-2-(5-oxo-1,3-diphenyl-1,5-dihydro-4H-pyrazol-4-ylidene)-

1384
G.G. Mohamed, M.A.M. Gad-Elkareem / Spectrochimica Acta Part A 68 (2007) 1382–1387
Scheme 1.
dination behaviour of these ligands towards some biologically
active metals under study.
in the free HL2 and HL3 ligands, respectively, are shifted to
1642–1670 and 1652–1672 cm−1 in the metal complexes. This
indicates the participation of the thiazoly and pyrimidine-N in
complex formation. A sharp bands due to the ν(C O) stretching
vibration of pyrazolone ring appeared at 1656–1743 cm−1 in
the free ligands. These bands are shifted to 1640–1753 cm−1
in the spectra of the metal complexes. These shifts refer to the
coordination through pyrazolone O atom.
The appearance of bands in the complexes in the 588–665 and
535–577, and 440–485 and 426–448 cm−1 regions which may
be assigned to the ν(M O) and ν(M N) stretching vibrations of
the coordinated O and N atoms of the ligands, respectively.
Therefore, fromtheIRspectra, itisconcludedthatL1behaves
as neutral bidentate ligand while HL2–3 ligands behave as neu-
tral tetradentate and HL4 ligand behaves as a uni-negatively
tetradentate ligand. They coordinated to the metal ions via the
azo N, carbonyl O, enolic sulfonamide OH and pyrazole or
thiazole-N.
3.2. Infrared spectra and mode of bonding
The IR spectra of the free ligands and their metal com-
plexes were carried out in the range of 4000–400 cm−1 and
listed in Tables 4S and 5S in supplementary data. The stretch-
ing vibration band; ν(NH), of the sulfonamide group, which
found at 3440–3448 cm−1 in the free ligands, was disappeared
or hidden under the peak of water molecules. The presence of
coordinated water molecules renders it difficult to confirm the
enolization of the sulfonamide group. The SO2 group modes
of the HL2–4 ligands appear as sharp bands at 1335–1337 and
1140–1160 cm−1 (νasym(SO2)) and (νsym(SO2)), respectively. In
the complexes, the asymmetric and symmetric modes are shifted
to 1312–1326 and 1122–1167 cm−1, respectively, upon coordi-
nation to the transition metals [21,22]. The blue shift of the SO2
stretching vibration to lower frequencies may be attributed to the
transformation of the sulfonamide ( SO2NH) to give the enol
form ( SO(OH) N) as a result of complex formation to give
more stable six-membered ring [21,22]. The two bands at 1340
and 1154 cm−1 for asymmetric and symmetric SO2 stretching
vibrations groups for L1 ligand are slightly shifted to higher
or lower frequencies upon chelates. As the SO2 group is not
involved in metal bonding, this shift to higher or lower fre-
quencies must be related to important hydrogen bonding effects.
Another possible explanation for this shift may be the electronic
density changes on the sulfur atom and in the ring after complex
formation.
3.3. Molar conductance data
The molar conductance of the solid complexes (Λm,
ꢁ
−1 cm2 mol−1) was calculated. The DMF solubility of the
above complexes made calculations of the molar conductiv-
ity (Λm) of 10−3 M solution at 25 ◦C possible. The data in
Tables 1S and 2S in supplementary data show that the molar con-
ductanceareofrelativelylowvaluesforCo(II), Ni(II), Cu(II)and
Zn(II), indicating the non-electrolytic nature of these complexes.
Therefore, the molar conductance data confirm the results of the
elemental analyses and IR spectral data.
The strong bands at 1545–1552 cm−1 in the spectra of the free
ligands may be attributed to the azo group stretching vibration.
These bands are shifted to higher or lower frequencies as the
results of complex formation. This indicates the involvement of
the azo group in chelate formation. The strong and sharp bands at
1659 and 1660 cm−1 of the thiazolyl and pyrimidine-N; ν(C N),
3.4. Solid reflectance spectra and magnetic susceptibility
measurements
For Co(II) complexes with L1, HL2 and HL3 ligands,
the reflectance spectra show three bands at 12,820–13,513,

G.G. Mohamed, M.A.M. Gad-Elkareem / Spectrochimica Acta Part A 68 (2007) 1382–1387
1385
17,421–18,484 and 22,471–23,255 cm−1 which are assigned to
The Zn(II) complexes are diamagnetic and are likely to be
octahedral with HL2 ligand and tetrahedral with L1, HL3 and
HL4 ligands.
4
4
4
4T1g(F) → T2g(F), 4T1g(F) → E2g(F) and 4T1g(F) → T2g(P)
transitions, respectively, which assume an octahedral geometry
for Co(II) complex [24–26]. The band at 25,641–26,595 cm−1
,
3.5. Thermal analysis data
refers to LMCT [25]. Co(II) complexes have μeff of 4.69–4.92
which assumes a high spin octahedral geometry [25], may arose
from spin–spin coupling and/or crystal distortion.
The TGA and DTA date of the thermal decomposition of the
complexes are listed in Tables 6S and 7S in supplementary data.
The thermodynamic parameters for the different decomposition
steps are deduced using Coats–Redfern method and listed in
Tables 8S and 9S in supplementary data, where the average val-
ues of these parameters are those considered in the discussion.
The correlations between the different decomposition steps of
the complexes with the corresponding weight losses are dis-
cussed in terms of the proposed formulae of the complexes as
follows:
4
Three spin allowed transition bands, 4A2(F) → T2(F) (ν1);
4
4
4
4A2(F) → T1(F) (ν2) and A2(F) → T1(P) (ν3) are expected
for tetrahedral symmetry of Co(II) complex with HL4 ligand. In
the present case, only two bands at 13,071 and 17,452 cm−1 have
been observed in the diffuse reflectance spectrum of Co(II) com-
plex which is assigned to ν2 and ν3, respectively, as ν1 occurs
in the range 3000–5000 cm−1 [25]. The band at 25,974 cm−1
,
refers to LMCT [22,25]. The Co(II) complex has magnetic
moment of 5.66 B.M. which is in agreement with the values
for high tetrahedral Co(II) complexes [26].
The Co(II), Ni(II), Cu(II) and Zn(II) complexes of L1 lig-
and were thermally decomposed in the same manner. They
decomposed in three to four successive decomposition steps
within the temperature range 30–800 ◦C. The Co(II) and Ni(II)
complexes loss their water of hydration within the tempera-
ture range 30–110 ◦C with an estimated mass loss of 5.66%
(calcd. 5.93%) and 6.15% (calcd. 5.93%) for Co(II) and Ni(II)
complexes, respectively. The activation energy of this dehydra-
tion step is 63.35 and 34.96 kJ mol−1. The complexes losses
coordinated water, HCl, 1/2O, CH4 and 2CO2 gases within
the temperature range 100–320 ◦C with an estimated mass loss
of 17.55% (calcd. 17.63%), 17.13% (calcd. 17.63%), 16.93%
(calcd. 16.74%) and 20.35% (calcd. 20.07%) for Co(II), Ni(II),
Cu(II) and Zn(II) complexes, respectively. The energies of acti-
vation were 102.6, 88.64, 62.52 and 42.85 kJ mol−1 for the
Co(II), Ni(II), Cu(II) and Zn(II) complexes, respectively. The
last steps found within the temperature range 280–800 ◦C with
an estimated mass loss 64.75% (calcd. 64.09%), 63.79% (calcd.
64.09%), 61.12% (calcd. 60.88%) and 66.58% (calcd. 66.16%)
for Co(II), Ni(II), Cu(II) and Zn(II) complexes, respectively,
which is responsibly accounted for the pyrolysis of L1 molecule
with a final oxide residue of CoO, NiO, CuO and ZnO. The acti-
vation energy is 182.5, 159.8, 107.7 and 135.9 kJ mol−1. The
DTA data listed in Tables 7S and 8S in supplementary data
show the exo and endothermic peaks accompanying the pro-
cesses of dehydration, anions and coordinated water removal
and decomposition of the ligand molecules.
The metal complexes of HL2 ligand were thermally
decomposed in five successive decomposition steps. The first
estimated mass loss of 3.51–6.68% within the temperature
range 30–140 ◦C may be attributed to the liberation of hydrated
water molecules (calcd. 3.69–6.08%). The activation energy
of this step is 43.45–73.05 kJ mol−1. The second and third
steps occurred within the temperature range 100–400 ◦C with
an estimated mass loss 14.00–24.60% (calcd. 13.43–24.10%)
which is accounted for the removal of coordinated water,
HCl, O2, CH4 and CO2 gases, with an activation energy of
65.89–92.49 kJ mol−1. The last two steps occur within the
temperature range 320–750 ◦C with an estimated mass loss
52.31–66.77% (calcd. 52.93–66.29%) and activation energies
of 137.4, 177.2, 117.6 and 172.4 kJ mol−1 for Co(II), Ni(II),
The electronic spectra of the Ni(II) complexes of
L1, HL2 and HL3 ligands displays three bands in the
solid reflectance spectra as follows: 12,850–13,368 cm−1
;
3
3
3
3A2g → T2g (ν1), 15,698–16,420 cm−1; A2g → T1g(F) (ν2)
−1 3
3
and 17,361–17,543 cm
A
→ T1g(P) (ν3). The band at
2g
25,252–26,809 cm−1, refers to LMCT [25]. This indicates octa-
hedral geometry of the Ni(II) complex [25,27]. The Ni(II)
complexes have μeff of 3.53–4.26 B.M., which suggest an octa-
hedral geometry [25].
The Ni(II) complex of HL4 ligand exhibits medium inten-
sity broad bands at 13,888 and 20,092 cm−1, attributed to the
1
1
1
1A1g → A2g and A1g → B1g transitions, respectively [27].
The observed band in the region 15,698 cm−1; attributed to the
3T1(F) → T1(P) transition, reveals that Ni(II) has tetrahedral
3
configuration [27]. The complex has μeff of 4.76 B.M., which is
consistent with the tetrahedral geometry with an orbital contri-
bution to magnetic moment [26].
The reflectance spectra of the Cu(II) complexes of L1, HL2
and HL3 ligands consists of a broad and low intensity shoul-
der band at 15,873–17,452 cm−1 that forms part of the charge
transfer band. The 2Eg and 2T2g states of the octahedral Cu(II)
ion (d9) split under the influence of the tetragonal distortion to
2
2
2
2
2
2
three transitions; B1g → B2g; B1g → Eg and B1g → A1g
to remain unresolved in the spectra [28]. It is concluded that, all
three transitions lie within the single broad envelope centered
at the same range previously mentioned. This assignment is in
agreement with the general observation that Cu(II) d–d transi-
tions are normally close in energy [25]. The Cu(II) complex has
μeff = 1.83–196 B.M., assuming a distorted octahedral structure
[28].
The solid reflectance spectrum of the Cu(II) complex with
HL4 ligand shows a broad band at 15,673 cm−1 assigned to
2Eg → T2g transition and broad band at 13,513 cm−1 which is
2
2
assigned to 2B1g → A1g transition as well as a shoulder band at
17,482 cm−1 characteristic of a square planer geometry for Cu-
complex [28]. In addition, a moderately intense peak observed
at 26,315 cm−1 is due to ligand to metal charge transfer transi-
tion [28]. The μeff value of the Cu(II) complex is 2.05 B.M.,
which assume a tetrahedral geometry for this complex
[26].

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G.G. Mohamed, M.A.M. Gad-Elkareem / Spectrochimica Acta Part A 68 (2007) 1382–1387
1/T gives a slope from which E* was calculated and A (Arrhenius
factor) was determined from the intercept. The entropy of acti-
vation (ꢀS*), enthalpy of activation (ꢀH*) and the free energy
change of activation (ꢀG*) were calculated. The calculated val-
ues of E*, A, ꢀS*, ꢀH* and ꢀG* for the decomposition steps are
given in Tables 8S and 9S in supplementary data. According to
the kinetic data obtained from the DTG curves, all the complexes
have a negative entropy, which indicates that the complexes are
formed spontaneously.
Cu(II) and Zn(II) complexes, respectively, which correspond to
the loss of ligand molecule leaving metal oxide residue.
The TGA data of the metal complexes of HL3 ligand
(Tables 6S and 7S in supplementary data) indicated that the
complexes are thermally decomposed in three to four steps. The
first decomposition step represent the loss of coordinated water,
HCl and O2 gases in the Co(II) and Ni(II) complexes only.
While the first decomposition step in Cu(II) and Zn(II) com-
plexes correspond to the loss of coordinated water molecules
within the temperature range 40.0–250 ◦C. The energy of acti-
vation of this step is 43.65, 23.95, 46.87 and 64.10 kJ mol−1
for Co(II), Ni(II), Cu(II) and Zn(II) complexes, respectively.
The remaining steps found in the temperature range 280–750
with an estimated weight loss of 56.95% (calcd. 56.09%) and
56.35% (calcd. 56.09%) and activation energy of 122.4 and
72.47 kJ mol−1 for Co(II) and Ni(II) complexes, respectively, is
due to the decomposition of HL3 molecule leaving metal oxide
residues (CoO and NiO). The last steps occur within the tem-
perature range 100–900 ◦C with an estimated mass loss 73.21%
(calcd. 72.91%) and 78.28 (calcd. 77.98%) for Cu(II) and Zn(II)
complexes, respectively, which are reasonably accounted for the
liberationHCl, CH4, CO2 andligandmoleculeleavingCu2Oand
ZnO residues. The energy of activation of this step is 89.67 and
118.3 kJ mol−1 for Cu(II) and Zn(II) complexes, respectively.
The metal complexes of HL4 ligand are thermally decom-
posed in three to four successive decomposition steps. The
first two steps with an estimated mass loss of 22.85–29.09%
(calcd. 23.60–28.13%) within the temperature range 30–290 ◦C
can be attributed to the liberation of hydrated water, HCl, O2,
H2, CH4 and CO2 gases. The energy of activation of this step
is 50.22, 42.33, 65.25 and 41.98 kJ mol−1 for Co(II), Ni(II),
Cu(II) and Zn(II) complexes, respectively. The remaining steps
found within the temperature range 250–900 ◦C with an esti-
mated weight loss of 56.93% (calcd. 56.58%), 56.85% (calcd.
56.58%), 57.83% (calcd. 57.26%) and 51.69% (calcd. 52.13%)
and activation energy of 117.6, 95.98, 155.3 and 115.6 kJ mol−1
for Co(II), Ni(II), Cu(II) and Zn(II) complexes, respectively,
is attributed to the removal of ligand molecule leaving MO as
metallic residue.
3.7. Structural interpretation
The structural information from these complexes is in
agreement with the data reported in this paper based on the
elemental and thermal analyses, IR and solid reflectance spec-
tra, molar conductance, and magnetic moment measurements.
Consequently, the structures proposed are based on octahedral,
tetrahedral and square planar geometric structures. The azo lig-
ands coordinate via the azo N, carbonyl O, enolic sulfonamide
OH and pyrazole or thiodiaza N groups forming two binding
chelating sites. According to the above data, the structures of
the complexes are shown in Figs. 1S–3S in supplementary data.
Supplemental information
Tables 1S and 2S contains the analytical and physical data
of the complexes. Table 3S contains the 1H NMR spectra
of the ligands while Tables 4S and 5S contain the IR data.
Tables 6S and 7S contain the TGA results while Tables 8S and 9S
have the kinetic data. Figs. 1S–3S contain the structures of the
isolated solid complexes.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.saa.2007.01.034.
References
[1] Y. Funahashi, N.H. Sugi, T. Semba, Y. Yamamoto, S. Hamaoka, N.
Tsukahara-Tamai, Y. Ozawa, A. Tsuruoka, K. nara, K. Takahashi, T. okabe,
J. Kamata, T. Owa, N. ueda, T. Haneda, M. Yonaga, K. Yoshimatsu, T.
Wakabayashi, Cancer Res. 62 (2002) 6116.
[2] T. Semba, Y. Funahashi, N. Ono, Y. Yamamoto, N.H. Sugi, M. Asada, K.
Yoshimatsu, T. Wakabayashi, Clin. Cancer Res. 10 (2004) 1430.
[3] J. Sławin´ski, M. Gdaniec, Eur. J. Med. Chem. 40 (2005) 377.
[4] Q. Chen, P.N.P. Rao, E.E. Knaus, Bioorg. Med. Chem. 13 (2005) 2459.
[5] A.K. Gadad, M.N. Noolyi, R.V. Karpoormath, Bioorg. Med. Chem. 12
(2004) 5651.
[6] V.K. Agrawal, S. Bano, C.T. Supuran, P.V. Khadikar, Eur. J. Med. Chem.
39 (2004) 593.
[7] C.M. Yeung, L.L. Klein, C.A. Flentge, J.T. Randolph, C. Zhao, M. Sun,
T. Dekhtyar, V.S. Stoll, D.j. Kempf, Bioorg. Med. Chem. Lett. 15 (2005)
2275.
3.6. Kinetic analysis
The thermodynamic activation parameters of decomposition
processes of dehydrated complexes namely activation energy
(E*), enthalpy (ꢀH*), entropy (ꢀS*) and Gibbs free energy
change of the decomposition (ꢀG*) were evaluated graphically
by employing the Coats–Redfern relation [29]:
ꢀ
ꢁ
2RT
E∗
log{Wf/(Wf − W)}
log
T2
ꢀ
ꢂ
ꢃꢁ
AR
θE∗
E∗
= log
1 −
−
(1)
2.303RT
[8] I. Enc´ıo, Dj. Morre´, R. Villar, Mj. Gil, V. Mart´ınez-Merino, Br. J. Cancer
92 (2005) 690.
[9] M.J. Nieta, F.L. Alovero, R.H. Manzo, M.R. Mazzieri, Eur. J. Med. Chem.
40 (2005) 361.
[10] J.N. Dom´ınguez, C. Leo´n, J. Rodrigues, N.G. de Dom´ınguez, J. Gut, P.J.
Rosethal, Il Farmaco 60 (2005) 307.
where Wf is the mass loss at the completion of the reaction,
W the mass loss up to temperature T, R the gas constant,
E* the activation energy in kJ mol−1, θ the heating rate and
*
∼
(1 − (2RT/E )) 1. A plot of the left-hand side of Eq. (1) against
=

G.G. Mohamed, M.A.M. Gad-Elkareem / Spectrochimica Acta Part A 68 (2007) 1382–1387
1387
[11] A. Bult, H. Sigel, Metal Ions in Biological Systems, vol. 116, Marcel
Dekker, New York, 1983, p. 261.
[20] J. Castro, S. Cabaleiro, P.P. Lourido, J. Romero, J.A.G. Vazquez, A. Sousa,
Polyhedron 20 (2001) 2329.
[12] J. Casanova, G. Alzuet, S. Ferrer, J. Borras, S.G. Granda, E.J. Carreno, J.
Inorg. Biochem. 51 (1983) 689, and references therein.
[21] G.G. Mohamed, C.M. Sharaby, Spectrochim. Acta, Part A 66 (2007)
949.
[13] O.P. Agrawal, Synthetic Organic Chemistry, Goel Publishing House, Mer-
rut, 1985.
[22] C.M. Sharaby, G.G. Mohamed, M.M. Omar, Spectrochim. Acta, Part A 66
(2007) 935.
[14] A.G. Raso, J.J. Fiol, S. Rego, A.I. Lopez, E. Molins, E. Espinosa, E. Borras,
G. Alzuet, J. Borras, A. Castineiras, Polyhedron 19 (2000) 991.
[15] R.C. Maurya, P. Patel, Spectrosc. Lett. 32 (2) (1999) 233.
[16] L. Gutierrez, G. Alzuet, J. Borras, M.L. Gonzalez, F. Sanz, A. Castineiras,
Polyhedron 20 (2001) 703.
[17] A.D. Garnoveskii, A.S. Burlok, D.A. Garnoveskii, I.S. Vasilchenko, A.S.
Antsyshkina, G.D. Sadekov, A. Sousa, J.A.G. Vazquez, J. Romero, M.L.
Duran, A.S. Pedrares, C. Gomez, Polyhedron 18 (1999) 863.
[18] A.S. Burlok, A.S. Antsyshkina, J. Romero, D.A. Garnoveskii, J.A.G.
Vazquez, A.D. Garnoveskii, Russ. J. Inorg. Chem. 40 (1995) 1427.
[19] S. Cabaleiro, J. Castro, J.A.G. Vazquez, J. Romero, A. Sousa, Polyhedron
19 (2000) 1607.
[23] M.A.M. Gad-Elkareem, Afinidad 63 (2006) 247.
[24] M.M. Moustafa, J. Therm. Anal. 50 (1997) 463.
[25] A. Kapahi, K.P. Pandeya, R.P. Singh, J. Inorg. Nucl. Chem. 40 (1987)
355.
[26] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inor-
ganic Chemistry, 6th ed., Wiley, New York, 1999.
[27] B.M. Badiger, S.D. Angadi, S.A. Patil, V.H. Kulkarni, Ind. J. Chem. Soc.
72 (1995) 80.
[28] (a) M.F. Eskander, T.E. Khalil, R. Werner, W. Haase, I. Svoboda, H. Fuess,
Polyhedron 19 (2000) 949;
(b) P.S. Reddy, K.H. Reddy, Polyhedron 19 (2000) 1687.
[29] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68.