Thermal and kinetic studies on solid complexes of 2-(2-benzimidazolylazo)-4-acetamidophenol with some transition metals

Article abstract of DOI:10.1016/S1386-1425(02)00122-1

The preparation and characterization of 2-(2-benzimidazolylazo)-4-acetamidophenol (BIAAP) complexes are reported. Different physico-chemical methods like IR, Magnetic, solid reflectance spectra and molar conductance, were used to investigate the structure of BIAAP complexes. In particular, the thermal decomposition of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of BIAAP is studied in nitrogen atmosphere. All the complexes do not contain coordinated water molecules but contain (2-4) water molecules of crystallization. The water molecules were removed in a single step. The complexes of Co(II) and Ni(II) ions exhibited a phase transition and the decomposition or combustion of BIAAP occurred in the second and subsequent steps. The final decomposition products were identified by mass spectrometry as the corresponding metal oxides or carbonate. The activation thermodynamic parameters, such as, energy of activation, enthalpy, entropy and free energy change of the complexes were evaluated and the stabilities of the thermal decomposition of the complexes are discussed. From the kinetic point of view, it is found that the thermal stability of the complexes follows the order Ni(II)>Cu(II)>Zn(II)>Fe(III)>Co(II)>Cd(II).

Full text of DOI:10.1016/S1386-1425(02)00122-1

:
Spectrochimica Acta Part A 58 (2002) 3167Á3178
/
www.elsevier.com/locate/saa
Thermal and kinetic studies on solid complexes of
-(2-benzimidazolylazo)-4-acetamidophenol with some
transition metals
2
G.G. Mohamed *, M.A. Zayed, Nadia E.A. El-Gamel
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
Received 12 February 2002; accepted 21 February 2002
Abstract
The preparation and characterization of 2-(2-benzimidazolylazo)-4-acetamidophenol (BIAAP) complexes are
reported. Different physico-chemical methods like IR, Magnetic, solid reflectance spectra and molar conductance,
were used to investigate the structure of BIAAP complexes. In particular, the thermal decomposition of Fe(III),
Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of BIAAP is studied in nitrogen atmosphere. All the complexes do
not contain coordinated water molecules but contain (2Á4) water molecules of crystallization. The water molecules were
/
removed in a single step. The complexes of Co(II) and Ni(II) ions exhibited a phase transition and the decomposition or
combustion of BIAAP occurred in the second and subsequent steps. The final decomposition products were identified
by mass spectrometry as the corresponding metal oxides or carbonate. The activation thermodynamic parameters, such
as, energy of activation, enthalpy, entropy and free energy change of the complexes were evaluated and the stabilities of
the thermal decomposition of the complexes are discussed. From the kinetic point of view, it is found that the thermal
stability of the complexes follows the order Ni(II)ꢀ
/
Cu(II)ꢀ
/
Zn(II)ꢀ
/
Fe(III)ꢀ
/
Co(II)ꢀCd(II).
/
#
2002 Published by Elsevier Science B.V.
Keywords: TG and DTA; 2-(2-Benzimidazolylazo)-4-acetamidophenol complexes; IR; Conductance; Solid reflectance; Mass
spectrometry
1
. Introduction
investigated their thermal transformation into
octahedral structure in the solid phase. Cu(OAc) L
2
Argoud et al. [1] used 2-aminobenzimidazole
and Cu(OAc) L (Lꢀ2-aminoimidazole, 2-ami-
/
2
2
and other benzimidazole derivatives as a complex-
ing agent in the purification of water from heavy
metals. Ihara et al. [2] prepared a square planar
Ni(II) complexes with 2-aminobenzimidazole and
nobenzimidazole) were prepared and characterized
by IR spectra. The decrease in the NH group
2
vibrational frequency was attributed to the inter-
or intra-molecular H-bonding [3]. Co(II) and
Fe(III) complexes with 2-substituted benzimida-
zole derivatives were prepared and characterized
by spectroscopic and magnetic measurements [4].
*
E-mail address: ggenidy@hotmail.com (G.G. Mohamed).
Corresponding author. Fax: ꢁ
/
20-202-572556
1386-1425/02/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 1 2 2 - 1

3168
G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á3178
/
A
comparative study on the stability and
type 1650 spectrophotometer. The solid reflectance
spectra were measured on a Shimadzu 3101 PC
spectrophotometer. The molar magnetic suscept-
ibilities were measured on powdered samples using
the Faraday method. The conductance measure-
extractability of Co(II), Ni(II), Cu(II) and Cd(II)
complexes of benzimidazole, 2-aminobenzimida-
zole and 2-methylbenzimidazole was done by
Lenarcik et al. [5]. The reaction of FeCl with
2
some
2-aminobenzimidazole
ligands
yield
monomeric and dimeric [Fe(L)Cl ] complexes.
ments were carried out using a SybronÁBarnstead
/
conductometer. A Shimadzu TGA-50H and DTA-
50H thermal analyzers were used to record simul-
taneously TG, DTG and DTA curves. The experi-
ments were carried out in dynamic nitrogen
2
These complexes were characterized by different
tools of analyses and found to have a pseudote-
trahedral structure [6Á8].
/
ꢂ1
The preparation and thermal characterization
TG and DTA) of the transition metal complexes
atmosphere (20 ml min ) with a heating rate of
ꢂ1
(
10 8C min
in the temperature range 20Á
/
of this new azo compound, 2-(2-benzimidazoly-
lazo)-4-acetamidophenol (BIAAP), have not been
reported earlier. The literature survey, concerning
the thermal behaviour of this ligand and its
complexes are scantly. Therefore, the present
work aimed chiefly to through more light on
thermal behaviour of BIAAP complexes of di-
and tri-valent transition metal ions. Scheme re-
presenting the thermal decomposition of these
metal complexes was suggested. Different activa-
tion thermodynamic data are calculated from the
DTG curve and correlated qualitatively and quan-
titatively with the atomic radii of the different
metal ions. The coordination behaviour of BIAAP
towards different transition metals is reported
using different analytical tools.
1000 8C using platinum crucibles. The sample
sizes ranged in mass from 1.2 to 3.5 mg. Highly
sintered a-Al O was used as a reference. The mass
spectra were recorded with EI technique at 70 eV
on a Hewlett-Packard Model MS-5988 GS-MS
instrument in the Microanalytical Center at Cairo
University. Metal contents were determined by
titration against standard EDTA after complete
decomposition of the complexes with aqua regia in
a Kjeldahl flask several times.
2
3
2.2. Synthesis of
2-(2-benzimidazolylazo)-4-acetamidophenol
2-Aminobenzimidazole (3.99 g, 100 mmol) was
mixed with HCl (11.5 M, 5 ml) and diazotized
below 5 8C with NaNO (2.07 g, 10 mmol). The
2
resulting diazonium chloride was coupled with an
alcoholic NaOH (3 g, 25 ml) solution of 4-
acetamidophenol (4.53 g, 10 mmol) below 5 8C.
The product was separated by filtration, purified
by crystallization from diethyl ether and dried in
vacuo over anhydrous calcium chloride. The red
azo product is produced in 70% yield with a
2
. Experimental
2
.1. Materials and methods
All chemicals used were of the analytical
reagent grade. They included 4-acetamidophenol
Sigma), 2-aminobenzimidazole (Aldrich),
sodium nitrite and hydroxide (BDH), ethyl alcohol
Adwic) and the disodium salt of ethylenediami-
(
m.p.ꢀ160 8C.
/
(
netetraacetic acid (Adwic). Cupric acetate
dihydrate (Prolabo), cobalt and nickel chlorides
hexahydrate (BDH), zinc chloride dihydrate and
cadmium chloride (Adwic) and ferric chloride
2.3. Preparation of complexes
The metal complexes of BIAAP were prepared
by the addition of the appropriate metal chloride
(
Riedel-de Ha e¨ n) were used as received. The
or acetate solutions (0.01 mole) in ethanolÁ
/
elemental anlyses (C, H, N) were made at the
Microanalytical Center at Cairo University. IR
spectra were recorded on a Perkin-Elmer FT-IR
water mixture (1:1) to the solution of the azo
compound (0.02 mole) in the same solvent (50
ml). The resulting mixture was stirred under

G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á
/3178
3169
reflux for one half-hour where upon the complexes
were precipitated. They were collected by filtra-
tion, washed with 1:1 ethanol:water mixture and
with diethylether. The general reaction for the
preparation of the metal complexes of BIAAP is:
3. Result and discussion
The results of the elemental analyses of BIAAP
metal complexes are shown in Table 1. In all cases
1:2 (M:L) solid complexes are isolated and found
to have the general formulae [ML ]×
/
xH O where
2 2
MAꢁ2BIAAPꢁxH O[[M(BIAAP) ]xH O
2
2
2
Mꢀ
/
Ni(II), Co(II), Cu(II), Zn(II) and Cd(II) or
where Mꢀ
and Cd(II), Aꢀ
and Cd(II) ions and OAc in case of Cu(II) and
Zn(II) ions; and xꢀ2Á4.
/
Fe(III), Co(II), Ni(II), Cu(II), Zn(II)
[ML ]Cl×
/
xH O where MꢀFe(III), that is in
/
2
2
/Cl in case of Co(II), Ni(II), Fe(III)
agreement with the stoichiometric ratio found by
the spectrophotometric methods. The DMF solu-
bility of the complexes permitted calculation of the
/
/
ꢂ3
molar conductivity (L ) of 10
M solution at
m
25 8C [10], and by comparison, the type of
electrolyte of each complex. The molar conductiv-
ity value for Fe(III) complex is 104
2
.4. Kinetic analysis
The first stage of dehydration of the complexes
ꢂ1
2
ohm cm mol
ꢂ1
indicating a 1:1 electrolyte
and on the other hand, the low conductivity values
of the remaining complexes prove their weak
molecular nature (Table 1).
was studied in detailed manner. The kinetic
parameters such as activation energy (DE*),
enthalpy (DH*), entropy (DS*) and free energy
change of the decomposition (DG*) were evalu-
ated graphically by employing the CoastÁ
/Redfern
relation [9]:
ꢀ
3
.1. IR spectra and mode of bonding
ꢁ
logfW =(W ꢂ W)g
f
f
log
The IR spectrum of the ligand shows a broad
ꢂ1
2
T
band at 3547 cm
group. This band is absent in all the complexes
due to nOH of the phenolic
ꢀ
ꢂ
ꢃꢁ
AR
2RT
1ꢂ E+
E+
ꢀ
log
ꢂ
(1)
uE+
indicating coordination through the deprotonated
2:303RT
phenolic OH group [11]. The NÄ
/N stretching
where W is the mass loss at the completion of the
f
vibration is shifted to lower frequencies or even
disappeared, hidden under other frequencies when
the spectra of the free ligand is compared with
those of the complexes. This indicates the involve-
reaction, W is the mass loss up to temperature T;
R is the gas constant, E is the activation energy in
ꢂ1
kJ mol , u is the heating rate and (1ꢂ(2RT/
/
E*))$1. A plot of the left-hand side of Eq. (1)
/
ment of the azo group in coordination to the metal
ꢂ1
against 1/T gives a slope from which E* was
calculated and A (Arrhenius constant) was deter-
mined from the intercept. The entropy of activa-
tion (DS*), enthalpy of activation (DH*) and the
free energy change of activation (DG*) were
calculated using the following equations:
ions [12]. The band at 1610 cm
due to the N3
imidazole nitrogen, could not be assigned in the
Fe(III), Co(II) and Ni(II) complexes, while de-
crease in intensity in case of Cu(II) complex
indicating that it has been affected upon coordina-
tion to the metal ions. But in case of Cd(II) and
Zn(II) complexes, this band is not affected indicat-
ing the non-involvement of the N3 imidazole
nitrogen in coordination to these metal ions [13].
DSꢃꢀ2:303[log(Ah=kT)]R
DHꢃꢀEꢃꢂRT
DGꢃꢀHꢃꢂTSꢃ
(2)
(3)
(4)
In the far IR spectra of all the complexes, the
ꢂ1
where k and h are the Boltzman and Blanck
constants, respectively. The calculated values of
E*, A, DS*, DH* and DG* for the decomposition
steps are given in Table 3.
bands observed at 515Á
/
573 cm
(MÃ
/
N) and
O) provide conclusive evi-
ꢂ1
414Á
/
432 cm
(MÃ
/
dence concerning the bonding of nitrogen and
oxygen to the metal ions [11].

Table 1
Analytical and physical data of BIAAP and its metal complexes
Compound
Colour (% yield)
M.P. (8C)
Found (calcd.)%
Molecular wt. found
calcd.)
meff (B.M.)
Conductance
ꢂ1
cm molꢂ1
)
2
(
(V
C
H
N
M
Ligand [H
3
L]
Red
70)
160
60.6
(61)
4.3
23.56
(23.73)
19.23
297
(295)
718
Á
/
Á
/
(
(4.4)
4.5
[
[
[
[
[
[
FeC30
2H
CoC30
2H
NiC30
4H
CuC30
4H
ZnC30
2H
CdC30
2H
H
24
N
10
O
4
]
Violet
(73)
ꢀ
/
300
300
300
300
300
300
49.7
7.7
(7.82)
8.29
4.15
5.2
104
16.7
×
/
2
O
(50.3)
52.45
(52.7)
50.2
(4.2)
4.1
(19.56)
20.08
(715.5)
680
H
24
N
10
O
4
]
Dark green
(80)
ꢀ
/
×
/
2
O
(4.3)
4.45
(4.7)
4.46
(20.49)
19.21
(8.63)
8.00
(683)
722
(719)
H
24
N
10
O
4
]
Greenish blue
(67)
ꢀ
/
3.1
16.1
10.0
16.7
22.2
×
/
2
O
(50.06)
49.28
(49.75)
50.09
(50.24)
47.2
(19.47)
8.43
(8.2)
720
H
24
N
10
O
4
]
Light green
(85)
ꢀ
/
1.7
×
/
2
O
(4.69) (19.35)
(8.77)
9.33
(723.5)
690
H
24
N
10
O
4
]
Blue
(75)
ꢀ
/
4.00
(4.3)
3.8
20.15
(20.32)
18.34
Diam.
Diam.
×
/
2
O
(9.43)
15.54
(15.21)
(689)
737
(736)
H
24
N
10
O
4
]
Reddish brown
(78)
ꢀ
/
×
/
2
O
(47.91)
(4.07) (19.02)

Table 2
Thermalanalytical results (TG, DTG, DTA) of the BIAAPÁ
/metal complexes
Complex
TG range (8C)
DTGmax (8C) Peak temp in
DTA (8C)
Estim (calc%)
Mass loss
Assignment
Total mass loss
88.83 (88.81)
[
FeC30
H
N
24 10
2H
50Á
202Á
/
202
665
80
303
60 (ꢁ
285 (ꢂ
80 (ꢁ
90 (ꢂ
360(ꢂ
/
)
10.09 (10.13)
), 78.74 (78.68)
2
Loss of two H O and one HCl molecules
O
4
]Cl×
/
2
O
/
/
), 330 (ꢁ
/
Loss of two ligand molecules and formation of 1
Fe
2
4
/)
2 3
O
[
CoC30H
24
N
10
50Á
205Á
/
205
650
49
447
/)
5.07 (5.27)
Loss of two H O molecules
2
O
4
]×2H
/
2
O
/
/
), 480(ꢁ
70 (ꢁ
70
/
), 83.72 (84.04)
88.79 (89.31)
Loss of two ligand molecules and formation of CoO
Phase transition
5
/)
7
[
[
NiC30
]×
H
24
4H
N
10
50Á
185Á
/
185
565
50
433
38 (ꢁ
350 (ꢂ
10
30 (ꢁ
350 (ꢂ
/
)
9.33 (10.01)
79.03 (79.55)
2
Loss of four H O molecules
O
4
/
2
O
/
/
), 480 (ꢂ
/
)
89.56 (88.36)
82.5 (82.93)
Loss of two ligand molecules and formation of NiO
Phase transition
6
CuC30
H
24
N
O
10
50Á
/
205
770
55
471, 666
/), 60 (ꢂ
/)
5.39 (4.98)
77.95 (77.11)
Loss of two H
Loss of two H
2
O molecules
O and ligand and formation of
O
4
]×
/
4H
2
205Á
/
/), 430(ꢁ
/)
2
CuCO
3
5
60 (ꢁ
100 (ꢂ
280 (ꢁ), 400 (ꢂ
500 (ꢁ), 600 (ꢁ
80 (ꢁ), 900 (ꢁ
130 (ꢁ
200 (ꢁ), 250 (ꢁ
400 (ꢁ), 460 (ꢁ
680 (ꢁ), 800(ꢂ
20 (ꢁ
/
), 660 (ꢁ
/
)
[
[
ZnC30
H
24
N
O
10
50Á
215Á
60Á
/
215
52
/)
7.49 (7.55)
19.25 (19.45)
60.45 (61.25)
Loss of two H
Loss of C
Loss of ligand molecules and formation of ZnO
2
O molecules and CH
4
gas
O
4
]×
/
2H
2
/460
335
723
/
/)
7
H
4
N
2
O molecule
4
/955
/
/)
87.19 (88.25)
82.41 (82.62)
6
/
/)
CdC30
H
24
N
O
10
50Á
/
190
74
/)
6.26 (7.07)
4.82 (4.35)
19.65 (19.7)
Loss of two H
Loss of CO and 2H
Loss of C O, molecule
Loss of ligand molecules and formation of CdO
2
O molecules and CH
4
gas
O
4
]×
/
2H
2
190Á
/
275
237
376
795
/
/)
2
gases
2
75Á
/
490
/
/)
7 3 3
H N
4
90Á
/
1000
/
/), 51.68 (51.5)
9
/)
(
ꢂ
/
) Exothermic, (ꢁ) endothermic.
/

3172
G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á3178
/
3.2. Magnetic susceptibility and electronic spectra
measurements
complexes of iron(III) ions. The zinc and cadmium
complexes are diamagnetic and are likely to
be tetrahedral.
The solid reflectance spectra of the Cu(II)
complex give band centered at 846 nm (m
ꢀ
/
1.7
eff
2
2
B.M.), which may be assigned to E 0
/
T2g
g
3
.3. Thermogravimetric analysis
transition in an approximately octahedral envir-
onment [11]. The magnetic moment of the Ni(II)
complex has been found to be 3.1 B.M., which is
within the range of values corresponding to
octahedral geometry. The solid reflectance spectra
of the Ni(II) complex are consistent with the
formation of an octahedral geometry with the
The importance of this study on the BIAAP
ligand and its complexes stems from their possible
biological activities. Therefore, they are widely
subjected to investigation by thermal analyses and
other physico-chemical methods. Thermal data of
the complexes are given in Table 2 and the
activation thermodynamic data associated with
the loss of water of crystallization (dehydration
process) and ligand molecules are listed in Table 3.
The previously reported data of microanalysis and
mass spectra of the solid complexes give the
general
where MÄ
and Cd(II); AÄ
case of Fe(III), Co(II), Zn(II) and Cd(II), and 4, in
case of Ni(II) and Cu(II).
The thermal analysis curve of Fe(III) complex of
appearance of three bands at: n (456 nm):
1
3
3
3
3
/
A 0 T ; n : (714 nm): A 0 T (F) and n :
/
2
g
2g
2
3 3
2g
1g
3
(
838 nm): A 0
/
T (P). The 10Dq value of 838
1g
2
g
nm confirm the octahedral configuration [14]. For
the cobalt complex, the magnetic moment (5.2
B.M) is within the range of octahedral cobalt(II)
complexes [11,14]. The solid reflectance spectrum
shows three bands of medium intensity at 568, 754
and 842 nm which are assigned, respectively, to the
formula:
Fe(III), Co(II), Ni(II), Cu(II), Zn(II)
Cl in case of Fe(III) and xꢀ2, in
[MC H N O ](A)×
/
xH O
3
0
24 10
4
2
/
/
/
4
4
4
4
/
transition T (F)0
/
T (P) (y ), T (F)0
A2g
1
4
g
1g
4
3
1g
(
F) (y ) and T (F)0
/
T (F) (y ) of an octahe-
2
1g
2g
1
dral cobalt(II) complex [14]. The magnetic mo-
ment of the iron(III) complex has been found
to be 4.15 B.M., which is within the range of
values corresponding to high-spin octahedral
the general formula [FeC H N O ]Cl×
/
2H O is
2
3
0
24 10
4
shown in Fig. 1a. It gives pattern two stages of
decomposition supported by DTA data (Table 2).
The first step in the decomposition is started at
Table 3
Thermodynamic data of the thermal decomposition of BIAAPÁ/metal complexes
Complex
Decomposition
range (8C)
E*
(kJ molꢂ1)
A (Sꢂ1
)
DS*
(JK
DH*
DG*
ꢂ1
molꢂ1
)
(kJ molꢂ1)
(kJ molꢂ1)
1
1
5
5
4
[
[
[
[
[
FeC30
]Cl×
CoC30
]×2H
NiC30
]×
CuC30
]×
ZnC30
]×
H
24
N
10
50Á
202Á
50Á205
205Á650
50Á185
185Á565
50Á205
205Á770
50Á215
215Á
60Á
50Á
190Á
/
202
161.60
43.68
37.39
27.39
148.4
190.1
34.00
112.4
22.83
91.00
89.02
106.9
178.1
123.3
209.4
3.21ꢄ
8.83ꢄ
2.75ꢄ
2.75ꢄ
/
10
10
10
10
3.50
157.7
38.74
34.71
31.42
144.2
183.1
60.05
100.2
20.13
85.94
80.64
103.6
173.5
117.8
203.0
156.1
53.98
40.19
44.2
4
O
4
/
2H
2
O
/665
/
ꢂ
/
25.68
17.02
17.82
H
24
N
10
/
/
ꢂ
/
O
4
/
2
O
/
/
ꢂ/
10
H
24
N
10
5.61ꢄ10
ꢂ
/
5.25
146.8
187.2
71.12
150.3
25.13
94.46
102.6
102.9
169.1
123.9
202.3
2
3
4
6
1
3
1
1
9
1
1
O
4
/4H
2
O
/
2.28ꢄ
5.82ꢄ
1.67ꢄ
1.41ꢄ
1.07ꢄ
7.12ꢄ
3.96ꢄ
3.86ꢄ
1.42ꢄ
4.01ꢄ
/
10
10
10
10
10
10
10
10
10
10
ꢂ
/
4.93
H
24
N
O
10
/
/
ꢂ
/
21.35
18.95
15.39
13.99
21.81
1.56
O
4
/4H
2
/
/
ꢂ/
H
24
N
O
10
/
/
7
O
4
/2H
2
/460
/
ꢂ
/
4
/955
/
ꢂ/
3
6
[
CdC30
H
24
N
O
10
/190
/
O
4
]×
/
2H
2
/275
/
8.12
275Á/490
/
ꢂ
/
9.19
3
490Á/1000
/
0.91

G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á
/3178
3173
Fig. 1. Thermal analysis (TG and DTA) of BIAAP complexes: (a) Fe(III); (b) Co(II) and (c) Ni(II).
5
the complex and loss of HCl gas with an estimated
0Á
/
202 8C and corresponding to dehydration of
duct of decomposition which correlated with the
mass spectra.
The cobalt complex of the formula
mass loss of 10.09% (calcd. mass loss
1
0.13%). This step is correlated with the endother-
[CoC30
posed in two successive decomposition steps. The
H
24
N
10
O
4 2
]×
/
2H O was thermally decom-
mic peak in DTA at 60 8C. The energy of activa-
tion of the thermal dehydration of the complex
first estimated mass loss of 5.07% within the
ꢂ1
was 161.57 kJ mol
(Table 3). In the second
temperature range 50Á205 8C with exotherm in
/
step, the decomposition of the two BIAAP mole-
cules takes place in the temperature range
the DTA at 90 8C, might be attributed to the
liberation of two molecules of hydrated water
(calcd. mass loss 5.27%). The energy of activation
2
02Á
/
665 8C with an estimated mass loss 78.74%
ꢂ1
(
calcd. mass loss 78.68%). This is confirmed by
of this step is 37.39 kJ mol . The second step
the presence of two endothermic peaks in the DTA
at 330 and 480 8C and exothermic peak at
occurs within the temperature range 205Á650 8C
/
with an estimated mass loss 83.72% (calcd. mass
loss 84.04%) which is reasonably accounted for the
decomposition of two ligand molecules leaving
CoO residue. The appearance of exothermic peak
2
85 8C due to the liberation of the BIAAP
molecules. The remainder was ferric hydroxide
M.wtꢀ107 (m/zꢀ106; RI. 34.59%)] as the pro-
[
/
/

3174
G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á3178
/
at 360 8C and two successive endothermic
peaks at 480 and 570 8C in the DTA curve (Fig.
The TG curve of the Zn(II) complex of the
formula [ZnC H N O ]×2H O indicates that, the
complex decomposed in three steps. The DTA curve
of the complex shows one exothermic peak at
100 8C. This peak is assigned as the dehydration of
the complex. This assignment was confirmed by the
/
3
0
24 10
4
2
1
b) is related to the loss and fragmentation of two
ligand molecules. The appearance of broad en-
dothermic peak at 770 8C may be due to the phase
transition occurs in the solid complex. The re-
maining CoO (M.wtꢀ
decomposition is confirmed by means of mass
spectra [m/zꢀ75, RI. 23.94%].
Fig. 1c illustrates the thermal analyses curves of
the Ni(II) complex with the general formula
/
75) was as a residue of the
mass loss 7.49% at the temperature range of 50Á
/
215 8C (calcd. mass loss 7.55%) obtained from the
TG curve. This corresponds to the loss of two water
molecules and methane gas. It is found that, the
/
activation energy of the dehydration step is equal to
ꢂ1
[
NiC H N O ]×
/
4H O. The first estimated mass
2
22.83 kJ mol . The second (215Á460 8C) and
/
3
0
24 10
4
loss of 9.33% (calcd. mass loss 10.0%) at 50Á
/
185 8C
third(460Á955 8C)stepscorrespondtothe removal
/
with one small endothermic peak at 38 8C
may be attributed to the thermal dehydration of
of the two BIAAP molecules as deduced from mass
loss calculations (estimated mass loss 87.19%, calcd.
mass loss 88.25%). The appearance of endothermic
peak in DTA at 280 8C followed by exothermic
peak at 400 8C may be attributed to the strong
vigorous chemical reaction of organic ligand
thecomplex.Theactivationenergyofdehydrationis
ꢂ1
1
48.4 kJ mol . In the second step, within the
temperature range 185Á565 8C, the organic part of
/
the anhydrous complex decomposed with an
estimated mass loss 79.03% (calcd. mass loss
molecule by loss of C H NO
leaving
[ZnC H N O ] as stable compound as given in
7
4
2
7
9.55%). Two successive exothermic peaks appear
2
2
16
9
2
at 350 and 480 8C as shown in the DTA curve may
be attributed to the decomposition of two BIAAP
molecules. The appearance of strong endothermic
peak at 610 8C may be reasonably related to phase
TG. Appearance of four successive endothermic
peaks at 500, 600, 680 and 900 8C respectively may
be related to further removal of the ligand molecule
from Zn(II) ion and constant weight of ZnO has
been formed which confirmed by mass spectra (m/
transition. The remaining NiO (M.wtꢀ
confirmed by mass spectra (m/zꢀ76, RI. 17.95%).
On the other hand, Cu(II) complex of the formula
CuC H N O ]×4H O exhibits two distinct de-
/75) was
/
zꢀ
/
81.8; RI. 49.43%).
The Cd(II) complex, [CdC H N O ]×
/2H O,
2
3
0
24 10
4
[
/
exhibits four steps of decomposition on TG and
eight peaks in DTA (Fig. 1f). The first endother-
mic peak at 130 8C corresponds to the loss of two
water molecules and methane gas with an esti-
mated mass loss 6.26% (calcd. mass loss 7.07%). It
is found that the value of activation energy for this
3
0
24 10
4
2
composition steps, as shown in Fig. 2d. The first
step, in the temperature range 60Á205 8C, with an
/
estimated mass loss of 5.39% and two small
exothermic peaks in the DTA may be attributed
to the liberation of two molecules of hydrated water
ꢂ1
(
the thermal dehydration of the complex is 64.36
calcd. mass loss 4.98%). The activation energy of
dehydration process is 106.9 kJ mol . Several
simultaneous decomposition processes with six
successive endothermic and exothermic DTA
peaks are observed between 193 and 1000 8C.
The appearance of two endothermic peaks at 200
and 250 8C may referred to the liberation of CO
ꢂ1
kJ mol . In the second step, DTA curve reveals an
exothermic peak at 350 8C followed by three
successive endothermic peaks at 430, 560 and
660 8C, respectively. This may be accounted to
the vigorous decomposition of the BIAAP mole-
and 2H gases. This is followed by another two
2
cules leaving CuCO as a metallic residue. The
3
successive endothermic peaks at 400 and 460 8C,
which may be attributed to the vigorous chemical
reaction and loss of [C H N O] from ligand
molecules and the rearrangement of complex
configuration. This is followed by another two
successive endothermic peaks followed by strongly
exothermic peaks at 680, 800 and 920 8C, respec-
overall loss of mass from the thermogravimetric
analysis (TG) curve is 82.50%, while the overall
calculated mass loss is 82.93%. The remaining
7
3
3
copper carbonate (M.wtꢀ
the product of thermal decomposition by means of
mass spectra (m/zꢀ123, RI. 59.06%).
/123.5) was confirmed as
/

G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á
/3178
3175
tively, which may be attributed to the decomposi-
tion of residual part of ligand molecules and
removal of [C H N O ] and formation of CdO
The anhydrous BIAAP complexes show great
thermal stability up to 215 8C and in the second
and subsequent stages, the decomposition and
combustion of the BIAAP molecules in the com-
plexes occur. The natures of the intermediates
formed in the other subsequent steps are proposed
and they give violent decomposition to give the
respective metal oxides or carbonate as the final
products. The formation of metal oxides or
carbonate was confirmed by mass spectra.
2
1
31
7
2
(
(
M.wtꢀ
m/zꢀ128, RIꢀ
In general, the stages of thermal decomposition
/
128) as illustrated in TG and mass spectra
/
/
10.62%).
of the complexes can be written as shown in
Scheme 1. The estimated mass losses of the
dehydration step are consistent with the calculated
data (Table 2).
Fig. 2. Thermal analysis (TG and DTA) of BIAAP complexes: (d) Cu (II); (e) Zn (II) and (f) Cd (II).

3176
G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á3178
/
the 3d- series of d-block elements, for the first
decomposition step of their complexes with
3
ꢁ
5
(d ), Ni
2ꢁ
8
(d )
BIAAP. The complexes of Fe
2
ꢁ
9
and Cd (d ) with BIAAP are present on the top
peaks of the energy curve. This means that these
complexes are stable at the beginning of the
decomposition than those on the bottom of the
2
ꢁ
7
2ꢁ
9
2ꢁ
10
(d )
curve (Co
(d ), Cu
(d ) and Zn
complexes). The same trend is gained for these
complexes at the second step of decomposition,
except they are become excited before going to
decompose. These qualitative explanations of
results mean also that the thermal stability is
mainly related to the stereo-structure of the
complexes and the electronic configuration of the
d-block elements. Therefore, after calculation of
Scheme 1. General equations for the decomposition of
BIAAPÁmetal complexes.
/
3
.4. Relation between thermal stability of the
hydrated complexes and initial temperature of
decomposition
In order to check the thermal stability of
complexes in the solid state, initial temperatures
of the decomposition of the anhydrous complexes
were compared. A plot of the initial decomposition
temperatures of the anhydrous complexes and the
corresponding reciprocal ionic radii of the di- and
tri-valent metal ions against the atomic number is
shown in (Fig. 3). The reciprocal of the ionic radii
of the divalent metal ions decreases from Fe(III) to
Co(II) with the decrease of initial temperatures of
decomposition. While the reciprocal of the ionic
radii increases from Co(II) to Ni(II) and the
thermal stabilities of these complexes also in-
creases. The same trend appears in comparing
between the thermal stabilities and the reciprocal
of ionic radii from Ni(II) to Cd(II) which decreases
from Ni(II) to Cd(II). It is evident that the thermal
stabilities of the complexes increase as the ionic
radii decreased [15,16]. From the above results, it
is qualitatively concluded that the thermal stability
of the complexes follow the order Ni(II)ꢀ
/
Cu(II)ꢀZn(II)ꢀFe(III)ꢀCo(II)ꢀCd(II). The
/
/
/
/
corresponding reciprocal ionic radii of the tri and
divalent metal ions against the atomic number
exhibit the same definite trend.
On the other hand Fig. 4 shows the change of
E* and DG* with the increase of atomic number in
Fig. 3. Initial temprature of hydrated complexes and recipro-
cals of ionic radii of di- and tri-valent metal ions vs. atomic
number.

G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á
/3178
3177
pairing up energy P and energy of splitting of
metal orbitals in octahedral D and tetrahedral D
in strong environment, those elements of Fe (d )
0
t
3
ꢁ
5
5
0
2ꢁ
8
6
2
(
t g eg , D ꢀ
0
/
ꢂ
/
10/12ꢂP), Ni (d ) (t g eg ,
/
2
0
2
2
ꢁ
9
6
3
D ꢀ
/
ꢂ
/
6/12ꢂ
/
2P) and Cd (d ) (t g eg , D ꢀ
/
ꢂ
/
2
t
3
/12) are stable due to they have high pairing up
2
ꢁ
7
6
1
energy. The other elements Co
2
(d ) (t g eg ,
2
ꢁ
9
6
3
D ꢀ
/
ꢂ
/
9/12), Cu
2
(d ) (t g eg , D ꢀ
/
ꢂ
/
3/12ꢂ
/
0
2
0
ꢁ
10
6
4
2
less stability due to the less pairing effect. Fe
P) and Zn
(d ) (t g eg , D ꢀ
/
0) have the
3
2
t
ꢁ
is
present in the middle; Cd is present in the top of
2
ꢁ
2
ꢁ
the curve while Zn
This may be due to the fact that Fe
is present at the bottom.
3
ꢁ
has a half
filled orbital due to competition between splitting
and pairing up effect and it’s odd electron system
2
ꢁ
while, Cd
(
may has completely filled d-orbital
2ꢁ
1
d ). The unusual behaviour of Cd
0
complex
may be also attributed to strong bonding of the
two BIAAP through their nitrogen and oxygen
donor atoms to this metal ions which make the
loss of these two ligands occurs in more than one
step. It can be concluded that, the relation between
E* and DG* vs. atomic number give a quantitative
interpretation to the thermal stability of the
complexes while the relation between the decom-
position temperature and (1/r) vs. atomic number
give a qualitative assignment. Also, the kinetic
data (Table 3) shows that, all the complexes have
Fig. 4. Activation energy and free energy change of di-and tri-
valent metal ions complexes of BIAAP vs. atomic number: (A)
at the first decomposition step; (B) at the second decomposition
step.
ꢂ
/
ve entropy which indicates that activated com-
plexes have more ordered systems than reactants.
Fig. 5. Proposed structural formulas of BIAAPÁmetal complexes.
/

3178
G.G. Mohamed et al. / Spectrochimica Acta Part A 58 (2002) 3167Á3178
/
[
[
2] Y. Ihara, R. Tsuchiya, Bull. Chem. Soc. Jpn 53 (1980)
614.
4
. Conclusion
1
3] D.A. Garnovskii, A.S. Antsyshkina, A.P. Sadimenko,
M.A. Porai-Koshits, O.A. Osipov, A.D. Garnovskii,
Dokl. Akad. Nauk. SSSR 296 (1987) 1119.
As a general conclusion, the BIAAP ligand
behaves as a monobasic ligand in 1:2 complex
with tridentate ONN donors derived from the
phenolic oxygen, a N of the azo group forming a
two binding chelating sites. In octahedral com-
plexes, the two extra positions are provided by the
pyridine like nitrogen of the imidazole moiety. The
proposed general structures are shown in Fig. 5.
The thermal stabilities of the complexes increase as
the ionic radii decrease [15,16]. From the above
results, it is quantitatively concluded that, the
thermal stability of the complexes follows the
[4] M. Cristina, A. Jose Garcia, J.R. Masaguer, Transition
Met. Chem. 12 (1987) 249.
[5] B. Lenarcik, J. Glowacki, M. Gabryszewski, R. Czopek,
Pol. J. Chem. 64 (1990) 43.
[6] A. Arquero, P. Souza, J.A. Garcia-Vazquez, J.R. Masa-
guer, Transition Met. Chem. 10 (1985) 424.
[7] P. Souza, J.A. Garcia-Vazquez, J.R. Masaguer, Transition
Met. Chem. 9 (1984) 318.
[8] M.A. Meudiola, J.R. Masaguer, C. Molleda, Synth. React.
Inorg. Met.-Org. Chem. 22 (1992) 955.
[9] A.W. Coats, J.P. Redfern, Nature 201 (1964) 64.
[
[
10] J.J. Fiol, A. Terron, D. Mulet, V. Merno, Inorg. Chim.
Acta 135 (1987) 197.
11] Z.M. Zaki, S.S. Haggag, A.A. Soayed, Spectrosc. Lett. 31
order
Co(II)ꢀ
Ni(II)ꢀ
/
Cu(II)ꢀ
/
Zn(II)ꢀ
/
Fe(III)ꢀ
/
/Cd(II). The corresponding reciprocal io-
(
1998) 757.
nic radii of the di- and tri-valent metal ions against
the atomic number exhibit the same definite
trends.
[
[
12] P.M. Drozdzewski, Spectrochim. Acta 44A (1988) 1297.
13] M.S. Nair, M.A. Neelakantan, S.S. Sunu, Theor. Anal.
Chem. 38A (1999) 1307.
[
[
14] G.G. Mohamed, Nadia E. El-Gamel, F.A. Nour El-Dien,
Synth. React. Inorg. Met.-Org. Chem. 31 (2) (2001) 347Á
58.
15] G.G. Mohamed, F.A. Nour El-Dien, N.E.A. El-Gamel, J.
Thermal Anal. Calorimetry 67 (2002) 135Á146.
/
3
References
/
[
1] J.C. Agroud, C. Disant, R. Massot, A. Cornu, Bull. Inf.
Sci. Tech. Commis. Energ. At. 230 (1979) 203.
[16] H. Icbudak, V.T. Yilmaz, H. Olmez, J. Thermal Analy. 53
(1998) 843.