Synthesis and characterization of Co(II), Ni(II) and Cu(II) complexes involving hydroxy antipyrine azodyes

Article abstract of DOI:10.1016/j.molstruc.2007.05.009

The complexes formed between some hydroxy antipyrine azodyes and Co(II), Ni(II) and Cu(II) ions were studied spectrophotometrically in solution. The stoichiometry and stability constants of the metal chelates were determined. The spectrophotometric determination of the titled metal ions and titration using EDTA were reported. The chelating behaviour of the azodyes was confirmed by preparing the solid chelates in which their structures are elucidated using molar conductance, elemental, thermogravimetric (TGA) analyses, IR, ESR and electronic spectra as well as the magnetic measurements. Kinetic parameters are computed from the thermal decomposition data. The electrical properties for the metal complexes are measured from which the activation energies are calculated.

Full text of DOI:10.1016/j.molstruc.2007.05.009

Available online at www.sciencedirect.com
Journal of Molecular Structure 875 (2008) 322–328
www.elsevier.com/locate/molstruc
Synthesis and characterization of Co(II), Ni(II) and Cu(II)
complexes involving hydroxy antipyrine azodyes
*
M. Gaber , A.M. Hassanein, A.A. Lotfalla
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
Received 26 January 2007; received in revised form 30 April 2007; accepted 4 May 2007
Available online 13 May 2007
Abstract
The complexes formed between some hydroxy antipyrine azodyes and Co(II), Ni(II) and Cu(II) ions were studied spectrophotomet-
rically in solution. The stoichiometry and stability constants of the metal chelates were determined. The spectrophotometric determina-
tion of the titled metal ions and titration using EDTA were reported. The chelating behaviour of the azodyes was confirmed by preparing
the solid chelates in which their structures are elucidated using molar conductance, elemental, thermogravimetric (TGA) analyses, IR,
ESR and electronic spectra as well as the magnetic measurements. Kinetic parameters are computed from the thermal decomposition
data. The electrical properties for the metal complexes are measured from which the activation energies are calculated.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Azoantipyrine; Complexes; Spectral and thermal studies
1. Introduction
2. Experimental
A lot of work has been reported on the spectrophoto-
metric studies of the heterocyclic azo compounds, their
metal complexes and analytical applications [1–14]. A
number of workers have used antipyrine and its derivatives
as ligands in synthesizing complexes with transition metal
ions [15]. Considerable studies have been devoted to azod-
yes derived from 4-aminoantipyrine and their metal com-
plexes [16]. Thus, we have initiated a program of
studying the metal complexes of some hydroxy azo com-
pounds derived from 4-aminoantipyrine.
The aim of the present work is to study of the most
favourable conditions for complex formation, stoichiome-
try and spectrophotometric determination of some metal
ions using the titled azodyes. The formation of the metal
complexes is confirmed by preparing the solid complexes
and studying their spectral, conductance, magnetic and
thermal properties.
2.1. Synthesis of azo compounds (L1AL3)
A solution of 4-aminoantipyrine (0.01 mol) was pre-
pared in a least amount of HCl (ꢀ2 ml, 10 M). A cold solu-
tion (0.01 mol) of NaNO2 below 5 ꢁC was then added to
the amine solution dropwise with continuous stirring. A
solution (0.01 mol) of resorcinol (L1), b-naphthol (L2) or
2-hydroxy-3-naphthoic acid (L3) was prepared by dissolv-
ing in NaOH solution (2–3 g of NaOH in 50 ml bidistilled
water), then colded to 0 ꢁC. The cold diazonium salt solu-
tion was added to the hydroxy solution dropwise with stir-
ring. The azodye was separated by slight acidification, then
filtered off, recrystallized from ethanol and dried in vacuo
over anhydrous CaCl2. The purity of the azodyes was con-
firmed by elemental analysis, m.p. constancy as well as by
IR spectral studies (L1: m.p. = 263 ꢁC, analysis: found, C
62.8; H 4.8; N 17.4%, Calcd for C17H16N4O3, C 62.96; H
4.93; N 17.28%; L2: m.p. = 165 ꢁC, analysis: found, C
69.9; H 4.8; N 15.3%, Calcd for C21H18N4O2, C 70.39; H
5.03; N 15.64%; L3: m.p. = 158 ꢁC, analysis: found, C
65.4; H 4.3; N 13.7%, Calcd for C22H18N4O4, C 65.67; H
*
Corresponding author. Tel.: +2 040 3350570; fax: +2 040 3350804.
E-mail address: abuelazm@yahoo.com (M. Gaber).
0022-2860/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.05.009

M. Gaber et al. / Journal of Molecular Structure 875 (2008) 322–328
323
4.48; N 13.93%. The azo compounds have the following
structures:
25–800 ꢁC with 10 ꢁC/min heating rate. IR spectra were
recorded over the 4000–200 cmꢁ1 range on a Perkin-Elmer
1430 spectrophotometer using KBr discs. Electronic spec-
tra in Nujol mull were determined using Shimadzu UV–
Vis 240 spectrophotometer. The magnetic measurements
were carried out at room temperature employing the Fara-
day balance technique. The equipment was calibrated with
Hg[Co(CNS)4]. Diamagnetic corrections were made using
Pascal’s constants. The ESR spectra of powder samples
were recorded by means of a Jeol model JES-FE 2XG
(Japan) spectrometer equipped with an E101 microwave
bridge. Diphenyl picrylhydrazide free radical (DPPH)
was used as a reference material (g = 2.0023). The electrical
conductivity measurements were made on a Super Meg-
ohmmeter (Model RM 170) electrometer. The samples
were pressed into discs of 13 mm diameter and 1.5–
1.6 mm thickness at a pressure ꢀ700 kg cmꢁ2. The surfaces
of the discs were painted carefully with a silver paste. The
temperature was measured in air using a Cu/CuNi Comark
thermometer placed closed to the sample.
X
OH
OH
O
O
N
N
HO
N
N
N
N
N
ph
ph
N
CH3
CH3
CH3
,
X= COOH ( L3 )
CH3
( L1 )
X=H ( L2 )
2.2. Synthesis of complexes
The solid complexes were synthesized by the addition of
the appropriate metal chloride, perchlorate or acetate solu-
tion (0.01 mol) in ethanol (10 ml) to the ethanolic solution
(20 ml) of the respective azodye (0.01 mol). The resulting
mixture was stirred under reflux for ꢀ2 h where upon the
complexes were precipitated. The solid chelates were fil-
tered off, washed several times with ethanol, dried, kept
in a desiccator over dried silica gel and then subjected to
elemental analyses. The analytical data along with the con-
ductance values of 10ꢁ3 M metal chelates in DMF at 25 ꢁC
are given in Table 1.
3. Results and discussion
3.1. Study of complexes in solution
The evaluation of the optimum conditions for complex-
ation of Co(II), Ni(II) and Cu(II) ions with antipyrine
azodyes includes a careful investigation of all factors
involved in the procedure such as pH, time, sequence of
addition. Selection of suitable wavelength is also included.
The results are listed in Table 2. The results indicate that
the optimum pH values recommended for the subsequent
studies of properties of the CuAL1 complexes are 9, 10
and 11 for chloro, acetato and perchlorato complexes,
respectively. For Cu(II) complexes of L2 and L3, the
optimum pH values are 4 and 8, respectively. Solutions
of pH 8–11 are the most suitable for the formation of
Co(II) and Ni(II) complexes with L1AL3. At the suitable
2.3. Measurements
The C, H and N elemental analyses were performed
using Heraeus CHN elemental analyzer. The metal con-
tents were estimated by compleximetric EDTA titration
(after complete decomposition of the complexes in aqua
regia several times) and atomic absorption technique. Con-
ductivity measurements were made using a Hanna 8733
conductometer. The thermogravimetric analysis (TGA) of
the solid complexes was performed using Shimadzu TG-
50 thermogravimetric analyzer in the temperature range
Table 1
Elemental analyses data, molar conductivities and magnetic values of the metal complexes
No.
Complex (colour)
Elemental analysis (a)
(b)
leff (BM)
%M
%C
%H
%N
1
2
3
4
5
6
7
8
9
[CoL1(AcO)(H2O)2]2H2O (faint brown)
[NiL1(AcO)(H2O)2]2H2O (faint brown)
[CuL1(AcO)(H2O)2]2H2O (reddish brown)
[CuL1Cl(H2O)2] (reddish brown)
[CuL1(ClO4)(EtOH)2] (reddish brown)
[CoL2(AcO)(H2O)2]H2O (brown)
[NiL2(AcO)(H2O)2]H2O (faint brown)
[NiL2Cl(H2O)2]2H2O (faint brown)
[CuL2(AcO)(H2O)2]H2O (brown)
[CoL3(AcO)]4H2O (brown)
11.3 (11.5)
11.2 (11.4)
12.0 (12.3)
13.7 (13.9)
10.8 (10.99)
10.9 (11.1)
10.8 (11.1)
10.9 (11.2)
11.8 (11.4)
10.0 (9.8)
44.4 (44.5)
44.2 (44.5)
43.7 (44.1)
44.3 (44.5)
43.8 (43.6)
51.9 (52.2)
51.8 (52.2)
47.8 (48.2)
51.3 (51.7)
48.7 (48.4)
50.2 (49.4)
51.5 (51.3)
3.4 (3.5)
3.4 (3.5)
3.3 (3.0)
3.4 (3.3)
4.6 (4.7)
3.6 (3.8)
3.5 (3.8)
3.0 (4.2)
3.5 (3.7)
3.4 (4.3)
3.5 (3.2)
3.6 (3.4)
10.7 (10.9)
10.6 (10.9)
10.5 (10.8)
11.9 (12.2)
9.9 (9.7)
10.2 (10.6)
10.3 (10.6)
10.8 (10.7)
10.4 (10.5)
9.5 (9.2)
12.9
10.8
10.8
19.9
20.3
13.3
11.4
19.3
11.3
12.9
12.2
11.9
4.7
2.9
1.8
1.82
1.8
4.9
2.95
2.85
1.79
4.7
–
10
11
12
[NiL3(AcO)]3H2O (orange brown)
[CuL3(AcO)]2H2O (reddish brown)
10.2 (10.0)
11.3 (11.0)
9.8 (9.4)
10.0 (9.8)
1.8
a, Calcd (found). b, Km (ohmꢁ1 cm2 molꢁ1).

324
M. Gaber et al. / Journal of Molecular Structure 875 (2008) 322–328
Table 2
Analytical data of the metal complexes of antipyrine azodyes
Lig.
L1
M2+
k (nm)
pH
Log b (MRM)
Log b (CVM)
e
Beer’s law up to M
SD
CC
1:1
1:2
1:1
1:2
Co
Ni
Cu
Cu
500
490
505
505
9.0
4.33
4.29
4.64
4.10
10.41
9.56
–
4.19
3.82
5.02
5.18
10.87
8.63
9.32
7.67
12,171
17,054
40,301
18,977
8 · 10ꢁ5
6 · 10ꢁ5
3.5 · 10ꢁ5
10 · 10ꢁ5
0.0003
0.006
0.006
0.022
0.999
0.988
0.994
0.994
9.0
10.0
–
9.05
L2
Co
Ni
Cu
Cu
510
495
500
505
9.0
8.0
4.0
–
4.86
4.79
4.74
–
9.87
10.21
10.31
–
5.23
8.89
5.29
4.41
–
–
–
–
–
–
–
–
–
–
–
–
22,040
19,210
3 · 10ꢁ5
0.0008
0.0007
0.996
0.996
4 · 10ꢁ5
L3
Co
Ni
Cu
Co
Ni
520
500
510
475
480
490
10.0
11.0
8.0
–
–
–
3.9
3.9
3.82
–
–
–
8.20
8.25
8.21
–
–
–
–
–
4.77
3.77
3.68
3.67
–
–
9.07
8.43
7.8
8.46
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Cu
23,422
4 · 10ꢁ5
0.0014
0.997
e, molar absorptivity (L molꢁ1 cmꢁ1); SD, standard deviation; CC, correlation coefficient.
wavelength the sequence of addition buffer—L1-metal and
L2 or L3-metal buffer are the most suitable.
The application of azodyes (L1AL3) as indicators for
spectrophotometric titration of Co(II), Ni(II) and Cu(II)
ions with EDTA has been ascertained. Cu(II) ion exhibits
a good response up to 23.2, 24.8 and 21.3 lg/ml for azod-
yes L1, L2 and L3, respectively. CoAL1 and NiAL1 com-
plexes show good response up to 16.5 and 15.6 lg/ml,
respectively.
Also, it was found that the complexes are completely
developed spontaneously and remain stable for more than
24 h. The stoichiometry of the metal complexes was inves-
tigated with the aid of the standard spectrophotometric
methods namely, mole ratio, MRM [17] and continuous
variation, CVM [18] methods. The results of the first
method indicate the formation of 1:1 and 1:2 (M:L) com-
plexes, except for CuAL1 complex at pH 10 which forms
1:1 complex only. The second method showed the forma-
tion of 1:1 and 1:2 (M:L) complexes, except for complexes
CuAL1 at pH 10, CuAL2, CuAL3 at pH 8, CoAL2 and
NiAL2 at pH 8 where only 1:1 complexes were formed.
The logarithmic stability constants of the formed com-
plexes were calculated from the data of the mole ratio
and continuous variation methods applying the Harvey
and Manning equation [19]. The results listed in Table 2
show that 1:2 (M:L) complexes are more or less twice as
stable as 1:1 (M:L) complexes.
3.2. Characterization of the solid complexes
The solid complexes of azodyes (L1AL3) with Co(II),
Ni(II) and Cu(II) ions were prepared and investigated by
elemental analysis, thermal analysis (TGA), IR, ESR, elec-
tronic spectra, magnetic measurements as well as conduc-
tance measurements. The complexes are air stable and
soluble in DMF or DMSO. The higher melting points of
the complexes than those of the ligands can be taken as
an evidence for the bonding to the metal ion with chelate
ring formation. The values of molar conductance in
10ꢁ3 M DMF (Table 1) indicate that the complexes are
non-electrolyte [20], i.e., the chloride, perchlorate and ace-
tate ions are involved inside the coordination sphere. The
presence of chloride ion inside the coordination sphere
was also confirmed by the chemical reaction with AgNO3
where precipitation of chloride ion was not observed.
Addition of the FeCl3 solution to the solution of the aceta-
to complexes dose not give red brown, confirming coordi-
nation of the acetate ion on complex formation. These
results are further confirmed from IR spectra.
At suitable pH characteristic for each system, the linear-
ity of the absorbance–concentration relation was satisfied
up to 8 · 10ꢁ5
, , ,
6 · 10ꢁ5 3.5 · 10ꢁ5 3 · 10ꢁ5 and
4 · 10ꢁ5 M for CoAL1, NiAL1, CuAL1, CuAL2 and
CuAL3, respectively. Without using buffer solutions the
relation was satisfied up to 10 · 10ꢁ5 and 4 · 10ꢁ5 M for
CuAL1 and CuAL2 complexes, respectively.
The standard deviation values are very low indicating
the high reproducibility coefficient of the results with high
correlation coefficient. The high molar absorptivity values
indicate the sensitivity of the present method for the spec-
trophotometric determination of the metal ion. CuAL1
complex has higher e value indicating high sensitivity more
than the CuAL2 and CuAL3 complexes. For one and the
same azodye, CuAL1 complex has higher molar absorptiv-
ity value than CoAL1 and NiAL1 complexes.
The mode of bonding of the azodyes complexes was elu-
cidated by investigating the IR spectra of the metal com-
plexes as compared with those of the free azodyes. The
N@N bands at 1488, 1499 and 1496 cmꢁ1 of the free dyes
L1, L2 and L3, respectively, exhibit a shift to higher wave
number on complexation which may taken as evidence
for the participation of the N@N group in coordination.

M. Gaber et al. / Journal of Molecular Structure 875 (2008) 322–328
325
This is supported by the appearance of a new band in the
region 423–467 cmꢁ1 due to t(MAN) [21]. The t(C@O) bands
at 1668, 1634 and 1630 cmꢁ1 for azo compounds L1, L2
and L3, respectively, exhibit a shift to lower value on com-
plex formation [22]. The appearance of new bands in the
region 503–523 cmꢁ1 due to t(MAO) supports the coordina-
tion of the C@O group to the metal ions [23]. Further
more, broad bands for all chelates, except complex 5, were
observed within the wave number range 3380–2474 cmꢁ1
attributed to the stretching frequency of water molecules.
The IR spectrum of complex 5 exhibits a strong splitted
bands at 1189, 1110 and 1042 cmꢁ1 assignable to coordi-
nated nature of the perchlorate anion [24]. The acetate
group in the acetato complexes act as monodentate ligand
lies in the range expected for tetrahedral Co(II) complexes
of a high spin type, i.e., this value is in agreement with the
spin value for three unpaired electrons (3.89 BM) [29].
The bands at 15,385 and 19,230 cmꢁ1 may be assigned to
the 4A2 fi 4T1(F) (t2) and 4A2 fi 4T1(P) (t3) transitions,
respectively, supporting the tetrahedral geometry [30].
For the Ni(II) complexes (2, 7 and 8), the spectra display
two bands within the ranges 15,152–15,625 and 19,230–
3
20,000 cmꢁ1 assignable to A2g(F) fi 3T1g(F) (t2) and
3A2g(F) fi 3T1g(P) (t3) transitions, respectively. These val-
ues are expected for the octahedral Ni(II) complexes [31].
The observed magnetic moments of the Ni(II) complexes
in the range 2.81–2.94 BM confirm the octahedral structure
of these complexes [32].
[25] and this is evidenced by the difference (140–145 cmꢁ1
)
)
The Ni(II) complex (11) exhibited a band at 19,608 cmꢁ1
corresponding to square planar geometry. This band may
between the tas (1560–1585 cmꢁ1) and ts (1420–1440 cmꢁ1
1
vibrations. The presence of the coordination water is sup-
ported by the presence of bands within the ranges 3420–
3380, 1610–1600 and 970–950 cmꢁ1 due to OH stretching,
HOH deformation and HOH rocking [25]. The presence
of the bands within the range 1697–1728 cmꢁ1 indicates
that the COOH group of L3 does not contribute to the
complex formation.
be assigned to A1g (D) fi 1B2g (G) transition. This com-
plex shows the diamagnetic behaviour indicating the
square planar environment around the Ni(II) ion.
The solid state spectra of the Cu(II) complexes (3–5 and
9) showed two bands at 19,417–18,939 and 17,544–
2
2
16,949 cmꢁ1, assigned to B1g fi 2Eg and B1g fi 2B2g
transitions, respectively [30], which are consistent with
distorted octahedral geometry. The electronic spectrum of
Cu(II) complex (12) exhibits a band at 16,950 cmꢁ1 which
is agreement with those observed for square planar
complex. The Cu(II) complexes have normal magnetic
moments values (1.85–1.8 BM) corresponding to the
mono-nuclear Cu(II) complexes [33].
The Co(II) complexes exhibited electronic spectral
bands at 15,625 and 18,182 cmꢁ1 for complex (1) and
15,748 and 18,519 cmꢁ1 for complex (6). These bands are
assigned to 4T1g(F) fi 4A2g(F)(t2) and 4T1g(F) fi
4T1g(P)(t3) transitions, respectively, characteristic of octa-
hedral geometry [26]. The room temperature magnetic
moment values for Co(II) complexes 1 and 6 are 4.79
and 4.98 BM, respectively, which are higher than the spin
only value due to orbital angular momentum contribution
in d7 system and closer to the value required for an octahe-
dral structure [27]. The relative strength of the ligand and
geometry of the complexes can be illustrated by calculating
the parameters of the ligand field splitting (10Dq) and of
interelectronic repulse (B). The values of 10Dq (t1) and B
are 8326 and 794 for complex 1 and 7350 and 815 for com-
plex 6. The ratio (t2/t1) is found to be ꢀ2.14 for complexes
1 and 6, as required for the octahedral Co(II) complexes
[28]. The values of the Nephelauxetic parameter b are
0.71 and 0.73 for complexes 1 and 6, respectively. These
values indicate the appreciable covalent character of the
metal ligand bond.
The ESR spectra of the Cu(II) complexes (3, 4, 5, 9 and
12) have been recorded as polycrystalline samples at room
temperature (25 ꢁC). The observed data show that for com-
plexes 3–5 and 9, gi = 2.229–2.266 and g^ = 2.055–2.065,
Table 3. The calculated gav values = (gi + 2g^)/3 are in
the range 2.112–2.132. The lowest g value was more than
2 consequently, to assign the tetragonal distorted symmetry
associated with dX2
ground state rather than d2Z [34]. The
ꢁY 2
value of the exchange interaction (G) between the Cu cen-
ters in a polycrystalline solid has been calculated using the
relation G = (gi ꢁ 2.0023)/(g^ ꢁ 2.0023) [35]. If G > 4, the
exchange interaction is negligible, while G < 4 indicates
considerable exchange interaction in the solid complexes.
The results listed in Table 3 indicate that there is no
exchange interaction between Cu(II) ions. Kivelson and
Neiman [36] noted that for an ionic environment gi > 2.3
and for a covalent environment gi < 2.3. All complexes
The Co(II) complex (10) is paramagnetic with room tem-
perature effective magnetic moment (4.1 BM) value which
Table 3
Electronic and ESR spectral parameters for Cu(II) complexes
No.
d–d Transition (cmꢁ1
)
gi
g^
gav
G
kk2
k?2
k2
D1
D2
3
4
5
9
12
19,230
19,417
19,305
18,939
19,800
17,391
17,543
17,391
16,949
17,400
2.229
2.229
2.229
2.266
2.260
2.054
2.058
2.055
2.065
2.060
2.112
2.115
2.113
2.132
2.127
4.24
4.00
4.20
4.10
4.33
0.595
0.60
0.595
0.675
0.677
0.60
0.599
0.635
0.608
0.703
0.686
0.653
0.614
0.717
0.689

326
M. Gaber et al. / Journal of Molecular Structure 875 (2008) 322–328
Table 4
Thermal analysis data of the complexes of antipyrine azo compounds
No.
Hydrated water
Coordinated water
Decomposition
Temp. (ꢁC)
% Found (calcd)
Temp. (ꢁC)
% Found (calcd)
Temp. (ꢁC)
% Found (calcd)
1
2
3
4
5
6
9
10
11
12
a
105
124
105
–
6.9 (7.1)
6.7 (7.0)
7.1 (7.0)
–
200–250
325–400
200–230
Up to 320a
280–300b
175–250, 300c
125–314c
–
7.5 (7.6)
7.3 (7.6)
6.97 (7.0)
16.0 (15.8)
15.0 (14.9)
6.8 (7.0), 12.5 (12.4)
17.3 (17.9)
–
–
–
250–556
400–600
230–650
320–750
325–700
300–600
314–800
200–500
150–500
200–500
11.3 (11.5)
11.8 (11.4)
12.2 (12.3)
13.5 (13.9)
10.5 (10.2)
10.9 (11.1)
11.86 (11.9)
9.9 (10.0)
–
–
105
125
100
95
3.5 (3.4)
3.5 (3.4)
11.9 (12.3)
9.5 (9.43)
6.24 (6.43)
–
–
9.99 (10.2)
11.1 (11.3)
100
Loss of H2O and Cl content.
Loss of ethanol.
Loss of H2O and/or acetate.
b
c
exhibit gi < 2.3 suggesting covalent character of the Cu–
ligand bonding in the present complexes. The g values of
copper(II) complexes with a B1g ground state (gi > g^)
uated graphically by using Coats–Redfern [38] method
using the relation:
2
1ꢁn
lnf½1 ꢁ ð1 ꢁ aÞ =½T 2ð1 ꢁ nÞꢂg ¼ ½M=Tꢂ þ B for n ¼ 1
may be expressed [37] by
lnf½ꢁ lnð1 ꢁ aÞ=T2g ¼ ½M=Tꢂ þ B for n ¼ 1;
k2k ¼ ðgk ꢁ 2:0023Þ D2=8k; k?2 ¼ ðg? ꢁ 2:0023ÞD1=2k;
k2 ¼ ½k2k þ 2k2?ꢂ=3;
where k2k and k2? are the parallel and perpendicular compo-
nents, respectively, of the orbital reduction factor k, k is the
spin–orbit coupling constant (ꢁ828 cmꢁ1) for free copper,
-13.2
-13.5
-13.8
2
D1 and D2 are the electronic transition B1g fi 2Eg and
2B1g fi 2B2g, respectively. The values listed in Table 3
showed that k2k < k?2 which is a good evidence for the as-
2
sumed B1g ground state. The lower values of k2 than the
unity are indicative of their covalent nature which in agree-
ment with the conclusion obtained from the values of gi.
The results of TGA are collected in Table 4. The metal
chelates degrade mainly in two or three stages from which
the percentage of water and the metal content were calcu-
lated. The first step corresponds to the loss of lattice water.
The second step represents the removal of coordinated
water and/or chloride (complex 4), ethanol (complex 5),
acetate (complexes 6 and 9). The third weight loss step cor-
responds to the decomposition of the complexes with the
formation of the metal oxide as a final product from which
the percentage of the metal content was calculated and
compared with those obtained from EDTA and atomic
absorption spectra.
-14.1
1
2
3
-14.4
-14.7
1.2
1.4
1.6
1.8
1000/T
-13.35
-13.50
-13.65
-13.80
9
8
6
The thermal decomposition processes underlying the
TGA of complexes 1–3, as example, can be schematically
represented as:
ꢃC
½MLðAcOÞðH2OÞ ꢂ2H2O 105–124
!
½MLðAcOÞðH2OÞ2ꢂ
2
ꢃ
200–400 ꢃC
230–650
!
½MLðAcOÞꢂ
!
C MO
The final stage of decomposition of selected complexes was
studied in more details. The kinetic parameters such as,
activation energy (E), enthalpy (DH), entropy (DS) and free
energy of the decomposition (DG) as well as the order of
the reaction (n) and the pre-exponential factor (A) are eval-
1.0
1.2
1.4
1000/T
Fig. 1. ln[ꢁln(1 ꢁ a)/T2 vs. (1000/T) plot for the final stage of decomposi-
tion of complexes 1–3, 6, 8 and 9.

M. Gaber et al. / Journal of Molecular Structure 875 (2008) 322–328
327
Table 5
The kinetic and thermodynamic data of the thermal decomposition of azodye complexes
No.
n
E (kJ molꢁ1
)
A (sꢁ1
)
ꢁDS (J molꢁ1 Kꢁ1
)
DH (kJ molꢁ1
)
DG (kJ molꢁ1
)
1
2
3
4
6
8
9
1
1
1
0.66
1
1
1
19.62
24.64
15.40
18.13
11.64
28.80
35.92
1.25 · 109
2.20 · 108
7.00 · 108
1.00 · 109
7.30 · 108
1.80 · 108
1.94 · 108
77.5
92.8
81.6
80.4
82.7
95.2
96.1
14.0
18.4
10.3
10.4
5.6
66.1
87.9
60.3
86.7
65.4
99.5
121.3
22.0
27.8
Table 6
Electrical conductivity data of azodye [L1] and its metal complexes
Comp.
Metallic
Semi.
Non temp. (ꢁC)
Phase transfer (ꢁC)
Temp. (ꢁC)
Ea (eV)
Temp. (ꢁC)
Ea (eV)
L1
2
40–103
158–227
30–50
0.11
0.10
0.28
103–130
130–158
50–91
91–132
89–135
0.36
0.08
0.17
0.46
0.35
–
–
130
91
132–227
–
135–253
–
109–170
–
34–60
100–189
140–186
–
3
37–89
0.18
0.03
0.01
0.05
–
–
70
4
37–50
50–70
70–109
60–100
0.07
0.02
0.01
5
182–253
186–222
–
–
92
6
40–92
92–140
0.02
0.03
Semi., semiconducting. Non, nonconducting.
where a is the fraction of the material decomposed at a gi-
ven temperature, M = ꢁE/R and B = ln[AR/QE], R is the
gas constant and Q is the heating rate.
X
Y
O
M
O
nH2O
Ph
HO
N
A plot of the left-hand side of these equations against 1/
T for different values of n, have been tested; Fig. 1. The cor-
rect value of (n) for the thermal reaction is the one which
gives the best straight line. From the slope and intercept,
the values of E and A were determined, respectively. The
other kinetic parameters were determined using the stan-
dard equations [39]. According to the data listed in Table
5 the complexes have ꢁve entropy which indicates that
the activated complexes have more ordered systems than
reactants and that the reactions are slower than normal
[40].
X
N
N
N
CH3
H3C
X = H2O , Y = AcO , n = 2 for complexes 1,2,3
X = H2O , Y = Cl , n = 0 for complex 4
X = EtOH , Y = ClO4 , n = 0 for complex 5
X
Y
For complexes 6, 8 and 9, the lower thermal stability of
the Co(II) complex 6 than the other two complexes may be
due to the higher repulsion between the multiple bonding
electron pairs (six bonds)] in the valence shell of cobalt as
well as to higher repulsion obtained by non-bonded pairs
of electrons on the axial donating oxygen of H2O molecule
and the bonded electrons [41].
O
Z
M
O
nH2O
Ph
N
X
N
N
N
CH3
H3C
The results of the electrical conductivity of azodye, L1,
and its Co(II), Ni(II) and Cu(II) complexes are listed in
Table 6. The discontinuity in the semiconducting region
can be ascribed to a molecular rearrangement or to crystal-
lographic transitions. The metallic behaviour observed in
the low temperature range may be attributed to the crea-
tion of some crystal voids and defects that function as traps
Z = H or COOH
X = H2O , Y = AcO ,
X = H2O , Y = Cl ,
n = 1 for complexes 6,7,9
n = 2 for complex 8
X = 0 ,
Y = AcO ,
n = 4 ,3 , 2 for complexes 10, 11, 12
Fig. 2. The structures of the metal complexes.

328
M. Gaber et al. / Journal of Molecular Structure 875 (2008) 322–328
F.A. El-Saied, M.I. Ayad, R.M. Issa, S.A. Aly, Pol. J. Chem. 75
(2001) 941;
F.A. El-Saied, M.I. Ayad, R.M. Issa, S.A. Aly, Pol. J. Chem. 75
(2001) 773, and references therein.
for the current carriers [42]. The temperature range in
which the conductivity values remain constant indicates
that the energy is consumed in the phase transition rather
than in the thermal agitation of electrons [42].
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4. Conclusion
The design and synthesis of a new hydroxy azodyes from
4-aminoantipyrine have been demonstrated. The IR spec-
tra of the complexes indicate that the azo-compounds coor-
dinate to the divalent metal ions (Co, Ni and Cu) through
ONO as tridentate ligands. From the electronic, ESR spec-
tra, conductance, magnetic moments and thermal analyses
measurements, the structures of the complexes are given in
Fig. 2. The reaction between the azodyes and Co(II), Ni(II)
and Cu(II) ions are also studied spectrophotometry in solu-
tion. The optimum conditions for complex formation, stoi-
chiometry and stability constants are determined. The
results indicate that the investigated azodye can be used
as an indicator for spectrophotometric determination of
Co(II), Ni(II) and Cu(II) ions.
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