Synthesis, spectral and thermal studies of Co(II), Ni(II) and Cu(II) complexes 1-(4,6-dimethyl-pyrimidin-2-ylazo)-naphthalen-2-ol

Article abstract of DOI:10.1016/j.saa.2005.02.039

The electronic absorption spectra of 1-(4,6-dimethyl-pyrimidin-2-ylazo)- naphthalen-2-ol is studied in organic solvents of different polarity as well as in buffer solutions of varying pH values at different temperatures and different ratios of methanol. T

Full text of DOI:10.1016/j.saa.2005.02.039

Spectrochimica Acta Part A 62 (2005) 694–702
Synthesis, spectral and thermal studies of Co(II), Ni(II) and Cu(II)
complexes 1-(4,6-dimethyl-pyrimidin-2-ylazo)-naphthalen-2-ol
∗
M. Gaber , M.M. Ayad, Y.S.Y. El-Sayed
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
Received 8 December 2004; received in revised form 21 February 2005; accepted 22 February 2005
Abstract
The electronic absorption spectra of 1-(4,6-dimethyl-pyrimidin-2-ylazo)-naphthalen-2-ol is studied in organic solvents of different polarity
as well as in buffer solutions of varying pH values at different temperatures and different ratios of methanol. The probable structure of the
1
azodye has been assigned on the basis of spectral studies (IR and H NMR). The effect of Co(II), Ni(II) and Cu(II) ions on the emission spectrum
of the free azodye is also assigned. The stoichiometry of the metal complexes is determined spectrophotometrically and conductometrically.
Novel complexes of Co(II), Ni(II) and Cu(II) with the pyrimidine azodye have been synthesized and characterized on the basis of elemental
analyses, molar conductance, magnetic susceptibility measurements, IR, electronic as well as ESR spectral studies The thermal decomposition
of the metal complexes is studied by TGA and DTA techniques. The kinetic parameters like activation energy, pre-exponential factor and
entropy of activation are estimated.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Azopyrimidine; Complexes; Spectral; Thermal studies
1
. Introduction
as ligand, as well as its Co(II), Ni(II) and Cu(II) metal
complexes.
Azodyes have the remarkable property of forming com-
The coordination behaviour of the azodye towards transi-
tion metal salts is investigated via the elemental analysis, IR,
electronic, ESR, magnetic moments and molar conductance
measurements. The thermal behaviour of the thermal decom-
position was also studied and the thermodynamic parameters
were reported.
plexes and serve as the most important class of N-donor
ligands. Azodyes and their metal complexes are becoming
increasing important as analytical agents [1]. Heterocyclic
azo compounds have been used to establish low oxida-
tion state of different metals ions [2]. Recent years have
a great deal of interest in the synthesis and characteriza-
tion of azo compounds [3] as well as their metal complexes
[
4]. Several transition metal azodye complexes have been
2
. Experimental
found to possess interesting biological properties [5]. In view
of the biological significance and coordination behaviour
of azo compounds, it was considered worthwhile to pre-
pare and study azodye complexes of Co(II), Ni(II) and
Cu(II) ions. In the present article we report the prepara-
tion and characterization of a hydroxy pyrimidine azodye
2.1. Synthesis of azodye ligand (L)
2-Amino-4,6-dimethyl pyrimidine (0.01 mol) was mixed
◦
with ∼3 ml HCl (10 M) and diazotized below 5 C with
(0.01 mol) NaNO2. The resulting diazonium chloride was
coupled with an alkaline solution of ␤-naphthol (0.01 mol)
below 0 C. The azodye product was filtered off, recrys-
tallized from ethanol and dried over vacuum CaCl2. The
purity of the azodye was firstly checked by the mp con-
∗
Corresponding author. Present address: Chemistry Department, Faculty
◦
of Science, King Fasial University, P.O. Box 1759, Al Hofuf 31982, Saudi
Arabia. Tel.: +966 509810818; fax: +966 35886437.
E-mail address: abuelazm@yahoo.com (M. Gaber).
1
386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.02.039

M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
695
Table 1
Analytical data of the isolated complexes
b
−1
Complex Formula
% Elemental analysisa
Λm
µeff (BM) IR spectra (cm
)
Electronic
spectra (cm 1)
−
C
H
N
Metal
N
N
M
O
M
N
1
2
3
4
5
6
[CoL(AcO)(H2O)3]H2O 46.4 (46.0) 5.1 (4.6) 12.0 (11.7) 12.4 (12.4)
0.05 4.82
0.05 4.95
0.05 2.74
0.06 2.85
0.05 1.20
0.04 1.69
1399 532
1396 484
1386 580
1462 520
1398 524
1459 569
453
455
424
425
433
437
17857, 20000
17857, 19230
15625, 25923
15625, 23809
20000
[CoL2(H2O)2]
59.2 (58.8) 4.6 (4.2) 17.3 (16. 9)
8.9 (8.9)
10.5 (9.9)
8.0 (7.9)
[NiL(AcO)(EtOH)3]H2O 52.4 (51.7) 6.5 (6.0) 10.2 (9.6)
[NiL2(EtOH)2]H2O
[CuL(AcO)H2O]
[CuL2]
59.8 (59.3) 5.5 (5.0) 11.1 (10.8)
51.7 (51.0) 4.3 (4.0) 13.4 (13.2) 15.2 (15)
62.2 (61.8) 4.2 (3.8) 18.1 (17.7) 10.4 (10.1)
19608
AcO = acetate.
a
Calc. (found).
b
−1
2
−1
ꢀ
cm mol .
stancy, elemental analyses and finally by spectral methods
lated from Pascal constants. The thermal analysis (TGA and
DTA) were carried out using computerized Shimadzu TG-50
◦
(mp 85 C; analysis found: C, 68.8; H, 4.9; N, 19.7%, Cal.
◦
◦
For C H14N4O, C, 69.0; H, 5.04; N, 20.1%
thermal analyzer up to 800 C at a heating rate 10 C/min.
in an atmosphere of N2. Microanalyses of C, H and N were
made using Heraeus CHN elemental analyzer. The Co(II),
Ni(II) and Cu(II) contents were estimated by complexometric
EDTA titration (after complete decomposition of the com-
plexes in aqua regia several times) using Xylenol Orange
16
(pH 6), Eriochrome Black T (pH 10) and Fast Sulphon Black
F (5 ml conc. NH3).
2
.2. Synthesis of metal complexes
3. Results and discussion
A solution of the appropriate metal acetate (0.01 mol) in
EtOH (10 ml) was mixed with a solution of the azodye (0.01
or 0.02 mol) in the same solvent (30 ml) and the resulting
mixture was stirred under reflux for ∼12 h where upon the
complexes precipitated after cooling. The solid complexes
were then filtered off, washed several times with ethanol,
dried and kept in a desiccator over dried silica gel. The ana-
lytical and spectral data are collected in Table 1.
3.1. Characterization of the ligand
The electronic spectrum of the pyrimidine azodye (L) in
methanol shows mainly three bands at 210 (medium energy
*
1
1
␲–␲ transition within the phenyl moiety L – A), 260 nm
a
*
1
1
(low energy ␲–␲ transition within the phenyl ring L – A)
b
and 375 nm (CT band within the whole molecule). The appli-
cation of the dielectric relations given by Gati and Szalay [6],
Suppan [7] or the molecular-microscopic solvent parameters
π (dipolarity), Z [8] and ET values [9] show non-linear rela-
tions indicating that the change in the position of the CT
band is to be considered as being the resultant of the differ-
ent factors governed by the various parameters. This may be
additive, counter-acting or may even cancel each other.
The electron absorption spectrum of the azodye (L) in
universal buffer solutions containing different percentage of
methanol is recorded. The spectra are approximatelythe same
within the pH range 2–5. In the pH range 6–7.5, only one
band is observed with λmax at 380 nm which splitted to two
bands at pH ≥ 8, one at 380 and the other at 420 nm. The pKa
value of the azodye is calculated using the recommended
methods at two different wavelengths [10]. The pKa values
decrease with increasing the percentage of methanol (Fig. 1).
The ionization of the azodye occurs in two steps. The first
step represents the ionization of the protonated form (pH 2–7)
while the second step involves the ionization of the deproto-
nated form at pH = 7. The ionization of both forms increases
2
.3. Measurements
The IR spectra were recorded as KBr discs on a Perkin
−
1
Elmer 1430 spectrophotometer in the 4000–200 cm range.
The electronic spectra were recorded using a Shimadzu 240
1
UV–vis spectrometer. The H NMR spectrum of the ligand
was performed using a Varian EM 390-90 NMR spectrometer
6
in d -DMSO as solvent using tetramethylsilane (TMS) as an
internal standard. The X-band ESR spectra of the complexes
were recorded at room temperature on a JOEL-X-band spec-
trometer equipped with an E 101 microwave bridge. Diphenyl
picryl hydrazide free radical (DPPH) was used as inter-
nal standard (g = 2.0036). The fluorescence measurements
were recorded with the aid of Shimadzu RF-510 spectroflu-
orometer; excitation and emission bandwidth was 10 nm,
scan rate 100 nm/min and excitation wavelength was 370 nm.
Magnetic susceptibilities were measured by employing the
Faraday balance technique. The equipment was calibrated
with Hg[Co(CNS)4]. Diamagnetic corrections were calcu-

6
96
M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
Fig. 1. Effect of vol.% of methanol on pKa values on azodye (L).
with increasing the methanol ratio due to the solvation effect
which stabilizes the ionized form.
OH group. The stretching vibration of the C N group of
−1
the pyrimidine ring appears at 1534 cm . The stretching
−1
The electronic spectra of the azodye in solutions of vari-
ous pH values and containing 50% methanol are recorded at
vibration of the azo group is observed at 1422 cm
.
A further support for the structure of the azodye is gained
◦
1
different temperatures (25–50 C). The pKa values increase
from the H NMR spectrum. The spectrum exhibits signals
with rising the temperature (Fig. 2). The thermodynamic
parameters ꢁG, ꢁH and ꢁS were calculated using the
data estimated from (Fig. 3). The negative value of ꢁH
at 2.2 and 9.15 ppm corresponding to the protons of CH3 and
OH groups, respectively. The multisignals within the range
7.4–8.15 ppm can be assigned to the aromatic protons.
−
1
(
−80.6 kJ mol ) reveals that the dissociation of the azodye
(L) is exothermic in 50% methanolic solution and the value
3.2. Study of complexes in solution
−
1
of ꢁS (−405.5 J mol ) due to increasing order as result of
−
1
solvation process. The positive value of ꢁG (45 kJ mol
)
Investigations were carried out to establish the most favor-
indicates that the dissociation of the azodye (L) is not spon-
taneous.
able conditions to give a highly color intensity and to achieve
maximum color development in the quantitative determina-
tion of the metal ions. The influence of each of the following
variables on the complexation reaction was tested.
The IR spectrum of the azodye exhibits a broad band at
−
1
3
405 cm corresponding to the stretching vibration of the
Fig. 3. pKa − 1000/T relationship for L in 50% (v/v) methanol-universal
Fig. 2. Effect of temperature on the pKa values of L in 50% methanol.
buffer media.

M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
697
The optimum pH for the complex formation was detected
by scanning the absorption spectra of the complexes using
different types of buffer solutions (universal, borate, acetate
and phosphate). The acetate buffer solutions of pH values
of the method for the determination of the metal ions. It
is clear that the molar absorptivity values follow the order
Co–L > Ni–L > Cu–L complexes. Ringbom [13] concentra-
tion range was also determined and the results are listed in
Table 2.
4
.5, 5.5 and 6.3 are suitable for Co(II), Ni(II) and Cu(II)
complexes, respectively. The complexes are formed insta-
neously and the color of the complexes is stable for 24 h.
Temperature exhibits no apparent influence on the color
development. The suitable wave length for the complex for-
mationwasalsodeterminedandfoundat440, 450and480 nm
for Co(II), Ni(II) and Cu(II) complexes, respectively. The
results of three different sequences of additions to select the
most suitable one for developing the color of the complexes
show the sequences, metal–buffer–azo, azo–metal–buffer
and azo–buffer–metal for Co(II), Ni(II) and Cu(II) com-
plexes, respectively.
The spectrophotometric titration of Co(II), Ni(II) and
Cu(II) ions with EDTA using azodye L as an indicator was
carried out in the presence of suitable buffer of the recom-
mended pH values. For this purpose, a series of methanolic
−
3
solutions containing 1.0 ml of 10 M of azodye, 0.25 ml of
−
4
10 M metal ion, 2.5 ml of the buffer of the recommended
pH value (taken the sequence of addition in consideration) are
−
3
prepared and successive amounts of 10 M aqueous solu-
tion of EDTA were added, then completed with MeOH up to
5 ml. The absorbance at the optimum wavelength was mea-
sured for each complex using the same volume of azodye
and buffer as a blank. The results indicated that the metal
ions under investigation are successfully determined up to
the range listed in Table 2 as well as the applied reagent can
be used as an indicator for the spectrophotometric titrations
of Co(II), Ni(II) and Cu(II) ions.
The composition of the complexes in solution was estab-
lished at the optimum conditions described above using the
molar ratio (MRM) and continuous variations (CVM) meth-
ods. The results indicate the presence of complexes in solu-
tion having the stoichiometric ratios 1:1 and 1:2 (M:L) com-
plexes. The conditional formation constant calculated using
Harvey and Manning equation applying the data obtained
from the above two methods are listed in Table 2. The values
obtained show that the species 1:2 (M:L) are nearly twice sta-
The effect of metal ions on the fluorescence spectrum of
the azodye was also considered. The fluorescence spectrum
of the azodye shows two bands and shoulder at 430, 460 and
490 nm respectively. In the presence of Co(II), Ni(II) and
Cu(II) ions, the fluorescence of the azodye was quenched.
The quenching behaviour generally adhered to the
Stern–Volmer equation [14]. At relatively high quencher con-
centrations Stern–Volmer plot (Fig. 4) shows positive devi-
ation. The Stern–Volmer second order rate constants of the
fluorescence quenching decrease with increasing ionic radius
of the metal ions (Table 2).
*
ble as 1:1 (M:L) species. The free energy (G ) of formation
of the metal complexes was also calculated. The stoichiome-
try of the complexes was also determined by conductometric
titrations. The data obtained indicate the formation of 1:1
(M:L) complexes. The increase in conductance indicates that
the reaction between the metal ions and azodye occurs via
the formation of a covalent linkage with the oxygen atom of
the OH group.
Table 2 lists the limits of obedience to Beer’s law,
molar extinction coefficient, specific absorptivity [11],
Sandell sensitivity [12], standard deviation and correlation
coefficient. These values confirm the possible application
3.3. Characterization of the solid complexes
Structure elucidation of Co(II), Ni(II) and Cu(II) com-
plexes was accomplished on the basis of elemental analyses,
Table 2
Analytical parameters for azodye (L) complexes
Parameter
Co
Ni
Cu
Wavelength (nm)
440
450
480
Buffer
pH
Acetate
4.5
4.52 (8.77)
6.16 (11.96)a
25.94
Acetate
5.5
4.23 (8.5)
5.77 (11.59)a
14.70
Acetate
6.3
4.34 (8.28)
5.92 (11.3)a
13.75
a
a
a
log βn
*
ꢁG
−
−
3
Molar absorptivity, ε (×10
)
Specific absorptivity, a(×10 2)
Sandell sensitivity, S
Standard deviation
40.76
23.09
21.61
4.63
2.454
0.43
−
4
−6
−4
10
8 × 10
8.3 × 10
Correlation coefficient
Beer’s limit (ppm)
Ringbom range (ppm)
0.9975
1.08
0.4–1.05
5
0.9989
0.83
0.9995
7.62
0.63–5.1
5
0.24–0.63
5
5.2
−
−
5
−1
−1
−1
A (×10 mol l
)
)
5
B (×10 mol l
5
5.1
20.0
−
3
Ksv (×10 l mol
)
39.17
37.5
A (concentration of prepared sample), B (concentration of sample determined experimentally).
a
−1 −1 −1
2
2
1
:2 (M:L) complexes ε (L mol cm ), a (cm g ), S (␮g cm ).

6
98
M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
tively. This frequency separation is characteristic of mon-
odentate acetate groups for 1:1 (M:L) complexes [19].
The electronic spectra of the complexes were measured
as Nujoll mull. In the spectra of the Co(II) complexes 1 and
−
1
2
, the two bands at 17,857 and 23,809 cm are assigned
4
4
4
4
to T1g → A2g and T1g → T1g(p) transitions [20], respec-
tively. Also, the values of the magnetic moments (4.82 BM
for complex 1 and 4.94 BM for complex 2) are in good
agreement with those reported for an octahedral structure
[
4
2
21]. The electronic spectra of the Ni(II) complexes 3 and
−1
exhibit two bands at (15,625, 24,390 cm ) and (15,625,
−
1
5,000 cm ), respectively. These bands correspond to the
3
3
3
3
A2g → T1g(F) (υ2) and A2g(F) → T1g(F) (υ3) transi-
tions, respectively indicating octahedral geometry [22]. The
magnetic moment values are 2.74 and 2.85 BM for complexes
3
and 4, respectively compared with the spin only value of
8
2.83 BM expected for a d system in O symmetry [23]. The
h
electronic spectra of Cu(II) complexes 5 and 6 show band at
−
1
2
0,000 and 19,608 cm , respectively. This band is assigned
2
2
Fig. 4. Fluorescence quenching of L (5 × 10 5) with metal ions: (a) Co2+
−
to E → B transition assuming square planar geometry
,
g
1g
2
+
2+
(
b) Ni and (c) Cu acetate.
around Cu atom [24]. The magnetic moment values are 1.2
and 1.69 BM for complexes 5 and 6, respectively, which are
less than the spin only value (1.73 BM). This may be due to an
antiferromagneticeffect. TheX-bandESRspectrumofCu(II)
complex 5, in the solid state, was measured at room temper-
ature. The spectrum shows an isotropic signal at g = 2.0061
which agrees with recently studied complexes of Cu(II) with
square planar configuration [25].
IR, UV–vis, ESR spectra, conductance and magnetic mea-
surements as well as the thermal analysis (TGA and DTA).
The analytical data of the isolated solid complexes are given
in Table 1 which is in good agreement with the proposed
structure. The solid complexes are stable in air and insoluble
in common organic solvents but soluble in DMF and DMSO.
The low molar conductance values of the isolated complexes
measured in DMF solution (10 M) at room temperature
suggest their non-electrolytic nature [15] indicating that the
acetate anion is absent or situated inside the metal coordi-
nation sphere. The addition of FeCl3 solution to 1:1 (M:L)
complexes did not give the red brown coloration confirming
coordination of the acetate ion.
The thermal behaviour of the prepared complexes can
be summarized in Table 3. The Co(II) complexes 1 and 2
decomposed in three steps. The initial weight loss occurring
−
3
◦
within the range 90–195 C is attributed to the removal of
hydrated and/or coordinated water molecules. This process
◦
is accompanied by two endothermic peaks at 90 and 187 C
for complexes 1 and 2, respectively. In the temperature range
◦
A comparison of the IR spectrum of the free azodye lig-
and (L) with those of the metal complexes has been carried
out to investigate the mode of bonding of the azodye ligand.
265–390 C, themasslossisinagoodagreementwiththeloss
of one molecule of the ligand. The DTA curves show exother-
◦
mic peaks at 330 and 260 C for complexes 1 and 2, respec-
−
1
In the IR spectrum of the free ligand, the band at 1422 cm
characteristic for N N bond is shifted to lower frequency
tively. The final step of the thermal decomposition in the
◦
temperature range 330–500 C is associated with exothermic
−
1
◦
by 35–23 cm upon coordination to the metal ions with the
peaks at 390 and 445 C for complexes 1 and 2, respectively.
−
1
appearance of another mode of vibration at 424–455 cm
It is due to the complete decomposition leading to CoO as a
final product from which the metal content was calculated.
The Ni(II) complexes 3 and 4 are thermally decomposed
in three decomposition steps. The first stage of decomposi-
corresponding to M N bond [16]. This confirms the involve-
ment of azo nitrogen in complex formation. The IR spectra
−
1
of the complexes show a new band at 520–584 cm due
to M O bond [17] resulting from the interaction between
phenolic oxygen atom and the metal ions. A broad band
◦
tion within the temperature range 50–90 C (associated with
◦
an endothermic peak at ∼90 C for the two complexes) may
−
1
at 3419–3473 cm is present in the spectra of the metal
complexes. The presence of this band is associated with
coordinated and/or hydrated water molecule [18]. The other
stretching vibration of the free azodye is less affected by com-
plex formation indicating that the azodye ligand behaves as
monobasic bidentate ligand via the azo nitrogen and pheno-
lic oxygen atoms. In the IR spectra of the acetate complexes,
bands due to υas and υs of the acetate group are displayed
be attributed to the loss of one hydrated water molecule. The
second step of decomposition occurs within the temperature
◦
ranges 290–310 and 295–305 C associated with exothermic
peaks at 300 and 299 C corresponding to the liberation of
◦
acetate and ethanol molecule for complex 3 and one ligand
molecule for complex 4, respectively. The remaining step
of decomposition occurs within the temperature ranges
◦
310–486 and 305–460 C, associated with exothermic peaks
−
1
◦
within the ranges 1610–1625 and 1380–1390 cm , respec-
at 402 and 403 C for complexes 3 and 4, respectively cor-

M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
699
Table 3
Thermal decomposition data of Co(II), Ni(II) and Cu(II) azodye complexes
◦
◦
Complex
Temperature ( C)
Peak temperature DTA ( C)
Mass loss (%); estim. (calc.)
Assignment
1
90–190
90(−)
330(+)
390(+)
15.9 (16.0)
60.0 (59.9)
9.8 (10.4)
Loss of 1H2O
Loss of 3H2O
Loss of ligand
310–390
90–420
3
2
3
4
5
6
120–195
187(−)
260(+)
445(+)
6.10 (5.5)
42.3 (43.0)
42.2 (43.0)
Loss of 2H2O
Loss of first L
Loss of second L
2
3
65–330
30–500
50–90
89(−)
300(+)
402(+)
3.3 (3.2)
35.0 (35.8)
51.3 (50.7)
Loss of H2O
Loss of EtOH, AcO
Loss of ligand
2
3
90–310
10–486
50–90
90(−)
299(+)
403(+)
2.5 (2.5)
42.5 (45.0)
45.0 (45.0)
Loss of H2O
Loss of first L
Loss of L, ethanol
2
3
95–305
05–460
90–130
80–230
50–450
120(−)
260(+)
410(+)
5.5 (4.3)
63.2 (64.5)
15.2 (14.1)
Loss of H2O
Loss of L
Loss of Cu(AcO)2
1
2
220–250
50–470
225(+)
400(+)
45.0 (44.8)
43.0 (44.8)
Loss of first L
Loss of second L
2
L = azodye ligand, AcO = acetate, (−) endothermic, (+) exothermic.
responding to the complete decomposition of the complexes
leading to NiO.
the complex. It undergoes two stage of decomposition pro-
◦
cess. The first step within the temperature range 220–250 C,
◦
Cu(II) complex 5 exhibits the first mass loss in the temper-
with an exothermic peak at 225 C is attributed to the decom-
◦
◦
ature range 90–130 C, with an endothermic peak at 120 C
in the DTA curve. It may be attributed to the liberation
of the hydrated water molecule. The second mass loss at
position of one ligand molecule. The second stage of decom-
◦
◦
position starts at 250 C and ends at 470 C, with an exother-
◦
mic peak at 400 C leaving CuO residue from which the Cu
◦
◦
1
80–230 C, with an exothermic peak at 200 C is due to the
content was calculated.
liberation of the organic ligand. Copper acetate was found as
the solid product of the second thermal decomposition pro-
The kinetic parameters of decomposition process of the
*
*
complexes namely, activation energy (E ), enthalpy (ꢁH ),
◦
*
*
cess which is transformed to the oxide at 250–450 C with
entropy (ꢁS ) and free energy of the decomposition (ꢁG )
as well as the order (n) and pre-exponential factor (A), are
evaluated graphically by using Coats–Redfern [26] method
as shown in (Fig. 5).
◦
an exothermic peak at 410 C.
◦
For Cu(II) complex 6, there is no mass loss up to 220 C
indicating that either water or solvent molecules are absent in
Table 4
Thermodynamic data of the thermal decomposition of Co(II), Ni(II) and Cu(II) azodye complexes
−1
*
−1
−1
*
−1
−1
*
−1
)
Complex
Step
n
T (K)
E* (kJ mol
)
ꢁH (kJ mol
)
A (S
)
−ꢁS (J k mol
)
ꢁG (kJ mol
8
1
First
Second
Third
1
1
1
318.64
559.65
655.52
65.12
41.08
174.1
62.46
36.42
168.65
7.6 × 10
75.46
202.9
225.9
86.55
149.98
165.96
2
2.94 × 10
224
6
2
3
4
5
6
First
Second
Third
0
0.66
1
343.40
550.90
675.00
48.08
83.81
67.58
45.22
79.23
61.96
3.4 × 10
79
62
121
232.8
236.5
120.8
145.9
221.5
First
Second
Third
1
0
1
332.02
550.18
658.85
41.33
136.83
86.1
38.57
132.26
80.62
39
132
8
215.3
209.4
234
110.1
247.5
234.8
First
Second
Third
1
1
1
318.98
553.63
640.56
32.32
202.72
108.49
29.66
198.12
103.16
29.7
198
103
217
206
213
98.9
312.2
239.6
First
Second
Third
1
0
0
421.03
468.30
589.54
102.46
117.27
63.95
98.96
113.38
59.05
99
113
59
209.5
209.4
216.7
187.2
211.4
186.8
2
First
Second
0.33
0
502.93
677.73
413.46
60.35
408.55
54.71
4.1 × 10
55
199.2
218.4
508.7
202.7

7
00
M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
Fig. 5. Coats–Redfern plots for the decomposition steps of (A) complex 1, (B) complex 2, (C) complex 3, (D) complex 4, (E) complex 5 and (F) complex 6:
ꢀ
1
−n
2
ln{[1 − (1 − α) ]/[T (1 − n)]} for n
ꢀ
(a) first step, (b) second step and (c) third step; Y =
2
ln{[−ln(1 − α)]/T }
for n = 1
The calculated values of n, E, A, ꢁS, ꢁH and ꢁG for the
decomposition steps are given in Table 4.
From the activation energy values, one can concluded that
the water molecules are easy to be eliminated from the com-
plexes according to the following order Ni > Co > Cu. Also,
the energy of activation for the second stage of decomposi-
tion for all complexes, except complexes 1 and 6, is higher
than that of the first stage due to the less steric strain in

M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
701
the intermediate compounds obtained after the first stage of
References
decomposition. On comparing the activation energy of the
first stage of decomposition of Cu(II) complex with the sec-
ond stage of Co(II) and Ni(II) complexes, Cu(II) complex
shows remarkably higher value. This may be due to the stereo
structure of the complexes and the electronic configuration
of the metal ion.
The ꢁS values for all complexes were found to be nega-
tive. This indicates that the activated complex is more ordered
than the reactants [27].
[
1] T. Katami, T. Hayakawa, Analyst 109 (1984) 731;
S. Balzamo, V. Carunchio, R. Galvani, A. Messina, Inorg. Chem.
Acta 97 (1985) 13;
B. Kuban, L. Sommer, Coll. Czechoslov. Chem. Commun. 53 (1988)
3040;
A. Amin, Anal. Lett. 32 (1999) 1575;
*
R.M. Issa, M. Gaber, A.M. Khedr, Egypt J. Anal. Chem. 10 (2001)
23;
E.Y. Hashem, Spectrochim. Acta A 58 (2002) 1401;
E.K. Paleologos, M.I. Prodromidis, D.L. Giokas, A.C. Pappas, M.I.
Karayannis, Anal. Chim. Acta 467 (2002) 205.
[
[
[
2] D. Datta, A. Chakravorty, Inorg. Chem. 22 (1983) 1085;
R.A. Krause, K. Krause, Inorg. Chem. 23 (1984) 2195;
M.R. Mahmoud, S.A. Elgyar, A.M. Hammam, S.A. Ibrahim, Mon-
tash. Chem. 117 (1986) 313;
4
. Conclusion
The electronic spectrum of the pyrimidine azodye (L) was
M. Kakoti, S. Choudhury, A.K. Deb, S. Goswami, Polyhedron 12
(1993) 783;
recorded in different solvents and in universal buffer solu-
tions containing different percentages of methanol. The pKa
of the azodye was determined at different temperatures. The
pKa values increase with the rise of the temperature and
decrease of the percentage of methanol. The various opti-
mum conditions for complex formation were detected. The
spectrophotometric titration of Co(II), Ni(II) and Cu(II) with
EDTA in presence of the pyrimidine azodye indicated that
the azodye can be used as an indicator. The fluorescence of
the azodye was quenched in presence of Co(II), Ni(II) and
Cu(II) ions. The calculated Stern–Volmer second order rate
constant decreases with increasing the ionic radius of the
metal ion. The solid complexes were prepared and character-
ized on the basis of elemental analysis, molar conductance,
magnetic moments, spectral and thermal studies. The pro-
posed chemical structures of the metal chelates suggest the
octahedral geometry for Co(II) and Ni(II) chelates and square
planar for Cu(II) chelate. From all of the above observations,
the structure of the complexes is given as follows:
B.K. Santra, G.K. Lahiri, J. Chem. Soc., Dalton Trans. (1997) 1883;
T.M. Misra, D. Das, C. Sinha, P. Ghosh, C.K. Pal, Inorg. Chem. 37
(1998) 1672.
3] H.A. El-Dessouki, R.M. Issa, M.M. Moustafa, Spectrochim. Acta A
45 (1989) 775;
H. Zhan, H. Tian, Dyes Pigments 40 (1998) 37;
A.D. Towns, Dyes Pigments 42 (1999) 3;
A. Lycka, Z. Vrba, M. Vrba, Dyes Pigments 47 (2000) 45;
K. Singh, S. Singh, J.A. Taylor, Dyes Pigments 54 (2002) 189;
R.M. Issa, S.A. El-Daly, N.A. Elwakiel, Spectrochim. Acta A 59
(2003) 723;
N.M. Rageh, Spectrochim. Acta A 60 (2004) 103.
4] P.K. Santra, D. Das, T.K. Misra, R. Roy, C. Sinha, S.M. Peng, Poly-
hedron 18 (1999) 1909;
P.K. Santra, T.K. Misra, D. Das, C. Sinha, A.M.Z. Slawin, J.D.
Woollins, Polyhedron 18 (1999) 2869;
S. Wang, S. Shen, H. Xu, Dyes Pigments 44 (2000) 195;
R. Roy, P.K. Santra, D. Das, C. Sinha, Synth. React. Inorg. Met.
Org. Chem. 30 (2000) 1975;
G.G. Mohamed, F.A. Nour El-Dien, N.E. El-Gamel, J. Therm. Anal.
Cal. 67 (2002) 135;
H.B. Hassib, S.A. Abdel-Latif, Spectrochim. Acta A 59 (2003) 2425;
J. Dinda, S. Jasimuddin, G. Mostafa, C.H. Hung, C. Sinha, Polyhe-
dron 23 (2004) 793.
[5] R.H. Holm, G.W. Everett, A. Chakravorty, Prog. Inorg. Chem. 7
(1966) 83.
[
[
[
[
6] L. Gati, L. Szalay, Acta. Phys. Chem. 5 (1957) 87.
7] P. Suppan, J. Chem. Soc. (A) (1968) 3125.
8] E.M. Kosower, J. Am. Chem. Soc. 78 (1956) 5700.
9] E.G. Brame, Applied Spectroscopy Reviews, vol. 8, No. 13, Marcel
Dekker, New York, 1974, p. 194.
[
10] I.M. Issa, R.M. Issa, M.S. El-Ezaby, Y.Z. Ahmed, Z. Physik. Chem.
Leipzig) 242 (1969) 169;
I.M. Issa, R.M. Issa, M.S. El-Ezaby, Y.Z. Ahmed, Z. Physik. Chem.
Leipzig) 250 (1972) 161;
R.M. Issa, J.Y. Maghrabi, Z. Physik. Chem. (Leipzig) 253 (1974)
53.
(
(
3
[
[
11] G.H. Ayers, B.D. Narang, Anal. Chim. Acta 24 (1961) 241.
12] E.B. Sandell, Calorimetric Determination of Traces of Metals, 3rd
ed., Interscience, New York, 1959.
[
[
13] A. Ringbom, Z. Anal. Chem. 115 (1939) 332.
14] A.M. Braun, M.T. Maurette, E. Oliveros, Photochemical Technology,
Wiely, New York, 1991, p. 41.
[
[
15] W.J. Greary, Coord. Chem. Rev. 7 (1971) 81.
16] B. Beeccroft, M.J.M. Campell, R. Grazeskowiak, J. Inorg. Nucl.
Chem. 65 (1974) 360.
[17] M.A. David, Metal–Ligand and Related Vibrations, Adward Arnold
Ltd., London, 1967.

7
02
M. Gaber et al. / Spectrochimica Acta Part A 62 (2005) 694–702
[
[
[
[
[
18] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Com-
[23] B.N. Figgis, J. Lewis, Modern Coordination Chemistry, Interscience,
New York, 1967;
pounds, Wiley, New York, 1970.
19] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, Wiley/Interscience, New York, 1986.
20] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amster-
dam, 1968.
21] M.E. Khalifa, T.H. Rakha, M.M. Bekheit, Synth. React. Inorg. Met.
Org. Chem. 26 (1996) 1149.
R. Galyer, Transition Met. Chem. 22 (1997) 97.
[24] M. Pulauniandavar, C. Natarajan, Aust. J. Chem. 33 (1985) 737.
[25] H. Beraldo, D.X. West, Transition Met. Chem. 22 (1997) 294;
R.M. El-Shazly, Transition Met. Chem. 25 (2000) 183.
[26] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68.
[27] C.R. Vinodkumar, M.K. Muraleedharan Nair, P.K. Radhakrishnan, J.
Therm. Anal. Cal. 61 (2000) 143.
22] A.A. El-Bindary, Spectrochim. Acta 57 (2001) 49.