Synthesis, spectroscopic characterization and thermal behavior of metal complexes formed with (Z)-2-oxo-2-(2-(2-oxoindolin-3-ylidene)hydrazinyl)-N- phenylacetamide (H2OI)

Article abstract of DOI:10.1016/j.molstruc.2011.10.036

Complexes of Co(II), Ni(II), Cu(II), Cd(II), Zn(II) and U(IV)O₂ with (Z)-2-oxo-2-(2-(2-oxoindolin-3-ylidene)hydrazinyl)-N-phenylacetamide (H₂OI) are reported and have been characterized by various spectroscopic techniques like (IR, UV-Vis, ESR ¹H and ¹³C NMR) as well as magnetic and thermal (TG and DTA) measurements. It is found that the ligand behaves as a neutral tridentate, neutral tetradentate, monoanionic tridentate, monoanionic tridentate and dianionic tridentate. An octahedral geometry for all complexes except [Cu₂(H₂OI)(OAc) ₄](H₂O)₂ and [Cu(HOI)Cl](H₂O) ₂ which have a square planar geometry. Furthermore, kinetic parameters were determined for each thermal degradation stage of some studied complexes using Coats-Redfern and Horowitz-Metzger methods. The bond lengths, bond angles, HOMO, LUMO and dipole moments have been calculated to confirm the geometry of the ligand and the investigated complexes.

Full text of DOI:10.1016/j.molstruc.2011.10.036

Journal of Molecular Structure 1007 (2012) 146–157
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterization and thermal behavior of metal
complexes formed with (Z)-2-oxo-2-(2-(2-oxoindolin-3-ylidene)hydrazinyl)-
N-phenylacetamide (H2OI)
T.A. Yousef a, T.H. Rakha b, Usama El Ayaan b, G.M. Abu El Reash b,
⇑
a Department of Toxic and Narcotic Drug, Forensic Medicine, Mansoura Laboratory, Medicolegal Organization, Ministry of Justice, Egypt
b Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Complexes of Co(II), Ni(II), Cu(II), Cd(II), Zn(II) and U(IV)O2 with (Z)-2-oxo-2-(2-(2-oxoindolin-3-yli-
dene)hydrazinyl)-N-phenylacetamide (H2OI) are reported and have been characterized by various spec-
troscopic techniques like (IR, UV–Vis, ESR 1H and 13C NMR) as well as magnetic and thermal (TG and DTA)
measurements. It is found that the ligand behaves as a neutral tridentate, neutral tetradentate, monoan-
ionic tridentate, monoanionic tridentate and dianionic tridentate. An octahedral geometry for all com-
plexes except [Cu2(H2OI)(OAc)4](H2O)2 and [Cu(HOI)Cl](H2O)2 which have a square planar geometry.
Furthermore, kinetic parameters were determined for each thermal degradation stage of some studied
complexes using Coats–Redfern and Horowitz–Metzger methods. The bond lengths, bond angles, HOMO,
LUMO and dipole moments have been calculated to confirm the geometry of the ligand and the investi-
gated complexes.
Received 25 May 2011
Received in revised form 26 September
2011
Accepted 18 October 2011
Available online 26 October 2011
Keywords:
Hydrazone derivatives
Metal complexes
Thermal analysis
PM3
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
N) were performed with a Perkin–Elmer 2400 series II analyzer.
IR spectra (4000–400 cmꢀ1) for KBr discs were recorded on a Matt-
The hydrazones and their metal complexes have many impor-
tant applications in analytical chemistry and pharmacology [1–3].
The biological activity of hydrazones becomes more carcinostatic
and bacteriostatic upon chelation [2,4]. The hydrazones derived
from simple aldehyde and ketones were reported [5–7].
Isatin is chemically 1H-indole-2,3-dione and is a versatile lead
molecule for potential bioactive agents and its derivatives were re-
ported to poss wide spectrum of activity like antibacterial [8], anti-
fungal [9], anticonvulsant [10], antiHIV [11], antidepressant [12]
and anti-inflammatory [13].
We were thus motivated to undertake a systematic study of prep-
aration and characterization of transition metal complexes formed
with (Z)-2-oxo-2-(2-(2-oxoindolin-3-ylidene)hydrazinyl)-N-phen-
ylacetamide (H2OI) and Co(II), Ni(II), Cu (II), Cd(II), Zn (II) and
U(IV)O2 ions.
son 5000 FTIR spectrophotometer. Electronic spectra were re-
corded on a Unicam UV–Vis spectrophotometer UV2. Magnetic
susceptibilities were measured with a Sherwood scientific mag-
netic susceptibility balance at 298 K. 1H and 13C NMR measure-
ments in DMSO at room temperature were carried out an EM-
390 (200 MHz) spectrometer. Thermogravimetric measurements
(TGA, DTA, 20–800 °C) were recorded on a DTG-50 Shimadzu ther-
mogravimetric analyzer at a heating rate of 10 °C/min and nitrogen
flow rate of 20 ml/min. ESR spectra were obtained on a Bruker EMX
spectrometer working in the X-band (9.78 GHz) with 100 kHz
modulation frequency. The microwave power and modulation
amplitudes were set at 1 mW and 4 Gauss, respectively. The low
field signal was obtained after four scans with 10-fold increase in
the receiver again. A powder spectrum was obtained in a 2 mm
quartz capillary at room temperature.
2. Experimental
2.2. Synthesis of (Z)-2-oxo-2-(2-(2-oxoindolin-3-ylidene)hydrazinyl)-
N-phenylacetamide (H2OI)
2.1. Physical measurements
All the chemicals were purchased from Aldrich and Fluka and
used without further purification. Elemental analyses (C, H and
(Z)-2-oxo-2-(2-(2-oxoindolin-3-ylidene)hydrazinyl)-N-phenyl-
acetamide (H2OI) was synthesized according to the following
scheme:
⇑
The pale yellow precipitate (H2OI) was filtered off, washed
several times with ethanol and recrystallized from hot ethanol
Corresponding author. Tel.: +20 100373155.
E-mail address: gaelreash@mans.edu.eg (G.M. Abu El Reash).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.10.036

T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
147
and finally dried in vacuum desiccators over anhydrous CaCl2 (m.p.
315 °C).
anhydrous CaCl2. The physical and analytical data of the isolated
complexes are listed in Table 1. The complexes have high melting
points and insoluble in common organic solvents; soluble in DMSO
and DMF and found to be non-electrolytes.
2.3. Synthesis of metal complexes
A hot ethanolic solution of the respective metal chlorides or
acetates Co(II), Ni(II), Cu(II), Cd(II), Zn(II) and U(VI)O2 (1.0 mmol)
was added to a hot ethanolic solution of H2OI (0.308 g, 1.0 mmol).
The resultant mixture was heated under reflux for 2–3 h. The
formed precipitates were filtered off, washed with ethanol fol-
lowed by diethyl ether and dried in a vacuum desiccator over
2.4. Molecular modeling
An attempt to gain a better insight on the molecular structure of
the ligand and its complexes, geometry optimization and confor-
mational analysis has been performed using MM + force-field as
implemented in hyperchem 8.03 [14]. The low lying obtained from
Table 1
Analytical and physical data of H2OI and its metal complexes.
Compound
Color
MP (°C)
Yield (%)
% Found (Calc. d)
Empirical formula (F.Wt.)
C
H
N
M
Cl
H2OIC16H12N4O3 (308.29)
[Co(OI)(H2O)3]C16H16N4CoO6 (419.25)
Yellow
Red
Brown
Dark yellow
Dark orange
Brown
Dark yellow
Brown orange
Orange
315
>300
>300
>300
>300
>300
>300
>300
>300
92
85
85
85
86
86
82
72
88
63.42 (63.33)
45.35 (45.8)
41.72 (40.74)
51.2 (50.9)
45.6 (45.8)
47.6 (47.7)
48.06 (48.2)
43.2 (43.1)
31.98 (32.2)
4.1 (3.9)
18.2 (18.7)
13.8 (13.4)
7.75 (7.92)
14.67 (14.8)
13.6 (13.4)
11.3 (11.1)
12.43 (12.5)
10.23 (10.1)
8.45 (8.33)
–
–
–
–
3.75 (3.8)
3.95 (3.98)
3.87 (4.0)
3.7 (3.8)
4.19 (4.0)
3.2 (3.4)
13.9 (14.1)
17.5 (17.9)
13.4 (13.8)
13.72 (14.0)
11.5 (11.7)
15.2 (14.6)
20.64 (20.2)
35.3 (35.4)
[Cu2(H2OI)(OAc)4](H2O)2C24H28Cu2N4O13 (707.59)
[Cu(HOI)Cl](H2O)2C16H15ClCuN4O5 (377.76)
[Ni(OI)(H2O)3]C16H16N4O6Ni (419.02)
[Ni(H2OI)(OAc)2(H2O)]C20H20NiN4O8 (503.08)
[Zn(HOI)(OAc)(H2O)]C18H16ZnN4O6 (448.72)
[Cd(H2OI)(OAc)2(H2O)]C20H20CdN4O8 (556.81)
[UO2(HOI)(OAc)(H2O)2]C18H18UN4O9 (672.39)
9.64 (9.38)
–
–
–
–
–
3.55 (3.6)
2.55 (2.7)

148
T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
Structure 1.
Table 2
IR spectral bands of H2OI and its metal complexes (cmꢀ1).
Compound
m
(CN)a
m
(C@O)is
m
(C@O)(5)
m
(C@O)(6)
m
(NH)(1,2)
m
(NH)is
m
(C@N)b
m(NAN)
m(CO)
m(MAO)
m(MAN)
H2OI
1619
1638
1630
1602
1610
1609
1611
1629
1610
1740
1690
1691
1692
–
1710
1667
1668
1687
1675
1665
–
1684
1682
1685
1665
1683
1681
1682
1682
1686
3205
3202
3203
3208
3208
3206
–
3290
3291
3291
3292
–
–
–
–
–
950
965
930
937
932
940
980
970
921
–
–
–
–
–
–
[Cd(H2OI)(OAc)2(H2O)]
[Ni(H2OI)(OAc)2(H2O)]
[Cu2(H2OI)(OAc)4](H2O)2
[Cu(HOI)Cl](H2O)2
[Zn(HOI)(OAc)(H2O)2]
[Co(OI)(H2O)3]
520
518
522
521
523
526
520
517
460
463
473
475
478
465
467
470
1635
1643
1640
1640
1642
1110
1127
1095
1198
1090
–
–
–
–
–
–
–
–
[Ni(OI)(H2O)3]
[UO2(HOI)(OAc)(H2O)2]
–
1708
–
3204
a
b
Azomethine.
New.
Isatin.
is
MM+[15] was then optimized at PM3 using the Polak–Ribiere algo-
rithm in RHF–SCF, set to terminate at an RMS gradient of
0.01 kcal molꢀ1
.
3. Results and discussion
The data of elemental analysis together with some physical
properties of the complexes are summarized in Table 1.
3.1. IR and 1H NMR Spectra
The most important infrared bands of H2OI (Structure 1) and its
metal complexes are listed in Table 2. The IR spectrum of H2OI dis-
plays four bands at 1740, 1710, 1684, 1619, 3205 and 3290 cmꢀ1
assigned to
and
(NH)(4) [17], respectively. Only one band is appeared related
to both
(C@O)(5) and (C@O)(6) groups.
m , m , m m(C@N) [16], m
(C@O)(is) (C@O)(5) (C@O)(6) (NH)(1,2)
m
m
m
In [Cd(H2OI)(OAc)2(H2O)] and [Ni(H2OI)(OAc)2(H2O)] (Structure
2) complexes, the ligand H2OI acts as a neutral tridentate coordi-
nating via carbonyl oxygen (C@O)(is), carbonyl oxygen (C@O)(5)
and azomethine nitrogen (C@N) groups. This mode of complexa-
Structure 2.
tion is supported by: (i) shift of
wavenumbers. (ii) shift of (C@N) and
ber. Moreover, the infrared spectra of these complexes showed
m
(C@O)(is) and
m
(C@O)(5) to lower
new bands at (520,518) and (460,463) cmꢀ1 assignable to
(MAO) and (MAN), respectively [18]. In addition, the bands of
coordinated water observed at (820,840) and (533,549) cmꢀ1
m
m(NAN) to higher wavenum-
m
m
,

T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
149
(C@N) groups. This mode of complexation is supported by the shift
of both (NAN) and (C@N) to low-
(C@O)(5) (C@O)(6) (C@O)(is)
er wavenumbers, Moreover, the infrared spectrum of the complex
showed new bands at 522 and 473 cmꢀ1 assignable to
(MAO) and
(MAN) respectively [18]. Moreover two new bands at 1381 and
m
,
m
,
m
,
m
m
m
m
1580 cmꢀ1, attributable to
ms(OACAO) and mas(OACAO) of acetate
group, the difference (199 cmꢀ1) between those two bands indi-
cates that the acetate group is monodentate [20].
In [Cu(HOI)Cl](H2O)2 (Structure 4) and [Zn(HOI)(OAc)(H2O)2]
complexes the ligand H2OI acts as a mononegative tridentate via
enolic carbonyl oxygen (C@O)(is), carbonyl oxygen (C@O)(1) and
azomethine nitrogen (C@N) groups. This mode of complexation is
supported by the following observations: (i) The disappearance
of
bands in the 1110–1127 cmꢀ1 region and at 1635–1641 cmꢀ1
which assignable to (CAO) and, (C@N*) respectively. (ii) The
(C@N) is shifted to higher wavenumber. (iii) The
(C@O)(5) and
(NAN) are shifted to lower wavenumber. Moreover, the infrared
m m
(C@O)(is) and (NH)4 with simultaneous appearance of new
m
m
m
m
m
spectra of these complexes showed new bands at (521,523) and
(475,478) cmꢀ1 assignable to
(MAO) and (MAN), respectively
[18]. In addition, the bands of coordinated water observed at 830
and 541 cmꢀ1, are assigned to
r(H2O) and w(H2O), respectively,
Structure 3.
m
m
are assigned to qr(H2O) and qw(H2O), respectively [19]. Moreover,
q
q
strong evidence for the presence or absence of coordinated water
supported by the thermogram of all complexes.
in case of zinc complex [19]. Moreover, strong evidence for the
presence or absence of coordinated water supported by the ther-
mogram of all complexes.
In [Co(OI)(H2O)3] (Structure 5) and [Ni(OI)(H2O)3] complexes
the ligand H2OI acts as a binegative tridentate coordinating via
enolic carbonyl oxygen (C@O)(is), enolic carbonyl oxygen (C@O)(1)
In the binuclear copper complex namely [Cu2(H2OI)(OA-
c)4](H2O)2 (Structure 3), the ligand H2OI behaves as a neutral tetra-
dentate coordinating via carbonyl oxygen of both
m ,
(C@O)(5)
m
(C@O)(6),carbonyl oxygen (C@O)(is) and azomethine nitrogen
m
Structure 4.
Structure 5.

150
T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
are assigned to
qr(H2O) and qw(H2O), respectively [19]. Further-
more, strong evidence for the presence or absence of coordinated
water supported by the thermogram of all complexes.
In [UO2(HOI)(OAc)(H2O)](H2O) complex (Structure 6) H2OI acts
as a mononegative bidentate ligand coordinating via enolic car-
bonyl oxygen (C@O)(is) and azomethine nitrogen (C@N) groups.
This mode of complexation is supported by the following observa-
tions: (i) The disappearance of
neous appearance of new bands in the 1090 cmꢀ1 region and at
1642 cmꢀ1 which may be assigned to
(CAO) and (C@N*), respec-
tively. (ii) The (C@N) and (NAN) are shifted to lower wavenum-
ber. Moreover, the infrared spectrum of the complexes showed
new bands at 517 and 470 cmꢀ1 assignable to
(MAO) and
(MAN), respectively [18]. In addition, the bands of coordinated
water observed at 844 and 542 cmꢀ1, are assigned to
r(H2O)
and w(H2O), respectively [19]. Furthermore, strong evidence for
m m
(C@O)(is) and (NH)4 with simulta-
m
m
m
m
m
m
q
q
the presence or absence of coordinated water supported by the
thermogram of all complexes.
The uranyl complex exhibits three bands at 921, 840 and
265 cmꢀ1, assigned to m3
,
m1 and m4 vibrations, respectively, of the
dioxouranium ion [21]. The m3 value is used to calculate the force
constant (F) of m(U@O) by the method of McGlynn and Smith [22]:
Structure 6.
2
2
ð
m3Þ ¼ ð1307Þ ðFu-oÞ=14:103
and azomethine nitrogen (C@N) groups. This mode of complexa-
tion is suggested by the following observations: (i) The disappear-
The force constant obtained for uranyl complex was then
substituted into the relation given by Jones [21]:
ance of both
appearance of new bands in the 1095–1136 cmꢀ1 region and at
1629–1640 cmꢀ1 which may be assigned to
(CAO) and (C@N*),
respectively. (ii) The (C@N) is shifted to lower wavenumber in
case of [Co(OI)(H2O)3] complex while shifted higher wavenumber
in case of [Ni(OI)(H2O)3] complex. (iii) shift of (NAN) to higher
m m
(C@O)(is), (C@O)(5) and (NH)4 with simultaneous
Ru-o ¼ 1:08ðFu-oÞꢀ1=3 þ 1:17
m
m
m
To give an estimate of the UAO bond length in Å. The calculated
Fu-o and Ru-o values are 7.1 mdynes Åꢀ1 and 1.75 Å, respectively,
fall in the usual range for the uranyl complexes [22]. The UAO
bond distance falls in usual region as reported earlier [23] and ex-
tremely is consistent with the bond length calculated by the use of
MM + force field (as implemented in hyperchem 8.03) [15].
m
wavenumber. Moreover, the infrared spectra of these complexes
showed new bands at (526,520) and (465,467) cmꢀ1 assignable
to
m(MAO) and m(MAN), respectively [18]. In addition, the bands
of coordinated water observed at (825,837) and (544,549) cmꢀ1
,
Fig. 1. 1H NMR spectrum of H2OI.

T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
151
3.2. Nuclear magnetic resonance spectral studies
hydrogen bond. The NH proton is disappeared due to the enoliza-
tion of (CO)(is). From 13C NMR spectrum data (Table 4), for the cad-
mium complex, the signals for the (CAO)is carbon and (CAO)(5)
carbon showed an downfield shift on complexation [24] while,
CAN carbon showed an upfield shift on complexation compared
with the free ligand. But in case of uranyl complex the signals for
the (CAO)is carbon showed an downfield shift on complexation
while, CAN carbon showed an upfield shift on complexation com-
pared with the free ligand. Furthermore, the appearance of new
signals at d = 179 ppm and d = 53 ppm give strong evidence for
the presence of the acetate group. The other ring carbon atoms
did not show significant shifts.
The 1H and 13C NMR spectra of H2OI (Figs. 1 and 2) and its Cd(II)
and U(VI)O2 complexes were recorded in DMSO. The 1H NMR spec-
trum of H2OI in DMSO shows three signals at 11.35, 11.30 and
11.04 ppm assignable to the protons of (NH)1, (NH)2 and (NH)4,
respectively. The appearance of the signal of (NH)1 and (NH)2 at
high value downfield from TMS suggests the presence of intramo-
lecular hydrogen bonding. The multiplet signals observed in the
7.16–7.65 ppm region are assigned to the aromatic protons (Table
3). Also, the 1H NMR spectrum of [Cd(H2OI)(OAc)2(H2O)] complex
in DMSO shows three signals at 10.22, 10.01 and 9.87 ppm assign-
able to the protons of (NH)1, (NH)2 and (NH)4, respectively, indicat-
ing that these groups play no part in coordination. Finally, the 1H
NMR spectrum of [UO2(HOI)(OAc)(H2O)](H2O) complex in DMSO
shows two signals at d = 11.05 and 8.15 ppm relative to TMS which
may be assigned to (NH)(1,2) amide protons. The NH proton shifted
to higher field region than of the free ligand due to the absence of
3.3. Electronic spectra and magnetic moments
The magnetic moments, electronic spectral bands in DMSO and
ligand field parameters of metal complexes are collected in Table 5.
Fig. 2. 13C NMR spectrum of H2OI.
Table 3
The 1H NMR spectral data of H2OI and its diamagnetic complexes.
Compound
NH1
NH2
NH4
Aromatic protons
H2OI
11.04
8.87
11.05
11.3
9.01
8.15
11.35
9.22
–
7.16–7.65
7.13–7.87
6.94–7.92
[Cd(H2OI)(OAc)2(H2O)]
[UO2(HOI)(OAc)(H2O)2]
Table 4
13C NMR chemical shifts in (ppm) assignments for H2OI and its diamagnetic complexes.
Compound
C1
C2
C3
C4
C5
C6
H2OI
115
114
112
145
143
142
165
176
174
134
124
125
156
168
160
158
160
162
[Cd(H2OI)(OAc)2(H2O)]
[UO2(HOI)(OAc)(H2O)2]

152
T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
Table 5
Magnetic moment, electronic bands and ligand field parameters of the complexes derived from H2OI.
Compound
Band position (cmꢀ1) (molar extinction coefficient,
e
, L molꢀ1 cmꢀ1
)
Dq
B
b
leff (B.M.)
[Co(OI)(H2O)3]
[Ni(OI)(H2O)3]
[Ni(H2OI)(OAc)2(H2O)]
[Cu(HOI)Cl](H2O)2
[Cu2(H2OI)(OAc)4](H2O)2
16,949(1146), 17,730(1330), 18,868(1604), 21,186(615), 22,124(401), 24,272(98)
16,667(940), 17,730(1173), 18,727(1585), 20,408(861), 23,148(532), 24,937(311)
14,599(820), 17,212(1189), 18,215(1429), 20,833(765), 23,041(473), 25,510(284)
14,085(1243), 18,083(1580), 19,268(2535), 20,325(1769)
918.6
1029
1054
–
957
0.85
0.97
0.96
–
4.55
2.82
3.22
2.1
1012
1006
–
17,331(1117), 17,953(1379), 19,685(1730), 21,222(628)
–
–
–
1.41
Table 6
ESR data of the Copper (II) complexes at room temperature.
Complex
gk
g?
A
(cmꢀ1
)
G
g =A
a2
b2
k
k
k
[Cu2(H2OI)(OAc)4](H2O)2
[Cu(HOI)Cl](H2O)2
2.20
2.26
2.05
2.08
–
174
3.7
3.2
–
130
–
0.81
–
0.7
The electronic spectrum of [Co(OI)(H2O)3] complex exhibits two
bands at 16,949 and 18,868 cmꢀ1 attributed to 4T1g ? 4A2g(F) and
4T1g ? 4T1g(P) transitions, respectively, in an octahedral configura-
tion [25]. The calculated Dq, B and b values are in the range re-
ported for an octahedral environment around Co(II) complexes.
Also, the value of the magnetic moment (4.55 B.M.) is additional
evidence for an octahedral geometry around the Co(II) ion.
are similar to the ESR spectra of the reported binuclear Cu(II) com-
plexes [35]. The appearance of the half-field signal confirms that
the complex [Cu2(H2OI)(OAc)4](H2O)2 has a binuclear unit that
there exist a magnetic interaction between the two Cu(II) ions
and in accordance with the subnormal effective magnetic moment.
The ESR spectra of [Cu2(H2OI)(OAc)4](H2O)2 exhibit broad single
line, nearly isotropic signal centered at g = 2.08 (Fig. 3) is attribut-
able to dipolar broadening and enhanced spin lattice relaxation
The electronic spectra of [Ni(OI)(H2O)3] and [Ni(HOI)(OAc)2]
complexes are consistent with octahedral geometry showing two
d–d transition bands in the 16,667–17,212 and 23,148–
25,510 cmꢀ1 regions, assignable to the 3A2g ? 3T1g(F) (
m
2) and
3) transitions, respectively [26,27]. The ligand
2/ 1 and the magnetic moment values lie in
3A2g ? 4T1g(P) (
field parameters,
m
m
m
the range of octahedral structures.
The electronic spectrum of [Cu(HOI)Cl](H2O)2 complex exhibits
two bands at 14,085 and at 20,325 cmꢀ1 regions. The first is cen-
tered at 14,085 cmꢀ1 and the other, which is more intense, is cen-
tered at 20,325 cmꢀ1. The band at 20,325 cmꢀ1 may be assigned to
a symmetry-forbidden ligand ? metal charge transfer band [28–
30] and band at 14,085 cmꢀ1 is assigned to the d-d transition cor-
responding to 2T2g ? 2Eg; the band position is in agreement with
those generally observed for planar copper(II) complexes.
The electronic spectrum of [Cu2(H2OI)(OAc)4](H2O)2 complex
show bands at 17,331, 17,953, 19,685, and 21,222 cmꢀ1 regions,
suggesting square-planar geometry [31]. The lowering in
leff
(1.41) of binuclear copper(II) complex may be attributed to the
covalent nature of the copper–copper bond.
Finaly the U.V. spectrum of the [UO2(HOI)(OAc)(H2O)2] shows a
band at 24,096 cmꢀ1 assinged to 1
Rg + ?3p4. This band is similar
to the OUO symmetric stretching frequency for the first excited
state [32].
3.4. ESR spectra
The room temperature solid state ESR spectra of the copper
complexes exhibit an axially symmetric g-tensor parameters with
gk > g? > 2:0023 indicating that the copper site has a dx2ꢀy2
ground-state characteristic of square planar or octahedral stereo-
chemistry [33]. In axial symmetry, the g-values are related by the
expression, G ¼ ðgk ꢀ 2Þ=ðg? ꢀ 2Þ ¼ 4. According to Hathaway
[34], as value of G is greater than 4, the exchange interaction be-
tween copper (II) centers in the solid state is negligible, whereas
when it is less than 4, a considerable exchange interaction is indi-
cated in the solid complex. The calculated G values for the copper
complexes except less than 4 suggesting copper–copper exchange
interactions (Table 6). A forbidden magnetic dipolar transition for
[Cu2(H2OI)(OAc)4](H2O)2 is observed at half-field (ca. 1600 G,
g ꢁ 4.0) but the intensity is very weak. The present ESR spectra
Fig. 3. ESR spectra of (a) [Cu2(H2OI)(OAc)4](H2O)2 and (b) [Cu(HOI)Cl](H2O)2 at
room temperature.

T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
153
[36]. This line broadening is probably due to insufficient spin-ex-
change narrowing toward the coalescence of four copper hyperfine
lines to a single line. Note that, the same kind of powder ESR line
shapes; have also been observed for many tetrahedral or square
planar binuclear Cu(II) complexes with a considerably strong intra-
nuclear spin-exchange interaction [37].
in-plane
r
-bonding between a copper 3d orbital and the ligand
orbitals) and b2 (covalent in-plane
p
-bonding), were calculated
by using the following equations [39–41]:
a2 ¼ ðA =0:036Þ þ ðg ꢀ 2:0023Þ þ 3=7ðg? ꢀ 2:0023Þ þ 0:04
k
k
b2 ¼ ðgk ꢀ 2:0023ÞE= ꢀ 8ka2
An index of the increase of the tetrahedral distortion in the
where k = ꢀ828 cm–1 for the free copper ion and E is the electronic
coordination sphere of copper is the decrease of A with the in-
k
crease of gk [38]. To quantify the degree of distortion of the Cu(II)
complexes, the f-factor g =A was calculated which is considered as
transition energy.
The covalency of the in-plane
plete ionic character, whereas
r
a
-bonding,
a
2 = 1 indicates com-
k
k
2 = 0.5 denotes 100% covalent
an empirical index of tetrahedral distortion [39]. Its value ranges
between 105 and 135 for square planar complexes, depending on
the nature of the coordinated atoms. In the presence of a distorted
tetrahedral structure, the values can be much larger [38]. In case of
[Cu(HOI)Cl](H2O)2 the value is 125 is evidence in support of the
square planar geometry with no appreciable tetrahedral distortion.
bonding, with the assumption of negligibly small values of the
overlap integral. The b2 parameter gives an indication of the cova-
lency of the in-plane p
-bonding. The smaller the b2 the larger is the
covalency of the bonding.
The values of a2 and b2 for the complexes indicate that the in-
Molecular orbital coefficients, a
2 (a measure of the covalency of the
plane r-bonding and in-plane p-bonding are appreciably covalent,
Table 7
The molecular parameters of the ligand and its complexes.
The assignment of the theoretical parameters
The compound investigated
H2OI
The theoretical data
Total energy
Total energy
=ꢀ83217.3495906 (kcal/mol)
=ꢀ132.615271563 (a.u.)
=ꢀ4001.9382726 (kcal/mol)
=ꢀ79215.4113180 (kcal/mol)
=ꢀ560381.4220464 (kcal/mol)
=477164.0724559 (kcal/mol)
=ꢀ11.7972726 (kcal/mol)
=1.893 (Debys)
Binding energy
Isolated atomic energy
Electronic energy
Core–core interaction
Heat of formation
Dipole moment
Homo
=ꢀ9.075751
Lumo
=ꢀ1.121118
Total energy
Total energy
[Co(OI)(H2O)3]
=ꢀ123681.9579372 (kcal/mol)
=ꢀ197.099721632 (a.u.)
=ꢀ5009.4754122 (kcal/mol)
=ꢀ118672.4825250 (kcal/mol)
=ꢀ916678.9720145 (kcal/mol)
=792997.0140773 (kcal/mol)
=ꢀ477.7474122 (kcal/mol)
=6.191 (Debys)
Binding energy
Isolated atomic energy
Electronic energy
Core–core interaction
Heat of formation
Dipole moment
Homo
=ꢀ0.07390385
Lumo
=ꢀ8.95602
Total energy
Total energy
[Ni(H2OI)(OAc)2(H2O)]
[Cu(HOI)Cl](H2O)2
[Cu2(H2OI)(OAc)4](H2O)2
=ꢀ155074.6517950 (kcal/mol)
=ꢀ247.127157515 (a.u.)
=ꢀ6026.9580220 (kcal/mol)
=ꢀ149047.6937730 (kcal/mol)
=ꢀ1299189.8594042 (kcal/mol)
=1144115.2076092 (kcal/mol)
=ꢀ535.8460220 (kcal/mol)
=6.837 (Debys)
Binding energy
Isolated atomic energy
Electronic energy
Core–core interaction
Heat of formation
Dipole moment
Homo
=ꢀ8.243506
Lumo
=ꢀ1.122439
Total energy
Total energy
=ꢀ117481.4214018 (kcal/mol)
=ꢀ187.218538916 (a.u.)
=ꢀ4090.8072558 (kcal/mol)
=ꢀ113390.6141460 (kcal/mol)
=ꢀ774194.8447954 (kcal/mol)
=656713.4233936 (kcal/mol)
=ꢀ43.0782558 (kcal/mol)
=9.884 (Debys)
Binding energy
Isolated atomic energy
Electronic energy
Core–core interaction
Heat of formation
Dipole moment
Homo
=ꢀ5.455019
Lumo
=ꢀ2.084122
Total energy
Total energy
=ꢀ218304.3220777 (kcal/mol)
=ꢀ347.890038533 (a.u.)
=ꢀ7154.5314157 (kcal/mol)
=ꢀ211149.7906620 (kcal/mol)
=ꢀ1865623.4495558 (kcal/mol)
=1647319.1274780 (kcal/mol)
=ꢀ534.1744157 (kcal/mol)
=8.264 (Debys)
Binding energy
Isolated atomic energy
Electronic energy
Core–core interaction
Heat of formation
Dipole moment
Homo
=ꢀ9.32396
Lumo
=ꢀ1.576875

154
T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
and are consistent with very strong in-plane
complexes. For the copper (II) complexes, the high values of b2
compared to a2 indicate that the in-plane
-bonding is less cova-
lent than the in-plane -bonding. These data are well consistent
r
-bonding in these
complex while in case of [Cu2(H2OI)(OAc)4](H2O)2 complex
the largest change affects N12AN5AC4 from 117.4° to 127.9°
finally in case of [Co(OI)(H2O)3] complex the largest change
affects O(22)AC(14)AN(15) from 128.7° to 119.5°.
p
r
with other reported values [40–43].
3. All bond angles in Co, Ni complexes are quite near to an octahe-
dral geometry predicting sp3d2 hybridization.
4. The bond angles in complexes namely [Cu(HOI)Cl](H2O)2 and
[Cu2(H2OI)(OAc)4](H2O)2 are quite near to a square planar
geometry predicting dsp2 hybridization
3.5. Molecular modeling
H2OI and its complexes are shown in (Structures 1–6). Analysis
of the data in Tables (1S–12S) (Supplementary Materials) calcu-
lated for the bond lengths and angles for the bond, one can con-
clude the following remarks:
5. All the active groups taking part in coordination have bonds
longer than that already exist in the ligand (like NAH and CAO).
6. There is a variation in C14AO22 bond lengths on complexation.
It becomes slightly longer as the coordination takes place via O
atoms of CAO group that is formed on deprotonation of CAOH.
7. There is a large variation in N5AN12 bond lengths on complex-
ation. It becomes longer as the coordination takes place via N11
atom of azomethine group.
1. The lower HOMO energy values show that molecules donating
electron ability is the weaker. On contrary, the higher HOMO
energy implies that the molecule is a good electron donor.
LUMO energy presents the ability of a molecule receiving elec-
tron [44] (Table 7).
2. The bond angles of the hydrazone moiety are altered somewhat
upon coordination; the largest change affects C4AC2AO3 angle
which are change from 127.5° on ligand to 119.6° on complexes
as a consequence of bonding in case of [Cu(HOI)Cl](H2O)2
3.6. Thermal analysis
The TG–DTA results for solid complexes are depicted in Table 8.
The results are in good agreement with the proposed formulae. Ta-
Table 8
TGA and DTA data for metal complexes.
Compound
Temp. range (°C)
% Weight loss
Assignment
Found
Calcd.
[Co(OI)(H2O)3]
130–190
190–800
12.81
–
12.89
–
Loss of 3 mol of coordinated water
Start of deligation
[Cu2(H2OI)(OAc)4](H2O)2
75–110
110–315
315–800
5.13
8.73
–
5.09
8.79
–
Loss of 2 mol of hydrated water
Loss of 4 coordinated acetate group
deligation
[Cu(HOI)Cl](H2O)2
77–110
110–255
255–800
7.87
8.31
–
7.83
8.35
–
Loss of 2 mol of hydrated water
Loss of 1 coordinated chloride ions
deligation
[Ni(OI)(H2O)3]
140–190
190–800
12.84
–
12.9
–
Loss of 3 mol of hydrated water
Start of deligation
[Zn(HOI)(OAc)(H2O)]
105–185
185–295
295–800
4.04
13.78
–
4.01
13.70
–
Loss of 1 mol of coordinated water
Loss of 1 coordinated acetate group
deligation
[Cd(H2OI)(OAc)2(H2O)]
[UO2(HOI)(OAc)(H2O)2]
[Ni(H2OI)(OAc)2(H2O)]
110–185
185–305
305–800
3.28
21.85
–
3.24
21.91
–
Loss of 1 mol of coordinated water
Loss of 2 coordinated acetate group
deligation
110–200
200–315
315–800
5.29
9.11
–
5.23
9.05
–
Loss of 2 mol of coordinated water
Loss of 1 coordinated acetate group
deligation
105–190
190–315
315–800
3.52
24.02
–
3.58
24.35
–
Loss of 1 mol of coordinated water
Loss of 2 coordinated acetate group
deligation
Table 9
Kinetic parameters of complexes evaluated by Coats–Redfern equation.
Compound
Peak
Mid temp. (K)
Ea (kJ/mol)
A (Sꢀ1
)
D
H* (kJ/mol)
D
S* (kJ/mol K)
DG* (kJ/mol)
[Co(OI)(H2O)3]
1st
313
533
696
937
49.40
56.24
56.79
99.44
4.33 ꢂ 104
1.70 ꢂ 105
4.72 ꢂ 105
7.82 ꢂ 105
46.79
ꢀ0.1565
ꢀ0.1491
ꢀ0.1433
ꢀ0.1416
95.85
127.05
150.77
224.45
2nd
3rd
4rd
52.06
51.01
91.64
[Ni(OI)(H2O)3]
1st
337
547
762
869
35.51
31.91
137.35
169.98
4.27 ꢂ 104
1.73 ꢂ 105
2.23 ꢂ 106
7.34 ꢂ 105
32.70
27.36
131.01
162.75
ꢀ0.1572
ꢀ0.1496
ꢀ0.1311
ꢀ0.1415
85.78
109.32
231.04
285.85
2nd
3rd
4th
[Cu(HOI)Cl](H2O)2
1st
2nd
3rd
547
677
852
167.08
72.41
139.03
5.06 ꢂ 105
4.06 ꢂ 105
1.14 ꢂ 107
162.53
66.78
131.94
ꢀ140.75
ꢀ0.1443
ꢀ0.1185
239.56
164.52
233.00

T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
155
ble 6 concludes that there is a general decomposition pattern,
whereby, the complexes decompose in three main stages. The first
stage for all studied complexes is the loss of hydrated water mol-
ecules at 75–110 °C, followed in a second decomposition stage by
the loss of the coordinated water, chloride or acetate ions at
110–315 °C, after that, the deligation process started at a temper-
ature range of 190–800 °C, finally metal oxide formation takes
place.
Horowitz–Metzger models [45,46]. Coats–Redfern relation is as
follows:
ꢀ
ꢁ
ꢂ
ꢃ
lnð1 ꢀ
aÞ
AR
bE
E
RT
ln ꢀ
¼ ln
ꢀ
ð1Þ
T2
where
fined by:
a
represents the fraction of sample decomposed at time t, de-
woꢀwt
a
¼
, wo, wt and w are the weight of the sample be-
1
woꢀw
fore the degradat1ion, at temperature t and after total conversion,
respectively. T is the derivative peak temperature. b is the heating
rate = dT/dt, E and A are the activation energy and the Arrhenius
3.7. Kinetic data
h
i
lnð1ꢀ
a
Þ
pre-exponential factor, respectively. A plot of ln ꢀ
versus
2
The kinetic and thermodynamic parameters of thermal degra-
dation process have been calculated using Coats–Redfern and
1/T gives a straight line whose slope (E/R) and the pre-Texponential
factor (A) can be determined from the intercept.
Table 10
Kinetic parameters of complexes evaluated by Horowitz–Metzger equation.
Compound
Peak
Mid temp. (K)
Ea (kJ/mol)
A (Sꢀ1
)
D
H* (kJ/mol)
D
S* (kJ/mol K)
DG* (kJ/mol)
[Co(OI)(H2O)3]
1st
313
533
696
937
49.40
56.24
56.79
99.44
4.33 ꢂ 104
1.70 ꢂ 105
4.72 ꢂ 105
7.82 ꢂ 105
46.79
52.06
51.01
91.64
ꢀ0.1565
ꢀ0.1491
ꢀ0.1433
ꢀ0.1416
95.85
127.05
150.77
224.45
2nd
3rd
4rd
[Ni(OI)(H2O)3]
1st
337
547
762
869
35.98
31.91
137.35
169.98
4.29 ꢂ 104
1.73 ꢂ 105
2.23 ꢂ 106
7.34 ꢂ 105
33.17
27.36
131.01
162.75
ꢀ0.1572
ꢀ0.1496
ꢀ0.1311
ꢀ0.1415
86.24
109.32
231.04
285.85
2nd
3rd
4th
[Cu(HOI)Cl](H2O)2
1st
2nd
3rd
547
677
852
167.08
72.41
139.03
5.06 ꢂ 105
4.06 ꢂ 105
1.14 ꢂ 107
162.53
66.78
131.94
ꢀ140.75
ꢀ0.1443
ꢀ0.1185
239.56
164.52
233.00
lnX n=1
lnX n=1
(a)
(b)-12.5
lnX n=0.66
lnX n=0.66
lnX n=0.33
lnX n=0
-10.5
lnX n=0.33
lnX n=0
lnX n = 0.5
lnX n = 0.5
-11.0
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
3.00
3.20
3.30
1.76
1.88
3.10
1.80
1.84
1000/T
1000/T
lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
(c) -12.75
(d)
-13.5
-13.00
-13.25
-13.50
-13.75
-14.00
lnX n = 0.5
lnX n = 0.5
-14.0
-14.5
-15.0
1.40
1000/T
1.45
1.50
1.35
1.00
1.05
1.10
1.15
1000/T
Fig. 4. Coats–Redfern plots of (a) first, (b) second, (c) third and (d) fourth degradation steps for [Co(OI)(H2O)3] complex.

156
T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
0.5
0.0
lnX n=1
lnX n=1
(a)
(b)
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
1.0
0.5
lnX n = 0.5
lnX n = 0.5
0.0
-0.5
-1.0
-0.5
-1.0
-10
0
10
20
40
50
T-Ts
60
70
T-Ts
lnX n=1
lnX n=1
1.0
0.5
(c)
(d)
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
0.5
0.0
lnX n = 0.5
lnX n = 0.5
0.0
-0.5
-0.5
-1.0
-1.0
-30 -15
0
15 30 45 60
T-Ts
-50 -25
0
25 50 75 100
T-Ts
Fig. 5. Horowitz–Metzger plots of (a) first, (b) second, (c) third and (d) fourth degradation steps for [Co(OI)(H2O)3] complex.
The Horowitz–Metzger relation [46] used to evaluate the degra-
dation kinetics is:
The high values of the energy of activation, Ea of the complexes
reveals the high stability of such chelates due to their covalent
bond character [49].
Eh
RT2s
The positive sign of
that the free energy of the final residue is higher than that of the
initial compound, and all the decomposition steps are non-sponta-
DG* for the investigated complexes reveals
ln½ꢀ lnð1 ꢀ
aÞꢃ ¼
ð2Þ
neous processes. Also, the values of the activation,
significantly for the subsequent decomposition stages of a given
complex. This is due to increasing the values of T S* significantly
H* [50–
DG* increases
where h = T–Ts, Ts is the DTG peak temperature, T is the temperature
corresponding to weight loss Wt. A straight line should be observed
E
D
between ln½ꢀ lnð1 ꢀ
a
Þꢃ and h with a slope of RT2. A number of pyro-
s
from one step to another which overrides the values of
52].
D
lysis processes can be represented as a first order reaction. Particu-
larly, the degradation of a series of H2OI complexes was suggested
to be first order [47], therefore we assume n = 1 for the remainder
of the present text. The other thermodynamic parameters of activa-
tion can be calculated by Eyring equation [48]:
Appendix A. Supplementary material
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.molstruc.2011.10.036.
D
D
D
Hꢄ ¼ Ea ꢀ RT
ð3Þ
ð4Þ
ð5Þ
hA
Sꢄ ¼ R ln
KBT
References
Gꢄ ¼
D
H ꢀ T
DS
[1] S. Jayasree, K.K. Arvindakshan, J. Indian Chem. Soc. 71 (1994) 97.
[2] R.K. Parashar, R.C. Sharma, Inorg. Chem. Acta 151 (1988) 201.
[3] M.C.R. Arguelles, M.B. Ferrari, F. Bisceglie, C. Plizzi, G. Pelosi, S. Pinelli, M. Sassi,
J. Inorg. Biochem. 98 (2004) 313.
[4] R. Sharma, S.K. Agarwal, S. Rawat, M. Nagar, Trans. Met. Chem. 31 (2006) 201.
[5] K. Krisinankutty, J. Michael, J. Indian Chem. Soc. 78 (1996) 1.
[6] S.A. AbouEl-Enein, F.A. El-Saied, T.I. Kasher, A.H. El-Wardany, Spectrochim.
Acta Part A 67 (2007) 737.
[7] P.K. Singh, D.N. Kumar, Spectrochim. Acta Part A 64 (2006) 853.
[8] S.N. Pandeya, D. Sriram, Acta Pharm. Tureica 40 (1) (1998) 33.
[9] S.N. Pandeya, P. Yogeeshwari, Indian J. Pharm. Sci. 64 (3) (2002) 209.
[10] V. Manjusha, S.N. Pandeya, N.S. Krishna, P.S. James, Acta Pharm. 54 (2004) 49.
[11] P. Selvam, N. Murugesh, M. ChandraMohan, Z. Debyser, M. Witvroum, Indian J.
Pharm. Sci. (2008) 779.
Thermodynamic parameters such as activation energy (Ea), pre-
exponential factor (A), entropy of activation ( S*), enthalpy of acti-
vation ( H*) and free energy of activation ( G*) of decomposition
steps were calculated using Coats–Redfern [45] and Horowitz–
Metzger [46] methods Tables 9 and 10. In both methods, the lift
side of Eqs. (3) and (4) are plotted against 1/T and h, respectively
(Figs. 4 and 5). From the results, the following remarks can be
pointed out:
D
D
D
The negative values of
DS* for the degradation process indicates
more ordered activated complex than the reactants or the reaction
is slow [48].
[12] G.S. Singh, T. Singh, R. Lakhan, Indian J. Chem. 36B (1997) 951.
[13] S.K. Sridhar, A. Ramesh, Pharm. Bull. 24 (10) (2001) 1149.

T.A. Yousef et al. / Journal of Molecular Structure 1007 (2012) 146–157
157
[14] HyperChem Version 8.03 Hypercube, Inc.
[34] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143;
B.J. Hathaway, Struct. Bond. (Berlin, Ger.) 57 (1984) 55.
[35] O. Khan, T. Mallah, J. Gouteron, S. Jeanin, Y. Jeanin, J. Chem. Soc. Dalton Trans.
1117 (1989).
[36] H. Yokoi, M. Chikira, J. Am. Chem. Soc. 97 (1975) 3975.
[37] S. Pal, Proc. Indian Acad. Sci. (Chem. Sci.) 114 (2002) 417.
[38] J.A. Wellman, F.B. Hulsbergen, J. Inorg. Nucl. Chem. 40 (1978) 143.
[39] V.T. Kasumo, Spectrochim. Acta A 57 (2001) 1649.
[40] N. Raman, Y. Pitchaikani Raja, A. Kulandaisamy, Proc. Indian Acad. Sci. 113
(2001) 183.
[15] N.L. Allinger, J. Am. Chem. Soc. 99 (1977) 8127.
[16] S.H. Guzar, J.I.N. Qin-han, J. Appl. Sci. 8 (2008) 2480.
[17] K.K. Narang, V.P. Singh, Transit. Met. Chem. 21 (1996) 507.
[18] D.X. West, D.L. Huffman, J. Trans. Met. Chem. 14 (1989) 190.
[19] G.A.A. Al-Hazmiy, M.S. El-Shahawiz, I.M. Gabr, A.A. El-Asmy, J. Coord. Chem. 58
(2005) 713.
[20] C.D. Rao, B. Paul, B.K. Mohapatra, S. Guru, J. Inorg. Nucl. Chem. 40 (1978)
134.
[21] L.H. Jones, Spectrochim. Acta 10 (1958) 395.
[22] S.P. McGlynn, J.K. Smith, J. Chem. Phys. 35 (1961) 105.
[23] T.H. Rakha, N. Nawar, G.M. Abu Reash, Synth. React. Inorg. Met.-Org. Chem. 26
(1996) 1705.
[41] R.P. John, Spectrochim. Acta A 59 (2003) 1349.
[42] G.A.A. Al-Hazmi, M.S. El-Shahawi, I.M. Gabr, A.A. El-Asmy, J. Coord. Chem. 58
(2005) 713.
´
[24] M.C. Rodríguez-Arguüelles, S. Mosquera-Vazquez, P. Tourón-Touceda, J.
[43] N.M. El-Metwally, I.M. Gabr, A.A. Abou-Hussen, A.A. El-Asmy, J. Transit. Met.
Chem. 31 (2006) 71.
[44] S. Sagdinc, B. Koksoy, F. Kandemirli, S.H. Bayari, J. Mol. Struct. 917 (2009) 63.
[45] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68.
[46] H.H. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464.
[47] A. Broido, J. Ploym. Sci., A-2 7 (1969) 1761.
[48] A.A. Frost, R.G. Pearson, Kinetics and Mechanisms, Wiley, New York, 1961.
[49] T. Taakeyama, F.X. Quinn, Thermal Analysis Fundamentals and Applications to
Polymer Science, John Wiley and Sons, Chichester, 1994.
[50] P.B. Maravalli, T.R. Goudar, Thermochim. Acta 235 (1999) 35.
[51] K.K.M. Yusuff, R. Sreekala, Thermochim. Acta 159 (1990) 357.
[52] S.S. Kandil, G.B. El-Hefnawy, E.A. Baker, Thermochim. Acta 414 (2004) 105.
Sanmartín-Matalobos, A.M. García-Deibe, M. Belicchi-Ferrari, G. Pelosi, C.
Pelizzi, F. Zani, J. Inorg. Biochem. 101 (2009) 138.
[25] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1968.
[26] M. Palaniandavar, C. Natarajan, Aust. J. Chem. 33 (1980) 737.
[27] M.M. Mostafa, M.A. Khattab, K.M. Ibrahim, Polyhedron 2 (1983) 583.
[28] A. Syamal, K.S. Kale, Indian J. Chem. 16A (1978) 46.
[29] L. Dubiki, R.L. Martin, Inorg. Chem. 5 (1966) 2203.
[30] A.K. Gregson, R.L. Martini, S. Mitra, Proc. Roy Soc. 320A (1971) 473.
[31] L. Sacconi, M. Ciampolini, J. Chem. Soc. 276 (1964).
[32] S.P. McGlynn, J.K. Smith, W.C. Neely, J. Mol. Spectros. 6 (1961) 164.
[33] G. Speier, J. Csihony, A.M. Whalen, C.G. Pie-Pont, Inorg. Chem. 35 (1996) 3519.