Thermal, spectroscopic, and solvent influence studies on mixed-ligand copper(II) complexes containing the bulky ligand: Bis[N-(p-tolyl)imino]acenaphthene

Article abstract of DOI:10.1016/j.saa.2006.07.012

Four mixed-ligand copper(II) complexes containing the rigid bidentate nitrogen ligand bis[N-(p-tolyl)imino]acenaphthene (abb. p-Tol-BIAN) ligand are reported. These complexes, namely [Cu(p-Tol-BIAN)₂](ClO₄)₂ 1, [Cu(p-Tol-BIAN)(acac)](ClO₄) 2, [Cu(p-Tol-BIAN)Cl₂] 3 and [Cu(p-Tol-BIAN)(AcOH)₂](ClO₄)₂ 4 (where acac, acetylacetonate and AcOH, acetic acid) have been prepared and characterized by elemental analysis, spectroscopic, magnetic and molar conductance measurements. ESR spectra suggest a square planar geometry for complexes 1 and 2. In complexes 3 and 4, a distorted tetrahedral arrangement around copper(II) centre was suggested. Solvatochromic behavior of all studied complexes indicates strong solvatochromism of their solutions. The observed solvatochromism is mainly due to the solute-solvent interaction between the chelate cation and the solvent molecules. Thermal properties and decomposition kinetics of all complexes are investigated. The kinetic parameters (E, A, ΔH, ΔS and ΔG) of all thermal decomposition stages have been calculated using the Coats-Redfern and other standard equations.

Full text of DOI:10.1016/j.saa.2006.07.012

Spectrochimica Acta Part A 67 (2007) 263–272
Thermal, spectroscopic, and solvent influence studies on mixed-ligand
copper(II) complexes containing the bulky ligand:
Bis[N-(p-tolyl)imino]acenaphthene
Usama El-Ayaan∗, I.M. Gabr
Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egypt
Received 3 March 2006; received in revised form 4 July 2006; accepted 5 July 2006
Abstract
Four mixed-ligand copper(II) complexes containing the rigid bidentate nitrogen ligand bis[N-(p-tolyl)imino]acenaphthene (abb. p-Tol-BIAN)
ligand are reported. These complexes, namely [Cu(p-Tol-BIAN)2](ClO4)2 1, [Cu(p-Tol-BIAN)(acac)](ClO4) 2, [Cu(p-Tol-BIAN)Cl2] 3 and [Cu(p-
Tol-BIAN)(AcOH)2](ClO4)2 4 (where acac, acetylacetonate and AcOH, acetic acid) have been prepared and characterized by elemental analysis,
spectroscopic, magnetic and molar conductance measurements. ESR spectra suggest a square planar geometry for complexes 1 and 2. In complexes
3 and 4, a distorted tetrahedral arrangement around copper(II) centre was suggested. Solvatochromic behavior of all studied complexes indicates
strong solvatochromism of their solutions. The observed solvatochromism is mainly due to the solute–solvent interaction between the chelate
cation and the solvent molecules. Thermal properties and decomposition kinetics of all complexes are investigated. The kinetic parameters (E, A,
ꢀH, ꢀS and ꢀG) of all thermal decomposition stages have been calculated using the Coats–Redfern and other standard equations.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Mixed-ligand copper(II) complexes; Thermal analysis; Spectroscopic
NO3− or a halogen) [6–10]. Solvatatochromism depends mainly
on the: (i) the more or less pronounced coordination of solvent
molecules to the complex and (ii) the more or less pronounced
coordination of anions (X−) to the complex. Both forms of coor-
dination lead to significant changes in the d–d transitions and to
a strong change in the color of the complexes in solution. The
former effect is governed by the donor strength of the respective
solvent molecules and, in fact, the observed solvatochromism
can be used to visualize and to measure donor properties of sol-
vents and even solvent mixtures.
In the present work, we report the syntheses, spectral,
thermal and solvatochromic behavior of four mixed-ligand
copper(II) complexes containing the bidentate nitrogen
ligand bis[N-(p-tolyl)imino]acenaphthene (Fig. 1). These
complexes, namely [Cu(p-Tol-BIAN)2](ClO4)2 1, [Cu(p-
1. Introduction
Mixed-ligand complexes are observed in biological sys-
tems or in the intermediate chemical reactions with metal
ions, which is important to understand the respective chem-
istry. Investigations concerning diimine mixed-ligand chelate
systems have a great help toward understanding the driving
forces that led to the formation of such mixed-ligand complexes
[1–3].
Solvatochromism in the mixed-ligand metal complexes has
received great attention because they may be used as a Lewis
acid–base color indicators [4] and also utilizes to develop
optical sensor materials to monitor pollutant levels in the
environment [5]. Extensive studies have been focused on
mixed-ligand copper(II) complexes containing ␤-diketonates
(dike) and N-alkylated diamines (diam) of the general formu−la
Tol-BIAN)(acac)](ClO4) 2, [Cu(p-Tol-BIAN)Cl2]
3 and
[Cu(dike)(diam)]X (X is an univalent anion, such as ClO4
,
[Cu(p-Tol-BIAN)(AcOH)2](ClO4)2 4. The kinetic parameters,
such as the reaction order, n, the activation energy, E and
the pre-exponential factor, A have been determined using
Coats–Redfern method [11]. The other kinetic parameters,
namely enthalpy, ꢀH, entropy, ꢀS, and activation energy, ꢀG,
have been calculated using the standard equations.
∗
Corresponding author. Present address: Department of Chemistry, College
of Science, King Faisal University, Hofuf 31982, P.O. Box 1759, Saudi Arabia.
Tel.: +966 553901011.
E-mail address: uelayaan@kfu.edu.sa (U. El-Ayaan).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.07.012

264
U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
Yield: 3.50 g (72%) of (p-Tol-BIAN) (360.45). Found: C,
86.60; H, 5.50; N, 7.66. Calcd. for C26H20N2 (360.45): C, 86.64;
H, 5.59; N, 7.77%. 1H NMR (CDCl3, recorded at 400 MHz at
23.6 ◦C) δ = 2.44 (s, p-Me), 6.92 (d, H3), 7.03 (d, H9), 7.26 (d,
H10), 7.37 (pst, H4), 7.86 (d, H5). 13C NMR (CDCl3, 400 MHz,
24.5 ◦C): δ = 21.06 (p-Me), 161.06 (C1), 128.49 (C2), 123.68
(C3), 127.38 (C4), 128.62 (C5), 131.0 (C6), 141.49 (C7), 149.0
(C8), 118.04 (C9, C13), 129.77 (C10, C12), 133.68 (C11).
2.3. Synthesis of metal complexes
Mixed-ligand copper complexes were prepared by adding the
appropriate amount of copper perchlorate or copper chloride (in
case of 3) to an ethanolic solution of the p-Tol-BIAN ligand.
To this mixture acac (in case of 2) or AcOH (in case of 4) was
added. The mixtures were stirred (while heating) for 1–3 h. The
resulting green solid product was filtered, washed with ethanol
and dried in air.
Yield: 0.20 g (80.0%) of [Cu(p-Tol-BIAN)2](ClO4)2 (1,
C52H40Cl2CuN4O8) (983.35): calcd. C 63.51, H 4.10, N 5.69%;
found C 62.28%, H 4.15%, N 5.44%. Magnetic moment
μeff/μBM = 1.39 at 297 K.
Fig. 1. Bis[N-(p-tolyl)imino]acenaphthene (p-Tol-BIAN).
2. Experimental
2.1. Instrumentation and materials
All starting materials were purchased from Wako Pure Chem-
ical Industries Ltd., and used without further purification. Ele-
mental analyses (C, H, N) were performed on a Perkin-Elmer
2400 Series II Analyzer. Electronic spectra were recorded on a
UV-UNICAM 2001 spectrophotometer using 10 mm pass length
quartz cells at room temperature. Magnetic susceptibility was
measured with a Sherwood Scientific magnetic susceptibility
balance at 297 K. Infrared spectra were recorded on a Perkin-
Elmer FT-IR Spectrometer 2000 as KBr pellets and as Nujol
mulls in the 4000–370 cm−1 spectral range. 1H and 13C NMR
measurements at room temperature were obtained on a Jeol JNM
LA 300 WB spectrometer at 400 MHz, using a 5 mm probe head
in CDCl3. Chemical shifts are given in ppm relative to internal
TMS (tetramethylsilane).
ESR spectrum was obtained on a Bruker EMX spectrometer
working in the X-band (9.78 GHz) with 100 kHz modulation fre-
quency. The microwave power was set at 1 mW and modulation
amplitude was set at 4 G. The low field signal was obtained after
four scans with a 10-fold increase in the receiver gain. A pow-
der spectrum was obtained in a 2 mm quartz capillary at room
temperature.
0.25 g
(74.0%)
of
[Cu(p-Tol-BIAN)(acac)](ClO4)
(2,C31H28ClCuN2O6) (623.56): calcd. C 59.71%, H 4.53%, N
4.49%; found C 60.07%, H 4.54%, N 4.27%. Magnetic moment
μeff/μBM = 1.56 at 297 K.
0.25 g (74.0%) of [Cu(p-Tol-BIAN)Cl2], (3, C26H20
Cl2CuN2) (494.9): calcd. C 63.10, H 4.10, N 5.66%; found C
62.47%, H 4.24%, N 5.27%. Magnetic moment μeff/μBM = 1.88
at 297 K.
0.25 g (74.0 of [Cu(p-Tol-BIAN)(AcOH)2](ClO4)2 (4,
C30H28Cl2Cu N2O12) (743.0): calcd. C 48.5, H 3.8, N
3.77%; found C 48.1%, H 3.66%, N 3.6%. Magnetic moment
μeff/μBM = 1.98 at 297 K.
3. Results and discussion
3.1. IR spectra of ligand and the complexes
2.2. Synthesis of bis[N-(p-tolyl)imino]acenaphthene
(p-Tol-BIAN)
Infrared spectral data for the free p-Tol-BIAN ligand and
complexes 1–4 are listed in Table 1. Formation of the free p-
Tol-BIAN ligand can be concluded from the IR spectroscopy
where only C N stretching vibrations were observed in the
1630–1675 cm−1 range and no C O stretching vibrations of
Preparation of the ligand was carried out in two steps (Fig. 2)
similarly as reported earlier [12] with the very similar bis[N-
(2,4,6-trimethylphenyl)imino]acenaphthene.
Fig. 2. Preparation of (p-Tol-BIAN) ligand.

U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
265
Table 1
Electrical conductivity data (Λm) and infrared data (cm−1) of complexes 1–4
Compound
Λm (ꢁ−1cm2 mol−1
)
IR (cm−1
)
)
−
Empirical formula
F Wt
AN
NM
ν (C N)
ν (ClO4
ν (AcOH)
p-Tol-BIAN
[Cu(p-Tol-BIAN)2](ClO4)2 (1)
C52H40Cl2Cu N4O8
360.45
1675, 1657, 1630
1652, 1622
330
180
25
192
100
5
1090, 623
1102, 623
983.35
623.56
494.9
[Cu(p-Tol-BIAN)(acac)](ClO4) (2)
1652, 1635
1667, 1624
1675, 1652
C31H28ClCuN2O6
[Cu(p-Tol-BIAN)Cl2] (3)
C26H20 Cl2CuN2
[Cu(p-Tol-BIAN)(AcOH)2](ClO4)2 (4)
1751, 1719
320
188
1123, 624
C30H28Cl2Cu N2O12
743.0
the starting diketones in the 1700–1800 cm−1 region. Bands
assigned to ν (C N) are shifted to lower wavenumbers in com-
plex spectra indicating the coordination of both diimine nitrogen
atoms of p-Tol-BIAN ligand to the copper ion.
parameters of the complexes were calculated and are summa-
rized in Table 3.
The room temperature solid state ESR spectra of all com-
plexes (Fig. 3) are quite similar and exhibit an axially symmetric
g-tensor parameters with g > g > 2.0023 indicating that the
Strong band observed at ∼1100 cm−1 (antisymmetric
stretch) and the sharp band at ∼620 cm−1 (antisymmetric bend),
suggest uncoordinated perchlorate anion [13] in complexes 1, 2
and 4 (Table 1).
||
⊥
copper site has a dx2−y2 ground-state characteristic of square
planar, square base pyramidal, tetrahedral or octahedral geom-
etry [17].
No band corresponding to the forbidden magnetic dipo-
lar transition for the complexes are observed at half-field (ca.
1500 G, g = 4.0), ruling out any Cu–Cu interaction and indicat-
ing that the complexes are mono nuclear copper(II) complexes.
Infraredspectroscopicdata(Table2)suggestthecoordination
of (acac) ligand to the copper(II) centre in 2 [14].
Generally, it is known that the aromatic rings with three
adjacent carbon–hydrogen bonds show strong bands in the
810–750 cm−1 region due to out-of-plane CH deformation
vibrations [15]. Their position is determined almost wholly
by their location on the ring rather than by the nature of
the substituent and, with certain limitations, they provide an
excellent method for recognition of the type of substitution.
The very high intensity and sensitivity of these characteris-
tic bands in this region make them particularly well suited
for quantitative work, too. The splitting of these out-of-plane
CH deformation vibrations bands in the 850–750 cm−1 region
of the complex 1 can be considered as a sign of the coor-
dination of two p-Tol-BIAN ligands to the copper(II) ion
[16].
3.2. ESR spectroscopy
To obtain further information about the stereochemistry and
the site of the metal ligand bonding and to determine the mag-
netic interaction in the metal complexes, ESR spectra of the
complexeswererecordedinthesolidstate. ThespinHamiltonian
Table 2
Infrared band positions and band assignments of complex 2
Band position (cm−1
)
Assignment
464
555
ν(Cu–O) + ν(C–CH3)
Ring def. + ν(Cu–O)
660
933
ν(C–CH3) + ring def. + ν(Cu–O)
ν(C C) + ν(C O)
1281
1520
1583
ν(C–CH3) + ν(C C)
ν(C C) + ν(C O) combination
Fig. 3. Solid state X-band ESR spectra of complexes 1–4.

266
U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
Table 3
ESR data of complexes at room temperature
Complex
g
||
G
⊥
A × 10−4 (cm−1
)
g /A
|| ||
G
α2
β2
||
[Cu(p-Tol-BIAN)2](ClO4)2 (1)
[Cu(p-Tol-BIAN)(acac)](ClO4) (2)
[Cu(p-Tol-BIAN)Cl2] (3)
2.25
2.27
2.38
2.35
2.04
2.05
2.08
2.06
178
175
170
165
126
129
140
142
6.25
5.4
4.75
5.8
0.78
0.81
0.92
0.87
0.73
0.82
0.99
0.99
[Cu(p-Tol-BIAN)(AcOH)2](ClO4)2 (4)
The lower value of α2 compared to β2 indicates that the in-
plane ␴-bonding is more covalent than the in-plane ␲-bonding.
In complexes 3 and 4, the α2 values are (0.92 and 0.87) indicate
the slight ionic nature of the metal–ligand ␴-bonding, and the
values of β2 are 0.99 indicates the presence of considerable in-
plane ␲-bonding contribution in metal–ligand ␲-bonding. These
data are well in accordance with other reported values [29].
In axial symmetry, the g-values are related by the expression,
G = (g − 2)/(g − 2) = 4, which measures the exchange inter-
||
⊥
action between copper centers in the solid.
According to Hathaway [18,19], if the value of G is greater
than four, the exchange interaction between copper(II) centers
in the solid state is negligible, whereas when is less than four, a
considerable exchange interaction is indicated in the solid com-
plex. The calculated G values are given in Table 3. The G values
are greater than four suggesting that there are no copper–copper
exchange interactions.
3.3. Solvatochromism
The tendency of A to decrease with an increase of g is an
||
||
The absorption spectra of complexes 1–4 were measured in
different organic solvents with different donor numbers (DN).
The donor number proposed by Gutmann [30,31] is a measure
of the donor ability or Lewis basicity of a solvent molecule
measured on the basis of the amount of heat evolved when the
same solvent is added to a solution of SbCl5 in DCE.
The absorption spectra show one broad band attributed to the
promotions of the electron in the lower energy orbitals to the
hole in dx2−y2 orbital of the copper(II) ion (d9). The position
of this band is shifted to longer wavelength (red shift) as the
donor number of solvent increases (Table 4). Assuming that the
approach of the solvent occurs along with z-axis, the solvent
molecules are repelled by the two electrons in the d2z orbital
of copper(II) and only the more species can force their way in
to form relatively strong bonds. Upon coordination, they exert
a z-component field proportional to their position in the spec-
trochemical series. Thus, while a solvent of low donor number
(basicity) have less effect in the band maxima, others with higher
values induce larger red shift.
index of an increase of the tetrahedral distortion in the coordi-
nation sphere of copper [20,21]. In order to quantify the degree
of distortion of the copper(II) complexes, we selected the f fac-
tor g /A obtained from the ESR spectra. Although the f factor,
|| ||
which is considered an empirical index of tetrahedral distortion
[22]. Its value ranges between 105 and 135 for square planar
complexes, depending on the nature of the coordinated atoms.
In the presence of a tetrahedrally distorted structure, the values
can be much larger. For complexes 1 and 2, the g /A quotient
|| ||
are 126 and 129, evidence in support of the square planar geom-
etry with no appreciable tetrahedral distortion. The ratio g /A
|| ||
for complexes 3 and 4 are 140 and 142 demonstrating the pres-
ence of significant dihedral angle distortion in the xy-plane and
indicating a tetrahedral distortion from square planar geometry
[23].
Superhyperfine structures for these complexes are not seen
at higher fields excluding any interaction of the nuclear spins of
the nitrogen (I = 1) with the unpaired electron density on Cu(II)
centre [24].
Conductivity data (Table 1) of studied complexes suggest
Molecular orbital coefficients, α2 (a measure of the covalency
of the in-plane ␴-bonding between a copper 3d orbital and the
ligand orbitals) and β2 (covalent in-plane ␲-bonding), were cal-
culated by using the following equations [25–28], where α2 = 1
indicates complete ionic character, whereas α2 = 0.5 denotes
100% covalent bonding, with the assumption of negligibly small
values of the overlap integral.
−
that ClO4 acts only as a counter ion and do not interact with
any solute (complex cation) [32]. Therefore, the complex struc-
ture depends only on the donor properties of the solvent used
(Gutmann’s donor number DN) [33], and only solute–solvent
interactions can be considered.
Table 4
ꢀ
ꢁ
Absorption maxima λmax (nm) of complexes, 1–4, in different solvents
A
3
ꢀ
α2 =
+ (g − 2.0023) +
+ 0.04
a
λmax (ε l mol−1 cm−1
)
ꢀ
Solvent
DN
0.036
7(g − 2.0023)
⊥
1
2
3
4
(g − 2.0023)E
ꢀ
β2 = −
,
CH2Cl2
CH3NO2
CH3CN
CH3OH
HCON(CH3)2
CH3SOCH3
0
2.7
14.1
19.1
26.6
29.8
656 (429)
661 (387)
693 (195)
714 (150)
740 (272)
763 (65)
610 (338)
630 (255)
n.d.
720 (209)
763 (331)
830 (44)
620 (215)
n.d.
720 (200)
750 (153)
769 (206)
868 (56)
607 (429)
n.d.
n.d.
745 (272)
763 (472)
845 (67)
8λα2
where λ = −828 cm−1 for the free copper ion and E is the
electronic transition energy. From Table 3, the α2 and β2 val-
ues indicate that there is a substantial interaction in the in-
plane ␴-bonding whereas the in-plane ␲-bonding is almost
ionic.
n.d. Not detected.
a
The extinction coefficient values are given in parenthesis.

U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
267
Fig. 6. TG and DTG of [Cu(p-Tol-BIAN)2](ClO4)2.
Fig. 4. Solvation free energy relationship (DN vs. νmax/103) secondary axis is
the ordinate of complex 1.
Solvatochromic behavior was studied quantitatively by
applying the linear solvation free energy relationship [17],
νmax/103 = ν◦ + a (DN); where νmax the measured d–d absorp-
tion frequency, ν◦ the extrapolated frequency and a is the slope,
represents the sensitivity of the complex toward solvent. Linear-
ity of the νmax versus DN, (Fig. 4) confirms the solvatochromic
behavior in perchlorate complexes. The slope value (a) is the
smallest in case of 1, in which two diimine ligand are coordi-
nated to the copper(II) centre imposing a large steric hindrance
to the axial coordination of incoming solvent leading to less
solvatochromic behavior.
3.4. Thermal analysis
Fig. 7. TG and DTG of [Cu(p-Tol-BIAN)(acac)](ClO4).
Thermogravimetric (TG) and differential thermogravimetric
(DTG) analysis were carried out for p-Tol-BIAN free ligand
and complexes 1–4 (Figs. 5–9). The stages of decomposition,
temperature ranges, decomposition product loss as well as the
found and calculated weight loss percentages of free ligand and
the complexes are given in Table 5.
The TG, DTG curves of p-Tol-BIAN free ligand indicate
that the ligand is thermally stable in the temperature range
25–226 ◦C. Decomposition of the ligand started at 227 ◦C and
finished at 694 ◦C with to stages (Fig. 5). The first stage of
decomposition occurs in the 227–356 ◦C temperature range, cor-
responding to the loss of two toluene (C6H5CH3) molecules.
The second stage of decomposition involves the cleavage of the
naphthalene backbone in the 580–787 ◦C temperature range, and
is accompanied by a weight loss of 27.8%, corresponding to the
loss of C8H6.
Fig. 5. TG and DTG of (p-Tol-BIAN) free ligand.
Fig. 8. TG and DTG of [Cu(p-Tol-BIAN)Cl2].

268
U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
Table 5
Thermal behavior of p-Tol-BIAN free ligand and complexes 1–4
Compound (molecular weight)
DTG peak
(◦C)
Temperature
range (◦C)
Decomposition product lost (formula wt.)
Wt. (%) found
(calculated)
p-Tol-BIAN (360.45)
289.0
694.0
294.0
227–356
580–786
249–367
50.0 (51.0)
27.8 (28.3)
17.6 (18.7)
C8H6 (102.13)
ClO4 (99.45)
[Cu(p-Tol-BIAN)2](ClO4)2 (983.35)
445
626
367–532
533–707
10.6 (10.1)
28.1 (28.8)
[Cu(p-Tol-BIAN)(acac)](ClO4) (623.56)
[Cu(p-Tol-BIAN)Cl2] (494.9)
280
661
241–348
546–759
23.5 (24.1)
45.7 (44.8)
246
586
216–290
461–647
Cl2 (70.9)
13.4 (14.3)
37.2 (37.2)
686
267
574
647–759
225–329
493–657
C8H6 (102.1)
21.0 (20.6)
16.2 (16.1)
51.57(51.57)
[Cu(p-Tol-BIAN)(AcOH)2](ClO4)2 (743.0)
2 (CH3COOH) (120.1)
The thermal decomposition process of [Cu(p-Tol-
BIAN)2](ClO4)2 involves three decomposition steps (Fig. 6).
The first decomposition step (within the temperature range
249–366 ◦C) corresponds to the loss of two terminal toluene
molecules attached to nitrogen atoms. The second decom-
position step accompanied by a weight loss of 10.6% in the
367–532 ◦C temperature range, corresponding to the elimi-
nation of one perchlorate molecule. The third decomposition
step centered at 626 ◦C DTG-peaks, involving weight loss of
27% corresponding to the elimination of another two toluene
molecules and one perchlorate molecule.
The thermal decomposition curves of the complex [Cu(p-Tol-
BIAN)(acac)](ClO4) show two decomposition steps (Fig. 7).
The first one corresponding to the loss of two methyl groups,
one ethylene and one toluene molecules, in the 241–280 ◦C tem-
perature range. The second decomposition step occurs in the
546–759 ◦C temperature range and is accompanied by a weight
loss of 45.7%, corresponding to the loss of 2CO2 + ClO4 +
C6H5CH3. Theresidueof0.071 mg(22.1%)exactlycorrespond-
ing to the fragment C4N2Cu.
The TG, DTG curves of [Cu(p-Tol-BIAN)Cl2] (Fig. 8) show
three steps of decomposition. The first step involves the elimina-
tion of chlorine molecule in the 216–290 ◦C temperature range.
The second decomposition step brings a weight loss of 37.25%
due to the loss of two toluene molecules in the 461–647 ◦C tem-
perature range. In the third decomposition step (647–759 ◦C), a
weight loss of 21.9% corresponding to the loss of (C8H6) frag-
ment resulting from breaking of naphthalene moiety. There is
no further mass loss beyond 760 ◦C and a plateau is obtained
exactly corresponding to C4N2Cu.
The thermal decomposition curves of the complex [Cu(p-
Tol-BIAN)(AcOH)2](ClO4)2 show two decomposition steps
(Fig. 9). The first one corresponding to the loss of two acetic acid
molecules in the 225–329 ◦C temperature range. In the second
decomposition step, a weight loss corresponding to two toluene
and two perchlorate molecules was obtained. The residue of
0.066 mg (23%) exactly corresponding to C7N2Cu.
In order to access the influence of the structural properties
of the ligand and the type of the metal on the thermal behavior
of the complexes, the order n, and the heat of activation E of
Fig. 9. TG and DTG of [Cu(p-Tol-BIAN)(AcOH)2](ClO4)2.

U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
269
Fig. 10. Coats–Redfern plots for p-Tol-BIAN free ligand, where Y = −ln(1 − α)/T2.
the various decomposition stages were determined from the TG
and DTG thermograms using the Coats–Redfern equations in
the following forms:
where M = −E/R and B = ln AR/ΦE; E, R, A and Φ are the heat
of activation, the universal gas constant, pre-exponential factor
and heating rate, respectively.
The correlation coefficient, r, was computed using the least
square method for different values of n by plotting the left-hand
ꢂ
ꢄ
ꢃ
1 − (1 − α)1−n
(1 − n)T2
M
T
ln
ln
=
+ B for n = 1
(1)
(2)
side of Eq. (1) or (2) versus 1000/T, Figs. 10–14. The n value
∼
which gave the best fit (r 1) was chosen as the order parameter
=
for the decomposition stage of interest. From the intercept and
linear slope of such stage, the A and E values were determined.
The other kinetic parameters, ꢀH, ꢀS and ꢀG were computed
ꢅ
− ln(1 − α)
M
=
+ B for n = 1
T2
T
Fig. 11. Coats–Redfern plots for [Cu(p-Tol-BIAN)2](ClO4)2, where Y = −ln(1 − α)/T2.

270
U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
Fig. 12. Coats–Redfern plots for [Cu(p-Tol-BIAN)(acac)](ClO4), where Y = −ln(1 − α)/T2.
using the relationships; ꢀH = E − RT, ꢀS = R[ln(Ah/kT) − 1]
and ꢀG = ꢀH − TꢀS, where k is the Boltzmann’s constant and
h is the Planck’s constant. The kinetic parameters are listed in
Table 6. The following remarks can be pointed out: (i) all com-
plexes decomposition stages show a best fit for (n = 1) indicating
a first order decomposition in all cases. Other n values (e.g. 0,
0.33 and 0.66) did not lead to better correlations. (ii) The value of
ꢀG increases significantly for the subsequently decomposition
stages of a given complex. This is due to increasing the values of
TꢀS significantly from one stage to another which override the
values of ꢀH. Increasing the values of ꢀG of a given complex
as going from one decomposition step subsequently to another
reflects that the rate of removal of the subsequent ligand will
be lower than that of the precedent ligand [34,35]. This may
be attributed to the structural rigidity of the remaining complex
after the expulsion of one and more ligands, as compared with
the precedent complex, which require more energy, TꢀS, for
its rearrangement before undergoing any compositional change.
(iii) The negative values of activation entropies ꢀS indicate a
more ordered activated complex than the reactants and/or the
reactions are slow [36]. (iv) The positive values of ꢀH mean
that the decomposition processes are endothermic.
Fig. 13. Coats–Redfern plots for [Cu(p-Tol-BIAN)Cl2], where Y = −ln(1 − α)/T2.

U. El-Ayaan, I.M. Gabr / Spectrochimica Acta Part A 67 (2007) 263–272
271
Fig. 14. Coats–Redfern plots for [Cu(p-Tol-BIAN)(AcOH)2](ClO4)2, where Y = −ln(1 − α)/T2.
Table 6
Temperature of decomposition, and the kinetic parameters of p-Tol-BIAN free ligand and complexes 1–4
Compound
Step
T (K)
A (S−1
)
E (kJ mol−1
)
ꢀH (kJ mol−1
)
ꢀS (kJ mol−1 K−1
)
ꢀG (kJ mol−1
)
p-Tol-BIAN
First
Second
562
967
11318.8
5021.2
135.7
139.7
131.0
131.7
−0.181
−0.192
232.7
317.5
[Cu(p-Tol-BIAN)2](ClO4)2
First
Second
Third
567
718
899
337
5553.4
4757.5
56.0
115.0
130.4
51.3
109.0
123.0
−0.210
−0.189
−0.192
170.5
244.6
295.6
[Cu(p-Tol-BIAN)(acac)](ClO4)
[Cu(p-Tol-BIAN)Cl2]
First
Second
553
933
1399.6
8833.7
67.2
157.6
62.6
150.0
−0.198
172.1
324.6
−0.187
First
Second
Third
519
859
959
12285.5
3921
13562.9
138.0
96.6
194.4
133.7
89.5
186.4
−0.180
−0.190
−0.184
226.8
255.5
362.7
[Cu(p-Tol-BIAN)(AcOH)2](ClO4)2
First
Second
540
847
15354.6
9079.0
162.3
150.2
157.8
143.2
−0.178
254.0
300.9
−0.186
4. Conclusion
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209.
In solid state, the ESR spectra gave good evidence for the
proposed structure and the bonding for all studied complexes.
Thermal analyses are investigated and allow calculating the
kinetic parameters of all thermal decomposition stages of all
complexes.
In solution, these mixed-ligand copper complexes showed a
good correlation between their d–d absorption maxima and the
donor strength of the solvent used (positive solvatochromism).
This behavior is further confirmed by applying the linear solva-
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