Supramolecular spectroscopic and thermal studies of azodye complexes

Article abstract of DOI:10.1016/j.saa.2014.02.037

A series of heterocyclic ligand of copper(II) complexes have been synthesized by the reaction of copper(II) acetate with 5-(4′-derivatives phenylazo)-2-thioxothiazolidin-4-one (HL_n) yields 1:1 and 1:2 (M:L) complexes depending on the reaction conditions. The elemental analysis, spectral (IR and ESR), conductance, magnetic measurements, and thermogravimetric analysis (TGA) are used to characterize the isolated complexes. It is found that the change of substituent affects the thermal properties of azodye rhodanine derivatives and their Cu(II) complexes. The molecular and electronic structures of the investigated compounds (HL_n) were also studied using quantum chemical calculations. According to intramolecular hydrogen bond leads to increasing of the complexes stability. The data revealed that the coordination geometry around Cu(II) in all complexes (1-4) exhibit a trans square planar by NO monobasic bidentate and the two monobasic bidentate in octahedral complexes (5-7). Electronic, magnetic data and ESR spectra proposed the square planar structure for all complexes (1-4) under investigation. The value of covalency factor (^{β1a?? -)2} and orbital reduction factor K accounts for the covalent nature of the complexes. The activation thermodynamic parameters, such as activation energy (E_a), enthalpy (ΔH ^*), entropy (ΔS^*), and Gibbs free energy change of the decomposition (ΔG^*) are calculated using Coats-Redfern and Horowitz-Metzger methods.

Full text of DOI:10.1016/j.saa.2014.02.037

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Supramolecular spectroscopic and thermal studies of azodye complexes
1
⇑
A.Z. El-Sonbati , M.A. Diab, A.A. El-Bindary, Sh.M. Morgan
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
The ligands (HLn) and their Cu(II)
complexes were prepared and
characterized.
The molecular and electronic
structures of the investigated
compounds (HLn) have been
discussed.
ESR calculations support the
characterization of the structures of
the complexes geometries.
Thermal data suggested that the
ligands are more stable as compared
to complexes.
R
R
S
N
ꢀ
S
N
H2O
O
C
S
N
N
S
C
NH
Cu
N
O
HN
.2H2O
H2O
NH
Cu
ꢀ
ꢀ
ꢀ
OH2
O
C
S
N
S
OAc
R
Different thermodynamic parameters
were discussed.
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of heterocyclic ligand of copper(II) complexes have been synthesized by the reaction of copper(II)
acetate with 5-(40-derivatives phenylazo)-2-thioxothiazolidin-4-one (HLn) yields 1:1 and 1:2 (M:L) com-
plexes depending on the reaction conditions. The elemental analysis, spectral (IR and ESR), conductance,
magnetic measurements, and thermogravimetric analysis (TGA) are used to characterize the isolated
complexes. It is found that the change of substituent affects the thermal properties of azodye rhodanine
derivatives and their Cu(II) complexes. The molecular and electronic structures of the investigated com-
pounds (HLn) were also studied using quantum chemical calculations. According to intramolecular hydro-
gen bond leads to increasing of the complexes stability. The data revealed that the coordination geometry
around Cu(II) in all complexes (1–4) exhibit a trans square planar by NO monobasic bidentate and the two
monobasic bidentate in octahedral complexes (5–7). Electronic, magnetic data and ESR spectra proposed
the square planar structure for all complexes (1–4) under investigation. The value of covalency factor
Received 21 December 2013
Received in revised form 5 February 2014
Accepted 14 February 2014
Available online 25 February 2014
Keywords:
Azodye rhodanine derivatives
Cu(II) supramolecular structure
ESR study
TGA and DSC
Thermodynamic parameters
2
ðbꢁ1Þ and orbital reduction factor K accounts for the covalent nature of the complexes. The activation
thermodynamic parameters, such as activation energy (Ea), enthalpy (D D
Hꢁ), entropy ( Sꢁ), and Gibbs free
energy change of the decomposition (
methods.
D
Gꢁ) are calculated using Coats–Redfern and Horowitz–Metzger
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
system due to their applicability as potential ligands for a large
number of metal ions. Diab et al. and his school survey reveal an
excellent work devoted to synthesis and characterization of azod-
yes as well as their complexes [1–8]. It is well known that azodyes
and their metal complexes have been widely used in different
fields such as dying of textile fibers [9], biological studies [10],
and high technology areas [11]. The variety of coordination modes
of rhodanine derivatives has been demonstrated in a number of
Heterocyclic azodye attracted a considerable interest and play
an important role in development of the chemistry of chelates
⇑
Corresponding author. Tel.: +201060081581; fax: +20 572403868.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
Abstracted from her Ph.D.
1
http://dx.doi.org/10.1016/j.saa.2014.02.037
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
311
complexes and their biological applications have been of consider-
General method of synthesis of complexes
able interest [12].
Although, neither structural chemistry nor coordinating studies
have been reported on ligands containing both azo and rhodanine
function groups. Data from our laboratory [13–17] have demon-
strated that the bidentate azodyes ligands play a key role in mak-
ing new complexes with transition metal ions. However, little is
known concerning the constitution of these complexes, as well as
the chemistry involved in their preparation, or the structural and
coordination in such complexes. It has been shown from the IR
spectral data [13–20] that the hydrogen bonding plays an impor-
tant role in biological systems. Moreover, Jorgensen and El-Sonbati
et al. [21,13–19] found out that the stability of multiple hydrogen
bonded depends not only on the number of hydrogen bonds but
also on the hydrogen bonding pattern.
The importance of clarifying the structure and stability of
hydrogen-bonded complexes has opened up an area of surface sci-
ence that has attracted a considerable attention in the environ-
mental chemistry. The azo group can act as a proton acceptor in
hydrogen bonds [14,19,22–24]. The role of hydrogen bonding in
azo aggregation has been accepted for sometime. Intarmolecular
hydrogen bonds involving OH group with the AN@NA group in-
creased their stabilities through chelate ring structure
[14,19,24,25]. The strength of the hydrogen bond of compounds
depends on the nature of substituents present in the coupling com-
ponent from the aryl azo group. Chelating rings formed by NHꢂ ꢂ ꢂN
bonds are less stable than corresponding rings formed by OHꢂ ꢂ ꢂN
bonds [26,27].
A hot ethanolic solution containing the azodyes (HLn) was
mixed with a hot ethanolic solution of Cu(OAc)2ꢂH2O (1 mmol).
The mixture was then refluxed on a water bath for ꢃ10 h and al-
lowed to cool whereby the solid complexes were separated, which
filtered off, washed several times with ethanol, dried and kept in a
desiccator over dried CaCl2. The analytical data are given in Table 2.
Measurements
Elemental microanalyses of the separated ligands and solid che-
lates for C, H, and N were performed in the Microanalytical Center,
Cairo University, Egypt. The analyses were repeated twice to check
the accuracy of the analyzed data. The metal content in the com-
plexes was estimated by standard methods [28]. X-ray diffraction
analyses of the powder HL2 and its complex [Cu(L2)(OAc)(OH2)]-
ꢂ2H2O (4) were performed at room temperature by a Philips X-
ray diffractometer equipped with utilized monochromatic Cu K
a
radiation (k = 1.5418 Å). The X-ray tube voltage and current were
40 kV and 30 mA, respectively. The 1H NMR spectrum was ob-
tained with a JEOL FX90 Fourier transform spectrometer with
DMSO-d6 as the solvent and TMS as an internal reference. The
infrared spectra were recorded as KBr discs using a Perkin–Elmer
1340 spectrophotometer. Ultraviolet–Visible (UV–Vis) spectra of
the compounds were recorded in Nuzol solution using a Unicom
SP 8800 spectrophotometer. The magnetic moment of the prepared
solid complexes was determined at room temperature using the
The objectives of the present work are the synthesis of 5-(40-
derivatives phenylazo)-2-thioxo-4-thiazolidinone (HLn) (Fig. 1)
and their Cu(II) complexes. The thermogravimetric analysis (TGA)
and differential scanning calorimetry analysis (DSC) studies for
HLn. Study the molecular and electronic structures of the investi-
gated compounds (HLn). The Cu(II) complexes are subjected to ele-
mental, thermogravimetric analysis, spectral studies (IR and ESR),
conductance and magnetic measurements for the purpose of struc-
tural elucidation. The optimum conditions and the stoichiometry
for the reaction of azodye rhodanine derivatives with Cu(II) in solu-
tion were considered. In addition to the activation thermodynamic
parameters are calculated using Coats–Redfern and Horowitz–
Metzger methods.
Gouy’s
method.
Mercury(II)
(tetrathiocyanato)cobalt(II),
[Hg{Co(SCN)4}], was used for the calibration of the Gouy’s tubes.
Diamagnetic corrections were calculated from the values given
by Selwood [29] and Pascal’s constants. Magnetic moments were
calculated using the equation, leff: ¼ 2:84½TvMcoor:
ꢄ
1=2. Thermogravi-
metric analysis (TGA) measurements were investigated using
Simultaneous Thermal Analyzer (STA) 6000 (Central Laboratory,
Tanta University, Egypt) with scan rate 15 °C/min under dynamic
nitrogen atmosphere in the temperature range from 50 to 800 °C.
ESR measurements of powdered samples were recorded at room
temperature (Central Laboratory, Tanta University, Egypt) using
an X-band spectrometer utilizing a 100 kHz magnetic field modu-
lation with diphenyl picrylhydrazyle (DPPH) as a reference mate-
rial. The conductance measurement was achieved using Sargent
Welch scientific Co., Skokie, IL, USA.
The molecular structures of the investigated compounds were
optimized initially with PM3 semiempirical method so as to speed
up the calculations. The resulting optimized structures were fully
re-optimized using an initio Hartree–Fock (HF) [30] with 6-31G ba-
sis set. The molecules were built with the Gauss View 3.09 and
optimized using Gaussian 03W program [31]. The corresponding
geometries were optimized without any geometry constraints for
full geometry optimizations. Frequency calculation was executed
successfully, and no imaginary frequency was found, indicating
minimal energy structures.
Quantum chemical parameters such as the highest occupied
molecular orbital energy (EHOMO), the lowest unoccupied molecu-
lar orbital energy (ELUMO), energy gap (DE), dipole moment (l)
and the total energy for the investigated molecules were
calculated.
Experimental
All the chemicals used were of British Drug House (BDH)
quality.
Synthesis of 5-(40-derivatives phenylazo)-2-thioxothiazolidin-4-one
(HLn)
In a typical preparation, 25 ml of distilled water containing
0.01 mol hydrochloric acid were added to aniline (0.01 mol) or p-
derivatives. To the resulting mixture stirred and cooled to 0 °C, a
solution of 0.01 mol sodium nitrite in 20 ml of water was added
dropwise. The formed diazonium chloride was consecutively cou-
pled with an alkaline solution of 0.01 mol 2-thioxo-4-thiazolidi-
none, in 10 ml of pyridine as shown in Scheme 1. The colored
precipitate, which formed immediately, was filtered through sin-
tered glass crucible, washed several times with water and ether.
The crude products was purified by recrystallization from hot eth-
anol, yield ꢃ 65% then dried in vacuum desiccator over P2O5. The
ligands were also characterized by elemental analysis (Table 1),
1H NMR and IR spectroscopy.
Results and discussion
Structure of the ligand
All five ligands HL1–HL5, gave satisfactory elemental analysis
(Table 1). The molecular structures of these ligands are such that

312
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
O
H
OH
C
H
O
C
O
C
HN
C
C
HN
C
C
HN
C
C
HN
C
C
N
R
N
R
CH
N
R
S
N
R
S
N
N
S
N
S
N
S
S
S
S
(C)
(D)
(A)
(B)
R
N
H
O
OH
S
N
S
HN
C
C
OH
C
NH
C
C
C
C
C
or
HN
C
C
S
C
N
R
C
NH
S
N
R
N
N
S
S
S
N
HO
S
N
R
R
(E)
(F)
S
N
O
S
O
HN
NH
C
C
HN
C
C
or
C
NH
C
S
N
S
R (G)
n = 1
n = 2
n = 3
n = 4
n = 5
R = OCH3
R = CH3
R = H
R = Cl
R = NO2
Fig. 1. Structure of azodye rhodanine derivatives (HLn).
they can exist in three tautomeric forms as shown in Fig. 1. De-
tailed solution and solid states studies of these ligands were car-
ried out to establish their geometry. As shown in Table 1, the
values of yield% and/or melting point is related to the nature of
the p-substituent as they increase according to the following order
p-(NO2 > Cl > H > CH3 > OCH3) [16–19]. This can be attributed to
the fact that the effective charge experienced by the d-electrons in-
creased due to the electron withdrawing p-substituent (HL4 and
HL5) while it decreased by the electrons donating character of
(HL1 and HL2).
According to the frontier molecular orbital theory, FMO, the
chemical reactivity is a function of interaction between HOMO
and LUMO levels of the reacting species [32]. The EHOMO often asso-
ciated with the electron donating ability of the molecule to donate
electrons to appropriated acceptor molecules with low-energy,
empty molecular orbital. Similarly, ELUMO indicates the ability of
the molecule to accept electrons. The lower value of ELUMO indicates
the high ability of the molecule is to accept electrons [33,34]. While,
the higher is the value of EHOMO of the compound, the easier is its
offering electrons. The HOMO and LUMO are shown in Fig. 4.
Quantum chemical parameters of organic compounds are ob-
tained from calculations such as energies of the highest occupied
molecular orbital, EHOMO, energies of the lowest unoccupied molec-
ular orbital ELUMO, total, binding and electronic energies; heats of
formation and dipole moments as presented in Table 3. Additional
The X-ray diffraction, XRD, patterns of the as-synthesized HL2
and [Cu(L2)(OAc)(OH2)]ꢂ2H2O (4) powder are shown in Fig. 2.
Many peaks are observed which indicate the polycrystalline nat-
ure of the as-synthesized HL2 ligand and [Cu(L2)(OAc)(OH2)]-
ꢂ2H2O (4).
Geometrical structures and electronic properties of the investi-
gated compounds and their protonated forms were calculated by
optimizing their bond lengths, bond angles and dihedral angles.
The calculated molecular structures with the optimized bond
lengths are shown in Fig. 3.
parameters such as separation energies,
D
E, absolute Electroneg-
, chemical potentials, Pi, absolute hardness, , absolute
, global electrophilicity, [35], global softness, S, and
Nmax, have been calculated accord-
ing to the following equations [36]:
ativities,
softness,
v
r
g
x
additional electronic charge,
D

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
313
NaNO2
+
-
HCl
R
NH2
R
N
Cl
N
0-5 oC
Diazonium Salt
O
alkaline
HN
C
solution
0-5 oC
S
S
R
N
R
R
N
HO
=
S
S
S
N
N
N
O
HN
N
S
S
S
C
C
C
NH
NH
NH
O
HO
Keto form
Hydrazon form
Enol form
n=1, R = OCH3 (HL1); n=2, CH3 (HL2); n=3, H (HL3); n=4, Cl (HL4); and n=5, NO2 (HL5)
Scheme 1. The formation mechanism of azodye rhodanine derivatives (HLn).
Table 1
Analytical data of azo rhodanine derivatives.
The concepts of the parameters
v
and Pi are related to each other.
The inverse of the global hardness is designated as the softness
[37]. From the obtained data (Table 3) we can deduced that:
Absolute hardness and softness are important properties to
r
Compounda Empirical
formula
Yield% M.p.°C Calc. (Exp.)%
C
H
N
g
r
measure the molecular stability and reactivity. A hard molecule
has a large energy gap and a soft molecule has a small energy
gap. Soft molecules are more reactive than hard ones because they
could easily offer electrons to an acceptor.
HL1
HL2
HL3
HL4
HL5
C10H9N3O2S2
Red
37.45
47.81
42.19
51.37
66.09
221
231
237
248
245
44.93
(44.82) (3.25) (15.85)
47.79 3.61 16.72
(47.88) (3.76) (16.61)
45.55 2.97 17.71
(45.68) (2.80) (17.85)
39.78 2.23 15.46
(39.65) (2.35) (15.58)
38.29 2.14 19.85
(38.42) (2.25) (19.98)
3.39
15.72
C10H9N3OS2
Dark Orange
C9H7N3OS2
Pale Yellow
C9H6N3OS2Cl
Light Orange
C9H6N4O3S2
Dark Yellow
1H NMR spectra
The 1H NMR spectra of azodye rhodanine derivatives are in
agreement with the proposed structures. Signal for CH
(ꢃ 4.42 ppm), favoring formation of an intramolecular hydrogen
bond with the AN@NA (azodye) group. Electron-withdrawing sub-
stituents reduce the intramolecular hydrogen bond as indicated by
the marked shift of the hydroxyl signal to higher field in the p-NO2
and p-Cl compounds. Electron-donating substituents give the
opposite effect, arising from the increasing basicity of the azo-
nitrogen. The broad signals assigned to the OH protons at
ꢃ11.36–11.88 ppm are not affected by dilution. The previous two
protons disappear in the presence of D2O. Absence of ACH proton
signal of the ligand moiety indicated the existence of the ligand in
the azo-enol form. According to El-Sonbati et al. [14–19,25],
a
The analytical data agree satisfactory with the expected formulae represented
as given in structures HL1–HL5. Air-stable, colored, insoluble in water, but soluble in
hot ethanol, and soluble in coordinating solvent.
D
v
g
r
E ¼ ELUMO ꢅ EHÞOMO
ꢅðEHOMO þ ELUMO
¼
¼
¼
2
ELUMO ꢅ EHOMO
2
1
;
Pi ¼ ꢅv
g
1
g
Pi2
2g
S ¼
;
x
¼
2
Pi
D
Nmax ¼ ꢅ g
Table 2
Analytical and magnetic moments of Cu(II) complexes.
Complex
l
eff. B.M.
Calc. (Exp.)%
C
H
N
S
M
[Cu(L1)(OAc)(OH2)]ꢂ2H2O
1.83
1.85
1.87
1.84
1.92
1.96
2.04
32.54
(32.47)
33.76
(33.60)
32.00
(31.86)
28.51
(28.40)
38.00
(37.84)
37.79
(37.62)
32.65
3.84
(3.72)
3.99
(3.82)
3.64
(3.44)
3.02
(2.89)
3.17
(3.00)
2.80
(2.64)
2.12
(2.01)
9.49
(9.13)
9.85
14.46
(14.07)
15.01
(14.86)
15.51
(15.27)
13.82
(13.65)
20.27
(19.74)
22.40
(22.03)
19.35
(19.07)
14.36
(14.06)
14.90
(14.72)
15.40
(15.17)
13.72
(13.47)
10.06
(9.87)
11.12
(10.84)
9.61
(9.48)
(1)
[Cu(L3)(OAc)(OH2)]ꢂ2H2O
(2)
(9.46)
10.18
(9.87)
9.07
(8.78)
13.30
(13.04)
14.70
(14.49)
16.93
(16.66)
[Cu(L5)(OAc)(OH2)]ꢂ2H2O
(3)
[Cu(L2)(OAc)(OH2)]ꢂ2H2O
(4)
[Cu(L1)2(OH2)2]
(5)
[Cu(L3)2(OH2)2]
(6)
[Cu(L5)2(OH2)2]
(7)
(32.44)

314
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
(1) Intramolecular hydrogen bond between the nitrogen atom
of the AN@NA system and hydrogen atom of the hydroxy
3000
2400
1800
1200
600
hydrogen atom (Fig. 1C). This is evident by the presence of
a broad band centered at 3460 cmꢅ1
.
(2) Hydrogen bonding of the OHꢂ ꢂ ꢂN type between the hydroxy
hydrogen atom and the N-ph group (Fig. 1C).
(3) Intermolecular hydrogen bonding is possible forming cyclic
dimer through NHꢂ ꢂ ꢂO@C (G), OHꢂ ꢂ ꢂN@N (F) or OHꢂ ꢂ ꢂOH
(E). (Fig. 1).
(b)
The presence of broad band located at ꢃ3200 cmꢅ1 is strong
indication by vNH (Fig. 1D). In general, the low frequency of such
region from its normal position is, again due to hydrogen bond
property gathered with keto , enol tautomerism.
(a)
Again the three bands located at 1380, 1340 and 1310 cmꢅ1
identified as dOH gathered with the two bands at 1240 cmꢅ1 as-
signed as vCAO are strong indication to keto,enol equilibria.
The presence of a medium band at ꢃ1605 cmꢅ1 assigned to vC@N
illustrates the tracing of keto structure (Fig. 1D).
0
10
20
30
40
50
60
70
80
2θ (Degree)
Fig. 2. X-ray diffraction pattern for (a) HL2 and (b) [Cu(L2)(OAc)(OH2)]ꢂ2H2O
powder form.
Structure of the metal complexes
hydrogen bonding leads to a large deshielding of the protons. The
shifts are in the sequence: p-(NO2 > Cl > H > OCH3 > CH3). In the
meantime, the 1H NMR of the HL2/HL1 exhibits signals at d(ppm)
[3.3(s, 3H, CH3)]/[3.9(s, 3H, OCH3)]. The aromatic protons have res-
onance at 7.10–7.45 ppm for the ligands. The position of the other
proton signals has also been observed in the expected regions and
has been shifted only slightly due to the coordination of the ligand
to metal ion. Absence of CH proton signal of the rhodanine azo
moiety indicated the existence of the ligand in the azo-enol form.
Diazonium coupling of the rhodanine with p-derivatives aro-
matic amine readily gives rise to azodye ligands. Their reactions
with copper(II) ion afford mono/binuclear metal complexes in
which the microanalytical data as well as metal and acetate esti-
mations are in good agreement with proposed stoichiometries, Ta-
ble 2. These complexes are found to be insoluble in common
organic solvents but soluble in coordinated solvents. The elemental
analysis confirms that the complexes are mono/binuclear and may
be formulated as: [Cu(Ln)(OAc)(OH2)]ꢂ2H2O/[Cu(Ln)2(OH2)2].
The reactions follow:
Infrared spectra of ligands (HLn)
CuðOAcÞ2 ꢂ H2O þ HL1ꢅ5 ! ½CuðL1ꢅ5ÞðOAcÞðOH2Þꢄ ꢂ 2H2O
þ CH3COOH
The infrared spectra of ligands (HLn) give two bands at ꢃ3200–
3040 cmꢅ1 due to asymmetric and symmetric stretching vibrations
of NAH group and intramolecular hydrogen bonding NHꢂ ꢂ ꢂO sys-
tems (Fig. 1D), respectively. When the OH group (Fig. 1C) is in-
volved in intramolecular hydrogen bond, the Oꢂ ꢂ ꢂN and Nꢂ ꢂ ꢂO
bond distances are the same. But, if such mechanism is happened
in case of intermolecular hydrogen bond, the Oꢂ ꢂ ꢂO and Oꢂ ꢂ ꢂN bond
distances differ.
CuðOAcÞ2 ꢂ H2O þ 2HL1ꢅ5 ! ½CuðL1ꢅ5Þ2ðOH2Þ2ꢄ þ 2CH3COOH
where L1–5 = deprotonated HL1, HL2, HL3, HL4, HL5.
The composition coordination mode and geometry of the com-
plexes were established on the basis of spectral analyses, conduc-
tivity measurements and magnetic properties and are discussed in
detail in the following sections.
The broad absorption band located at ꢃ3400 cmꢅ1 is assigned to
vOH. The low frequency bands indicate that the hydroxy hydrogen
atom is involved in keto , enol (A , B) tautomerism through
hydrogen bonding (Fig. 1C). Bellamy [38] made detailed studies
on some carbonyl compounds containing ANHA group. The
D
vNH
Conductivity measurements
values were used to study the phenomena of association.
On the other hand, the OH group (Fig. 1-B) exhibits more than
one absꢅo1rption band. The two bands located at 1330 and
1130 cmꢅ1 is due vCAOH.
Conductivity measurements have been used in structural eluci-
dation of metal complexes (mode of coordination) within the lim-
its of their solubility. The molar conductance of 10ꢅ3 M of solutions
of the complexes in DMSO is measured at room temperature. It is
concluded from the results that Cu(II) chelates with HLn ligand un-
der investigation were found to have molar conductance values in
the range from ꢃ1.85 to 0.55 Oꢅ1 molꢅ1 cm2 for 1:1 and 1:2 (M:L)
complexes, indicating non-electrolytic nature of these compounds
and there is no counter ion present outside the coordination sphere
of copper complexes [24,39]. This is in accordance with the fact
that conductivity values for a non-electrolyte are below 50 Oꢅ1
molꢅ1 cm2 in DMSO solution [39]. Such a non-zero molar conduc-
tance value for each of the complex in the present study is most
probably due to the strong donor capacity of DMSO, which may
lead to the displacement of anionic ligand and change of electro-
lyte type [24,39].
1370 cm
are assigned to in-plane deformation and that at
However, the 860 cmꢅ1 band is probably due to the out-of-
plane deformation of the AOH group. On the other hand, the two
bands located at 650 and 670 cmꢅ1 are identified as vC@O and NH.
Similar to the other investigated compounds, the different
modes of vibrations of CAH and CAC band are identified by the
presence of characteristic bands in the low frequency side of the
spectrum in 600–200 cmꢅ1
.
The infrared spectra of ligands shows medium broad band lo-
cated at ꢃ3460 cmꢅ1 due the stretching vibration of some sort of
hydrogen of hydrogen bonding. El-Sonbati et al. [18,24] made de-
tailed studies for the different types of hydrogen bonding which
are favorable to exist in the molecule under investigation:

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
315
HL1
HL2
HL3
HL4
HL5
Fig. 3. The calculated molecular structures of the investigated compounds (HLn).

316
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
HOMO
LUMO
HL1
HL2
HL3
HL4
HL5
Fig. 4. The Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) of the investigated compounds (HLn).
Table 3
The calculated quantum chemical parameters of the investigated compounds (HLn).
Compound
HOMO (a.u)
LUMO (a.u)
D
E (a.u)
l
(D)
T.E (a.u)
v
g
r
Pi
S
x
DNmax
HL1
HL2
HL3
HL4
HL5
ꢅ0.327
ꢅ0.337
ꢅ0.348
ꢅ0.355
ꢅ0.367
0.048
0.047
0.044
0.034
ꢅ0.004
0.375
0.384
0.432
0.389
0.363
5.358
4.554
3.950
2.001
3.712
ꢅ1491.580
ꢅ1416.775
ꢅ1377.752
ꢅ1836.627
ꢅ1581.099
0.139
0.145
0.152
0.161
0.186
0.188
0.192
0.196
0.195
0.182
5.333
5.208
5.102
5.141
5.509
ꢅ0.139
ꢅ0.145
ꢅ0.152
ꢅ0.161
ꢅ0.186
2.667
2.604
2.551
2.571
2.755
0.052
0.055
0.059
0.066
0.095
0.744
0.755
0.776
0.825
1.022
Infrared spectra of complexes and nature of coordination
The broad/strong absorption bands located at ꢃ3450–3434 and
at ꢃ1710–1695 cmꢅ1 region assigned to the
t(NH) stretching
The bonding of the metal ion to the ligand can be clarified by
comparing the IR-spectra of the complexes with those of the
ligands.
vibrations mode and carbonyl stretching vibrations. The three
bands in the 1600–1500 cmꢅ1 region are characteristic for most
six-membered aromatic ring system. The frequencies for the

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
317
N@N stretching lie in the region 1440–1435 cmꢅ1. The region be-
tween 1500–1900 cmꢅ1 is due CAN stretching, NAH in plane or
out of plane bending and out-of-plane CAH bending vibrations
[3–6]. The symmetric and antisymmetric (C@C) stretching vibra-
tion modes are expected to exist in this region. Thus, this ligand
(HLn) contains four potential donor sites (Fig. 1): (i) the ring nitro-
gen NH, (ii) the ring CS, (iii) the carbonyl group, and (iv) the nitro-
gen of azo (N@N) group. However, considering the planarity of the
ligand, it is unlikely that this ligand could be tetradentate on a sin-
gle metal center. Hence, this ligand is expected to be bidentate and
the three favorable possibilities of donor sites are: (i) the carbonyl
oxygen and (ii) the nitrogen atom of azo (N@N) group or (i) the car-
bonyl oxygen and (ii) the CS. The coordination of the ring nitrogen
(NH) is unlikely due to the Zwitterions [4] formation, thereby low-
ering the electron density on N. The ring thion (CS) in this ligand is
found to be inert towards coordination to copper as revealed by the
compared to the free ligand due to the conversion of hydro-
gen bonded structure into a covalent metal bonded structure
[41].
(4) Furthermore, the bands in the regions 545–560 and 420–
428 cmꢅ1 can be assigned to the stretching modes of the
metal to ligand bonds,
1:2 (M:L) complexes, respectively, [4,17,41]. Absence of
(MAS) band in the far IR spectra gives added evidence for
t(CuAO) and t(CuAN) for 1:1 and
t
the non-participation of ring sulfur atom in bond formation.
(5) The variation in the spectral bands of the CAC, C@C, CAN
and CAH different modes of vibrations of the complexes lead
to that, probably, the aromaticity of the complex is differ
from one to other [14,22].
(6) The band due to vOH is masked by the intense absorption
due to water molecule, and hence no definite conclusion
can be drawn for this region. However, dOH at 1299 cmꢅ1
,
appearance of the
t
(C@S)(ring) mode at 820 cmꢅ1 of the uncoordi-
vCAOH at 1207 and c
OH at 822 cmꢅ1 display a sharp
nated ligand after complexation. The absence of CH2 and NH2
stretching in the spectra of the ligands (HLn), related to active
methane and amino groups respectively, indicating occurrence of
azodye diazonium and formation of the proposed skeleton of
ligands.
decrease in their intensities to such an extent those they
nearby vanish. This can be taken as an indication for the
complete removal of OH-group by the Cu(II) ion reacting
with the ligands. Since the ligand reacts with Cu(II) ion, as
gathered from the results of elemental analysis, then each
Cu(II) ion would displace only one proton from the OH group
contained in each ligands molecule.
In the IR spectra of all metal complexes (1–7) a number of
changes are observed:
(7) To confirm the presence of coordinating H2O molecules in
the complex we carried out thermogravimetric analysis of
all the complexes. This study shows loss of weight corre-
sponding to one water molecule in the temperature up to
ꢃ190 °C, indicating that the water molecule in these com-
plexes is coordinated to the metal ion.
(8) The participation of the OH group in Cu(II) complexes is con-
firmed by the appearance of new bands in Cu(II) complexes
is confirmed by the appearance of new bands at 555–
525 cmꢅ1 for 1:1 and 1:2 (M:L) complexes respectively,
related to the CuAO vibration [24]. The acetate complexes
show two new bands at 1600 and 1390 cmꢅ1 attributed to
tas and ts of the acetate group. The difference between the
two bands indicates the monodentate nature of the acetate
group [5,8].
(1) The appearance of a new bands around ꢃ3380 cmꢅ1 and two
sharp bands at ꢃ715 and 420 cmꢅ1, the latter two can be
assigned to the wagging and rocking modes of vibration of
the water molecule, respectively, [39] in the prepared com-
plexes (1–7) may be taken as a strong evidence for the pres-
ence of coordinated water. Such region, however, is not
initially present in the free ligands. This is confirmed by
the elemental analysis of these complexes (Table 2).
(2) The N@N stretching frequency of the azo groups is shifted to
lower frequency by ꢃ15–25 cmꢅ1 due to the involvement of
one of the azo nitrogen atoms in coordination with metal ion
[4,24,40]. This lowering of frequency can be explained by the
transfer of electrons from nitrogen atom to the Cu(II) ion due
to coordination.
(3) In solution and in the presence of Cu(II) ions these com-
pounds exist in
a
tautomerism equilibrium [24,25]
On the basis of all these data, the molecular structure of the
Cu(II) complexes could be suggested based on:
A , B , C (Fig. 1). The tautomeric form (C) react with metal
ions by loss of phenolic proton as mononegative chelating
agents producing of CO/OH mode of the free ligands. The
internally hydrogen enolic band disappeared in the spectra
the metal complexes, indicating the deprotonation and for-
mation of metal–oxygen bond. This is further supported by
(i) the presence of anion, (ii) the disappearance of C@O, (iii) the
coordination of azo-group and (iv) the presence of water.
According to the structure shown in Fig. 5 the ligand (HLn) takes
its usual anionic form (Ln) to chelate Cu(II) through NA of azo
group with enol group (Fig. 1C) as the potential binding sites.
the shifting of
t(CAO) towards higher frequency as
R
R
S
N
S
N
H2O
O
C
S
N
N
S
C
NH
Cu
N
O
HN
.2H2O
H2O
NH
Cu
OH2
C
O
S
N
S
OAc
R
(A)
(B)
Fig. 5. Structures of (A) [Cu(Ln)(OAc)(OH2)]ꢂ2H2O and (B) [Cu(Ln)2(OH2)2].

318
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
14070–14290 cmꢅ1 assigned to 2B1g ? 2A1g transition as reported
Table 4
ESR spectral parameters for the Cu(II) complexes (1–3).
for square planar Cu(II) complexes [44].
Complexa
gll
g
gav.
All
G
a2
b2
b
?
1
2
3
2.210
2.230
2.250
2.040
2.050
2.060
2.097
2.110
2.123
56.57
65.83
76.17
5.614
4.804
4.293
0.421
0.471
0.524
0.80
0.89
0.95
Copper(II) complexes (5–7)
Where spin–spin coupling between unpaired electrons belong-
ing to different copper ions is absent, leff varies between 1.92 and
a
2.04 B.M., depending on the geometries of the complexes due to
difference in orbital contribution [45]. The observed leff values
for the Cu(II) complexes in this study are in the 1.92–2.04 B.M.
range, corresponding to one unpaired electron. Electronic absorp-
tion spectra arise from the electronic transitions within a molecule
or ion from a lower to a higher electronic energy level. The transi-
tion metal ions generally show a number of d–d transition bands
depending on their electronic configuration from d1 to d9 in
UV–Vis regions. The copper(II) complexes generally show the d–d
Numbers as given in Table 2.
A values in 10ꢅ4 (cmꢅ1).
b
Magnetic and spectral studies
Copper(II) complexes (1–4)
Magnetic measurements and electronic spectra were conducted
in order to obtain information about the geometry of the com-
plexes. The magnetic susceptibility values (1.83–1.87 B.M.) which
was consistent with presence of a single unpaired electron [42].
This behavior suggest square planar geometry for the copper(II)
complexes [43]. The electronic spectra of [CuLn(OAc)(OH2)]ꢂ2H2O
transition bands in the range 13100–15500 (dz2 ? dx2ꢅy2
1), 18640–19100 (dxy ? dx2ꢅy2)(t2
and 24410–27330 cmꢅ1
(dxz,dyz ? dx2ꢅy2)( 3) transitions. The spectra are typical of Cu(II)
)
(t
)
t
complexes with an elongated tetragonal. The spectra of all the
complexes have been assigned to D4h symmetry with a dx2ꢅy2
complexes exhibit
a
broad band with
a
maximum at
Table 5
ESR spectral and calculated bonding parameters for the Cu(II) complexes (5–7).
b
Complexa
gll
g
gav.
All
G
a2
b2
K2
d2
b12
K2ll
K?2
?
5
6
7
2.1839
2.2402
2.2421
2.0216
2.0311
2.0319
2.0757
2.1013
2.1020
39.65
46.72
35.14
6.306
8.238
8.101
0.34
0.42
0.39
0.53
0.58
0.60
1.5
1.6
1.7
0.51
0.67
0.69
0.18
0.24
0.23
0.29
0.38
0.38
0.64
0.77
0.87
a
Numbers as given in Table 2.
A values in 10ꢅ4 (cmꢅ1).
b
80
75
70
65
60
55
3
(a)
(b)
2.25
2.24
2.23
2.22
2.21
3
2
2
1
1
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
)
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
R
Hammett's substituent coefficients (σR
)
Hammett's substituent coefficients (σ
(c)
0.60
7
0.58
0.56
0.54
6
5
0.52
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
Hammett's substituent coefficients (σR
)
Fig. 6. The relation between Hammett’s substituent coefficients (
r
R) vs. (a) gll, (b) All ꢆ 10ꢅ4 (cmꢅ1) and (c) b2.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
319
ESR spectra of copper(II) complexes
(a)
(b)
0.96
g
3
3
ll
2
2.25
2.24
2.23
2.22
2.21
ESR spectra of copper(II) complexes (1–3)
To obtain further information about the stereochemistry and
the site of the metal ligand bonding and to determine the magnetic
interaction in the metal complexes. ESR spectra of the complexes
were recorded in the solid state. The spin Hamiltonian parameters
of the complexes were calculated and summarized in Table 4. The
analysis of spectra of all copper(II) complexes agree well with the
values reported for distorted square planar geometry around Cu(II)
ion [46,47]. The spectra shows the relation gll > g? > ge which is
typical of axially symmetric d9 Cu(II) having one unpaired electron
in dx2ꢅy2 orbital [48]. The absence of signal corresponding to
(Ms = 2) in the half field indicates the absence of any CuACu
interaction thus ruling out possibility of dimeric structure.
In the axial spectra, the g-values are related with exchange inter-
action coupling constant (G). The geometric parameter G i.e. the
measurement of exchange between the copper centers in the poly-
crystalline compounds, is calculated by using the expression:
G = (gllꢅ2.0023)/(g\ꢅ2.0023). In the present work, G value comes
outtobe4.0 whichagainindicateabsenceofCuACuinteraction, thus
supporting proposed monomeric structure. Kivelson and Neiman
have reported that gll values less than 2.3 indicates considerable
β
0.93
0.90
0.87
0.84
0.81
0.78
2
2
1
1
55
60
65
70
cm
75
80
-4
-1
A
x 10
(
)
ll
Fig. 7. The relation between All ꢆ 10ꢅ4 (cmꢅ1) vs. (a) gll and (b) b2.
ground state. The most active vibration in this point group appears
to be b1u symmetry and its efficiency may arise from its being the
only out-of-the-xy-plane vibration. The complexes are with one
electron sequence i.e. dx2ꢅy2 > dz2 > dxy > dxz,dyz [45].
(a)
(c)
(b)
80
75
70
65
60
55
3
0.96
2.125
3
3
0.93
0.90
0.87
0.84
0.81
0.78
2.120
2.115
2.110
2.105
2.100
2.095
2
2
A
x 10-4 (cm-1)
ll
2
g
av.
2
1
1
β
1
0.42
0.44
0.46
0.48
0.50
0.52
0.54
2
α
Fig. 8. The relation between a2 vs. (a) All ꢆ 10ꢅ4 (cmꢅ1), (b) gav. and (c) b2.
2.250
2.235
2.220
2.205
2.190
2.175
7
(a)
(b)
6
2.032
2.030
2.028
2.026
2.024
2.022
2.020
7
6
5
5
0.18
0.20
0.22
0.24
0.52
0.56
0.60
0.64
0.68
2
2
k
T
k
ll
Fig. 9. The relation between (a) K2ll vs. gll and (b) K2 vs. g?
.
?

320
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
the copper dx2ꢅy2 orbital of most of the Cu(II) species concerned.
100
80
60
40
20
0
TGA
DSC
(a)
0
The g values obtained from ESR spectra indicate, as has been
pointed out by Kivelson and Neiman [49], that covalent bonding
reduces the magnitude of the g factor.
100
200
300
400
500
ESR spectra of copper(II) complexes (5–7)
The ESR technique is very sensitive tool for obtaining the forma-
tion on the chemical environments and the coordination states of
Cu(II) in the materials. The intensity of the ESR signals from a para-
magnetic Cu(II) ion dependents on both the condition spheres of
this ion and the degree of the dispersion [50].
The spin Hamiltonian, orbital reduction and bonding parame-
ters of these complexes are given in Table 5. The observed gll values
for all complexes are less than 2.3 commensurate a significant
covalent character of the metal–ligand bond in agreement with
600
0
-20
100
TGA
DSC
(b)
100
200
300
400
500
80
60
40
20
0
the observation of Kivelson and Neiman [49]. The trend gll > g\
>
ge > 2.0023 for these complexes suggests that the unpaired elec-
tron is localized in the dx2ꢅy2 orbital [51] of the Cu(II) ion. The g
values reflect that the Cu(II) center has a tetragonal distorted octa-
hedral geometry with dx2ꢅy2 orbital as a ground state [24,52]. The
gll values are an important function for indicating covalent charac-
ter of MAL; for ionic character, gll > 2.3 and for covalent character
gll < 2.3. In the present complex, the gll is less than 2.3 indicating
appreciable covalent character for the CuAL bond. The unpaired
electron in this 3d9 case assigned to 3dx2ꢅy2 orbital, and the over-
600
-20
(c)
100
-120
lapping of this antibonding orbital with the ligand 2s and 2p
r
TGA
DSC
orbital is often determined by the use of the following equation:
80
60
40
20
0
0
a2 ¼ All=Po þ ðgll ꢅ 2:0023Þ þ Koðg? ꢅ 2:0023Þ þ 0:04
120
240
360
480
600
where a2 gives an approximate indication of the strength of the
interaction between the metal and the ligands. Po is the dipolar con-
tribution to the hyperfine splitting value A, which is negative quan-
tity, and usually assigned the free ion value of 0.036 cmꢅ1. The
constant term of Ko = 3/7 is equated to the Fermi hyperfine contact
term of the free ion, which corrects for the Fermi contact contribu-
tions from excited state configurations of Cu(II), notably the 3s1
3d10 and 3s2 3d8 4s1 configurations [53]. This is usually considered
to be a constant term for Cu(II) complexes since there is little ligand
orbital density at the copper nucleus and the ratio of copper s to d
character is assumed to be unchanged in the presence of ligands
[54]. The addition of 0.04 to the sum is an approximate correction
due to the molecular orbital coefficients of the complex that arise
-20
0
100 200 300 400 500 600 700 800
Temperature (°C)
Fig. 10. TGA and DSC thermo graphs for (a) HL1, (b) HL3 and (c) HL5.
from in plan
d
p
bonding (dxy; b2) and out of plan
p
bonding (dxz,
1
yz, b2). Thus a2 represents the extent to which the unpaired elec-
covalent character of MAL bond and greater than 2.3 indicates ionic
character. The present value comes out to less than 2.3 which indi-
cate considerable covalent character of CuAL bond [49].
tron resides on the central metal ion in the dx2ꢅy2 orbital (B1g
ground state) and reflects the extent of -bonding to the ligand.
Consequently, a decline in the value of a2 indicates an increase in
the covalencey of the bond. The in-plane -covalence parameter
r
As a measure of the covalence of the in-plane
indicates complete covalent character, whereas
r
-bonding, a2
2 = 0.5 denotes
r
a2 values account for the fraction of the unpaired electron density
to be populated around the Cu(II) ion. In addition, the g values
are related to the G-factor by the expression, G = (gllꢅ2)/
(g? ꢅ 2) = 4, which measures the exchange interaction between
copper centers in the solid state. According to Hathaway [55], if
the value of G is greater than 4, the exchange interaction between
Cu(II) centers in the solid state is negligible, whereas when it is less
a
100% covalent bonding, with the assumption of negligible small
values of the overlap integral [49]. The b2, the larger the covalence
of the bonding. From this analysis, the in-plane bonds of the com-
plexes correspondent to signals 1, 2 and 3 are largely covalent,
with the covalent character increasing from 1 to 3. The values of
a2 indicate that approximately 90% of the spin population is in
Table 6
Weight losses percentage of HL1, HL3 and HL5.
Compounds
First stage
Second stage
Third stage
Remaining weight after 650 °C
Temperature (°C)
Weight loss (%)
Temperature (°C)
Weight loss (%)
Temperature (°C)
Weight loss (%)
HL1
HL3
HL5
200
145
112
61.9
59.8
5.4
320
400
225
38.1
39.9
33.6
–
–
284
–
–
58.7
Ash
Ash
Ash

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
321
Table 7
Thermal analyses data of the Cu(II) complexes (1–4).
Complexa
Temp. range (°C)
Found mass loss (calc.)%
Assignment
(1)
45–189
7.24 (8.13)
16.67 (17.39)
24.43 (24.17)
14.38 (14.46)
Loss of two water molecule in outside of the coordination sphere
Loss of one coordinated water and one coordinated acetate group
Further decomposition of a part of the ligand (C7H7O)
189–331
331–506
506–709
Evolution of SO2 gas leaving CuO residue with contaminated carbon atoms
(2)
(3)
(4)
45–178
7.91 (8.73)
18.61 (18.66)
18.06 (18.42)
6.64 (6.79)
Loss of two water molecule in outside of the coordination sphere
Loss of one coordinated water and one coordinated acetate group
Further decomposition of a part of the ligand (C6H4)
Evolution of N2 gas
178–273
273–514
514–560
560–640
15.43 (15.51)
Evolution of SO2 gas leaving CuO residue with contaminated carbon atoms
45–189
4.15 (7.87)
16.72 (16.83)
10.46 (10.05)
13.72 (13.98)
22.44 (22.73)
Loss of two water molecule in outside of the coordination sphere
Loss of one coordinated water and one coordinated acetate group
Evolution of NO2 gas
189–288
288–400
400–592
592–670
Evolution of SO2 gas
Decomposition of a part of the ligand (C6H4N2) leaving CuO residue with contaminated carbon atoms
40–189
5.22 (8.44)
18.00 (18.05)
20.47 (21.33)
15.45 (15.00)
Loss of two water molecule in outside of the coordination sphere
Loss of one coordinated water and one coordinated acetate group
Further decomposition of a part of the ligand (C7H7)
189–316
316–533
533–670
Evolution of SO2 gas and CuO residue with contaminated carbon atoms
a
Numbers as given in Table 2.
(a)
(b)
100
80
100
80
60
60
40
40
20
0
20
100 200 300 400 500 600 700 800
0
100 200 300 400 500 600 700 800
Temperature (°C)
Temperature (°C)
(c)
(d)
100
80
100
80
60
40
60
40
20
0
0
100 200 300 400 500 600 700 800
100 200 300 400 500 600 700 800
Temperature (°C)
Temperature (°C)
Fig. 11. TGA curves for complexes (a) [Cu(L1)(OAc)(OH2)]ꢂ2H2O, (b) [Cu(L3)(OAc)(OH2)]ꢂ2H2O, (c) [Cu(L5)(OAc)(OH2)]ꢂ2H2O and (d) [Cu(L2)(OAc)(OH2)]ꢂ2H2O.
than 4,a considerable exchange interaction exists in the solid com-
plex. The calculated G value for these complexes indicates that
there are no interactions between the copper centers (see Table 5).
The a2 value of 0.5 indicates complete covalent bonding, while
Here k = 828 cmꢅ1 for free Cu(II) ion and E is the electronic transi-
tion energy. This is also confirmed by orbital reduction factors K,
which can be estimated using the following equations:
Kll
¼
a
2b2
that of 1.0 suggests complete ionic bonding. The out-of-plane
p-
bonding (d2) and in-plane
p-bonding (b) parameters are calculated
K
¼
a
2d2
using the following equations:
?
b2 ¼ ðgll ꢅ 2:0023ÞE= ꢅ 8ka2
Significant information about the nature of bonding in the Cu(II)
complex can be derived from the relative magnitudes of Kll and
d2 ¼ ðg? ꢅ 2:0023ÞE= ꢅ 2ka2
K . In the case of pure
r
-bonding, K ꢇ K = 0.77, whereas K < K
?
?
?
ll
ll

322
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-12.5
HL1
HL1
-11.5
-12.0
-12.5
-13.0
-13.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
498-624 oC
211-346 oC
-16.0
0.00111 0.00114 0.00117 0.00120 0.00123 0.00126 0.00129
0.00161 0.00168 0.00175 0.00182 0.00189 0.00196
(1/T(K))
(1/T(K))
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
-16.0
HL3
HL3
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
502-643 oC
158-401 oC
0.0016 0.0017 0.0018 0.0019 0.0020 0.0021 0.0022 0.002
0.00108 0.00112 0.00116 0.00120 0.00124 0.00128
(1/T(K))
(1/T(K))
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
-16.0
HL5
HL5
-12.0
-12.8
-13.6
-14.4
-15.2
-16.0
-16.8
-17.6
225-271 oC
443-630oC
0.00186
0.00189
0.00192
0.00195
0.00198
0.00110 0.00115 0.00120 0.00125 0.00130 0.00135
(1/T(K))
(1/T(K))
Fig. 12. Coats–Redfern (CR) of the ligands (HLn).
ꢀ The value of All ꢆ 10ꢅ4 cmꢅ1 increases with increasing gll and b2
(Fig. 7).
implies considerable in-plane
p-bonding, while for out-of-plane
p
r
-bonding Kll > K . Molecular orbital coefficients a2 (in-plane
?
-bonding), b2 (in-plane
p
-bonding) and d2 (out-plane
p
-bonding)
ꢀ The value of a2 increases with increasing All ꢆ 10ꢅ4 (cmꢅ1), gav
and b2 (Fig. 8).
were calculated using the last equations (see Table 5). The lower
value of b2 indicates that the in-plane
-bonding is more covalent
than the in-plane
ꢀ K2ll and K?2 increase with increasing gll and g? (Fig. 9).
p
r
-bonding, the data in a good agreement with
the data reported earlier [24]. The a2 values for copper(II) com-
plexes indicates a considerable covalencey in the bonding between
the Cu(II) ion and the metal. In this study, a2 is less than b2
Thermal analyses
Thermogravimetric analysis of ligands (HLn)
indicating that in-plane
r-bonding is more covalent than in-plane
The thermal properties of ligands were characterized on the ba-
sis of thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) methods in the temperature range 50–800 °C.
The TGA and DSC curves for HLn (where n = 1, 3 and 5) is shown
in Fig. 10. The temperature intervals and the percentage of loss
of masses are listed in Table 6. For HL1 and HL3 there are two steps
of the loss of masses, while for HL5 there are three steps. Fig. 10(a)
p-bonding. These ESR data showed that:
ꢀ gll, All ꢆ 10ꢅ4 cmꢅ1 and b2 values are dependent of the substitu-
ents effect of the p-position of the ligand and can be order as: p-
(OCH3 < H < NO2) (Fig. 6). The reverse order is observed for the
electronic spectral data.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
323
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-12.0
[Cu(L1)(OAc)(OH2)].2H2O
[Cu(L1)(OAc)(OH2)].2H2O
(1)
(1)
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
142-240 oC
301-418 oC
0.00145
0.00150
0.00155
0.00160
0.00165
0.00170
0.00175
0.00196 0.00203 0.00210 0.00217 0.00224 0.00231 0.00238
(1/T(K))
(1/T(K))
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-11.5
[Cu(L3)(OAc)(OH2)].2H2O
[Cu(L3)(OAc)(OH2)].2H2O
(2)
(2)
-12.0
-12.5
-13.0
-13.5
-14.0
127-372 oC
496-715 oC
0.0016
0.0017
0.0018
0.0019
0.0020
0.0021
0.0022
0.00100
0.00105
0.00110
0.00115
0.00120
0.00125
(1/T(K))
(1/T(K))
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
-16.0
[Cu(L5)(OAc)(OH2)].2H2O
[Cu(L5)(OAc)(OH2)].2H2O
(3)
(3)
189-292 oC
349-403 oC
0.00150
0.00152
0.00154
0.00156
0.00158
0.00160
0.00180 0.00185 0.00190 0.00195 0.00200 0.00205 0.00210 0.00215
(1/T(K))
(1/T(K))
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
-12.0
[Cu(L2)(OAc)(OH2)].2H2O
[Cu(L2)(OAc)(OH2)].2H2O
(4)
(4)
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
599-715 oC
142-399 oC
0.001008
0.001036
0.001064
0.001092
0.001120
0.001148
0.00150
0.00165
0.00180
0.00195
0.00210
0.00225
(1/T(K))
(1/T(K))
Fig. 13. Coats–Redfern (CR) of the Cu(II) complexes (1–4).
reveals that the HL1 decomposes in two steps, the first stage,
61.9%. The second stage, weight loss starts at 320 °C with a weight
weight loss starts at 200 °C with a weight loss percentage of
loss percentage of 38.1%. The HL3 decomposes in two steps as

324
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
0.4
0.2
0.2
HL1
HL1
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
o
211-346 C
o
498-624 C
-1.6
-60 -50 -40 -30 -20 -10
0
10 20 30 40 50 60 70
-60 -50 -40 -30 -20 -10
0
10 20 30 40 50 60 70
θ
(K)
θ (K)
0.3
0.0
HL3
HL3
0.0
-0.3
-0.6
-0.9
-1.2
-1.5
-1.8
-0.3
-0.6
-0.9
-1.2
-1.5
o
o
158-401 C
502-643 C
-60
-40
-20
0
20
40
60
80
-120 -100 -80 -60 -40 -20
0
20
40
60
θ
(K)
θ
(K)
0.2
0.0
0.0
-0.3
-0.6
-0.9
-1.2
-1.5
-1.8
-2.1
-2.4
-2.7
HL5
HL5
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
o
o
225-271 C
443-630 C
-80
-60
-40
-20
0
20
40
60
80
-25
-20
-15
-10
-5
0
5
10
15
20
θ (K)
θ (K)
Fig. 14. Horowitz–Metzger (HM) of the ligands (HLn).
shown in Fig. 10(b), the first stage, weight loss starts at 145 °C with
a weight loss percentage of 59.8%. The second stage, weight loss
starts at 400 °C with a weight loss percentage of 39.9%. Fig. 10(c)
reveals that the HL5 decomposes in three steps, the first stage,
weight loss starts at 112 °C with a weight loss percentage of
5.4%. The second stage, weight loss starts at 225 °C with a weight
loss percentage of 33.6%. The third stage, weight loss starts at
284 °C with a weight loss percentage of 58.7%.
The DSC data for HL3 and HL5 ligands show two exothermic and
endothermic peaks except HL1 ligand show one exothermic peak is
shown in Fig. 10(a–c). For the HL1 ligand the recorded DSC curve
show only one exothermic peak at 220 °C. Simultaneously, the re-
corded DSC curve of the HL3 ligand show two exothermic and
endothermic peaks at 190 °C and 180 °C, respectively, while the re-
corded DSC curve of the HL5 ligand show two exothermic and
endothermic peaks at 245 °C and 120 °C, respectively. These
endothermic peaks can be attributed to the loss of residual solvent
trapped in the ligands matrices.
Thermogravimetric analysis of complexes (1–4)
The TGA of the isolated complexes was taken as a proof for the
existing of water molecules as well as the anions in the coordina-
tion sphere. The thermal analyses data for the [CuLn(OAc)(OH2)]-
ꢂ2H2O complexes (n = 1, 2, 3, and 5) are summarized in Table 7.
It can be seen that the TGA curves of the complexes
[CuLn(OAc)(OH2)]ꢂ2H2O complexes show loss of masses down to
100 °C, indicating that the presence of two water molecules in
outside of the coordination sphere, while up to 189 °C above which
the dehydration begins are shown in Fig. 11. In the temperature
range ꢃ189–331 °C, the lost of the one coordinated water molecule
as well as the lost of acetate group. The weight loss stages
(ꢃ270–500 °C) are due to the decomposition of a part of the ligand.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
325
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
[Cu(L1)(OAc)(OH2)].2H2O
[Cu(L1)(OAc)(OH2)].2H2O
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
(1)
(1)
o
o
301-418 C
142-240 C
-60 -50 -40 -30 -20 -10
0
10 20 30 40 50
-50
-40
-30
-20
-10
0
10
20
30
40
θ (K)
θ (K)
0.4
0.2
0.6
0.4
[Cu(L3)(OAc)(OH2)].2H2O
[Cu(L3)(OAc)(OH2)].2H2O
(2)
(2)
0.0
0.2
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
o
o
496-715 C
127-372 C
-100 -80 -60 -40 -20
0
20 40 60 80 100
-120 -100 -80 -60 -40 -20
0
20 40 60 80 100 120
θ (K)
θ (K)
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
-1.8
-2.0
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
[Cu(L5)(OAc)(OH2)].2H2O
[Cu(L5)(OAc)(OH2)].2H2O
(3)
(3)
o
o
189-292 C
349-403 C
-50
-40
-30
-20
-10
0
10
20
30
40
-25
-20
-15
-10
-5
0
5
10
15
20
θ
θ
(K)
(K)
0.2
0.0
0.4
0.2
[Cu(L2)(OAc)(OH2)].2H2O
[Cu(L2)(OAc)(OH2)].2H2O
(4)
(4)
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
0.0
-0.2
-0.4
-0.6
o
o
599-715 C
142-399 C
-100 -80 -60 -40 -20
0
20 40 60 80 100 120
-60 -50 -40 -30 -20 -10
0
10 20 30 40 50
θ
θ
(K)
(K)
Fig. 15. Horowitz–Metzger (HM) of the Cu(II) complexes (1–4).

326
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
Table 8
Thermodynamic data of the thermal decomposition of HLn and their Cu(II) complexes (1–4).
Compounda
Decomposition
Method
Parameter
r
temperature (°C)
Ea (kJ molꢅ1
)
A (sꢅ1
)
D
Sꢁ (J molꢅ1 Kꢅ1
)
D
Hꢁ (kJ molꢅ1
)
D )
Gꢁ (kJ molꢅ1
HL1
211–346
498–624
158–401
502–643
225–271
443–630
142–240
301–418
127–372
496–715
189–292
349–403
142–399
599–715
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
CR
45.8
53.6
180
193
46.9
48.4
162
173
329
338
108
120
70.9
80.8
102
114
31.2
39.2
108
119
106
115
235
250
31.8
41.0
171
187
7.58 ꢆ 101
4.18 ꢆ 102
4.43 ꢆ 108
6.40 ꢆ 109
7.11 ꢆ 101
1.17 ꢆ 102
2.34 ꢆ 107
2.50 ꢆ 108
2.54 ꢆ 1030
1.70 ꢆ 1032
1.51 ꢆ 104
2.05 ꢆ 105
5.53 ꢆ 105
1.40 ꢆ 107
1.31 ꢆ 106
2.10 ꢆ 107
3.31 ꢆ 100
3.59 ꢆ 101
1.59 ꢆ 104
5.78 ꢆ 104
3.74 ꢆ 108
7.73 ꢆ 109
9.36 ꢆ 1016
2.09 ꢆ 1018
2.10 ꢆ 100
3.60 ꢆ 101
4.27 ꢆ 107
2.01 ꢆ 108
ꢅ214
ꢅ200
ꢅ87.9
ꢅ65.8
ꢅ215
ꢅ210
ꢅ113
ꢅ92.2
333
41.2
49
159
159
247
241
161
160
250
245
151
142
242
236
131
129
181
179
152
150
254
255
146
142
182
180
160
156
264
268
0.99221
0.99398
0.99355
0.99169
0.99322
0.99788
0.98442
0.99156
0.99453
0.99452
0.99432
0.9939
0.99122
0.98595
0.99104
0.99064
0.99523
0.98744
0.98712
0.98669
0.99596
0.99460
0.99590
0.99435
0.99161
0.98130
0.98947
0.99112
174
186
42.3
43.8
155
166
325
333
101
113
67.1
76.9
96.5
108
26.9
34.9
101
112
102
111
230
244
27.3
36.5
163
179
HL3
HL5
1
367
ꢅ173
ꢅ152
ꢅ139
ꢅ112
ꢅ134
ꢅ111
ꢅ240
ꢅ220
ꢅ173
ꢅ163
ꢅ85.3
ꢅ60.0
73.5
2
3
99.3
4
ꢅ244
ꢅ220
ꢅ108
ꢅ95.4
HM
a
Numbers as given in Table 2.
where kB is the Boltzmann constant, h is the Plank’s constant and Ts
is the TG peak temperature.
According to literature the azo bonds in the azo metal complexes
breakdown when the temperature is higher than 260 °C
[25,56,57]. The final weight losses (ꢃ500–670 °C) are largely
attributed to complete decomposition of other part of the ligand
molecule with evolution of SO2 gas. The remaining final product
is CuO.
Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the approx-
imation methods. These authors derived the relation:
"
#
1ꢅn
1 ꢅ ð1 ꢅ
a
1 ꢅ n
Þ
Eh
Calculation of activation thermodynamic parameters
log
¼
;
for n – 1
ð4Þ
2:303RT2s
The thermodynamic activation parameters of decomposition
when n = 1, the LHS of Eq. (4) would be log[ꢅlog(1ꢅ
a
)] (Figs. 14 and
processes of complexes namely activation energy (Ea), enthalpy
15). For a first order kinetic process, the Horowitz–Metzger equa-
(D D
Hꢁ), entropy ( Sꢁ), and Gibbs free energy change of the decom-
tion may write in the form:
position (D
Gꢁ) are evaluated graphically by employing the Coast–
ꢂ
ꢀ
ꢁꢃ
Redfern [58] and Horowitz–Metzger [59] methods.
Wa
Eh
log log
¼
ꢅ log 2:303
ð5Þ
2:303RT2s
W
c
Coast–Redfern equation
where h = TꢅTs, w = w ꢅw, w = mass loss at the completion reac-
The Coast–Redfern equation, which is a typical integral method,
can represent as:
c
a
a
tion; w = mass loss up to time t. The plot of log [log (w /w )] vs. h
a
c
was drawn and found to be linear from the slope of which Ea was
calculated. The pre-exponential factor, A, calculated from equation:
ꢀ
ꢁ
Z
Z
a
T2
dx
ð1 ꢅ
A
u
Ea
RT
¼
exp
ꢅ
dt
ð1Þ
n
a
Þ
0
T1
Ea
A
h
ꢄ
ꢅi
¼
ð6Þ
RT2s
Ea
s
u
exp ꢅ RT
For convenience of integration, the lower limit T1 usually taken as
zero. This equation on integration gives:
The entropy of activation,
py activation,
D
Sꢁ, is calculated from Eq. (3). The enthal-
ꢂ
ꢃ
ꢂ
ꢃ
lnð1 ꢅ
aÞ
Ea
RT
AR
uEa
D D
Hꢁ, and Gibbs free energy, Gꢁ, calculated from:
ln ꢅ
¼ ꢅ
þ ln
ð2Þ
T2
D
D
Hꢁ ¼ Ea ꢅ RT
ð7Þ
A plot of left-hand side (LHS) against 1/T was drawn (Figs. 12 and
13). Ea is the energy of activation in J molꢅ1 and calculated from
the slop and A in (sꢅ1) from the intercept value. The entropy of acti-
Gꢁ ¼
D
Hꢁ ꢅ T
D
Sꢁ
ð8Þ
The calculated values of Ea, A,
D
Sꢁ,
D
Hꢁ and
D
Gꢁ for the decomposi-
vation
D
Sꢁ in (J Kꢅ1 molꢅ1) calculated by using the equation:
tion steps for ligands (HLn) and their complexes (1–4) are summa-
rized in Table 8.
The complex (3) is the highest value of Ea. This can be attributed
to the fact that the effective charge experienced by the d-electrons
ꢂ
ꢀ
ꢁꢃ
Ah
D
Sꢁ ¼ 2:303 log
R
ð3Þ
kBTs

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 310–328
327
b N.A. El-Ghamaz, M.A. Diab, A.Z. El-Sonbati, O.L. Salem, Spectrochim. Acta A
83 (2011) 61–66.
[9] H. Kocaokutgen, S. Ozkinali, Dyes Pigments 63 (2004) 83–88.
[10] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, H.A. Seyam, Spectrochim. Acta A
104 (2013) 213–221.
[11] H. Bock, K. Wittle, M. Veit, N. Wiberg, J. Am. Chem. Soc. 98 (1976). p. 109.
[12] M.I. Abou-Dobara, A.Z. El-Sonbati, Sh.M. Morgan, World J. Microbiol.
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[13] A.Z. El-Sonbati, A.A. Belal, S.I. El-Wakel, M.A. Hussien, Spectrochim. Acta A 60
(2004) 965–972.
increases due to the electron withdrawing p-substituent NO2 while
it decreases by the electron donating character of OCH3 and CH3.
This indicates that, the complex (3) is more thermally stable than
the other complexes.
From the values of the energy of activation (Ea) of the ligands
(HLn) and their complexes (1–4), it is observed that the complexes
(1–4) are less stable than the ligand (HLn) and may be attributed to
the loss of water molecules from complexes. These results are
inconsistent with our previous results [60].
[14] A.Z. El-Sonbati, R.M. Issa, A.M. Abd El-Gawad, Spectrochim. Acta A 68 (2007)
134–138.
From these results we can say that, the high values of activation
energies reflect the thermal stability of the compounds. The entro-
py of activation energies reflects the thermal stability of the com-
[15] A.Z. El-Sonbati, A.S. Shihri, A.A. Bindary, Spectrochim. Acta A 60 (2004) 1763–
1768.
[16] N.A. El-Ghamaz, A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, H.A. Seyam, Solid
State Sci. 19 (2013) 19–26.
[17] A.Z. El-Sonbati, A.A. El-Bindary, A.A. Sarawy, Spectrochim. Acta A 58 (2002)
2771–2778.
[18] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Met. Chem. Phys.
123 (2010) 439–449.
pounds. The negative values of activation entropies (
D
Sꢁ) indicate a
more ordered activated compounds than the reactants and/or the
reactions are slow [61]. The values of
as favorable or spontaneous reaction.
D
Gꢁ is positive considered
[19] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Spectrochim. Acta A
77 (2010) 755–766.
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(2011) 1119–1125.
[22] A.Z. El-Sonbati, M.A. Diab, Physico-chemical Studies on the Complexes, LA
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