DFT, characterization and investigation of vibrational spectroscopy of 4-(4-hydroxy)-3-(2-pyrazine-2-carbonyl)hydrazonomethylphenyl-diazen-yl- benzenesulfonamide and its copper(II) complex

Article abstract of DOI:10.1016/j.molstruc.2014.02.051

Azo-Schiff-base complex of Cu(II) has been synthesized and characterized by elemental, spectral and thermal studies. The conductance data indicate the non-electrolytic nature of the complex. The IR spectra of the prepared complex was suggested that the az

Full text of DOI:10.1016/j.molstruc.2014.02.051

Journal of Molecular Structure 1067 (2014) 94–103
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
DFT, characterization and investigation of vibrational spectroscopy
of 4-(4-hydroxy)-3-(2-pyrazine-2-carbonyl)
hydrazonomethylphenyl-diazen-yl-benzenesulfonamide
and its copper(II) complex
b,c
Reda A.A. Ammar a, Abdel-Nasser M.A. Alaghaz b, , Ahmed A. Elhenawy
⇑
a Chemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia
b Chemistry Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo 11884, Egypt
c Chemistry Department, Faculty of Science and Arts, Al-Baha University, Al-Mukhwah, Al-Baha, Saudi Arabia
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
ꢀ
The ligand and its Cu(II) complex
were synthesized and characterized.
Spectroscopic properties of the ligand
and its Cu(II) complex were carried
out.
ꢀ
ꢀ
Geometrical optimization of ligand
calculated using DFT/B3LYP with 6-
31GÃ and 6-311GÃÃ level.
The calculated vibrational
frequencies showed slight deviation
from experimental frequencies for
the ligand.
ꢀ
The reactivity descriptors for ligand
H2L and its Cu(II) complex were
computed and showed increasing
dipole moment of ligand.
a r t i c l e i n f o
a b s t r a c t
Article history:
Azo-Schiff-base complex of Cu(II) has been synthesized and characterized by elemental, spectral and
thermal studies. The conductance data indicate the non-electrolytic nature of the complex. The IR spectra
of the prepared complex was suggested that the azo-Schiff-base ligand [4-((4-hydroxy-3-(2-(pyrazine-2-
Received 16 November 2013
Received in revised form 7 February 2014
Accepted 26 February 2014
Available online 19 March 2014
carbonyl) hydrazono)methyl)phenyl)diazen-yl)benzenesulfonamide] (H2L) behaves as
a tri-dentate
ligand through the carbonyl oxygen atom, azomethine nitrogen atom and phenolic oxygen atom
(ONO). The surface morphology (SEM) of the ligand and its copper(II) complex was studied using SEM
analysis. X-ray powder diffraction (XRD) helps to determine the cell parameters of the complex. Trans-
mission electron microscopy (TEM) indicated spherical particles of ꢁ200 nm diameter. The physico-
chemical studies revealed octahedral geometry around copper ion. The EPR spectra of copper complex
in DMSO at 300 and 77 K were recorded and their salient feature was reported. The redox behavior of
the ligand and its copper(II) complex were studied using cyclic voltammetry. Thermal properties and
decomposition kinetics of copper(II) complex was investigated. The interpretation mathematical analysis
Keywords:
Azo-Schiff base
IR
EPR
Cyclic voltammetry
DFT/B3LYP
and evaluation of kinetic parameters (E, A,
DH, DS and DG) of all thermal decomposition stages have been
evaluated using Coats–Redfern (CR), Horowitz–Metzger (HM) and Piloyan–Novikova (PN) equations.
Moreover, the density functional theory studies are discussed for ligand, using DFT/B3LYP with 6-31GÃ
⇑
Corresponding author at: Chemistry Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo 11884, Egypt. Tel.: +20 1003358476.
E-mail addresses: aalajhaz@hotmail.com, aalajhaz@yahoo.com (Abdel-Nasser M.A. Alaghaz).
http://dx.doi.org/10.1016/j.molstruc.2014.02.051
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
95
and 6-311GÃ level of theory, the absorption spectra has been computed by using time dependent at TD-
DFT/B3LYP with 6-31GÃ and 6-311GÃ level of theory. The HOMO–LUMO energy gap of studied systems
has been discussed.
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
100 kHz magnetic field modulation. The investigated sample was
in a fine powder form [28]. Powder XRD data were collected on a
During the past two decades, considerable attention has been
paid to the chemistry of the transition metal complexes of Schiff
bases containing oxygen and other donors [1–6]. Schiff bases are
a class of important compounds in medicinal and pharmaceutical
field. They show biological activities including antibacterial [7–
10], antifungal [11,12], anticancer [13–15], and herbicidal [16]
activities. Furthermore, Schiff bases are utilized as starting mate-
rial in the synthesis of industrial [17] and biological compounds
such as b-lactons [18]. Azo compounds have been used for a long
time as dyes in industry [19]. In addition, azo compounds are used
in analytical chemistry as indicators in pH, redox, or complexomet-
ric titration [20,21]. Some azo compounds have shown a good anti-
bacterial activity [22]. The existence of an azo moiety in different
types of compounds has caused them to show pesticidal activity
[16]. Sulfonamides are important class of drugs with several types
of pharmacological agents possessing antibacterial [23], antithy-
roid [24], diuretic [25] and hypoglycaemic [26]. Based on the men-
tioned properties for Schiff base and azo compound, was reported
herein the syntheses and characterization of a novel azo-dye Schiff
base derivative derived from sulfanilamide and its Cu(II) complex.
PW1710 diffractometer. The operating voltage of the instrument
was 30 kV and the operating current was 20 mA. The intensity data
were collected at room temperature over a 2h range of 5.025–
79.925° with a continuous scan mode. Scanning electron micro-
scope (SEM) measurements were carried out using small pieces
of prepared samples on different sectors to estimate the actual mo-
lar ratios by using ‘‘TXA-840, JEOL-Japan’’ attached to XL30 appara-
tus with EDX unit, accelerant voltage 30 kV, magnification 10Â up
to 500,000Â and resolution 3 nm. The samples were coated with
gold. Transmission electron microscopy (TEM) images were ob-
tained on a Tecnai 30 G2S–Twin electron microscope with an
accelerating voltage of 300 kV on the surface of a carbon coated
copper grid. The thermal analyses (TGA and DTA) were carried
out in dynamic nitrogen atmosphere (20 mL minÀ1) with a heating
rate of 10 °C minÀ1 using Shimadzu TG-50H and DTA-50H thermal
analyzers.
Preparation of the Schiff base compound
Diazotization and coupling
In 1 l beaker, dissolve (56.76 g, 0.33 mol) of 4-aminobenzene-
sulfonamide in 85 ml of concentrated hydrochloric acid and
85 ml of water. Cool the mixture to 0 °C in an ice–salt bath with
stirring and the addition of a little crushed ice. Add during 10–
15 min a solution of (24 g, 0.33 mol) of sodium nitrite in 50 ml of
water, stir the solution well during the diazotization, and keep
the mixture at a temperature of 0–5 °C by the addition of a little
crushed ice from time to time. The very soluble diazonium salt is
formed. Dissolve (40.26 g, 0.33 mol) of salicylaldehyde in a solu-
tion of 21 g of sodium hydroxide in 75 ml water, cool in ice and
add the diazotized solution slowly and with stirring. Then add con-
centrated hydrochloric acid slowly and with constant stirring to
the cold mixture until the pH of solution become 5.5. Filter the pre-
cipitated substance, 4-((3-formyl-4-hydroxyphenyl)diazenyl)ben-
zenesulfonamide, with gentle suction, wash with water until free
from acid and dried upon filter paper in the air.
Experimental
Materials
All chemicals used in the present work were of highest purity
and of the analytical reagent grade (AR). The solvents used were
either spectroscopic pure from BDH or purified by the recom-
mended method [27].
The apparatus and physical measurements
The C, H, N and S data were obtained by using a Carlo-Erba 1106
elemental analyzer. Copper content was determined complexo-
metrically by standard EDTA titration. The infrared spectra were
recorded on a Shimadzu FT-IR spectrometer using KBr discs. The
molar conductance measurements were carried out using a Sy-
bron-Barnstead conductometer. The 1H NMR (300 MHz) spectrum
was recorded using 300 MHz Varian–Oxford Mercury. The deuter-
ated solvent used was dimethylsulphoxide (DMSO) and the spec-
trum extended from 0 to 15 ppm. The sample was dissolved in
DMSO-d6 using tetramethylsilane as internal references. The solid
reflectance spectra were measured using a Shimadzu PC3101
UV–VIS–NIR scanning spectrophotometer. Magnetic susceptibility
of the copper(II) complex was measured by the Gouy method at
room temperature using a Johnson Matthey, Alpha products,
model MKI magnetic susceptibility balance and the effective
Preparation of the Schiff base H2L
The Schiff base H2L was prepared by mixing hot solution 60 °C
of 4-((3-formyl-4-hydroxyphenyl)diazenyl)benzenesulfonamide
(100.75, 0.33 mol) with hot solution 60 °C of pyrazine-2-carbohyd-
razide (45.54 g, 0.33 mol) in 50 ml ethanol. The mixture was re-
fluxed for 3 h. The formed solid product was separated by
filtration, purified by crystallization from ethanol, washed several
times with diethyl ether and dried in vacuum over anhydrous cal-
cium chloride to give orange crystals, yield 85%.
magnetic moments were calculated using the relation
l
eff = 2.828
(
vmÁT)1/2B.M., where
vm is the molar susceptibility corrected using
Preparation of the copper(II) complex
Pascal’s constants for diamagnetism of all atoms in the compounds.
The ultraviolet spectra were recorded on a Perkin–Elmer Lambda–
3B UV–VIS spectrophotometer. The mass spectra were performed
using a Shimadzu-Ge-Ms-Qp 100 EX mass spectrometer using
the direct inlet system. The electron paramagnetic resonance
(EPR) spectrum was recorded on a conventional X-band Bruker
ELEXSYS E 500 CW-spectrometer operating at 9.5 GHz with a
Copper(II) complex of H2L ligand was prepared by the addition
of a hot solution 60 °C of the appropriate CuCl2Á2H2O (1 mmol) in
ethanol (25 ml) to the well stirred hot solution of the Schiff base
(2 mmol) in the same solvent (25 ml). The mixture was left under
reflux with continuous stirring for 4 h where upon the solid com-
plex precipitated. The obtained solid was washed with ethanol fol-
lowed by diethyl ether and dried in vacuum over anhydrous

96
R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
Table 1
Physical data of Ligand (H2L) and corresponding metal complexes.
Compound no. M.F. (M.Wt.)
H2L C18H15N7O4S (425.42)
Yield
(%)
m.p.
(°C)
Color
Elemental analyses % calculated (found)
leff
K
(
X
À1 molÀ1 cm2)
(B.M.)
M
–
C
H
N
S
85
64
160–
162
>300
Orange
50.82
(50.78)
47.39
3.55
23.05
(22.99)
21.49
7.54
(7.53)
7.03
–
–
(3.52)
3.09
[Cu(L)2] C36H28CuN14O8S2
(912.37)
Dark
brown
6.96
2.13
1.53
(6.94) (47.32)
(3.03)
(21.42)
(6.99)
calcium chloride. The analytical data of the copper(II) complex are
collected in Table 1.
elemental analyses, spectroscopic characterization, this mononu-
clear complex is presumed to have the coordination environment
shown in Scheme 2.
Computational detail
Elemental analyses
All electronic structure calculations were performed using the
Spartan 08 program [28]. Geometry optimizations have been
achieved using semi-empirical AM1 molecular orbital for density
functional theory [29,30] with a B3LYP/6-31GÃ and 6-311GÃ basis
sets [29–32]. The structural parameters, such as the dipole mo-
ment of the molecules, the energy of the highest occupied molec-
ular orbital EHOMO and the lowest unoccupied molecular orbital
ELUMO, atomic charges derive from Mulliken population analysis
[33] were obtained. The vibration frequency calculation also, was
computed. For each stationary point was performed at DFT with
B3LYP using 6-31GÃ and 6-311GÃÃ, to characterize its nature as
minima or transition states and to correct energies. The graphical
representation of the molecular electrostatic potential surface
(MEP or ESP), as implemented within the SPARTAN program
[34,35].
The novel Azo-dye Schiff base (H2L) is prepared and subjected
to elemental analyses, mass and IR spectral analyses. The results
of elemental analyses (C, H, N, S) with molecular formula and the
melting point are presented in Table 1. The results obtained are
in good agreement with those calculated for the suggested formula
and the melting point is sharp indicating the purity of the prepared
Azo-dye Schiff base. The structure of the Azo-dye Schiff base under
study is as shown in Scheme 1.
IR spectrum
The IR spectrum (Fig. S1; Table 2) of azo-dye Schiff base ligand
(H2L) is given in synthetic procedures. Vibration bands with the
wave nuÀm1bers of 3522 cmÀ1
(m
OAH), 3075 cmÀ1
(m
CAH, ArAH),
1683 cm
(
m
C@O), 1627 cmÀ1
(m
C@N), 1565 cmÀ1
(mC@C),
1212 cmÀ1
(mCAO, ArAO) was observed for azo-dye Schiff base li-
gand (H2L). The stretching frequency observed at 2852 cmÀ1 in H2L
shows the presence of OAH—N intramolecular hydrogen bond.
Schiff base ligand H2L with strong band at 1212 cmÀ1 possesses
highest percentage of enolimino tautomer due to the stabilization
of phenolic CAO bond. H2L ligand shows bands at 1435, 1325 and
Results and discussion
The ligand (H2L)
The Azo-dye Schiff base ligand, H2L has been prepared by the
condensation between 4-((3-formyl-4-hydroxyphenyl)-diaze-
1155 cmÀ1 due to
mN@N, mSO2-asy and mSO2 sym, respectively.
nyl)benzenesulfonamide
with
pyrazine-2-carbohy-drazide,
(1:1 M ratio) in EtOH as shown in Scheme 1. The level of the purity
of the ligand and the complex were checked by T.L.C. on silica gel-
coated plates. H2L Schiff base ligand give the complex with Cu(II)
salt. The complex was synthesized by the general equations shown
below. The ligand is stable at room temperature and soluble in
common organic solvents such as DMSO, DMF, EtOH and MeOH.
The complex is also stable at room temperature. Based on the
1H NMR spectrum
1H NMR spectral data of the ligand (Fig. S2) relative to TMS in
DMSO-d6 without and with D2O give further support of the sug-
gested structure of the ligand. The broad signal at d = 13.78 ppm
is assigned to the proton of the hydroxyl group. This peak is due
to hydrogen bonded phenolic proton and the integration is gener-
ally less than 2.0 due to this intramolecular hydrogen bonding. The
Scheme 1. Synthesis of ligand (H2L).

R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
97
IR-spectra
On comparing the IR-spectra of the free ligand with the IR spec-
tra (Fig. S1; Table 2) of their complex the following can be pointed
out:
(i) The IR spectrum of complex displayed absorption band at
1557 cmÀ1 which can be assigned to C@N stretching fre-
quency of coordinated ligand, whereas for free ligand this
band was at 1577 cmÀ1.The shift to lower frequencies (as
compared to free ligand) indicated donation of the lone pair
of electrons on azomethine nitrogen to copper center, this
has been strengthened by the shift of
1052 cmÀ1 in free ligand to 1025 cmÀ1 in complex.
(ii) The OH phenolic and OH enolic of the free ligand is absent
m(N–N) band at
m
m
from the IR spectrum of the complex which indicates that,
the phenolic (OH) and enolic (OH) groups contribute to the
formation of complex by H+ ions displacement [37] which
points that the free ligandis considered in complex forma-
tion as monoanionic ligand.
Scheme 2. Synthesis of Cu(II) complex of ligand (H2L).
(iii) The bands of
SO2asym and
m
NH2asy,
mNH2sym, mC@N ring, mN@N,
m
mSO2sym, in the IR spectra of the free ligand
still lie at the same position in the IR spectrum of the cop-
per(II) complex. These indicate that these groups did not con-
tribute to the coordination of the copper ion in the complex.
(iv) The spectrum exhibits the IR band at 1683 which may be
hydrogen proton of NH group assigned at 10.08 which disappeared
with D2O, signal for the methine proton of the characteristic azo-
methine group for azo-dye Schiff base, AN@CHA was observed
at 8.98 ppm. The shielding hydrogen atoms of amino group for
SO2NH2 moiety at 7.83 (s, 2H, NH2 disappeared with D2O). In the
region of 7.32–6.86 ppm chemical shifts were assigned for
aromatic protons Structure S1.
assigned to the amide [m(C@O)] stretching vibration. On
complex formation, the position of amide is shifted to the
lower wave numbers [37]. This indicates that the amide oxy-
gen atom is coordinated to the copper ion.
(v) For the copper(II) complex two new bands appear in their IR
spectrum at 336 cmÀ1 and 292 cmÀ1 respectively, which are
absent from the IR spectrum of the free ligand, these can be
Mass spectrum
The electron impact mass spectrum (Fig. S3) of the free ligand,
confirms the proposed formula by showing a peak at 425 u corre-
sponding to the ligand moiety [(C18H15N7O4S) atomic mass 425 u].
The series of peaks in the range, i.e. 57, 136, 200, 250, 318 and
385u, attributable to different fragments of the ligand. These data
suggest the condensation of keto group with amino group. The
molecular ion peak (425 u) is in good agreement with the sug-
gested molecular formula indicated from elemental analyses.
assigned to mCu–O and mCu–N bands, respectively [37].
Mass spectrum of copper(II) complex
The mass spectrum of complex (Fig. S3) showed peaks attrib-
uted to the molecular ions m/z at 912 M+ for copper(II) complex.
This data is in good agreement with the proposed molecular for-
mula for this complex i.e. [Cu(L)2]. The purity of the ligand and
their complex was checked using LC-mass technique. This confirms
the formation of the Schiff-base frame.
UV–vis spectrum
Electronic, magnetic and ESR spectral studies
The electronic spectral data of the free ligand and Cu(II) com-
plex, in the range 200–400 and 200–700 nm, respectively, in
The UV–vis spectrum of the ligand (Fig. S4) show three bands in
the range 223, 284 and 378 nm which can be assigned to
transitions within the aromatic rings,
C@N and intramolecular charge transfer (CT) transition with the
p–
pÃ
p
–
pà transitions within
DMF solvent as well as their magnetic susceptibility (leff) and mo-
lar conductance values are displayed in Table 1. Electronic spec-
trum of the free ligand in DMF solution displayed two absorption
bands at 35,211 and 26,455 cmÀ1, the first band could be attrib-
whole molecule.
uted to the
p ?
pà transition of the azomethine group (K-band),
and the second band might arises from the n ? pà transitions
resulting from nitrogen and oxygen atoms (R-band) [34]. These
bands exhibit more or less shift in complexes.
Characterization of the metal complex
The structure of the complex was elucidated with use of IR, UV–
visible spectra and elemental analyses. Conductivity value for the
The observed magnetic moment of the Cu(II) complex is 2.13
B.M., which confirms the octahedral structure of this complex
[38,39]. The electronic spectrum of the Cu(II) complex (Fig. S4)
[Cu(L)2] compound in MeOH is at 1.53 (X
À1 cm3 molÀ1) indicating
that they are non-electrolytes [36]. Single crystal of the compound
could not be isolated from any organic solution, thus no definite
structures can be described.
gave a band at 11,788 cmÀ1 = 56 L molÀ1 cmÀ1), 18,312 cmÀ1
) (e
= 94 L molÀ1 cmÀ1 and 21,300 cmÀ1 = 152 L molÀ1 cmÀ1),
(e
(e
these bands may be assigned to 2B1g ? 2B2g, 2B1g ? 2A1g and
2B1g ? 2Eg transitions, respectively, another band observed at
21,300 cmÀ1 suggesting the existence of a transition from dxy,
dz2 and dxz, dyz transfer to the antibonding and half-filled dx2 -
À dy2 level which is consistent with an octahedral configuration.
The X-Band ESR spectrum of [Cu(L)2] complex at room temper-
ature was shown in (Fig. S5). The spectrum of the Cu(II) complex
exhibits two broad band with g|| = 2.16 and g\ 2.05 so,
Elemental analyses of the complex
The results of elemental analyses, Table 1 are in good agree-
ment with those required by the proposed formula. The data show
the complexation of 1:2 [Copper:ligand] ratio of the formulae of
[Cu(L)2]. However, the analytical and spectroscopic data enables
us to predict possible structure as shown in Scheme 2.

98
R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
Table 2
Experimental and computational calculated vibrational wavenumbers (harmonic frequency (cmÀ1)), IR intensities and assignments for HMQ at B3LYP utilizing 6-31GÃ and
6-311GÃÃ basis sets of H2L ligand and its Cu(II) complex with their assignments.
Assignments
(H2L)
Exp.
B3LYP/6-31GÃ
B3LYP/6-311GÃÃ
Cu(II)
Exp.
Wave number
IR Intensity
Wave number
IR Intensity
IR Intensity
m
m
m
m
m
m
(OH)phenolic
(OH)enolic
as(NH2)
s(NH2)
as(NH)
s(NH)
(NH)
(C@N)azomethine
(C@O)
(CAO)
as(SO2)
s(SO2)
(N@N)
(NAN)
(CAH)aromatic
(C@C)phenyl
3545br
2975br
3312br
3282br
3271br
3199br
1567m
1577m
1683m
1212m
1325s
1155m
1435s
1052s
3075m
1565m
–
3614
3330
3471
3385
3388
3386
1669
1581
1687
1217
1241
1149
1459
1029
3356
1581
–
140
9.17
122
136
122
94
21.33
19.60
4.85
64.15
54.08
11.11
270.26
128.36
7.44
19.60
–
3579
3432
3518
3345
3188
3145
1554
1535
1650
1216
1322
1156
1449
1089
3113
1594
–
185.02
133.90
147.01
74.45
74.54
54.65
29.54
28.45
81.5
–
–
3312br
3280br
3271br
3199br
1567m
1557m
1669m
1202m
1322s
1155m
1434s
1025m
3074m
1565m
189 w
218w
292m
336m
q
m
m
m
m
m
m
m
m
m
21.44
5.62
221.36
123.32
33.91
59.36
69.9
–
–
–
–
d(OAMÀO)
d(OAMAN)
–
–
–
–
–
–
–
–
–
–
–
–
m
m
(MAN)
(MAO)
Where br = broad, s = strong, m = medium, w = weak.
g|| > g\ > 2.0023, indicating that the unpaired electron of Cu(II) ion
is localized in the dx2 À y2 orbital [40]. In axial symmetry, the g-
values are related to the G-factor by the expression G = (g||À2)/
(g\À2) = 4. According to Hathaway and Billing [41]. The G values
of the Cu(II) complex are <4 suggesting that the considerable ex-
change interaction in the solid state. Further, the shape of the
ESR spectrum of Cu(II) complex indicates that the geometry around
the Cu(II) ions are elongated octahedron [42,43]. Molecular orbital
Table 3
Crystallographic data for the azo-dye Schiff base complex [Cu(L)2].
Data
[Cu(L)2]
C36H28CuN14O8S2
912.37
1.54044
Cubic
Empirical formula
Formula weight (g/mol)
Wavelength (Å)
Crystal system
Space group
P4/m
coefficients,
The lower value of a2 (0.43) compared to b2 (1.02) in Cu(II)
complex indicate that the covalent in-plane -bonding is more
-bonding character.
a
2 and b2 were calculated as described previously [44].
Unit cell dimensions (Å,°)
a (Å)
b (Å)
16.1045
16.1045
16.1045
90
r
c (°)
pronounced than the covalent in-plane
p
a
(°)
b (°)
90
c
(°)
90
5168.15
1.24
16.12–63.65
3 6 h 6 10, 1 6 k 6 6, 3 6 l 6 10
6
Electrochemical behavior
Volume (Å3)
(Calc.) density (g/cmÀ3
2h range
Limiting indices
Z
)
Cyclic voltammetry is the most widely used technique for
acquiring qualitative information about electrochemical reactions.
It offers a rapid location of redox potentials of the electro active
species. The cyclic voltammograms of ligand and its copper
complex (Fig. S6) were recorded at 300 K in DMF solution in the
potential range À1.0 to 1.3 V with scan rate 0.1 V/s.
Rf
0.000011
298
Temperature (K)
The Azo-dye Schiff base ligand shows one irreversible couple
with Epc = À0.93 V vs Ag/AgCl and the associated anode peak at
Scanning electron microscopy
Epc = 0.17 V. The large separation
D
E = 0.76 V indicates irreversible
The SEM pictures of H2L and [Cu(L)2] are shown in Figs. S8a and
b, respectively. SEM image of azo-dye Schiff base ligand, H2L
(Fig. S8a) displays more extensive three-dimensional network than
the smooth lacunose surface of the benzenesulfonamide and this
might be due to chemical modification of benzenesulfonamide
through the condensation of pyrazine-2-carbohydrazide with free
amino groups available on azo-dye Schiff base ligand surface. Be-
cause of this modification, particle sizes of the ligand, H2L get suc-
cessively reduced, which further increases the adsorption capacity
towards the copper ion by complex formation. The surface of
[Cu(L)2] (Fig. S8b) do not exhibits the same morphology compared
to that of H2L. The difference in the morphology of H2L and the
complex could be due to the imprinting of the copper ion on the
modified azo-dye Schiff base ligand (H2L) which leaves the
footprints on the surface of the complex and thus increase in the
porosities is occurred on the surface of the complex. This charac-
teristic may be assigned to the coordination of the copper ion with
the active sites of H2L.
couple. The Cu(II) complex shows irreversible cathodic peak at
Epc = 0.62 V vs Ag/AgCl corresponding to Cu(II)/(III) couple and
the associated anode peak at Epa = À0.54 V corresponding to the
formation of Cu(II)/I couple. The peak to peak separation
1.16 V confirming the process as irreversible.
DE is
Powder X-ray diffraction spectroscopy
Single crystals of the ligand and its copper complex could not be
prepared to get the XRD and hence the powder diffraction data
(Fig. S7) were obtained for structural characterization. Structure
determination by X-ray powder diffraction data has gone through
a recent surge since it has become important to get to the
structural information of materials, which do not yield good
quality single crystals. The indexing procedures were performed
using (CCP4, UK) CRYSFIRE program [45] giving cubic crystal sys-
tem for [Cu(L)2] having M(9) = 13 as the best solution. Their cell
parameters are shown in Table 3.

R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
99
Table 4
Kinetic parameters of [Cu(L)2]:
Stage
Using Coats–Redfern equation
Decomposition range (°C)
A(SÀ1
)
Ea (kJ/mol)
D
H (kJ/mol)
D
S (kJ/mol K)
DG (kJ/mol)
1st
2nd
3rd
465
577
800
3.07 Â 109
5.44 Â 1011
2.22 Â 106
43.65
72.07
111.76
55.15
76.86
106.98
À0.030
À0.072
À0.096
167
186
199
Using Horowitz–Metzger equation
1st
465
577
800
2.89 Â 109
4.99 Â 1011
2.87 Â 106
42.13
70.26
110.24
54.23
72.87
105.45
À0.030
À0.071
À0.093
165
183
194
2nd
3rd
Using Piloyan–Novikova equation
1st
465
577
800
3.04 Â 109
5.42 Â 1011
2.87 Â 106
40.44
71.79
110.57
52.46
73.78
102.67
À0.031
À0.070
À0.093
163
184
195
2nd
3rd
Transmission electron microscopy
peak at 770 K (the maximum peak temperature). Total estimated
mass loss is 91.23% (calculated mass loss = 91.18%).
The thermodynamic activation parameters of decomposition
processes of dehydrated complexes namely activation energy (E),
TEM image for the Cu(II)complex is given in Fig. S9. The mor-
phology of complex was observed to have spherical particles of
43 nm average diameter. This is lying in good agreement with
the calculated value (37 nm) obtained from Scherrer’s equation.
enthalpy (DH), entropy (DS) and free energy of decomposition
(D
G) (Table 4), were evaluated by employing the Horowitz–Metz-
ger [46] (HM), Coats–Redfern [47] (CR), and Piloyan–Novikova [48]
(PN) methods and were helpful in assigning the strength of the
complexes. According to the kinetic data obtained from the TG
curves, all the complexes have negative entropy which indicates
that the complex is formed spontaneously. The negative value of
entropy also indicates a more ordered activated state that may
be possible through the chemisorption of oxygen and other decom-
position products. The negative values of the entropies of activa-
tion are compensated by the values of the enthalpies of
activation, leading to almost the same values for the free energy
of activation [49].
Kinetics of thermal decomposition
Recently, there has been increasing interest in determining the
rate-dependent parameters of solid-state non-isothermal decom-
position reactions by analysis of TG curves [23,24]. Thermogravi-
metric (TG) and differential thermogravimetric (DTG) analyses
was carried out for Cu(II) complex in ambient conditions. The cor-
relations between the different decomposition steps of the com-
plex with the corresponding weight losses are discussed in terms
of the proposed formula of the complex.
The complex [Cu (L)2] with the molecular formula [C36H28N14
O8S2Cu] is thermally decomposed in two successive decomposition
steps (Fig. S10). The first estimated mass loss of 44.72% (calculated
mass loss = 44.63%) within the temperature range 540–590 K may
be attributed to the loss of (C18H14N7O3S) fragment. The DTG curve
gives an exothermic peak at 553 K (the maximum peak tempera-
ture). The second step occurs within the temperature range 661–
853 K with the estimated mass loss 46.51% (calculated mass
loss = 46.44%) which corresponds to the loss of C18H14N7O4S frag-
ment leaving CuO as residue. The DTG curve gives an exothermic
Computational studies
It is clearly that, a possibility existence of the prepared ligand in
the stereoisomer forms were depicted in Scheme 3.
The major tautomeric structures for the ligand were repre-
sented in Scheme 4.
In order to achieve the better insight into the molecular struc-
ture of the most preferentially steroisomer and/or tautomeric
Scheme 3. Steroisomers of ligand.

100
R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
Scheme 4. Proposed tautomer structures of most stable stereoisomer ligand.
Table 5
Calculated energies of possible stereo isomers and tautomer forms of ligand at B3LYP utilizing 6-31GÃ and 6-311GÃÃ basis sets.
Cpd.
E
HF
HOMO
LUMO
Dipole
ZPE
6-31GÃ
(E–E)
(Z–Z)
(E–Z)
(Z–E)
(E–E)a
(E–E)b
(E–E)c
6-311GÃÃ
(E–E)
(Z–Z)
(E–Z)
(Z–E)
(E–E)a
(E–E)b
(E–E)c
À9184.13
À8789.65
À8489.07
À8445.16
À9140.90
À8829.23
À8452.00
49.30732
53.07945
73.76387
53.89782
53.72245
53.90171
44.97201
À9.30446
À9.22826
À8.9824
À9.184
À0.92831
À1.4131
2.31762
202.06
202.46
202.03
202.06
202.04
202.09
202.03
5.799222
9.216577
8.842497
7.766137
6.014287
8.842496
À1.12168
À1.42712
À1.33573
À1.3042
À9.60642
À9.41322
À9.55931
À1.73782
À9081.96
À8816.27
À8493.96
À8429.24
À9053.27
À8691.51
À8409.68
151.6332
153.6283
154.1982
136.0901
158.858
À9.02917
À9.42276
À9.18962
À9.25689
À9.60390
À9.43391
À9.34235
À1.31209
À1.65030
À1.38296
À1.64373
À1.71561
À1.67879
À1.45775
7.187144
3.313277
9.532563
6.25245
8.801717
8.402874
9.615270
222.12
222.10
222.12
222.12
222.14
222.11
222.16
149.3277
149.3631
E: The total energy (kcal/mol), HF: heat of formation (kcal/mol), HOMO: highest occupied molecular orbital (eV), LUMO: lowest occupied molecular orbital (eV), Dipole: dipole
moment calculate, ZPE: Zero point energy (kcal/mol).
forms for ligand H2L, conformational analysis of the target com-
pounds have been performed using Spartan 08 program [28] with
AM1 semi-empirical molecular orbital for density functional the-
ory [29] with a B3LYP/6-31GÃ and 6-311GÃÃ basis sets [29–32].
The computed molecular parameters, total energy, electronic en-
ergy, heat of formation, the highest occupied molecular orbital
(HOMO) energies, the lowest unoccupied molecular orbital
(LUMO) energies and the dipole moment for studied compounds
were calculated, which have been used to investigate the most sta-
ble stereoisomer form and/or tatoumer structure of the prepared
ligand (Table 5). The minimal optimization energy of most stable
stereoisomer forms and major tatoumer structures for ligand were
represented at (Fig. S11).
isomer is stabilizing by adjusting two phenyl rings in plane with
each other, as the same time with pyrazine ring. The bond
length for PhNNPh (H2L) is equal for four tatoumeric structures
1.266 Å (Fig. S12). The decreasing bond length of PhCHN
(ꢁ1.27) for hydrazonesulfonamide than PhCHN (ꢁ1.47) of diaze-
nylsulfonamide may be due to extension conjugated
p electron
of the phenyl ring (Table S1 in Supplementary material). Another
evidence supported explanation, the Nhydrazonyl atom with sp2
hybrid orbitals has more s-character, and the maximum of the
electron density is closer to the nuclei compared with the elec-
tron density distribution at sp3 hybridized Ndiazenyl atom, which
leads to lengthening the PhCNdiazenyl bonds (Table S1 in Supple-
mentary material).
The calculated molecular parameters showed, the most stable
stereoisomer is the (E–E) form and most stable tatoumer struc-
ture is hydrazone-sulfonamide H2L, this may be explained by
presence the intra-molecular interaction of H-hydroxyl moiety
with N-imino moiety, and owing to slightly reduces it’s calcu-
lated energy, and leads to predominance this structures (E–E
and hydrazone-sulfonamide H2L) over other forms. The E–E
Comparison of the vibrational frequencies calculated at DFT/
B3LYP level utilizing 6-311G basis set with experimental values
(Fig. S13, Table 2). There assumable deviations between the
experimental values and calculated, may be due to the fact that,
the calculations have been actually performed on
a single
molecule in the gaseous state contrary to the experimental val-
ues recorded in the presence of intermolecular interactions.

R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
101
Table 6
The optimized calculations energies and reactivity descriptor parameters for ligand H2L at B3LYP/6-311GÃÃ basis sets and Cu(II) complex at AM1 semi-empirical.
CPD
E
H.F.
HOMO
LUMO
D
G
H
S
v
l
x
D
H2L
[Cu(L)2]
À9081.96
À250186
24.46
63.14
À9.01
À8.48
À1.42
À1.43
7.58
7.06
3.79
3.53
0.26
0.28
À5.22
À4.95
5.22
4.95
3.59
3.47
8.14
7.06
E: The total energy (kcal/mol)., H.F.: heat of formation (kcal/mol), HOMO: highest occupied molecular orbital (eV)., LUMO: lowest occupied molecular orbital (eV), HLG:
difference between HOMO and LUMO energy levels (eV), g: Hardness (eV), S: Softness (eV), v: electronegativity (eV), l: chemical potential (eV), x: electrophilicity (eV), D:
dipole moment (Debye).
Table 7
Mulliken q(M) charges for H2L at using DFT/B3LYP with 6-311GÃÃ basis set and AM1 semi-empirical for complex [Cu(L)2].
Atom
q(M)
Atom
q(M)
Atom
q(M)
Atom
q(M)
H2L
1 C0:
2 C1:
3 C2:
4 C3:
5 C4:
6 C5:
7 S6:
8 O7:
À0.614
+0.015
À0.128
+0.476
À0.382
À0.015
+2.550
À0.971
À0.976
À0.946
À0.273
À0.236
+0.514
À0.535
+0.001
+0.247
À0.213
À0.288
+0.373
À0.469
À0.186
+0.477
À0.516
+0.338
+0.120
À0.430
À0.492
+0.284
+0.084
À0.519
+0.122
+0.199
+0.201
+0.119
+0.297
+0.298
+0.258
+0.137
+0.214
+0.031
41 H11:
42 H12:
43 H13:
44 H14:
45 H15:
[Cu(L)2]
+0.284
+0.081
+0.031
+0.073
+0.392
35 C34
36 C35
37 S36
38 O37
39 O38
40 N39
À0.265
42 N41
43 C42
44 C43
45 C44
46 C45
47 C46
48 C47
49 C48
50 N49
51 N50
52 C51
53 O52
54 C53
55 C54
56 N55
57 N56
58 C57
59 C58
60 O59
61 Cu1
62 H1
63 H2
64 H3
65 H4
66 H5
67 H6
68 H7
69 H8
70 H9
71 H10
72 H11
73 H12
74 H13
À0.252
+0.127
+2.839
À1.036
À1.037
À1.101
81 H20
À0.135
+0.263
À0.033
À0.505
+0.566
À0.183
À0.284
+0.174
+0.294
À0.673
+0.547
À0.488
+0.263
+0.175
À0.458
À0.499
+0.309
+0.136
À0.439
+0.202
+0.108
+0.151
+0.166
+0.107
+0.303
+0.298
+0.131
+0.170
+0.100
+0.118
+0.323
+0.100
+0.026
75 H14
76 H15
77 H16
78 H17
79 H18
80 H19
+0.342
82 H21
83 H22
84 H23
85 H24
86 H25
87 H26
88 H27
89 H28
+0.062
+0.080
+0.158
+0.169
+0.081
+0.344
41 N40
À0.503
+0.022
À0.266
+0.396
À0.282
+0.014
+2.576
À0.977
À0.976
À0.967
À0.293
À0.141
+0.294
À0.285
À0.354
+0.567
À0.365
À0.052
+0.205
+0.198
À0.632
+0.486
À0.466
+0.310
+0.153
À0.466
À0.499
+0.321
+0.118
À0.407
À0.757
+0.128
À0.238
1 C0
2 C1
3 C2
4 C3
5 C4
6 C5
7 S6
8 O7
+0.092
+0.136
+0.145
+0.113
+0.327
+0.096
+0.031
+0.053
9 O8:
10 N9:
11 N10:
12 N11:
13 C12:
14 C13:
15 C14:
16 C15:
17 C16:
18 C17:
19 C18:
20 N19:
21 N20:
22 C21:
23 O22:
24 C23:
25 C24:
26 N25:
27 N26:
28 C27:
29 C28:
30 O29:
31 H1:
32 H2:
33 H3:
34 H4:
35 H5:
36 H6:
37 H7:
38 H8:
39 H9:
40 H10:
9 O8
10 N9
11 N10
12 N11
13 C12
14 C13
15 C14
16 C15
17 C16
18 C17
19 C18
20 N19
21 N20
22 C21
23 O22
24 C23
25 C24
26 N25
27 N26
28 C27
29 C28
30 O29
31 C30
32 C31
33 C32
The computed vibrations to OAH aromatic (3614 and
respectively which have shown a comparable agreement with
experimental results at 1577 cmÀ1
The lowest minimization energy for Cu(II) complex exhibited a
common feature:
3330 cmÀ1
)
at B3LYP/31GÃ, and (3579 and 3432 cmÀ1
)
with
.
B3LYP/6-311GÃÃ basis set, respectively, have shown a comparable
agreement with our experimental results.
The calculated vibrations for (mNH2asym) of H2L assigned at
B3LYP utilizing 6.31GÃ set are 3471, 3385, 3388 and 3386 cmÀ1
,
I. The higher HOMO energy values show the molecule is a
good electron donor, in other hand, the lower HOMO energy
values indicate that, a weaker ability of the molecules for
donating electron. LUMO energy presents the ability of a
molecule for receiving electron (Tables 5 and 6).
II. Phenyl and pyrazine rings, showing highly free rotations,
two phenyl rings for ligands formed complex were stabilized
by arranged in plane with each other and co-planner with
pyrazine ring, its phenyl rings approximately arranged
coplanar with the metal core of complex (Figs. S1 and S2
in Supplementary material).
and using 6.311GÃÃ set exhibit vibrational bands at 3518, 3345,
3188 and 3145 cmÀ1, which agreement our experimental results
3312 cmÀ1 NH2asym), 3282 cmÀ1 NH2sym), 3075 cmÀ1
(m (m .
The present work displayed computed vibrations to C@O
stretching vibrations at 1687 cmÀ1 and at 1650 cmÀ1 at B3LYP uti-
lizing 6-31GÃ and 6-311GÃÃ basis sets respectively which have
shown a comparable agreement with our experimental results at
1683 cmÀ1
The computed vibrations for
at 1535 cmÀ1 at B3LYP utilizing 6-31GÃ and 6-311GÃÃ basis sets
.
m
(C@N)azomethine at 1581 cmÀ1 and

102
R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
[H2L]
[CuL]
Fig. 1. The ESP surfaces for H2L with based on DFT-B3LYP /6-311GÃÃ and AM1 semi-empirical for complex [Cu(L)2] calculations.
III. The bond lengths of all the active groups taking part in coor-
dination are longer than that already exist in the ligand.
IV. The bond angles of the N17AN18AC19 fragment, changed due
to coordination; which are altered from 120° on ligand to
121.12 for complex.
and increasing the polar area, decreasing polar area(in
green) on surface for Ligand H2L, these results indicate the
importance of polarity surface for activity of complexes.
Conclusion
V. All bond angles in complex are quite near to an octahedral
geometry predicting sp3d2 hybridization.
Our proposed structure of azo-dye Schiff base ligand on the ba-
sis of the IR, 1H NMR, EI mass, UV–vis. spectra has potential binding
sites towards the copper ion and act as tridentate chelate by coor-
dinating through carbonyl oxygen, hydroxyl oxygen and azome-
thine nitrogen. Spectral characterizations of the new complex
showed that Cu(II) form six coordinate distorted octahedral com-
plex with 1:2 (copper:ligand) stoichiometry. The most stable form
of ligand are optimized using DFT/B3LYP with 6-31GÃ and 6-311GÃÃ
level. The calculated frequencies showed slight deviation from
experimental frequencies for the ligand and supported the struc-
ture. The high dipole moment value for ligand 8.14 is showed
increasing its ability to interact with the surrounding environment.
VI. Furthermore, the global and local chemical reactivity
descriptors for molecules have been defined (Table 6), like
softness (measures stability of molecules and chemical reac-
tivity, hardness (reciprocal of softness), chemical potential,
electronegativity (strength atom for attracting electrons to
itself), electrophilicity index (measuring lowering energy
due to maximal flowing electron between donor and accep-
tor) [50–55]. The results were concluded, the complex have
lower energy gap, higher softness (most stable), lower hard-
ness, higher chemical potential and higher electrophilicity.
The lower dipole moment value for Cu(II) 7.06 Debye than
ligand 8.14 Debye, indicate ability interaction of ligand with
the metal to form complex.
Acknowledgment
VII. The Mulliken q(M), charges were computed within full
Bond Orbital analysis at with B3LYP/6-311GÃÃ for the most
stable ligand H2L and AM1 semiempirical for [Cu(L)2] are
shown in (Table 7). The charge distributions over the
atoms suggest that, the formation of donor and acceptor
pairs involving the charge transfer in the molecule. In gen-
eral in both compounds, the hydrogen, Copper and some
carbon atoms are positively charged, the O and N atoms
have negative charges, and accepted the electrons. The
complexation with copper metal ion leads to a redistribu-
tion of electron density of molecule (S Table 3 in Supple-
mentary material). The most negative centers in H2L and
[Cu(L)2] involved in oxygen of sulfonyl group, on the other
hand the most positive charge are located on the S of sul-
fonyl group, the maximum positive charge on the C1 atom
are due to attachment of the electronegative oxygen atom
(withdrawing nature).
VIII. The electrostatic potentials mapped (ESP) (Fig. 1) was
drawn, it represents a balance between repulsive interac-
tions of the nuclei (positively-charged) and attractive inter-
actions for the electrons (negatively-charged). The colors
toward red depict negative potential (high electron density
area, representing a strong attraction between the proton
and the points on the molecular surface), while colors
toward blue depict positive potential, and colors in between
(orange, yellow, green) depict intermediate values of the
potential. Comparison of the electrostatic mappings of H2L
and its complex [Cu(L)2] showed, increasing negative
charges (in red) located on the surface of complex [Cu(L)2]
This project was supported by King Saud University, Deanship
of Scientific Research, College of Science Research Center.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2014.02.
051.
References
[1] X. Tai, X. Yin, Q. Chen, M. Tan, Molecules 8 (2003) 439–443.
[2] M. Sonmez, A. Levent, M. Sekerci, Russ. J. Coord. Chem. 30 (9) (2004) 655–660.
[3] M. Tuncel, S. Serin, Synth. React. Inorg. Met. Org. Nano Met. Chem. 35 (2005)
203–212.
[4] A.A. Khandar, K. Nejati, Z. Rezvani, Molecules 10 (2005) 302–309.
[5] A.D. Garnovskii, I.S. VasilChenko, Russ. Chem. Rev. 71 (2002) 943–954.
[6] A.D. Garnovskii, A.L. Nivorozhkin, V.I. Minkin, Coord. Chem. Rev. 126 (1993) 1–
69.
[7] F.D. Karia, P.H. Parsania, J. Chem. Soc. 11 (3) (1999) 991–995.
[8] P.G. More, R.B. Bhalvankar, S.C. Pattar, J. Indian Chem. Soc. 78 (9) (2001) 474–
475.
[9] A.H. El-masry, H.H. Fahmy, S.H.A. Abdelwahed, Molecules 5 (2000) 1429–1438.
[10] M.A. Baseer, V.D. Jadhav, R.M. Phule, Y.V. Archana, Y.B. Vibhute, Orient. J.
Chem. 16 (3) (2000) 533–542.
[11] S.N. Pandeya, D. Sriram, G. Nath, E. De Clercq, IL Farmaco 54 (1999) 624–628.
[12] W.M. Singh, B.C. Dash, Pesticides 22 (11) (1988) 33–37.
[13] E.M. Hodnett, W.J. Dunn, J. Med. Chem. 13 (1970) 768–770.
[14] S.B. Desai, P.B. Desai, K.R. Desai, Hetrocycl. Commun. 7 (1) (2001) 83–90.
[15] P. Pathak, V.S. Jolly, K.P. Sharma, Orient. J. Chem. 16 (1) (2000) 161–162.
[16] S. Samadhiya, A. Halve, Orient. J. Chem. 17 (1) (2001) 119–122.
[17] F. Aydogan, N. Ocal, Z. Turgut, C. Yolacan, Bull. Korean Chem. Soc. 22 (2001)
476–480.

R.A.A. Ammar et al. / Journal of Molecular Structure 1067 (2014) 94–103
103
[18] A.E. Taggi, A.M. Hafez, H. Wack, B. Young, D. Ferraris, T. Lectka, J. Am. Chem.
Soc. 124 (2002) 6626–6635.
[38] B. Garcia, A.M. Lozano-Vila, F. Luna-Giles, R. Pedrero-Marin, Polyhedron 25
(2002) 1399–1407.
[19] K. Hansongnern, S. Tempiam, J.C. Liou, F.L. Laio, T.H. Lu, Anal. Sci. 19 (2003) 13–
16.
[39] G. Speier, J. Csihony, A.M. Whalen, C.G. Pierpont, Inorg. Chem. 35 (1996) 3519–
3524.
[20] P.L. Coort, M. Johansson, Electroanalysis 12 (2000) 565–571.
[21] D. Choi, S.K. Lee, T.D. Chung, H. Kim, Electroanalysis 12 (2000) 477–482.
[22] P. Alka, P. Vinod, V.S. Jolly, Orient. J. Chem. 10 (1) (1994) 73–74;
J. Drews, Science 287 (5460) (2000) 1960–1964.
[23] C.W. Thornber, Chem. Soc. Rev. 8 (1979) 563–580.
[24] C.T. Supuran, A. Scozzafava, Exp. Opin. Ther. Patents 10 (26) (2000) 575–600.
[25] T.H. Maren, Annu. Rev. Pharmacol. Toxicol. 16 (1976) 309–327.
[26] A.E. Boyd, Diabetes 37 (1988) 847–850.
[40] M. Sebastian, V. Arun, P.P. Robinson, A.A. Varghese, R. Abraham, E. Suresh,
K.K.M. Yusuff, Polyhedron 29 (2010) 3014–3020.
[41] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143–207.
[42] A. Bencini, D. Gattechi, EPR of Exchange Coupled Systems, Springer-Verlag,
Berlin, 1990.
[43] O.M.I. Adly, A. Taha, S.A. Fahmy, J. Mol. Struct. 1054–1055 (2013) 239–250.
[44] A.M.A. Alaghaz, R.A. Ammar, Eur. J. Med. Chem. 45 (2010) 1314–1322.
[45] R. Shirley, The CRYSFIRE System for Automatic Powder Indexing: Users
Manual, Lattice Press, 2002.
[46] H.H. Horowitz, G. Metzger, J. Anal. Chem. 35 (1963) 1464–1468.
[47] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68–69.
[48] G.O. Piloyan, T.D. Pyabonikar, C.S. Novikova, Nature 212 (1966) 1229–1304.
[49] B.K. Singh, R.K. Sharma, B.S. Garg, Spectrochim. Acta A 63 (2006) 96–102.
[50] R.G. Parr, P.K. Chattaraj, J. Am. Chem. Soc. 113 (1991) 1854–1855.
[51] R.G. Parr, L.V. Szentpaly, S. Liu, J. Am. Chem. Soc. 121 (1999) 1922–1924.
[52] P.K. Chattaraj, B. Maiti, U. Sarkar, J. Phys. Chem. A 107 (2003) 4973–4975.
[53] R.G. Parr, R.A. Donnelly, M. Levy, W.E. Palke, J. Chem. Phys. 68 (1978)3801–3807.
[54] R.G. Parr, R.G. Pearson, J. Am. Chem. Soc. 105 (1983) 7512–7516.
[55] R.G. Parr, W. Yang, Density Functional Theory of Atoms and Molecules, Oxford
University Press, Oxford, UK, 1989.
[27] A.M. Tawfik, M.A. El-ghamry, S.M. Abu-El-Wafa, N.M. Ahmed, Spectrochim.
Acta A 97 (2012) 1172–1180.
[28] Spartan 08, Wave function Inc., Irvine, CA 92612, USA, 2008.
[29] P. Hohenberg, W. Kohn, Phys. Rev. B136 (1964) 864–873.
[30] W. Kohn, L.J. Sham, Phys. Rev. A140 (1965) 1133–1138.
[31] W.J. Hehre, L. Radom, P.V.R. Schleyer, J.A. Pople, Ab Initio Molecular Orbital
Theory, John Wiley & Sons, New York, 1986.
[32] J. Sauer, Chem. Rev. 89 (1989) 199–255.
[33] J.J.P. Stewart, J. Comput. Chem. 10 (1989) 209–220.
[34] U.C. Singh, P.A. Kollman, J. Comput. Chem. 5 (1984) 129–145.
[35] M.L. Connolly, Science 221 (1983) 709–713.
[36] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122.
[37] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fourth ed., Wiley Interscience, New York, 1986.