Supramolecular structure, molecular docking and thermal properties of azo dye complexes

Article abstract of DOI:10.1016/j.molliq.2015.09.038

The complexes of [Pt(L_n)₂] and [M(L_n)₂(OH₂)₂]Cl (M = Rh(III) and Ir(III)), where L_n = monobasic bidentate 5-(4-derivatives phenylazo)-2-thioxo-4-thiazolidinone (HL_n) have been prepared and characterized by elemental analyses, conductivity measurements, magnetic susceptibility measurements and spectroscopic (IR, Uv.-Vis. and ¹H NMR) studies. The X-ray diffraction (XRD) pattern of the ligand (HL₂) is polycrystalline nature. The molecular, electronic structures and quantum chemical parameters of the ligands (HL_n) were studied. Molecular docking was used to predict the binding between ligands (HL_n) and the receptor of breast cancer 3HB5 oxidoreductase. The Rh(III) and Ir(III) complexes are six-coordinate distorted octahedral, whereas Pt(II) is four coordinated. The ligand coordinates through the azo dye nitrogen atom and enolic oxygen atom after deprotonation. The molar conductivities show that all the complexes of Pt(II) are non-electrolytes while Rh(III) and Ir(III) complexes are electrolytic nature. The ligands field parameters were calculated using various energy level diagrams.

Full text of DOI:10.1016/j.molliq.2015.09.038

Journal of Molecular Liquids 212 (2015) 487–502
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Supramolecular structure, molecular docking and thermal properties of
azo dye complexes
b
a
b
a
A.Z. El-Sonbati a, , G.G. Mohamed , A.A. El-Bindary , W.M.I. Hassan , M.A. Diab ,
⁎
Sh.M. Morgan c, A.K. Elkholy a,1
a
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
Environmental Monitoring Laboratory, Ministry of Health, Port Said, Egypt
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 June 2015
Received in revised form 22 September 2015
Accepted 24 September 2015
Available online xxxx
The complexes of [Pt(Ln)2] and [M(Ln)2(OH2)2]Cl (M = Rh(III) and Ir(III)), where Ln = monobasic bidentate 5-
(4-derivatives phenylazo)-2-thioxo-4-thiazolidinone (HLn) have been prepared and characterized by elemental
analyses, conductivity measurements, magnetic susceptibility measurements and spectroscopic (IR, Uv.-Vis. and
1H NMR) studies. The X-ray diffraction (XRD) pattern of the ligand (HL2) is polycrystalline nature. The molecular,
electronic structures and quantum chemical parameters of the ligands (HLn) were studied. Molecular docking
was used to predict the binding between ligands (HLn) and the receptor of breast cancer 3HB5 oxidoreductase.
The Rh(III) and Ir(III) complexes are six-coordinate distorted octahedral, whereas Pt(II) is four coordinated.
The ligand coordinates through the azo dye nitrogen atom and enolic oxygen atom after deprotonation. The
molar conductivities show that all the complexes of Pt(II) are non-electrolytes while Rh(III) and Ir(III) complexes
are electrolytic nature. The ligands field parameters were calculated using various energy level diagrams.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Azo rhodanine derivatives
Molecular docking
Pt(II)/Rh(III) and Ir(III) complexes
TGA
Quantum chemical parameters
1. Introduction
complexes with rhodanine derivatives as a novel chelating bidentate
azo dyes models [1,3]. The use of protein-ligand docking has become a
Interest in coordination chemistry is increasing continuously with
the preparation of organic ligands containing a variety of donor groups.
Ligands with potential sulfur, oxygen and nitrogen donors, such as
rhodanine and its derivatives are quite interesting which have gained
special attention in the last decade, not only because of the structural
chemistry and their importance in medical chemistry, but also because
these materials are used as drugs and they are reported to possess a
wide variety of biological activities against bacteria and fungi [1]. They
are also becoming a useful model for bioinorganic processes, which
has many biochemical and pharmacological applications. Great efforts
have therefore been made to synthesize metal(II)/(III) complexes of
high biological activity and low toxicity which are readily absorbed.
Azo dyes of rhodanine derivatives are a good series of ligands capable
of binding metal ions leading to metal complexes [2]. The high stable
potential of rhodanine derivative complexes in different oxidation
states increased the application of these compounds in a wide range.
Efforts have been made to carry out detailed studies to synthesize and
elucidate the structural and electronic properties of novel families of
standard method in many studies. Molecular docking is widely used
to predict protein-ligand [4] and to screen large libraries for molecules
that will modulate the activity of a biological receptor.
Considerable research aimed at explaining the chemistry and
biochemistry of platinum group metal complexes, which behave as
cytotoxic agents, has given an impetus to the search for new
antitumour agents of platinum and other transition metals. The
interaction of platinum metals with biologically important
molecules began when Rosenberg et al. [5], discovered that cis-
diammine dichloroplatinum(II) (cis-platin) exhibited anti-cancer
activity.
Azo rhodanines and their derivatives have been extensively used as
ligands in transition metal coordination chemistry [6–8]. Ease of synthe-
sis, favorable steric arrangement and variability of donor sites that these
ligands possess with suitable constituents, make this family an excellent
candidate for constructing new families of complexes which are of great
intriguing interest for the coordination chemist. This research includes
the molecular docking of synthesized compounds with the receptor of
breast cancer 3HB5 oxidoreductase. The molecular and electronic
structures of the ligands (HLn) were studied as well as the calculated
quantum chemical parameters. Also, the present paper describes the
preparation and characterization of platinum(II), rhodium(III) and
⁎
Corresponding author.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
Abstracted from her Ph.D.
1
http://dx.doi.org/10.1016/j.molliq.2015.09.038
0167-7322/© 2015 Elsevier B.V. All rights reserved.

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2. Experimental
2.1. Synthesis of 5-(4-derivatives phenylazo)-2-thioxothiazolidin-4-one
(HLn)
Azo rhodanine derivatives prepared by, 25 cm3 of distilled water
containing 0.01 mol conc. Hydrochloric acid was 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 cm3 of water was
added dropwise. The formed diazonium chloride was consecutively
coupled with an alkaline solution of 0.01 mol 2-thioxo-4-thiazolidinone,
in 10 cm3 of pyridine as shown in Fig. 1. The colored precipitate formed
was filtered through sintered glass crucible and washed several times
by distilled water. The crude products were purified by recrystallization
from hot ethanol and dried in a vacuum desiccator over anhydrous
CaCl2. The elemental analyses of ligands (HLn) are given in Table 1.
The resulting formed ligands are:
Fig. 1. R = -OCH3 (HL1), -CH3 (HL2), -H (HL3), -Cl (HL4) and -NO2 (HL5)Fig. 1 The
formation mechanism of azo rhodanine derivatives (HLn).
HL1: 5-(4-methoxyphenylazo)-2-thioxo-4-thiazolidinone;
HL2: 5-(4-methylphenylazo)-2-thioxo-4-thiazolidinone;
HL3: 5-(phenylazo)-2-thioxo-4-thiazolidinone;
HL4: 5-(4-chlorophenylazo)-2-thioxo-4-thiazolidinone; and
HL5: 5-(4-nitrophenylazo) -2-thioxo-4-thiazolidinone.
Table 1
Physical properties and elemental analyses data of ligands (HLn).
Compounda Empirical formula Yield % M.p. °C Calc. (Exp.)%
C
H
N
2.2. Preparation of the complexes
HL1
HL2
HL3
HL4
HL5
C10H9N3O2S2
Red
37.45
47.81
42.19
51.37
221
231
237
248
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
An aqueous solution (20 cm3) of the metal chloride of platinum(II),
rhodium(III) or iridium(III) (0.01 mol) was mixed with an EtOH
solution (20 cm3) of the respective ligands (0.02 mol) in the presence
of few drops of conc. HCl. The mixture was stirred for 2–16 h at room
temperature to yield the desired solid chelates. For the iridium(III) com-
plexes, the solution was boiled under reflux for 6–8 h on a water bath to
effect precipitation of the solid chelates. The complexes were filter off,
washed several times with EtOH followed by diethyl ether and dried
in a desiccator over anhydrous CaCl2. The analytical data of complexes
are given in Table 2.
C10H9N3OS2
Dark orange
C9H7N3OS2
Pale yellow
C9H6N3OS2Cl
Light orange
C9H6N4O3S2
Dark yellow
66.087 245
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.
iridium(III) metal complexes with 5-(4-derivatives phenylazo)-2-
thioxo-4-thiazolidinone (HLn) using different spectroscopic techniques.
The thermodynamic parameters of the ligands are calculated using
Coats–Redfern and Horowitz–Metzger methods.
2.3. Measurements
Elemental microanalyses of the separated compounds for C, H and N
were performed. The analyses were repeated twice to check the
Table 2
Elemental analyses data of complexesa.
Complexesb,c
Calc. (Exp.)%
C
Cl
H
N
M
[Rh(L1)2(OH2)2]Cl (1)
[Rh(L3)2(OH2)2]Cl (2)
[Rh(L5)2(OH2)2]Cl (3)
[Ir(L1)2(OH2)2]Cl (4)
[Ir(L3)2(OH2)2]Cl (5)
[Ir(L5)2(OH2)2]Cl (6)
[Pt(L1)2] (7)
33.98
(34.14)
33.42
(33.54)
29.33
(29.53)
30.16
(30.24)
29.36
(29.45)
26.16
(26.26)
33.00
2.83
(2.94)
2.48
(2.52)
1.90
(2.22)
2.51
(2.59)
2.18
(2.27)
1.70
(1.83)
2.20
11.89
(12.33)
13.00
(13.44)
15.21
(15.29)
10.56
(10.83)
11.42
(11.53)
13.56
(13.76)
12.93
14.57
(14.75)
15.91
(16.33)
13.97
(14.22)
24.16
(24.39)
26.13
(26.33)
23.28
(23.45)
26.83
5.03
(5.34)
5.49
(5.53)
4.82
(4.94)
4.46
(4.58)
4.83
(4.96)
4.30
(4.58)
–
(33.21)
36.79
(36.77)
28.53
(2.32)
2.04
(2.19)
1.32
(13.12)
14.31
(14.42)
14.79
(26.98)
33.23
(33.33)
25.77
[Pt(L3)2] (8)
–
–
[Pt(L5)2] (9)
(28.64)
(1.44)
(14.98)
(25.89)
L1–L5 are the anions of the ligands HL1–HL5 as given in Fig. 2.
a
Microanalytical data as well as metal estimations are in good agreement with the stoichiometries of the proposed complexes, air stable, non-hydroscopic, high melting temperature
and colored.
b
c
The excellent agreement between calculated and experimental data supports the assignment suggested in the present work.
All the complexes are diamagnetic.

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
489
Fig. 2. The Structure of ligands (HLn).
accuracy of the analyzed data. The 1H NMR spectrum was obtained 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 disks using a Perkin-Elmer 1340 spectrophotometer.
Ultraviolet–Visible (UV–Vis) spectra of the compounds were recorded
in nujol mulls using a Unicom SP 8800 spectrophotometer. X-ray
diffraction analysis of the ligand (HL2) were performed at room temper-
ature by a Philips X-ray diffractometer equipped with utilized mono-
chromatic Cu Kα radiation (λ=1.5418 Å). The X-ray tube voltage and
current were 40 kV and 30 mA, respectively. The magnetic moment of
the prepared solid complexes was determined at room temperature
using the Gouy's method. Mercury(II) (tetrathiocyanato)cobalt(II),
[Hg{Co(SCN)4}], was used for the calibration of the Gouy's tubes. Dia-
magnetic corrections were calculated from the values given by Selwood
[9] and Pascal's constants. Magnetic moments were calculated using the
(STA) 6000 with scan rate 15 °C/min under dynamic nitrogen
atmosphere in the temperature range from 50 to 800 °C. The molecular
structures of the investigated compounds were optimized initially with
the PM3 semiempirical method so as to speed up the calculations. The
resulting optimized structures were fully re-optimized using ab initio
Hartree–Fock (HF) [10] with 6-31G basis set. The molecules were built
with the Gauss View 3.09 and optimized using Gaussian 03 W program
[11]. The actual docking process in which the ligand–protein pair-wise
interaction energies are calculated using a Docking Server [4]. The
MMFF94 Force field was for used energy minimization of ligands mole-
cule using a Docking Server. Gasteiger partial charges were added to the
ligands atoms. Non-polar hydrogen atoms were merged and rotatable
bonds were defined. Docking calculations were carried out on 3HB5
oxidoreductase protein model. Essential hydrogen atoms, Kollman unit-
ed atom type charges, and solvation parameters were added with the
aid of AutoDock tools [12]. Affinity (grid) maps of 20 × 20 × 20 Å grid
points and 0.375 Å spacing were generated using the Autogrid program
[13]. AutoDock parameter set- and distance-dependent dielectric
functions were used in the calculation of the van der Waals and the
electrostatic terms, respectively.
equation, μeff. = 2.84 [TχMcoor. 1/2
. Thermogravimetric analysis (TGA)
]
measurements were investigated using Simultaneous Thermal Analyzer
3. Results and discussion
3.1. Characterization of the ligands
The ligands (HL1–HL5), gave satisfactory elemental analyses
(Table 1). The molecular structures of these ligands can exist in three
Table 3
Energy values obtained in docking calculations of ligands with receptor breast cancer
mutant 3HB5.
Compound
Free energy of
binding
Electrostatic
energy
Total intercooled
energy (kCal/mol)
Interact
surface
(kCal/mol)
(kCal/mol)
HL1
HL2
HL3
HL4
HL5
−6.47
−6.8 l
−6.50
−4.92
−7.24
−0.24
−0.16
−0.07
−0.00
−0.07
−7.86
−7.75 l
−7.10
−5.50
−8.26
677.863
646.097
615.505
439.768
694.223
Fig. 3. X-ray diffraction pattern of ligand (HL2).

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
491
Fig. 4. The ligands (HLn) (green in (A) and blue in (B)) in interaction with receptor breast cancer mutant 3HB5. (For interpretation of the references to color in this figure legend, the reader
is referred to the web version of this article). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
tautomeric forms as shown in Fig. 2. Detailed solution and solid states
studies of these ligands were carried out to establish their geometry.
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 N Cl N H N CH3 N OCH3) (as shown in Table 1) [14]. This can be
attributed to the fact that the effective charge experienced by the d-
electrons increased due to the electron withdrawing character (Cl and
NO2 groups) while it decreased by the electrons donating character of
(OCH3 and CH3 groups). It is important to note that the existence of a
methyl and/or methoxy group enhances the electron density on the
coordination sites and simultaneously decreases the values of yield%.
The X-ray diffraction, XRD, pattern of the ligand (HL2) is shown in
Fig. 3. Many peaks are observed which indicate the polycrystalline
nature of ligand (HL2).
the higher is the value of EHOMO of the compound, the easier is its offer-
ing electrons. The HOMO and LUMO of ligands are shown in Fig. 7.
Quantum chemical parameters of ligands are obtained from calcula-
tions such as energies of the highest occupied molecular orbital, EHOMO
,
energies of the lowest unoccupied molecular orbital ELUMO, total binding
and electronic energies; heats of formation and dipole moments as
presented in Table 4. Additional parameters such as separation energies,
ΔE, absolute electronegativities, χ, chemical potentials, Pi, absolute
hardness, η, absolute softness, σ, global electrophilicity, ω, [16], global
softness, S, and additional electronic charge, ΔNmax, have been calculat-
ed according to the following Eqs. ((1)–(8)) [16,17]:
ΔE ¼ ELUMO−EHOMO
ð1Þ
ð2Þ
−ðEHOMO þ ELUMO
Þ
χ ¼
2
3.2. Molecular docking
ELUMO−EHOMO
Molecular docking is a key tool in computer drug design [15]. The
focus of molecular docking is to simulate the molecular recognition pro-
cess. Molecular docking aims to achieve an optimized conformation for
both the protein and drug with relative orientation between them such
that the free energy of the overall system is minimized [4].
The results of molecular docking between ligands (HLn) and recep-
tor breast cancer (3HB5) showed a possible arrangement between
ligands and receptor (3HB5). On a docking study showing a favorable
interaction between ligands and the receptor (3HB5) and the calculated
of energy are listed in Table 3 and Fig. 4. 2D plot curves of docking with
ligands are shown in Fig. 5. This interaction could activate apoptosis in
cancer cells energy of interactions with ligands. Binding energies are
most widely used mode of measuring binding affinity of ligands. Thus,
decrease in binding energy due to mutation will increase the binding
affinity of the ligands towards the receptor. The characteristic feature
of ligands represent in presence of several active sites available for
hydrogen bonding.
η ¼
ð3Þ
2
1
σ ¼
η
ð4Þ
ð5Þ
ð6Þ
Pi ¼ −χ
1
S ¼
2η
Pi2
ω ¼
ð7Þ
ð8Þ
2η
Pi
ΔN max ¼ −
η
3.3. Geometrical structure of the ligands
The concepts of the parameters χ and Pi are related to each other.
The inverse of the global hardness is designated as the softness [17].
From the obtained data (Table 4) we can deduced that:
Geometrical structures and electronic properties of the investigated
compounds were calculated by optimizing their bond lengths, bond
angles and dihedral angles. The calculated molecular structures with
the optimized bond lengths of the ligands are shown in Fig. 6. The
EHOMO often associated with the electron donating ability of the mole-
cule 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 [10,17]. While,
Absolute hardness and softness are important properties to measure
the molecular stability and reactivity. A hard molecule has a large ener-
gy 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. The values of ΔNmax for ligands (HLn) are calculated
and found to be in the range of 0.744 - 1.022 dependent on the nature
of the substituent. It was found that the values of ΔNmax for HLn increase
with increasing Hammett's constant coefficients (σR) as shown in Fig. 8.

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
Fig. 5. 2D plot of interaction between ligands (HLn) with receptor breast cancer mutant 3HB5.

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
493
(CS) (n-π*) transition shifts slightly to lower energy and remains almost
constant. The (CO) (n → π*) transition disappears with the simulta-
neous appearance of new bands, being attributed to π → π* (C = C) as
a sequences of enolization. The band due to π → π* transition moves
to lower energy. These shifts or disappearance of the bands are indica-
tive of coordinating of the ligands to metal.
3.6. Structural of the metal complexes
Following the successful preparation of the ligand, attention was di-
rect towards the chemical behavior of the ligand towards M(II)/M(III)
chloride. When a mixture of ligands in ethanol was reacted with
M(II)/M(III) chloride in ethanol (1:2) under reflux condition, a change
in color was observed and the complex compounds precipitated. The
products were purified by washing with dry ethanol, and gave elemen-
tal analyses compatible with the suggested formulae given in Table 2
according to the following general equation:
ꢀ
ꢁ
MCl3 þ HLn→ MðLnÞ2ðOH2Þ2 Cl þ 2 HCl
ð1 ꢀ 6Þ
ð7 ꢀ 9Þ
ꢀ
ꢁ
PtCl2 þ HLn→ PtðLnÞ2 þ 2 HCl
where Ln = deprotonated HL1, HL3, HL5 and M = Rh(III) or Ir(III).
The resulting compounds are non-hygroscopic and air-stable solids.
The C, H, N and metal percentage of these complexes are presented in
Table 2. The analytical data supports the above said molecular composi-
tion for these complexes.
3.7. Molar conductance of the complexes
The molar conductance of 10−3 M of solutions of the complexes in
DMSO is calculated at 25 2 °C. It is concluded from the results that
Pt(II) chelates with HLn ligand under investigation were found to have
molar conductance values in the range from 11.85 to 17.55 Ω−1
mol−1 cm2, indicating non-electrolytic nature of these compounds
and there is no counter ion present outside the coordination sphere of
Pt(II) complexes [18]. This is in accordance with the fact that conductiv-
ity values for a non-electrolyte are below 50 Ω−1 mol−1 cm2 in DMSO
solution [19]. While Rh(III)/Ir(III) complexes were found to be 1:2 elec-
trolytes [20]. Such a non-zero molar conductance 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 electrolyte type [18].
Fig. 5 (continued).
3.4. 1H NMR spectra
The 1H NMR spectra of azo rhodanine and its derivatives were inves-
tigated by El-Sonbati and coworkers [2,3,14]. The broad signals assigned
to the OH protons at ~11.36–11.88 ppm are not affected by dilution.
Signal for CH (~4.42 ppm), favoring formation of an intramolecular hy-
drogen bond with the N=N group (azo dye). The previous two protons
disappear in the presence of D2O. Absence of −CH proton signal of the
ligand moiety indicated the existence of the ligand in the azo-enol form.
In the meantime, the 1H NMR of the HL1/HL2 exhibits signals at δ(ppm)
[3.9 (s, 3H, OCH3)]/[3.3 (s, 3H, CH3)]. The aromatic protons have
resonance at 7.10–7.45 ppm for the ligands. In the spectrum of Pt(II)
complex (7), the proton signal due to −OH disappears and this is a
clear indication that the enolic oxygen is bonded to the metal ion after
deprotonation. 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. The chemical shifts,
δ, ppm owing to NH proton (of rhodanine) remain practically
unchanged in the complexes, indicating that (NH of rhodanine) nitro-
gen does not involved in ligand coordination to the metal. Absence of
CH proton signal of the rhodanine azo moiety indicated the existence
of the ligand in the azo-enol form.
3.8. IR spectra and the mode of bonding in the complexes
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.
The IR spectra of the complexes (1-9) show the ligands behaves as a
bidentate ligand depending on the metal salt used, the reaction condi-
tions and the pH of the medium.
The ligands gives two bands at ~3200 and 3040 cm−1 due to
asymmetric and symmetric stretching vibrations of N–H group and
intramolecular hydrogen bonding NH…O systems (Fig. 2-D), respec-
tively. The broad absorption band located at ~3400 cm−1 is assigned
to νOH. The low frequency bands indicate that the hydroxy hydrogen
atom is involved in keto ⇔ enol (A⇔B) tautomerism through hydro-
gen bonding (Fig. 2-C). The OH group (Fig. 2-B) exhibits more than
one absorption band. The two bands located at 1330 and 1370 cm−1
are assigned to in-plane deformation and that at 1130 cm−1 is due
νC-OH. When the OH group (Fig. 2-C) is involved in intramolecular hy-
drogen bond, the O…N and N…O bond distances are the same [14]. But,
if such mechanism is happened in case of intermolecular hydrogen
bond, the O…O and O…N bond distances are differ. However,
the 860 cm−1 band is probably due to the out-of-plane deformation of
3.5. Spectral studies of ligands
HLn ligands exhibits bands at 26,360-26,280 cm−1 (CS) (n → π*),
30,560-30,260 cm−1 (CO) (n → π*), 32,980-33,180 cm−1 (H-bonding
and association), 40,250-39,900 cm−1 (phenyl) (Ph-Ph*), (π-π*) [14]
and 29,620-29,350 cm−1 transition of phenyl rings overlapped by
composite broad π-π* of azo structure. In the complexes, the (n → π*)
transition shifts to lower energy at 28,660 cm−1 and the band due to
the H-bonding and association is absent as expected. Furthermore, the

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
the –OH group. On the other hand, the two bands located at 650 and
670 cm−1 are identified as δ C_O and NH.
• Hydrogen bonding of the OH…N type between the hydroxy hydrogen
atom and the N-ph group (Fig. 2-C).
El-Sonbati et al. [2,21] made detailed studies for the different types
of hydrogen bonding which are favorable to exist in the molecule
under investigation:
The presence of broad band located at ~3200 cm−1 is strong
indication by νNH (Fig. 2-D). In general, the low frequency of such
region from its normal position is, again due to hydrogen bond prop-
erty gathered with keto ⇔ enol tautomerism.
• Intramolecular hydrogen bond between the nitrogen atom of the azo
dye (−N_N−) system and hydrogen atom of the hydroxy hydrogen
atom (Fig. 2-C). This is evident by the presence of a broad band
The frequencies for the N_N stretching located in the range of 1440-
centered at 3460 cm−1
.
1435 cm−1. The region between 1500 and 900 cm−1 is due C–N
Fig. 6. The calculated molecular structures of the ligands (HLn).

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
495
Fig. 6 (continued).
stretching, N–H in plane or out of plane bending and out-of-plane C–H
bending vibrations [14].
By comparing the infrared spectra of free ligands to that of the pre-
pared complexes the following points could be outlined:
The 1H NMR spectral data of the Pt(II) complexes recorded in DMSO-
d6 further substantiate the mode of coordination suggested by the IR
spectral studies. In the spectrum of Pt(II) complexes, the proton signal
due to –OH disappears and this is a clear induction that the enolic oxy-
gen is bonded to the metal ion after deprotonation. Signal for methoxy
proton do not show any significant change when compared to the free
ligand (HL1). Comparison of the position of the other resonance signals
in the Pt(II) complexes with those of the ligand indicates downward
shifting by about ~0.2 ppm in the metal complex. The positions of the
other proton signals have also been observed in the expected regions
and have been shifted only slightly due to the coordination of the ligand
to metal ion. Thus, from the IR and NMR spectral data it is clear that the
ligand is bonded to the metal ion in a bidentate fashion through the
deprotonated enolate oxygen and one of the azo nitrogen atoms.
• The appearance of υ(N_N) and the disappearance of frequency
bands of the υ(C_O) group in the free ligands (HLn) suggest that
there is no hydrazo-keto transformation; this is similar to that
reported in the literature [2,19]. The N_N stretching frequency
of azo group is shifted to lower frequency by ~ 25–35 cm−1 due
to the involvement of one of the azo nitrogen atoms in coordina-
tion with metal ion [6–8]. This lowering of frequency can be
explained by the transfer of electrons from the nitrogen atom to
the metal ion due to coordination.
• In solution and in the presence of Pt(II) ions these compounds exist
in a tautomerism equilibrium [1] A⇔B⇔C (Fig. 2). The internally
hydrogen bonded enolic –OH band disappeared in the spectra of
the metal complexes, indicating the deprotonation and formation
of metal-oxygen bond. This is further supported by the shifting of
υ(C–O) towards higher frequency as compared to the free ligands
(HLn) due to the conversion of hydrogen bonded structure into a
covalent metal bonded structure [22].
• The low intensity of bands of non-ligand appearing in the region 415–
465 cm−1 (M–N) and 435–460 cm−1 (M–O).
On the basis of all these data, the molecular structure of the M(II)/
M(III) complexes could be suggested based on, the absence of anion,
ii) the disappearance of C_O, iii) the coordination of azo-group. It
found that the ligands (Ln) is behaving as a bidentate monobasic
[(O,N)] nature with respect to the evidence above, the structure for
the novel complexes are tentatively proposed as shown in Fig. 9.
• The appearance of new bands around ~3290 cm−1 and two sharp
bands at ~725 and 430 cm−1, the latter two can be assigned to the
wagging and rocking modes of vibration of the water molecule,
respectively [23] in the prepared M(III) complexes may be taken
as a strong evidence for the presence 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).
According to the structure shown in (Figs. 2 & 9) the HLn ligand takes
its usual anionic form (Ln) to chelate M(II)/M(III) through N- of azo
group with enol group (Figs. 2-C & 9) as the potential binding sites. At-
tempts have been made to grow X-ray quality single crystals of these
complexes; however, this has been unsuccessful so far.

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
3.9. Eelectronic spectra of complexes (1–9)
p-substituent (HL5) while it increased by the electrons donating
character of (HL1). It is clear that all these values decrease with
increasing σR. It is important to note that the existence of a methyl
and/or methoxy group enhances the electron density on the coordi-
nation sites and simultaneously decreases the values of electronic
spectral. The plot of single electron parameter (Δ1) vs. σ [σ =
Hammett's substituent coefficients (σR) of the substituent (R)]
(Fig. 10) shows a linear relationship between Δ1 and σ for each chro-
mospheres. The Δ1 and σ values are relatively insensitive to the in-
ductive effect of the phenyl ring substituent and chiefly depend on
the stereochemical factors as the redox properties. The Δ1 values
are weaker in the complex (7) in agreement with the more electrons
donating character atom. As can be seen from (Fig. 11), the plot of
υ2/υ1 values (for Pt complexes) versus σ [σ = Hammett's substitu-
ent coefficients (σR) of R] is linear. The values bare relationship in-
sensitive to the inductive effect of the phenyl ring substituent and
chiefly depend on the stereochemical factor. Furthermore, values
are weaker in complex (9) in agreement with the more electron
withdrawing p-substituent character.
The electronic spectra of platinum complexes exhibit bands in the
ranges of 14,710-16,050 cm−1 (1A1g
→
1A2g), 20,100-20,980 cm−1
(1A1g → 1B1g) and 24,895-26,070 cm−1 (1A1g → 1Eg), in order of increas-
ing energy, respectively [24], characteristic of square planar arrange-
ment around the metal atom. These transitions are assuming the
effective symmetry to be D4h. The values of ligand field parameters Δ1,
Δ
2 and Δ3 as shown in Table 5 were calculated [25,26] using various
energy level diagrams. These are consistent with the values reported
earlier for such complexes [27,28]. The values of Δ1 lie between those
observed for cyanide (~30,000 cm−1) and chloride complexes
(~19,000 cm−1) and are consistent with intermediate ligand strength
[28]. The relationship between electronic spectral data (Table 5)
and Hammett's substituent coefficients (σR) illustrated that the
values of electronic spectral is related to nature of the p-substituent as
they increase according to the following order p-(NO2 b H b OCH3).
This can be attributed to the fact that the effective charge experi-
enced by the d-electrons decreased due to the electron withdrawing
Fig. 7. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of ligands (HLn).

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
497
(υ2)) and 37,000-37,990 (1A1g → 1T1u) transitions The υ2/υ1 transitions
have been used to evaluate the ligand field parameter (Table 5), which
are comparable to data reported for other octahedral iridium(III)
complexes [23] involving N and O donor atoms. The ground state in
1
both the Rh(III) and Ir(III) complexes in an octahedral field is A1g
.
The general pattern of the spectra indicates octahedral geometry
around the metal ions [30]. The Rh(III) and Ir(III) complexes exhibit dia-
magnetic behavior due to their d6 (low spin) system.
3.10. Thermal analysiss
3.10.1. Thermogravimetric analysis of ligands (HLn)
Thermal data of ligands were characterized on the basis of thermo-
gravimetric 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. 12. For HL1 and
HL3 there are two steps of the loss of masses, while for HL5 there are
three steps. Fig. 12 reveals that the HL1 decomposes in two steps, the
first stage and weight loss starts at 200 °C with a weight loss percentage
of 61.9%. The second stage, weight loss starts at 320 °C with a weight
loss percentage of 38.1%. The HL3 decomposes in two steps as shown
in Fig. 12, 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%. The HL5 ligand decomposes in
three steps, the first stage and 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% [21].
Fig. 7 (continued).
The electronic spectra of the radium(III) complexes (1–3) display
bands in the ranges of 17,500–17,980 cm−1 (1A1g
→
3T1g), 20,100–
20,400 cm−1 (1A1g
→ → )
1T1g) and 24,700–25,100 cm−1 (1A1g 1T2g
transitions in increasing order of energy which resemble those of
other six-coordinate rhodium(III) complexes [29]. Electronic spectra of
iridium(III) complexes (4–6) display bands in the ranges of 30,750–
The ligands (HL3 and HL5) show two exothermic and endothermic
peaks except HL1 ligand show one exothermic peak is shown in
Fig. 12. For the HL1 ligand the recorded DSC curve show only one
exothermic peak at 220 °C. Simultaneously, the recorded DSC curve of
30,890 cm−1 (1A1g
→ →
1T1g(υ1)), 34,000–34,400 cm−1 (1A2g 1T2g
Table 4
The calculated quantum chemical parameters of the ligands.
Compound
EHOMO (a.u)
ELUMO (a.u)
ΔE (a.u)
μ (D)
T.E (a.u)
χ (a.u)
η (a.u)
σ (a.u)−1
Pi (a.u)
S (a.u)−1
ω (a.u)
ΔNmax
HL1
HL2
HL3
HL4
HL5
−0.327
−0.337
−0.348
−0.355
−0.367
0.048
0.047
0.044
0.034
−0.004
0.375
0.384
0.432
0.389
0.363
5.358
4.554
3.950
2.001
3.712
−1491.580
−1416.775
−1377.752
−1836.627
−1581.099
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
−0.139
−0.145
−0.152
−0.161
−0.186
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
Fig. 8. The relation between Hammett's substituent coefficients (σR) vs. ΔNmax for ligands (HLn).

498
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
Fig. 9. The structure proposed for M(II)/(III)-complexes (1–9).
the HL3 ligand show two exothermic and endothermic peaks at 190 °C
and 180 °C, respectively, while the recorded DSC curve of the HL5 ligand
show two exothermic and endothermic peaks at 245 °C and 120 °C,
respectively.
and a molecule of chlorine. The next two steps, which take place
within the temperature range of 350–550 °C, may involves the release
of one Ln molecule. The total mass observed between 520 and 530 °C
corresponded to a residue Rh2O3 and Ir2O3.
The TG curve for complexes (7–9), all the complexes show similar
decomposition with weight losses in two stages. In the first stage, in
the temperature range of ~280–320 °C is attributed to the weight loss
of one molecule of ligands. The total mass loss observed at 480–540 °C
was found to be stable metal oxides. The fragmentation patterns of
the thermograms agree well with theoretical calculations and support
the stereochemical assignments [31].
3.10.2. Thermogravimetric analysis of complexes
The thermal stability and decomposition of the complexes was
studies. Thermogravimetric analysis of the complexes (1–6) shows
that the complex decomposed in four steps. These steps extended
between 50 and 290 and 300–550 °C. The first and second steps accom-
panied with weight loss which may be attributed to the loss of 2H2O
3.11. Calculation of activation thermodynamic parameters
The thermodynamic activation parameters of decomposition
processes of complexes namely activation energy (Ea), enthalpy
Table 5
Electronic spectra and single electron parameters.
⁎
⁎
(ΔH ), entropy (ΔS ), and Gibbs free energy change of the decomposi-
Complexa
Bands cm−1
Assignments
Δ1
Δ2
Δ3
υ2/υ1
⁎
tion (ΔG ) are evaluated graphically by employing the Coast–Redfern
(1)
17,500
20,250
24,700
17,800
20,100
25,000
17,980
20,400
25,100
30,800
34,000
37,000
30,750
34,200
37,800
30,890
34,400
37,990
14,710
20,100
24,895
15,880
20,836
25,540
16,050
20,980
26,070
1A1g
1A1g
1A1g
-do-
-do-
-do-
-do-
-do-
-do-
1A1g
1A1g
1A1g
-do-
-do-
-do-
-do-
-do-
-do-
→
→
→
3T1g
1T1g
1T2g
–
–
–
1.157
[32] and Horowitz–Metzger [33] methods.
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
–
–
–
1.129
1.140
1.104
1.112
1.114
1.366
1.312
1.307
–
–
–
→
→
→
1T1g
1T2g
1T1u
–
–
–
–
–
–
–
–
–
1A1g
1A1g
1A1g
-do-
-do-
-do-
-do-
-do-
-do-
→
1A2g
1B1g
16,810
17,980
18,150
6590
4956
6130
4490
5604
4790
→
→
1Eg
Fig. 10. The relation between Hammett's substituent coefficients (σR) vs. for Pt(II)-
complexes (7–9).
a
Numbers as given in Table 2.

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
499
calculated. The pre-exponential factor, A, calculated from equation:
Ea
RT2S
A
ꢄ
ꢂ
ꢃꢅ
¼
ð14Þ
Ea
RTS
φ exp
−
⁎
The entropy of activation, ΔS , is calculated from Eq. (11). The
⁎
⁎
enthalpy activation, ΔH , and Gibbs free energy, ΔG , calculated from:
ΔHꢁ ¼ Ea−RT
ð15Þ
ð16Þ
ΔGꢁ ¼ ΔHꢁ−T ΔSꢁ:
⁎
⁎
⁎
The calculated values of Ea, A, ΔS , ΔH and ΔG for the decomposi-
tion steps for ligands are summarized in Table 6. The high values of
activation energies and the entropy of activation of the ligands reflect
the thermal stability of the compounds. The negative values of activa-
Fig. 11. The relation between υ2/υ1 and Hammett's substituent coefficients (σR) for Pt(II)-
complexes (7–9).
⁎
tion entropies (ΔS ) indicate a more ordered activated compounds
⁎
than the reactants and/or the reactions are slow [2]. The values of ΔG
3.11.1. Coast–Redfern equation
is positive considered as favorable or spontaneous reaction.
The Coast–Redfern equation, which is a typical integral method, can
represent as:
ꢂ
ꢃ
Z
Z
a
T2
T1
dx
A
φ
Ea
RT
¼
exp
−
dt:
ð9Þ
n
0 ð1−αÞ
For convenience of integration, the lower limit T1 usually taken as
zero. This equation on integration gives:
ꢄ
ꢅ
ꢄ
ꢅ
lnð1−αÞ
Ea
RT
AR
φEa
ln −
¼ −
þ ln
:
ð10Þ
T2
A plot of left-hand side (LHS) against 1/T was drawn (Fig. 13). Ea is
the energy of activation in J mol−1 and calculated from the slop and A
in (s−1) from the intercept value. The entropy of activation ΔS in
⁎
(J K−1 mol−1) calculated by using the equation:
ꢄ
ꢂ
ꢃꢅ
Ah
kBTs
ΔSꢁ ¼ 2:303 log
R
ð11Þ
where kB is the Boltzmann constant, h is the Plank's constant and Ts is
the TG peak temperature.
3.11.2. Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the approxima-
tion methods. These authors derived the relation:
"
#
1−n
1−ð1−αÞ
1−n
Ea
θ
log
¼
;
for n≠1
ð12Þ
2:303RT2S
when n = 1, the LHS of Eq. (12) would be log[−log(1-α)] (Fig. 14).
For a first order kinetic process, the Horowitz–Metzger equation may
write in the form:
ꢄ
ꢂ
ꢃꢅ
Wα
Wγ
Ea
θ
log log
¼
− log 2:303
ð13Þ
2:303RT2s
where θ = T-Ts, wγ = wα- w, wα = mass loss at the completion reac-
tion; w = mass loss up to time t. The plot of log [log (wα/wγ)] vs. θ
was drawn and found to be linear from the slope of which Ea was
Fig. 12. TGA and DSC thermographs for ligands (HL1, HL3 and HL5).

500
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
Fig. 13. Coats–Redfern (CR) of the ligands.
4. Conclusions
M(III) complexes. The results of molecular docking between ligands
(HLn) and receptor breast cancer (3HB5) showed a possible arrange-
ment between ligands and receptor (3HB5). The values of ΔNmax for
HLn are calculated and found to be in the range of 0.744 - 1.22
The present paper reports the synthesis, characterization and their
electronic absorption spectra of ligand (azo rhodanine) and M(II)/

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
501
Fig. 14. Horowitz–Metzger (HM) of the ligands.
dependent on the nature of the substituent. It was found that the
values of ΔNmax for ligands increase with increasing Hammett's
constant coefficients (σR). The synthetic procedure in this work
resulted the formation of complexes in the molar ratio
(1:2)(M:Ln), respectively. In these complexes the azo ligand acts
as a monobasic bidentate ligand and coordinated to metal ion
through the azo-nitrogen, enolic oxygen atoms forming stable
six-membered heterocyclic rings. The present study revealed
square planar (Pt(II)) and octahedral geometry around M(III)-
complexes. From conductance measurements Pt(II)-complexes
are non-electrolytes, while M(III) complexes are electrolytic
nature. The values of ligand field parameters orbital parameters
were calculated. The thermal properties of the ligands and their
complexes were investigated by thermogravimetry analysis (TGA)
and different thermodynamic parameters are calculated using
Coats–Redfern and Horowitz–Metzger methods. The thermogravi-
metric analysis confirms the presence of coordinated two water
molecule in the complexes (1–6).

502
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 212 (2015) 487–502
Table 6
Thermodynamic parameters of the ligands.
Compounda
Decomposition temperature (°C)
Method
Parameter
r
−1
−1
a (kJ mol−1
)
A (s−1
)
ΔS (J mol−1 K−1
⁎
)
ΔH (kJ mol
)
ΔG (kJ mol
)
⁎
⁎
E
HL1
211-346
498-624
158-401
502-643
225-271
443-630
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
7.58 × 101
4.18 × 102
4.43 × 108
6.40 × 109
7.11 × 101
1.17 × 102
2.34 × 107
2.50 × 108
2.54 × 1030
1.70 × 1032
1.51 × 104
2.05 × 105
−214
−200
−87.9
−65.8
−215
−210
−113
−92.2
333
41.2
49
159
159
247
241
161
160
250
245
151
142
242
236
0.99221
0.99398
0.99355
0.99169
0.99322
0.99788
0.98442
0.99156
0.99453
0.99452
0.99432
0.99390
174
186
42.3
43.8
155
166
325
333
101
113
HL3
HL5
367
−173
−152
HM
M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.
Pople, Gaussian 03, Revision C.01, Gaussian, Inc., Wallingford CT, 2004.
[12] T.A. Halgren, J. Comput. Chem. 17 (1998) 490–519.
[13] G.M. Morris, D.S. Goodsell, J. Comput. Chem. 19 (1998) 1639–1662.
[14] M.I. Abou-Dobara, A.Z. El-Sonbati, Sh.M. Morgan, World J. Microbiol. Biotechnol. 29
(2013) 119–126.
References
[1] M.A. Diab, A.Z. El-Sonbati, A.A. El-Bindary, G.G. Mohamed, Sh.M. Morgan, Res. Chem.
Intermed. (2015), http://dx.doi.org/10.1007/s11164-015-1946-0.
[2] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, A.M. Eldesoky, Sh.M. Morgan,
Spectrochim. Acta A 135 (2015) 774–791.
[15] A. Beteringhe, C. Racuciu, C. Balan, E. Stoican, L. Patron, Adv. Mater. Res. 787 (2013)
[3] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, Sh.M. Morgan, Inorg. Chim. Acta 404
236–240.
(2013) 175–187.
[16] A.A. El-Bindary, A.Z. El-Sonbati, M.A. Diab, Sh.M. Morgan, J. Mol. Liq. 201 (2015)
36–42.
[17] N.A. El-Ghamaz, M.A. Diab, A.A. El-Bindary, A.Z. El-Sonbati, H.A. Seyam, Mater. Sci.
Semicond. Process. 27 (2014) 521–531.
[18] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122.
[4] A.Z. El-Sonbati, G.G. Mohamed, A.A. El-Bindary, W.M.I. Hassan, A.K. Elkholy, J. Mol.
Liq. 209 (2015) 625–634.
[5] B. Rosenberg, L. Van Camp, J.E. Trosks, V.H. Mansour, Nature (London) 222 (1969)
385–386.
[6] A.M. Eldesoky, M.A. El-Bindary, A.Z. El-Sonbati, Sh.M. Morgan, J. Mater. Environ. Sci.
6 (2015) 2260–2276.
[7] N.A. El-Ghamaz, A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, G.G. Mohamed, Sh.M.
[19] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, G.G. Mohamed, Sh.M. Morgan, Inorg.
Chim. Acta 430 (2015) 96–107.
[20] L.K. Thompson, F.L. Lee, E.J. Gabe, Inorg. Chem. 27 (1988) 39–46.
[21] N.A. El-Ghamaz, A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, Sh.M. Morgan, Mater.
Res. Bull. 65 (2015) 293–301.
[22] F.C.L.J. Bellamy, The Infrared Spectra of Complex Molecules, Wiley, New York, 1958.
[23] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, Sh.M. Morgan, Spectrochim. Acta A 127
(2014) 310–328.
Morgan, Spectrochim. Acta A 147 (2015) 200–211.
[8] N.A. El-Ghamaz, A.Z. El-Sonbati, Sh.M. Morgan, J. Mol. Struct. 1027 (2012) 92–98.
[9] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Met. Chem. Phys. 123
(2010) 439–449.
[10] N.A. El-Ghamaz, A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, M.K. Awad, Sh.M.
Morgan, Mater. Sci. Semicond. Process. 19 (2014) 150–162.
[24] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1968.
[25] M.A. Diab, A.Z. El-Sonbati, R.H. Mohamed, Spectrochim. Acta A 77 (2010) 795–801.
[26] J.C. Ballahausen, H.B. Gray, Inorg. Chem. 1 (1962) 111–122.
[27] V.B. Rana, S.K. Sahni, S.K. Sangal, Acta Chem. Scand. 10 (1979) 405.
[28] B.N. Figgis, Introduction to Ligand Field, Wiley Eastern, New Delhi, 1976.
[29] C. Preti, G. Tosi, Transit. Met. Chem. 3 (1978) 17–25.
[30] J. Lewis, B.N. Figgs, Prog. Inorg. Chem. 6 (1964) 105.
[31] N.A. El-Ghamaz, A.A. El-Bindary, A.Z. El-Sonbati, N.M. Beshry, J. Mol. Liq. 211 (2015)
628–639.
[11] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A.
Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian,
J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P.
Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O.
Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui,
A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara,
[32] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68–79.
[33] H.W. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464–1468.