Correlation between ionic radii of metals and thermal decomposition of supramolecular structure of azodye complexes

Article abstract of DOI:10.1016/j.saa.2014.07.055

An interesting azodye heterocyclic ligand of copper(II), cobalt(II), nickel(II) and uranyl(II) complexes have been synthesized by the reaction of metal salts with 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4- thiazolidinone (HL) yields 1:1 and 1:2 (M:L) complexes depending on the reaction conditions. The elemental analysis, magnetic moments, spectral (UV-Vis, IR, ¹H and ¹³C NMR and ESR) and thermal studies were used to characterize the isolated complexes. The molecular structures of the ligand tautomers are optimized theoretically and the quantum chemical parameters are calculated. The IR spectra showed that the ligand (HL) act as monobasic tridentate/neutral bidentate through the (NN), enolic (CO)^- and/or oxygen keto moiety groups forming a five/six-membered structures. According to intramolecular hydrogen bond leads to increasing of the complexes stability. The molar conductivities show that all the complexes are non-electrolytes. The ESR spectra indicate that the free electron is in d_xy orbital. The calculated bonding parameter indicates that in-plane σ-bonding is more covalent than in-plane π-bonding. The coordination geometry is five/six-coordinated trigonal bipyramidal for complex (1) and octahedral for complexes (2-6). The value of covalency factor β₁² and orbital reduction factor K accounts for the covalent nature of the complexes. The activation thermodynamic parameters are calculated using Coats-Redfern and Horowitz-Metzger methods. The synthesized ligand (HL) and its Cu(II) complexes (1, 2 and 4) are screened for their biological activity against bacterial and fungal species. The ligand (HL) showed antimicrobial activities against Escherichia coli. The ligand (HL) and its Cu(II) complexes (2 and 4) have very high antifungal activity against Penicillium italicum. The inhibitive action of ligand (HL), against the corrosion of C-steel in 2 M HCl solution has been investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).

Full text of DOI:10.1016/j.saa.2014.07.055

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Correlation between ionic radii of metals and thermal decomposition
of supramolecular structure of azodye complexes
A.Z. El-Sonbati a, , M.A. Diab , A.A. El-Bindary , A.M. Eldesoky b,2, Sh.M. Morgan a,1
⇑
a
a
a
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
Engineering Chemistry Department, High Institute of Engineering & Technology, Damietta, Egypt
b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The structure of the metal complexes.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Complexes of monobasic tridentate/
neutral bidentate ligand were
synthesized and characterized.
X-ray diffraction pattern show
polycrystalline phase for pyrazolone
azodye.
Molecular structures of ligand are
optimized theoretically and quantum
parameters are calculated.
The ligand and its Cu(II) complexes (2
and 4) have very high antifungal
activity against P. italicum.
The inhibition efficiency of the tested
ligand increase with increasing of its
concentrations.
3
H C
N
CH3
N
S
N
O
H
2
O
N
S .n H O
C
2
O
M
NH
O
H
3
C
O
OH
2
M= Cu(II) (4), Co(II) (5), Ni(II) (6)
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 May 2014
Received in revised form 4 July 2014
Accepted 17 July 2014
Available online 1 August 2014
An interesting azodye heterocyclic ligand of copper(II), cobalt(II), nickel(II) and uranyl(II) complexes have
been synthesized by the reaction of metal salts with 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-2-thi-
oxo-4-thiazolidinone (HL) yields 1:1 and 1:2 (M:L) complexes depending on the reaction conditions. The
1
13
elemental analysis, magnetic moments, spectral (UV–Vis, IR, H and C NMR and ESR) and thermal studies
were used to characterize the isolated complexes. The molecular structures of the ligand tautomers are
optimized theoretically and the quantum chemical parameters are calculated. The IR spectra showed that
Keywords:
ꢁ
the ligand (HL) act as monobasic tridentate/neutral bidentate through the (AN@N), enolic (CAO) and/or
Pyrazolone azodye
Supramolecular structure of complexes
ESR study
Thermodynamic parameters
Corrosion inhibition
EIS study
oxygen keto moiety groups forming a five/six-membered structures. According to intramolecular
hydrogen bond leads to increasing of the complexes stability. The molar conductivities show that all
the complexes are non-electrolytes. The ESR spectra indicate that the free electron is in dxy orbital. The cal-
culated bonding parameter indicates that in-plane
r-bonding is more covalent than in-plane p-bonding.
The coordination geometry is five/six-coordinated trigonal bipyramidal for complex (1) and octahedral for
2
1
complexes (2–6). The value of covalency factor b and orbital reduction factor K accounts for the covalent
nature of the complexes. The activation thermodynamic parameters are calculated using Coats–Redfern
and Horowitz–Metzger methods. The synthesized ligand (HL) and its Cu(II) complexes (1, 2 and 4) are
screened for their biological activity against bacterial and fungal species. The ligand (HL) showed antimi-
crobial activities against Escherichia coli. The ligand (HL) and its Cu(II) complexes (2 and 4) have very high
antifungal activity against Penicillium italicum. The inhibitive action of ligand (HL), against the corrosion of
⇑
Corresponding author. Tel.: +20 1060081581; fax: +20 572403868.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
Abstracted from her Ph.D.
1
2
Present address: Al-Qunfudah Center for Scientific Research (QCSR), Al-Qunfudah,
Umm Al-Qura University, Saudi Arabia.
http://dx.doi.org/10.1016/j.saa.2014.07.055
1
386-1425/Ó 2014 Elsevier B.V. All rights reserved.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
775
C-steel in 2 M HCl solution has been investigated using potentiodynamic polarization and electrochemical
impedance spectroscopy (EIS).
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
resulting mixture stirred and cooled to 0 °C,
a solution of
0
.01 mol sodium nitrite in 20 ml of water was added dropwise.
Diab et al. [1–4] reveals an excellent work devoted to synthesis
and characterization of azodyes as well as their metal complexes.
The variety of coordination modes of rhodanine azo derivatives
and/or pyrazolone Schiff base derivatives has been demonstrated
in a number of complexes and their biological applications have
been of considerable interest.
The field of azodye complexes was fast developing on account
of the wide variety of possible structures for the ligands depending
upon the amines. Many attempts were done to prepare symmetric/
asymmetric polydentate ligands in order to achieve rare coordina-
tion number with divalent metal ions whose importance was
mainly due to their ability to form metal chelates. Because of
new interesting applications found in the field of pesticides and
medicine, the metal complexes with bi/tridentate O, N/O, N, O
types of alternative structures had attracted the attention of chem-
ists by El-Sonbati et al. [5,6].
The formed diazonium chloride was consecutively coupled with
an alkaline solution of 0.01 mol 2-thioxo-4-thiazolidinone, in
10 ml of pyridine. Immediately, the orange precipitate formed
was filtered through sintered glass crucible, washed several times
by distilled water. The crude products was purified by recrystalli-
zation from hot ethanol, yield ꢂ77% then dried in vacuum desicca-
2 5
tor over P O . The elemental analysis of the HL is collected in
Table 1. The present ligand (HL) was previously prepared under
the method described elsewhere [18,19] by coupling an equimolar
of 1-phenyl-2,3-dimethyl-4-amino pyrazol-5-one and 2-thioxo-
4-thiazolidinone in ethanol (30 ml) (Fig. 1). The structure of
1
formed azodye was established by IR and H NMR spectroscopes.
General method of synthesis of complexes
2
Complexes of M(II)/UO (II) (1, 2 and 4–7) were prepared by
The pyrazolone derivatives and their metal complexes have
been played an important role in the development of coordination
chemistry and potentiometric studies as they readily form stable
complexes with most transition metals by El-Bindary et al. [3,7–9].
Rhodanine azo compounds have been studied the antimicrobial
activity and comparing antimicrobial activity results of rhodanine
azo compounds with the standard antibacterial and antifungal
drugs in addition to studying optical absorption properties [2,10].
Carbon steel is the major structural material in industry, the
protection of steel against corrosion has attracted much attention
refluxing the respective methanolic solutions of the metal salts
and the HL in 1:1 except complex (7) (1:2) molar ratio for 4–6 h.
The resulting solution, on cooling yielded respective solids, which
were filtered, washed with methanol and ether and dried over
2 5
P O in vacuum. Complex (3) was prepared by a methanolic dis-
placement of the acetate anion of the copper acetate by the addi-
tion of 1 mmol each of the methanolic solutions of KSCN to the
reaction mixture of the ligand and copper acetate in methanol.
The resulting solution was refluxed for 3 h and left overnight.
The solid separated were filtered, washed with methanol and ether
[
11]. Inhibitors are used in this process to control metal dissolu-
2 5
and dried over P O in vacuum. The elemental analyses of the HL
and its metal complexes are given in Table 1.
tion. Most of the well-known acid inhibitors are organic
compounds containing O, S and/or N atoms [12–17]. Corrosion
inhibition occurs via adsorption of the organic molecule on the cor-
roding metal surface following some known adsorption isotherms
with the polar groups acting as active centers in the molecules.
The objectives of the present work are (i) the synthesis of 5-(2,3-
dimethyl-1-phenylpyrazol-5-one azo)-2-thioxo-4-thiazolidinone
Biological activity investigation
For this investigation the agar well diffusion method was
applied [2,4]. The antibacterial activities of the investigated com-
pounds were tested against two local Gram positive bacterial spe-
cies (Bacillus cereus and Staphylococcus aureus) and two local Gram
negative bacterial species (Escherichia coli and Klebsiella pneumo-
niae) on nutrient agar medium. Also, the antifungal activities were
tested against four local fungal species (Aspergillus niger, Alternaria
alternata, Penicillium italicum and Fusarium oxysporium) on DOX
(
HL) (Fig. 1); (ii) the synthesis of M(II) complexes derived from this
ligand and characterization by elemental analysis, spectral studies,
conductance, magnetic measurements as well as thermal analysis
studies; (iii) the molecular structures of the ligand tautomers have
been discussed; (iv) investigation the stereochemistry of the com-
plexes according to the electronic spectra and other measurements;
(
v) study the antimicrobial activity of (HL) and Cu(II) complexes (1, 2
agar medium. The concentrations of each solution were 50
100 g/ml and 150 g/ml. By using a sterile cork borer (10 mm
diameter), wells were made in agar medium plates previously
seeded with the test microorganism. 200 l of each compound
lg/ml,
and 4) and (vi) study the effect of ligand (HL) as inhibitor for the cor-
rosion of C-steel in 1 M HCl solution and determining the corrosion
rate in the absence and presence of different concentrations of HL by
the electrochemical techniques (potentiodynamic polarization
methods and impedance method) at 25 °C.
l
l
l
was applied in each well. The agar plates were kept at 4 °C for at
least 30 min. to allow the diffusion of the compound to agar med-
ium. The plates were then incubated at 37 °C or 30 °C for bacteria
and fungi, respectively. The diameters of inhibition zone were
determined after 24 h and 7 days for bacteria and fungi, respec-
tively. Penicillin and miconazole were used as reference substances
against bacteria and fungi, respectively.
Experimental
All the chemicals used were of British Drug House (BDH)
quality.
Synthesis of the ligand (HL)
Corrosion measurements
In a typical preparation, 25 ml of distilled water containing
.01 mol hydrochloric acid were added to 1-phenyl-2,3-dimethyl-
-amino pyrazol-5-one (0.01 mol) as shown in Scheme 1. To the
Tests were performed on C-steel specimens of the following
composition (weight%): 0.200 C, 0.350 Mn, 0.024 P, 0.003 S, and
the remainder Fe.
0
4

7
76
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
H C
H3C
CH3
3
CH3
H C
CH3
3
N
N
N
N
S
N
S
N
N
N
S
N
N
N
H
S
S
C
C
N
H
S
O
O
C
O
NH
O
NH
O
NH
O
A
B
C
Azo-keto form
Azo-enol form
H C
3
CH3
H C
3
CH3
N
N
N
S
N
N
S
N
S
N
H
N
H
C
S
C
O
O
NH
NH
O
O
D
E
Keto-hydrazo form
Important resonance structure
H C
CH3
N
3
N
H C
CH3
3
N
N
S
N
S
C
N
S
N
O
N
S
C
NH
NH
HO
O
H
O
or
OH
O
HN
C
OH
N
O
N
HN
C
N
S
N
S
N
N
N
S
CH3
S
N
H3C
CH3
H3C
CH3
N
H C
3
G
N
S
N
F
N
H
S
C
O
N
H
N
NH
O
O
S
C
or
S
NH
O
N
H C
N
3
CH3
H
Fig. 1. The structure of pyrazolone azodye (HL).
Solutions
a saturated calomel electrode (SCE) coupled to a fine Luggin capil-
lary as reference electrode. The working electrode was in the form
of a square cut from mild steel embedded in epoxy resin of polytet-
The aggressive solutions 2 M HCl were prepared by dilution of
analytical grade (37%) HCl with bi-distilled water. The concentra-
tion range of the ligand (HL) used was 1 ꢃ 10ꢁ6–11 ꢃ 10 M.
ꢁ6
2
rafluoroethylene (PTFE) so that the flat surface (1 cm ) was the
only surface of the electrode. Tafel polarization curves were
obtained by changing the electrode potential automatically from
ꢁ500 to +500 mV at open circuit potential with a scan rate of
Polarization measurements
Polarization experiments were carried out in a conventional
three-electrode cell with a platinum foil as counter electrode and
ꢁ1
1 mV s . Stern–Geary method used for the determination of

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
777
H C
H C
3
CH3
N
3
CH3
S
N
N
1-NaNO2 HCl
S
C
+
N
S
N
2- alkaline solution
N
NH2
NH
o
S
0-5 C
O
C
O
O
NH
O
Azo-keto form
H C
CH3
H C
CH3
3
3
NH
O
N
N
O
N
S
N
S
N
N
N
N
H
S
S
C
N
C
O
O
H
O
NH
NH
O
OH
Keto-hydrazo form
Azo-enol form
H C
3
CH3
N
N
S
N
N
S
C
O
H
NH
O
Scheme 1. The formation mechanism of pyrazolone azodye (HL).
corrosion current is performed by extrapolation of anodic and
cathodic Tafel lines to a point which gives logicorr and the corre-
sponding corrosion potential (Ecorr) for inhibitor free acid and for
each concentration of inhibitor. Then icorr was used for calculation
of inhibition efficiency and surface coverage (h) as in Eq. (1):
Table 1
a
Elemental analysis (C, H, S, N and M) of the ligand (HL) and its complexes.
Compoundb
Found (calculated) %
C
H
N
S
M
%
IE ¼ h ꢃ 100 ¼ ½1 ꢁ ðicorrðinhÞ=icorrðfreeÞÞꢄ ꢃ 100;
ð1Þ
HL
48.21
3.64
19.88
18.22
–
–
(
48.42) (3.75) (20.17) (18.44)
where icorr(free) and icorr(inh) are the corrosion current densities in the
absence and presence of ligand (HL), respectively.
[
[
[
[
[
[
[
Cu(L)Cl(OH
2
)] (1)
36.40
3.19
15.32
14.12
13.89
(
36.28) (3.02) (15.12) (13.82) (13.72)
Impedance measurements
Cu(L)(ONO
2
)(OH
2
)
2
] (2)
] (3)
]ꢅH O (4)
]ꢅ2H
]ꢅ2H
] (7)
33.23
3.28
16.87
12.76
12.79
(
33.10) (3.15) (16.55) (12.51) (12.52)
All EIS measurements were performed at open circuit potential
Eocp at room temperature over a wide frequency range of (20 kHz
Cu(L)(NCS)(OH
2
)
2
2
35.87
3.33
16.99
19.34
12.77
(
35.75) (3.18) (16.68) (19.07) (12.62)
to 0.5 Hz). The sinusoidal potential perturbation was 10 mV in
amplitude peak to peak.
Cu(L)(OAc)(OH
2
)
2
36.85
3.86
13.82
12.55
12.45
(
36.74) (3.64) (13.40) (12.25) (12.25)
Co(L)(OAc)(OH
Ni(L)(OAc)(OH
UO (L) (OH
2
)
2
2
O (5) 35.94
3.73
13.45
12.32
11.36
Analytical and physical measurements
(
35.83) (3.55) (13.06) (11.94) (11.00)
3.68 13.44 12.24 11.33
35.84) (3.55) (13.07) (11.95) (10.96)
33.74 3.01 14.42 13.21 24.43
33.67) (2.81) (14.03) (12.83) (23.85)
2
)
2
2
O (6) 36.00
Elemental microanalyses of the separated ligand and solid che-
lates for C, H, and N were determined on Automatic Analyzer CHNS
Vario ELIII, Germany. The analyses were repeated twice to check
the accuracy of the analyzed data. The metal content in the com-
(
2
2
2 2
)
(
1
a
plexes was estimated by standard methods [20]. The H NMR spec-
The excellent agreement between calculated and experimental data supports
trum was obtained with
spectrometer with DMSO-d
reference. The infrared spectra were recorded as KBr disks using a
a
JEOL FX90 Fourier transform
the assignment suggested in the present work.
b
L is the anions of the ligand HL as given in Scheme 1, insoluble in water, but
as the solvent and TMS as an internal
6
partially soluble in ethanol and completely soluble in DMF.

7
78
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
Azo-keto form (A)
Azo-enol form (C)
Azo-enol form (B)
Keto-hydrazo form (D)
Fig. 2. The optimized structures of ligand tautomers within numbering of atoms.
Table 2
Net charges on active centers of the ligand tautomers.
were recorded at room temperature using an X-band spectrometer
utilizing a 100 kHz magnetic field modulation with diphenyl pic-
rylhydrazyle (DPPH) as a reference material. The conductance
measurement was achieved using Sargent Welch scientific Co.,
Skokie, IL, USA.
a
Atom
Charges
A)
(
(B)
(C)
(D)
N(15)
O(21)
N(23)
O(6)
S(16)
S(22)
ꢁ0.171
ꢁ0.570
ꢁ0.246
ꢁ0.570
ꢁ0.371
ꢁ0.380
ꢁ0.171
ꢁ0.527
ꢁ0.171
ꢁ0.570
ꢁ0.242
ꢁ0.380
ꢁ0.384
ꢁ0.356
ꢁ0.417
ꢁ0.570
ꢁ0.242
ꢁ0.380
ꢁ0.427
ꢁ0.138
ꢁ0.492
ꢁ0.570
ꢁ0.282
ꢁ0.380
Computational methods
The calculations of geometry optimization were performed
using Perkin Elmer ChemBio 3D software by HF method with
3-21G basis set [22]. Geometry optimization option was employed
to obtain the most stable structure.
a
Symbols as given in Fig. 2.
Perkin–Elmer 1340 spectrophotometer. X-ray diffraction analysis
of the HL and its complexes (4–6) powder forms was recorded
on X-ray diffractometer in the range of diffraction angle 2h° =
Results and discussion
Structure of the ligand
4
(
4
–70°. This analysis was carried out using Cu K
k ¼ 1:541874 Å). The applied voltage and the tube current are
0 kV and 30 mA, respectively. Ultraviolet–visible (UV–Vis) spectra
a radiation
Theoretical approaches made by Liang and Lipscomb [23] indi-
cate that the nitrogen atom is more negatively charged than the
oxygen atom in the isolated metal ion and consequently it may
account for the coordination of the nitrogen atom rather than the
oxygen atom, to the metal ion. Moreover, these authors have found
that in the presence of the metal, the bidentate binding conforma-
tion with both N and O atoms coordinated to the metal ions is
favored.
of the compounds were recorded in nuzol solution using a Unicom
SP 8800 spectrophotometer. The magnetic moment of the prepared
solid complexes was determined at room temperature using the
Gouy’s
method.
Mercury(II)
(tetrathiocyanato)cobalt(II),
[
Hg{Co(SCN)
4
}], was used for the calibration of the Gouy tubes.
Diamagnetic corrections were calculated from the values given
by Selwood [21] and Pascal’s constants. Magnetic moments were
The optimized structures and bond length of the ligand tautom-
ers (A–D) are presented in Fig. 2. From Table 2, the computed net
charges on active centers for the ligand tautomers (A–D), it is
found that the most negative charges in ligand tautomers are
N(15), O(6) and O(21) for azo-enol form (C) and N(15) and O(21)
for keto-hydrazo form (D) that makes it react stronger with the
metal ion. Both the highest occupied molecular orbital (HOMO)
coor. 1/2
calculated using the equation,
l
eff. = 2.84 [Tv
M
]
. Thermal stud-
ies were computed on Simultaneous Thermal Analyzer (STA) 6000
system using thermogravimetric analysis (TGA) method. Thermal
properties of the samples were analyzed in the temperature range
from 50 to 800 °C at the heating rate of 15 °C/min under dynamic
nitrogen atmosphere. ESR measurements of powdered samples

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
779
and lowest unoccupied molecular orbital (LUMO) are the main
IR spectra and the mode of bonding in the complexes
The IR spectra of the ligand showed the absence of the band at
orbital takes part in chemical stability. The HOMO represents the
ability to donate an electron, LUMO as an electron acceptor repre-
sents the ability to obtain an electron. The HOMO and LUMO
energy for ligand tautomers (A–D) calculated by HF method with
ꢁ1
ꢂ3405 cm due to amino
t
(NH
2
) stretching vibration and, instead
(N@N) linkage appeared at
a new band assigned to azodye
t
ꢁ1
3
-21G basis set is presented in Fig. 3. This electronic absorption
1540 cm [5,18]. This suggested that amino group of the start
reagent 1-phenyl-2,3-dimethyl-4-amino pyrazol-5-one (HL) has
been converted into their corresponding ligand (Fig. 1).
corresponds to the transition from the ground state to the first
excited state and is mainly described by one electron excitation
from the highest occupied molecular orbital to the lowest unoccu-
pied molecular orbital. Quantum chemical parameters of the ligand
tautomers are obtained from calculations such as energies of the
highest occupied molecular orbital (EHOMO) and the lowest unoccu-
The ligand may exist in keto-hydrazo and azo-enol tautomeric
forms as shown in Fig. 1. It has be shown conclusively from a series
1
of investigations using various techniques, such as IR and H NMR
spectra, that hydrazo containing rhodanine groups exist exclu-
sively in the keto-hydrazo form both in solution and in solid state
[27]. An intramolecular hydrogen bridge linking one of the car-
bonyl groups to the NHA moiety of the hydrazo unit was found
to be a characteristic feature of this compound class (Fig. 1D and
E). The six-membered intramolecular hydrogen bonding ring is
possible in the keto-hydrazo tautomer as shown in Fig. 1D. The
solid state IR spectra of the ligand shows two intense carbonyl
pied molecular orbital (ELUMO) as listed in Table 3. Additional
*
parameters such as HOMO–LUMO energy gap,
tronegativities,
absolute softness,
and additional electronic charge,
equations mentioned in [18,22,24].
D
E , absolute elec-
v
, chemical potentials, Pi, absolute hardness,
, global electrophilicity, , global softness, S,
max, are calculated using the
g,
r
x
D
N
Recently, the energy gap between HOMO and LUMO has been
used to prove the activity and stability of the compounds
bands (
t
C@Oꢅ ꢅ ꢅH), (
tC@O) consistent with a keto-hydrazo form
*
[
8,18,22]. The value of
D
E for tautomers (A), (C) and (D) was found
with extensive five/six membered intramolecular hydrogen bond-
ing, and this has been confirmed by El-Sonbati et al. [28] and a
number of previous published reports of keto-hydrazo analogues
[29].
0
.1011, 0.0637 and 0.0472 a.u., respectively. The calculations indi-
cated that the azo-enol form (C) and keto-hydrazo form (D) are
more stable forms and highly reactive than azo-keto form (A).
Our earlier studies on coordination behavior of rhodanine deriv-
atives has shown that this 5-(2,3-dimethyl-1-phenylpyrazol-5-one
azo)-2-thioxo-4-thiazolidinone (HL) (Fig. 1) presents a variety of
chelating coordination behavior, depending on the nature of the
metal ion and the deprotonation of the ligand.
In general, reactions of metal(II) acetate with HL were faster and
gave better yields than reactions of metal(II) different anions.
Molar conductance data showed that the metal complexes are
non-electrolytes in DMSO [25,26].
ꢁ1
The strong band located at ꢂ1725 cm due to carbonyl stretch-
ꢁ1
ing vibration mode [18]. The three bands in the 1600–1500 cm
region are characteristic for most six-membered aromatic ring
system. The frequencies for the N@N stretching lie in the region
ꢁ1
ꢁ1
1540–1454 cm . The region between 1500 and 900 cm is due
CAN stretching, NAH in plane or out of plane bending and
out-of-plane CAH bending vibrations. The symmetric and antisym-
metric (C@C) stretching vibration modes are expected to exist in
this region.
The data of elemental analysis as given in Table 1 denote that
two types of complexes were formed. For the first case the ligand
behave as a monobasic and contains one anion (complexes with
half equivalent anions) (1 M:1 L molar ration, as shown in Figs. 4
and 5).
The infrared spectrum of HL gives interesting results and con-
ꢁ1
clusions. The ligand give two bands at ꢂ3190–2965 cm due to
asymmetric and symmetric stretching vibrations of NAH group
and intramolecular hydrogen bonding NHꢅ ꢅ ꢅO systems (Fig. 1D),
respectively. It seems that, the OH group (Fig. 1C) is involved in
intramolecular hydrogen bond, the Oꢅ ꢅ ꢅN and Nꢅ ꢅ ꢅO bond distances
are the same. But, if such mechanism is occurred in case of inter-
molecular hydrogen bond, the Oꢅ ꢅ ꢅO and Oꢅ ꢅ ꢅN bond distances
are differ.
CuCl
2
ꢅ 2H
2
O þ HL ! ½CuðLÞðClÞðOH Þꢄ ð1Þ
2
ꢁ1
The broad absorption band located at ꢂ3400 cm is assigned to
CuX
2
ꢅ nH
2
O þ HL ! ½CuðLÞðXÞðOH Þ2ꢄ ð2; 3Þ
2
t
OH. The low frequency bands indicate that the hydroxy hydrogen
atom is involved in keto () enol (A () B) tautomerism through
hydrogen bonding (Fig. 1C). Bellamy [30] made detailed studies
MðCH
3
COOÞ ꢅ nH
2
O þ HL ! ½MðLÞðCH
3
COOÞðOH
2
Þ2ꢄ ꢅ nH O ð4—6Þ
2
2
on some carbonyl compounds containing ANH group. The
DmNH
values were used to study the phenomena of association.
where L = deprotonated HL, X = NO
4), Co(II) (5), M = Ni(II) (6).
For the second case the ligand behave as a monobasic and not
contains anion (complex without acetate anions) (1 M:2 L molar
ratio, Fig. 6).
3
(2) or SCN (3) and M = Cu(II)
On the other hand, the OH group (Fig. 1B) exhibits more than
one absorption band. The two bands located at 1303 and
(
ꢁ1
1
1346 cm
1170 cm is due
are assigned to in-plane deformation and that at
CAOH.
ꢁ
t
ꢁ1
However, the 870 cm
band is probably due to the
out-of-plane deformation of the AOH group. On the other hand,
ꢁ
1
the two bands located at 670 and 700 cm are identified as dC@O
and NH.
UO
2
ðCH
3
COOÞ ꢅ 2H
2
O þ 2HL ! ½UO
2
ðLÞ ðH
2
OÞ2ꢄ ð7Þ
2
2
The number of water molecules (n) varies according to the nat-
The infrared spectrum of ligand shows medium broad band
ꢁ
1
ure of the metals. Thus the results of elemental analysis clarify,
that three types of bonding are formed between the M2+ ions and
the ligand under study, those with covalent, ionic and partially
ionic and covalent bonds.
located at ꢂ3400 cm due the stretching vibration of some sort
of hydrogen of hydrogen bonding. El-Sonbati et al. [18,31] made
detailed studies for the different types of hydrogen bonding which
are favorable to exist in the molecule under investigation:
All the complexes have high melting point, denoting a strong
bonding between the ligand and metal ions. It is interesting to
point out that, the data of elemental analysis are in satisfactory
agreement with the expected formula which gives support for
the suggested composition.
(1) Intramolecular hydrogen bond between the nitrogen atom
of the AN@NA system and hydrogen atom of the hydroxy
hydrogen atom (Fig. 1C). This is evident by the presence of
ꢁ1
a broad band centered at 3460 cm
.

7
80
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
Excited States
(A)
(B)
ELUMO = -0.0082 a.u.
ELUMO = 0.0019 a.u.
Ground States
Excited States
EHOMO = -0.1092 a.u.
EHOMO = -0.0713 a.u.
(C)
(D)
ELUMO = 0.0072 a.u.
ELUMO = 0.0067 a.u.
Ground States
EHOMO = -0.0399 a.u.
EHOMO = -0.0570 a.u.
Fig. 3. HOMO and LUMO molecular orbital of ligand tautomers.
Table 3
The calculated quantum chemical parameters for ligand tautomers.
Tautomera
E
HOMO (a.u.)
E
LUMO (a.u.)
DE* (a.u.)
v
(a.u.)
g
(a.u.)
r
(a.u.)
ꢁ1
Pi (a.u.)
S (a.u.)
ꢁ1
x
(a.u.)
DN
max
(A)
(B)
(C)
(D)
ꢁ0.1092
ꢁ0.0713
ꢁ0.0570
ꢁ0.0399
ꢁ0.0082
0.0019
0.0067
0.0072
0.1011
0.0733
0.0637
0.0472
0.0587
0.0347
0.0252
0.0163
0.0505
0.0366
0.0319
0.0236
19.7902
27.2933
31.3883
42.3558
ꢁ0.0587
ꢁ0.0347
ꢁ0.0252
ꢁ0.0164
9.8951
13.6467
15.6942
21.1779
0.0341
0.0164
0.0099
0.0057
1.1615
0.9468
0.7901
0.6934
a
Symbols as given in Fig. 2.
ꢁ
1
(
2) Hydrogen bonding of the OHꢅ ꢅ ꢅN type between the hydroxy
hydrogen atom and the NAPyrazole group (Fig. 1C).
The presence of broad band located at ꢂ3190 cm
is
strong indication by NH (Fig. 1D). In general, the low fre-
t
(
3) Intermolecular hydrogen bonding is possible forming cyclic
dimmer through NHꢅ ꢅ ꢅO@C (H), OHꢅ ꢅ ꢅN@N (G) or OHꢅ ꢅ ꢅOH
quency of such region from its normal position is, again due
to hydrogen bond property gathered with keto () enol
tautomerism.
(
F) (Fig. 1).

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
781
are strong indication to keto () enol equilibria. The presence of a
CH3
ꢁ1
medium band at ꢂ1604 cm
tracing of keto structure (Fig. 1D). Band at 1620 cm
(C@O) stretching frequency of antipyrine moiety.
The following features for some of the prepared complexes are
observed:
assigned to tC@N illustrates the
ꢁ1
due to
H C
N
S
3
N
t
N
S
C
Y
N
Cu
NH
O
1. The infrared spectrum of the free ligand shows no charac-
teristic absorption assignable to NH function. This
confirms the formation of the azo compounds.
O
2
`
Y
X
ꢁ1
2
. The band located at ꢂ1540 cm assigned to
t(N@N) is
`
ꢁ1
X= Cl (1), Y= H
X= ONO (2), SCN (3) Y=Y = H
2
O; Y = nil
highly affected by ꢂ20 cm on complexation (1–3), where
it is disappeared in complexes (4–7). This focused the
attention to that the azo-group takes part on complexes
`
2
2
O
(
1–3).
. In solution and in the presence of CuX
ions, these compounds exist in a tautomerism equilibrium
Fig. 4. The structure of the copper complexes.
3
2
2
(Cl, ONO , SCN)
[
25,26] A () B () C (Fig. 1). The tautomeric form (C)
H C
3
react with metal ions by loss of phenolic proton as mono-
negative chelating agents producing of CO/OH mode of
N
CH3
ꢁ1
the free ligand. New bands for
t
(CAO) (ꢂ1106 cm
)
N
O
[
25,26] in the IR spectra of the complexes indicate the
S
coordination to that metal via deprotonation.
N
H
O
2
N
S .n H O
4. The variation in the spectral bands of the CAC, C@C, CAN
and CAH different modes of vibrations of the complexes
lead to that, probably, the aromaticity of the complex is dif-
fer from one to other.
C
2
O
M
NH
O
ꢁ1
H C
O
5. A broad band at ꢂ3400–3275 cm is attributed to
t(OAH)
3
OH2
aqua of coordinated water.
6
. The band due to tOH is masked by the intense absorption
due to water molecule, and hence no definite conclusion
can be drawn for this region. However, dOH at
M= Cu(II) (4), Co(II) (5), Ni(II) (6)
ꢁ
1
ꢁ1
ꢂ1190 cm
,
t
CAOH at ꢂ1106 and
c
OH at ꢂ835 cm dis-
Fig. 5. The structure of the metal complexes.
play a sharp decrease in their intensities to such an extent
that they nearby vanish. This can be taken as an indication
for the complete removal of OH-group by the Cu2+ ions
(1–3) reacting with the ligand. Since the ligand react with
Cu ions, as gathered from the results of elemental analy-
sis, then each Cu ion would displace only one proton from
H C
3
2
+
N
CH3
2+
N
O
the OH group contained in the ligand molecule.
S
7. Band due to C@O stretching frequency of antipyrine moi-
N
N
H O
2
ety, in the free ligand shift toward lower value in the spec-
S
C
2+
tra of complexes of the Cu (1–3) in accordance with the
O
coordination of oxygen atom of carbonyl a function. This
is due to the decrease in electron density around the
oxygen atom of the carbonyl group.
O
U
N
NH
HN
O
O
O
8. For the nitrato complex (2), three strong bands at 1540,
C
OH2
S
ꢁ
1
N
1385 and 1295 cm are observed corresponding to
and of the nitrato group indicating the presence of a ter-
minal monodentate coordination of the nitrato group [32].
A combination of ( ) which is considered as diagnos-
tic for the monodentate coordination nitrato group has
1 2
t , t
S
t
4
N
1 2
t + t
N
H C
3
ꢁ1
been observed at 1695 cm . The bands due to
3 5
t , t and
CH3
t
6
could not be assigned due to the richness of the spec-
(7)
trum of the complex. Thiocyanato complex (3) has a very
ꢁ
1
ꢁ1
strong band at 2090 cm , a medium band at 775 cm
Fig. 6. The structure of the uranyl complex.
ꢁ
1
and a weak band at 495 cm
corresponding to
t
(CN),
t
(CS) and d(NCS), respectively [33]. The intensity and band
In general, hydrogen bonding involving both NH and OH groups
are proton donors and both AN and AO atoms are proton accep-
tors. It is of interest since much multiplicity of proton donor and
acceptor sites are prevalent in biological systems. Both intra- and
intermolecular OHꢅ ꢅ ꢅN and NHꢅ ꢅ ꢅO may form leading to a number
of structures in simultaneous equilibrium.
position indicate the unidentate coordination of the thiocy-
anate through nitrogen atom.
The possible structure of the Cu(II) complexes (1–3) could be
suggested based on:
(i) the absence of one anion, (ii) the disappearance of C@O, (iii)
the coordination of azo-group, and (iv) the shift of CO group of
antipyrine moiety.
ꢁ1
Again the bands located at 1346 and 1303 cm identified as
ꢁ1
dOH gathered with the two bands at 1228 cm assigned as tCAO

7
82
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
The HL ligand takes its usual anionic form (L) to chelate Cu(II)
through CO of antipyrine moiety, NA of azo group with enol group
Fig. 1C) as the potential binding sites, the aqua ligand and differ-
ent anions just fit the remaining free coordination position.
Under such condition the ligand is of tridentate monobasic nat-
ure with respect to the evidence above, the structure for the novel
complexes are tentatively proposed as follows:
with one proton and there is no other fragment(s) of this signal,
which suggests that only one tautomeric form of the ligand exist
in solution under the experimental conditions. Absence of ACH
(4.40 ppm) proton signal of the ligand (HL) moiety indicated the
existence of the ligand in the azo-enol form. According to
El-Sonbati et al. [5,26,31,37], hydrogen bonding leads to a large
deshielding of the protons. Comparing with the solid state study,
we prefer to assign this signal to NH in complex (7), however,
assignment of this peak to NH cannot be ruled out provided solid
state structural evidence is not considered [38,39]. The main pro-
ton chemical shifts of HL appeared at different values depending
upon the metal anions. As reported in a previous study [38], this
hydrogen bonding leads to a large deshielding of these protons.
(
9
. The absence of any peak attributed to the AN@NA moiety,
implies that the ligand exist predominantly in solution as
the form shown in Fig. 1D. However, in solution and in
the presence of acetate-metals ion, these compounds exist
in a tautomeric equilibrium 1C () 1D. The main change is
observed in the azo stretching vibration, thus suggesting
that the form shown in Fig. 1D prevails. This is rather con-
firmed from the observation of Karabatoses et al. [34]
where the hydrazo formed is more than the azo structure
for similar compounds. This tautomeric form losses
hydrazo proton when complexed with acetato-metals ion
as mononegative chelating agents produces the N@N/NH
1
The H NMR spectral data are reported along with the possible
assignments was found as to be in their expected region [38].
The conclusion drawn from these studies lend further support to
the mode of bonding discussed in their IR spectra. In the spectrum
2
of diamagnetic UO (II) complex, the resonance arising from NH
proton disappears, indicating the chelation of the ligand through
the deprotonated hydrazo NH group. The appearance of signals
due to HC@N [ꢂ8.94 ppm (1H)] protons of the same positions in
the ligand and its diamagnetic complex shows the non-involve-
ment of this group in coordination. Also there is a peak found at
mode of the free ligand. New band assigned to
t(NH) in
the free ligand is absent, suggesting the cleavage of intra-
molecular hydrogen bonding of
tNH group and coordina-
tion of nitrogen to the metals ion.
2
4.66 ppm in the UO (II) complex indicating that coordinated water
1
1
0. The carbonyl absorption band
t
(CO) (of the rhodanine ring)
molecules are presented in the complex (7).
ꢁ1
was shifted to frequencies higher by 25–10 cm for all
complexes (4–7). The change in the carbonyl band position
On the basis of all the above spectral data, an internally hydro-
gen boned azo-enol structure has been proposed for the ligand
(Fig. 1).
[
28] in the IR spectra of the metal complexes (4–7) indi-
cates that the carbonyl group is coordinated to the metals
ions (Figs. 5 and 6).
The 13C NMR spectra of ligand (HL) and diamagnetic complex
(7) display the signals at ꢂ10.86 and 35.82 ppm are due to carbon
1. The ligand orbitals of hydrazo are group theoretically, ener-
getically and occupationally suitable for participation in
3
atoms of methyl groups attached to the pyrazolone rings (H CAC
3
and H CAN). The two kinds of C-atoms of the pyrazolone rings
both donor (M ? L) and acceptor (L ? M)
with the metal ions [35]. Convincing evidence [35] has
been adduced that M ? L -bonding makes a significant
contribution to the bonding in metal complexes, whereas
in Cu(II)-hydrazo rhodanine, Cu ? O -bonding is generally
p-interactions
(MeAC and NAC) give signals at ꢂ136.24 and 138.64 ppm. The
1
3
C NMR spectrum of complex (7) shows signals at ꢂ150.18 and
p
195.86 ppm are due to C-atoms of C@N and C@O group, respec-
tively [26].
p
Therefore, it is clear from these results that the data obtained
1
13
considered to be relatively weak [36]. This idea is sup-
ported by our thermal stability measurements.
from the elemental analyses, IR and H and C NMR spectral mea-
surements are in agreement with each other.
1
2. The acetato-metal(II) complexes (4–6), display bands at
ꢁ1
ꢂ1590 and ꢂ1450 cm due to the asymmetric and sym-
metric modes of vibration characteristic of CH COO,
= 140 cm which is consistent
with the bidentate nature of the acetate group [37].
X-ray diffraction
3
ꢁ1
respectively, and with
D
m
The X-ray diffraction, XRD, patterns of the as-synthesized pow-
der of HL and complexes (4–6) are shown in Fig. 7. The XRD pat-
terns of the ligand (HL) has many sharp diffraction peaks at
around 2h = 10–15° and 2h = 20–25° this indicate that HL is a poly-
crystalline phase (Fig. 7a). For complexes (5) and (6) the peak
According to the structure shown in (Fig. 5) the HL ligand takes
its usual anionic (L) to chelate acetate-Cu(II), Ni(II) and Co(II)
through NA of hydrazo group and oxygen atom of carbonyl group
(Fig. 5) as the potential binding sites, whereas the acetate/aqua
1600
anion just fit the remaining free coordination position.
1
1
1
440
280
120
960
1
13
H and C NMR spectra
1
The H NMR spectrum of the ligand was recorded in DMSO-d
6
at
room temperature supports the occurrence of the form depicted in
Fig. 1. The @CACH and ANACH protons were observed as singlet
at d 2.37–2.55 ppm, respectively, and equivalent to three protons
each. In the aromatic region, a few doublets and in few cases some
overlapping doublets/multiplets are observed in the range d 6.78–
8
6
4
3
00
40
80
20
3
3
(a)
b)
(
8
.40 ppm. These doublets/multiplets are due to aryl protons of
160
0
(
(d)
c)
three rings. Another singlet corresponding to one proton for com-
pound is observed in the range d ꢂ 9.2–9.6 ppm. This signal disap-
1
0
20
30
40
50
60
70
2
peared when a D O exchange experiment was carried out. It can be
2
θ°
assigned either to OH or NH, in either case it is strongly deshielded
because of hydrogen bonding with the other atom (N/O) (Fig. 1). It
may be noted that the integration of this signal perfectly matches
Fig. 7. X-ray diffraction patterns for powder forms (a) HL, (b) [Cu(L)(OAc)(OH
O, (c) [Co(L)(OAc)(OH O and (d) [Ni(L)(OAc)(OH ]ꢅ2H O.
]ꢅ2H
)
2 2
]ꢅ
H
2
2
)
2
2
2
)
2
2

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
783
appeared at 2h = 18° and 2h = 18–26°, respectively, indicates that
both of complexes (5) and (6) are a mixture of crystalline and
amorphous phases (Fig. 7c and d). While complex (4) there is no
significant reflection peaks indicating that the complex (4) is
completely amorphous phase (Fig. 7b).
spectrum for complex (1) present a single absorption band at
ꢁ1
14,880 cm corresponding to the d–d transition, indicating the
2
+
low C
ESR spectra
The spin-Hamiltonian parameters of copper complexes are
2t
symmetry of the Cu ion [45].
Electronic spectra and magnetic moments
listed in Table 5. The spin-Hamiltonian parameters, electronic
absorption spectra and magnetic moment values for the copper
complexes (2–4) elongated distorted octahedral Cu(II) complexes,
bonding parameters can be obtained from the ESR spectrum of
ꢁ
1
*
HL exhibits bands at ꢂ26,360–26,280 cm
(CS) (n ?
p
),
ꢁ1
*
ꢁ1
ꢂ30,560–30,260 cm
(CO) (n ?
p
), ꢂ32,980–33,180 cm
ꢁ1
(
(
H-bonding and association), 40,250–39,900 cm
(phenyl)
*
*
ꢁ1
Ph–Ph ), (
p
–
p
) [5] and ꢂ29,620–29,350 cm transition of phenyl
the complex. The g|| and g
using DPPH free radical as g marker. The variation values in g|| and
of these complexes indicate that the geometry of the com-
\
values were computed from the spectra
*
rings overlapped by composite broad
complexes, the (n ?
p–p
of azo structure. In the
) transition shifts to lower energy at
ꢂ28,660 cm and the band due to the H-bonding and association
*
p
g
\
ꢁ
1
pounds in the solid state is affected by the nature of the coordinat-
*
9
is absent as expected. Furthermore, the (CS) (n–
p
) transition shifts
ing genious. The unpaired electron in this 3d case assigned to
slightly to lower energy and remains almost constant. The (CO)
3dx2ꢁy2 orbital, and the overlapping of this antibonding orbital
with the ligand 2s and 2p r orbital is often determined by the
use of the following equation [46]:
*
(
n ?
of new bands, being attributed to (C@C) as a sequences of
enolization. The band due to ? p transition moves to lower
p
) transition disappears with the simultaneous appearance
*
p
?
p
*
p
2
a
¼ A
k
=P
o
þ ðg ꢁ 2:0023Þ þ K
o
ðg? ꢁ 2:0023Þ þ 0:04
energy. These shifts or disappearance of the bands are indicative
of coordinating of the ligand to metal.
The geometry of the metal complexes has been deduced from
electronic spectra and magnetic moment data of the complexes.
The values of magnetic moment (1.76–2.06 B.M.) for complexes
k
2
where
a
gives an approximate indication of the strength of the
is the dipolar con-
tribution to the hyperfine splitting value A, which is a negative
interaction between the metal and the ligand. P
o
ꢁ1
quantity, and usually assigned the free ion value of 0.036 cm
47]. The constant term of K = 3/7 is equated to the Fermi hyperfine
(1–4) suggest the presence of an unpaired electron.
[
o
The magnetic moment of all the Cu(II) complexes at room
contact term of the free ion, which corrects for the Fermi contact
contributions from excited state configurations of Cu(II), notably
temperature lie in the range of 1.90–2.06 B.M., corresponding to
one unpaired electron. This indicates that these complexes are
monomeric in nature and the absence of metal–metal interaction.
1
10
2
8
1
the 3s 3d and 3s 3d 4s configurations [48]. This is usually con-
sidered to be a constant term for Cu(II) complexes since there is lit-
tle ligand orbital density at the copper nucleus and the ratio of
copper s and d character is assumed to be unchanged in the pres-
ence of ligand [46]. The addition of 0.04 to the sum is an approxi-
mate correction due to the molecular orbital coefficients of the
Electronic spectra of six-coordinate Cu(II) complexes have
2
either D4h or C4v symmetry, and the e
ion term will split B1g, A1g and E
g
and t2g level of the D free
g
level, respectively, (Table 4). Thus
the three spin allowed transitions are expected in the visible and
near IR region. But only few complexes are known in which such
bands are resolved either by Gaussian Analysis or single crystal
polarization studies [40]. These bands may be assigned to follow-
complex that arise from in plane
plane bonding (dxz, dyz, b), where the
= b = 1.0 and where the in plane -bonding (dx2ꢁy2
represents the extent to which the unpaired
electron residues on the central metal ion in the dx2ꢁy2 orbital
1g ground state) and reflects the extent of -bonding to the
ligand. Consequently, a decline in the value of
increase in the valency of the bond. The in-plane
p
bonding (dxy, b
bonding is negligible
) coefficient
1
) and out of
p
p
2
2
2
2
b
1
r
, r
ing transition B1g ? A1g (dx2ꢁy2 ? dz2), B1g ? B2g (dx2ꢁy2 ? dxy
)
2
2
2
is about 0.9. Thus, a
and B1g ? Eg (dx2ꢁy2 ? dzx
d
yz) in order of increasing energy. The
energy level sequency will depend on the amount of distortion due
(
B
r
to ligand field and Jahn–Teller effect [41]. Strong bands in the
2
ꢁ
1
a
indicates an
-covalency
values account for the fraction of the unpaired elec-
tron density to be populated around the Cu(II) ion. In the present
ꢆ24,000 cm observed in the spectra of all Cu(II) complexes are
assigned to O ? Cu and N ? Cu LMCT transitions. In the chloro
r
2
ꢁ1
parameter a
complex (1), a shoulder observed at 23,350 cm is assigned as
Cl ? Cu charge-transfer transition [42]. All the complexes gave
2
ꢁ1
case, the in plane
the above equation, and its value found to be
r-covalency parameter a is calculated by using
d–d bands in the 14,500–1600 cm range [43,44]. The reflectance
2
a
= 0.92 which pro-
vide a reliable measure of the covalency of Cu(II) ions with ligand.
The observed nearly axial symmetry of the g and A tensors can
be explained in terms of the slightly distorted octahedral coordina-
tion around the Cu(II) ion. An octahedral complex with a tetragonal
Table 4
Electronic spectral assignments of the Cu(II) complexes.
Complexa
*
*
p–
p
n–p
LMCT
d–d
elongation would give g|| > g
|| ꢁ g )/g ꢁ g ) with the ground state is B1g
The spectra of the complexes (2–4) show typical axial behavior
with slightly different g|| and g values (Table 5). In these Cu(II)
complexes tensor values of g|| > g > 2.0023 are consistent with
\ e
> g and the tetragonality measure
2
3
4
38,700
38,680
38,670
32,030
32,020
32,170
23,900
23,910
23,910
15,200
14,600
16,000
2
(g
e
\
e
.
a
\
Numbers as given in Table 1.
\
Table 5
The spin Hamiltonian parameters of Cu(II) complexes.
Complexa
g
g
g
G
A
b
a
2
b2
K
2
K
2
c
2
||
\
av.
||
||
\
2
3
4
2.234
2.223
2.241
2.047
2.046
2.050
2.109
2.105
2.114
5.18
5.05
5.00
71.33
62.13
86.35
0.489
0.452
0.539
1.09
1.08
1.07
0.54
0.47
0.55
0.45
0.42
0.49
0.92
0.93
0.91
a
Numbers as given in Table 1.
b
ꢁ4
ꢁ1
A values in 10 cm
.

7
84
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
d
x2ꢁy2 orbital having 2B1g as a ground state term [49,50]. The geo-
for acetate, nitrate and isothiocyanate. Our results are in
agreement with the respective position of the anions as
given in the spectrochemical series [18,25,26].
metric parameter G, which is a measure of the exchange interac-
tion between the copper centers in the polycrystalline
compound, is calculated using the reported equation by others
2. The value of g|| increases with increasing A|| ꢃ 10ꢁ (cm
4
ꢁ1
)
[
51,52]. If G is higher than 4, exchange interaction is negligible,
(Fig. 8).
2
but if G is less than 4, considerable exchange interaction is indi-
cated in the solid complex.
3. The value of
4. The value of
(Fig. 10).
a
a
increases with increasing gav. (Fig. 9).
increases with increasing A|| ꢃ 10 (cm
2
ꢁ4
ꢁ1
)
\
The parameters g||, g and A|| of complexes and the energies of
the d–d transitions are used to calculated the orbital reduction
2
2
\
parameters (K||, K ) and the bonding parameter (a and b ). The
2
factor b which can be evaluated by the expression:
4
2
.114
b ¼ ðg ꢁ 2:0023ÞE= ꢁ 8a2
2
k
o
j
2
¼ ðg ꢁ 2:0023ÞExy= ꢁ 2a2
c
k
o
k
2.112
2.110
2.108
ꢁ1
where k
o
= ꢁ828 cm for the free copper ion and E is the electronic
2
transition energy. The covalency of the in-plan
r
-bonding,
= 0.5 denotes 100%
a values for the present copper complexes
a = 1
2
2
indicates complete ionic character, whereas
covalent bonding. The
a
2
are 0.489 (2), 0.452 (3) and 0.539 (4), supporting that the covalent
2
nature [18] of the bonding. The b parameter gives an indication of
2
2
.106
.104
3
the less covalent. Hathaway [53] pointed out that for pure
ing, K|| ꢆ K = 0.77 and for in-plane -bonding K|| < K , while for
out-of-plane -bonding K < K||. The following simplified expres-
sions are used to calculated K|| and K
r-bond-
\
p
\
p
\
0.44
0.46
0.48
0.50
0.52
0.54
\
:
K
K
k
¼ ðg ꢁ 2:0023ÞE=8k
o
k
2.
Fig. 9. The relation between gav. vs.
a
?
¼ ðg ꢁ 2:0023ÞE=2k
?
o
The observed K|| (0.47–0.55) > K
that the absence of significant in-plane
The g tensor values for the complex (1) indicate distorted trigo-
nal bipyramidal geometry (C ) [54]. The term of fundamental
state may be defined with the help of geometric parameter R
deduced from the relation R = (g )/(g ꢁ g ) [45,51]. If R > 1,
ꢁ g
\
(0.42–0.49) relation indicates
p-bonding.
9
8
0
5
4
2
t
2
3
1
2
2
80
75
z
the term of the ground state is defined by the orbital d , but if
R < 1 it is defined by their orbital d x2 ꢁy. For the complex (1)
2
(R = 2.44), it is clear that the ground state term is d
z
. As g|| > g
\
,
2
the possibility of trigonal bipyramidal geometry has been ruled out
and square pyramidal structure is suggested.
7
0
g1 ¼ 2:262
g2 ¼ 2:2209
g3 ¼ 2:076
65
3
These ESR data showed that:
6
0
0
1
. g|| Values are dependent on the nature of the second coor-
.44
0.46
0.48
0.50
0.52
0.54
dinated ligand (other than L) and can be ordered as:
3
OAc > NO > NCS which in agreement with the electronic
ꢁ
4
ꢁ1
spectral data. For A|| ꢃ 10 (cm ), also, this appears to
Fig. 10. The relation between A|| ꢃ 10ꢁ4 (cm ) vs.
ꢁ1
2.
a
be the order of the strength of metal–anion interactions
4
4
2
2
.050
.049
2
2
2
2
2
.240
.236
.232
.228
.224
2
2.048
2.047
2
3
3
2
.046
60
65
70
75
80
85
90
0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.50
x 10-4 (cm-1)
k 2
A
T
ll
Fig. 8. The relation between g|| vs. A|| ꢃ 10ꢁ (cm ).
4
ꢁ1
Fig. 11. The relation between K2
vs. g .
\ \

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
785
(Fig. 13a). In the present study, the TGA of M(II) complexes (4–6) is
4
taken as a proof for the existing of water molecules as well as the
anions to be coordination sphere. The TGA curves of complexes (4–
2
2
2
2
.240
.235
.230
.225
6) (Fig. 13b–d) show four steps of losing mass. The first step at
2
ꢂ45–125 °C, can be attributed to loss of lattice water molecules.
The second step at 125–227 °C, can be attributed to loss of two
coordinated water molecules. The third step at ꢂ227–437 °C, is
due to loss of one coordinated acetate group for complexes, in
addition to decomposition of a part of the ligand for complexes
(5 and 6). The final weight losses are due to the decomposition
3
of the rest of the ligand molecule leaving metal oxides residue with
contaminated carbon atoms.
2
There are three decomposition stages for UO (II) complex (7).
The first step corresponds to the removal of coordinated water
molecules followed by the subsequent elimination of the ligand
0.46
0.48
0.50
0.52
0.54
0.56
2
kll
3 8
and finally it leaves air stable metal oxide (U O ) as residue at high
temperatures in the range 659–800 °C. The result is in accord with
2
Fig. 12. The relation between K|| vs. g||
.
the composition of metal chelates.
. K|| and K2
2
5
\ \
increase with increasing g|| and g (Figs. 11 and
Kinetic studies
12), respectively.
The kinetic parameters such as activation energy (E
a
), enthalpy
Thermogravimetric analysis
*
*
(DH ), entropy (DS ), and Gibbs free energy change of the
*
decomposition (DG ) are evaluated graphically by employing the
The TGA curves for HL and its M(II) complexes (4–6) are shown
in Fig. 13. The temperature intervals and the percentage of loss of
masses are listed in Table 6. TGA curve of HL, the small loss of mass
Coast–Redfern [55] and Horowitz–Metzger [56] methods.
(
4.77%) in temperature interval range ꢂ65–178 °C is due to evolu-
tion of NH gas. The decomposition of HL starts at about 178 °C via
evolution of H
Coast–Redfern equation
The Coast–Redfern equation, which is a typical integral method,
can represent as:
3
2
S gas, further decomposition of a part of the ligand
100
(a)
100
(b)
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
100
200
300
400
500
600
0
100
200
300
400
500
600
700
800
Temperature (°C)
Temperature (°C)
(c)
(d)
1
00
100
80
8
6
4
2
0
0
0
0
60
4
2
0
0
0
100
200
300
400
500
600
700
800
0
100
200
300
400
500
600
700
800
Temperature (°C)
Temperature (°C)
Fig. 13. TGA curves for (a) HL, (b) [Cu(L)(OAc)(OH
)
2 2
]ꢅH
2
O, (c) [Co(L)(OAc)(OH
)
2 2
]ꢅ2H
2
O and (d) [Ni(L)(OAc)(OH
2 2 2
) ]ꢅ2H O.

7
86
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
Table 6
The thermal analyses data of the HL and its complexes.
Compounda Temp. range
°C)
Found mass loss (calc.) Assignment
%
(
HL
65–178
4.53 (4.89)
3
Evolution of NH gas
178–238
238–357
357–607
10.43 (9.79)
28.36 (28.82)
40.70 (42.65)
Evolution of H S gas
Decomposition of a part of the ligand (C
Decomposition of a part of the ligand (C
2
3
H
H
2
SNO)
O)
7
6
N
3
4
45–114
3.13 (3.44)
8.19 (6.89)
26.40 (25.46)
Loss of one water molecule in outside of the coordination sphere
Loss of two coordinated water molecules
1
2
14–202
02–335
Loss of one coordinated acetate group, further evolution of H
N)
9 8 4
Decomposition of a part of the ligand (C H SN O) leaving CuO residue with contaminated carbon atoms
2
S gas and decomposition of a part of the ligand
2 2
(C H
335–665
39.88 (42.01)
5
6
45–125
7.68 (6.72)
8.06 (6.72)
33.31 (33.01)
25.12 (26.12)
Loss of two water molecules in outside of the coordination sphere
Loss of two coordinated water molecules
Loss of one coordinated acetate group, further decomposition of a part of the ligand (C H S N )
2 2 2 2
125–227
227–437
437–785
6 10 3
Decomposition of a part of the ligand (C H N O) leaving CoO residue with contaminated carbon atoms
45–124
7.18 (6.72)
7.20 (6.72)
33.91 (33.04)
32.52 (32.85)
Loss of two water molecules in outside of the coordination sphere
Loss of two coordinated water molecules
Loss of one coordinated acetate group, further decomposition of a part of the ligand (C H S N )
2 2 2 2
124–222
222–421
421–795
Decomposition of a part of the ligand (C
H
9 10
N
3
O) leaving NiO residue with contaminated carbon atoms
a
Numbers as given in Table 1.
-
-
-
-
-
-
-
-
-
-
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
16.0
-
11.5
12.0
HL
(4)
-
-12.5
-13.0
-13.5
-14.0
-14.5
-15.0
-15.5
o
1
70-359 C
o
142-375 C
0
.0016 0.0017 0.0018 0.0019 0.0020 0.0021 0.0022
(1/T(K))
0.00150
0.00165
0.00180
0.00195
1/T(K))
0.00210
0.00225
(
-
-
-
-
-
-
-
12.0
12.5
13.0
13.5
14.0
14.5
-
-
-
-
-
-
-
12.5
(
5)
(6)
13.0
13.5
14.0
14.5
15.0
15.5
o
1
41-441 C
o
15.0
0
1
50-425 C
.00136 0.00153 0.00170 0.00187 0.00204 0.00221
0
.00150 0.00165 0.00180 0.00195 0.00210 0.00225
(1/T(K))
(1/T(K))
Fig. 14. Coats–Redfern (CR) of the ligand (HL) and its complexes (4–6).
Z
Z
ꢀ
ꢁ
a
T
2
dx
ð1 ꢁ
A
u
E
RT
a
1
For convenience of integration, the lower limit T usually taken
as zero. This equation on integration gives:
¼
exp
ꢁ
dt
ð2Þ
n
0
aÞ
T
1

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
787
0
0
.2
.0
0
.3
.0
HL
(4)
0
-
-
-
-
-
-
-
-
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-
0.3
0.6
-
-0.9
-1.2
-1.5
-1.8
o
o
1
42-375 C
1
70-359 C
-80
-60
-40
-20
0
20
40
60
80
-100 -80 -60 -40 -20
0
20
40
60
80 100
θ (K)
θ (K)
0
.0
(5)
0.0 (6)
0.3
-
-
-
-
-
-
-
-
-
-
-
-
0.3
0.6
0.6
0.9
1.2
1.5
1.8
0.9
1.2
1.5
o
o
1
41-441 C
141-441 C
1.8
-120
-90
-60
-30
0
30
60
90
120
-120 -100 -80 -60 -40 -20
0
20 40 60 80 100
θ (K)
θ (K)
Fig. 15. Horowitz–Metzger (HM) of the ligand (HL) and its complexes (4–6).
Table 7
Kinetic parameters of the HL and its complexes.
Compounda Decomposition temperature
Method Parameter
Correlation coefficient
(°C)
ꢁ1
D *
(J mol
D *
(kJ mol
D *
(kJ mol )
(r)
E
(
a
A (s
)
S
H
G
kJ mol 1
ꢁ
)
ꢁ1 ꢁ1
K
)
ꢁ1
)
ꢁ1
2
3
2
HL
4
170–359
142–375
141–441
150–425
CR
HM
52.2
56.1
3.19 ꢃ 10
1.63 ꢃ 10
ꢁ2.02 ꢃ 10
ꢁ1.88 ꢃ 10
47.9
51.6
156
153
0.9979
0.9977
2
0
1
2
CR
HM
35.4
43.3
7.32 ꢃ 10
8.12 ꢃ 10
ꢁ2.33 ꢃ 10
ꢁ2.13 ꢃ 10
31.0
38.8
155
152
0.9848
0.9756
2
ꢁ
1
2
5
CR
HM
27.6
37.5
4.37 ꢃ 10
ꢁ2.57 ꢃ 10
ꢁ2.31 ꢃ 10
22.9
32.8
168
163
0.9939
0.9918
1
2
1.06 ꢃ 10
0
1
2
6
CR
HM
46.3
45.0
1.76 ꢃ 10
4.43 ꢃ 10
ꢁ2.45 ꢃ 10
ꢁ2.19 ꢃ 10
41.6
40.3
179
163
0.9873
0.9969
2
a
Numbers as given in Table 1.
ꢂ
Þꢃ
ꢂ
ꢃ
lnð1 ꢁ
a
E
RT
a
AR
where k is the Boltzmann constant, h is the Plank’s constant and Ts
is the TG peak temperature.
B
ln ꢁ
¼ ꢁ
þ ln
ð3Þ
2
T
uE
a
A plot of left-hand side (LHS) against 1/T was drawn (Fig. 14). E
is the energy of activation and calculated from the slop and A in
a
Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the approx-
imation methods. These authors derived the relation:
ꢁ1
(
s
) from the intercept value. The entropy of activation calculated
by using the equation:
"
ꢁn#
1
ꢂ
ꢀ
ꢁꢃ
1
ꢁ ð1 ꢁ
a
ꢁ n
Þ
a
E h
Ah
k T
B s
ꢇ
log
¼
;
2
for n – 1
ð5Þ
D
S ¼ 2:303 log
R
ð4Þ
1
2:303RTs

7
88
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
5
4
4
3
3
2
0
5
0
5
0
5
where h = T ꢁ T
reaction; w = mass loss up to time t. The plot of log [log (w
vs. h was drawn and found to be linear from the slope of which E
was calculated. The pre-exponential factor, A, calculated from
equation:
s
, w
c
= w
a
ꢁ w, w
a
= mass loss at the completion
6
a
c
/w )]
a
E
a
2
A
4
¼ h
ꢄ
ꢅi
ð7Þ
DS , is calculated from Eq. (4). The
E
RT
a
RTs
u
exp ꢁ
s
*
The entropy of activation,
*
*
enthalpy activation,
from:
D
H , and Gibbs free energy,
D
G , calculated
5
ꢇ
D
D
H ¼ E
a
ꢁ RT
ð8Þ
ð9Þ
0
.690 0.695 0.700 0.705 0.710 0.715 0.720
ꢇ
ꢇ
ꢇ
o
G ¼
D
H ꢁ T
DS
Ionic radii (A)
*
*
*
a
The calculated values of E , A, DS , DH and DG for the decom-
a
Fig. 16. The relation between E and ionic radii of metal complexes (4–6).
position steps for ligand (HL) and its complexes (4–6) are summa-
rized in Table 7. The kinetic data obtained from the two methods
are comparable and can be considered in good agreement with
each other.
when n = 1, the LHS of Eq. (5) would be log[ꢁlog(1 ꢁ
a)] (Fig. 15).
For a first order kinetic process, the Horowitz–Metzger equation
may write in the form:
ꢂ
ꢀ
ꢁꢃ
As shown in Fig. 16 the activation energy (E
is expected to increase with the increasing thermal stability of
complexes. Therefore, the E value for the complex (6) is higher
a
) of the complexes
W
W
a
c
a
E h
log log
¼
ꢁ log 2:303
ð6Þ
2
2:303RTs
a
Table 8
Antibacterial activity data of ligand (HL) and its Cu(II) complexes. The results were recorded as the diameter of inhibition zone (mm).
Compounda
Concentration (
l
g/ml)
Gram positive bacteria
Gram negative bacteria
Bacillus cereus
Staphylococcus aureus
Escherichia coli
Klebsiella pneumoniae
HL
50
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
2
2
ꢁve
ꢁve
ꢁve
ꢁve
100
50
1
1
50
00
50
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
1
1
2
50
00
50
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
1
1
4
50
00
50
1
1
1
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
1
1
1
1
1
Penicillin
50
00
50
1
3
3
2
2
2
1
3
3
ꢁve
ꢁve
ꢁve
1
1
a
Numbers as given in Table 1.
Table 9
Antifungal activity data of ligand (HL) and its Cu(II) complexes. The results were recorded as the diameter of inhibition zone (mm).
Compounda
HL
Concentration (
l
g/ml)
Aspergillus niger
Fusarium oxysporum
Alternaria alternata
Penicillium italicum
50
ꢁve
ꢁve
ꢁve
1
1
1
2
6
5
7
1
1
00
50
ꢁve
ꢁve
1
50
00
50
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
1
3
ꢁve
ꢁve
1
1
1
2
50
00
50
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
5
5
1
1
4
50
00
50
2
2
2
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
ꢁve
9
4
5
1
1
Miconazole
50
00
50
1
3
4
2
3
3
5
6
6
1
1
2
1
1
a
Numbers as given in Table 1.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
789
one test organism used tested to increase the chance of detection
of their antimicrobial activities.
The results of the antibacterial activities of the synthesized com-
pounds were recorded in Table 8. The ligand (HL) has low antibacte-
rial activity only against E. coli (inhibition zone = 2 mm at
-
-
-
-
-
-
-
-
-
-
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
concentrations = 50 and 100 lg/ml) while no antibacterial activities
for other types of bacteria. Cu(II) complexes of HL have no antibac-
terial activities for all antibacterial activities except complex (4)
has low antibacterial activity only against B. cereus and
K. pneumoniae (inhibition zone = 1 mm for all concentrations).
From Table 8 it is observed that the complex (4) was more
potent antibacterial than the ligand (HL) and the other complexes
against K. pneumoniae. This may support the argument that some
type of biomolecular binding to the metal ions or interchelation
or electrostatic interactions causes the inhibition of biological syn-
thesis. So it can be concluded that the some complexes exhibits
higher antimicrobial activity than the free ligand [58].
The results of the antifungal activities of the synthesized com-
pounds were recorded in Table 9. It found that the ligand (HL)
has no antifungal activities against A. niger. The ligand (HL) was
found to has low antifungal activity against F. oxysporium and A.
alternata (inhibition zone = 1, 1 and 2 mm at concentrations = 50,
Blank
-6
1
3
5
x10
x10
x10
M
M
M
M
M
-
-
-
-
6
6
6
6
7x10
9
1
x10
-6
1x10
M
-
1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0
0.2
E (mV vs. SCE)
Fig. 17. Potentiodynamic polarization curves for the corrosion of C-steel in 2 M HCl
in the absence and presence of various concentrations of HL at 25 °C.
100 and 150
against P. italicum (inhibition zone = 6, 5 and 7 mm at concentra-
tions = 50, 100 and 150 g/ml, respectively). Cu(II) complexes (1,
and 4) of HL have no antifungal activities for A. alternata and F.
lg/ml, respectively), but high effect was observed
l
2
oxysporium activities except complex (1) has low antifungal activ-
ity against A. alternata (inhibition zone of complex (1) = 1 and
3
mm at concentrations = 100 and 150 lg/ml, respectively). It
found that complexes (4) has low antifungal activity against A.
niger (inhibition zone of complex (4) = 2 mm for all concentrations)
and high effect against P. italicum (inhibition zone of complex
(
4) = 9, 4 and 5 mm at concentrations = 50, 100 and 150
respectively), and inhibition zone of complex (2) = 5 and 5 mm at
concentrations = 100 and 150 g/ml, respectively.
lg/ml,
Fig. 18. Equivalent circuit model used to fit the impedance spectra.
l
It is observed that the complex (4) is more potent antifungal
than the ligand (HL) and the other complexes against P. italicum
at concentration = 50 lg/ml.
compared to the other complexes, due to the lower ionic radius
which indicate that the complex (6) is more stable than other
complexes [57].
a
From the values of the energy of activation (E ) of the ligand
(
(
HL) and its complexes (4–6), it is observed that the complexes
4–6) are less stable than the ligand (HL) and may be attributed
Potentiodynamic polarization
to the loss of water molecules from complexes. These results are
inconsistent with our previous results [18].
The entropy of activation energies reflects the thermal stability
of the compounds. The entropy of activation is found to be of neg-
ative values in the HL and its complexes (4–6) which indicate that
Anodic and cathodic polarizations were carried out potentiody-
namic in unstirred 2 M HCl solution in the absence and presence of
various concentrations of the HL at 25 °C over potential range
300 mV ± OCP. The results are represented in Fig. 17. The obtained
potentiodynamic polarization parameters are given in Table 10.
These results indicate that the cathodic and anodic curves obtained
exhibit Tafel-type behavior. Additionally, the form of these curves
is very similar either in the cathodic or in the anodic side, which
indicates that the mechanisms of C-steel dissolution and hydrogen
reduction apparently remain unaltered in the presence of this
additive. Addition of HL decreased both the cathodic and anodic
current densities and caused mainly parallel displacement to the
more negative and a positive value, respectively, i.e. the presence
the decomposition reactions proceed spontaneously [18]. The val-
*
ues of
D
G
is positive considered as favorable or spontaneous
reaction.
Microbiological investigation
The antimicrobial activity of ligand and its complexes (1, 2 and
4) was tested against some bacterial and fungal species. More than
Table 10
Data from potentiodynamic polarization of C-steel in 2 M HCl containing various concentrations of HL at 25 °C.
corr (mA cm 2
ꢁ
)
b
c
(mV decade
ꢁ1
)
ꢁ1
h
%IE
Concentration (molar)
ꢁEcorr (mV vs. SCE)
i
a
b (mV decade )
0
1
3
5
7
9
1
.0
535
516
520
502
515
503
504
21.420
10.820
8.779
8.029
5.878
4.872
4.502
550
451
435
450
399.9
377
379
521
385
370
363
325.4
300
303
–
–
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
6
6
6
6
6
ꢃ 10
0.495
0.590
0.625
0.726
0.773
0.790
49.5
59.0
62.5
72.6
77.3
79.0
ꢃ 10
ꢃ 10
ꢃ 10
ꢃ 10
1 ꢃ 10ꢁ
6

7
90
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
Table 11
EIS data of C-steel in 2 M HCl in the absence and presence of different concentrations of HL at 25 °C.
cm2)
Y
o
(
lX
ꢁ1
s cm
n
ꢁ2
)
n
R
ct
(X
cm2)
C
dl
(
lF cm
ꢁ2
)
h
%IE
Concentration (molar)
R
S
(X
0
1
3
5
7
9
1
.0
2.529
2.419
2.483
3.182
4.721
5.203
6.187
192.70
105.50
87.16
74.24
60.60
51.58
31.89
0.853
0.856
0.863
0.866
0.855
0.884
0.872
31.77
87.01
99.27
145.80
187.00
226.90
279.20
80.13
48.08
46.68
41.36
37.58
31.84
19.50
–
–
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
6
6
6
6
6
ꢃ 10
0.635
0.680
0.782
0.830
0.860
0.886
63.5
68.0
78.2
83.0
86.0
88.6
ꢃ 10
ꢃ 10
ꢃ 10
ꢃ 10
1 ꢃ 10ꢁ
6
of HL in solution inhibits both the hydrogen evolution and the ano-
dic dissolution processes with overall shift of Ecorr to more negative
values with respect to the OCP.
1
00
Potentiodynamic polarization data
EIS data
The results also show that the slopes of the anodic and the
80
a c
cathodic Tafel slopes (b and b were slightly changed on increasing
the concentration of the tested HL. This indicates that there is no
change of the mechanism of inhibition in presence and absence
6
4
2
0
0
0
0
of HL. The fact that the values of b
c
are slightly higher than the val-
ues of b suggesting a cathodic action of the inhibitor. This could be
a
interpreted as an action of mixed inhibitor control over the electro-
chemical semi-reactions. This means that the HL is mixed type
inhibitor, but the cathode is more preferentially polarized than
the anode. The higher values of Tafel slope can be attributed to sur-
face kinetic process rather the diffusion-controlled process [59].
The constancy and the parallel of cathodic slope obtained from
the electrochemical measurements indicate that the hydrogen evo-
lution reaction was activation controlled [60] and the addition of
Pyrazolone azodye did not modify the mechanism of this process.
This result suggests that the inhibition mode of the Pyrazolone
azodye did was by simple blockage of the surface by adsorption.
-
6
-6
-6
-6
-6
-6
0
.0 1 x 10 3 x 10 5 x 10 7 x 10 9 x 10 11 x 10
Concentration (Molar)
Fig. 20. Comparative analysis of ligand (HL) for potentiodynamic polarization
measurements and electrochemical impedance spectroscopy (EIS).
charge transfer resistance and constant phase element, respec-
tively. EIS parameters and % IE were calculated and tabulated in
Table 11. In order to correlate impedance and polarization meth-
ods, icorr values were obtained from polarization curves and
Nyquist plots in the absence and presence of different concentra-
tions of HL using the Stern–Geary equation:
Electrochemical impedance spectroscopy
Impedance diagram (Nyquist) at frequencies ranging from 1 Hz
to 1 kHz with 10 mV amplitude signal at OCP for C-steel in 2 M HCl
in the absence and presence of different concentrations of HL. The
equivalent circuit that describes our metal/electrolyte interface is
babc
i
corr
¼
ð10Þ
s
shown in Fig. 18 where R , Rct and CPE refer to solution resistance,
2:303ðb þ b ÞR
a
c
ct
The obtained Nyquist plot for HL is shown in Fig. 19. Each spec-
trum is characterized by a single full semicircle. The fact that
impedance diagrams have an approximately semicircular appear-
ance shows that the corrosion of C-steel is controlled by a charge
transfer process. Small distortion was observed in some diagrams,
this distortion has been attributed to frequency dispersion [61].
The diameters of the capacitive loop obtained increases in the pres-
ence of HL, and were indicative of the degree of inhibition of the
corrosion process [62].
-
-
-
-
160
140
120
100
Blank
1
3
5
7
9
1
x10-6
x10-6
x10-6
x10-6
x10-6
1x10-6
M
M
M
M
M
M
It was observed from the obtained EIS data that Rct increases
and Cdl decreases with the increasing of inhibitor concentrations.
The increase in Rct values, and consequently of inhibition effi-
ciency, may be due to the gradual replacement of water molecules
by the adsorption of the inhibitor molecules on the metal surface
to form an adherent film on the metal surface. And this suggests
that the coverage of the metal surface by the film decreases the
double layer thickness. Also, this decrease of Cdl at the metal/solu-
tion interface with increasing the inhibitor concentration can
result from a decrease in local dielectric constant which indicates
that the inhibitor was adsorbed on the surface at both anodic
and cathodic sites [63].
-
-
-
-
80
60
40
20
0
0
40 80 120 160 200 240 280 320 360
(Ω cm2)
Comparative analysis for inhibition efficiency (%IE) study of
ligand (HL) is shown in Fig. 20. It is observed that the %IE obtained
from EIS measurements are close to those deduced from polariza-
tion measurements.
Z
real
Fig. 19. Electrochemical Impedance Spectroscopy (EIS) Nyquist plots for C-steel in
M HCl in the absence and presence of different concentrations of HL at 25 °C.
2

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 774–791
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8
(
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Acknowledgement
8
The authors would like to thank Dr. M.I. Abou-Dobara, Botany
Department, Faculty of Science, Damietta University, Egypt for
her help during testing antimicrobial activity.
[
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