Synthesis, structural and corrosion inhibition studies on cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone

Article abstract of DOI:10.1016/j.ica.2011.09.037

Cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, electronic, IR, NMR and ESR spectral techniques. The molecular structures of ligand and its copper(II) complex have been determined by single crystal X-ray diffraction technique. The Cu(II) complex possesses a CuN₂O₂ chromophore with a considerable delocalization of charge. The structure of the complex is stabilized by intermolecular π-π stacking and C-H...π interactions. Hatbh acts as a monobasic bidentate ligand in all the complexes bonding through a deprotonated C-O^- and >CN groups. Electronic spectral studies indicate an octahedral geometry for the Ni(II) complex while square planar geometry for the Co(II) and Cu(II) complexes. ESR spectrum of the Cu(II) complex exhibits a square planar geometry in solid and in DMSO solution. The trend g_|| > g_⊥ > 2.0023 indicates the presence of an unpaired electron in the d_x2-y2 orbital of Cu(II). The electro-chemical study of Cu(II) complex reveals a metal based reversible redox behavior. The Ni(II) complex shows exothermic multi-step decomposition pattern of the bonded ligand. The ligand and its most of the metal complexes show appreciable corrosion inhibition properties for mild steel in 1 M HCl medium. [Co(atbh)₂] complex exhibited the greatest impact on corrosion inhibition among the other compounds.

Full text of DOI:10.1016/j.ica.2011.09.037

Inorganica Chimica Acta 379 (2011) 56–63
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, structural and corrosion inhibition studies on cobalt(II), nickel(II),
copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone
a
b
Vinod P. Singh a, , Pooja Singh , Ashish K. Singh
⇑
a Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
b Department of Chemistry, North West University (Mafikeng Campus), Mmabatho 2735, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 June 2011
Received in revised form 28 August 2011
Accepted 16 September 2011
Available online 24 September 2011
Cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene benzoylhydrazone have
been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, elec-
tronic, IR, NMR and ESR spectral techniques. The molecular structures of ligand and its copper(II) complex
have been determined by single crystal X-ray diffraction technique. The Cu(II) complex possesses a
CuN2O2 chromophore with a considerable delocalization of charge. The structure of the complex is sta-
bilized by intermolecular
p
–
p
stacking and C–Hꢀ ꢀ ꢀ
p interactions. Hatbh acts as a monobasic bidentate
Keywords:
ligand in all the complexes bonding through a deprotonated C–Oꢁ and >C@N groups. Electronic spectral
studies indicate an octahedral geometry for the Ni(II) complex while square planar geometry for the
Co(II) and Cu(II) complexes. ESR spectrum of the Cu(II) complex exhibits a square planar geometry in
solid and in DMSO solution. The trend g|| > g\ > 2.0023 indicates the presence of an unpaired electron
Transition metal complexes
2-Acetylthiophene benzoylhydrazone
Single crystal X-ray diffraction
NMR and ESR studies
in the dx2
orbital of Cu(II). The electro-chemical study of Cu(II) complex reveals a metal based revers-
ꢁy2
Corrosion inhibition
ible redox behavior. The Ni(II) complex shows exothermic multi-step decomposition pattern of the
bonded ligand. The ligand and its most of the metal complexes show appreciable corrosion inhibition
properties for mild steel in 1 M HCl medium. [Co(atbh)2] complex exhibited the greatest impact on cor-
rosion inhibition among the other compounds.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
carboxaldehyde hydrazones [15,16] but the work on 2-acetylthio-
phene hydrazone complexes are rarely reported. In view of the sig-
Thiophene ring containing compounds have been used in tech-
nology as a constructing unit for the synthesis of charge transport-
ing molecules in transistors, organic solar cells and organic light
emitting diodes [1–7]. Because of the bigger radius of the sulfur
atom than carbon, nitrogen and oxygen atoms, its lone pair of elec-
trons can be more easily delocalized within the heterocyclic ring
and the ligand exhibits good charge transfer ability [8]. Some thio-
phene ring containing Schiff bases have been reported as effective
corrosion inhibitors for various metals in acid media [9,10]. Hydra-
zones containing heterocyclic moieties are well known for their
metal binding ability and exhibit interesting coordination behavior
with transition metal ions [11]. Various publications on the metal
complexes of 2-thiophene derivatives have reported the involve-
ment of thiophene–S atom also in coordination with metal along
with N and O [12,13].
nificant role played by the metal complexes of 2-thiophene
derivatives in biological systems and in various other fields, we
motivated to synthesize Co(II), Ni(II), Cu(II) and Zn(II) complexes
with 2-acetylthiophene benzoylhydrazone (Hatbh) and study their
physico-chemical properties and coordination behavior. Since, sev-
eral Schiff bases have recently been investigated as corrosion inhib-
itors for various metals and alloys in acid media [17–20], it was
worthwhile to investigate the effect of synthesized ligand and its
metal complexes on corrosion behavior of mild steel in acid solution.
2. Experimental
2.1. Materials and methods
All analytical reagent grade chemicals were obtained from the
commercial sources and used without further purification. 2-Acet-
yl thiophene was purchased from Spectrochem Pvt. Ltd., India.
Methyl benzoate, hydrazine hydrate (S.D. Fine Chemicals, India)
and solvents (Merck Chemicals, India) were used as such.
Acid hydrazides, hydrazones and their transition metal
complexes have shown their applications in biological systems, ana-
lytical chemistry and as catalysts [14]. Although some work have
been reported on transition metal complexes of 2-thiophene
The precursor benzoylhydrazine, C6H5CONHNH2, was synthe-
sized according to the reported literature method [21] by refluxing
methyl benzoate and hydrazine hydrate in 1:1 M ratio for 4 h.
⇑
Corresponding author. Tel.: +91 9450145060.
E-mail address: singvp@yahoo.co.in (V.P. Singh).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.09.037

V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
57
2.2. Synthesis of ligand
1555 m;
380 m.
m
(C–O)ꢁ 1375;
m
(N–N) 1035w;
m(M–O) 458 m;
m
(M–N)
The ligand, 2-acetyl thiophene benzoylhydrazone (Hatbh) was
synthesized by reacting 25 ml aqueous solution of benzoylhydr-
azine (10 mmol, 1.36 g) with 25 ml methanolic solution of
2-acetylthiophene (10 mmol, 1.10 ml) in a round bottom flask. A
pale yellow colored product was obtained on refluxing the reaction
mixture for 3 h and on cooling at room temperature. The product
was filtered on a Buckner funnel and washed several times with
water followed by methanol. The pure compound was recrystal-
lized from hot methanol and dried in a desiccator over anhydrous
calcium chloride at room temperature. Yield (70%). M.p. 443 K.
Anal. Calc. for C13H12N2OS (244): C, 63.93; H, 4.91; N, 11.47; S,
2.3.3. [Cu(atbh)2]
Brown, yield (60%). M.p. 519 Kd.
l
eff = 1.83 B.M. Anal. Calc. for
C26H22N4O2S2Cu (549): Cu, 11.48; C, 56.83; H, 4.01; N, 10.20; S,
11.66. Found: Cu, 11.50; C, 56.55; H, 3.98; N, 10.16; S, 11.55%. IR
(
m
cmꢁ1
,
m
KBr):
m
(CH3) 3057w;
m
(N@C–Oꢁ) 1580 m;
(C@N)
(M–O) 452 m; m(M–N)
m
1550 m;
(C–O)ꢁ 1369;
m
(N–N) 1039w;
m
370w.
2.3.4. [Zn(atbh)2]
13.11. Found: C, 63.65; H, 4.94; N, 11.40; S, 13.19%. IR (
KBr): (NH) 3328 m; (CH3) 3072w; (C@O) 1650 m;
1577 m;
(N–N) 998w. 1H NMR (DMSO-d6; d ppm): 2.367 (s, 3H,
m
cmꢁ1
m(C@N)
,
Yellow, yield (60%). M.p. 545 K. Anal. Calc. for C26H22N4O2S2Zn
(551): Zn, 11.80; C, 56.62; H, 3.99; N, 10.16; S, 11.62. Found: Zn,
m
m
m
11.70; C, 56.82; H, 4.04; N, 10.26; S, 11.57%. IR (
(CH3) 3062w; (C@N) 1548 m;
(N@C–Oꢁ) 1579 m;
1372; (N–N) 1030w; (M–O) 484 m; (M–N) 357 m. 1H NMR
m
cmꢁ1, KBr):
m
m
m
m
m
(C–O)ꢁ
CH3); 10.765 (s, 1H, NH); 7.596–7.473 (m, 5H, Ar–H); 7.847 (d,
2H, J = 6.3 Hz, thiophene moiety); 7.096 (t, 1H, J = 3.6, thiophene
moiety). 13C NMR (DMSO-d6; d ppm): 14.97 (CH3); 127.59 (C11);
127.83 (C10, C12); 128.35 (C9, C13); 128.88 (C8); 129.11 (C4);
131.55 (C5); 133.99 (C3); 143.24 (C2); 152.69 (C@N); 163.54
(C@O).
m
m
m
(DMSO-d6; d ppm): 2.866 (s, 3H, CH3); 8.281 (d, 2H, J = 2.7,
Ar–H); 7.484 (t, 3H, J = 2.1, Ar–H); 7.970 (d, 1H, J = 4.8, thiophene
moiety); 7.844 (d,1H, J = 3.3, thiophene moiety); 7.239 (t, 1H,
J = 4.5 thiophene moiety). 13C NMR (DMSO-d6; d ppm): 21.71
(CH3); 125.88 (C11); 127.99 (C10, C12); 128.05 (C9, C13); 130.31
(C8); 131.57 (C4); 134.32 (C5); 134.87 (C3); 136.04 (C2); 150.70
(C@N); 160.19 (N@C–Oꢁ).
12
13
14
CH3
N
O
1
S
5
4
2
6
11
7
8
2.4. Physico-chemical measurements
N
H
3
9
10
For the analysis of metal content in the complexes, the complex
was treated with aqua-regia to decompose the organic ligand and
the residue was evaporated to dryness with concentrated sulfuric
acid. The dry residue was dissolved in distilled water and the solu-
tion was used to determine the metal content gravimetrically by
the literature procedure [22]. Carbon, hydrogen and nitrogen con-
tents were determined on an Exeter Analytical Inc. CHN Analyzer
(Model CE-440). The molar conductance of 10ꢁ3 M solutions of
the complexes in DMSO was measured at room temperature on a
Eutech Con 510 Conductivity meter. 1H and 13C NMR spectra of
the ligand and Zn(II) complex were recorded in DMSO-d6 on a JEOL
AL-300 FT-NMR multinuclear spectrometer. Chemical shifts were
reported in parts per million (ppm) using tetramethylsilane
(TMS) as an internal standard. All exchangeable protons were con-
firmed by addition of D2O. Infrared spectra were recorded in KBr on
a Varian 3100 FT-IR spectrophotometer in 4000–400 cmꢁ1 region.
Electronic spectra of the complexes were recorded on a Shimadzu
spectrophotometer, model, Pharmaspec UV-1700 in Nujol. Mag-
netic susceptibility measurements were performed at room tem-
-Acetylthiophene benzoylhydrazone (Hatbh)
2.3. Synthesis of the metal complexes
The cobalt(II), nickel(II), copper(II) and zinc(II) complexes of
2-acetylthiophene benzoylhydrazone (Hatbh) were synthesized
by reacting 25 ml ethanolic solutions of each metal(II) acetate
(5 mmol) with 25 ml hot ethanolic solution of the ligand Hatbh
(10 mmol, 2.54 g) separately, in 1:2 (M:L) M ratio in a round bot-
tom flask. The Co(II), Ni(II) and Zn(II) complexes were formed as
insoluble precipitates after refluxing the reaction mixture for
2–5 h, whereas, the Cu(II) complex was precipitated immediately
during stirring the reaction mixture on a magnetic stirrer at room
temperature. The metal complexes were filtered in a glass crucible,
washed several times with ethanol and finally with diethyl ether
and dried in a desiccator at room temperature. Single crystal of
the copper(II) complex was obtained from dichloromethane solu-
tion by slow evaporation at room temperature.
perature on
a Faraday balance using Hg[Co(SCN)4] as the
calibrant. ESR spectra of the copper(II) complex in solid state at
298 K and in DMSO solution at 77 K was recorded on a Varian
E112 X-band spectrometer using 100 kHz field modulation. The g
factors were quoted relative to the standard g marker TCNE
(g = 2.00277). Electrochemical measurements were performed on
a CHI620c electrochemical analyzer. The electrochemical behavior
of ligand and complexes was examined by employing glassy car-
bon working electrode, Ag/AgCl as reference electrode and plati-
num wire as auxiliary electrode. The working media consisted of
DMSO and tetra (n-butyl) ammonium perchlorate (TBAP) as sup-
porting electrolyte. The cyclic voltammograms of ligand and com-
plexes were recorded at room temperature in the potential range
ꢁ2.2 to ꢁ0.6 V with a scan rate 100 mV sꢁ1. The thermograms
(TGA and DTA) of [Ni(atbh)2(H2O)2] complex was recorded on
NETZSCH-Geratebau GmbH Thermal analyzer, in the temperature
range room temperature to 1000 °C at the rate of 10 °C/min in inert
atmosphere.
2.3.1. [Co(atbh)2]
Reddish brown, yield (70%). M.p. 501 K.
leff = 2.20 B.M. Anal.
Calc. for C26H22N4O2S2Co (545): Co, 10.83; C, 57.25; H, 4.04; N,
10.28; S, 11.74. Found: Co, 10.70; C, 57.02; H, 4.07; N, 10.36; S,
11.62%. IR (
m
cmꢁ1, KBr):
(C–O)ꢁ 1368 m;
m
(CH3) 2924w;
m
(N@C–Oꢁ) 1576 m;
(M–O) 489w;
m
m
(C@N) 1565 m;
(M–N) 375w.
m
m
(N–N) 1027w; m
2.3.2. [Ni(atbh)2(H2O)2]
Green, yield (80%). M.p. 535d K.
leff = 3.14 B.M. Anal. Calc. for
C26H26N4O4S2Ni (581): Ni, 10.15; C, 53.70; H, 4.74; N, 10.20; S,
11.66. Found: Ni, 10.00; C, 53.52; H, 4.70; N, 10.11; S, 11.56%. IR
(
m , KBr): m(CH3) 3066w; m m(C@N)
cmꢁ1 (N@C–Oꢁ) 1580 m;

58
V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
2.5. Crystal structure determination
complex is also soluble in dichloromethane and chloroform. The
complexes melt with decomposition in the temperature range
Single Crystal X-ray diffraction data of the ligand Hatbh and
[Cu(atbh)2] complex were obtained at 295(2) K, on a Oxford Dif-
fraction Gemini diffractometer equipped with CrysAlis Pro., using
501–545 K. The 10ꢁ3 M solutions of the complexes in DMSO show
low molar conductance values (7.93–16.52
room temperature indicating that they are non-electrolytes [27].
X
ꢁ1 molꢁ1 cm2) at
a
graphite mono-chromated Mo Ka (k = 0.71073 Å) radiation
source. The structures were solved by direct methods (SHELXL-97)
and refined against all data by full matrix least-square on F2 using
anisotropic displacement parameters for all non-hydrogen atoms.
All hydrogen atoms were included in the refinement at geometri-
cally ideal position and refined with a riding model [23,24]. The
MERCURY package and ORTEP-3 for Windows program were used
for generating structures [25,26].
3.1. IR spectra
The IR spectral bands observed at 3328, 1650, 1577 and
998 cmꢁ1 in the free ligand are assigned to
m
(N–H),
(N–N), respectively [28]. The bands due to
m(C@O) are not observed in the metal complexes due to enoli-
m
(C@O),
m
and
(C@N) and
m
m(N–H)
zation of carbonyl group of the ligand during complex formation
2.6. Corrosion inhibition measurement
with the metal ion [29]. The appearance of a new m
(C–O)ꢁ band
in all the metal complexes in the range 1366–1375 cmꢁ1 suggests
bonding of ligand to the metal through deprotonated C–Oꢁ group.
In order to study the effect of the synthesized compounds on
corrosion of mild steel in 1 M HCl solution, electrochemical imped-
ance spectroscopy (EIS) of mild steel were carried out in the ab-
sence and presence of different concentrations of ligand and its
complexes. The EIS tests were performed at 303 1 K in a three
electrode assembly. A saturated calomel electrode was used as
the reference and a 1 cm2 platinum foil was used as counter elec-
trode. All the potentials were reported versus SCE. The electro-
chemical impedance spectroscopy measurements (EIS) were
performed using a Gamry instrument Potentiostat/Galvanostat
with a Gamry framework system based on ESA 400 in a frequency
range of 100000 to 0.01 Hz under potentiodynamic conditions,
with amplitude of 10 mV peak-to-peak, using AC signal at Ecorr.
Gamry applications include software DC105 for corrosion, EIS300
for EIS measurements and Echem Analyst version 5.50 software
packages for data fitting. Stock solutions of the studied compounds
were prepared in 10:1 ratio water: DMSO mixture to ensure solu-
bility. The experiments were measured after 30 min of immersion
in the testing solution (no deaeration, no stirring). The working
electrode was prepared from a square sheet of mild steel such that
the area exposed to solution was 1 cm2. The composition of mild
steel used for corrosion experiments was (wt.%) C = 0.17,
Mn = 0.46, Si = 0.26, S = 0.017, P = 0.019 and balance Fe. The charge
transfer resistance values were obtained from the diameter of the
semi circles of the Nyquist plots. The inhibition efficiency of the
inhibitor was calculated from the charge transfer resistance values
using the following equation:
The complexes show two
1565–1548 cmꢁ1. The first one appears due to enolization of the li-
gand and the second one results due to down shift of (C@N) by
12–30 cmꢁ1 on coordination with metal [30]. Furthermore, the
(N–N) has been shifted to higher frequency (30–40 cmꢁ1) in the
m(C@N) in the ranges 1580–1576 and
m
m
complexes compared to the free ligand, indicating the involvement
of one of the nitrogen atom of N–N moiety in bonding with metal.
The Ni(II) complex shows a broad band centered at 3380 cmꢁ1 due
to m(OH) of water molecules. The weak bands observed at 956, 745
and 660 cmꢁ1 in the same complex also suggests the presence of
coordinated water molecules. The bands observed in the range
850–840 cmꢁ1 due to
m(C–S–C) of thiophene ring in ligand remain
at the same position in the metal complexes [31], which indicates
non-involvement of thiophene–S in bonding. The non-ligand bands
in the 445–489 and 353–391 cmꢁ1 ranges have been tentatively
assigned to m(M–O) and m(M–N), respectively.
3.2. 1H and 13C NMR spectra
The 1H NMR spectra of Hatbh in DMSO shows a low field signal
at 10.765 ppm for –NH proton confirming existence of the ligand in
keto form. The disappearance of –NH proton signal in the Zn(II)
complex shows that –NH group of the ligand deprotonates during
complex formation. The resonance signals due to phenyl ring pro-
tons are observed as multiplet between 7.596 and 7.473 ppm in
the ligand and as a doublet and as triplet at 8.281 and 7.484 ppm
in the Zn(II) complex. A sharp singlet at 2.367 ppm due to the
methyl (–CH3) protons of the ligand Hatbh, undergoes a downfield
shift (2.866 ppm) in its Zn(II) complex due to coordination of the
azomethine nitrogen [32,33].
Rict ꢁ R0ct
lR % ¼
ꢂ 100
ð1Þ
ct
Rict
where, R0ct and Rci t are the charge transfer resistance in absence and
in presence of inhibitor, respectively.
The 13C NMR spectrum of ligand Hatbh shows a cluster of peaks
between 143.24 and 127.59 ppm corresponding to the aromatic
carbons of thiophene and phenyl rings. Only four signals for six
phenyl carbons have been observed in the spectra of Hatbh and
its Zn(II) complex because of free rotation about the C7–C8 bond
which lead to C9 and C13 being equivalent, and C10 and C12 being
equivalent. There are separate carbon signals for each thiophene
ring carbon. The peaks observed at 160.19 and 150.70 ppm in the
Zn(II) complex may be due to N@C–Oꢁ and C@N carbons, respec-
tively, showing the presence of two type of >C@N groups in the
complex [34].
For further confirmation of the assignments 2D NMR (HSQC)
spectra were recorded for the ligand and its Zn(II) complex. The
HSQC spectra show no proton signal attached with C8, C7, C6, and
C2 carbon signals in the ligand and its Zn(II) complex, indicating that
they are quaternary carbons. The signals for aromatic protons show
their attachment with the corresponding carbons in the spectra.
3. Results and discussion
It appears from the analytical data that reactions between me-
tal(II) acetates and the ligand Hatbh occur in 1:2 (M:L) M ratio and
Hatbh enolizes and deprotonates during complexation. The reac-
tions may be written as:
2Hatbh þ MðCH3COOÞ2 ꢀ xH2O ! ½MðatbhÞ2ꢃ þ 2CH3COOH þ xH2O
where, M = Co(II), Cu(II), Zn(II)
2Hatbh þ NiðCH3COOÞ2 ꢀ xH2O ! ½NiðatbhÞ2ðH2OÞ2ꢃ þ 2CH3COOH
þ ðx ꢁ 2ÞH2O
The metal complexes are insoluble in water and most of the or-
ganic solvents like ethanol, methanol, chloroform, benzene and
diethyl ether but are soluble in DMF and DMSO. The copper(II)

V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
59
3.3. Electronic spectra and magnetic moments
Copper(II) complex in this study shows eff value 1.83 B.M. cor-
potential located at E1/2 = ꢁ1.23 V, the difference between the
peak, Ep = 0.42 V and peak current ratio Ipa/Ipc = 0.91, suggest
that it is a one electron, quasi reversible process.
D
l
responding to one unpaired electron. This complex exhibits a broad
band centered at 14084 cmꢁ1 which may be due to the envelope of
transitions 2B1g ? 2A1g, ? 2B2g, and ?2Eg suggesting a square pla-
nar geometry for the complex [35]. The leff value, 3.14 B.M. ob-
tained for the nickel(II) complex is in good agreement with a
high spin octahedral species, establishing the triplet ground state.
3.6. Thermal studies
TGA and DTA curves of [Ni(atbh)2(H2O)2] complex (Fig. 2) show
that it loses weight between 120 and 180 °C corresponding to two
water molecules. The removal of water molecules at high temper-
ature indicates that they are coordinated water as indicated by IR
spectra of the complex. The complex shows multi-step decomposi-
tion patterns involving both endothermic and exothermic pro-
cesses. The removal of CH3, thiophene ring and >C@N moieties of
the ligand molecules occurs in the temperature ranges 180–275
and 275–340 °C, respectively. The complex further looses weight
appreciably in the temperature range 340–540 °C due to removal
of C6H5+C@N moieties exothermically and changes to NiO2. The
complex finally, looses oxygen in the range 540–700 °C to form
NiO as the stable end product. The proposed decomposition
scheme for the complex has been given in the Table 1.
Its d–d transition spectra show three bands at 10870, 16530,
3
26485 cmꢁ1 assigned to A2g (F) ? 3T1g(F) (
m
1), ? 3T2g(F) (
m
2) and
?3T1g(P) (
m3) transitions, respectively, are consistent with the
presence of octahedral geometry around the nickel(II) ion [36].
[Co(atbh)2] complex shows leff value, 2.20 B.M. corresponding to
one unpaired electron and suggest a square planar geometry for
the complex [37]. The bands observed for [Co(atbh)2] complex
are in good agreement with the bands reported for the cobalt(II)
square planar complexes [35] showing transition as 2B2g ? 2Eg
and ?2A1g
.
3.4. ESR spectra
3.6.1. Crystal structure of ligand (Hatbh)
Analysis of the ESR spectra of Cu(II) complex in solid state gives
axial signal with g|| = 2.1275, g\ = 2.0227, A|| = 160 and A\ = 63.
These values suggest a square planar stereochemistry for the
complex. The high-field region of the spectrum is partially resolved
into its gx and gy components with gx = 2.0731 and gy = 1.9723, and
g\ was calculated as g\ = ½(gx + gy). This may result as a conse-
quence of the non-equivalence of Cu–O and Cu–N bonds formed
in the XY plane [38]. From the observed trend g|| > g\ > 2.0023, it
The crystallographic data, structural refinement details, se-
lected bond lengths and bond angles of free ligand and the cop-
per(II) complex are given in Tables 2 and 3, respectively. Fig. 3
shows the ORTEP diagram of ligand with the atomic numbering
scheme. The molecule displays an E configuration about the C@N
bond [46]. All the C–C bond lengths (1.383 Å) and C–C–C bond an-
gles (111.86°) of the thiophene ring as well as the C–S bond lengths
(1.713 Å) and C–S–C angle (91.94°) are in accordance with that of a
typical thiophene moiety [47]. The C@O, C(7)–O(1) displays a bond
distance of 1.225 Å which is consistent with a carbonyl double
bond [48]. Both inter- and intra-molecular hydrogen bonding are
clearly visible in crystal structure of the ligand, which stabilize
the molecular conformation. The intra-molecular hydrogen bond
C(9)–H(01)ꢀ ꢀ ꢀN(1), is formed between C(9)–H(01) of the phenyl
ring and imine–N atom, whereas, intermolecular hydrogen bonds
N(2)–H(6)ꢀ ꢀ ꢀO(1) are formed between amido N(2)–H(6) and
carbonyl–O atoms of two adjacent ligand molecules (Table 4),
resulting a dimeric structure (Fig. 4). The torsion angles S(1)–
C(2)–C(6)–N(1) [3.80°], O(1)–C(7)–N(2)–N(1) [ꢁ176.8°] and S(1)–
C(2)–C(6)–C(14) [175.8°] indicate that S(1)–N(1) are cis to each
other but N(1)–O(1) and S(1)–C(14) are trans to each other.
is clear that the unpaired electron lies predominantly in dx2
orbi-
ꢁy2
tal, giving 2B1g as the ground state [39–42]. The exchange interac-
tion parameter (G), defined as G = g|| ꢁ 2.0023/g\ ꢁ 2.0023 for the
present copper(II) complex is 6.137, suggests that the local tetrag-
onal axes are aligned parallel and the exchange interactions be-
tween copper(II) centers in solid state are negligible [43].
The ESR parameters and the d–d transition energies were used
to evaluate the bonding parameters
the covalence of in-plane -bonds, out-of-plane
of-plane -bonds, respectively. The in-plane -bonding parameter
2, as calculated by using Kivelson and Neiman expression [44,45],
is 0.60 which indicates a substantial interaction in the in-plane
a
2, b21 and a0 which measure
2
r
p-bonds and out-
r
r
a
r
-
2
bonding. The a0 parameter is 0.44, suggests that the out-of-plane
-bond strength increases with a corresponding decrease in
2, indicating that the axial
-bonding is decreasing with a corre-
sponding increase in the in-plane
-bonding. The b21 value (0.69)
also indicates a significant out-of-plane bonding in the complex.
r
a
r
r
8
6
p
The solid state ESR spectra at 298 K and DMSO solution spectra
at 77 K give similar type ESR signals with nearly same g and A val-
ues. These observations show that copper stereochemistry is main-
tained in both medium and there is no interaction of DMSO solvent
molecule with the complex.
4
3.5. Cyclic voltammetry
2
The redox potential is an important parameter as it character-
izes the ability of the redox center to transfer electrons and also
to act as a redox catalyst. In metal complexes, the redox behavior
of metal center is also influenced by the nature of the bonded li-
gands to the metal.
The copper(II) complex shows redox reaction in the applied po-
tential range, whereas, the ligand does not show electrochemical
response, revealing that the redox behavior exhibited by the cop-
per(II) complex is purely metal based. In Fig. 1, the CV of
[Cu(atbh)2] shows an anodic peak at the potential Epa = ꢁ1.02 V
and a cathodic peak at the potential Epc = ꢁ1.44 V. The half wave
0
-2
-4
-2.2
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
Potential (V)
Fig. 1. Cyclic voltammogram of the [Cu(atbh)2] complex.

60
V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
Fig. 2. TGA and DTA curves of the [Ni(atbh)2(H2O)2] complex.
Table 1
Thermal decomposition scheme of the complex [Ni(atbh)2(H2O)2].
Sl. no.
Decomp. temp. range (°C)
% Weight loss
Calculated
Energy change
Inference
Observed
1.
2.
3.
4.
5.
120–180
180–275
275–340
340–540
540–700
6.19
6.30
Endothermic
Endothermic
Endothermic
Exothermic
Exothermic
Loss of two coordinated water molecules from the complex
Decomposition of CH3 groups from the two bonded ligand
Decomposition of the thiophene and C@N moieties from the two ligands
Loss of C6H5 and C@N moieties from the two ligands and formation of NiO2
Loss of one oxygen atom to form NiO as the end product
11.35
48.87
82.60
85.35
11.55
49.10
83.00
86.00
Table 3
Table 2
Selected bond lengths (Å) and angles (°).
Crystallographic data for Hatbh and [Cu(atbh)2].
Hatbh
[Cu(atbh)2]
Hatbh
[Cu(atbh)2]
Bond length
N2–C7
N1–C6
N(1)–N(2)
C(7)–C(8)
O(1)–C(7)
Cu–N(1)
Cu–N(1)i
Cu–O(1)
Cu–O(1)i
Empirical formula
Formula weight
T (K)
C13H12N2OS
244.31
293(2)
0.71073
triclinic
P-1
3.9591(3)
10.6343(8)
14.4124(11)
74.653(7)
82.610(6)
79.392(6)
573.11(8)
2
C26H22CuN4O2S2
550.14
293(2)
0.71073
monoclinic
C2/c
19.320(2)
7.6638(7)
16.2932(13)
90
100.723(9)
90
2370.3(4)
4
1.542
1.131
1.344(4)
1.284(4)
1.385(3)
1.500(3)
1.225(3)
1.313(3)
1.305(3)
1.388(3)
1.475(3)
1.300(3)
1.988(2)
1.988(2)
1.9005(16)
1.9005(16)
k (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(°)
Bond angle
b (°)
O(1)–C(7)–N(2)
O(1)–C(7)–C(8)
C(7)–N(2)–N(1)
C(6)–N(1)–N(2)
C(14)–C(6)–N(1)
O(1)–Cu–O(1)i
N(1)–Cu–N(1)i
O(1)–Cu–N(1)
O(1)i–Cu–N(1)i
N(1)–Cu–O(1)i
N(1)i–Cu–O(1)
120.8(3)
119.8(3)
121.0(2)
117.3(2)
126.5(2)
123.60(2)
117.66(19)
110.87(18)
116.10(9)
118.80(2)
153.74(7)
168.51(7)
81.41(7)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.416
0.265
256.0
l
(mmꢁ1
)
F(000)
Crystal size (mm)
h Range for data collection (°)
Number of reflections collected
1132.0
0.35 ꢂ 0.30 ꢂ 0.28 0.39 ꢂ 0.30 ꢂ 0.27
2.18–28.74
2391
2.54–26.47
3569
1960 (0.0185)
81.41(7)
101.23(7)
101.23(7)
Number of independent reflections 1915 (0.0103)
(Rint
)
Number of data/restraints/
parameters
1915/0/155
1960/0/159
3.6.2. Crystal structure of [Cu(atbh)2]
Goodness-of-fit (GOF) on F2
1.071
0.0504, 0.1426
0.0613, 0.1491
0.997
a,b
Fig. 5 shows the ORTEP diagram of [Cu(atbh)2] with the atomic
numbering scheme. Packing diagram of [Cu(atbh)2] on b-axis
showing intra-molecular H-bonding is shown in Fig. 6. In
[Cu(atbh)2] complex, the ligand acts as a monobasic bidentate
ligand coordinating through azomethine nitrogen and a deproto-
nated carbonylate oxygen atom, and the two ligands bond with
R1, wR2
[(I > 2
r
(I))]
0.0299, 0.0753
0.0418, 0.0783
0.277 and ꢁ0.274
a,b
R1, wR2 (all data)
Largest difference in peak and hole 0.473 and 0.600
(e Åꢁ3
)
a
R1
R2 = [
=
R
R
||Fo| ꢁ |Fc||
R|Fo|.
w(|F2o|| ꢁ |F2c|)2/
R .
w|F2o|2]1/2
b

V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
61
Fig. 3. ORTEP diagram of the ligand (Hatbh) showing atomic numbering scheme with
ellipsoid of 30% probability.
Fig. 5. ORTEP diagram of the [Cu(atbh)2] showing atomic numbering scheme with
ellipsoid of 30% probability.
Table 4
Hydrogen bond parameters [Å and °].
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
\(DHA)
Hatbh
N(2)–H(6)ꢀ ꢀ ꢀO(1)i
C(9)–H(01)–N(1)
i = 3 ꢁ x, ꢁy, ꢁz
0.86
0.93
2.12
2.60
2.965(3)
2.943(4)
170
102
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
\(DHA)
[Cu(atbh)2]
C(13)–H(009)ꢀ ꢀ ꢀO(1)
C(14)–H(01A)–O(1)i
i = ꢁx, y, ½ ꢁ z
0.93
0.96
2.46
2.29
2.776(3)
3.110(4)
100
142
Fig. 6. Packing diagram of the [Cu(atbh)2] on b-axis showing intramolecular
H-bonding.
(O(1)–Cu(1)–N(1) = 81.41(7)°),
(O(1)–Cu(1)–N(1i) = 101.24(7)°)
show deviation from the ideal value of 90° suggesting that the
square planar coordination geometry is slightly distorted [51].
The C(6)–N(1) distance (1.305(3) Å) in the complex is longer than
the ligand (1.284(4) Å) due to coordination of azomethine nitrogen
to the metal ion. The N(2)–C(7) distance (1.313(3) Å) in the com-
plex is significantly shorter than the free ligand (1.344(4) Å) as a
result of deprotonation of immine group and formation of >C@N.
The O(1)–C(7) bond length (1.300(3) Å) is significantly longer than
the free ligand (1.225(3) Å) due to enolization of >C@O group dur-
Fig. 4. Diagram showing the formation of intermolecular hydrogen-bonded dimers.
Hydrogen bonds are shown by dashed lines.
ing complexation. These evidences show that the
p electrons orig-
the metal ion in a trans manner of their coordinating sites. The
average bond lengths in the complex are: N(1)–N(2) = 1.388(3)
(L), N(2)–C(7) = 1.313(3) (S), C(7)–C(8) = 1.475(3) (S), N(1)–C(6) =
1.305(3) (L), O(1)–C(7) = 1.300(2) (L) Å (L = Longer, S = shorter)
(Table 3) which are longer or shorter than those of the correspond-
ing distances in the free ligand due to bonding of Cu(II) with the
ligand. In the Cu(II) complex C(7)–O(1), N(1)–N(2) and C(7)–N(2)
bond distances show a partial double bond character due to delo-
inated from deprotonation of the oxamido group are delocalized to
form a conjugated system including N(2), C(7) and O(1) [52]. The
torsion angles of ꢁ177.72(19)° exhibited by S(1)–C(2)–C(6)–C(14)
indicate that the C(14) of methyl group is in trans position to the
sulfur of thiophene moiety. The torsion angles S(1)–C(2)–C(6)–
N(1) [ꢁ4.4°], O(1)–C(7)–N(2)–N(1) [+1.0°] and C(6)–N(1)–N(2)–
C(7) [ꢁ170.8°] indicate that S(1)–N(1) and O(1)–N(1) are cis to
each other but C(6)–C(7) are trans to each other [53].
calization of
p-electrons throughout the CuO(1)C(7)N(2)N(1) ring
The intermolecular N(2)–H(6)ꢀ ꢀ ꢀO(1) and intra-molecular C(9)–
H(01)ꢀ ꢀ ꢀN(1) hydrogen bonding as observed in the ligand are ab-
sent in the complex due to involvement of carbonyl oxygen and
azomethine nitrogen in coordination with Cu(II). Two new intra-
molecular C–Hꢀ ꢀ ꢀO interactions, C(13)–H(009)ꢀ ꢀ ꢀO(1) and C(14)–
H(01A)ꢀ ꢀ ꢀO(1)i are observed in the complex. Crystal packing of
[49]. The Cu–O(1) and Cu–N(1) bond distances are 1.9005 and
1.988 Å which fall in the range reported for Cu(II) square planar
complexes [50]. The shorter Cu–N(1) bond length as compared to
Cu–O(1) indicates that the azomethine nitrogen bonds more
strongly than the carbonylate oxygen. The cis angles in the basal
plane involving the carbonylate oxygen and azomethine nitrogen
the complex is stabilized by
p
–p
and C–Hꢀ ꢀ ꢀ
p interactions

62
V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
Table 5
Different electrochemical impedance parameters for mild steel in 1 M HCl in absence
and presence of 30 ppm concentration of different inhibitors.
Name of
inhibitor
Concentration Cdl (ppm) Rct
of inhibitor
(l
F cm-2
)
E% (X
cm2)
–
–
30
30
41
27
27
29
57
26
16.0 0.43
86.5 0.52
988.9 1.47
601.5 3.37
13.8 3.37
444.5 1.74
–
Hatbh
[Co(atbh)2]
[Ni(atbh)2 (H2O)2] 30
[Cu(atbh)2]
[Zn(atbh)2]
81.5
99.4
96.4
–
30
30
Fig. 7.
along ‘c’ axis.
p–p stacking and C–Hꢀ ꢀ ꢀp interactions between the adjacent molecules
94.7
(Fig. 7). Face to face
phenyl rings of the adjacent molecules with a contact distance of
3.851 Å while the methyl proton approaches the centroid of the
p–p stacking occurs between the centroid of
the reduction of Co as an element due to its less negative
standard electrode potential compared to Fe(II), it seems that a
complex film of cobalt is formed. This process might be occurred
for Co(II), because Hatbh ligand could prevent Co(II)/Co reduc-
tion on the mild steel surface. In presence of [Co(atbh)2], charge
thiophene ring resulting in C–Hꢀ ꢀ ꢀ
p interaction with a contact dis-
tance of 2.966 Å [54,55].
transfer resistance was increased from 16
X
cm2 in blank to
888.9
X
cm2. Similar behavior was observed for Ni(II) complex
3.7. Corrosion inhibition efficiency
but due to its nonplanar structure, inhibition effect caused by
[Ni(atbh)2(H2O)2] is smaller in comparison to that of Co(II) com-
plex [60]. The complex formation between [Zn(atbh)2] and iron
oxide and hydroxide is responsible for corrosion inhibition activ-
ity of [Zn(atbh)2], resulting into precipitation of insoluble Zn(II)
compounds on the surface and hence, further deterioration of
metal is decreased. The least inhibition efficiency of [Cu(atbh)2]
is due to more positive standard electrode potential Cu(II)/Cu
(+0.34 V SCE) compared to Fe(II)/Fe (ꢁ0.44 V SCE), led reduction
of Cu(II) on the surface. Although negatively charged ligands like
Hatbh could stabilize the higher oxidation states of metal [61], it
seems that the change cannot overcome the big difference be-
tween standard electrode potentials of Fe(II)/Fe and Cu(II)/Cu.
Deposition of copper on the steel surface could lead to galvanic
coupling which in turn results in decrease of charge transfer
resistance. This behavior of [Cu(atbh)2] may also be due to dis-
torted square planar geometry. The increased efficiency of metal
complexes compared to Hatbh may be attributed to their larger
size and molecular planarity. Thus, the order of efficiency is as
[Co(atbh)2] > [Ni(atbh)2(H2O)2] > [Zn(atbh)2] > Hatbh > [Cu(atbh)2].
The EIS experiment involves the application of a sinusoidal elec-
trochemical perturbation (potential or current) to the sample that
covers a wide range of frequencies. This multi-frequency excitation
allows (1) the measurement of several electrochemical reactions
that take place at different rates and (2) the measurement of the
capacitance of the electrode. The Nyquist plots for steel in 1 M
hydrochloric acid solution containing different concentrations are
shown in Fig. 8. These plots indicate that the dissolution process
occurs under activation control [56]. The impedance response con-
sists of characteristic semicircles. These semicircles are of a capac-
itive type whose size increases with increasing concentration. The
values of Rct and Cdl, for steel in 1 M hydrochloric acid solution con-
taining 30 ppm concentrations of all the studied compounds are
presented in Table 5. The inhibition efficiency depends on many
factors including adsorption centers, mode of interaction, molecu-
lar size and geometry [57,58]. The adsorption behavior of ligand
Hatbh is argued to presence of unshared electron pair on hetero
atom, p-electrons of aromatic ring and double bond and 3d-orbital
of S-atom [59].
All the complexes, except [Cu(atbh)2], resulted in an increase
of charge transfer resistance and decrease of double layer capac-
itance which would be connected to adsorption or film forma-
tion. Samples exposed to [Co(atbh)2] solution exhibited the
greatest impact among the other studied complexes. Despite
4. Conclusions
The present work describes the synthesis of 2-acetylthiophene
benzoylhydrazone ligand and its Co(II), Ni(II), Cu(II) and Zn(II)
complexes and their characterization by various spectroscopic
techniques. The molecular structures of the ligand and its Cu(II)
complex have also been determined on the basis of their single
crystal X-ray diffraction studies. The intermolecular
p–p and
C–Hꢀ ꢀ ꢀ interactions have been observed in the Cu(II) complex.
p
The two molecules of ligand bond in a trans manner to their coor-
dinating sites with the metal ion through C–Oꢁ and >C@N groups.
The Co(II) and Cu(II) complexes form four-coordinate square planar
geometry, Zn(II) complex tetrahedral, whereas, Ni(II) complex has
six-coordinate octahedral geometry. The cyclic voltammetry of
Cu(II) complex reveals reversible redox behavior. Most of the metal
complexes show appreciable corrosion inhibition properties for
mild steel in 1 M HCl medium.
Acknowledgments
The authors thank the Head, S.A.I.F., Indian Institute of Technol-
ogy, Mumbai for recording the ESR spectra. One of the authors
V.P.S. is grateful to CSIR, New Delhi for financial assistance.
Fig. 8. Nyquist plots for the ligand (Hatbh) and its complexes in 1 M HCl solution.

V.P. Singh et al. / Inorganica Chimica Acta 379 (2011) 56–63
63
[25] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P. McCabe, J.
Pearson, R. Taylor, Acta Crystallogr., Sect. B 58 (2002) 389.
[26] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
Appendix A. Supplementary material
CCDC 770585 and 776075 contain the supplementary crystallo-
graphic data for ligand (Hatbh) and [Cu(atbh)2]. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.09.037.
[27] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[28] A.A. El-Sherif, Inorg. Chim. Acta 362 (2009) 4991.
[29] T. Ghosh, B. Mondal, T. Ghosh, M. Sutradhar, G. Mukherjee, M.G.B. Drew, Inorg.
Chim. Acta 360 (2007) 1753.
[30] S. Banerjee, S. Mondal, W. Chakraborty, Soma Sen, R. Gachhui, R.J. Butcher,
Alexandra M.Z. Slawin, Chitra Mandal, Samiran Mitra, Polyhedron 28 (2009)
2785.
[31] Md.A. Affan, S.W. Foo, I. Jusoh, S. Hanapi, R.T. Tiekink, Inorg. Chim. Acta 362
(2009) 5031.
[32] M.R. Maurya, S. Agrawal, C. Bader, D. Rehder, Eur. J. Inorg. Chem. (2005) 147.
[33] M.R. Maurya, S. Khurana, C. Schulzke, D. Rehder, Eur. J. Inorg. Chem. (2001)
779.
[34] K.K. Narang, M.K. Singh, Inorg. Chim. Acta 131 (1987) 241.
[35] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed., Elsevier,
Amsterdam, 1984.
[36] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bachmann, Advanced Inorganic
Chemistry, sixth ed., Wiley, New York, 2003.
[37] R.L. Dutta, A. Syamal, Elements of Magnetochemistry, Affiliated East-West
Press Pvt. Ltd., New Delhi, 1993.
References
[1] H. Zhang, S. Shiino, A. Shishido, A. Kanazawa, O. Tsutsumi, T. Shiono, T. Ikeda,
Adv. Mater. 12 (2000) 1336.
[2] A.A. Kiryanov, A.J. Seed, P. Sampson, Tetrahedron Lett. 57 (2001) 5755.
[3] T. Narasimhaswamy, N. Somanathan, D.K. Lee, A. Ramamoorthy, Chem. Mater.
17 (2005) 2013.
[4] A.P. Ferreira, J.L. Ferreira da Silva, M.T. Duarte, M.F. Minas da Piedade, M.P.
Robalo, S.G. Harjivan, C. Marzano, V. Gandin, M.M. Marques, Organometallics
28 (2009) 5412.
[5] C.L. Guo, X. Zhuo, Y.-Z. Li, H.G. Zheng, Inorg. Chim. Acta 362 (2009) 491.
[6] B.L. Chen, K.F. Mok, S.C. Ng, M.G.B. Drew, Polyhedron 18 (1999) 1211.
[7] T. Narasimhaswamy, N.S. Somanathan, D.K. Lee, A. Ramamoorthy, Chem.
Mater. 17 (2005) 2013.
[38] V.P. Singh, Spectrochim. Acta, Part A 71 (2008) 17.
[39] A. Sreekanth, M.R.P. Kurup, Polyhedron 22 (2003) 3321.
[40] O.I. Singh, M. Damayanti, N.R. Singh, R.K.H. Singh, M. Mohapatra, R.M. Kadam,
Polyhedron 24 (2005) 909.
[41] M. Base, K. Ohta, Y. Babu, M.D. Sastry, Chem. Phys. Lett. 324 (2000) 330.
[42] R.K. Ray, G.B. Kauffman, Inorg. Chim. Acta 173 (1990) 207.
[43] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143.
[44] D. Kivelson, R. Neiman, J. Chem. Phys. 35 (1961) 149.
[45] H. Maki, B.R. McGarvey, J. Chem. Phys. 29 (1958) 35.
[46] V.P. Singh, S. Singh, Acta Crystallogr., Sect. E 66 (2010) o1172.
[47] J.P. Conde, M.R.J. Elsegood, K.S. Ryder, Acta Crystallogr., Sect. C 60 (2004) o166.
[48] Y.M. Chumakov, B.Y. Antosyak, M.D. Mazus, V.I. Tsapkov, N.M. Samus, J. Struct.
Chem. 41 (5) (2000) 905.
[49] M. Singh, R.J. Butcher, N.K. Singh, Polyhedron 28 (2009) 1197.
[50] M.E. Bluhm, M. Ciesielski, H. Gorls, O. Walter, M. Doring, Inorg. Chem. 42
(2003) 8878.
[51] K. Sundaravel, E. Suresh, M. Palaniandavar, Inorg. Chim. Acta 362 (2009) 199.
[52] J.X. Wang, X.Z. Li, L.N. Zhu, J.Y. Wang, H. Qu, J. Chem. Crystallogr. 40 (2010)
726.
[8] Y. Gong, T. Wang, M. Zhang, C.W. Hu, J. Mol. Strct. 833 (2007) 1.
[9] M. Behpour, S.M. Ghoreishi, N. Soltani, M. Salavati-Niasari, Corros. Sci. 51
(2009) 1073.
[10] Yurt, A. Balaban, S.U. Kandemir, G. Bereket, B. Erkb, Mater. Chem. Phys. 85
(2004) 420.
[11] G.G. Mohamed, M.M. Omar, Ahmed M.M. Hindy, Spectrochim. Acta, Part A 62
(2005) 1140.
[12] H. Abd El-Wahab Zeinab, Spectrochim. Acta, Part A 67 (2007) 25.
[13] N. Nawar, N.M. Hosny, Chem. Pharm. Bull. 47 (7) (1999) 944.
[14] A.S. Pedrares, N. Camina, J. Romero, M.L. Duran, J.A. Garcia Vazquez,
Polyhedron 27 (2008) 3391.
[15] S. Naskar, S. Naskar, M.G.B. Drew, S.I. Gorelsky, B. Lassalle-Kaiser, A. Aukauloo,
D. Mishra, S.K. Chattopadhyay, Polyhedron 28 (2009) 4101.
[16] S.G. Teoh, S.H. Ang, H.K. Fun, Chi-Wi Ong, J. Organomet. Chem. 580 (1999) 17.
[17] M.G. Hosseini, M. Ehteshamzadeh, T. Shahrabi, Electrochim. Acta 52 (2007)
3680.
[18] M. Behpour, S.M. Ghoreishi, N. Soltani, M. Salavati-Niasari, Corros. Sci. 51
(2009) 1073.
[19] R.A. Prabhu, T.V. Venkatesha, A.V. Shanbhag, G.M. Kulkarni, R.G. Kalkhambkar,
Corros. Sci. 50 (2008) 3356.
[53] K.B. Gudasi, R.V. Shenoy, R.S. Vadavi, S.A. Patil, M. Nethaji, J. Mol. Struct. 788
(2006) 22.
[54] M. Singh, A.K. Pandey, R.J. Butcher, N.K. Singh, Polyhedron 28 (2009) 461.
[55] M. Singh, V. Aggarwal, U.P. Singh, N.K. Singh, Polyhedron 28 (2009) 195.
[56] A.M. Abdel-Gaber, M.S. Masoud, E.A. Khalil, E.E. Shehata, Corros. Sci. 51 (2009)
3021.
[20] H. Derya Lece, K.C. Emregül, O. Atakol, Corros. Sci. 50 (2008) 1460.
[21] K.K. Narang, J.P. Pandey, V.P. Singh, Polyhedron 13 (1994) 529.
[22] G.H. Jeffery, J. Bassett, J. Mendham, R.C. Denney, Vogel’s Textbook of
Quantitative Chemical Analyses, fifth ed., Longman, Amsterdam, 1989.
[23] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[24] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, University
of Gottingen, Germany, 1997.
[57] Aytac, J. Mater. Sci. 45 (2010) 6812.
[58] K.C. Emregu, O. Atakol, Mater. Chem. Phys. 83 (2004) 373.
[59] M. Elayyachy, A. El Idrissi, B. Hammouti, Corros. Sci. 48 (2006) 2470.
[60] A.K. Singh, M.A. Quraishi, Corros. Sci. 51 (2009) 2752.
[61] M. Gerloch, E.G. Constable, Transition Metal Chemistry, VCH
Verlagsgesellschaft mbH, Weinheim, 1994. p. 176.