Synthesis, spectral characterization and thermal studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes with 2-amino benzoic acid- and 2-hydroxy benzoic acid thiophen-2-ylmethylene hydrazide

Article abstract of DOI:10.1016/j.molstruc.2012.11.032

A series of metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) with 2-amino benzoic acid thiophen-2-ylmethylene hydrazide (Habth) and 2-hydroxy benzoic acid thiophen-2-ylmethylene hydrazide (Hhbth) have been synthesized. The complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, electronic, IR, NMR, ESR spectra and thermal studies (TGA and DTA). Molecular structure of the Habth ligand was determined by single crystal X-ray diffraction technique. Habth acts as a monobasic bidentate ligand in all its complexes bonding through a deprotonated CO^- and CN groups whereas, Hhbth acts as a monobasic bidentate in its Co(II) and Ni(II) complexes, bonding through a deprotonated CO^- and CN groups and as monobasic tridentate in Cu(II) and Zn(II) complexes bonding through CO, CN and deprotonated (CO)^- groups with the metal ion. Electronic spectra suggest a square planar geometry for Co(II), Ni(II) and Cu(II) complexes of Habth and Co(II) and Ni(II) complexes of Hhbth. However, the Cu(II) and Zn(II) complexes of Hhbth have octahedral geometry. The ESR spectra of Cu(II) complex of Hhbth in the solid state and in DMSO frozen solution show axial signals and suggest the presence of unpaired electron in d^x2-^y2 orbital of Cu(II). The Cu(II) complex of Habth in solid state shows isotropic signal, whereas, axial signal in DMSO frozen solution in the range of tetragonally distorted octahedral geometry due to interactions of DMSO molecules at axial positions. Thermal studies of some of the metal complexes show a multi-step decomposition pattern of bonded ligands in the complex.

Full text of DOI:10.1016/j.molstruc.2012.11.032

Accepted Manuscript
Synthesis, spectral characterization and thermal studies of Co(II), Ni(II), Cu(II)
and Zn(II) complexes with 2-amino benzoic acid- and 2-hydroxy benzoic acid
thiophen-2-ylmethylene hydrazide
Vinod P. Singh, Pooja Singh
PII:
S0022-2860(12)01073-3
DOI:
http://dx.doi.org/10.1016/j.molstruc.2012.11.032
MOLSTR 19369
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
1 October 2012
15 November 2012
16 November 2012
Please cite this article as: V.P. Singh, P. Singh, Synthesis, spectral characterization and thermal studies of Co(II),
Ni(II), Cu(II) and Zn(II) complexes with 2-amino benzoic acid- and 2-hydroxy benzoic acid thiophen-2-ylmethylene
hydrazide, Journal of Molecular Structure (2012), doi: http://dx.doi.org/10.1016/j.molstruc.2012.11.032
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Synthesis, spectral characterization and thermal studies of Co(II),
Ni(II), Cu(II) and Zn(II) complexes with 2-amino benzoic acid- and
2-hydroxy benzoic acid thiophen-2-ylmethylene hydrazide
Vinod P. Singh* and Pooja Singh
Department of Chemistry, Banaras Hindu University, Varanasi-221005, India
Abstract
A series of metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) with 2-amino benzoic
acid thiophen-2-ylmethylene hydrazide (Habth) and 2-hydroxy benzoic acid thiophen-2-
ylmethylene hydrazide (Hhbth) have been synthesized. The complexes were characterized by
elemental analyses, molar conductance, magnetic susceptibility measurements, electronic, IR,
NMR, ESR spectra and thermal studies (TGA & DTA). Molecular structure of the Habth ligand
was determined by single crystal X-ray diffraction technique. Habth acts as a monobasic
bidentate ligand in all its complexes bonding through a deprotonated C-O- and >C=N- groups
whereas, Hhbth acts as a monobasic bidentate in its Co(II) and Ni(II) complexes, bonding
through a deprotonated C-O- and >C=N- groups and as monobasic tridentate in Cu(II) and Zn(II)
complexes bonding through >C=O, >C=N- and deprotonated (C-O)- groups with the metal ion.
Electronic spectra suggest a square planar geometry for Co(II), Ni(II) and Cu(II) complexes of
Habth and Co(II) and Ni(II) complexes of Hhbth. However, the Cu(II) and Zn(II) complexes of
Hhbth have octahedral geometry. The ESR spectra of Cu(II) complex of Hhbth in the solid state
and in DMSO frozen solution show axial signals and suggest the presence of unpaired electron in
2
2
dx -y orbital of Cu(II). The Cu(II) complex of Habth in solid state shows isotropic signal,
whereas, axial signal in DMSO frozen solution in the range of tetragonally distorted octahedral
geometry due to interactions of DMSO molecules at axial positions. Thermal studies of some of
the metal complexes show a multi-step decomposition pattern of bonded ligands in the complex.
Keywords: Thiophene-2-carbaldehyde Schiff bases; Metal complexes; Electronic spectra; NMR
spectra; ESR spectra; Single crystal X-ray diffraction.
___________________________
* Corresponding author.
E-mail address: singvp@yahoo.co.in

1. Introduction
Multidentate acylhydrazone ligands have been extensively used in coordination
chemistry because of their physiological activities, coordinative capabilities and wide range of
applications in various areas. The metal complexes of Schiff bases have been found to exhibit
biological, physicochemical, stereo-chemical, electrochemical, and structural properties [1].
These properties are not inherent due to the Schiff base alone, but also due to the participation of
the metal atom in the complexes. Thiophene ring containing compounds have been used to
synthesize materials such as conjugated polymers, conductivity-based sensory devices, novel
drugs, optoelectronic devices, bio-diagnostics devices, nonlinear optical compounds and
catalysts [2-6].
Thiophene ring containing compounds show an array of biological activities ranging
from anti-microbial, anti-tumour and anti-inflammatory activities [7-9]. In the present study,
thiophene aldehyde was selected for the synthesis of Schiff bases to mimic biological systems
and its involvement in the process of drug design. In view of the analytical, catalytic and
biological applications of the thiophene-2-carbaldehyde Schiff bases and their complexes, we
have synthesized Co(II), Ni(II), Cu(II) and Zn(II) complexes with 2-amino benzoic acid
thiophen-2-ylmethylene hydrazide and 2-hydroxy benzoic acid thiophen-2-ylmethylene
hydrazide ligands and studied their physico-chemical properties and coordination behavior.
2. Experimental
2.1 Materials and methods
All analytical reagent grade chemicals were obtained from the commercial sources and
used without further purification. Thiophene-2-carbaldehyde was purchased from Spectrochem
Pvt. Ltd., India. Methyl anthranilate, methyl salicylate, hydrazine hydrate (S.D. Fine Chemicals,
India) and solvents (Merck Chemicals, India) were used as such.
The precursors 2-amino benzoic acid hydrazide, (NH2)C6H4CONHNH2 and 2-hydroxy
benzoic acid hydrazide, (OH)C6H4CONHNH2 were prepared by refluxing methyl anthranilate
and methyl salicylate, separately with hydrazine hydrate for 4 h in ethanol by using the literature
method [10].
2.2 Preparation of ligands

2.2.1 Preparation of 2-amino benzoic acid thiophen-2-ylmethylene hydrazide (Habth)
The ligand, 2-amino-benzoic acid thiophen-2-ylmethylene-hydrazide (Habth) was
synthesized by reacting 50 ml ethanolic solution of thiophene-2-carbaldehyde (10 mmol, 0.92
ml) with 50 ml ethanolic solution of 2-amino benzoic acid hydrazide (10 mmol, 1.51 g) in a
round bottom flask. The reaction mixture was refluxed for 4 h and a pale yellow colored product
was crystallized on cooling the above solution at room temperature. The product was filtered on
a Buckner funnel and washed several times with ethanol. The pure compound was recrystallized
from hot methanol and dried in a desiccator over anhydrous calcium chloride at room
temperature. Yield (70%). M.p. 457 K. IR (ν cm-1, KBr): ν(NH2) 3459s and 3356s; ν(NH)
1
3178m; ν(C=O) 1645m; ν(C=N) 1616m; β(NH2) 1570w; ν(N−N) 990w. H NMR (DMSO-d6; δ
ppm): 11.567 (s, 1H, NH); 8.579 (s, 1H, HC=N); 6.358 (s, 2H, NH2); 7.219-6.541 (m, 4H, Ar-
13
H); 7.771-7.420 (m, 3H, thiophene moiety). C NMR (DMSO-d6; δ ppm): 116.839 (C4, C5);
117.746 (C6); 119.256 (C3); 127.578 (C11); 128.246 (C10); 129.012 (C12); 130.430 (C9);
133.339 (C1); 143.023 (C2); 156.548 (C8); 161.789 (C7). The single crystal structure of the
ligand was confirmed by XRD.
4
3
2
O
5
13
N
7
8
6
S
1
N
12
11
H
H
9
H2N
10
2-Amino benzoic acid thiophen-2-ylmethylene hydrazide
2.2.2 Preparation of 2-hydroxy benzoic acid thiophen-2-ylmethylene hydrazide (Hhbth)
2-Hydroxy benzoic acid thiophen-2-ylmethylene hydrazide (Hhbth) was synthesized by
reacting 50 ml ethanolic solution of each of thiophene-2-carbaldehyde (10 mmol, 0.92 ml) and 2-
hydroxy benzoic acid hydrazide (10 mmol, 1.52 g) in a round bottom flask. After refluxing the
reaction mixture for 5 h, the solution was cooled at room temperature to crystallize the cream
colored product. The product was filtered on a Buckner funnel and washed several times with
ethanol. The pure compound was recrystallized from hot methanol and dried in a desiccator at
room temperature. Yield (72%). M.p. 435 K. IR (ν cm-1, KBr): ν(OH) 3548b; ν(NH) 3250m;
ν(C=O) 1636m; ν(C=N) 1610m; ν(N−N) 978w. 1H NMR (DMSO-d6; δ ppm): 11.782 (s, 2H, OH

+ NH); 8.664 (s, 1H, HC=N); 7.489-7.407 (m, 2H, Ar-H); 6.978-6.923 (m, 2H, Ar-H); 7.848 (d,
1H, J = 6.9 Hz, thiophene moiety); 7.697 (d, 1H, J = 6.6 Hz, thiophene moiety); 7.155 (t, 1H, J =
4.5, thiophene moiety). 13C NMR (DMSO-d6; δ ppm): 115.941 (C5); 117.260 (C4); 118.949
(C6); 127.924 (C3); 128.477 (C11); 129.326 (C10); 131.394 (C12); 133.784 (C9); 138.828 (C1);
143.765 (C8); 158.946 (C2); 164.583 (C7). The single crystal structure of ligand has been
reported elsewhere [11].
4
3
O
OH
5
2
9
N
7
6
8
S
10
11
N
1
H
H
13
12
2-Hydroxy benzoic acid thiophen-2-ylmethylene hydrazide
2.3 Synthesis of the metal complexes
The cobalt(II), nickel(II), copper(II) and zinc(II) complexes of 2-amino benzoic acid
thiophen-2-ylmethylene hydrazide (Habth) and 2-hydroxy benzoic acid thiophen-2-ylmethylene
hydrazide (Hhbth) were synthesized by reacting 50 ml methanolic solution of each metal(II)
acetate (5 mmol ) in a round bottom flask with 50 ml hot methanolic solution of each ligand
Habth (10 mmol, 2.45 g) and Hhbth (10 mmol, 2.46 g), separately in 1:2 (M:L) molar ratio. The
Co(II), Ni(II) and Zn(II) complexes were formed as insoluble precipitates after refluxing the
reaction mixture for 2-5 h, whereas, Cu(II) complex was precipitated immediately on stirring the
reaction mixture at room temperature. The metal complexes were filtered in a glass crucible and
purified by washing several times with hot methanol to remove the unreacted components and
finally with diethyl ether. The pure complexes were dried in a desiccator over anhydrous calcium
chloride at room temperature.
[Co(abth)2]
Reddish brown, yield (60%). M.p. 515d K. μeff = 2.21 BM. IR (ν cm-1, KBr): ν(NH2)
3449, 3374s; ν(C=N) 1600m; ν(C−O)- 1319m; β(NH2) 1572w; ν(N−N) 1010w; ν(M−O) 452m;
ν(M−N) 383m.
[Ni(abth)2]

Orange, yield (72%). M.p. 525d K. IR (ν cm-1, KBr): ν(NH2) 3452, 3338w; ν(C=N)
1598m; ν(C−O)- 1321m; β(NH2) 1574w; ν(N−N) 1018w; ν(M−O) 448m; ν(M−N) 377m.
[Cu(abth)2]
Brown, yield (72%). M.p. 509d K. μeff = 1.63 BM. IR (ν cm-1, KBr): ν(NH2) 3422, 3321s;
ν(C=N) 1595m; ν(C−O)- 1316m; β(NH2) 1572w; ν(N−N) 1005w; ν(M−O) 448m; ν(M−N) 369w.
[Zn(abth)2]
Yellow, yield (60%). M.p. 535 K. IR (ν cm-1, KBr): ν(NH2) 3451, 3351s; ν(C=N)
1
1593m; ν(C−O)- 1325m; β(NH2) 1578w; ν(N−N) 1015w; ν(M−O) 445m; ν(M−N) 365m. H
NMR (DMSO-d6; δ ppm): 8.197 (d, J = 7.8, 1H, HC=N); 6.543 (s, 2H, NH2); 7.206-6.685 (m,
4H, Ar-H); 7.983-7.699 (m, 3H, thiophene moiety). 13C NMR (DMSO-d6; δ ppm): 114.680 (C5);
116.024 (C4); 116.493 (C6); 126.878 (C3); 130.603 (C11); 131.089 (C10); 133.339 (C12);
133.537 (C9); 133.883 (C1); 140.724 (C2); 149.649 (C8); 173.814 (C7).
[Co(hbth)2]
Reddish brown, yield (62%). M.p. 503d K. μeff = 2.16 BM. IR (ν cm-1, KBr): ν(OH)
3542b; ν(C=N) 1595m; ν(C−O)- 1294m; ν(N−N) 1010w; ν(M−O) 459m; ν(M−N) 393m.
[Ni(hbth)2]
Orange, yield (70%). M.p. >573 K. IR (ν cm-1, KBr): ν(OH) 3550b; ν(C=N) 1583m;
ν(C−O)- 1309m; ν(N−N) 1009w; ν(M−O) 461m; ν(M−N) 386m.
[Cu(hbth)2]
Light green, yield (80%). M.p. 509d K. μeff = 1.85 BM. IR (ν cm-1, KBr): ν(NH) 3251m;
ν(C=O) 1620s; ν(C=N) 1591m; ν(N−N) 999w; ν(M−O) 445m; ν(M−N) 395m.
[Zn(hbth)2]
Yellow, yield (65%). M.p. 535 K. IR (ν cm-1, KBr): ν(NH) 3255m; ν(C=O) 1618s;
1
ν(C=N) 1589m; ν(N−N) 1004w; ν(M−O) 454m; ν(M−N) 389m. H NMR (DMSO-d6; δ ppm):
12.703 (s, 1H, NH); 8.158 (d, J = 7.8, 1H, HC=N); 7.980-7.951 (m, 2H, Ar-H); 7.738 (d, J = 3.9,
1H, thiophene moiety); 7.228 (d, J = 3.9, 1H, thiophene moiety); 7.333 (t, J = 7.2, 1H, thiophene
moiety); 6.914-6.841 (m, 2H, Ar-H). 13C NMR (DMSO-d6; δ ppm): 116.625 (C5); 118.339 (C4);
118.537 (C6); 127.249 (C3); 129.532 (C11); 132.540 (C10); 133.084 (C12); 134.097 (C9);
134.757 (C1); 141.548 (C8); 159.646 (C2); 172.009 (C7).
2.4 Physico-chemical measurements

Carbon, hydrogen and nitrogen contents were determined on an Exeter Analytical Inc.
CHN Analyser (Model CE-440). The molar conductance of 10-3 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 ligands and their Zn complexes 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
confirmed by addition of D2O. Infrared spectra were recorded in KBr on a Varian 3100 FT-IR
spectrophotometer in the 4000-200 cm1 region. Electronic spectra of the complexes were
recorded on a Shimadzu spectrophotometer, model, Pharmaspec UV-1700 in Nujol. Magnetic
susceptibility measurements were performed at room temperature on a Faraday balance using
Hg[Co(SCN)4] as the calibrant and corrected for diamagnetism [12]. The ESR spectra of
copper(II) complexes in solid state at 298 K and in DMSO solution at 77 K was recorded with a
Varian E112 X-band spectrometer using 100 KHz field modulation. g factors were quoted
relative to the standard g marker TCNE (g = 2.00277). The thermograms (TGA & DTA) of the
complexes were recorded on NETZSCH-Geratebau GmbH Thermal analyzer, in the temperature
range room temperature to 1200 0C at the rate of 10 0C/min in inert atmosphere.
2.5 Crystal structure determination
Single Crystal X-ray diffraction data of Habth ligand was obtained at 295(2) K, on a
Oxford Diffraction Gemini diffractometer equipped with CrysAlis Pro., using a graphite mono-
chromated Mo Kα (λ = 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 geometrically ideal position and refined with a riding model [13,
14]. The MERCURY package and ORTEP-3 for Windows program were used for generating
structures [15, 16].
3. Results and discussion
It appears from the analytical data (Table 1) that reactions between metal(II) acetates and
the ligands Habth and Hhbth occur in 1:2 (M:L) molar ratio. In all the complexes of Habth as
well as Co(II) and Ni(II) complexes of Hhbth, the ligands enolize and deprotonate during

complexation, whereas, deprotonation of phenolic proton takes place in Cu(II) and Zn(II)
complexes of Hhbth. The reactions may be written as:
M(CH3COO)2.xH2O + 2Habth
M(CH3COO)2.xH2O + 2Hhbth
[M(abth)2] + 2CH3COOH + xH2O
[M(hbth)2] + 2CH3COOH + xH2O
where, M = Co(II), Ni(II), Cu(II) and Zn(II).
The metal complexes are colored powdery solids. They are insoluble in common organic
solvents viz. ethanol, methanol, chloroform, benzene, cyclohexane, acetone, diethyl ether, DMF
etc., but are soluble in DMSO. In spite of all the effort, none of the metal complexes could be
crystallized for their single crystal X-ray diffraction studies. Most of the complexes melt with
decomposition in the temperature range 503-535 K and a few Hhbth complexes do not melt upto
573 K. 10-3 M solutions of the complexes in DMSO at room temperature show low molar
conductance values (10.93-20.52 ohm-1 mol-1 cm2) and indicate that they are non-electrolytes
[17].
3.1 Electronic spectra and magnetic moments
In the present study, the room temperature magnetic moment data of Cu(II) complexes
with Habth and Hhbth show
values 1.77 and 1.81 B.M., respectively, corresponding to one
eff
unpaired electron. [Cu(abth)2] shows a broad band around 14330 cm-1 which may be due to the
2
2
2
envelope of transitions B1g → A1g, → 2B2g and → Eg suggesting a square planar geometry for
the complex [18]. The [Cu(hbth)2] shows two bands at 15384 and 24315 cm-1 which may be
2
2
2
assigned to the transitions, B1g → B2g (ν1) and → A1g (ν2) suggesting a tetragonally distorted
octahedral geometry [10].
The
values (2.21 and 2.16 B.M.) observed for cobalt(II) complexes correspond to one
eff
unpaired electron and suggest a low spin square planar geometry for both the complexes [12].
The geometry of the complexes are further confirmed by their electronic spectral bands, as
observed at 21768 and 27735 cm-1 for [Co(abth)2], and at 21956 and 27681 cm-1 for [Co(hbth)2].
2
2
2
These bands correspond to the transitions B2g → Eg and → A1g as reported for the cobalt(II)
square planar complexes [18]. The [Ni(abth)2] and [Ni(hbth)2] complexes are diamagnetic,
suggesting a square planar geometry and show two d-d electronic spectral bands for the
1
1
1
transitions, A1g → B1g, → B2g and a charge transfer band, similar to that reported for many
Ni(II) square planar complexes [19].

1
3.2 H and 13C NMR
1H NMR spectra of Hhbth shows an overlapped signal due to >NH proton of >CONH
group and phenolic−OH proton at 11.782 ppm. The disappearance of >NH and Ar−OH protons
in their D2O exchanged 1H NMR spectra confirm their assignments. The downfield shift of >NH
proton in Zn(II) complex suggests the coordination of >C=O to the metal. The disappearance of
phenolic-OH proton signal in the Zn(II) complex indicates the bonding through a phenolate-
oxygen with metal. The −CH=N− proton signal observed at 8.664 ppm in Hhbth, splits into two
resonances in its Zn(II) complex and appears at 8.158 ppm. The shift of −CH=N− signal of
ligand Hhbth to high field in the complex, indicates the participation of azomethine group in
coordination with metal. The multiplet signals observed in the region 7.860-6.923 ppm in Hhbth
are attributed to the aromatic protons overlapped with the thiophene ring protons [20].
Habth exhibits signals at 6.358, 8.579 and 11.567 ppm, which are attributed to the
protons of –NH2, −CH=N- and >NH, respectively. Absence of the >NH proton in the spectra of
the Zn(II) complex, suggests enolization of >C=O, which deprotonates during complexation and
bonding occurs through the enolate-oxygen of the ligand [21)]. A number of signals observed in
Habth around 7.40-6.36 ppm are assigned to the aromatic and thiophene ring protons and show
minor shift in its Zn(II) complex. The signal due to –NH2 protons occurs almost at the same
position in the Zn(II) complex as in the parent ligand. The upfield shift of −CH=N proton in the
Zn(II) complex as compare to the ligand, suggests the coordination of azomethine group to the
metal ion.
13C NMR spectra of Hhbth and Habth show a cluster of peaks between 138.828-115.941
and 143.023-116.839 ppm, respectively, corresponding to aromatic carbons of thiophene and
phenyl ring. In Hhbth, the signals at 143.765, 158.946 and 164.583 ppm, are attributed to -
CH=N-, C-OH and NH-C=O carbons, respectively. These signals shift to 141.54, 159.64 and
172.009 ppm, respectively, in the complex, indicating coordination through the azomethine-N,
phenolate-oxygen and >C=O oxygen. The signals observed at 161.789 and 156.548 ppm in
Habth due to >C=O and HC=N carbons, respectively, are shifted to 173.814 and 149.649 ppm in
its Zn(II) complex, suggesting involvement of these groups in bonding.
3.3 ESR spectra

[Cu(abth)2] exhibits isotropic spectra with intense broad signal having no hyperfine
structure in the solid state at room temperature, 298 K. The complex has giso = 2.0533 and Aiso
=
97, suggesting a geometry with grossly misaligned tetragonal axes. The isotropic spectra arise
due to dipolar exchange and unresolved hyperfine interactions in solid state [19]. ESR spectra of
[Cu(hbth)2] shows an axial signal in solid state with poorly resolved hyperfine structure. The g∥
and g⊥ values (2.3282 and 2.0404, respectively) are >2.04, which indicates that the copper(II) ion
is present in an axial symmetry with all the principal axes aligned parallel. This would be
consistent with a distorted octahedral stereochemistry.
DMSO frozen solution spectra of both the copper(II) complexes at 77 K give axial
signals with well resolved hyperfine structure in the low field region. [Cu(hbth)2] displays ESR
signals nearly at the same positions in the solid state as well as in DMSO frozen solution with
nearly same g and A values. This observation suggests that the copper stereochemistry is
maintained in both medium and there is no interaction of DMSO solvent molecule with the
complex. The g∥ values, 2.3282 and 2.3000 calculated for [Cu(hbth)2] and [Cu(abth)2]
complexes, respectively, fall in the range of distorted octahedral geometry. It has been observed
that the electronic spectra predicted square planar geometry for [Cu(abth)2] in solid state,
whereas, ESR spectra shows a distorted octahedral geometry in DMSO frozen solution. This
may be due to the interaction of DMSO solvent molecules on axial positions of the complex
raising its coordination number. The high field region of spectrum of [Cu(abth)2] is resolved into
gx and gy components, gx = 2.0309, and gy = 1.9966, and g┴ was calculated as g┴ = ½( gx + gy).
This may result as a consequence of the non-equivalence of the Cu−O and Cu−N bonds formed
in the XY plane [22]. The observed trend g∥ >g┴ > 2.0023, indicates that the unpaired electron
2
2
2
lies predominantly in dx -y orbital, giving B1g as the ground state [23-25]. The gav and Aav
values were calculated using the equation; gav = (g∥ + 2g┴)/3; Aav = (A∥ + 2A⊥)/3.
2
Various bonding parameters (α2, α’2 and β1 ) are calculated for both Cu(II) complexes
(Table 2). The in-plane σ bonding parameter α2 calculated for Habth and Hhbth complexes, are
0.769 and 0.861, respectively, which suggest appreciable covalency of the in-plane σ-bonding.
The α’2 parameter (0.263 and 0.176), indicates that the out–of-plane σ-bond strength increases
with the corresponding decrease in α2, and suggests that the axial σ-bonding is decreasing with a
2
corresponding increase in the in-plane σ-bonding. The β1 values (0.84 and 0.88) also indicate a
significant out-of-plane π bonding in the complex [26].

3.4 IR spectra
The IR spectra of the free ligands and their corresponding metal(II) complexes were
compared to get information about the coordination behavior of the ligands with metals. The IR
spectra of Habth show bands at 3178 cm-1 assigned as ν(NH), at 1645 cm-1 as ν(C=O), and at
1616 cm-1 as ν(C=N). In all the Habth complexes, ν(N-H) and ν(C=O) bands are absent. This
indicates the enolization of >C=O group of Habth and deprotonation of enolic proton during
complexation. The appearance of a new ν(C−O)- band in all Habth complexes in the range 1325-
1316 cm-1 suggests bonding of the ligand through deprotonated C−O- group to the metal [27]. In
the complexes, ν(C=N) shifts to lower frequency (15−25 cm-1) than the free ligand suggesting
the coordination of >C=N- group with metal. The ligand Habth shows two sharp bands of
medium intensity at 3356 and 3459 cm-1 assigned as ν(NH2)asym and ν(NH2)sym of free -NH2
group, respectively. In the metal complexes, these bands occur either at the same wave number
as in the ligand or at slightly shifted wave number, indicating the non involvement of -NH2 group
in bonding.
The ligand Hhbth exhibits a broad peak at 3548 cm-1 assigned as ν(OH). The absence of
ν(OH) in its Cu(II) and Zn(II) complexes, indicates deprotonation of –OH group during
complexation. The ν(NH) occurs at 3250 cm-1 in Hhbth, remains unshifted in its Cu(II) and
Zn(II) complexes suggesting no participation of >NH group in bonding [28]. The ν(C=O) band
observed at 1636 cm-1 in Hhbth is shifted to lower wave number by 16−20 cm-1 in its Cu(II) and
Zn(II) complexes indicating the coordination of >C=O group to the metal ion [29, 30]. The
ν(C=N) observed at 1610 cm-1 in the spectra of Hhbth, shifted to lower frequency (15−27 cm-1)
in its all the metal complexes suggesting coordination of the azomethine group with metal [31].
In [Co(hbth)2] and [Ni(hbth)2] complexes, the bands due to ν(N–H) and ν(C=O) are not
observed due to enolization of carbonyl group of the ligand during complex formation. The
appearance of a new ν(C–O)- band in these complexes in the range 1294–1309 cm-1 suggests
bonding of ligand to the metal through deprotonated C–O- group. The ν(N−N) observed at 990
and 978 cm-1 in Habth and Hhbth, respectively, shifts to higher frequency by 15−32 cm-1 in their
complexes, indicates the coordination of one of the nitrogen atom of the >N-N< group with
metal [32]. The metal complexes also show non-ligand bands in the ranges 445-461 cm-1 and
365-395 cm-1, which are tentatively assigned to ν(M-O) and ν(M-N), respectively. On the basis
of above discussion the general structures have been proposed for the metal complexes (Fig. 1.)

3.5 Thermal studies
Thermal studies (TGA and DTA) on [Zn(abth)2] complex indicate that the complex is
highly stable and shows no weight loss upto 240 0C. The partial decomposition of organic ligand
in the complex starts above 240 °C by an endothermic process and removal of thiophene moiety
of the bonded ligands takes place between 240-360 °C. The complex shows multi-step
decomposition pattern of its bonded ligand and removal of (NH2)C6H4 occurs in the temperature
range 360-600 °C through an exothermic process. The bonded HC=N−N=C−O- moiety is
removed from the complex finally by an endothermic process near 1100 °C.
TGA and DTA curves of [Ni(hbth)2] complex show no weight loss upto 314 °C. Then
after, it decomposes through various steps involving both endothermic and exothermic processes.
The removal of thiophene moiety and hydroxy phenyl groups occur in the temperature ranges
314-408 °C and 408-523 °C, respectively, by an exothermic process. The bonded
HC=N−N=C−O- moiety is finally removed near 1200 °C from the complex by an endothermic
process. The proposed decomposition schemes for both the complexes have been given in the
Table 3.
3.6 Crystal structure of 2-amino benzoic acid thiophen-2-ylmethylene hydrazide (Habth)
Fig. 2. shows the ORTEP diagram of the ligand Habth with atomic numbering scheme.
The crystallographic data, structural refinement details, selected bond lengths and bond angles of
free ligand are given in Tables 4 and 5, respectively. The molecule exists in the keto tautomeric
form and displays an E configuration about the >C=N- bond [33]. All the C−C bond lengths
(1.386
) and C−C−C bond angles (112.19º) of the thiophene ring as well as the C−S bond
) and C−S−C angle (91.19º) are in accordance with the reported compounds
lengths (1.712
[34]. The C(7)−O(1) bond length (1.239 A°) is longer than the standard >C=O bond length 1.21
A° and N(2)−C(7) bond length (1.356 A°) is shorter than standard N−C single bond length (1.47
A°). This indicates the delocalization of π electrons in the central part of the molecule. The
C(1)−C(7)−N(2) angle is 116.7 as for an sp2 hybridized C(7) carbon.
The intra-molecular hydrogen bond N(1)−H(1B)∙∙∙O(1), is formed between N(1)−H of
the amino group and carbonyl O atom and C(06)−H(05)∙∙∙N(5), is formed between C(06)−H of
the phenyl ring and N atom of amide group (Table 6). There are five inter molecular hydrogen
bonds which stabilize the molecular conformation (Fig. 3.). The torsional angles

S(1)−C(9)−C(8)−N(3) [-1.93º], O(1)−C(7)−N(2)−N(3) [9.87º], O(1)−C(7)−C(1)−C(2) [18.78º],
N(1)−C(2)−C(1)−C(7) [0.61°] and C(2)−C(1)−C(7)−N(2) [-161.13] indicate that C(2)−N(2) are
trans to each other but S(1)−N(3), O(1)−N(3), O(1)−C(2), N(1)−C(7) are cis to each other.
4. Conclusion
The present work describes the synthesis of 2-amino benzoic acid thiophen-2-
ylmethylene hydrazide (Habth) and 2-hydroxy benzoic acid thiophen-2-ylmethylene hydrazide
(Hhbth) and their Co(II), Ni(II), Cu(II) and Zn(II) complexes and their characterization by
various spectroscopic techniques. The single crystal structure of the ligand Habth has also been
discussed. The Habth ligand bonds with the metal ions through C-O- and >C=N groups forming
four-coordinate square planar geometry. However, Hhbth ligand bonds with Co(II) and Ni(II)
through C-O- and >C=N- but with Cu(II) and Zn(II) through >C=O, Ar-O- and >C=N- groups
2
forming six-coordinate octahedral geometry. ESR spectra of Cu(II) complexes suggest B1g as
the ground state. Thermal studies (TGA & DTA) show multi-step decomposition patterns of the
bonded ligands in the complexes.
5. Supplementary data
CCDC 868514 contains the supplementary crystallographic data for Habth ligand. This
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
The authors thank the Head, S.A.I.F., Indian Institute of Technology, Mumbai for
recording the ESR spectra. One of the authors V.P.S. is grateful to UGC, New Delhi for financial
assistance.
References
[1] F.B. Tamboura, M. Gaye, A.S. Sall, A.H. Barry and T. Jouini, Inorg. Chem. Comm. 5
(2002) 235.
[2] D.M. Vriezema, J. Hoogboom, K. Velonia, K. Takazawa, P.C.M. Christianen, J.C. Maan,
A.E. Rowan and R.J.M. Nolte, Angew. Chem. Int. Ed. 42 (2003) 772.

[3] C. Wu, E.R. Decker, N. Blok, H. Bui, T.J. You, J. Wang, A.R. Bougoyne, V. Knowles,
K.L. Berens, G.W. Holland, T.A. Brock and R.A.F. Dixon, J. Med. Chem. 47 (2004)
1969.
[4] K. Dore, S. Dubus, H.A. Ho, I. Levesque, M. Brunette, G. Corbeil, M. Boissinot, G.
Boivin, M.G. Bergeron, D. Boudreau and M. Leclerc, J. Am. Chem. Soc. 126 (2004)
4240.
[5] M.M.M. Raposo, A.M.R.C. Sousa, G. Kirsch, P. Cardoso, M. Belsey, E.D. Gomes and
A.M.C. Fonseca, Org. Lett. 8 (2006) 3681.
[6] J. Wiedermann, K. Mereiter and K. Kirchner, J. Molecular Catalysis A 257 (2006) 67.
[7] S. Tehranchian, T. Akbarzadeh, M.R. Fazeli, H. Jamalifar and A. Shafiee, Bioorg. Med.
Chem. Lett. 15 (2005) 1023.
[8] K. Starcevic, M. Kralj, I. Piantanida, L. Suman, K. Pavelic and G.K. Zamola, Eur. J.
Med. Chem. 41 (2006) 925.
[9] A.D. Pillai, P.D. Rathod, F.P. Xavier, H. Padh, V. Sudarsanam and K.K. Vasu, Bioorg.
Med. Chem. 13 (2005) 6685.
[10] K.K. Narang, J.P. Pandey and V.P. Singh, Polyhedron 13 (1994) 529.
[11] F.Y. Pan and J.G. Yang, Acta Cryst. E61 (2005) o1172.
[12] R.L. Dutta and A. Syamal, Elements of Magnetochemistry, Affiliated East-West Press
Pvt. Ltd., New Delhi, 1993.
[13] G.M. Sheldrick, Acta Crystallogr. Sect. A 46 (1990) 467-473.
[14] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, University of
Gottingen, Germany, 1997.
[15] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P. McCabe, J. Pearson
and R. Taylor, Acta Crystallogr. Sect. B 58 (2002) 389-397.
[16] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[17] W. J. Geary, Coord. Chem. Rev. 7 (1971) 81-122.
[18] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., New York, Elsevier, 1984.
[19] K.K. Narang and V.P. Singh, Trans. Met. Chem. 18 (1993) 287.
[20] M.A. Affan, S.W. Foo, I. Jusoh, S. Hanapi and E.R.T. Tiekink, Inorg. Chim. Acta 362
(2009) 5031.
[21] H. Yin, J. Li, M. Hong, J. Cui, L. Dong and Q. Zhang, J. Mol. Str. 985 (2011) 261.

[22] A. Sreekanth and M.R.P. Kurup, Polyhedron 22 (2003) 3321.
[23] M. Bose, K. Ohta, Y. Babu and M.D. Sastry, Chem. Phys. Lett. 324 (2000) 330.
[24] R.K. Ray and G.B. Kauffman, Inorg. Chim. Acta 173 (1990) 207.
[25] B.J. Hathaway and D.E. Billing, Coord. Chem. Rev. 5 (1970) 143.
[26] D. Kivelson and R. Neiman, J. Chem. Phys. 35 (1961) 149.
[27] R.J. Butcher, J. Jasinski, G.M. Mockler and E. Sinn, J. Chem. Soc. Dalton Trans. (1976)
1099.
[28] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds,
fourth ed., Wiley Interscience, New York, 1993.
[29] V.P. Singh, A. Katiyar and S. Singh, Biometals 21 (2008) 491-501.
[30] S.A. Shama and H. Omara, Spectroscopy Lett. 34 (2001) 49.
[31] V.P. Singh, Spectrochim. Acta Part-A 71 (2008) 17.
[32] Z.H. Chohan, M.A. Farooq, A. Scozzafava and C.T. Supuran, J. Enz. Inhb. Med. Chem.
17 (2002) 1.
[33] V.P. Singh and S. Singh, Acta Cryst. E66 (2010) o1172.
[34] K.B. Gudasi, R.V. Shenoy, R.S. Vadavi, S.A. Patil and M. Nethaji, J. Mol. Str. 788
(2006) 22.

Figure Captions:
Fig. 1. General structures of the metal complexes.
Fig. 2. ORTEP diagram of Habth ligand showing atomic numbering scheme with ellipsoid of
30 % probability.
Fig. 3. Diagram showing intra-molecular and inter-molecular hydrogen-bonding in Habth.
Hydrogen bonds are shown by dashed lines.

S
H
C
N
O
N
C
N
NH2
M
H2N
C
O
N
C
H
S
[M(abth)2]
Where, M = Co(II), Ni(II), Cu(II) & Zn(II)
S
C
H
C
O
H
N
N
N
O
O
C N
C
N
OH
H
M
S
M'
S
HO
H
O
C
O
N
C
N C
O
C
H
N
H
S
[M(hbth)2]
[M’(hbth)2]
Where, M = Co(II) & Ni(II);
M’ = Cu(II) & Zn(II)
Fig. 1. General structures of the metal complexes.

Figure(s)
Fig. 2. ORTEP diagram of Habth ligand showing atomic numbering scheme with ellipsoid of 30
% probability.

Figure(s)
Fig. 3. Diagram showing intra-molecular and inter-molecular hydrogen-bonding in Habth.
Hydrogen bonds are shown by dashed lines.

Table(s)
Table 1
Analytical data of the ligands and their metal complexes
Compound
(Colour)
Empirical formula
(Formula weight)
M.P./
Decomp. (K)
Analyses found (calc) %
Yield
(%)
ΛM (Ω-1
mol-1cm2)
in DMSO
Metal
C
H
N
Habth
(Light yellow)
C12H11N3OS
(245)
457
435
-
-
58.59
(58.77)
4.53
(4.49)
17.25
(17.14)
70
72
60
72
72
-
Hhbth
(Cream yellow)
C12H10N2O2S
(246)
58.37
(58.54)
4.15
(4.07)
11.50
(11.38)
-
[Co(abth)2]
(Reddish brown)
C24H20N6O2S2Co
(546.9)
515d
525d
509d
10.71
(10.77)
52.49
(52.66)
3.69
(3.65)
15.46
(15.35)
18.71
18.02
15.13
[Ni(abth)2]
(Orange)
C24H20N6O2S2Ni
(546.7)
10.80
(10.74)
52.51
(52.68)
3.62
(3.66)
15.45
(15.37)
[Cu(abth)2]
(Brown)
C24H20N6O2S2Cu
(551.5)
11.48
(11.52)
52.45
(52.22)
3.65
(3.63)
15.34
(15.23)
[Zn(abth)2]
(Yellow)
C24H20N6O2S2Zn
(553)
535
503d
>573
509d
535
11.70
(11.75)
52.21
(52.04)
3.58
(3.61)
15.24
(15.18)
60
62
70
80
65
19.85
16.68
20.01
10.93
17.91
[Co(hbth)2]
(Reddish brown)
C24H18N4O4S2Co
(548.9)
10.66
(10.73)
52.63
(52.47)
3.30
(3.28)
10.33
(10.20)
[Ni(hbth)2]
(Orange)
C24H18N4O4S2Ni
(548.7)
10.80
(10.70)
52.53
(52.49)
3.25
(3.28)
10.09
(10.21)
[Cu(hbth)2]
(Light green)
C24H18N4O4S2Cu
(553.5)
11.55
(11.47)
51.88
(52.03)
3.21
(3.25)
10.20
(10.12)
[Zn(hbth)2]
(Yellow)
C24H18N4O4S2Zn
(555)
11.83
(11.71)
51.69
(51.89)
3.26
(3.24)
10.21
(10.09)
d = decomposition point

Table(s)
Table 2
ESR spectral parameters for copper(II) complexes
2
Complex
Medium
Temp.
(K)
A∥
A⊥
Aav
(G)
g∥
-
g⊥
gav
α2
α'2
β1
(G)
(G)
-
[Cu(abth)2] Solid state
DMSO solution
[Cu(hbth)2] Solid state
DMSO solution
300
77
-
-
Aiso = 97
117
-
giso = 2.0533
2.1092
-
-
180
170
170
86
73
73
2.3000 2.0138
2.3282 2.0404
2.3282 2.0404
0.769 0.263
0.84
300
77
115
2.1363
115
2.1363
0.861 0.176
0.88

Table(s)
Table 3
Thermal decomposition scheme of the complexes
Sl.
Decomp. Temp.
range (ﾷC)
% Weight loss
Energy
Inference
Observed
Calculated
No.
changes
(A)
1.
[Zn(abth)2]
0 - 240
0
0
Endothermic
Endothermic
Complex is stable upto 240 ﾷC.
2.
240 - 360
30.05
29.49
Decomposition of thiophene moiety from the two
bonded ligands of the complex.
3.
4.
360 – 600
62.40
86.75
62.17
86.68
Exothermic
Decomposition of (NH2)C6H5 groups from the bonded
ligands.
Decomposition of HC=N-N=C-O- moiety from the
above partially decomposed ligands of the complex.
~1100
Endothermic
(B)
[Ni(hbth)2]
1.
0 - 314
0
0
Endothermic
Exothermic
Complex is stable upto 314 ﾷC.
2.
3.
4.
314 - 408
408-523
~1200
30.50
30.24
Decomposition of the thiophene moiety from the two
bonded ligands of the complex.
64.25
89.60
64.12
89.86
Exothermic
Decomposition of (OH)C6H5 groups from the bonded
ligands.
Decomposition of HC=N-N=C-O- moiety from the
above partially decomposed ligand of the complex.
Endothermic

Table(s)
Table 4
Crystallographic data for Habth ligand
Habth
C12H11N3OS
245.30
Empirical Formula
Formula weight
Temp, K
293(2) K
0.71073
λ (Å)
Crystal system
Orthorhombic
P212121
Space group
a (Å)
9.4097(12)
14.1614(16)
18.609(2)
90
b (Å)
c (Å)
γ (º)
V (Å3)
2479.7(5)
8
Z
Dcalc (g/cm3)
1.314
μ (mm-1)
0.248
F(000)
1024
Crystal size (mm)
0.31×0.26×0.23
3.08−29.20
9439
θ range for data collection (º)
No. of reflections collected
No. of independent reflections (Rint)
Number of data/restraints/parameters
Goodness-of-fit on F2
R1, wR2 a,b[(I>2σ(I))]
R1, wR2a,b (all data)
Largest difference in peak and hole (e.Å-3)
a R1 = Σ||Fo| – |Fc||Σ|Fo|.
b R2 = [Σw(|F2 | – |F2 |)2/Σw|F2 |2]1/2
4838(0.0348)
4838/0/308
1.011
0.0536, 0.1033
0.0987, 0.1229
0.203 and -0.300
o
c
o

Table 5
Selected bond lengths (Å) and angles (°)
Bond length
N(2)−C(7)
1.355(4)
1.240(3)
1.374(3)
1.366(5)
1.478(4)
1.281(4)
1.435(4)
1.413(5)
1.395(5)
C(3) –C(4)
C(4) –C(5)
C(5) –C(6)
S(1) –C(9)
1.356(6)
1.390(6)
1.379(5)
1.7269(4)
1.415(5)
1.426(6)
1.318(6)
1.696(4)
O(1)−C(7)
N(3) –N(2)
N(1) –C(2)
C(1)−C(7)
C(9) –C(10)
C(10) –C(11)
C(11) –C(12)
S(1) –C(12)
N(3) –C(8)
C(8) –C(9)
C(1)–C(2)
C(2) –C(3)
Bond Angle
N(1) –C(2) –C(1)
C(2) –C(1) –C(7)
C(1)−C(7) –O(1)
O(1) –C(7) –N(2)
C(7) –N(2) –N(3)
N(2)−N(3)−C(8)
N(3)−C(8)−C(9)
C(1)−C(7)−N(2)
122.6(3)
119.6(3)
123.3(3)
120.0(3)
118.6(3)
116.6(3)
121.8(3)
116.7(3)
C(8)–C(9)–S(1)
C(8)–C(9)–C(10)
C(9)–C(10)–C(11)
C(2)–C(1)–C(6)
C(1)–C(6)–C(5)
C(6)–C(5)–C(4)
C(5)–C(4)–C(3)
C(4)–C(3)–C(2)
122.1(3)
126.2(3)
108.8(4)
119.0(3)
121.3(4)
118.7(4)
121.2(4)
121.3(4)

Table 6
Hydrogen bond parameters [Å and ˚] in Habth
D−H∙∙∙A
D−H
0.86
0.86
0.86
0.86
0.86
0.86
0.93
0.93
H∙∙∙A
2.04
2.01
2.84
2.02
2.05
2.58
2.54
2.59
D∙∙∙A
< (DHA)
130
N(1)−H(1B)∙∙∙O(1)
N(2)−H(2)∙∙∙O(2) #1
N(4)−H(4A)∙∙∙S(1) #2
N(4)−H(4B)∙∙∙O(2)
N(5)−H(5A)∙∙∙O(1)
N(5)−H(5A)∙∙∙N(3)
C(06)−H(05)∙∙∙N(5)
C(6)−H(5)∙∙∙O(2) #1
2.676(4)
2.852(4)
3.664(4)
2.659(5)
2.860(4)
3.206(4)
2.846(5)
3.269(4)
167
161
130
157
131
100
130
#1 = 1-x,1/2+y,1/2-z, #2 = 2-x,-1/2+y,1/2-z

*Highlights (for review)
S
H
C
N
O
N
C
N
NH2
M
H2N
C
O
N
C
H
S

*Highlights (for review)
 The ligands enolize and deprotonate during complexation
 Most of the complexes have square planar geometry
 Single crystal structure of Habth ligand displays an E configuration to >C=N- bond
 ESR spectra of a Cu(II) complex show axial interaction of DMSO solvent molecules
 TGA & DTA show a high thermal stability of the complexes