Metal-ion directed synthesis of N2O2 type chelate complexes of Ni(II), Cu(II) and Zn(II): Spectral, thermal and single crystal studies

Article abstract of DOI:10.1016/j.saa.2012.08.004

A set of Ni(II), Cu(II) and Zn(II) complexes of Schiff base have been synthesized by one pot condensation reaction of 2-hydroxy-4-methoxybenzophenone with 1,3-diaminopropane in 1:2:1 molar ratio. They have been characterized by elemental analysis, conductance measurement, thermal analysis (TGA/DTA), FT-IR, ¹H-NMR, EPR spectra, ESI-MS and electronic spectral studies. In order to establish the geometry, a single crystal X-ray structure for [Ni(L)] complex was determined. It crystallizes in monoclinic system having unit cell parameters a = 14.015(5) A, b = 13.391(5) A, c = 14.931(5) A and α = 90.000(5)^o, β = 112.237(5)^o, γ = 90.000(5)^o with P 2₁/c space group. No π-π stacking interaction was obtained in molecular packing diagram. A square-planar geometry has been confirmed for Ni(II) complex. Furthermore, on the basis of elemental analysis, IR, UV-visible and EPR data a square-planar geometry for Cu(II) and a distorted octahedral geometry for the Zn(II) complex has been established. In case of Zn(II) complex NO3- group was found to be coordinated in monodentate fashion. The low molar conductivity values of the complexes measured in chloroform and DMSO suggest their non-ionic nature.

Full text of DOI:10.1016/j.saa.2012.08.004

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 240–246
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Metal-ion directed synthesis of N2O2 type chelate complexes of Ni(II), Cu(II)
and Zn(II): Spectral, thermal and single crystal studies
Seema Yadav a, Musheer Ahmad b, K.S. Siddiqi a,
⇑
a Department of Chemistry, Aligarh Muslim University, Aligarh 202 002, India
b Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
"
Central metal ion is coordinated
with azomethine nitrogen and
phenolic oxygen atoms.
Ni(II) and Cu(II) are square-planar
however Zn(II) is octahedral in
geometry.
Exocyclic –OCH3 facilitates
deprotonation of phenolic oxygen by
resonance.
Single crystal studies of Ni(II)
complex reveal monoclinic crystal
system.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 May 2012
Received in revised form 1 August 2012
Accepted 7 August 2012
Available online 16 August 2012
A set of Ni(II), Cu(II) and Zn(II) complexes of Schiff base have been synthesized by one pot condensation
reaction of 2-hydroxy-4-methoxybenzophenone with 1,3-diaminopropane in 1:2:1 molar ratio. They
have been characterized by elemental analysis, conductance measurement, thermal analysis (TGA/
DTA), FT-IR, 1H-NMR, EPR spectra, ESI–MS and electronic spectral studies. In order to establish the geom-
etry, a single crystal X-ray structure for [Ni(L)] complex was determined. It crystallizes in monoclinic sys-
tem having unit cell parameters a = 14.015(5) Å, b = 13.391(5) Å, c = 14.931(5) Å and
a
= 90.000(5)o,
Keywords:
b = 112.237(5)o, = 90.000(5)o with P 21/c space group. No
c
p–p
stacking interaction was obtained in
Benzophenone
Schiff base
Crystal structure
UV–vis spectra
TGA–DTA
molecular packing diagram. A square-planar geometry has been confirmed for Ni(II) complex. Further-
more, on the basis of elemental analysis, IR, UV–visible and EPR data a square-planar geometry for Cu(II)
and a distorted octahedral geometry for the Zn(II) complex has been established. In case of Zn(II) complex
NOꢀ3 group was found to be coordinated in monodentate fashion. The low molar conductivity values of
the complexes measured in chloroform and DMSO suggest their non-ionic nature.
Ó 2012 Elsevier B.V. All rights reserved.
EPR
Introduction
shown to exhibit antitumor, anti HIV and antimicrobial properties
[3]. Singh and co-workers have shown that Zn(II), Cd(II), Sn(II) and
Schiff bases derived from the condensation of amines with alde-
hyde/ketone are multifunctional macrocyclic ligands and quite of-
ten they mimic the biological molecules [1]. They may be
symmetrical or highly unsymmetrical. It has been reported that
Schiff base complexes of the metal ions with completely filled d orbi-
tals such as, Zn(II) and Cd(II) can be used as an effective emitting
layer showing photophysical properties [2]. They have also been
Pb(II) complexes with Schiff base derived from carboxaldehye and
2-aminophenol are four coordinated. The phenolic group is coordi-
nated after deprotonation. Molecular structure of these complexes
has been optimized and suggested tetrahedral geometry for them
[4].
The property of the complexes depends on the nature of metal
and the ligand. The Schiff base derived from the condensation of
diamines with ketone generally, gives a macrocylic ligand with
cavity of different dimensions. Sometimes, it is made very selective
for certain metal ions owing to their ionic radii which allow them
⇑
Corresponding author. Tel.: +91 9837284930.
E-mail address: ks_siddiqi@yahoo.co.in (K.S. Siddiqi).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.08.004

S. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 240–246
241
2H2O
N
N
O
2
NH2
Reflux 4 h
NH2
OH
OH
OH
H3CO
Scheme 1. Synthesis of ligand (H2L).
H3CO
OCH3
to be appropriately fitted in the cavity. On the other hand the Schiff
bases derived from the condensation of an aldehyde with mono-
amines are unsymmetrical and open at one end. Their selectivity
is therefore, lost and metal ions of varying ionic radii may be coor-
dinated [5–7].
It has been shown from a study of Ni(II) and Cu(II) complexes of
thiosemicarbazone derived from hydroxybenzophenone and 3,4-
methylsemicarbazide that the ligand coordinates in three different
modes. Mononuclear and polynuclear complexes of Cu(II) with thi-
osemicarbazone act as models for galactose oxidase and as a redox
catalyst [8]. Complexes of lanthanides with tripodal ligands con-
taining OH group has been reported. On the basis of their interac-
tion with DNA it has been shown that they have potential as
therapeutic agent and DNA probes [9].
In a very recent paper [10] it has been reported that the Mn(II),
and Cu(II) complexes with thiocarbazide derivatives have different
stereochemistry. The Mn(II) is octahedral while the Cu(II) has been
reported to be square-planar. They are nano crystalline in nature.
The tetradentate N2O2 type Schiff base complexes with Cu(II),
Ni(II) and Zn(II) ions are square-planar [11]. They have been shown
to be active against Staphylococcus aureus, Pseudomonas aeruginosa
and Excherichia coli. The activity of Schiff base against microbes is
enhanced after complexation with metal ions. Bimetallic com-
plexes with Schiff bases have been studied mainly to explore their
stereochemistry and activity against bacteria and fungi. The homo-
bimetallic Cu(II) complexes are of special interest so as to correlate
the spin–spin interaction between the two metal ions. They also
exhibit enzymatic properties [12]. Intelligent design of Schiff base
may lead to the formation of supramolecule which may be sym-
metrical or unsymmetrical and can be used as spin cross over
molecular magnetic material [13,14]
ity bridge in chloroform and DMSO. The IR spectra (600–
4000 cmꢀ1) were recorded on a Spectrolab Interspec FT/IR-2020
spectrometer as KBr disc. Far IR spectra (200–500 cmꢀ1) were re-
corded using CsBr. Electronic spectra were recorded at room tem-
perature on a Perkin Elmer Lambda-35 UV–vis spectrophotometer
in chloroform and DMSO solutions. 1H NMR spectrum of the ligand
was recorded on Bruker Advance 500 MHz Spectrometer in CDCl3
at IIT, Madras. The EPR spectrum of the copper complex was re-
corded at liquid N2 temperature in DMSO with JEOL FA 200 EPR
spectrometer operating at X-band microwave frequency region
(8.65–9.75 GHz) with 100 kHz modulation frequency using DPPH
as standard g marker at University of Hyderabad, India. The TGA/
DTA was done with a Simultaneous DTG-60H thermal analyzer un-
der static nitrogen atmosphere at a heating rate of 10 °C/min. using
Al2O3 as reference. The ESI–MS were recorded with a Waters
Micromass Q-Tof Micro LC-MS system at SAIF, Punjab University,
Chandigarh, India.
Synthesis of ligand (H2L)
The ligand H2L (L = 1-Phenyl-1-(20-hydroxy-40-methoxy)meth-
ylidene-1,3-propanediamine) was synthesized (Scheme 1) by
refluxing for 4 h a methanolic (15 ml) solution of 1,3-propanedi-
amine (1 mmol, 0.083 ml) and 15 ml solution of 2-hydroxy-4-
methoxybenzophenenone (2 mmol, 0.456 g) in the same solvent.
A yellow precipitate appeared under reflux. It was cooled to room
temperature, filtered and washed with cold methanol and dried in
vacuum over CaCl2.
Synthesis of complexes
In this project we are reporting the synthesis of a novel sym-
metrical N2O2 tetradentate open ended Schiff base ligand and its
complexes with Ni(II), Cu(II) and Zn(II) by in situ condensation of
the two essential components of the ligand 2-hydroxy-4-methoxy-
benzophenone and 1,3-propanediamine in presence of the metal
ions. The crystal and molecular structure of the Ni(II) complex
has been determined by a single crystal x-ray diffraction study.
An effort has been made to see the influence of exocyclic –OCH3
group on the structure and properties of the coordinated ligand.
The complexes were synthesized by direct method (Scheme 2).
To a boiling methanolic (15 ml) solution of hydrated metal nitrates
(1 mmol), was added 2-hydroxy-4-methoxybenzophenone
(2 mmol, 0.456 g) (20 ml) drop wise followed by the addition of
one mmol of 1,3-propanediamine (0.083 ml) dissolved in metha-
nol. In case of Ni(II) the resulting solution was refluxed for about
20 h. The product was monitored by TLC and when a single spot
was obtained the clear solution was left for seven days which
yielded good quality single crystals. However, in the case of Cu(II)
and Zn(II) violet and white precipitates were obtained after 10 h of
refluxing. It was cooled to room temperature and filtered. They
were washed with cold methanol and dried in vacuum over anhy-
drous CaCl2.
Experimental
Material and methods
X-ray crystallographic study and structure refinement
1,3-Diaminopropane (Fluka), M(NO3)2.nH2O (BDH) were used
as supplied. 2-Hydroxy-4-methoxybenzophenone (Sigma) and
methanol were of analytical grade.
Single crystal X-ray data of complex [Ni(L)] were collected at
100 K on a Bruker SMART APEX CCD diffractometer using graphite
Elemental analysis was carried out with Carlo-Erba 1106. The
molar conductivity was measured with a CM-82 ELICO conductiv-
monochromator MoK
absorption coefficients, scattering factors for the atoms and the
a radiation (k = 0.71073 Å). The linear

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S. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 240–246
Table 1
Crystal data and structure refinement of [Ni(L)].
[Ni(L)]
Empirical formula
Color/shape
Crystal size
Formula weight
Space group
Temperature (K)
Cell lengths
C31H28N2ꢁNiO4
Dark green/square shaped/Block
O
M(NO3)2. nH2O
2
0.15 mm ꢂ 0.17 mm ꢂ 0.23 mm
NH2
NH2
551.26
P 21/c
100
OH
a = 14.015(5) Å, b = 13.391(5) Å,
c = 14.931(5) Å
= 90.000(5)o, b = 112.237(5)o,
Reflux
2 H2O
Cell angles
a
c
H3CO
= 90.000(5)o
Cell volume (Å3)
Formula units/unit cell
GOOF
2593.77(16)
4
1.025
F (000)
1152
h max
26
h min
2.12
1.412
0.789
Densitycalc. (g cmꢀ3
)
l
(mmꢀ1
)
Diffractometer/scan
Radiations used, graphite
monochromator
Refl. collected
Independent refl.
Index ranges
Data completeness
Final R indices
[I > 2r(I)]
Bruker SMART CCD
Mo Ka (k = 0.71073)
N
N
O
M
5106
4370
17(h),16(k),18(l)
1.000
R1 = 0.0283
wR2 = 0.0723
0.0361
O
H3CO
OCH3
R indices
R(reflections)
Number of parameters
0.0283(4370)
343
[M= Ni(II), Cu(II)]
Scheme 2. Synthesis of complexes.
Table 2
Analytical data.
S. No.
Complexes
Yield (%)
M.P. (°C)
Color
Analysis (%) (calcd.) found
K
m (scm2 molꢀ1
)
C
H
N
1
2
3
4
H2L
[Ni(L)]
[Cu(L)]
[Zn(H2L)(NO3)2]
65
35
54
50
230
300
330
120
Yellow
Dark green
Violet
(75.19) 74.86
(67.31) 66.96
(66.87) 67.01
(54.56) 55.01
(6.06) 5.94
(5.42) 5.03
(5.03) 4.97
(4.10) 4.31
(5.65) 4.89
(5.06) 5.23
(5.03) 5.15
(8.21) 7.90
–
20.20
19.22
35.46
White
anomalous dispersion corrections were taken from the Interna-
tional Tables for X-ray Crystallography [15]. The data integration
and reduction were carried out with SAINT [16] software. Empiri-
cal absorption correction was applied to the collected reflections
with SADABS [17] and the space group was determined using
XPREP [18]. The structure was solved by the direct methods using
SHELXTL-97 [19] and refined on F2 by full-matrix least-squares
using the SHELXL-97 program [20] package. All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms attached
to carbon atoms were positioned geometrically and treated as rid-
ing atoms using SHELXL default parameters. Several DFIX and
DANG commands were used to fix the bond distances.
in all the complexes but we succeeded in case of Ni(II) only. They
are stable at room temperature and can be stored for a long time
without any decomposition. Ni(II) and Cu(II) complexes are soluble
in chloroform, however Zn(II) complex is soluble in DMSO. A sim-
ilar effort of one pot synthesis with 1,2-phenylenediamine in place
of 1,3-propanediamine and 2-hydroxy-4-methoxybenzophenone
and metal chloride was however, unsuccessful under similar
experimental conditions.
Infrared spectra
The IR spectrum (Table 3) of the ligand shows a band in 3200–
3350 cmꢀ1 region corresponding to phenolic –OH group in solid
state [22]. This band disappears in Ni(II) and Cu(II) complexes
although it persists in Zn(II) complex indicating the involvement
of phenolic oxygen in coordination which is supported by the shift
Results and discussion
Reaction of Ni(II), Cu(II) and Zn(II) nitrate with 2-hydroxy-4-
methoxybenzophenone and 1,3-propanediamine in 1:2:1 ratio re-
sults into complex formation. The Schiff base was separately syn-
thesized and characterized in order to ensure the spectral
variation in free and ligated states. The elemental analysis is con-
sistent with their composition (Table 2). The molar conductance
(20–35 S cm2 molꢀ1) of their millimolar solution measured in chlo-
roform and DMSO at room temperature indicates their non ionic
nature [21]. Several attempts were made to obtain a single crystal
of
gion. It is due to weakening of (C–O) bond and formation of stron-
m
(C–O) at 1261 cmꢀ1 of the free ligand to a lower frequency re-
ger (M–O) bond. The m(C@N) in free ligand exhibits a bathochromic
shift of 19–51 cmꢀ1 in all the complexes. It is consistent with the
coordination of azomethine nitrogen [23,24]. However this band
is greatly affected in shape and position upon complexation.
The –OCH3 being an electron releasing group may increase elec-
tron density due to resonance and, OH thus becomes more acidic

S. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 240–246
243
Table 3
Infrared spectral data.
-
S. No.
Complexes
m(OH)
m
(C–O)
m
(CH2)
m
(C@N)
m(M–O)
m(M–N)
m(NO3 )
1
2
3
4
H2L
[Ni(L)]
[Cu(L)]
[Zn(H2L)(NO3)2]
3200–3350
–
–
1261
1214
1218
1171
2932
2942
2964
2955
1602
1569
1578
1576
–
–
–
–
–
560
563
566
514
493
482
3257–3100
1509,1394,1104
Fig. 1. 1H-NMR of ligand (H2L).
Table 4
Electronic spectral data.
ylene group attached to amine nitrogen resonate at d 3.55 ppm
[28,29]. A signal at d 15.88 ppm is assigned to phenolic –OH pro-
ton. Since this phenolic proton has less electron density due to res-
onance effect of m-methoxy group, it is far downfield shifted. Two
double doublets in d 6.44–6.64 ppm region have been assigned to
asymmetric aromatic protons.
S. No. Complex
Uv region
kmax Abs.
291
Visible region Assignments
kmax Abs.
1
[Ni(L)]
[Cu(L)]
0.965 587
0.029
3T1g (P) 3A2g (F)
407
2.48
675
687
548
0.0063 3T1g (F) 3A2g (F)
0.0048 3T2g (F) 3A2g (F)
Electronic spectra
2
3
300
355
2.48
2.22
0.29
0.116
0.278
2B1g
–
2Eg
The UV–vis spectra of Ni(II) and Cu(II) complexes [Fig. 2S:(a),(b)]
were recorded in chloroform and that of Zn(II) complex in DMSO.
The absorption band observed in the region 255–300 nm and
[Zn(H2L)(NO3)2] 256
311
–
–
310–410 nm were assigned to
p ?
p⁄ and n ? p⁄ transitions
and its deprotonation was facilitated. The new bands observed in
the region 560–570 cmꢀ1 and 480–510 cmꢀ1 are assigned to
respectively of azomethine group and are due to ligand to metal
charge transfer. The wavelengths of absorption maxima and band
assignment for the proposed geometries of the complexes are given
in Table 4.
m
(M–O) and m(M–N) respectively [25,26]. It is known that the
NOꢀ3 coordinates as symmetrical or asymmetrical chelating biden-
tate, bridging bidentate or as monodentate ligand. For both types
of coordination three well separated bands appear in about
1020–1510 cmꢀ1 region. When the difference between the two
highest frequencies is very large (ꢃ200 cmꢀ1) the NO3ꢀ ion is sup-
posed to act as bidentate ligand while a difference of approxi-
mately 100–115 cmꢀ1 refers to monodentate nature of NOꢀ3 . We
have observed three bands at 1509, 1394 and 1104 cmꢀ1. The dif-
ference between the two highest peaks in our case comes out to be
113 cmꢀ1 [27] which suggests that NOꢀ3 is acting as a monodentate
ligand in the present case.
The light green Ni(II) ion in aqueous medium exhibits weak
band in the visible region of the spectrum. The d–d band in our case
in chloroform, appears as twin peaks around 587 nm assigned to
the 3T1g (P) 3A2g suggesting square-planar geometry for the com-
plex. A set of two peaks at 675 nm and 687 nm may be attributed
3
3
to T1g (F) 3A2g (F) and T1g (F) 3A2g (F) transitions, respec-
tively [30,31]. We observed a peak at 410 nm which is generally
obscured for Ni(II) ion in aqueous medium.
The Cu(II) complex showed a broad peak at 548 nm correspond-
2
ing to B1g 2Eg transition indicating square-planar geometry
around the Cu(II) ion [32,33].
1H-NMR spectrum
ESI–Mass spectra
The 1H-NMR spectrum of ligand was recorded in CDCl3 (Fig. 1).
The spectrum showed multiplet in d 7.1–7.2 ppm region due to
symmetric aromatic protons of the ligand. The methoxy protons
showed a singlet at d 3.8 ppm. However, aliphatic protons of meth-
The ESI–MS of complexes and the ligand has been recorded
using the positive ion mode. They display prominent peaks corre-
sponding to the molecular ion fragments. Their intensity gives an

244
S. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 240–246
4000
2000
0
-2000
-4000
-6000
0
200
400
600
800
Field (mT)
Fig. 3. EPR spectrum [Cu(L)] at Liquid N2 temperature.
Fig. 4. ORTEP diagram of [Ni(L)].
Thermal analysis (TGA and DTA)
TGA was carried out between 30–800 °C at a heating rate of
10 °C/min in a static nitrogen atmosphere. The TGA and DTA of
all the complexes show three stages of decomposition (Fig. 2).
Since all the complexes decompose in a similar pattern the result
of the Zn(II) complex is discussed here in detail. The first step
(50–295 °C) shows a loss of 53.49% which is close to the calculated
value (ꢃ54.38%) corresponding to benzylidene-1,3-propanedi-
amine and two nitrates. The second step shows a weight loss of
28.48% (calc. ꢃ27.48%) between (275–550 °C), which is consistent
with the loss of (C6H5OH)2 group. The bent part of the graph in the
range 550–600 °C corresponds to –OCH3 equal to loss of 8.48%. The
flat of the thermogram which remains constant up to 800 °C corre-
sponds to Zn metal as residue.
Fig. 2. TGA–DTA diagram of (a) [Ni(L)] (b) [Cu(L)] (c) [Zn(H2L)(NO3)2].
idea of the molecular ion peak and has been used to confirm the
proposed formula and stability of fragments. In the present inves-
tigation, the mass spectrum of H2L shows a molecular ion peak at
m/z 493 [M+] corresponding to C32H28N2O4 ion. The molecular ion
peak for Cu(II) complexes is observed at m/z 557 [M+] along with
many other intermediary fragment peaks. The mass spectrum of
the Zn(II) complex (Fig. 3S) is discussed here in detail. It displays
a molecular ion peak at m/z 681due to [M+] and other intermediate
fragments, at m/z 435 corresponding to [C6H5)2C2N2(CH2)3-
ꢁZn(NO3)2]+, at m/z 190 due to [Zn(NO3)2]+ and at m/z 124 due to
[(NO3)2]+ respectively, showing usual degradation pattern. The
complex has two nitrate ions axially coordinated to the Zn(II) me-
tal. Likewise, the peaks are attributable to other complexes.
EPR spectrum
X-band EPR spectrum of Cu(II) complex recorded at liquid nitro-
gen temperature exhibits three well resolved peaks with low
intensities in the low field region and one intense peak in the high
field region (Fig. 3). From the spectral data it is found that g|| (2.40,
2.25, 2.14), g\ (2.05, 1.96) > 2.003 which supports the dx2
as
ꢀy2
ground state which is consistent with distorted square-planar

S. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 240–246
245
Fig. 5. Different view of phenyl rings.
stability of the complex. The [Ni(L)] crystallizes in monoclinic sys-
tem having space group P2 1/c. The two cis-coordinated phenolic
oxygen and two imine nitrogen atoms exhibit almost regular
square-planar geometry, as there are no considerable differences
in bond lengths and bond angles of the donor atoms coordinated
to central metal ion. The complex is dsp2 hybridized which is sup-
ported by the diamagnetic behaviour of Ni(II) ion. The crystallo-
graphic data and structural refinement are summarized in
Table 1. The selected bond angles and bond lengths are given in Ta-
bles 2(S) and 3(S) respectively. The nickel oxygen distances, Ni–O1
(1.828 Å) and Ni–O2 (1.836 Å) are shorter than nickel nitrogen dis-
tances Ni–N1 (1.881 Å) and Ni–N2 (1.888 Å) as a consequence of
negative charge borne by the phenolic oxygen atoms. Although
the two phenyl rings are identical, nevertheless one of them is
slightly tilted where the other stays in the plane (Fig. 5). The
molecular packing diagram has shown four formula units per unit
cell (Fig. 6) with no p–p stacking interaction.
Conclusion
The complexes have been found to be N2O2 type chelates in
which Ni(II) and Cu(II) are coordinated through azomethine nitro-
gen and phenolic oxygen of the ligand exhibiting square-planar
geometry which has been supported by IR, EPR, Electronic spectra
and x-ray crystallographic studies. In case of Zn(II) complex two ni-
trate ions were also found to be coordinated as monodentate li-
gand conferring an octahedral geometry to the metal.
Fig. 6. Packing diagram of [Ni(L)].
geometry for the Cu(II) complex. The absence of any half field sig-
nal suggests the presence of only one Cu(II) ion in the complex. The
axial symmetry parameter (G) is related by the expression,
Acknowledgements
The authors express their sincere thanks to the Chairman,
Department of Chemistry, Aligarh Muslim University, Aligarh for
providing necessary research facilities. The authors also acknowl-
edge their thanks to Centre of Excellence in Material Science,
Department of Applied Physics A.M.U. Aligarh for spectrophotom-
eter, Central University of Hyderabad for EPR, SAIF Punjab Univer-
sity for ESI-MS and SAIF IIT Madras for providing NMR facility.
ðgjj ꢀ 2:0023Þ ð2:40136 ꢀ 2:0023Þ ð0:39836Þ
G ¼
¼
¼
¼ 7:11
ðg? ꢀ 2:0023Þ ð2:05898 ꢀ 2:0023Þ ð0:05598Þ
It measures the extent of exchange interaction between the
copper centers in polycrystalline solid. Since the calculated G > 4,
the exchange interaction between Cu–Cu ions in the complex is ru-
led out [34,35].
The extent of geometrical distortion is measured by the g||/A||
ratio [31]. It is known that this ratio for square-planar complex
falls between 105–135 cmꢀ1 and, for tetragonally distorted com-
plex it is 135–250 cmꢀ1 [36]. The present complex has g||/A|| =
120 cmꢀ1 showing square-planar geometry.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.08.004.
References
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