Structural analysis of complexes formed by ethyl 4-phenylthiocarbamoyl piperazine-1-carboxylate with Ni(II), Zn(II) and Cd(II) through spectroscopic and DFT techniques

Article abstract of DOI:10.1016/j.molstruc.2014.01.027

A piperazine derivative, ethyl 4-phenylthiocarbamoyl piperazine-1- carboxylate and its Ni(II), Zn(II) and Cd(II) complexes have been synthesized and characterized by elemental analyses, magnetic susceptibility measurement, UV-Visible, FTIR, Raman spectroscopic and DFT methods. The Ni(II) and Zn(II) bind through the N and S sites of the two ligand Heptpc and N site of two pyridine molecules. However, the Cd(II) binds through the only N sites of the two ligand Heptpc and N site of two pyridine molecules. On the basis of various techniques used for the characterizations of the complexes, we found that the most possible geometry of the Ni(II) and Zn(II) complexes are distorted octahedral and of the Cd(II) complex is distorted tetrahedral.

Full text of DOI:10.1016/j.molstruc.2014.01.027

Accepted Manuscript
Structural analysis of complexes formed by Ethyl 4-phenylthiocarbamoyl pi-
perazine-1-carboxylate with Ni(II), Zn(II) and Cd(II) through spectroscopic and
DFT techniques
Om Prakash, Priyanka Gautam, R.K. Dani, Abhisikta Nandi, N.K. Singh, Ranjan
K. Singh
PII:
S0022-2860(14)00061-1
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.01.027
MOLSTR 20304
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
1 September 2013
4 January 2014
6 January 2014
Please cite this article as: O. Prakash, P. Gautam, R.K. Dani, A. Nandi, N.K. Singh, R.K. Singh, Structural analysis
of complexes formed by Ethyl 4-phenylthiocarbamoyl piperazine-1-carboxylate with Ni(II), Zn(II) and Cd(II)
through spectroscopic and DFT techniques, Journal of Molecular Structure (2014), doi: http://dx.doi.org/10.1016/
j.molstruc.2014.01.027
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Structural analysis of complexes formed by Ethyl 4-phenylthiocarbamoyl
piperazine-1-carboxylate with Ni(II), Zn(II) and Cd(II) through
spectroscopic and DFT techniques
Om Prakasha, Priyanka Gautama, R.K. Danib, Abhisikta Nandia, N.K. Singhb, Ranjan K.
Singh*a
aDepartment of Physics, Banaras Hindu University, Varanasi- 221005, India
bDepartment of Chemistry, Banaras Hindu University, Varanasi- 221005, India
Abstract:
A Piperazine derivative, Ethyl 4-phenylthiocarbamoyl piperazine-1-carboxylate and
its Ni(II), Zn(II) and Cd(II) complexes have been synthesized and characterized by elemental
analyses, magnetic susceptibility measurement, UV-Visible, FTIR, Raman spectroscopic and
DFT methods. The Ni(II) and Zn(II) bind through the N and S sites of the two ligand Heptpc
and N site of two pyridine molecules. However, the Cd(II) binds through the only N sites of
the two ligand Heptpc and N site of two pyridine molecules. On the basis of various
techniques used for the characterizations of the complexes, we found that the most possible
geometry of the Ni(II) and Zn(II) complexes are distorted octahedral and of the Cd(II)
complex is distorted tetrahedral.
Keywords: Piperazine derivatives, Heptpc, UV-Visible, FTIR, Raman, DFT.
*Corresponding Author: Department of Physics, Banaras Hindu University, Varanasi-
221005, India, Tel. /Fax: +91 542 6701569, Electronic mail: ranjanksingh65@rediffmail.com
1

1. Introduction
Piperazine derivatives are among the important groups of the heterocyclic
compounds, which consist of a six-membered ring containing two nitrogen atoms at opposite
positions in the ring. The Piperazine derivatives are classified to have privileged structure
and are frequently found in biologically active compounds across a number of different
therapeutic uses such as antimicrobial, anti-tubercular, anticonvulsant, antidepressant, anti-
inflammatory, antimalarial, antiarrhythmic, antioxidant and antiviral etc. [1-3]. From the
view point of coordination chemistry, the compounds which contain thiourea group are
extremely versatile due to the ability to bridge a wide range of metals by coordinating
through nitrogen or sulphur. Due to the catalytic, biologically induced reaction and clinical
applications, there is an increasing interest to study the metal complexes of piperazine
derivatives specially the transition metal complexes [4-6]. In present study, ethyl 4-
phenylthiocarbamoyl piperazine-1-carboxylate (Heptpc) and its complexes with Ni(II), Zn(II)
and Cd(II) were synthesized. The synthesized complexes were formulated on the basis of
analytical, spectral and magnetic measurement methods. The most possible geometry of the
complexes was proposed using spectroscopic technique viz. elemental analyses, UV-Visible,
FTIR and Raman spectroscopy. The density functional theory (DFT) approach has been also
employed to obtain the geometry of the ligand (Heptpc) and its complexes. The Molecular
electrostatic potential mapped surfaces and HOMO-LUMO of the Heptpc and the complexes
are also computed by DFT method.
2

2. Experimental Details:
2.1 Materials and Instrumentations:
Ethylpiperazine-1-carboxylate and phenylisothiocyanate were purchased from Sigma-
Aldrich and used without further purification. All solvents were purchased from Merck
Chemicals, India and were dried and distilled following standard procedure before use. All
reactions were carried out in open atmosphere. Carbon, Hydrogen and Nitrogen contents
were estimated on a CHN Model CE-440 analyzer and on an Elemental Vario EL III Carlo
Erba 1108 analyzer. By following standard procedures, the complexes were analyzed for their
metal content, after decomposition with a mixture of conc. HNO3 and HCl, followed by conc.
H2SO4 [7]. Magnetic susceptibility measurements were performed at room temperature on a
Cahn Faraday balance using Hg[Co(NCS)4] as the calibrant. The UV-Visible spectroscopy is
used to obtain the geometry of the coordination compounds. The electronic spectra were
recorded on a SIMADZU 1700 UV/VIS spectrophotometer at 300 K in DMSO solution. The
FTIR technique is used to know the functional groups present in compounds. In order to
assess the structures of the metal complexes with better precision, FTIR and Raman spectra
of metal complexes were measured. The FTIR spectra were recorded in the range 400-4000
cm-1 in KBr pellets on Spectrum 65 FT-IR spectrometer from PerkinElmer. The laser Raman
spectra were recorded on a Raman spectrometer was from Renishaw Model: RM 1000 having
grating of 2400 grooves/mm giving spectral resolution of ~1 cm-1 at 50 micron slit opening
The 514.5 nm Ar+ -laser was used as an excitation source delivering ~5 mW intensity at the
sample. A microscope from Olympus with 50 x objectives was used to focus the laser on the
sample and to collect the Raman scattered signal in back scattering geometry. The Raman
spectra were recorded in the range 200-3500 cm-1. Spectrometer scanning, data collection and
processing were done by a dedicated computer using Gram Wire software.
3

2.2 Synthesis of ligand (Heptpc):
A
mixture of ethylpiperazine-1-carboxylate (3 mL, 20 mmol) and
phenylisothiocyanate (2.4 mL, 20 mmol) was refluxed in benzene (20 mL) at 45 0C for 6 h. A
white precipitate was obtained upon cooling the reaction mixture in ice, which was filtered
off, washed with methanol and ether and recrystallized from MeOH: CHCl3 mixture (50:50
v/v).
2.3 Synthesis of the complexes [M(eptpc)2(py)2] {where M = Ni(II), Zn(II) and Cd(II)}:
The Synthesis procedure of metal complexes [M(eptpc)2(py)2] is as follow;
M(OAc)2·xH2O (1 mmol) and Heptpc (2 mmol) were dissolved separately in 10 mL
methanol-acetonitrile(1:1 v/v). The two mixtures thus prepared were mixed together and
stirred for 2h. The solid precipitate was filtered, washed successively with ethanol-water
mixture (50:50) and air dried. The precipitate was suspended in methanol to which pyridine
(0.5 mL) was added and stirred for 1h. The resulting solution was filtered and kept for
crystallization. Colored compound for analyses were obtained by slow evaporation of its
methanol solution over a period of 25 days. All the complexes are air stable, non-hygroscopic
amorphous solids. They are partially soluble in common organic solvents but soluble in DMF
and DMSO and can be kept in desiccators over a prolonged period without any sign of
decomposition. Scheme 1 depicts the synthesis of the ligand ethyl 4-phenylthiocarbamoyl
piperazine-1-carboxylate (Heptpc) and metal complexes. For the preparation of the metal
complexes, (Heptpc) is used as ligand and pyridine as coligand. The analytical Data, Color,
Melting Point and Percentage Yield of ligand and the Metal Complexes are shown in table
[1]
4

O
O
O
O
S
Reflux, 45 0C
6Hr
N
N
N
NH +
NCS
HN
ethyl piperazine-1-carboxylate
Phenylisothiocyanate ethyl 4-(phenylthiocarbamoyl)piperazine-1-carboxylate
Ni(OAc)2.4H2O
Pyridine
Zn(OAc)2.2H2O
Pyridine
Cd(OAc)2.2H2O
Pyridine
N
N
N
N
N
O
O
O
O
O
O
S
S
N
S
O
O
S
Zn
N
N
N
N
Cd
N
N
N
N
Ni
N
S
N
N
N
N
N
N
O
N
S
N
O
N
O
O
Scheme [1]: Synthesis of ligand (Heptpc) and its metal complexes [M(eptpc)2(py)2]
3. Results and Discussion:
3.1 UV-Visible Spectra:
The UV-Visible spectra of the ligand Heptpc and the metal complexes
[M(eptpc)2(py)2] are shown in the figure [1(a), (b), (c), (d) ]. The absorption region, band
assignment and the geometry of the complexes are given in table [2]. The Ni(II) complex
3
3
exhibited the absorption bands at 21010 and 27910 cm-1, attributed to A2g→ A1g(F) (ν ),
2
3
3
and A2g→ T1g(P) (ν ) transitions [8]. The magnetic susceptibility measurements were
3
performed at room temperature on a Cahn Faraday balance using Hg[Co(NCS)4] as the
calibrant and observed the magnetic moment 2.88 B.M . This suggests the Ni(II) coordinate
to (Heptpc+pyridine) in the distorted octahedral fashion whereas the Zn(II) and Cd(II)
complexes have diamagnetic nature. But Zn(II) and Cd(II) complexes exhibit high energy
5

bands at 367, 310, 303 and 291–243 nm due to charge transfer/intraligand transitions [8].
Since Zn(II) may coordinate in the distorted octahedral as well as the distorted tetrahedral
fashion according to nature but the spectral pattern of UV-Visible suggest for distorted
octahedral geometry. However absorption bands of the Cd(II) complex suggest for its
distorted tetrahedral geometry.
3.2 Quantum chemical calculations of Heptpc and its metal complexes [M(eptpc)2(py)2]:
All quantum chemical calculations of Heptpc as well as its complexes with Ni(II),
Zn(II) and Cd(II) have been performed with Gaussian 03 and Gauss View 4.1 program
packages [9]. The optimization of the structures of ligand Heptpc have been done using DFT
method with functional B3LYP and basis set 6-311++G(d,p) [10-13] whereas the geometry
optimizations of complexes [M(eptpc)2(py)2]{where M = Ni(II), Zn(II) and Cd(II)} have
been done using DFT method with functional B3LYP and basis sets 6-311++G(d,p){for
C,H,N,O,S}/Lanl2DZ{for M = Ni(II), Zn(II) and Cd(II)}. The basis set Lanl2DZ [10-13]
serves the purpose of including the pseudo potential of the core electrons in the metal atoms.
Furthermore, this basis set is also compatible with other elements viz. C, H, N, S and O which
are present in the complexes. The absence of imaginary harmonic frequencies confirms that
the optimized structures are the global minimum energy conformations. The optimized
structures of Heptpc and complexes [M(eptpc)2(py)2]{where M = Ni(II), Zn(II) and Cd(II)}
are shown in the figures [2], [3], [4] and [5] respectively. The geometrical parameters viz.
bond lengths and bond angles between the atoms participating in the coordination
phenomenon are given in the table [3(a) and (b)].
3.3 Molecular electrostatic potential and Frontier molecular orbital analysis:
The molecular electrostatic potential (MEP) mapped surfaces illustrate the continuous charge
distributions of molecules three dimensionally which give clear signature of the interactions
6

and the reactive sites of the molecules. The MEP mapped surface of the molecules are
computed by DFT method at 6-311++G(d,p){for C,H,N,O,S}/Lanl2DZ{for M = Ni(II),
Zn(II) and Cd(II)}level of calculation. The MEP mapped surfaces of the Heptpc (a) and its
complexes ([b] Ni (II), [c] Zn (II), [d] Cd (II) ) are shown in figure [6]. In color scheme of the
MEP plot, the red region shows the negative electrostatic potentials i.e atoms with lone pairs;
the blue region shows the positive electrostatic potentials and the green region cover the parts
of the molecule where electrostatic potentials are close to zero. The intensity of the color is
directly proportional to the absolute value of the potential energy. Frontier molecular orbitals
(FMOs) refer to the highest occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) which is used to determine the molecular reactivity, excitation
properties and the electron transport phenomenon [14, 15]. The outermost higher energy
orbital (HOMO) acts as an electron donor while the lowest energy orbital (LUMO) acts as an
electron acceptor. The energies of the HOMO-LUMO orbital of the molecules, calculated by
DFT method, are found to be negative, this signifies that the molecules are stable [16]. The
HOMO-LUMO plots for the Heptpc (a) and its complexes ([b] Ni (II), [c] Zn (II), [d] Cd (II)
) are shown in figure [7]. The electronic transition from the ground state to the excited state
due to a transfer of electrons from the HOMO to LUMO levels is mainly due to π···π
transition. The positive phases are red and the negative ones are green. The small energy gap
of molecules is termed as soft while the large energy gaps are termed as hard molecules. The
hardness value (η) of a molecule can be defined by the formula [17]
η = {-εHOMO + εLUMO}/2
where εHOMO and εLUMO are the energies of the HOMO and LUMO molecular orbital. The soft
molecules are high reactive, high polarisable and less stable than the hard ones because soft
molecules need small energy for excitation. It can be seen from figure [6] the Cd-complex is
softest among the other complexes and Heptpc, which needs less energy for the excitation
7

from the ground state to excited state i.e. the polarisability vary as Cd→Ni≈Zn in decreasing
order. The HOMO-LUMO energy gap for the Ni and Zn complexes are approximately equal
values. This suggests the same type of geometrical structures of the Ni and Zn complexes.
This confirms the results obtained by the UV-Visible spectral analysis.
3.2 Vibrational (FTIR and Raman band) analysis of Heptpc and the Complexes:
The FTIR and Raman spectra of the ligand Heptpc and the metal complexes
[M(eptpc)2(py)2]{where M = Ni(II), Zn(II) and Cd(II) are recorded to obtain the binding sites
of the metals to the ligand. The FTIR and Raman spectra of the ligand Heptpc and the metal
complexes are shown in the figures [8] and [9] respectively. The bands, which show clear
changes after the complex formation have been emphasized. The vibrational modes of Raman
and IR bands are assigned [18-20] with the help of DFT calculation and the DFT results have
been also used to understand the experimental results.
The ν(C-H) of the two pyridine molecules in Ni and Zn complexes exhibited a very
weak IR band at 3243 cm-1, whereas it was found to be absent in Cd complex. But a broad
band at 3239 cm-1 in the Raman spectra is observed in all the three complexes corresponding
to ν(C-H) vibration. This may be due to different type of geometry of Cd complex than those
of Ni and Zn complexes, which influences the charge distribution i.e. vibrational energy
responsible for ν(C-H) vibration of pyridine. A very strong and sharp Raman band is
observed at 3069 cm-1 in all the three complexes, which is assigned as ν(C-H) of the both
ligand molecules present in complexes. The Raman band at 3012 cm-1 and IR bands at 3011
and 2983 cm-1 corresponding to N-H stretching are observed in the ligand Heptpc but these
are completely absent in all the three complexes, which suggested that the removal of H atom
from –NH group and concomitant binding of metals to N sites of two ligand Heptpc and two
coligands pyridine leads to the complex formation. The Raman bands at 2998 cm-1 and 2913
cm-1 and IR band at 2983 cm-1 attributed to C-H stretching of piperazine rings in pure ligand
8

Heptpc are observed, but after the complexation the Raman bands at 2998 cm-1 is shifted to
the higher wavenumber at 3006 cm-1 whereas the Raman band at 2913 cm-1 and IR band at
2983 cm-1 disappeared. A very weak band at 2870 cm-1 in Raman spectra of pure ligand
Heptpc is shifted to the lower wavenumber 2866 cm-1 after complexation in all the three
complexes. The IR band at 1698 cm-1 corresponding to ν(C=O) of pure Heptpc disappeared in
the complexes. Similarly, the two very sharp bands at 1596 and 1527 cm-1 in the Raman
spectra of the three complexes are observed which was not found in the Raman spectra of
pure heptpc. These bands are assigned as scissoring of C-H group. This signifies the change
in the charge cloud of ligand Heptpc before and after the complex formation. The two
neighbouring Raman bands at 1457 and 1441 cm-1 attributed to the contributions of N-H
bending, scissoring of C-H mode and C=N stretching of thiourea group of pure Heptpc are
shifted to lower wavenumber at 1454 and 1438 cm-1 respectively in all three complexes. This
is due to removal of H from –NH group and binding of metals to same N site. Therefore, the
Raman bands at 1454 and 1438 cm-1 complexes exhibited the vibrational modes [β (M-Np-Cp)
+ ν (C=C)p1+p2 + β (C-H)] where M= Ni, Zn and Cd. We observed three new bands at 1332,
1311 and 1293 cm-1 in the Raman spectra of the complexes, which is assigned as contribution
of vibrational modes [β (Np1-M-Np2) + ν (C-N)p1+p2+ ν (C-C)p1+p2 ]. This again proves the
as
as
binding of metals through N site of pyridine molecules. The Raman band at 1257 cm-1
attributed to the twisting of CH2 of piperazine ring plus N=C=N(H) bending of thiourea in the
pure Heptpc is split into two bands at 1252 and 1241 cm-1 after the complex formation. The
removal of H atom from -NH group leads to the formation of deprotonated thiourea group,
which give two bands at 1252 and 1241 cm-1. A very strong and sharp band at 1206 cm-1 is
assigned as C-H bending of the benzene ring in Heptpc which is red shifted with decreasing
Raman activity as we go Cd→Ni≈Zn. This suggests interestingly that the complexes are less
polarisable as we go to Cd→Ni≈Zn order which is also explained by theoretically calculated
9

HOMO-LUMO energy gap as shown in figure [7]. The new band at 1081 cm-1 in Raman
spectra of complexes (Fig 3), assigned as the vibrational modes [ν (N-M)p1+p2+ βas(tr) (C-N-
as
C)p1+P2+ β (C-C-C)p1+p2 ], gives clear evidence of metal binding. The two Raman bands at
(tr)
1046 (vw) and 1033 cm-1 due to the vibrational modes [ν (C-C)pz+ β (C-N-C)pz+ β
(tr)
(thiourea)+ ν (C-O)] are coupled and shifted to the lower wavenumber at 1029 cm-1 in the Zn
and Ni complexes having contribution from the a new vibrational modes [ν (N-Ni)p1+p2+φ
as
(p1+p2)] whereas in case of Cd complex, the band at 1046 cm-1 is not found to be shifted and
the band at 1033 cm-1 is shifted to the same position at 1029 cm-1 in all complexes. This
shows that the different type of coordination property of thiourea group with Cd(II) and
Ni(II) (or Zn(II)). The most strong and highest Raman active band in the whole range of
Raman spectra appeared at 998 cm-1 in all the three complexes, which is not present in the
Heptpc before the complex formation. This band belongs to the metal coordinated modes in
addition to the possible contribution of vibrational modes of pyridine molecules i.e. [γ(C-N-
M)p2+r(C-H)op+r (ring)p2]. A strong Raman band at 934 cm-1 attributed to [{β (N=C=NH)+ν
(tr)
(C-S)pz }thiourea+ ν(ring)pz+ φ(bz)] of the pure Heptpc was absent in the complexes. However,
it is split in two components, one at 952 cm-1 assigned as ν(ring)pz+ ν (C-O)+ φ(bz) and other
at 922 cm-1 corresponding to metal coordinated mode and pyridine molecules, τ(M-
Np)+r(C2H2)p.
The IR band at 880 cm-1 [β(ring)pz+r(CH2)pz+scis(Npz=C=O)+ν(C-O)] shifted to 871
cm-1 due to redistribution of charge over the Heptpc molecule on complex formation leading
to the red shift of this band. Whereas, the band at 817 cm-1 in the IR spectra of pure Heptpc,
which is mainly due to ring breathing of piperazine and benzene disappeared in the
complexes. In Raman spectra of the complexes, a strong band due to rocking modes of the
M-N (M = Ni, Zn, Cd) and C-H bonds of two pyridine molecules is observed at 770 cm-1.
The Raman spectra of the complexes exhibited two strong and very sharp bands at 701 and
10

679 cm-1. Similarly the IR spectra of the complexes exhibited a new band at 698 cm-1, which
was not observed in pure Heptpc. The Raman band at 701 cm-1 and IR band at 698 cm-1 are
due to the asymmetric stretching of the metal coordinated bond with N atoms of both ligand
Heptpc (i.e M-NL bond) and the band at 679 cm-1 is due to the asymmetric stretching of the
metal coordinated bond with N atoms of both pyridine molecules (i.e M-Np bond) and
trigonal bending of (C-N-C) plus (C-C-C) of pyridine rings. A very sharp band at 629 cm-1 of
the pure Heptpc is split into the two weak bands on either side of the 629 cm-1, one towards
higher wavenumber at 638 cm-1 which gets broadened in the complexes and the other towards
lower wavenumber at 614 cm-1.
Appearance of a new band at 532 cm-1 [ν(M-N)p] in the Raman spectra of Cd complex
suggests the formation of bond between the Cd2+ and N sites of both pyridine. In case of Zn
and Ni complexes the bands corresponding to ν(M-N)p and ν(M-S)L appeared at 580 and 427
cm-1 respectively. The IR band at 477 cm-1[β(N-H)+ β(thiourea)] of Heptpc split into two
components in the complexes, one at 474 cm-1 due to [β(Np-M-S)+γ(ring)p, where M=Zn and
Ni] in case of the Zn and Ni complexes whereas due to [β(Np-Cd-Np)+γ(ring)p] for Cd
complex and the other at 490 cm-1 that is more clear and sharp in the Zn and Ni complexes
than in Cd complex. The IR band at 490 cm-1 mainly corresponds to [β(Np-M-S)+r(NL-M-
NL)+γ(ring)p] in the Zn and Ni complexes and [β(Np-Cd-Np)+r(NL-Cd-NL)+γ(ring)p] in the
Cd complex. The above discussion suggests that the metal ions (Zn(II) and Ni(II)) bonded
through nitrogen and thione sulfur sites of deprotonated ligand (eptpc) and nitrogen site of
co-ligand (pyridine) form a chelate ring whereas Cd(II) bonded through only nitrogen site of
deprotonated ligand (eptpc) and nitrogen site of co-ligand (pyridine). This indicates the
similar type of the geometry of the complexes of Zn(II) and Ni(II) whereas Cd(II) complex
has different type geometry. This support the result obtained by UV-Visible absorption
11

technique i.e. distorted octahedral geometry of the complexes [Zn(eptpc)2(py)2] and
[Ni(eptpc)2(py)2] and distorted tetrahedral geometry of the complex [Cd(eptpc)2(py)2].
The IR band at 429 cm-1 due to bending of N-H bond in the Heptpc disappeared after
the complex formation. This shows the removal of H atom from –NH group and binding of
the metals to this site. The Raman bands at 359 and 225 cm-1 of pure Heptpc due to the
vibrations of the thiourea group disappeared completely after the complex formation and a
broad Raman band at 395 cm-1 of the Heptpc is shifted and converted to a sharp and strong
band at 408 cm-1 due to ν(M-S) [where M = Ni, Zn, Cd]. This again confirms the formation
of metal complexes.
4. Conclusion and Output:
This study was undertaken in many stages. In first stage, ligand Heptpc was
synthesized as depicted in scheme 1. In second stage, metal complexes of Ni, Zn and Cd were
prepared using Heptpc as ligand and pyridine as coligand (scheme 1). Since the Single
crystals of the complexes could not be isolated from the solutions, no direct structural
information could be obtained. Therefore, in third stage, the most possible geometries of the
complexes were proposed using elemental analyzer, Magnetic data and UV-Visible
spectroscopy. Further in fourth stage, we characterized the ligand Heptpc and the metal
complexes using the vibrational spectroscopic (FTIR and Raman) techniques to access the
binding of metals. The Zn and Ni bind with N and S sites of the two ligand Heptpc and two
N sites of two pyridine molecules in Zn/Ni complex but in Cd complex, Cd binds to only N
sites of the two ligand Heptpc and two N sites of two pyridine molecules. The results of all
techniques complement to confirm the binding phenomenon. The DFT calculations were
performed with many possible structures of the complexes as input for geometry
optimizations but only the geometry presented in this work are converged, for which the
harmonic frequency found to be imaginary. Thus DFT calculation further strongly proves that
12

the proposed geometry of the complexes is most possible and acceptable. By using various
technique, we proposed the distorted octahedral geometry of complexes - [Zn(eptpc)2(py)2]
and [Ni(eptpc)2(py)2] and distorted tetrahedral geometry of complex - [Cd(eptpc)2(py)2]. This
study concludes that the technique viz. elemental analyses, UV-Visible, FTIR, Raman and
DFT method are good enough to propose the most possible geometry of complex molecules.
a Abbreviations:
ν = stretching; β =bending; δ= deformation; γ = out-of-plane bending; τ =torsion; r = rocking;
φ= ring breathing; twist= twisting; ω=wagging; tr= trigonal; pz= piperazine ring; bz=
benzene ring; op= out of plane.
p1 and p2 are the two pyridine rings; L1 and L2 are the two ligand (Heptpc/eptpc), where
Heptpc is pure and eptpc (deprotonated Heptpc) is coordinating ligand.
Acknowledgments:
Om Prakash and PG (Junior Research Fellow) are grateful to the UGC, India for providing
research fellowship, RKD is grateful to UGC for awarding Senior Research Fellowships.
RKS is grateful to AvH Foundation, Germany, and DST and CSIR, New Delhi for support to
procure micro-Raman setup. Authors are also grateful to biophysics lab; department of
Physics and department of Chemistry, BHU, Varanasi-221105, for providing lab facilities.
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14

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Figure Captions
Figure 1(a): The UV/VIS. spectra of the pure ligand Heptpc in the region 200-500 nm
Figure 1(b): The UV/VIS. spectra of the [Ni(eptpc)2(py)2] in the region 200-500 nm
Figure 1(c): The UV/VIS. spectra of the [Zn(eptpc)2(py)2] in the region 200-500 nm
Figure 1(d): The UV/VIS. spectra of the [Cd(eptpc)2(py)2] in the region 200-500 nm
Figure 2: Optimized structure of the Heptpc by DFT method
Figure 3: Optimized structure of [Ni(eptpc)2(py)2] by DFT method.
Figure 4: Optimized structure of [Zn(eptpc)2(py)2] by DFT method.
Figure 5: Optimized structure of [Cd(eptpc)2(py)2] by DFT method.
Figure 6: Molecular Electrostatic potential surface maps of Heptpc (a) and its metal
complexes ( [b] Ni (II), [c] Zn (II), [d] Cd (II) ).
Figure 7: The HOMO-LUMO plots for the (a) Heptpc and its complexes ( [b] Ni (II), [c] Zn
(II), [d] Cd (II) ).
Figure 8: Experimental FT-IR spectra of Heptpc and Ni(II), Zn(II) and Cd(II) complexes in
the region 350-4000 cm-1.
Figure 9(a): Experimental Raman spectra of Heptpc and Ni(II), Zn(II) and Cd(II) complexes
in the region 200-1000 cm-1.
Figure 9(b): Experimental Raman spectra of Heptpc and Ni(II), Zn(II) and Cd(II) complexes
in the region 900-1750 cm-1.
15

Figure 9(c): Experimental Raman spectra of Heptpc and Ni(II), Zn(II) and Cd(II) complexes
in the region 2600-3500 cm-1.
Tables Captions:
Table 1: Analytical Data, Colour, Melting Point, and Percentage Yield of ligand and the
Metal Complexes
Table 2: Electronic absorption spectral data of the ligand(Heptpc) and complexes in DMSO
Solution
Table 3(a): Selected bond lengths of complexes [M(eptpc)2(py)2] (where M=Ni, Zn, Cd)
calculated by DFT method.
Table 3(b): Selected bond angles of complexes [M(eptpc)2(py)2] (where M=Ni, Zn, Cd)
calculated by DFT method.
16

Table 1
Empirical
Yield
(%)
Elemental
Analysis
%Found
(calcd.)
H
Compounds
formula
M.P.
(0C)
Colour
(Weight in gm.)
(mg)
C
N
S
M
Heptpc
C14H19N2O2S
235
320
White
85
78
67
74
60.27
( 60.18)
6.81
10.02
(10.03)
11.47
(11.45)
-----
( 6.78)
(279.50)
[Ni(eptpc)2(py)2]
[Zn(eptpc)2(py)2]
[Cd(eptpc)2(py)2]
C38H46N6O4S2Ni
Brown
62.07
6.31
11.48
8.74
7.98
(62.05)
(6.26)
(11.52)
(8.76)
(7.90)
(734.98)
C38H46N6O4S2Zn 278
Colorless
Colorless
61.47
6.20
11.34
8.65
8.80
(61.45)
(6.16)
(11.25)
(8.70)
(8.85)
(742.36)
C38H46N6O4S2Cd 286
57.87
5.88
10.68
8.14
14.35
(57.82)
(5.83)
(10.72)
(8.17)
(14.28)
(788.82)
Table 2
Magnetic
Compounds
moment (B.M.)
Absorption (cm-1)
Band assignment
Geometry
----
Heptpc
LCT
[Ni(eptpc)2(py)2]
2.88
21010, 27910
3A2g→ 3A1g(F) (ν ), 3T1g(P) Distorted Octahedral
2
(ν )
3
[Zn(eptpc)2(py)2]
[Cd(eptpc)2(py)2]
Diamagnetic
Diamagnetic
29500-31000
29500-31000
IL/CT
IL/CT
Distorted Octahedral
Distorted tetrahedral
17

Table 3(a):
Bond
Bond length (M=Ni)
Bond length (M=Zn)
Bond
Bond length
(where M=Ni, Zn)
M-Np1
1.911
1.913
2.988
2.988
2.348
2.348
2.276
2.288
2.144
2.144
2.741
2.741
Cd-Np1
Cd-Np1
Cd-N1
Cd-N1
2.399
2.399
2.234
2.234
M-Np2
M-N1
M-N2
M-S1
M-S2
Table 3(b):
Bond angle
Bond angle
(M=Ni)
Bond angle
(M=Zn)
Bond angle
Bond angle
(where M=Ni, Zn)
Np1-M-Np2
Np1-M-S1
Np2-M-S2
Np1-M-N1
Np2-M-N2
Np2-M-N1
Np1-M-N2
Np1-M-S2
Np2-M-S1
S1-M-S2
179.99
89.88
90.12
93.65
93.65
86.34
86.34
89.88
90.12
86.34
172.69
179.99
89.88
92.43
92.19
92.19
87.81
87.81
87.57
92.43
87.81
175.62
Np1-Cd-Np2
N1-Cd-N2
Np1-Cd-N1
Np2-Cd-N2
Np2-Cd-N1
Np1-M-N2
80.10
120.94
95.88
95.89
127.30
127.30
N1-M-N2
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24

25

26

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