Synthesis and spectral characterization of copper(II) complexes derived from 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone: Crystal structure of a binuclear complex

Article abstract of DOI:10.1016/j.poly.2014.02.042

Six copper(II) complexes [Cu₂(L)₂SO ₄]·H₂O (1), [Cu₂(L)₂(OAc) ₂]·H₂O (2), [Cu(L)NO₃]₂ (3), [Cu(L)N₃]₂·H₂O (4), [Cu(L)NCS] ·H₂O (5) and [Cu(L)I] (6) of 2-benzoylpyridine-N ⁴,N⁴-dimethyl-3-thiosemicarbazone (HL) were prepared and characterized using partial elemental analysis, magnetic susceptibility, conductivity measurements, FT-IR, UV-Vis and EPR studies. The molecular structure of [Cu₂(L)₂(OAc)₂] (2a) was resolved using single crystal X-ray diffraction studies and it was found to have distorted square pyramidal geometry with the basal plane occupied by thiosemicarbazone and the acetate oxygen O2. The compound crystallized in monoclinic space group P2₁/n and formed a centrosymmetric dimer, bridged through oxygen of the acetate moiety. From the physicochemical studies, it was found that thiosemicarbazone coordinates through one of the pyridyl nitrogen, azomethine nitrogen and thioiminolate sulfur atoms. Binuclear nature of some of the complexes was confirmed from EPR parameters and magnetic moment values. In all complexes g values in frozen DMF, indicate the presence of the unpaired electron residing in the d_x²_{- y}² orbital.

Full text of DOI:10.1016/j.poly.2014.02.042

Polyhedron 75 (2014) 50–56
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and spectral characterization of copper(II) complexes derived
from 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone: Crystal
structure of a binuclear complex
K. Jayakumar a, M. Sithambaresan b, A. Ambili Aravindakshan a, M.R. Prathapachandra Kurup a,
⇑
a Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India
b Department of Chemistry, Faculty of Science, Eastern University, Sri Lanka, Chenkalady, Sri Lanka
a r t i c l e i n f o
a b s t r a c t
Article history:
Six copper(II) complexes [Cu2(L)2SO4]ꢀH2O (1), [Cu2(L)2(OAc)2]ꢀH2O (2), [Cu(L)NO3]2 (3), [Cu(L)N3]2ꢀH2O
(4), [Cu(L)NCS]ꢀH2O (5) and [Cu(L)I] (6) of 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone
(HL) were prepared and characterized using partial elemental analysis, magnetic susceptibility, conduc-
tivity measurements, FT-IR, UV–Vis and EPR studies. The molecular structure of [Cu2(L)2(OAc)2] (2a) was
resolved using single crystal X-ray diffraction studies and it was found to have distorted square pyrami-
dal geometry with the basal plane occupied by thiosemicarbazone and the acetate oxygen O2. The com-
pound crystallized in monoclinic space group P21/n and formed a centrosymmetric dimer, bridged
through oxygen of the acetate moiety. From the physicochemical studies, it was found that thiosemicar-
bazone coordinates through one of the pyridyl nitrogen, azomethine nitrogen and thioiminolate sulfur
atoms. Binuclear nature of some of the complexes was confirmed from EPR parameters and magnetic
moment values. In all complexes g values in frozen DMF, indicate the presence of the unpaired electron
Received 13 December 2013
Accepted 28 February 2014
Available online 12 March 2014
Keywords:
2-Benzoylpyridine
Thiosemicarbazone
Copper(II) complex
EPR
X-ray crystal structure
2
2
residing in the dxꢁy orbital.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
procedures. 2-Benzoylpyridine (Aldrich), N4,N4-dimethyl-3-thiosemi-
carbazide (Aldrich), CuSO4ꢀ5H2O, CuNO3ꢀ5H2O, Cu(CH3COO)2ꢀH2O,
NaN3, KSCN, NaI (all are BDH, AR quality) were used as received.
Caution! Metal complexes with organic ligands containing azide
are potentially explosive. So they should be prepared in small
quantities and handled with care.
Thiosemicarbazones are versatile class of ligand systems
formed by the condenzation of thiosemicarbazides with aldehydes
or ketones. The remarkable features lie in their wide range of
biological applications such as antitumor [1], antibacterial [2],
anti-viral [3] and anticarcinogenic properties [4] and structural
diversity due to their variable coordinative abilities [5,6]. 2-Benzo-
ylpyridine thiosemicarbazone was proved as a novel reagent for
the single pot synthesis of dinuclear Cu(I)–Cu(II) complexes with
stable copper(II)–iodide bonds [7]. This paper reports the synthesis
and spectral characterization of copper(II) complexes derived from
2.2. Synthesis of the thiosemicarbazone HL and its copper(II)
complexes
2.2.1. Synthesis of thiosemicarbazone HL
The thiosemicarbazone was synthesized according to the re-
ported procedure [8] and its crystal structure has been published
[9]. The structural formula of the ligand (HL) is represented in
the Scheme 1.
2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone
with the crystal structure of a binuclear copper(II) complex.
along
HL: Yield: 70%; M.P. 140 °C; C15H16N4S; C 63.35 (63.85); H 5.67
2. Experimental
(5.86); N 19.70 (20.01); S 11.28 (11.00); IR (cmꢁ1): 1575s,
m
(C@N);
(py(ip)); 3055 m,
(2N–H); Mass to charge ratio (m/z): 285.2 (M+1); 1H NMR
1115s,
m(N–N); 1420s, 805s, m(C@S); 699s, m
2.1. Materials
m
(d ppm in CDCl3): 14.365 (1H, b), 8.753–7.347 (aromatic protons),
3.452 (6H, s).
All chemicals were of reagent grade and purchased from com-
mercial sources. The solvents were purified according to standard
2.2.2. Synthesis of copper(II) complexes
⇑
2.2.2.1. Synthesis of [Cu2(L)2SO4]ꢀH2O (1), [Cu2(L)2(OAc)2]ꢀH2O (2),
Corresponding author. Tel.: +91 484 2862423; fax: +91 484 2575804.
E-mail addresses: mrpcusat@gmail.com, mrp_k@yahoo.com (M.R.P. Kurup).
[Cu(L)NO3]2 (3). A solution of thiosemicarbazone, HL (0.284 g,
http://dx.doi.org/10.1016/j.poly.2014.02.042
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

K. Jayakumar et al. / Polyhedron 75 (2014) 50–56
51
used for data acquisition and Bruker SAINT software for data integra-
tion [10]. Absorption corrections were carried out using SADABS
based on Laue symmetry using equivalent reflections [11]. The
structure was solved by direct methods and refined by full-matrix
least-squares calculations with the SHELXL-97 software package
[12]. The graphics tool used was DIAMOND version 3.2 g [13]. All
non hydrogen atoms were refined anisotropically and positions
of hydrogen atoms were derived from Fourier difference maps
and were placed geometrically and refined with a riding model.
The crystallographic data along with details of structure solution
refinements are given in Table 1.
Scheme 1. Structure of 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone.
3. Results and discussion
1 mmol) in 10 mL of methanol was mixed and refluxed with meth-
anolic solution (10 mL) of appropriate copper(II) salt (1 mmol) for
4 h. On cooling, the complexes formed was filtered, washed with
The copper(II) complexes 1, 2 and 3 were prepared by the reac-
tion of the thiosemicarbazone, HL with appropriate copper(II) salts
in 1:1 M ratio. The complexes 4 and 5 were prepared by refluxing
the thiosemicarbazone with copper(II) acetate and NaN3 or KSCN
in 1:1:1 M ratio. For the synthesis of complex 6, metathetical
replacement was used. Binuclearity of some complexes was con-
firmed from EPR studies.
few drops of methanol and ether and dried in vacuo over P4O10
.
2.2.2.2. Synthesis of [Cu(L)N3]2ꢀH2O (4) and [Cu(L)NCS]ꢀH2O (5). A
solution of thiosemicarbazone, HL (0.284 g, 1 mmol) in 10 mL of
hot methanol was treated with aqueous solution of Cu(OAc)2ꢀH2O
(0.199 g, 1 mmol). To this 1 mmol NaN3/KSCN was added and re-
fluxed for 4 h. On cooling, the compounds separated was filtered,
washed with few drops of methanol and ether and dried over
P4O10 in vacuo.
Molar conductance of the complexes measured using 10ꢁ3
M
DMF solutions showed that all the complexes except 3 are found
to be non electrolyte in nature [14]. Higher conductance of the
complex 3 is due to the partial ionization of complex in the DMF
solvent. Magnetic moments of the complexes were calculated from
magnetic susceptibility measurements. Copper(II) complexes for-
mulated as mononuclear exhibit magnetic moments in the range
1.60–1.78 B.M., which are close to the spin only value [15]. The
magnetic moments of the binuclear complexes were found to be
in the range 1.37–1.63 B.M. These low magnetic moments may
be attributed to the presence of a strong antiferromagnetic interac-
tion. All complexes except 5 and 6 are binuclear in nature. The ana-
lytical data of the complexes are listed in Table 2.
2.2.2.3. Synthesis of [Cu(L)I] (6). For the synthesis of this complex, a
solution of CuNO3ꢀ5H2O (0.246 g, 1 mmol) in 10 mL of methanol
and a solution of NaI (0.1525 g, 1 mmol) in 10 mL of methanol
were mixed and boiled for 15 min and then chilled in ice. The pre-
cipitated CuI was filtered and CuI was treated with a solution of
thiosemicarbazone, HL (0.284 g, 1 mmol) in 10 mL hot methanol
and refluxed for 4 h and cooled. The dark green shining crystals
formed were filtered, washed with few drops of methanol and
ether and dried over P4O10 in vacuo.
3.1. Crystal structure of [Cu2L2(OAc)2] (2a)
2.3. Physical measurements
The molecular structure of the compound along with atom
numbering scheme is given in Fig. 1 and selected bond lengths
(Å) and bond angles (°) are shown in Table 3.
Even though the compound is isolated as monohydrate, the sin-
gle crystals do not have any water of hydration. This compound
crystallized in monoclinic space group P21/n and it is a dimer
bridged through oxygen of the acetate moiety. The asymmetric
unit is formed by one half of the molecule and the other half is gen-
erated by a center of inversion.
The structure contains two copper centers where each cop-
per(II) center is pentacoordinated with azomethine nitrogen N2,
pyridyl nitrogen N1, thioiminolate sulfur S1 of thiosemicarbazone
moiety and oxygens (O2, O2A) from two acetate groups. The trigo-
The partial elemental analyses of the thiosemicarbazone and its
complexes were carried out using a Vario EL III CHNS analyzer at
SAIF, Kochi, India. IR spectra were recorded on a JASCO FT-IR-
5300 spectrometer in the range 4000–400 cmꢁ1 using KBr pellets.
Electronic spectra were recorded on a Cary 5000, version 1.09 UV–
Vis–NIR spectrophotometer using acetonitrile solutions. Magnetic
susceptibility measurements were made in the polycrystalline
state in a simple Gouy balance using cobaltmercuric thiocyanate,
Hg[Co(SCN)4] at room temperature at the Department of Applied
Chemistry, CUSAT, Kochi, India. The EPR spectra were recorded in
a Varian E-112 X-band spectrometer using TCNE (g = 2.00277) as
standard at the SAIF, IIT, Bombay, India. The molar conductivities
of the complexes in DMF solutions (10ꢁ3 M) at room temperature
were measured using a direct reading conductivity meter.
nality index
perfect square pyramidal and trigonal bipyramidal geometries the
values of are zero and unity respectively). The value of for the
s is calculated using the equation s = (b–a)/60 [16] (for
s
s
molecule is 0.217 which shows that the compound exhibits a dis-
torted square pyramidal geometry with the basal plane occupied
by thiosemicarbazone and the acetate oxygen O2.
2.4. X-ray crystallography
Single crystals of complex [Cu2(L)2(OAc)2] (2a) suitable for
X-ray diffraction studies were obtained by slow evaporation of
its methanolic solution over a period of one week at room temper-
ature. A single crystal of dimensions 0.36 ꢂ 0.20 ꢂ 0.20 mm3 was
selected and mounted on a Bruker SMART APEX diffractometer,
equipped with a graphite crystal incident-beam monochromator,
The oxygen O2A from acetate group of the adjacent monomer
plugs into the axial position resulting in a dimer with a Cuꢀ ꢀ ꢀCu
separation of 3.500 Å. The four coplanar basal atoms show a
significant distortion from a square geometry as indicated by the
N1–Cu1–S1 bond angle of 163.20(5)°. The deviation of the central
copper atom from the basal plane in the direction of the axial
oxygen is evident from the bond angles of N2–Cu1–O2,
176.22(6)° and N1–Cu1–O2, 96.85(7)°. Most of the angles involving
the central copper atoms are widely different from 90° and 180°,
and a fine focus sealed tube with Mo K
a (k = 0.71073 Å) as the
X-ray source. The unit cell dimensions were measured and the data
collection was performed at 293(2) K. Bruker SMART software was

52
K. Jayakumar et al. / Polyhedron 75 (2014) 50–56
Table 1
Crystal refinement parameters of [Cu2(L)2(OAc)2] (2a).
Empirical formula
Formula weight
T (K)
C34H36Cu2N8O4S2
811.91
293(2)
Wavelength (Å)
Crystal system
space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
P21/n
8.808(2)
b (Å)
16.589(5)
c (Å)
12.391(3)
a
(°)
b (°)
(°)
90
93.909(10)
90
c
V (°)
1806.3(8)
Z
2
Calculated density (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
1.493
1.342
836
)
Fig. 1. The molecular structure of [Cu2(L)2(OAc)2] (2a) along with the atom
numbering scheme.
Crystal size (mm)
h (°)
0.30 ꢂ 0.20 ꢂ 0.20
2.05–28.05
Limiting indices
ꢁ11 6 h 6 11, ꢁ21 6 k 6 21,
ꢁ15 6 l 6 16
Reflections collected/unique (Rint
Completeness to h (%)
Absorption correction
Maximum and minimum
transmission
)
21166/4381 (0.0290)
25.00 (100.0)
Table 3
Selected bond lengths (Å) and bond angles (°) of [Cu2(L)2(OAc)2] (2a).
semi-empirical from equivalents
0.801 and 0.722
Cu(1)ꢁN(1)
2.0227(17)
1.9651(16)
1.9432(13)
2.2601(8)
1.730(2)
1.299(2)
1.328(3)
1.357(2)
3.500
Cu(1)ꢁN(2)
Refinement method
full-matrix least-squares on F2
4381/0/229
1.035
Cu(1)ꢁO(2)
Data/restraints/parameters
Cu(1)ꢁS(1)
Goodness-of-fit (GOF) on F2
C(15)ꢁS(1)
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0327, wR2 = 0.0831
R1 = 0.0480, wR2 = 0.0902
0.281 and ꢁ0.269
C(8)ꢁN(2)
C(15)ꢁN(3)
Largest difference in peak and hole
N(2)–N(3)
(e Åꢁ3
)
Cu1ꢀ ꢀ ꢀCu1A
P
P
P
P
|Fo|; wR2 = [ w(F2o ꢁ Fc2)2/ w(F2o)2]1/2
.
O(2)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
N(2)–Cu(1)–N(1)
O(2)–Cu(1)–S(1)
N(2)–Cu(1)–S(1)
N(1)–Cu(1)–S(1)
176.22(6)
96.85(7)
80.26(7)
98.56(5)
84.04(5)
163.20(5)
R1
=
||Fo| ꢁ |Fc||
/
indicating significant distortion from the square pyramidal
geometry.
Weak non-classical intramolecular hydrogen bonding interac-
tions (Fig. 2) make the molecule more rigid and the two types of
C–Hꢀ ꢀ ꢀ
p interactions mainly involve in interconnecting the neigh-
boring molecules with Hꢀ ꢀ ꢀCg distances of 3.2523 and 3.3856 Å
bond strength, confirming the coordination via the azomethine
(Table 4). Very weak
tal system.
p p interactions are also present in the crys-
ꢀ ꢀ ꢀ
nitrogen [17]. In the spectrum of HL, two strong bands at 1420
and 805 cmꢁ1 are assigned to
m(C@S), whereas in the complexes
these bands are found to shift to lower frequencies in the ranges
1340–1310 and 796–777 cmꢁ1 respectively. This characteristic
3.2. IR spectra
shift of the
via the thioiminolate sulfur atom. Formation of a new band at ca.
1510 cmꢁ1 assigned to
(C = N) bond and disappearance of med-
ium band at 3055 cmꢁ1 assigned to (2N–H) vibration provides a
m(C@S) in the complexes confirms the coordination
The tentative assignments of the significant IR spectral bands of
HL and its copper(II) complexes are presented in Table 5. The
m
m
(C@N) band at 1575 cmꢁ1 is shifted to lower energies in the spec-
m
strong evidence for the ligand coordination around Cu(II) ion in
the deprotonated form. Coordination of pyridine ring nitrogen in
the complexes is indicated by a shift of in-plane and out-of-plane
ring deformation bands [18]. Based on the above spectral evidence,
tra of the complexes indicating coordination through azomethine
nitrogen [17]. The strong band at 1115 cmꢁ1 is assigned to
m(N–N)
band of the thiosemicarbazone. In complexes, the frequency of this
band was found to increase and may be due to the increase in the
Table 2
Colors, partial elemental analyses and magnetic moments of 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone and its copper(II) complexes.
Compounds
Color
Found (Calc.)%
C
l
(B.M.)
K*
M
H
N
S
HL
yellow
black
black
63.85 (63.35)
44.75 (44.60)
48.55 (49.20)
43.94 (44.06)
45.33 (45.27)
45.27 (45.43)
38.09 (38.02)
5.86 (5.67)
4.18 (3.99)
4.77 (4.62)
3.77 (3.70)
3.84 (4.05)
3.39 (4.05)
3.60 (3.19)
20.01 (19.70)
13.60 (13.87)
12.97 (13.50)
17.14 (17.13)
24.68 (24.68)
17.46 (16.56)
11.78 (11.82)
11.00 (11.28)
12.00 (11.91)
7.23 (7.73)
8.08 (7.84)
8.50 (8.06)
[Cu2(L)2SO4]ꢀH2O (1)
[Cu2(L)2(OAc)2]ꢀH2O (2)
[Cu(L)NO3]2 (3)
[Cu(L)N3]2ꢀH2O (4)
[Cu(L)NCS]ꢀH2O (5)
[Cu(L)I] (6)
1.38
1.37
1.52
1.63
1.60
1.78
5.8
1.6
71
3
14.2
4.5
black
brown
brown
black
14.48 (15.16)
6.31 (6.77)
*
10ꢁ3 M solutions in DMF.

K. Jayakumar et al. / Polyhedron 75 (2014) 50–56
53
are typical for unidentate N-bonded thiocyanate complexes [23].
The presence of lattice water was confirmed from the broad band
obtained above 3400 cmꢁ1 [24].
3.3. Electronic spectra
The electronic spectral data of thiosemicarbazone and its Cu(II)
complexes in acetonitrile solution are given in Table 6.
The spectrum of thiosemicarbazone, HL consists of broad band
at 36580 cmꢁ1. This band remained almost unshifted in the com-
plexes and is due to
p–
p⁄ transition of the thiosemicarbazone.
The n–p⁄ band which is found at 29820 cmꢁ1 in the spectrum of
thiosemicarbazone was slightly shifted due to complexation. This
is an indication of the enolization followed by deprotonation of
the ligand during complexation [25]. The charge transfer bands
were observed in the 23000–25000 cmꢁ1 range, and their broad-
ness can be explained as due to the combination of S ? Cu and pyr-
idine N ? Cu LMCT transitions [25]. All complexes exhibit d–d
bands as shoulders in the 14430–18230 cmꢁ1 region.
Fig. 2. Molecular structure showing intramolecular hydrogen bonding interactions.
Table 4
3.4. EPR studies
Hydrogen bonding interactions.
DꢁHꢀ ꢀ ꢀA
DꢁH (Å)
0.9602
0.9609
Hꢀ ꢀ ꢀA (Å)
2.3131
2.4833
Dꢀ ꢀ ꢀA (Å)
2.670(3)
2.982(3)
\DꢁHꢀ ꢀ ꢀA (°)
101.13
112.19
The EPR spectra of the complexes in polycrystalline state at
298 K and solution state at 77 K were recorded in the X band, using
100 kHz field modulation and the g factors were quoted relative to
the standard marker TCNE (g = 2.00277). The EPR spectra are sim-
ulated using EasySpin 4.0.0 package [26] and the experimental
(red) and simulated (blue) best fits are included. The EPR parame-
ters of the copper(II) complexes were presented in Table 7.
C(16)–H(16C)ꢀ ꢀ ꢀN(3)
C(17)–H(17A)ꢀ ꢀ ꢀS(1)
XꢁH(I)ꢀ ꢀ ꢀCg(J)
Hꢀ ꢀ ꢀCg (Å)
Xꢀ ꢀ ꢀCg (Å)
\XꢁHꢀ ꢀ ꢀCg (°)
CꢁHꢀ ꢀ ꢀ
p interactions
C(16)–H16BꢀꢀꢀCg(1)a
3.2523
3.3856
3.657(3)
4.179(3)
107.43
141.35
C(16)–H16BꢀꢀꢀCg(1)a
In polycrystalline state at 298 K, compounds 1, 4 and
5
Equivalent position code: a = ꢁ1 + x, y, z.
Cg(1) = N1, C3, C4, C5, C6, C7.
D, donor; A, acceptor; Cg, centroid;
displayed isotropic spectra with giso = 2.080, 2.053 and 2.060
respectively, arising from extensive exchange coupling through
misalignment of the local molecular axes between different mole-
cules in the unit cell and enhanced spin lattice relaxation. Unfortu-
nately this type of spectra give no information on the electronic
ground state of Cu(II) ion present in the complexes. However the
dimeric nature of the complex 1 is evident from the half field signal
at 1540 G (g = 4.200), with a sevenfold hyperfine splitting.
EPR spectra of compounds 2, 3 and 6 showed typical axial
behavior with slightly different g|| and g\ values in the polycrystal-
line state. The variation in the g|| and g\ values indicated that the
geometry of the compounds in the solid state is affected by the -
it is confirmed that the thiosemicarbazone HL is tridentate in nat-
ure coordinating via the azomethine nitrogen, the pyridyl nitrogen
and thioiminolate sulfur.
Sulfato complex 1 showed strong band at 1029 cmꢁ1 due to m1
and weak band at 962 cmꢁ1 due to
m3 can be assigned to the sulfato
anion existing in the bridged bidentate form [19]. This type of sulf-
ato complex with bridged bidentate nature has been proved for
copper complex derived from di-2-pyridyl ketone thiosemicarba-
zone [20]. The bands at 1551 [m [ms(COO)]
a(COO)] and 1387 cmꢁ1
support the bridging nature of acetate group in complex 2 [21].
Table 6
Electronic spectral assignments, k (cmꢁ1) for HL and its copper(II) complexes.
In the nitrato complex 3, three strong bands at 1459, 1392 and
1140 cmꢁ1 indicates the m4
, m1 and m2 modes of the nitrato group
Compound
d ? d
LMCT
n ? p⁄
p ?
p⁄
and it confirms the presence of terminal monodentate nitrato
group [19]. The azido complex 4 shows a single strong band at
2055 cmꢁ1 due to the asymmetric stretching mode and the band
associated with symmetric stretching mode is located at
1386 cmꢁ1 [22]. Thiocyanato complex 5 exhibit strong band at
2073 cmꢁ1 and weak bands at 747 and 489 cmꢁ1, which can be
HL
–
–
29820
32720
32720
32340
32910
32780
31790
36580
37940
37740
38060
38000
37910
40610, 37320
[Cu2(L)2SO4]ꢀH2O (1)
[Cu2(L)2(OAc)2]ꢀH2O (2)
[Cu(L)NO3]2 (3)
[Cu(L)N3]2ꢀH2O (4)
[Cu(L)NCS]ꢀH2O (5)
[Cu(L)I] (6)
16120
16430
16370
17310
16970
15820
23210
23520
23210
23210
23220
23770
attributed to m(CN), m(CS), and m(NCS) respectively. These values
Table 5
Infrared spectroscopic assignments (cmꢁ1) for the 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone and its copper(II) complexes.
Compounds
m
(C@N)
m(NꢁN)
m(C@S)
m
(2NH)
m
(C@N)a
m(CuꢁNazo
)
m(py(ip))
HL
1575
1551
1545
1539
1539
1545
1545
1115
1122
1140
1122
1146
1120
1122
1420, 805
1340, 796
1315, 784
1321, 790
1310, 777
1315, 790
1320, 790
3055
–
–
699
670
655
649
643
636
612
[Cu2(L)2SO4]ꢀH2O (1)
[Cu2(L)2(OAc)2]ꢀH2O (2)
[Cu(L)NO3]2 (3)
[Cu(L)N3]2ꢀH2O (4)
[Cu(L)NCS]ꢀH2O (5)
[Cu(L)I] (6)
–
–
–
–
–
–
1514
1509
1514
1514
1502
1514
544
526
544
532
532
502
a
Newly formed C@N bond.

54
K. Jayakumar et al. / Polyhedron 75 (2014) 50–56
Table 7
Spin Hamiltonian and bonding parameters of copper(II) complexes of 2-benzoylpyridine-N4,N4-dimethyl-3-thiosemicarbazone.
Compounds
Polycrystalline state (298 K)
DMF solution (77 K)
giso
g||
g\
G
g||/g3
g
\/g1, g2
gav
A||
A\
38
Aav a2
0.601
b2
c2
K||
K\
f
[Cu2(L)2SO4]ꢀH2O (1)
[Cu2(L)2(OAc)2]ꢀH2O(2)
[Cu(L)NO3]2 (3)
[Cu(L)N3]2ꢀH2O (4)
[Cu(L)NCS]ꢀH2O (5)
[Cu(L)I] (6)
2.080
2.200
2.197
2.15
2.16
2.192
2.204
2.044, 2.090
2.052
2.110
1.970, 2.060
2.044
2.055
2.111
2.100
2.123
2.063
2.093
2.053
0.529
0.872
1.028
–
0.843
0.831
1.536
0.881
1.757
–
0.791
0.849
0.319
0.695
0.604
–
0.697
0.694
0.924
0.702
1.032
–
0.654
0.709
2.128
2.104
2.047
2.060
–
2.812
1.763
–
194
127
–
208
205
90
0.797
0.587
–
127
168.6
–
104.9
107
2.053
2.060
–
38
38
–
–
–
–
95
94
0.827
0.835
2.073
2.057
1.300
A values in 10ꢁ4 cmꢁ1
.
nature of the coordinating gegenions. The geometric parameter G is
a measure of exchange interaction between the copper centres and
is calculated for each species using the equation G = (g||–2.0023)/
(g\–2.0023) for all axial spectra. If G > 4, exchange interaction is
negligible and if it is less than 4, considerable exchange interaction
is indicated in the solid complex [27]. The calculated G values are
less than 4 which indicate that considerable exchange interaction
is present in complexes. The g|| values are nearly the same for all
the complexes indicating that the bonding is dominated by the thi-
osemicarbazone moiety. The gav values of all the complexes in the
solution state are consistent with the giso values suggesting that
they are not undergoing any kind of dissociation in the solution
state. The g|| values are less than 2.3 is an indication of significant
covalent character to the M–L bond [28]. Although the compounds
1 (Fig. 3) and 4 displayed isotropic nature in polycrystalline state,
they show rhombic symmetry with no hyperfine splittings in the
parallel and perpendicular regions in the solution at 77 K. For the
compound 4, very weak signal obtained at 1600 G (g = 4.04) may
be due to the dimeric nature of the compound.
In DMF solution at 77 K, the spectra of compounds 2, 3 (Fig. 4), 5
and 6 showed axial behavior with well defined g|| and g\ values.
For the compounds 2, 5 and 6, axial spectra with four hyperfine
lines both in the perpendicular and parallel regions were obtained
due to the interaction of electron spin with copper(II) nuclear spin.
In compounds 2 and 5, superhyperfine splitting are seen both in
the perpendicular and parallel regions which gives an evidence
for the coordination of azomethine and pyridyl ring nitrogens in
the complexes. For complex 2 the presence of half field (g = 4) ca.
at 1600 G confirms the binuclearity of the complex. Hyperfine
splittings are not observed due to high Cuꢀ ꢀ ꢀCu (3.500 Å) distance
separation as obtained from X-ray structural analysis [29].
Even though compound 3 gave axial spectrum in DMF solution
at 77 K, the hyperfine structure is not well resolved and this may
be due to the poor glass formation. Expected superhyperfine split-
ting due to nitrogen atoms are missing in this compound. The
interesting fact of the spectrum of the compound is that the pres-
ence of seven hyperfine splitting for the half field signal, due to the
coupling of the electron spin with the nuclear spin of the two cop-
per centers (2nI + 1 = 2 ꢂ 2 ꢂ 3/2 + 1).
In frozen state, compound 6 showed two different species due
to the formation of solvent coordinated complex along with 6
which is evidenced by seven hyperfine lines at the parallel region.
Superhyperfine splittings both in perpendicular and parallel re-
gions were observed. The absence of any half field signals rules
out the possibility of any significant coupling between the copper
centers.
The EPR parameters g||, g\, gav, A|| (Cu) and A\ (Cu) and the ener-
gies of d–d transition were used to evaluate the bonding parame-
ters
covalency of the in-plane
a
2, b2 and c2 which may be regarded as measures of the
r
-bonds, in-plane p-bonds and out-of-
plane p-bonds respectively.
The value of in-plane sigma bonding parameter a2 was esti-
mated from the expression [30]
a2 ¼ ꢁA =0:036 þ ðg ꢁ 2:0023Þ þ 3=7ðg? ꢁ 2:0023Þ þ 0:04
jj
jj
The following simplified expression were used to calculate the
bonding parameters
K2jj ¼ ðgjj ꢁ 2:0023ÞEdꢁd=8k0
Fig. 3. EPR spectrum of [Cu2(L)2SO4]ꢀH2O (1) in DMF at 77 K.

K. Jayakumar et al. / Polyhedron 75 (2014) 50–56
55
Fig. 4. EPR spectrum of [Cu(L)NO3]2 (3) in DMF at 77 K.
K2jj ¼ ðg? ꢁ 2:0023ÞEdꢁd=2k0
acknowledges CSIR for the award of Junior Research Fellowship. The
authors are thankful to the Sophisticated Analytical Instrumenta-
tion Facility, IIT Madras, India for single crystal X-ray diffraction
measurements and SAIF Kochi for IR, UV-Vis studies and IIT Bombay
for providing EPR results.
K2jj
¼
¼
a
2b2
K?2
a2c2
Appendix A. Supplementary data
Where K|| and K\ are orbital reduction factors and k0 represents the
one electron spin orbit coupling constant which equals ꢁ828 cmꢁ1
.
CCDC 904873 contains the supplementary crystallographic data
for [Cu2(L)2(OAc)2]. These 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, IEZ, UK; fax: (+44) 1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk.
Hathaway [31] has pointed out that for pure sigma bonding
K|| ꢃ K\ ꢃ 0.77, for in plane
plane -bonding, K\ < K||. In all complexes except for 5, it is ob-
served that K|| < K\.which indicates the presence of significant in
plane -bonding. For complex 5, K\ < K|| indicates that significant
out-of-plane -bonding is present in complex. The metal–ligand
bond is purely ionic, if the value of
2 is unity and it is completely
covalent, if
2 = 0.5 [31]. Here a2 values calculated for the com-
p -bonding K|| < K\ and for out-of-
p
p
p
a
References
a
plexes lie in between 0.5 and 1, which means that the metal–ligand
bonds in the complexes under investigation are partially ionic and
partially covalent in nature. The empirical factor f = gjj/A|| is an in-
dex of tetragonal distortion. The value may vary from 105–135 for
small to medium distortion and depends on the nature of the coor-
dinated atom [32]. High distortion occurs for the nitrato complex
(f = 168). In all other complexes distortion is medium and is found
to be in the range 105–130 cm [33].
[1] C. Stefani, G. Punnia-Moorthy, D.B. Lovejoy, P.J. Jansson, D.S. Kalinowski, P.C.
Sharpe, P.V. Bernhardt, D.R. Richardson, J. Med. Chem. 54 (2011) 6936.
[2] G. Pelosi, F. Bisceglie, F. Bignami, P. Ronzi, P. Schiavone, M.C. Re, C. Casoli, E.
Pilotti, J. Med. Chem. 53 (2010) 8765.
[3] A. Garoufis, S.K. Hadjikakou, N. Hadjiliadis, Coord. Chem. Rev. 253 (2009) 1384.
[4] I. Dilovic, M. Rubcic, V. Vrdoljak, S.K. Pavelic, M. Kralj, I. Piantanida, M. Cindric,
Bioorg. Med. Chem. 16 (2008) 5189.
[5] S. Dutta, F. Basuli, A. Castineiras, S.M. Peng, G.H. Lee, S. Bhattacharya, Eur. J.
Inorg. Chem. (2008) 4538.
[6] A. Amoedo, L.A. Adrio, J.M. Antelo, J. Martínez, M.T. Pereira, A. Fernández, J.M.
Vila, Eur. J. Inorg. Chem. (2006) 3016.
[7] T.S. Lobana, S. Khanna, R.J. Butcher, Dalton Trans. 41 (2012) 4845.
[8] D.X. West, J.S. Ives, J. Krejci, M.M. Salberg, T.L. Zumbahlen, G.A. Bain, A.E.
Liberta, Polyhedron 14 (1995) 2189.
[9] K. Jayakumar, M. Sithambaresan, M.R.P. Kurup, Acta Crystallogr., Sect. E 67
(2011) o3195.
4. Conclusion
Copper(II) complexes of 2-benzoylpyridine-N4,N4-dimethyl-3-
thiosemicarbazone (HL) were synthesized and characterized using
various physicochemical techniques. The NNS chelating mode of
the thiosemicarbazone was proved in one complex. The molecular
structure of [Cu2(L)2(OAc)2] (2a) showed that each copper center
have distorted square pyramidal geometry. Presence of half field
signal with sevenfold splittings at EPR spectra confirmed the bin-
uclearity of some complexes. For all complexes, g||>g\ > 2.0023
showed that single electron of copper(II) nucleus resides in the
[10] SMART and SAINT, Area Detector Software Package and SAX Area Detector
Integration Program, Bruker Analytical X-ray, Madison, WI, USA, 1997.
[11] SADABS, Area Detector Absorption Correction Program, Bruker Analytical X-ray,
Madison, WI, USA, 1997.
[12] G.M. Sheldrick, SHELXTL-PLUS, Crystal Structure Analysis Package, Bruker
Analytical X-Ray, Madison, WI, USA, 1997.
[13] K. Brandenburg, Diamond Version 3.1d, Crystal Impact GbR, Bonn, Germany,
2006.
[14] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[15] B.S. Garg, M.R.P. Kurup, S.K. Jain, Y.K. Boon, Transition Met. Chem. 13 (1988)
309.
[16] A.W. Addison, T.N. Rao, R. Reedijk, J.V. Rijn, G.C. Verschoor, J. Chem. Soc.,
Dalton Trans. 7 (1984) 1349.
2
2
dxꢁy orbital which is the ground state.
[17] E.B. Seena, M.R.P. Kurup, Spectrochim. Acta Part A 69 (2008) 726.
[18] B.S. Garg, M.R.P. Kurup, S.K. Jain, Y.K. Boon, Transition Met. Chem. 16 (1991)
111.
[19] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fifth ed., John Wiley & Sons, NewYork, 1997. p. 86.
Acknowledgments
K. Jayakumar thanks the University Grants Commission,
Bangalore, India for financial support. A.A. Aravindakshan gratefully

56
K. Jayakumar et al. / Polyhedron 75 (2014) 50–56
[20] V. Philip, V. Suni, M.R.P. Kurup, Polyhedron 25 (2006) 1931.
[21] S.M. Roy, M.R. Sudarsanakumar, S. Suma, M.R.P. Kurup, V.S. Dhanya, R.M. Nair,
Inorg. Chem. Commun. 40 (2014) 200.
[22] T.A. Reena, M.R.P. Kurup, Spectrochim. Acta Part A 76 (2010) 322.
[23] R.A. Bailey, S.L. Kozak, T.W. Michelsen, W.N. Mills, Coord. Chem. Rev. 6 (1971)
407.
[28] D. Kivelson, R. Neiman, J. Chem. Phys. 35 (1961) 149.
[29] V. Philip, V. Suni, M.R.P. Kurup, M. Nethaji, Polyhedron 24 (2005) 1133.
[30] B.N. Figgis, Introduction to Ligand fields, Interscience, New York, 1996. p. 295.
[31] B.J. Hathaway, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty (Eds.),
Comprehensive Coordination Chemistry, vol. 5, Pergamon, Oxford, 1987, p.
533.
[24] V. Stefov, V.M. Petrusevski, B. Soptrajanov, J. Mol. Struct. 293 (1993) 97.
[25] P.F. Rapheal, E. Manoj, M.R.P. Kurup, Polyhedron 26 (2007) 818.
[26] S. Stoll, Spectral Simulations in Solid-State Electron Paramagnetic Resonance,
Ph.D. thesis, ETH, Zurich, 2003.
[32] L. Latheef, M.R.P. Kurup, Spectrochimica Acta, Part A 70 (2008) 86.
[33] R.P. John, A. Sreekanth, V. Rajakannan, T.A. Ajith, M.R.P. Kurup, Polyhedron 23
(2004) 2549.
[27] M. Joseph, V. Suni, M.R.P. Kurup, M. Nethaji, A. Kishore, S.G. Bhat, Polyhedron
23 (2004) 3069.