Full text of DOI:10.1016/j.poly.2020.114687

Polyhedron 188 (2020) 114687
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Two new copper(II) binuclear complexes with 2-[(E)-(pyridine-2yl-
hydrazono)methyl]phenol: Molecular structures, quantum chemical
calculations, cryomagnetic properties and catalytic activity
a,
a
b
c
c
c
R.N. Patel a, , S.K. Patel , D. Kumhar , Nirmala Patel , A.K. Patel , R.N. Jadeja , Neetu Patel ,
⇑
⇑
R.J. Butcher d, M. Cortijo e, S. Herrero e
a Department of Chemistry, APS University, Rewa 486003, India
b Department of Botany, Govt. Science College, Rewa 486003, India
c Department of Chemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390002, India
d Department of Inorganic and Structural Chemistry, Howard University, Washington DC 22031, USA
e Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The Schiff base is synthesized by the reaction of 2-hydrazinopyridine and salicylaldehyde. The copper(II)
binuclear complexes [Cu2(m-ClO4)(L)2(H2O)2](ClO4)ꢀH2O(1) and [Cu2(m-pyrazine)(L)2](ClO4)2(2)with
2-[(E)-(pyridine-2yl-hydrazono)methyl]phenol (HL), were synthesized and characterized using various
physicochemical techniques. The molecular structures of both binuclear complexes were evaluated by
single-crystal X-ray analysis. Analysis of the supramolecular synthons and their effect on crystal packing
is conferred in the context of crystal engineering. The electron paramagnetic spectra are reported as well.
The electrochemical behavior of both complexes was explored using cyclic voltammetry (CV) and differ-
ential pulse voltammetry (DPV) techniques. The electronic and spectral properties are described by quan-
tum chemical calculations (TD and DFT).The cryomagnetic investigation (2–300 K) reveal
antiferromagnetic exchange coupling between two copper(II) centres of different strength:
JCuCu = ꢁ21.6 and JCuCu = -6.8 cmꢁ1 for 1 and 2, respectively. The strong antiferromagnetic coupling
between the copper centers found in 1 could be explained not only by magnetic exchange through hydro-
Received 20 May 2020
Accepted 19 June 2020
Available online 26 June 2020
Keywords:
Copper(II) complexes
Crystal structure
Biological activity
Quantum chemical calculations
Superoxide dismutase
gen bonds but also through the p-p stacking of the Schiff base ligands. Both binuclear complexes exhibit
catalytic activity toward the dismutation of superoxide anion at physiological pH. Although the activity in
both complexes is lower than the native enzyme, they have potential as antioxidant SOD model for phar-
maceutical applications.
Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction
developments between molecules and therefore mediate self-
assembly of defined supramolecular synthons [15]. The role of
The design of binuclear complexes using tridentate Schiff bases
and bridging ligands have been carried out by many inorganic che-
mists [1–6]. The binuclear metal complexes with chelate ligands
such as tridentate Schiff bases are interesting to study to mimic
the biological properties of Cu-Zn superoxide dismutase [7]. In par-
ticular, copper(II) binuclear complexes are of significance owing to
their structural versatility, and variety of magnetic couplings they
can present [8–14]. Supramolecular interactions such as hydrogen
hydrogen-bonded supramolecular synthons is approved in crystal
engineering [16]. Copper complexes have been studied extensively
mainly because of its biologically relevant redox properties and to
mimic the functions of proteins [7,15–20].
The metal complexes used in the study were binuclear copper
(II) complexes 1 and 2 having a Schiff base ligand 2-[(E)-(pyri-
dine-2yl hydrazono)methyl]phenol (HL), with one pyridine, one
imine, one phenolic donor groups, and bridging pyrazine or per-
chlorate attached to it. The coordination behavior of transition
metals with azo ligands (-C@N-NH- or -C-N@N-) is of importance
bonds and
p-p stacking show an important role in crystal engi-
neering as they advance to directional molecular recognition
for their
p-acidity, functional coordination modes, and molecular
structures, dye and pigmenting behavior, redox, photophysical
⇑
and biological properties [21,22]. These properties are ascribed to
Corresponding author.
E-mail address: patelsatish33@yahoo.co.in (S.K. Patel).
the low-lying
p* orbitals of azo functionality. Hydrazones are an
https://doi.org/10.1016/j.poly.2020.114687
0277-5387/Ó 2020 Elsevier Ltd. All rights reserved.

2
R.N. Patel et al. / Polyhedron 188 (2020) 114687
example of azo chelate ligands. The coordination chemistry of
hydrazone ligands is continuing to be an interesting field of
research. Hydrazone is a class of compounds that have potential
applications as catalysts [23,24], molecular sensors [25], lumines-
cent probes [26], and also as therapeutic agents [27]. The biological
properties and diversity of binding modes of such ligands inspired
us to explore the nature of coordination as well as the structural
features of binuclear copper(II) complexes with 2-[(E)-(pyridine-
2yl hydrazono)methyl] phenol ligand. Both redox and cryomag-
netic data were explored. Molecular structures of the present
complexes were determined using a single-crystal X-ray diffrac-
tion technique. Further, both complexes were characterized by
different physicochemical techniques viz., elemental analysis,
infrared (IR), and UV–visible (UV–vis) spectroscopy and electro-
chemical techniques like cyclic voltammetry (CV) and differential
pulse voltammetry (DPV). Both complexes were also studied using
electron paramagnetic resonance spectroscopy (EPR) and cryomag-
netic technique. These two techniques are widely used for the
identification and characterization of paramagnetic transition
metal complexes [21,22,28–30]. Binuclear transition metal com-
plexes show significant structural variation and can act as potent
magnetic materials. These techniques enable important insight
and binding properties of such transition metal complexes. Their
antioxidant properties were also studied and it was demonstrated
that copper(II) ion plays a key role in the mechanism of activity.
Determination of the antioxidant activity in the reaction with
superoxide radical-anion O2ꢀꢁis the most perspective approach.
We have already reported transition metal mono- and binuclear
complexes bearing NNO/NOO donor set [5,31–33]. Thus, in contin-
uation of these studies bearing similar donor set with heterocyclic
bases, we report here the synthesis, structural characterization and
electrochemical studies of copper(II) complexes with a new hydra-
zone Schiff base ligand 2-[(E)-(pyridine-2yl-hydrazono)methyl]
phenol (HL) obtained from the condensation of 2-hydrazinopy-
ridine and salicylaldehyde. Multinuclear metal clusters comprise
a small subset of a larger family of metal-based supramolecular
assemblies. The self-assembly of supramolecular structures com-
pressed via metal–ligand coordinate bonds along with other weak
interactions continues to attract considerable attention [34–36]. Of
particular relevance to the present work are the many supramolec-
ular complexes that utilize ligands which contain a pyridyl moiety.
As a result, several supramolecular metal(II) complexes are well
documented in the literature [37–40].
indicated the formation of the Schiff base ligand precursor (HL).
During this period a yellow solid slowly precipitated. The solid
mass was filtered, recrystallized from ethanol and characterized
by analytical and spectral techniques. Yield: ~83%. Anal. Calcd.
(%) for C12H11N3O (M = 213.23 g molꢁ1): C, 67.60; H, 5.20; N,
19.70. Found: C, 67.53; H, 5.02; N, 19.94. FT-IR bands (KBr, cmꢁ1
)
m
(C@N) 1654 m, m(–OH) 3186b, m
(–NH-) 2988 m (Fig. S1). 1H
NMR (CDCl3, 400 MHz) d = 10.73 (Ar-OH), 7.96 (CH = N) and 7.68
(–NH-), 7.26 (2H, py), 7.22 (4H, py), 6.96 to 6.85 (Ar-H) (Fig. S2).
3.2. Synthesis of [Cu2(m-ClO4)(L)2(H2O)2](ClO4)ꢀH2O(1)
To a 20 mL methanolic solution of HL (0.213 g, 1 mmol), copper
perchlorate hexahydrate (0.370 g, 1 mmol) was added and stirred
for 2 h at room temperature. The green solution was left undis-
turbed fora few days for evaporation at ambient temperature to
get green crystals. These green crystals were filtered off, washed
with ether, and dried in a desiccator over calcium chloride. Yield:
~73%. Anal. Calcd. (%) for C24H26Cl2Cu2N6O13 (M = 804.49 g molꢁ1):
C, 35.83; H, 3.26; N, 10.45. Found: C, 35.63; H, 3.18; N, 10.64. Con-
ductance (Ʌm/s cm2 molꢁ1) in DMSO 123. Electronic absorption
spectrum in DMSO (kmax, 648 nm e, 167 Mꢁ1 cmꢁ1). FT-IR bands
(KBr, cmꢁ1): (ClOꢁ4 ) 1077 (Fig. S1).
m(C@N) 1563, m(C@O) 1611, m
3.3. Synthesis of [Cu2(m-pyrazine)(L)2](ClO4)2(2)
To a 20 mL methanolic solution of HL (0.213 g, 1 mmol) copper
(II) perchlorate hexahydrate (0.370 g, 1 mmol) was added with
constant stirring. After 20 min pyrazine (0.040 g, 0.5 mmol) was
added to the above solution with stirring. The resulting green solu-
tion was left for few days undisturbed for evaporation at ambient
temperature to obtain green crystals. The crystals were collected
by filtration and dried over calcium chloride desiccator. Yield:
~73%. Anal. Calcd (%) for C28H24Cl2Cu2N8O10 (M = 830.53 g/mol):
C, 40.49; H, 2.91; N, 13.49. Found: C, 40.06; H, 2.48; N, 13.54. Con-
ductance (Ʌm/s cm2 molꢁ1) in DMSO 235. The electronic absorp-
tion spectrum in DMSO (kmax, 638 nm e, 168 Mꢁ1 cmꢁ1).FT-IR
bands (KBr, cmꢁ1):
(Fig. S1).
m(C@N) 1561, m(C@O) 1610, m
(ClOꢁ4 ) 1075
4. Physical measurements
Elemental analyses were performed at SAIF, CDRI, Lucknow. The
UV–vis spectra were recorded on a Shimadzu UV-1601. The Fourier
transform infrared (FTIR) spectral data were obtained on a Perkin-
2. Experimental section
Elmer IR
a-T spectrophotometer. NMR spectra of ligand were
All used reagents and chemicals were of reagent grade.
2-hydrazinopyridine, salicylaldehyde, and copper(II) salts were
purchased from Across Organics and used as supplied.
recorded on a Bruker Avance III 400 MHz spectrometer. TMS was
used as an internal standard. The electron paramagnetic resonance
(EPR) spectra of copper(II) complexes in solid and solutions were
measured on Varian E-line Century Series Spectrometer operating
at X-band (9.25 G Hz) modulation frequency at room and low tem-
peratures. The EPR spectra were calibrated with tetracya-
noethylene(TCNE) as a field marker. Cyclic voltammetry (CV) and
differential pulse voltammetry (DPV) measurements were per-
formed with a BAS-100 electrochemical analyzer under a dry nitro-
gen atmosphere. Ag/AgCl electrode was used as the reference
electrode and ferrocene as an internal standard in cyclic voltam-
metry [43]. Before the electrochemical measurements, a glassy car-
bon working electrode was polished, rinsed with distilled water,
washed with DMSO, and dried. Magnetic susceptibility measure-
ments were performed using a Quantum Design MPMSXL SQUID
magnetometer operating under an applied dc magnetic field of
5000 Oe in the 2–300 K temperature range. Finely ground crystals
of 1 (28.64 mg) and 2 (10.45 mg) were employed for the measure-
ments. The data were corrected for the sample holder, the intrinsic
3. Caution
Although no problems were encountered during the synthesis
of copper(II) complexes, perchlorate salts are potentially explosive
and must be handled with extreme care.
3.1. Synthesis of Schiff base ligand (HL)
The Schiff base (HL) was synthesized according to the reported
method [41,42]. The Schiff base 2-[(E)-(pyridine-2yl-hydrazono)
methyl]phenol (HL) was synthesized by the condensation of
100 mL of 2-hydrazinopyridine (1.091 g, 10 mmol) and salicylalde-
hyde (0.8 mL, 10 mmol) in presence of glacial acetic acid (0.5 mL,
10 mmol) in ethanol (20 mL). The reaction mixture was refluxed
in a water bath for 3 h. The resulting pale yellow coloration

R.N. Patel et al. / Polyhedron 188 (2020) 114687
3
diamagnetic contributions of the compounds, and the tempera-
ture-independent paramagnetism.
supports the condensation of 2-hydrazinopyridine with salicy-
laldehyde is the single-crystal X-ray structures of 1 and 2 which
demonstrate the coordination of the deprotonated Schiff base
(Lꢁ)to the copper(II) center. Elemental analysis and FTIR data of 1
and 2 are consistent with the proposed formulae. The molar con-
ductance data reveal the ionic nature of both complexes, 1 and 2,
in accordance with the proposed formulations. Both complexes
4.1. X-ray crystallographic studies
Suitable air-stable single crystals for X-ray diffraction were
obtained by slow cooling of methanolic solutions containing 1
and 2. The X-ray diffraction data were measured on a Bruker D8
Venture diffractometer at 100(2) K. The intensity data were cor-
rected for absorption. All non-hydrogen atoms were refined
anisotropically. The structures were solved by the direct method
[44] and refined on F2 by a full-matrix least-squares procedure
using anisotropic displacement parameters [45]. All geometrical
calculations were performed using PLATON [46] and WINGX [47]
programs. The hydrogen atom positions were initially estimated
by geometry with anisotropic displacement data.
retain the band corresponding to m(NAH) with small shifts. The
infrared spectra of both complexes 1 and 2 display a IR band at
1625 cmꢁ1 which could be assigned to azo (>C@N) stretching fre-
quencies of the coordinated Schiff base (Lꢁ).The shift of this band
on complexation towards lower frequency with respect to the free
ligand also points out the coordination of the N-atom of the azo-
methine group. The coordination of the Schiff base is also substan-
tiated by a band in the range ~ 410–490 cmꢁ1 for both complexes
corresponding to MꢁO and MꢁN stretching vibrations [59]. The
splitting of bands at 1210, 1121, 1000, and 911 cmꢁ1 indicates
the presence of coordinated perchlorate in complex 1whereas in
complex 2 the bridging mode of pyrazine is observed at 554 and
708 cmꢁ1 [59,60]. Both complexes exhibit the presence of bands
at 1092, 1012, 790 and 696, for complex 1, and 1091, 1013, 789,
and 702 cmꢁ1, for complex 2, that indicate a Td symmetry of
ClOꢁ4 and suggest the presence of ionicClOꢁ4 [61,62].
4.2. Biological (SOD) activity
The superoxide dismutase activity of complexes 1 and 2 was
assayed by its ability to inhibit the reduction of nitroblue tetra-
zolium by alkaline DMSO in phosphate buffer solution [48–50].
The course of the reaction was monitored spectrophotometrically
at 560 nm. A unit of antioxidant SOD activity is the concentration
of the complex, which causes 50% (IC50) inhibition of alkaline
DMSO and mediated reduction of NBT. The catalytic rate constants
5.2. Molecular geometries and supramolecular features: A
crystallographic study
were calculated as KM ¼ KNBT[NBT]/IC50, where KNBTðpH7:8Þ ¼
CCF
5:94 ꢂ 104Mꢁ1Sꢁ1 [51,52].
The molecular structures of 1 and 2 were determined by single-
crystal X-ray diffraction (SCXRD) technique and ORTEP diagrams
are shown in Figs. 1 & 2. The crystallographic parameters, bond
angles, and bond parameters are presented in Tables 1–2 respec-
tively. The molecular structure of 1 reveals that it is a binuclear
perchlorate-bridged complex. Each of the subunits involves depro-
tonated tridentate (NNO) Schiff base ligand and one water mole-
cule. In this complex two subunits are connected by bridging
perchlorate anion. The copper–copper distance remains 4.867 Å,
which is similar to other similar perchlorate bridged complexes
[63]. As a result of the overall, the coordination in each copper(II)
center is pentacoordinate and geometry of both copper(II) centers
4.3. Computational method
All DFT calculations were performed starting from the single-
crystal X-ray data. Theoretical calculations were performed regard-
ing molecular structure optimization and HOMO-LUMO energies of
complexes 1 and 2. All calculations were performed with the
GAUSSIAN09 program [53], with the aid of the Gauss View visual-
ization program. Full geometry optimizations were carried out
using the density functional theory (DFT) method at the B3LYP
level [54]. All elements except Cu were assigned the LANL2DZ basis
set [55]. LANL2DZ with effective core potential for Cu atom was
used [56]. The vibration frequency calculations were estimated to
ensure that the optimized geometries represented the local min-
ima and that there was only positive Eigenvalue. In the computa-
tional model, the cationic complex was taken into account.
Vertical electronic excitations based on B3LYP optimized geome-
tries were evaluated using the time-dependent density functional
theory (TDDFT) formalism [57] in DMSO, using a conductor-like
polarizable continuum model (CPCM) [58].
is distorted square pyramidal with
= (b- )/60, where, b and are the two largest angles around
the center atom; = 0 and 1 for the perfect square pyramidal
s = 0.1 for Cu(1) and Cu(2),
[s
a
a
s
and trigonal bipyramidal geometries] [64]. In complex 1 the square
base of each copper(II) center is comprised by NNO of Schiff base
(Lꢁ), with bond distances in the range 1.9086–1.968 Å and one
oxygen atom of coordinating water molecule at a distance of
1.9590 Å, whereas the apical site is occupied by the oxygen atom
of perchlorate anions at a longer distance of 2.4061 Å. For the coor-
dination sphere of Cu(2), atoms O1B, N1B, N3B, and O2W define
the basal plane while perchlorate O12 [Cu(2)-O(12) 2.9251(2) Å]
occupies the axial position which is a short contact. The copper
atom from the basal plane is shifted by 0.116 Å towards the axially
bound perchlorate anion.
5. Results and discussion
5.1. Synthesis and general characterization
The synthetic route to prepare the Schiff base (HL) and the cop-
per(II) complexes 1 and 2 are shown in Scheme 1. The formation of
the Schiff base ligand precursor 2-[(E)-(pyridine-2yl hydrazone)
methyl]phenol (HL) is supported by elemental analyses and infra-
The model of this complex constitutes many inter- and
intramolecular hydrogen bonds. These hydrogen bonds are respon-
sible for forming various heterosynthons viz., R12ð6Þ, R22ð6Þ, R22ð8Þ
and R66ð3Þ. These graph set motifs (heterosynthons) are shown in
Fig. 1(b). In the crystal packing of 1, the O2W and C7A atoms are
intermolecularly hydrogen-bonded to perchlorate oxygen atoms
(O22 and O21) via a pair of O2W-H2W1ꢀ ꢀ ꢀO22 and C7-H7AAꢀ ꢀ ꢀO21
hydrogen bonds leading to the formation of inversion dimmers of
red (IR) spectroscopy. The IR spectrum of HL shows
m(NAH)
at ~ 2990 cmꢁ1. The IR band at 1654 cmꢁ1 indicates the presence
of an imine group as a result of the condensation of 2-hydrazinopy-
ridine with salicylaldehyde. The absence of the bands at 3335 and
3305 cmꢁ1due to asymmetric and symmetric for –NH2 stretching
bonds modes indicates that the primary amine group of 2-
hydrazinopyridine has completely condensed with the carbonyl
group of salicylaldehyde. The most conclusive evidence that
the dimer with R66ð34Þ graph set motif (cyclic dimmers) [65]
(Fig. 1b). Such hydrogen bonds are also responsible for dimer like
association, function, and dynamics of biological and chemicals

4
R.N. Patel et al. / Polyhedron 188 (2020) 114687
Scheme 1. Synthetic route of HL and complexes 1 and 2.
angles Nð1Þ ꢁ Cu ꢁ Nð3Þ ¼ 82:42ð8Þꢃ and Oð1Þ ꢁ Cu ꢁ Nð3Þ ¼
models [66]. The hydrogen bonds are given in Table S1. These var-
ious hydrogen bonds form the supramolecular network (Fig. S3).
The comparison of bond distances Cu(1)ꢁO(11) [2.4061 (18)A]
and Cu(2)ꢁO(12) [2.925 (2)A] confirms the possibility of a bridging
dinuclear structure. The CuꢁN and CuꢁO bond distances are smal-
ler 1.969(2), 1.948(2) and 1.9086(18 A) suggesting the domination
of the deprotonated Schiff base (Lꢁ) in bonding. It is found that
CuꢁN pyridyl bonds are 0.021ꢁ0.042 A larger than CuꢁN imine
bonds showing the strength of azomethine nitrogen coordination.
The unit cell packing diagram of complex 1 viewed along the a-axis
is shown in Fig. 1(d). It is clear from the packing diagram that the
molecules are packed in a two-dimensional manner with two coor-
dinated water molecules.
92:06ð7Þꢃ are generated by the chelating of deprotonated Schiff
base ðLꢁÞ [71]. Two noncoordinated perchlorate anions are present
to neutralize the charge of the complex. These anions are located
at both side of the cation in such a way that it forms sym-
metric hydrogen bondsðC13 ꢁ H13A ꢀ ꢀ ꢀ O11; C7 ꢁ H7A ꢀ ꢀ ꢀ O12 and
N2 ꢁ H2B ꢀ ꢀ ꢀ O13) leading to the formation of inversion dimers
with R22ð8Þ and R44ð34Þ graph-set ring motif (cyclic dimmers) [65]
(Fig. 2b). The cohesion of packing in 2 is further insured by Cl-O-
Cg[
p
] weak contracts.
Lone pair-aryl
(lpꢀ ꢀ ꢀ
electrons of oxygen atoms of ionic perchlorates and
of bridging pyrazine ligand (Fig. 2c). These lp ꢁ (aryl) interactions
p
p
) interactions are operated by lone pair
electrons
p
p
The structure of complex 2 is different from that of 1 with
respect to the coordination environment of the copper(II) center.
In this complex, each copper atom has distorted square planar
geometry. In each subunit, the copper center is coordinated by
one pyridine nitrogen, one imine nitrogen, and one phenolic oxy-
gen atom of the tridentate deprotonated Schiff base (Lꢁ) and the
nitrogen atom of bridged pyrazine ligand. Some of the angles
around the copper(II) center ~ 172° and ~ 87° indicating a distorted
square planar geometry around each copper(II) center [67,68].
Also, bond angles are around copper centers deviate from 90° con-
firming a distorted square planar geometry for this binuclear com-
plex. Yang and co-workers [69] have suggested the geometry index
are also responsible for dimer like association, function, and
dynamics of biological and chemical models [66]. The unit cell dia-
gram of complex 2 shown along the b-axis is shown in Fig. 2(d). In
this diagram, it can be observed that the molecules are in a two-
dimensional manner with parallel arrangements of the rings with
two ionic perchlorates.
5.3. EPR spectroscopy
The X-band electron paramagnetic resonance (EPR) spectra of
both complexes in polycrystalline solids at room temperature
360ꢁð
a
(s4) for four coordinate complexes s4
¼
þbÞ, where
a and b are
141ꢃ
(RT) and in DMSO (3:0 ꢂ 10ꢁ3M) solutions at liquid nitrogen tem-
perature (LNT) were recorded to obtain information about the
nuclearity and coordination geometry in the complexes (Fig. 3).
The epr spectra of both complex 1 and 2 in polycrystalline samples
are typical of S = 1 systems [72,73]. The polycrystalline samples at
RT exhibit the expected spectral features of singlet–triplet
the two largest angles in the four coordinate species subtracted
from 360°, all divided by 141° A perfect tetrahedral structure
yields s4 = 1 while a square planar structure gives s4 = 0. The
s4 = ~ 0.2–0.3 of this complex reflects the distorted square planar
geometry. The CuꢁCu distance in a dinuclear unit is 6.807A, which
is in agreement with those reported in the literature [70]. The bite
transition (DMs ¼ ꢄ2) at a low magnetic field (ge ꢅ 4Þ [74]. These

R.N. Patel et al. / Polyhedron 188 (2020) 114687
5
Fig. 1. (a) ORTEP view of 1, (b) partial packing diagram (dimer of dimer model), and (c) packing diagram along a-axis.

6
R.N. Patel et al. / Polyhedron 188 (2020) 114687
Fig. 2. (a) ORTEP view of complex 2, (b) partial packing diagram (dimer of dimer model) showing H-bondings with synthons, (c) lp ꢁ
p(aryl) centroid interactions, and (d)
packing diagram with ionic perchlorate.

R.N. Patel et al. / Polyhedron 188 (2020) 114687
7
The EPR parameters gk, g? and Ak (cmꢁ1) and d-d energies were
used to estimate the bonding parameters (
2; b2and 2). These
bonding parameters are used to measure the covalency in the in-
plane -bonding, in-plane -bondings and out-of-plane -bond-
ings. The orbital reduction factors (K andK ) were also estimated
Table 1
Crystal data and structure refinement parameters of synthesized copper(II)
complexes.
a
c
1
2
r
p
p
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C24 H26 Cl2 Cu2 N6 O13 C28 H24 Cl2 Cu2 N8 O10
804.49
100(2)
0.71073
Triclinic
P-1
8.0343(3)
11.2399(5)
17.2657(7)
105.094(3)
100.673(3)
92.804(3)
1471.56(11)
2
k
?
830.53
100(2)
0.71073
Triclinic
P-1
6.7110(3)
10.8068(4)
11.1131(4)
99.618(3)
94.535(3)
106.393(3)
755.52(5)
1
for the present complexes. The value of K ’ K ’ 0.77 is for pure
k
?
sigma bonding [88] and in-plane
out-of-plane -bonding K < K . In both complexes, it is found
that K < K which indicates in-plane
p-bonding, K < K , while for
k ?
p
?
k
p
-bonding. Other bonding
k
?
parameters (
a
2andb2) value is found to be less than 1.0 and there-
b (Å)
c (Å)
fore indicating the covalent nature of the bonds.
a
(°)
b (°)
5.4. Electrochemical studies
c
(°)
Volume (Å3)
The electrochemical studies of both complexes 1 and 2 were
Z
Density (calculated) (Mg/
1.816
1.825
examined using cyclic voltammetry (CV) and differential pulse
m3)
voltammetry (DPV)in DMSO ð3:0 ꢂ 10ꢁ3MÞin the presence of 0.1
Mtetrabutylammonium perchlorate (TBAP) as the supporting elec-
trolyte in the potential range ꢁ1.0 to 0.6 V (Fig. 4). The cyclic
voltammogram of both complexes shows a similar type of pattern
(Fig. 4). The cyclic voltammogram of complexes shows two redox
processes (Table 4). The corresponding redox peaks observed in
the CVs of each complex (1 and 2) were verified by comparing
the voltammogram at different scan rates maintaining the identi-
cal experimental conditions and also by comparing its wave height
with that of the ferrocene/ferrocenium couple. Both redox pro-
cesses are irreversible and identical numbers of electrons as sup-
ported by differential pulse voltammetric (DPV) experiments.
DPV is a good technique for identifying reduction peaks having
small differences in the peak potentials, provided the two peaks
differ in their formal potential by more than 0.18 V.
Absorption coefficient
1.705
1.659
(mmꢁ1
)
F(000)
Theta range for data
collection (°)
816
420
1.248 to 30.628
2.004 to 33.271
Index ranges
ꢁ11ꢇhꢇ11,
ꢁ10ꢇhꢇ10,
ꢁ16ꢇkꢇ16, ꢁ24ꢇlꢇ24 ꢁ16ꢇkꢇ16,
ꢁ17ꢇlꢇ17
Reflections collected
Independent reflections
Completeness to
theta = 25.242°
Absorption correction
50,750
21,193
5762 [R(int) = 0.0612]
99.6%
9056 [R(int) = 0.0719]
100.0%
None
None
Refinement method
Full-matrix least-
squares on F2
9056/9/456
Full-matrix least-
squares on F2
5762/0/226
Data/
restraints/parameters
Goodness-of-fit on F2
Final R indices [I greater
than 2sigma(I)]
1.050
1.017
R1 = 0.0398,
wR2 = 0.0931
R1 = 0.0672,
wR2 = 0.1016
n/a
R1 = 0.0480,
wR2 = 0.0876
R1 = 0.0898,
wR2 = 0.1006
n/a
5.5. Electronic spectra
R indices (all data)
UV–visible spectra of both complexes have been recorded in
Extinction coefficient
3:0 ꢂ 10ꢁ3M DMSO. UV–visible spectroscopy is one of the most
used methods for characterizing the transition metal complexes.
The d-d spectra of present complexes are of little help in these
two complexes since the d-d transitions are masked by strong
charge transfer transitions. These bands observed at a higher con-
centration at 648 nm in 1 and 638 nm in 2are assigned to d-d tran-
sitions (in in-set) (Fig. 5). Furthermore, a shoulder at ~ 980 nm is
observed for both complexes. The apperence of a ~ 980 nm is
indicative of bridging mode of sulphate anion and pyrazine co-
ligands. The intense band noticed in the UV- the region is due to
the overlap of the transition of the azomethane with the charge
transfer band from bridging perchlorate oxygen to the vacant d
orbital (N/O ? M) of the copper (II) [22,89,90].
Largest diff. peak and hole 0.680 and ꢁ0.777
0.755 and ꢁ1.231
(eꢀÅꢁ3
)
observations are in agreement with the antiferromagnetic interaction
between the copper(II) ions in the binuclear complexes [5,75–79]. In
spin coupled systems, spin Hamiltonian parameter (H) for an S = 1
state interacting with a magnetic field (H) is given as:
ꢀ
ꢁ
H ¼ gbHs þ DS2 þ E S2 ꢁ S2 ꢁ ð2=3ÞD
z
x
y
where D and E are the zero-field splitting parameters. The values for
gk; g?, D and E which fit with experimental X-band spectra of
bridged systems are presented in Table 4. The values for both com-
plexes are in the range. Thus, EPR spectra are in agreement with the
geometry confirmed by single-crystal X-ray analysis. The exchange
parameter G, which characterizes the exchange interaction between
copper centers in polycrystalline compounds, was estimated using
the expression G ¼ ðgk ꢁ 2Þ=ðg? ꢁ 2Þ [76–82]. The estimated G, val-
ues for 1 and 2 are less than 4 (G < 4Þ, suggesting that there is an
exchange interaction between copper centers (Table 3). The low
5.6. Catalytic activity
Both complexes (1 and 2) are exhibit catalytic activity toward
antioxidant SOD which was evaluated using the alkaline DMSO-
nitroblue tetrazolium (NBT) assay method [49,91,92]. The obtained
SOD results show how much superoxide radical production was
inhibited for each concentration of complex 1 and 2. The IC50 value
i.e. concentration of metal complexes which inhibits 50% of the
Oꢀ2ꢁ/NBT reaction is used in the equation of the line which relates
the different concentrations of the complexes analyzed with the
respective percentage of NBT photoreduction inhibition. As the
reaction proceeds, the photoreduction of NBT to MF+is measured
at 560 nm. The dismutation of superoxide anions takes place at
physiological pH. Additionally, the SOD data of similar complexes
of biologically important ligands as well as the values of the best
SOD models reported in the literature so far are also presented in
values of G of both complexes indicate a dx2
the ground state
ꢁy2
has a weak exchange coupling which may be propagated through
½Cu ꢁ N2=O2Cl ꢁ Cuꢆ cores [83,84]. The low-temperature EPR spectra
of samples dissolved in DMSO indicate the existence of different
species in solution and yielded the values (gk > g? > ge) for 1 and
2 consistent with the dx2
ground state for copper(II) ions typical
ꢁy2
for square pyramidal and square planar geometry [85–87] (Fig. 3).

8
R.N. Patel et al. / Polyhedron 188 (2020) 114687
Table 2
Coordination bond lengths [Å] and angles [°] for complexes 1 and 2.
X-ray
DFT
X-ray
DFT
Complex 1
Bond length
Cu(1)-O(1A)
Cu(1)-N(1A)
Cu(1)-O(1 W)
Cu(1)-N(3A)
Cu(1)-O(11)
1.9086(18)
1.948(2)
1.9590(18)
1.969(2)
1.9086
1.9481
1.9590
1.9692
2.4061
Cu(2)-O(1B)
Cu(2)-N(1B)
Cu(2)-O(2 W)
Cu(2)-N(3B)
O(12)-Cu(2)
1.8811(18)
1.9351(19)
1.9577(17)
1.977(2)
1.8812
1.9351
1.9577
1.9773
2.9251
2.4061(18)
2.925(2)
Perchlorate anion
Cl(1)-O(14)
Cl(1)-O(13)
Cl(1)-O(11)
Cl(1)-O(12)
1.435(2)
1.4345
1.4441
1.4460
1.4523
Cl(2)-O(23)
Cl(2)-O(24)
Cl(2)-O(22)
Cl(2)-O(21)
1.414(2)
1.420(2)
1.429(2)
1.459(2)
1.4143
1.4210
1.4293
1.4591
1.4441(19)
1.4460(19)
1.452(2)
Bond angle
O(1A)-Cu(1)-N(1A)
O(1A)-Cu(1)-O(1 W)
N(1A)-Cu(1)-O(1 W)
O(1A)-Cu(1)-N(3A)
N(3A)-Cu(1)-O(11)
N(1A)-Cu(1)-N(3A)
O(1 W)-Cu(1)-N(3A)
O(1A)-Cu(1)-O(11)
N(1A)-Cu(1)-O(11)
O(1 W)-Cu(1)-O(11)
91.96(8)
91.40(8)
170.77(8)
172.14(8)
90.23(7)
81.76(9)
94.11(8)
95.83(7)
103.28(8)
84.91(7)
91.9643
91.4009
176.1223
176.3804
90.2367
81.7629
94.1089
95.8313
103.2847
84.9102
O(1B)-Cu(2)-N(1B)
O(1B)-Cu(2)-O(2 W)
N(1B)-Cu(2)-O(2 W)
O(1B)-Cu(2)-N(3B)
N(1B)-Cu(2)-N(3B)
O(2 W)-Cu(2)-N(3B)
O(1B)-Cu(2)-O(12)
N(1B)-Cu(2)-O(12)
O(2 W)-Cu(2)-O(12)
N(3B)-Cu(2)-O(12)
93.06(8)
93.11(8)
164.22(9)
170.92(8)
81.65(9)
93.90(8)
83.00(7)
121.20(7)
74.01(7)
93.39(7)
93.0588
93.1113
164.2159
176.0681
81.6510
93.8985
83.9961
121.1959
73.9961
93.3926
Perchlorate anion
O(14)-Cl(1)-O(13)
O(14)-Cl(1)-O(11)
O(13)-Cl(1)-O(11)
O(14)-Cl(1)-O(12)
O(13)-Cl(1)-O(12)
O(11)-Cl(1)-O(12)
110.38(12)
109.49(12)
109.11(12)
109.77(12)
108.63(11)
109.42(12)
110.3816
109.4981
109.1132
109.7753
108.6263
109.4221
O(23)-Cl(2)-O(24)
O(23)-Cl(2)-O(22)
O(24)-Cl(2)-O(22)
O(23)-Cl(2)-O(21)
O(24)-Cl(2)-O(21)
O(22)-Cl(2)-O(21)
110.7(2)
110.6653
109.9263
109.5801
109.4246
108.9431
108.2113
109.92(16)
109.58(16)
109.41(14)
108.94(14)
108.21(13)
Complex 2
Bond length
Cu–O(1)
1.8651(17)
1.9366(18)
1.8651
1.9366
Cu–N(3)
Cu–N(4)
1.958(2)
2.0183(18)
1.9581
2.0183
Cu–N(1)
Bond angle
O(1)-Cu–N(1)
O(1)-Cu–N(3)
N(1)-Cu–N(3)
92.06(7)
172.83(7)
82.42(8)
92.0638
176.1224
82.4225
O(1)-Cu–N(4)
N(1)-Cu–N(4)
N(3)-Cu–N(4)
86.80(7)
172.69(8)
99.25(8)
86.7981
178.6688
99.2464
Table 5 for comparison [6,31,91,93–95]. The high SOD activity can
be associated with the coordinately metal centers and the flexibil-
ity of the used tridentate Schiff base, which would permit molecu-
lar rearrangement along the catalytic pathway [96]. SOD enzymes
have demonstrated pharmacological efficacy in some animal mod-
els of ROS-related diseases [97]. Their therapeutic use has been
limited by their high production cost, molecular size, and antigenic
activity [98]. Synthetic SOD mimetic compounds of low molecular
weight could compensate for the limitations of SOD because of the
lack of antigenicity, higher stability in solution, longer half-life, and
lower production cost [99,100]. The lower SOD activity of these
complexes compared to the best SOD models can be interpreted
by considering a possible correlation between the strength of the
equatorial field and the SOD activity [100]. Complex 2 showed less
SOD activity than 1. In complex 2 Cu(II) ion experiences a strong
equatorial field which makes difficult for the Oꢀ2ꢁ radical to bind
axially, due to the coordination of the metal by four nitrogen
atoms. Similar SOD data have been obtained for other copper(II)
complexes [101]. The present complexes based on SOD may be
considered as potent SOD mimics [93–95,102,103].
calculated values of bond distances and bond lengths slightly
divert from those observed experimentally. Such discrepancy of
bond parameters occurs owing to the crystal packing which mod-
ifies the parameters of the relaxed molecules. The density func-
tional theory (DFT) method at the B3LYP level is used to calculate
the HOMO-LUMO energies for complexes 1 and 2. The HOMO-
LUMO energies are popular quantum mechanical descriptors that
play an important role in governing a wide range of chemical inter-
actions [107]. These energy levels are shown in Fig. 6. During
HOMO-LUMO analysis of 1 and 2, the fifth-highest and highest
occupied MO’s (HOMO and HOMO-5), the lowest and lowest unoc-
cupied MO’s (LUMO and LUMO + 5) are considered. Energy gaps are
shown in Table 6. The energy gap was estimated at 16.0568 eV for
1 and 4.7435 eV for 2. The energy gap for 1 is greater than 2.
Graphical representations of the Mulliken atomic spin densities
of both complexes were calculated using B3LYP/LanL2DZ basic set
for comparative purposes (Fig. 7). The delocalization of the single
unpaired electron is to the dx2
orbital with a less contribution
ꢁy2
of dz2 of both copper centers and donor atoms of both complexes.
The -conjugated hydrocarbon network of Schiff base and triden-
p
tate ligand also carry spin density in both complexes due to the
5.7. Quantum chemical calculations
spin-polarization mechanism [108,109].
The structure of both binuclear complexes was also optimized
by DFT methods [104–106]. Based on the SCXRD analysis, a dis-
torted square pyramidal for 1 and a distorted square planar for 2
was considered. In Table 2, the comparison between experimental
and calculated bond parameters is summarized. As expected,
5.8. Magnetic measurements
The cryomagnetic susceptibility data for complexes 1 and 2
were measured in the temperature range 2–300 K. Plots of

R.N. Patel et al. / Polyhedron 188 (2020) 114687
9
Fig. 3. EPR spectra of complexes (a) 1 and (b) 2 (half field spectra of complexes 1 and 2 indicated in the inset).
magnetic susceptibility vs. temperature are shown in Figs. 8 and
10. The magnetic measurements obtained for 1 agree with previ-
(Derived from the H = -JS1ꢀS2Hamiltonian. N, b and k have their
usual meanings).
ously reported data [110]. The value obtained for the
v
MT product
The best fit of our data (r2 = 1.8 ꢂ 10ꢁ5) led to g = 2.16,
J = ꢁ 21.6 and P = 0.05. The fit estimates the existence of a para-
magnetic impurity of a 5% that could not be anticipated by the ele-
mental analysis (35.64% C; 3.35% H; 10.35% N) obtained for the
sample batch used for the magnetic measurements. An antiferro-
magnetic exchange pathway, Cu1Cu2, through hydrogen bonds
was proposed in the literature [110]. However, the magnitude of
this coupling could be explained by an additional exchange
of 1 at 300 K is 0.83 cm3ꢀKꢀmolꢁ1, slightly larger than the one
expected for two isolated copper(II) ions with a g value of 2. This
value is constant until approximately 90 K. Further cooling of the
sample leads to a decrease of
vMT caused by antiferromagnetic
interactions. This decrease is especially pronounced bellow 50 K,
reaching a value of 0.02 cm3ꢀKꢀmolꢁ1 at 2 K. The
vM vs T plot shows
a maximum at 18 K, indicative of antiferromagnetic coupling, and a
small paramagnetic tail bellow 4.4 K (Fig. 8).
through p-p interactions, which looks particularly strong between
The magnetic data of 1 were fitted using the following equation
that considers an intradimer coupling (J) through the Bleany-Bow-
ers expression and the existence of a small S = ½ paramagnetic
impurity (P), responsible of the small paramagnetic tail observed
the Schiff base ligands bonded to Cu2 centers [111] (Fig. 9). This
hypothesis is supported by the spin density structure around the
ligands of 1 deduced from DFT calculations.
The dinuclear 2 complex displays a constant value, 0.79 cm3-
ꢀKꢀmolꢁ1, of the molar magnetic susceptibility-temperature pro-
in the
vM data and the plateau at low temperature in the vMT data:
duct (vMT) from 300 K to approximately 35 K. This value is
2Ng2b2
3KT
3
P
T
consistent with the existence of two S = ½ ions in the structure
vM ¼ ð1 ꢁ PÞ
À
Á þ 0:375
J
(calculated Curie constant of 0.75 cm3ꢀKꢀmolꢁ1). Lowering the
3 þ exp ꢁ KT

10
R.N. Patel et al. / Polyhedron 188 (2020) 114687
Fig. 4. (a) Cyclic voltammogram of complexes 1–2 in DMSO ð3:0 ꢂ 10ꢁ3MÞ solution, (b) DPV of complexes 1–2 in DMSO ð3:0 ꢂ 10ꢁ3MÞ solution.
Table 3
EPR parameters of copper(II) complexes.
EPR parameter
1
2
Polycrystalline state (298 K)
gk
2.187
2.185
g?
2.074
2.52
0.019
0.00
2.074
2.50
0.033
0.01
G
D (cmꢁ1
)
)
E (cmꢁ1
Frozen solution in DMSO (77 K)
gk
gk
2.251
2.251
2.222
2.207
g?
k
2.067
175
2.068
127
A (1)
A (2)
k
175
175
f (cm) (1)
f (cm) (2)
a2
138
138
0.768
0.951
190
138
0.727
0.993
b2
c2
1.011
0.761
0.761
0.776
15,432
1.084
0.721
0.696
0.788
15,677
K (1)
Fig. 5. Absorption spectra of 3:0 ꢂ 10ꢁ3 M DMSO solution of complexes 1 and 2.
k
K (2)
k
K
E
?
dꢁd=kmax(cmꢁ1
)
Table 4
Electrochemical data for binuclear copper(II) complexes 1 and 2 in DMSO ð3:0 ꢂ 10ꢁ3MÞ containing 0.1 M TBAP as a supporting electrolyte.
E11=2ðVÞ
E21=2ðVÞ
Complex
Epc1ðVÞ
Epa1ðVÞ
Epc2ðVÞ
Epa2ðVÞ
DEpc1ðVÞ
DEpc2ðVÞ
DDpcðVÞ
DE1=2ðVÞ
1
2
0.127
0.080
0.388
0.425
ꢁ0.492
ꢁ0.519
0.193
0.256
0.208
0.192
ꢁ0.473
ꢁ0.469
0.681
0.661
0.257
0.254
ꢁ0.149
ꢁ0.131
0.406
0.385
Table 5
SOD activities (IC50 values kinetic catalytic constant and SOD activity) Cu(II) complexes.
Compound
IC50
KM
C CF
(molLꢁ1
)
ꢁ1Sꢁ1
SOD activity (
l
Mꢁ1
)
Reference
[Cu(L)(H2O)2](NO3)
6
55.44
8.75
9.50
–
15.12
–
15.84
19.57
41.58
–
85.24
38.87
166.66
26.31
28.57
31.25
45.45
909.09
47.62
58.82
125.00
847.5
256.41
116.27
6
96
96
99
100
99
31
31
6
101
This work
This work
[Cu2(L1)2(HL2)2(H2O)](NO3)2ꢀꢀ2H2O
[Cu2(L1)2(HL2)2] (NO3)2ꢀH2O
[Cu2(bdpi)(CH3CN)2](ClO4)3CH3CNꢀ3H2O
[(bipy)2Cu–Im–Cu(bipy)2] (ClO4)3ꢀCH3OH
[Cu2(Me4bdpi)(H2O)2](ClO4)3ꢀꢀ4H2O
[Cu(L)(neocuprin)](NO3)ꢀH2O
[Cu2(2-(2-pyridyl)benzimidazole)2(L)2](ClO4)
[Cu(L)(H2O)(NO3)]ꢀH2O
38
35
0.32
22
1.1
21
17
8
[Cu(idb)]
1
2
1.18
3.9
8.6
KM
¼ KNBT ꢂ ðNBTÞ=IC50, KNBT ¼ 5:94 ꢂ 10ꢁ4Mꢁ1Sꢁ1, [NBT] = 56 Mꢁ1).
lM, SOD activity = 1000/IC50 (l
C CF

R.N. Patel et al. / Polyhedron 188 (2020) 114687
11
Fig. 6. Frontier molecular diagram of complexes (a) 1 and (b) 2.
Table 6
Theoretical transition levels between HOMO and LUMO frontier orbital were calculated by B3LYP/LanL2DZ method in complexes 1 and 2.
Level
MO Energy (eV)
D
E (eV)
1
2
1
2
HOMO
LUMO
ꢁ7.2514
8.8054
ꢁ5.4773
ꢁ0.7338
ꢁ5.4773
ꢁ0.7327
ꢁ5.5368
ꢁ0.5983
ꢁ5.5347
ꢁ0.3945
ꢁ5.5510
ꢁ0.0353
ꢁ5.5510
ꢁ0.0353
16.0568
16.0490
18.0535
18.5714
17.5864
17.1891
4.7435
HOMO-1
LUMO + 1
HOMO-2
LUMO + 2
HOMO-3
LUMO + 3
HOMO-4
LUMO + 4
HOMO-5
LUMO + 5
ꢁ7.2354
4.7446
4.9385
5.1402
5.5157
5.5157
8.8136
ꢁ7.9338
10.1197
ꢁ7.3932
11.1782
ꢁ8.3510
9.2354
ꢁ7.1592
10.0299
temperature further results in a sharp decrease of the
v
MT product,
estimate the J and g values. The best fit of the data
ascribed to intradimer antiferromagnetic interactions (Fig. 10).
The existence of antiferromagnetic interactions is also sup-
ported by the maximum at 6.4 K observed in the representation
of the temperature dependence of the molar magnetic susceptibil-
ity (Fig. 9). Taking into account the dimeric nature of 2, the exper-
imental data were fitted using the Bleany-Bowers equation to
(
r2 = 1.6 ꢂ 10ꢁ4) with this model led to g and J values of 2.08
and ꢁ 6.8 cmꢁ1, respectively. The value of the coupling constant
obtained from this fit agrees well with that of other similar cop-
per(II) complexes in which pyrazine bridges mediate antiferromag-
netic interactions with jJj values in the range of 3 to 12 cmꢁ1
[6,112].

12
R.N. Patel et al. / Polyhedron 188 (2020) 114687
Fig. 7. Graphical illustrations of the Mulliken atomic spin densities for the ground state (S = ½) of 1 and 2 with a surface threshold level of 0.004.
Fig. 8. Temperature dependence of
vM(blue circles) and vMT (red squares) of 1.
Fig. 10. Temperature dependence of
vM(blue circles) and vMT (red squares) of 2.
Solid lines represent the fit of the experimental data as described in the main text.
Solid lines represent the fit of the experimental data as described in the main text.
whereas in pyrazine bridged binuclear complex 2, both copper cen-
ters have square planar geometry. Both complexes showed two
reduction waves. Spin density on both copper(II) center was also
calculated. Cryomagnetic magnetic susceptibility measurements
showed that both complexes exhibit antiferromagnetic interac-
tions. From the coupling parameter (JCuCu) values of 1 and 2, it is
confirmed that 1 possesses stronger antiferromagnetic interaction
6. Conclusions
Based on the single crystal X-ray crystallography and theoreti-
cal techniques, molecular geometries, weak interactions, electron-
ics and catalytic properties of two new binuclear complexes (1 and
2) have been investigated. In perchlorate bridged binuclear com-
plex 1, both copper(II) centers have square pyramidal geometry
Fig. 9. Representation of the structure of 1 showing its main p-p interactions. The shortest distances between atoms of different units are given inÅ. Perchlorates are omitted
for clarity.

R.N. Patel et al. / Polyhedron 188 (2020) 114687
13
[11] E. Pardo, J. Faus, M. Julve, F. Lloret, M.C. Mun-oz, J. Cano, X. Ottenwaelder, Y.
Journaux, R. Carrasco, G. Blay, I. Fernandez, R. Ruiz-Garcı-a, J. Am. Chem. Soc.
125 (2003) 10770–10771.
[12] G. Psomas, C.P. Raptopoulou, L. Iordanidis, C. Dendrinou-Samara, V. Tangoulis,
D.P. Kessissoglou, Inorg. Chem. 39 (2000) 3042–3048.
[13] S. Ferlay, A. Jouaiti, M. Loi, M.W. Hosseini, A. De Cian, P. Turek, New J. Chem.
(2003) 1801–1805.
[14] J. Cano, E. Ruiz, P. Alemany, F. Lloret, S. Alvarez, J. Chem. Soc., Dalton Trans.
(1999) 1669–1676.
[15] K.J. Humphreys, K.D. Karlin, S.E. Rokita, J. Am. Chem. Soc. 124 (2002) 8055–
8066.
compared to 2, probably due to exchange through H-bonds and
also through stacking. The supramolecular chemistry of
p-p
supramolecular synthons is also observed. It is capable of further
self-assembly into chains and sheets. Both complexes showed good
antioxidant SOD activity, which indicated that both complexes
have the potential possibility to sure as antioxidant SOD mimics
for pharmaceutical applications.
[16] K. Jitsukawa, M. Mizutani, H. Arii, I. Kubo, Y. Izu, T. Ozawa, H. Masuda, Chem.
Lett. 33 (2004) 1302–1303.
CRediT authorship contribution statement
[17] Y. Singh, R.N. Patel, Y.P. Singh, A.K. Patel, N. Patel, R. Singh, R.J. Butcher, J.P.
Jasinski, E. Colacio, M.A. Palacios, Dalton Trans. 46 (2017) 11860–11874.
[18] R.N. Patel, Y. Singh, Y.P. Singh, R.J. Butcher, A. Kamal, I.P. Tripathi, Polyhedron
117 (2016) 20–34.
[19] R.N. Patel, V.P. Sondhiya, K.K. Shukla, D.K. Patel, Y. Singh, Polyhedron 50
(2013) 139–145.
[20] R.N. Patel, Y. Singh, Y.P. Singh, A.K. Patel, N. Patel, R. Singh, R.J. Butcher, J.P.
Jasinski, E. Colacio, M.A. Palacios, New J. Chem. 42 (2018) 3112–3136.
[21] S. Roy, M. Bohme, S.P. Dash, M. Mohanty, A. Buchholz, W. Plass, S. Majumder,
S. Kulanthaivel, I. Banerjee, H. Reuter, W. Kaminsky, R. Dinda, Inorg. Chem. 57
(2018) 5767–5781.
R.N. Patel: Conceptualization, Supervision, Visualization, Writ-
ing - original draft, Writing - review & editing. S.K. Patel: Project
administration, Investigation, Methodology. D. Kumhar: . Nirmala
Patel: Formal analysis. A.K. Patel: Resources, Software. R.N. Jadeja:
Conceptualization, Project administration, Resources, Software,
Visualization. Neetu Patel: . R.J. Butcher: Validation. M. Cortijo:
Validation. S. Herrero: Validation.
[22] A. Bianchi, E. Delgado-Pinar, E. Garcia-Espana, C. Giorgi, F. Pina, Coord. Chem.
Rev. 260 (2014) 156–215.
[23] J. Pisk, B. Prugovecki, D. Matkovic-Calogovic, T. Jednacak, P. Novak, D. Agustin,
V. Vrdoljak, RSC Adv. 4 (2014) 39000–39010.
[24] O. Pouralimardan, A.C. Chamayou, C. Janiak, H.H. Monfared, Inorg. Chim. Acta
360 (2007) 1599–1608.
[25] M. Bakir, O. Green, W.H. Mulder, J. Mol. Struct. 873 (2008) 17–28.
[26] C. Basu, S. Chowdhury, R. Banerjee, H.S. Evans, S. Mukherjee, Polyhedron 26
(2007) 3617–3624.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
[27] M. Alagesan, N.S.P. Bhuvaneshb, N. Dharmaraj, Dalton Trans. 42 (2013) 7210–
7223.
Acknowledgments
[28] W.E. Antholine, B. Bennett, G.R. Hanson, Copper Coordination Environments,
in: S.K. Misra (Ed.), Multifrequency Electron Paramagnetic Resonance: Theory
and Applications, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany,
2011.
[29] J. Jezierska, V. Kokozay, A. Ozarowski, Res. Chem. Intermed. 33 (2007) 901–
914.
[30] F.E. Mabbs, Chem. Soc. Rev. 22 (1993) 313–324.
[31] Y.P. Singh, R.N. Patel, Y. Singh, R.J. Butcher, P.K. Vishakarma, R.K.B. Singh,
Polyhedron 122 (2017) 1–15.
[32] A.K. Patel, R.N. Jadeja, H. Roy, R.N. Patel, S.K. Patel, R.J. Butcher, J. Mole. Struct.
1185 (2019) 341–350.
[33] S.K. Patel, R.N. Patel, Y. Singh, Y.P. Singh, D. Kumhar, R.N. Jadeja, H. Roy, A.K.
Patel, N. Patel, N. Patel, A. Banerjee, D. Choquesillo-Lazarted, A. Gutierrez,
Polyhedron 161 (2019) 198–212.
[34] S.R. Seidel, P.J. Stang, Acc. Chem. Res. 35 (2002) 972–983.
[35] J.-M. Lehn, PNAS 99 (2001) 4763–4768.
Authors thanks RSIC (SAIF) IIT, Bombay for EPR measurements.
SAIF, Central Drug Research Institute, Lucknow, are thankfully
acknowledged for providing analytical, spectral facilities. The
authors wish to acknowledge the assistance of Dr. Matthias Zeller
in the collection of diffraction data and NSF Grant CHE 0087210,
Ohio Board of Regents Grant CAP-491 and by Youngstown State
University for funds to purchase the X-ray diffractometer. Financial
assistance from CSIR [Scheme No. 01(2917)/18/EMR-II] New Delhi
is also gratefully acknowledged. M. C. and S. H. acknowledge the
financial support received by the Comunidad de Madrid (project
B2017/BMD-3770-CM).
[36] B.J. Holliday, C.A. Mirkin, Angew. Chem. Int. Ed. 40 (2001) 2022–2043.
[37] F.M. Tabellion, S.R. Seidel, A.M. Arif, P.J. Stang, J. Am. Chem. Soc. 123 (2001)
7740–7741.
Appendix A. Supplementary data
[38] Y.K. Kryschenko, S.R. Seidel, D.C. Muddiman, A.I. Nepomuceno, P.J. Stang,
J. Am. Chem. Soc. 125 (2003) 9647–9652.
[39] M. Barboiu, G. Vaughan, R. Graff, J.-M. Lehn, J. Am. Chem. Soc. 125 (2003)
10257–10265.
[40] R.N. Patel, D.K. Patel, V.P. Sondhiya, K.K. Shukla, Y. Singh, A. Kumar, Inorg.
Chim. Acta 405 (2013) 209–217.
[41] S. Mamour, D. Mayoro, T.E. Ibrahima, G. Mohamed, B.A. Hamady, J. Ellena,
Acta Cryst. Sect. E 74 (2018) 642–645.
CCDC No. 1957632 and 1957633 contain the supplementary
crystallographic data for compounds 1 and 2 respectively. 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 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data to this article can be found online at https://doi.org/10.1016/j.
poly.2020.114687.
[42] M.S. Shongwe, K.S. Al-Barhi, M. Mikuriya, H. Adams, M.J. Morris, E. Bill, K.C.
Molloy, Chem. Eur. J. 20 (2014) 9693–9701.
[43] R.R. Gagne, C.A. Koval, G.C. Lisensky, Inorg. Chem. 19 (1980) 2854–2855.
[44] G.M. Sheldrick, Acta Cryst. A 46 (1990) 467–473.
[45] Acta Crystallogr. Vnir. Gottingen: Gottingen, Germany, 1997.
[46] A.L. Spek, Acta Crystallogr. D 65 (2009) 148–155.
[47] L.J. Ferrugia, J. Appl. Crystallogr. 45 (2012) 849–854.
[48] R.N. Patel, A. Singh, K.K. Shukla, D.K. Patel, V.P. Sondhiya, J. Coord. Chem. 64
(2011) 902–919.
[49] R. Konecny, J. Li, C.L. Fisher, V. Dillet, D. Bashford, L. Noodleman, Inorg. Chem.
38 (1999) 940–950.
[50] R.G. Bhirud, T.S. Srivastava, Inorg. Chimca Acta 173 (1999) 121–125.
[51] Z.R. Liao, X.F. Zheng, B.S. Luo, L.R. Shen, D.F. Li, H.L. Liu, W. Zhao, Polyhedron
20 (2001) 2813–2821.
References
[1] R. Karmakar, C.R. Choudhury, D.L. Hughes, G.P.A. Yap, M.S.E. Fallah, C.
Desplanches, J.-P. Sutter, S. Mitra, Inorg. Chim. Acta 359 (2006) 1184–1192.
[2] C. Adhikary, D. Mal, K.-I. Okamoto, S. Chaudhuri, S. Koner, Polyhedron 25
(2006) 2191–2197.
[3] S. Banerjee, M.G.B. Drew, C.-Z. Lu, J. Tercero, C. Diaz, A. Ghosh, Eur. J. Inorg.
Chem. (2005) 2376–2383.
[4] N.R. Sangeetha, S. Pal, Polyhedron 19 (2000) 1593–1600.
[5] Y. Singh, R.N. Patel, S.K. Patel, A.K. Patel, N. Patel, R. Singh, R.J. Butcher, J.P.
Jasinski, A. Gutierrez, Polyhedron 171 (2019) 155–171.
[6] Y.P. Singh, R.N. Patel, Y. Singh, D.C. Lazarteb, R.J. Butcher, Dalton Trans. 46
(2017) 2803–2820.
[7] N. Petrovic, A. Comi, M.J. Ettinger, J. Biol. Chem. 271 (1996) 28331–28334.
[8] P. Kapoor, A. Pathak, R. Kapoor, P. Venugopalan, M. Corbella, M. Rodriguez, J.
Robles, A. Llobet, Inorg. Chem. 41 (2002) 6153–6160.
[9] M. Rodrı-guez, A. Llobet, M. Corbella, Polyhedron 19 (2000) 2483–2491.
[10] M. Rodrı-guez, A. Llobet, M. Corbella, A.E. Martell, Reibenspies, J. Inorg. Chem.
38 (1999) 2328–2334.
[52] R.N. Patel, Y.P. Singh, Y. Singh, R.J. Butcher, J.P. Jasinski, Polyhedron 133
(2017) 102–109.
[53] R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett. 256 (1996) 454–464.
[54] G.A. Petersson, M.A. Al-Laham, J. Chem. Phys. 94 (1991) 6081–6090.
[55] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270–283.
[56] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G.
Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A.

14
R.N. Patel et al. / Polyhedron 188 (2020) 114687
Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. [84] M.J. Bew, B.J. Hathaway, R.J. Fereday, J. Chem. Dalton Trans. (1972) 1229–
Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E.
Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L.
Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg,
S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J.
Fox, Gaussian 09, Revision D.01, Gaussian Inc., Wallingford, CT, 2009.
1237.
[85] E. Garribba, G. Micera, J. Chem. Educ. 83 (2006) 1229–1232.
[86] G. Kolks, C.R. Frihart, P.K. Coughlin, S.J. Lippard, Inorg. Chem. 20 (1981) 2933–
2940.
[87] C.-L. O’Young, J.C. Dewan, H.R. Lilienthal, S.J. Lippard, J. Am. Chem. Soc. 100
(1978) 7291–7300.
[88] , Comprehensive Coordination Chemistry Vol. 5 (1987) 533.
[89] H. Okawa, M. Tadokoro, Y. Aratake, M. Ohba, K. Shindo, M. Mitsumi, M.
Koikawa, M. Tomono, D.E. Fenton, J. Chem. Soc., Dalton Trans. (1993) 253–
258.
[57] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 224 (2003) 669–
681.
[58] T. Mosmann, J. Immunol. 65 (1993) 55–63.
[59] K. Nakamoto, John Wiley & Sons, Inc., New York-London, 1963.
[60] R.N. Patel, Y.P. Singh, Y. Singh, R.J. Butcher, J.P. Jasinski, Polyhedron 129
(2017) 164–181.
[61] B.J. Hathaway, A.E. Underhill, J. Chem. Soc. (1961) 3091–3096.
[62] R.N. Patel, Y.P. Singh, Y. Singh, R.J. Butcher, Polyhedron 104 (2016) 116–126.
[63] B. Cheng, P.H. Fries, J.-C. Marchon, W.R. Scheidt, Inorg. Chem. 35 (1996)
1024–1032.
[90] J.V. Folgado, R. Ibanez, E. Coronado, D. Beltran, J.M. Savariault, J. Galy, Inorg.
Chem. 27 (1988) 19–26.
[91] R.N. Patel, Y.P. Singh, Y. Singh, R.J. Butcher, M. Zeller, RSC Adv. 6 (2016)
107379–107398.
[92] R.G. Bhirud, T.S. Srivastava, Inorg. Chim. Acta 173 (1990) 121–125.
[93] H. Ohtsu, Y. Shimazaki, A. Odani, O. Yamauchi, W. Mori, S. Itoh, S. Fukuzumi,
J. Am. Chem. Soc. 122 (2000) 5733–5741.
[64] A.W. Addison, T.N. Rao, J. Reedijk, J.V. Rijn, G.C. Verschoor, J. Chem. Soc.,
Dalton Trans. (1984,) 1349–1356.
[94] R.N. Patel, N. Singh, K.K. Shukla, V.L.N. Gundla, U.K. Chauhan, J. Inorg.
Biochem. 99 (2005) 651–663.
[65] J. Bernstein, R.E. Davis, L. Shimoni, N.-L. Chang, Angew. Chem. Int. Ed. 34
(1995) 1555–1573.
[95] X. Meng, M. Wang, N. Jiang, D. Zhang, L. Wang, C. Liu, J. Agric. Food Chem. 60
(2012) 11211–11221.
[66] G.A. Jeffrey, W. Saenger, Hydrogen Bonding in Biological Structures, Springer-
Verlog Berlin, 1996, pp. 3–14.
[96] A. Maroz, G.F. Kelso, R.A.J. Smith, D.C. Ware, R.F. Anderson, J. Phys. Chem. A
112 (2008) 4929–4935.
[67] M. Gonzalez-Álvarez, G. Alzuet, J. Borrás, L. del Castillo-Agudo, S. Garcia-
Granda, J.M. Montejo-Bernardo, Inorg. Chem. 44 (2005) 9424–9433.
[68] T. Suksrichavalit, S. Prachayasittikul, C. Nantasenamat, C. Isarankura-Na-
Ayudhya, V. Prachayasittikul, Eu. J. Med. Chem. 44 (2009) 3259–3265.
[69] L. Yang, D.R. Powell, R.P. Houser, Dalton Trans. (2007) 955–964.
[70] J. Lu, T. Paliwala, S.C. Lim, C. Yu, T. Niu, A.J. Jacobson, Inorg. Chem. 36 (1997)
923–929.
[97] ] I.B. -Haberle, J.S. Rebouças and I. Spasojevic, Redox Signaling, 2010, 13, 877–
918.
[98] D.P. Riley, Chem. Rev. 99 (1999) 2573–2587.
[99] R.S. Nicholson, I. Shain, Anal. Chem. 37 (1965) 178–190.
[100] S.W. Feldberg, L. Jeftic, J. Phys. Chem. 76 (1972) 2439–2446.
[101] C. Amar, E. Vilkas, J. Foos, J. Inorg. Biochem. 17 (1982) 313–323.
[102] N.A. Roberts, P.A. Robinson, Br. J. Rheumatol. 24 (1985) 128–136.
[103] J.A. Tainer, E.D. Getzoff, J.S. Richardson, D.C. Richardson, Nature 306 (1983)
284–287.
´
[71] R. Atencio, K. Ramırez, J.A. Reyes, T. González, P. Silva, Inorg. Chim. Acta 358
(2005) 520–526.
[72] J. Lewis, F.E. Mabbs, L.K. Royston, W.R. Smail, J. Chem. Soc., A (1969) 291–296.
[73] N.D. Chasteen, R.L. Belford, Inorg. Chem. 9 (1970) 169–175.
[74] J. Reedijk, D. Knetsch, B. Nieuwenhuijse, Inorg. Chem. Acta 5 (1971) 568–572.
[75] W.E. Estes, J.R. Wasson, J.W. Hall, W.E. Hatfield, Inorg. Chem. 17 (1978) 3657–
3664.
[104] G. Micera, E. Garribba, Int. J. Quantum Chem. 112 (2012) 2486–2498.
[105] L. Pisano, K. Varnagy, S. Timári, K. Hegetschweiler, G. Micera, E. Garribba,
Inorg. Chem. 52 (2013) 5260–5272.
[106] D. Sanna, K. Várnagy, N. Lihi, G. Micera, E. Garribba, Inorg. Chem. 52 (2013)
8202–8213.
[76] R.C. Aggarwal, N.K. Singh, R.P. Singh, Inorg. Chem. 20 (1981) 2794–2798.
[77] W.A. Alves, S.A.A. Filho, R.H.A. Santos, A.M.C. Ferreira, Inorg. Chem. Commun.
6 (2003) 294–299.
[78] O. Kahn, Moleculer Magneetism, Wiley VCH, Newyork, 1993.
[79] R.N. Patel, Inorg. Chim. Acta 363 (2010) 3838–3846.
[80] E.B. Seena, M.R.P. Kurup, Polyhedron 26 (2007) 829–836.
[81] J.R. Wasson, C. Trapp, J. Phy. Chem. 73 (1969) 3763–3772.
[82] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143–207.
[83] S.K. Jain, B.S. Garg, Y.K. Bhoon, D.L. Klayman, J.P. Scovill, Spectrochim Acta A
41 (1985) 407–413.
[107] R.N. Patel, Y. Singh, Y.P. Singh, R.J. Butcher, J. Coord. Chem. 69 (2016) 2377–
2390.
[108] S.K. Silverman, D.A. Dougherty, J. Phys. Chem. 97 (1993) 13273–13283.
[109] A. Rajca, Chem. Rev. 94 (1994) 871–893.
[110] J. Tang, J.S. Costa, A. Golobi, B. Kozlev, A. Robertazzi, A.V. Vargiu, P. Gamez,
J. Reedijk, Inorg. Chem. 48 (2009) 5473–5479.
[111] Y.-H. Chi, J.-M. Shi, H.-N. Li, W. Wei, E. Cottrill, N. Pan, H. Chen, Y. Liang, L. Yu,
Y.-Q. Zhang, C. Hou, Dalton Trans. 412 (2013) 15559–15569.
[112] V. Selmani, C.P. Landee, M.M. Turnbull, J.L. Wikaira, F. Xiao, Inorg. Chem.
Commun. 13 (2010) 1399–1401.