Synthesis, crystal structure and superoxide dismutase activity of two new bis(μ-acetato/μ-nitrato) bridged copper(II) complexes with N′-[phenyl(pyridin-2-yl)methylidene]benzohydrazone

Article abstract of DOI:10.1016/j.ica.2013.05.024

Two homodinuclear copper(II) end-on bis(μ-acetato/μ-nitrato) bridged complexes with two NNO donor ligands, viz., [(L)Cu(μ-CH₃COO) ₂Cu(L)] (1) and [(L)Cu(μ-NO₃)₂Cu(L)] (2) (where L = N′-[phenyl(pyridin-2-yl)methylidene]benzohydrazone) are reported. Both complexes are structurally characterized using single crystal X-ray diffraction studies and belong to monoclinic crystal system having space group P2₁/n. The distance between two copper centers is 3.344(8) and 3.406(7) A? respectively for 1 and 2. On the basis of density function theory (DFT) calculations, the electronic excitations involve transitions mainly from metal-ligand bonding MOs to the β-LUMO within the dominant Cu d _xy character and to β-LUMO+1. Epr spectra for polycrystalline samples exhibited the copper(II) hyperfine structures as well as zero-field splitting which are appropriate for triplet state of such a dimmers. Complexes effectively catalyze the dismutation of superoxide (O₂) in alkaline nitro blue tetrazolium chloride assay and IC₅₀ values were determined.

Full text of DOI:10.1016/j.ica.2013.05.024

Accepted Manuscript
Synthesis, crystal structure and superoxide dismutase activity of two new
bis(μ-acetato/μ-nitrato) bridged copper(II) complexes with N ’-[phenyl(pyri‐
din-2-yl)methylidene]benzohydrazone
R.N. Patel, Dinesh K. Patel, Vishnu P. Sondhiya, K.K. Shukla, Y. Singh, A.
Kumar
PII:
S0020-1693(13)00297-1
http://dx.doi.org/10.1016/j.ica.2013.05.024
ICA 15479
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
7 September 2012
10 May 2013
14 May 2013
Please cite this article as: R.N. Patel, D.K. Patel, V.P. Sondhiya, K.K. Shukla, Y. Singh, A. Kumar, Synthesis, crystal
structure and superoxide dismutase activity of two new bis(μ-acetato/μ-nitrato) bridged copper(II) complexes with
N ’-[phenyl(pyridin-2-yl)methylidene]benzohydrazone, Inorganica Chimica Acta (2013), doi: http://dx.doi.org/
10.1016/j.ica.2013.05.024
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Synthesis, crystal structure and superoxide dismutase activity of two new bis(μ-acetato/μ-nitrato)
bridged copper(II) complexes with N'-[phenyl(pyridin-2-yl)methylidene]benzohydrazone
R.N. Patela*, Dinesh K. Patela, Vishnu P. Sondhiyaa, K.K. Shuklaa, Y. Singha and A. Kumarb
aDepartment of Chemistry, A.P.S. University, Rewa (M.P.) India- 486003
bFaculty of Sciences, Lucknow University, Lucknow (U.P.) India
Two homodinuclear copper(II) end-on bis(μ-acetato/μ-nitrato) bridged complexes with two NNO donor
ligands, viz., [(L)Cu(µ-CH3COO)2Cu(L)] (1) and [(L)Cu(µ-NO3)2Cu(L)] (2) (where L = N'-
[phenyl(pyridin-2-yl)methylidene]benzohydrazone) are reported. Both complexes are structurally
characterized using single crystal X-ray diffraction studies and belong to monoclinic crystal system
having space group P 21/n. The distance between two copper centers is 3.344(8) and 3.406(7) Å
respectively for 1 and 2. On the basis of density function theory (DFT) calculations, the electronic
excitations involve transitions mainly from metal-ligand bonding MOs to the β-LUMO within the
dominant Cu dxy character and to β-LUMO + 1. Epr spectra for polycrystalline samples exhibited the
copper(II) hyperfine structures as well as zero-field splitting which are appropriate for triplet state of such
-
a dimmers. Complexes effectively catalyze the dismutation of superoxide (O2 ) in alkaline nitro blue
tetrazolium chloride assay and IC50 values were determined.
Keywords: Crystal structure, hydrazone, density functional theory, epr, superoxide dismutase activity.
1. Introduction:
Binuclear complexes have been receiving considerable interest due to their biological and
industrial relevance [1]. Mixed ligand complexes formed between metal ions, Schiff bases and
hetero aromatic nitrogen bases may be considered as models for substrate metal ion–enzyme
interaction. Chelation causes changes in the biological properties of the ligands and also the
metal. A number of Schiff-base complexes [2] have been tested for antibacterial activities,
antibacterial [3], antifungal [4], anticancer [5], and herbicidal [6] activities. Superoxide ion is
toxic to cells; a defense mechanism must have been initiated by nature.
Schiff base ligands, particularly molecules possessing nitrogen, oxygen and sulfur
donor sites are important in the development of coordination chemistry as well as in the
biomimetic chemistry of a number of metal ions, particularly the transition metals [7]. The
ability of nitrogen and sulfur based donors to stabilize reduced and oxidized forms of
copper(II) has sparked interest in their bioinorganic systems [8,9]. The properties of Schiff
1
*Corresponding author
E-mail address: rnp64@ymail.com (R.N. Patel)
Tel.: +91 7662 233683: fax +91 7662 230819

base metal complexes stimulated much interest for their contributions to single molecule-based
magnetism, material sciences, catalysis of many reactions like carbonylation, oxidation,
reduction and epoxidation, their industrial applications and complexing ability towards some
toxic metals. The high affinity of the chelation of the Schiff bases towards the transition metal
ions is utilized in preparing their solid complexes [10]. Schiff base complexes containing
nitrogen and oxygen atom as donor atoms play an important role in biological systems and
represent models for metallo-proteins and metallo-enzymes that catalyze the reduction of
nitrogen and oxygen [11].
In continuation of our previous work [12], herein we report the synthesis of two μ-
acetato/μ-nitrato bridged copper(II) complexes using Schiff base ligand (HL). X-ray
crystallography, epr, electronic spectroscopy, and magnetic susuptibility measurements have
been carried out to characterize these two copper(II) complexes. Their redox properties using
cyclic voltammetry along with SOD activity have also been measured and discussed.
2. Experimental
2.1. Materials and Instrumentation
All reagents used in the syntheses were of analytical grade. The elemental analysis for
carbon, hydrogen and nitrogen were performed on an Elementar Vario ELIII Carlo Erba 1108
Elemental analyzer. UV-vis spectra were recorded at room temperature on Shimadzu 1601
spectrophotometer. IR spectra were recorded in KBr medium on a Perkin-Elmer
spectrophotometer. Cyclic voltammetry was carried out on a BAS-100 Epsilon electrochemical
analyzer having an electrochemical cell with a three-electrode system. Ag/AgCl was used as the
reference electrode, glossy carbon as the working electrode and platinum wire as the auxiliary
electrode. NaClO4 (0.1M) was used as supporting electrolyte and DMSO as solvent. All
measurements were carried out at 298 K under a nitrogen atmosphere. Magnetic susceptibility
measurements were made on a Gouy balance using a mercury(II) tetrathiocynato cobaltate(II) as
calibrating agent(χg=16.44 × 10-6 c.g.s. units). Electron paramagnetic resonance (e.p.r.) spectra
were recorded with a Varian E-line Century Series epr spectrometer equipped with a dual cavity
and operating at X-band of 100 kHz modulation frequency. Tetracyanoethylene (TCNE) was
used as field marker (g = 2.00277).The EPR Parameters for copper(II) complexes determined
accurately from a computer simulation program[13-16].
2

4.2. Synthesis of complexes
4.2.1. Syntheses of Schiff base ligand (HL)
The Schiff base L1 was synthesized [17,18] by the condensation of benzoyalpyridine and
benzoyl hydrazide in equimolar ratio 1:1. The reaction mixture in ethanol was stirred for 4 h, A
colorless solution was obtained, which was filtered off and allowed for slow evaporation at room
temperature. White block shape crystals were collected by filtration and washed with diethyl
ether. Anal. Calc. C19H15N3O: C, 75.73; H, 5.02; N, 13.94 %. Found: C, 75.50; H 4.98; N,
14.02%. FAB-mass (m/z) Calc. 301.34; Found, 301.
4.2.2. Synthesis of [Cu2(µ-CH3COO)2L2] (1)
.
A mixture of Cu(OAc)2 2H2O (1 mmol, 0.199g) and HL (1 mmol, 0.301g) in methanol
was stirred for 5 h. Dark green solution was filtered and after slow evaporation green block
shape crystals suitable for single crystal X-ray were obtained. Yield: 0.352 g, 70.57%. Elemental
analysis (%): calc. for C42H34Cu2N6O6 (Mr = 845.84): C 59.64, H 4.05, N 9.94; found: C 59.36,
H 4.52, N 9.89. IR (cm-1): 3424, 3020, 1541, 1422, 1375, 1217, 1082, 928, 770, 671, 625, 532,
488.
4.2.3. Synthesis of [Cu2(µ-NO3)2L2] (2) Complex 2 was prepared in the similar way that
.
.
described for 1, except that Cu(NO3)2 3H2O (M.W. 241.60) was replaced Cu(OAc)2 2H2O. Yield:
0.411 g, 79.76%. Elemental analysis (%): calc. for C38H28Cu2N8O8 (Mr = 845.84): C 53.58, H
3.31, N 13.16; found: C 53.32, H 3.80, N 13.05. IR (cm-1): 3448, 3278, 3021, 1555, 1491, 1428,
1372, 1217, 1083, 929, 769, 671, 625, 559, 498.
4.3. Single crystal X-ray crystallography
Single crystal X-ray data were collected on CCD detector based Oxford Diffractometer
using graphite monochromatized MoKα (λ = 0.71073Å). The diffraction data was solved using
SIR-92[19] with GUI control and structure was refined by SHELXL-97 [20] refinement of F2
against all reflections. Non-hydrogen atoms were refined anisotropicaly and all hydrogen atoms
3

were geometrically fixed and allowed to refine using a riding model. Molecular graphics was
generating using different software such as Diamond, ORTEP-3v2 for WINDOWS [21],
PLATON and Mercury [22].
4.4. Density functional theory calculations
Density Functional Theory (DFT) calculations on the complexes 1 and 2 with spin
multiplicity were performed with the Gaussian 03 (G03) [23]. Optimized geometries were
calculated with the widely adopted U-B3LYP [24] functional. For all the atoms 6-31G** basis
set was employed. The X-ray coordinates were used as starting positions in the optimization.
Natural Bond Orbital (NBO) wave function analysis for the optimized structures was performed
with NBO 3.1 [25]. Franck–Condon electronic excitation spectra were calculated on the
optimized structures both in vacuum and in DMSO using the polarized continuum model (PCM)
[26] within the Time Dependent-Density Functional Theory (TD-DFT) taking into account the
lowest 30 excitations.
4.4. Superoxide dismutase activity (SOD)
The in vitro SOD activity was measured using alkaline DMSO method, where alkanine
-
DMSO was a source of superoxide radical (O2-) and nitro blue tetrazolium chloride (NBT) as O2
scavenger [27].
3. Results and discussion
3.1 Synthesis of complexes
Both complexes were prepared by the interaction of copper(II) salt with hydrazone Schiff
base ligand directly by conventional solution method and crystalline product suitable for single
crystal X-ray diffraction studies obtained. The protocol used for the syntheses of these two bis(μ-
acetato/μ-nitrato) copper(II) complexes is shown in Scheme I. The suitable crystals were selected
for single crystal X-ray analysis.
4

.
Cu(AcO)2 H2O
Complex 1
NH
Cu(NO3).3H2O
N
N
O
Complex 2
Scheme I- Synthesis of complex 1 and 2
3.2. X-ray crystallography structural characterization
Single crystal X-ray analysis indicates that copper(II) center is penta coordinated and
OAc is making bridge between two copper ions in complex 1. Crystal structure refinement data
related to both complexes are given in Table 1. ORTEP view of complex 1 is presented in Fig. 1.
The lattice nature is monoclinic with space group P21/n. The compound exhibits a distorted
square pyramidal geometry with the basal plane occupied by hydrazone ligand and acetate
oxygen (O2) for both metal centre. The relevant bond lengths and angles are given in Table 2.
The oxygen (O2a) from acetate group of the adjacent monomer plugs in to the axial position
resulting in a dimer with a Cu-Cu separation 3.34 Å. The comparison of bond distances (Table 2)
confirms the possibility of dinuclear structure. The Cu-N/O bond lengths and bond angles around
the copper(II) ions are [Cu(1)-N(2) = 1.927 Å, Cu(1)-O(1) = 1.984 Å, Cu(1)-O(2) = 1.926 Å,
Cu(1)-O(2a) = 2.312, Cu(1a)-O(2) = 3.312 and O(2)-Cu(1)-N(2) = 172.88°, O(2)-Cu(1)-O(1) =
102.90°, N(2)-Cu(1)-O(1) = 79.30°, O(2)-Cu(1)-N(1) = 97.99°, N(2)-Cu(1)-N(1) = 79.65, O(1)-
Cu(1)-N(1) = 158.95] are similar to the recently reported bridged copper(II) complexes [28]. It is
observed that copper atom is closer to hydrazone ligand moiety than the acetato group. Cu-
Npyridyl bonds large than Cu-Nimine bonds show the strength of azomethine nitrogen coordination.
Most of the angles involving the central copper atoms are widely different from 90° and 180°
indicating a significant distortion from the square pyramidal geometry.
5

The five coordinated copper(II) centre with distorted geometry is indicated by the
structural index parameter τ, which measures the degree of trigonality of penta coordinated
geometry between the ideal square pyramidal (τ = 0) and a trigonalbipyramidal (τ = 1) extremes
[29,30]. For the complex 1, τ value is 0.23. Coordination sphere of 1 is presented in Fig. 2. The
bridging angle of O (2)-Cu(1)-O(2a) and Cu(1)-O(2)-Cu(1a) are 76.20º and 103.8º, respectively.
An ORTEP view of complex 2 is presented in Fig. 3. The complex crystallizes in
monoclinic crystal system with the space group P21/n. The structure of 2 is very similar to
complex 1 and two copper centers are bridged with nitrato group. Both copper centers adopt a
distorted square pyramidal structure. The τ value for complex 2 0.26, confirms the distorted
square pyramidal structure of the penta coordinated complex. The distorted basal planes are
defined by N(1), N(2), O(1) and O(2). O(2a) of other nitrato group is present in the axial
position. Coordination sphere is presented in Fig. 4. The bridging angle of O(2)-Cu(1)-O(2a) and
Cu(1)-O(2)-Cu(1a) are 73.44º and 106.56º respectively. All the Cu-O/N bond distances [Cu(1)-
N(2) = 1.927 Å, Cu(1)-N(1) = 1.991 Å, Cu(1)-O(1) = 1.946 Å, Cu(1)-O(2) = 1.960 Å, Cu(1)-
O(2a) = 2.355 Å, Cu(1a)-O(2) = 2.355 Å] and the bond angles around the copper(II) ions [N(2)-
Cu(1)-O(1) = 80.46º, N(2)-Cu(1)-O(2) = 177.41º, O(1)-Cu(1)-O(2) = 98.99º, N(2)-Cu(1)-N(1) =
81.23º, O(1)-Cu(1)-N(1) = 161.69º, O(2)-Cu(1)-N(1) = 99.32º] fall in to the normal range. The
Cu-Cu separation in complex 2 is 3.40 Å. Both complexes 1 and 2 have essentially similar
structures with identical metrical parameters (Table 2). A ball and stick view (Fig. S1 and S2) of
the 2D-helical layer constructed by HL and the bridging ligands forms a structural assembly. It
can be observed that the molecules are packed in a 2D helical layered arrangement of the rings.
3.3. Density functional theory
Natural Bond Orbital (NBO) wave function analysis [25] has been performed in order to
gain insight into the molecular orbitals. The main compositions of the LUMO and HOMO
orbitals for 1 are shown in Fig 5. The electronic excitations involve transitions mainly from
metal–ligand bonding MOs to the β-spin LUMO with dominant Cu dxy character, and to β-
LUMO+1. Since each absorption line in a TD-DFT spectrum (Fig. 5) can arise from a several
single orbital excitations, a description of the transition character is generally not
straightforward. However, approximate assignments can be made, although they provide a
simplified representation of the transitions. TD-DFT excitations were calculated both in the gas
6

phase and in the solvent using the PCM (DMSO). By comparing the calculated spectra it is
evident that calculated transitions do not exhibit significant solvatochromic effects. In this view,
only the PCM model results are presented in the Table 3. The experimental UV-Vis spectrum
presents a very weak and broad absorption centered at ~700 nm and 400 nm alongwith the
shoulder at ~820 nm. The calculated electronic excitations give rise to the same pattern of bands,
at energies in good agreement with the experimental ones.
2.3. Magnetic studies
The magnetic data of the complexes were collected at 278 K on a Gouy Balance. The
effective magnetic moment (μeff) of [Cu2(µ-CH3COO)2L2] (1) and [Cu2(µ-NO3)2L2] (2) were
measured to be 1.67 and 1.68 B.M. The effective magnetic moment (μeff) for both complexes at
room temperature is below the theoretical value expected for a copper(II) centre with S = ½ and
indicative of net antiferromagnetic couple between the copper(II) ions through bridging units in
the polycrystalline state [31]. The antiferromagnetic behavior of the binuclear complexes is
attributed to spin-spin interaction via the super-exchange pathway provided by the bridging
groups rather than a direct metal-metal interaction [32]. The copper-copper distance in complex
1 and 2 are observed to be 3.34 and 3.40 Å respectively from X-ray diffraction studies. This
separation generally rules out any significant amount of direct copper-copper interactions.
2.4. Epr spectral study
The X-band epr spectra of complexes 1 and 2 in polycrystalline state at room temperature
and in frozen DMSO solution at 77 K was recorded. These spectra are shown in Fig. 6 and 7.
The epr spectra of the complexes provide information about the coordination environment
around copper(II) in these complexes The epr spectra in polycrystalline state at room
temperature showed two broad signals (~2835 and ~3500 G). The half-field signals ( Ms = ±2)
are observed inboth complexes and polycrystalline spectra at room temprature at round 1600 G
with gnf = ~4.16. These characters reveals clearly the presence of magnetic interaction between
two copper(II) ions through µ-nitrato/µ-acetato bridge.
The geometric parameters (G) also estimate from g-values of polycrystalline spectra. The
parameter is the measure of the exchange interaction between the copper centers in
polycrystalline state and this could be calculated using the equation G = (g║ - 2.0023)/(g┴-
7

2.0023) for axial spectra and G = (g1 - 2.0023)/(g2 - 2.0023) for rhombic spectra [33]. The
value of g less than 4 for present complexes reveal the considerable exchanges interaction and if
G > 4, the exchange interaction is negligible [34]. The frozen solution epr spectra of complexes 1
and 2 are axially symmetric (g║ > g┴ > 2.0023) having a quartet hyperfine structures on the
parallel components. Frozen solution spectra of these complexes with g║ > g┴ > 2.0023 are
consistent with a dx2-y2 ground state in a square planner or square pyramidal geomentry [35,36].
The epr spectra of complexes 1 and 2 showed seven and five nitrogen superhyperfine lines in the
g┴ region. On expanded scale superhyperfine nitrogen lines (AN = 15.7 × 10-4 cm-1) are more
clear. Still the pattern in the g║ region and specially the feature at ~3615 G are typical of a
bridge species. The “g value” is 1.83 for complex 1 and 2 which is not a value that can be
attributed to a monomeric copper species. Thus these are the experimental evidence for the Cu-
Cu moiety in the complex and epr observations are consistent with single crystal X-ray data.
2.5. UV-Visible Spectrometry
UV-spectra of the complexes 1 and 2 have been recorded in DMSO and in solid state
(reflectance spectra). In the visible region, each of these spectra involves two ligand field bands
appearing at 680 nm and 1100 nm regions, corresponding to the transitions dz2→dx2-y2 and dxz,
dyz→dx2-y2 respectively, as expected for distorted square pyramidal geometry [37,38]. The longer
wavelength absorption for 1 and 2 in DMSO suggests the typical signals for bridged dicopper
systems in solution and is in agreement with their single crystal x-ray structural analysis. The
complexes also show strong band in the near UV region at 400nm (Fig. S3) and is tentatively
assigned to µ-acetato/µ-nitrato...Cu(II) charge transfer. These types of spectra are characteristic of
dinuclear copper(II) complexes in which there is a magnetic interaction between the two copper
centers [39-41].
2.6. Electrochemistry
The electrochemical properties of two complexes have been studied by cyclic
voltammetry in DMSO solution with 0.1 M NaClO4 as supporting electrolyte at glassy carbon
working electrode. The cyclic voltammogram (CV) of the complexes are displayed in (Fig. 8).
The CV of the complexes show two reduction waves at E11/2 = -0.135 V and E21/2 = 0.205 V for
complex 1 and E11/2 = -0.120 V and E21/2 = 0.250 V for complex 2, corresponding to the CuII CuII
8

CuII CuI
CuI CuI redox couples respectively [42]. These kinds of observations are
indicative of significant metal coupling for both complexes [43,44]. The observed redox couples
are irreversible with peak separation ~0.210 V. The stability of the mixed valent complexes is
expressed by the conproportionation constant (Kcon) for the following equilibrium,
[CuII CuII] + [CuI CuI]
2 [CuII CuI]
The Kcon is usually estimated from the difference in the half-wave potential between
metal center couples, logKcon = 16.9 (ΔE1/2) [12]. The observed value of Kcon for both complexes
is given in Table 4. From Table 4, it is evident that the large Kcon values indicate that the addition
of a second electron is most difficult than of the first electron and the CuII CuI mixed valence
species is stable with respect to conproportionation. This kind of observation is more common in
several binuclear complexes [45-47].
2.7. Superoxide dismutase activity (SOD)
The superoxide dismutase activity of complex 1 and 2 were investigated by NBT assay
method and catalytic activity towards the dismutation of superoxide anion was measured.
Superoxide dismutation is a redox process. IC50 value for SOD activity has been defined as the
chromophore concentration required to yield 50% inhibition of the reduction of NBT. The IC50
value of the complexes 1 and 2 are 35±5 and 26±5 µM, respectively. Present compounds showed
SOD activity but are less active than the native SOD (IC50 = 0.04 μM). The good activities of
these complexes may be attributed to the flexible nature of ligand used, which is able to
accommodate the geometrical change from copper(II) to copper(I) [48] in catalytic process, just
-
like the O2 in place of the water molecule bound to the copper site in the mechanism of
-
dismutation of O2 by native SOD. The SOD activities exhibited by the two complexes survive
in a bovine serum albumin. This kind of observation clearly shows that Schiff base is a stronger
of copper(II) ions than bovine serum albumin. The inhibition concentration (IC50) of complex 2
is lower than complex 1. In other words, complex 2 is actually more active than complex 1. The
SOD graph of 1 and 2 is presented in Fig. 9. The difference in the IC50 values for the two
complexes should be ascribed to the evidence of discrepancy in the structures between them. The
distorted geometry of complexes may favor the geometrical change, which is essential for the
catalytic property of the complexes. Similar results have been reported by our group [49,14] and
others [50,51] (Table 5). The higher IC50 can only be accredited to the vacant coordination site,
9

which facilitate the binding of superoxide anion, electron of aromatic ligands that stabilize Cu-
•-
O2 interaction and not only to the partial dissociation of complex in solution.
4. Conclusions
We have synthesized two new copper(II) complexes viz., [(L)Cu(µ-CH3COO)2Cu(L)] (1)
and [(L)Cu(µ-NO3)2Cu(L)] (2) and characterized by various physicochemical techniques. The
epr spectra for polycrystalline samples exhibited the copper(II) hyperfine structures as well as
zero-field splitting which are appropriate for triplet state of such a dimers. Complex 2 showed
the highest SOD activity. This activity however was still much lesser than the native enzyme. It
was also observed that nitrato bridged complex is more bioactive than acetato bridged complex.
Abbreviations
HL/L
DMSO
Epr
N'-[phenyl(pyridin-2-yl)methylidene]benzohydrazone
Dimethyl sulphoxide
Electron paramagnetic resonance
Density functional theory
DFT
NBT
MO
Nitro blue tetrazolium chloride
Molecular orbital
SOD
Superoxide dismutase
Acknowledgements
Our grateful thanks to School of Chemistry, University of Hyderabad, Hyderabad for
Single Crystal X-ray data collection, RSIC (SAIF) IIT, Bombay for epr measurements and SAIF,
Central Drug Research Institute, Lucknow is thankfully acknowledged for providing elemental
and IR spectral analysis. Financial assistance from CSIR New Delhi [Scheme no.
01(2451)/11/EMR-II] and MPCST, Bhopal [Project no. 5986/CST/R&D/2012] are also
thankfully acknowledged.
10

Appendix. Supplementary material
CCDC 827920 and 827921 contain the supplementary crystallographic data for
[(L)Cu(µ-CH3COO)2Cu(L)] (1) and [(L)Cu(µ-NO3)2Cu(L)] (2). These data can be obtained free
of
charge
from
the
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif or from the Director, CCDC, 12 Union Road, Cambridge,
CB2, IEZ, UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk).
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14

Figure Captions:
Fig.1 ORTEP view of [(L)Cu(µ-CH3COO)2Cu(L)] (1).
Fig. 2 Co-ordination sphere of [(L)Cu(µ-CH3COO)2Cu(L)] (1).
Fig. 3 ORTEP view of [(L)Cu(µ-NO3)2Cu(L)] (2).
Fig. 4 Co-ordination sphere of [(L)Cu(µ-NO3)2Cu(L)] (2).
Fig. 5 Selected orbital excitations for complex 1 (orbital contour value 0.005).
Fig. 6 EPR spectra of [(L)Cu(µ-CH3COO)2Cu(L)] (1) in polycrystalline state (RT) and in DMSO
solution at LNT.
Fig. 7 EPR [(L)Cu(NO3)2Cu(L)] (2) in polycrystalline state (RT) and in DMSO solution at LNT.
Fig. 8 Cyclic voltammograme of complex 1 and 2; scan rate 300 mV/s
Fig. 9 Graphical representation of SOD activity of complexes 1 and 2.
15

Figure(s)
Fig. 1
Fig.2

Fig. 3
Fig.4

Fig. 5

TCNE
Fig.6
Fig.7

Fig. 8
Fig. 9

Supplementary Info (for publication online)
Supplementary Figure Caption:
Fig.S1 Supramolecular structure of [(L)Cu(µ-CH3COO)2Cu(L)] (1).
Fig. S2 Supramolecular structure of [(L)Cu(µ-NO3)2Cu(L)] (2).
Fig.S3 UV- vis spectra of complexes 1 and 2 in 100% DMSO
Fig. S1

Fig. S2

1
2
Fig S3

Table(s)
Table 1 Crystal data and structure refinement parameters for complexes 1 and 2.
1
C42 H34 Cu2 N6 O6
845.848
293(2)
0.71073
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
space group
Unit cell dimensions
a(Å)
C38 H28 Cu2 N8 O8
851.78
293(2)
0.71073
Monoclinic
P 21/n
Monoclinic
P21/n
9.5631(17)
9.3768(16)
b(Å)
13.101(2)
13.473(2)
c(Å)
15.193(3)
14.752(3)
α(˚)
90
90
β(˚)
100.668(3)
99.468(3)
γ(˚)
90
90
Volume (Å3)
Z
Calculated density
Absorption coefficient
F(000)
1870.6(6)
1838.3(5)
2
2
1.509 Mg/m3
1.542 Mg/m3
1.195 mm-1
1.222 mm-1
868.0
872
Crystal size
θ range for data collection
Limiting indices
0.26 × 0.22 × 0.16 mm
2.07 to 25.00˚
-11<=h<=11, -15<=k<=15, -
18<=l<=18
0.41 × 0.36 × 0.26 mm
2.06 to 25.99˚
-11<=h<=11, -16<=k<=16, -
18<=l<=18
Reflections collected / unique
Completeness to θ = 25.00˚
Absorption correction
17678 / 3299 [R(int) = 0.0331]
100.0 %
Semi-empirical from
equivalents
18652 / 3590 [R(int) = 0.0283]
99.9 %
None
Max. and min. transmission
Refinement method
1.0000 and 0.8846
Full-matrix least-squares on F2
3299 / 0 / 253
1.038
-
Full-matrix least-squares on F2
3590 / 2 / 253
Data / restraints / parameters
Goodness-of-fit on F2
1.045
Final R indices [I >2σ(I)]
R indices (all data)
R1 = 0.0346, wR2 = 0.0914
R1 = 0.0401, wR2 = 0.0953
0.406 and -0.233 e.A-3
R1 = 0.0360, wR2 = 0.0975
R1 = 0.0411, wR2 = 0.1013
0.571 and -0.377 e.A-3
Largest diff. peak and hole (e A-3)

Table 2 Bond lengths [A˚] and angles [˚] for 1 and 2.
Complex 1
N(1)-Cu(1)
2.0195(19)
O(2)-Cu(1)
1.9261(16)
N(2)-N(3)
N(2)-Cu(1)
O(1)-Cu(1)
1.366(3)
1.927(2)
1.9843(16)
O(2)-Cu(1)#1
Cu(1)-O(2)#1
2.3120(18)
2.3120(18)
C(1)-N(1)-C(5)
119.1(2)
O(2)-Cu(1)-N(2)
O(2)-Cu(1)-O(1)
N(2)-Cu(1)-O(1)
O(2)-Cu(1)-N(1)
N(2)-Cu(1)-N(1)
O(1)-Cu(1)-N(1)
O(2)-Cu(1)-O(2)#1
N(2)-Cu(1)-O(2)#1
O(1)-Cu(1)-O(2)#1
N(1)-Cu(1)-O(2)#1
172.88(8)
102.90(7)
79.30(7)
97.99(7)
79.65(8)
158.95(7)
76.20(7)
110.49(7)
95.29(7)
92.09(7)
C(1)-N(1)-Cu(1)
C(5)-N(1)-Cu(1)
C(6)-N(2)-N(3)
C(6)-N(2)-Cu(1)
N(3)-N(2)-Cu(1)
C(13)-N(3)-N(2)
C(13)-O(1)-Cu(1)
C(20)-O(2)-Cu(1)
C(20)-O(2)-Cu(1)#1
Cu(1)-O(2)-Cu(1)#1
127.46(17)
113.43(15)
122.2(2)
120.03(16)
117.57(14)
107.76(19)
109.91(14)
119.81(16)
135.08(16)
103.80(7)
Complex 2
Cu(01)-N(2)
Cu(01)-O(1)
Cu(01)-O(2)
1.912(3)
1.946(3)
1.960(3)
Cu(01)-N(1)
Cu(01)-O(2)#1
O(2)-Cu(01)#1
1.991(3)
2.355(3)
2.355(3)
N(2)-Cu(01)-O(1)
N(2)-Cu(01)-O(2)
O(1)-Cu(01)-O(2)
N(2)-Cu(01)-N(1)
O(1)-Cu(01)-N(1)
O(2)-Cu(01)-N(1)
N(2)-Cu(01)-O(2)#1
80.46(11)
177.41(12)
98.99(12)
81.23(12)
161.69(12)
99.32(12)
109.07(12)
O(1)-Cu(01)-O(2)#1
O(2)-Cu(01)-O(2)#1
N(1)-Cu(01)-O(2)#1
C(13)-O(1)-Cu(01)
N(4)-O(2)-Cu(01)
92.04(11)
73.45(12)
93.67(12)
109.8(2)
119.8(3)
128.3(3)
N(4)-O(2)-Cu(01)#1
Cu(01)-O(2)-Cu(01)#1
106.55(12)
Symmetry transformations used to generate equivalent atoms: #1 -x+1,-y,-z

Table 3 TD-DFT calculated excitations and approximate assignments for 1
Excitation Wavelength Oscillator Composition (%) Nature of the transition and
Energy
(eV)
(nm)
Strength
(f)
approximate assignment
1.511
820
0.011
β HOMO-2→ β LUMO+2
(21%)
Cu (dz2)→Cu (dx2-y2)
Cu (dz2)→Cu (dx2-y2)
β HOMO-2→ β LUMO+3
(32%)
1.840
673
0.004
β HOMO→ β LUMO (45%) π→ π* and Cu (dz2)→Cu (dx2-y2)
2.942
2.971
421
417
0.493
0.045
β HOMO→ β LUMO (28%) π→ π* and Cu (dz2)→Cu (dx2-y2)
β HOMO-1→ β LUMO+1
π→ π*
(40%)
3.075
403
0.363
β HOMO-1→ β LUMO+1
(24%)
β HOMO-1→ β LUMO+3
(18%)
π→ π*
π→ π* and π→ Cu (dx2-y2) and π*
π→ Cu (dx2-y2)
β HOMO→ β LUMO+2
(25%)
3.163
392
0.077
β HOMO-2→ β LUMO+3
(66%)
Cu (dz2)→Cu (dx2-y2) and π*
Table 4 Cyclic voltammetric data for 0.003 M solution of the Cu(II) complexes in
DMSO containing 0.1 M NaClO4 as supporting electrolyte.
Epc1
(V)
Epa1
(V)
Epc2
(V)
Epa2
(V)
E1
(V)
E2
(V)
Kcon
1/2
1/2
Complex
5.6 × 105
1.8 × 106
0.10
0.32
-0.37
0.09
-0.135
0.205
1
2
0.15
0.38
-0.39
0.12
-0.120
0.250

Table 5 Superoxide dismutase activity of some copper(II) complexes
IC50 (mol dm-3)
S. No. Complexes
Reference
1. [(L1)Cu-(μ-CH3COO)2Cu(L1)]∙4,4’-bipy
2. [(L2)Cu-(μ-NO3)2Cu(L2)]
3. [Cu(L)X2]
52
58
22
18
27
62
132
32
35
35
26
12
12
45
4. [Cu(L)Br2]
45
5. [Cu(L)2(ImH)2]∙CH3OH
6. [Cu(L)(bipy)]
46
46
7. [Cu(glygly)]∙3H2O
47
47
8. [Cu(glygly)(Phen)]∙3H2O
9. [Cu(PSBP)2(NO3)(BF4)]
10. [(L)Cu(µ-CH3COO)2Cu(L)]
11. [(L)Cu(µ-NO3)2Cu(L)]
48
Present work
Present work

*Highlights (for review)
Highlight
1. Homo bi-nuclear complex
2. Schiff base hydrazone ligand
3. Density functional theory
4. Epr spectroscopy
5. Superoxide dismutase activity

*Graphical abstract (synopsis) (for review)
Graphical Abstract
Two homodinuclear copper(II) end-on bis(μ-acetato/μ-nitrato) bridged complexes are
synthesized. Both complexes structurally characterized using single crystal X-ray diffraction
studies and belong to monoclinic crystal system having space group P 21/n.