Synthesis, structural characterization, superoxide dismutase and antimicrobial activities studies of copper (II) complexes with 2-(E)-(2-(2-aminoethylamino) methyl)-4-bromophenol and (19E, 27E)-N1, N2-bis (phenyl (pyridine-2-yl)-methylene)-ethane-1, 2-diamine as ligands

Article abstract of DOI:10.1016/j.molstruc.2014.04.018

Three new copper (II) complexes, [Cu(L)(H₂O)]ClO₄ (1), [Cu(L¹)(ClO₄)]⁺ (2) and [Cu(L ¹)]²⁺ (3), where HL = 2-(E)-(2-(2-aminoethylamino)methyl)- 4-bromophenol, L¹ =(19E, 27E)-N¹,N²- bis(phenyl(pyridine-2-yl)-methylene)-ethane-1, 2-diamine, have been synthesized and characterized by using various physic-chemical and spectroscopic methods. The solid-state structures of 1 and 2 were determined by single crystal X-ray crystallography. Infrared spectra, ligand field spectra and magnetic susceptibility measurements agree with the observed crystal structures. The molecular structure of copper complexes showed that the ligands occupies the basal plane of square pyramidal geometry with the H₂O of 1 or the ClO₄ of 2 occupying the remaining apical position. Complexes 1 and 2 crystallize in the monoclinic system of the space group P2_1/c, a = 10.5948(6)?, b = 19.6164(11)?, c = 8.6517(5)?, α = 90°, β = 108.213(2)°, γ = 90° and Z = 4 for 1, a = 9.5019(3)?, b = 11.3 801(3)?, c = 25.3168(14)?, α = 90°, β = 100.583(4)°, γ = 90°, and Z = 4 for 2. The synthesized Schiff base (HL/L¹) was behaves as tetradentate ON ₃/N₄ ligands with donor groups suitable placed for forming 2 or 3 five membered chelate rings. Copper (II) complexes display X-band EPR spectra in 100% DMSO at 77 K giving g_∥ > g_⊥ > 2.0023 indicating d_x²_-y ² ground state. The half-wave potential values for Cu (II)/Cu (I) redox couple obtained in the reaction of the copper (II) complexes with molecular oxygen and superoxide radical (O₂^-) electronegated in DMSO are in agreement with the SOD-like activity of the copper (II) complexes. In vitro antimicrobial activities of the complexes against the two bacteria (Escherichia coli, Salmonella typhi) and the two fungi (Penicillium, Aspergillus sp.) have been investigated comparing with the Schiff base ligands.

Full text of DOI:10.1016/j.molstruc.2014.04.018

Journal of Molecular Structure xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural characterization, superoxide dismutase
and antimicrobial activities studies of copper (II) complexes with
2-(E)-(2-(2-aminoethylamino) methyl)-4-bromophenol and
(19E, 27E)-N1, N2-bis (phenyl (pyridine-2-yl)-methylene)-
ethane-1, 2-diamine as ligands
b
b
Mukesh Choudhary a, , R.N. Patel , S.P. Rawat
⇑
a Department of Chemistry, National Institute of Technology Patna, Ashok Raj Path, Patna 800005, Bihar, India
b Department of Chemistry, Awadhesh Pratap Singh University, Rewa 486003, M.P., India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
Three new copper (II) complexes, [Cu(L)(H2O)]ClO4 (1), [Cu(L1)(ClO4)]+ (2) and [Cu(L1)]2+ (3), derived from
2-(E)-(2-(2-aminoethylamino)methyl)-4-bromophenol (HL) and (19E, 27E)-N1,N2-bis(phenyl (pyridine-2-
yl)-methylene)-ethane-1, 2-diamine(L1), were synthesized and characterized by using various
physic-chemical and spectroscopic methods. The solid-state structures of complexes 1 and 2 (Fig. 4) were
determined by single crystal X-ray crystallography which revealed distorted square pyramidal geometry
around Cu (II) ion.
ꢀ
Design of new ligands (HL/L1) and
copper (II) complexes.
Single crystal X-ray analysis.
Superoxide dismutase activity
determination.
Magnetic susceptibility
measurements.
Antimicrobial activity.
ꢀ
ꢀ
ꢀ
ꢀ
a r t i c l e i n f o
a b s t r a c t
Three new copper (II) complexes, [Cu(L)(H2O)]ClO4 (1), [Cu(L1)(ClO4)]+ (2) and [Cu(L1)]2+ (3), where
HL = 2-(E)-(2-(2-aminoethylamino)methyl)-4-bromophenol, L1 =(19E, 27E)-N1,N2-bis(phenyl(pyridine-
2-yl)-methylene)-ethane-1, 2-diamine, have been synthesized and characterized by using various phy-
sic-chemical and spectroscopic methods. The solid-state structures of 1 and 2 were determined by single
crystal X-ray crystallography. Infrared spectra, ligand field spectra and magnetic susceptibility measure-
ments agree with the observed crystal structures. The molecular structure of copper complexes showed
that the ligands occupies the basal plane of square pyramidal geometry with the H2O of 1 or the ClO4 of 2
occupying the remaining apical position. Complexes 1 and 2 crystallize in the monoclinic system of the
Article history:
Received 5 February 2014
Received in revised form 7 April 2014
Accepted 7 April 2014
Available online xxxx
Keywords:
SOD activity
Schiff bases
Copper (II) complexes
Single crystal X-ray analysis
Antimicrobial activity
space group P21/c, a = 10.5948(6)Å, b = 19.6164(11)Å, c = 8.6517(5)Å,
Z = 4 for 1, a = 9.5019(3)Å, b = 11.3 801(3)Å, c = 25.3168(14)Å, = 90°, b = 100.583(4)°,
for 2. The synthesized Schiff base (HL/L1) was behaves as tetradentate ON3/N4 ligands with donor groups
a
= 90°, b = 108.213(2)°,
c = 90° and
a
c
= 90°, and Z = 4
⇑
Corresponding author.
E-mail address: choudharydr.mukesh@yahoo.in (M. Choudhary).
http://dx.doi.org/10.1016/j.molstruc.2014.04.018
0022-2860/Ó 2014 Published by Elsevier B.V.
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2
M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
suitable placed for forming 2 or 3 five membered chelate rings. Copper (II) complexes display X-band EPR
2
2
spectra in 100% DMSO at 77 K giving g|| > g\ > 2.0023 indicating dx–y ground state. The half-wave poten-
tial values for Cu (II)/Cu (I) redox couple obtained in the reaction of the copper (II) complexes with molec-
ular oxygen and superoxide radical (Oꢁ2 ) electronegated in DMSO are in agreement with the SOD-like
activity of the copper (II) complexes. In vitro antimicrobial activities of the complexes against the two bac-
teria (Escherichia coli, Salmonella typhi) and the two fungi (Penicillium, Aspergillus sp.) have been investigated
comparing with the Schiff base ligands.
Ó 2014 Published by Elsevier B.V.
Introduction
complexes namely [Cu(L1)(bipy)]ꢂ2H2O 1, [Cu(L1)(dmp)]ꢂCH3CN 2
and [Cu(L1)(phen)] 3 where, L1H2 = 2-{[(Z)-(5-bromo-2-hydroxy-
Transition metal complexes with Schiff base ligands have been
widely investigated since such ligands can bind metal centers at
more than one site and thus allow the successful synthesis of metal
complexes with interesting stereochemistry and model enzymes/
biological systems. The Schiff base of 5-bromo-2-hydroxybezalde-
hyde with N-(2-aminoethyl) ethane-1, 2-diamine has created a
well-known class of metallo-biomolecules [1,2]. Similarly, a het-
erocyclic nucleus, namely pyridine base ligands has also been
reported in many biochemical reactions to design and develop
molecular systems of biological and medicinal importance. Ben-
zoyl pyridine derivatives are important compounds in organic
chemistry because of their application in heterocyclic synthesis
and such ligating species on coordination with metal ions may
emerge as a metal-mediated drugs. A 2-benzoyl pyridine derived
Schiff base (19E, 27E)-N1, N2-bis (phenyl (pyridine-2-yl)-methy-
lene)-ethane-1, 2-diamine has been used as a good chelating agent
with 3d-metal ions [3–8].
The activity of low-molecular weight copper (II) complexes
mimicking the superoxide dismutase (SOD) activity [9–11], pro-
vide models for metalloproteins active sites and lend insight
toward the design of new catalysts. Copper is a biologically rele-
vant element and many enzymes that depend on copper for their
activity have been identified. Among these complexes, copper (II)
complexes are known to play a significant role in naturally occur-
ring biological systems [12], like (Cu, Zn-SOD) superoxide dismu-
tase. Superoxide dismutase (SOD) which can destroy the
superoxide very rapidly is nature’s agent for protection of the
organism from this radical burden. In fact native SOD enzymes
have been shown in many studies to exhibit protection in animal
models of inflammatory diseases [13]. Oberley and Buettner [14]
have reported that cancer cells had less superoxide dismutase
(SOD) activity than normal cells. The SOD shows bio-catalytic
activity towards the superoxide ion (Oꢁ2 ) is toxic to cells; a
defense mechanism must have been initiated by nature. All
organisms, which use dioxygen and many that have to survive
an oxygenated environment, present SOD in their metabolism.
These SODs disproportionate the toxic Oꢁ2 to molecular oxygen
and hydrogen peroxide [15,16]. All SOD employ the two step
Ping–Pong mechanism shown in Eqs. (1) and (2), where Cu is
the redox active metal center capable of both oxidizing and
reducing superoxide activity.
phenyl)methylidene]amino}benzoic acid. The solid-state structures
of 1 and 2 were determined by single crystal X-ray crystallography,
which revealed distorted square pyramidal geometry around Cu (II)
ion.
In continuation of our work on Schiff base copper (II) complexes
[24], we describes the synthesis, structural characterization, super-
oxide dismutase and antimicrobial activities studies of three new
copper (II) complexes with 2-(E)-(2-(2-aminoethylamino) methyl)
-4-bromophenol and (19E, 27E)-N1,N2-bis (phenyl (pyridine-2-yl)-
methylene)-ethane-1, 2-diamine as ligands. The copper (II) com-
plexes were formulated as [Cu(L)(H2O)]ClO4 (1), [Cu(L1)(ClO4)]+
(2) and [Cu(L1)]2+ (3). The crystal structure of these complexes
[Cu (L) (H2O)] ClO4 (1), [Cu (L1) (ClO4)]+ (2), are described. The 2-
(E)-(2-(2-aminoethylamino) methyl)-4-bromophenol and (19E,
27E)-N1,N2-bis(phenyl(pyridine-2-yl)-methylene)-ethane-1, 2-dia-
mine Schiff bases behaves as a tetradentate ON3/N4 donor ligands
(Schemes 1 and 2) with donor groups suitable placed for forming 2
or 3 five membered chelate rings. The mononuclear complexes (1)
and (2) show pentacoordiated copper (II) ion with distorted square
pyramidal coordination geometry whereas complex (3) have
square planar geometry. The SOD activities have been measured
using alkaline DMSO as a source of superoxide radical (Oꢁ2 ) and
nitro blue tetrazolium (NBT) as Oꢁ2 scavenger.
Experimental
Materials used for synthesis
All the chemicals and solvents used were synthetic grade, pur-
chased from the commercial source and used without further
purification.
Synthesis of ligands
Schiff bases (HL/L1) were prepared by standard literature proce-
dure [23,24] and recrystallized from ethanol or methanol.
2.2.1 Synthesis of 2-(E)-(2-(2-aminoethylamino) methyl)-4-
bromophenol (HL)
The
2-(E)-(2-(2-aminoethylamino)methyl)-4-bromophenol
Oꢁ2 þ CuII ꢁ SOD ! O2 þ CuI ꢁ SOD
ð1Þ
Schiff base was synthesized by the condensation of an equimolar
ratio of 5-bromo-2-hydroxybezaldehyde (20.0 mmol, 4.02 g) and
N-(2-aminoethyl) ethane-1, 2-diamine, (20.0 mmol, 2.16 mL) dis-
solved in ethanol (Scheme 1). The resulting reaction mixture
was refluxed on a water bath for 4 h and then allowed to cool
overnight. The colored crystalline solid of the obtained Schiff base
was filtered, washed with cold ethanol several times and dried in
air at room temperature and finally preserved under reduced
pressure in a desiccator. Yield: 80%. Anal. Found (%): C, 46.12;
H, 5.59; N, 14.67. Calcd for C11H16BrN3O (%): C, 46.15; H, 5.58;
N, 14.69.
Oꢁ2 þ CuI ꢁ SOD þ 2Hþ ! H2O2 þ CuII ꢁ SOD
ð2Þ
Copper complexes (II) complexes have a wider range of coordina-
tion geometries than any other transition metal ions [17]. Copper
complexes have shown anti-inflammatory, antitumor, anticonvul-
sant, anti- diabetic, anticancer, anti- carcinogenic, anti- mutagenic,
radio protectant, antibacterial and antifungal activities in animal
models of diseased states [18–22]. In a previous paper [23], we have
reported 5-bromo-2-hydroxybezaldehyde Schiff base copper (II)
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M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
3
Scheme 1. Synthesis of HL Schiff base ligand.
Scheme 2. Synthesis of L1 Schiff base ligand.
2.2.2 Synthesis of (19E, 27E)-N1, N2-bis (phenyl (pyridine-2-yl)-
methylene)-ethane-1, 2-diamine (L1)
anhydrous CaCl2 in a desiccator. They were further dried in an elec-
tric oven at 50–60 °C. Yield: 65–70%. Anal Found (%): C, 28.31; H,
3.65; N, 9.01. Calcd (%) for C11H17BrClCuN3O6 (1): C, 28.33; H,
3.67; N, 9.00. FAB- mass (m/z): Obs. (Calcd) 367.28(369). Anal
Found (%): C, 56.31; H, 3.97; N, 10.11. Calcd for C26H22ClCuN4O4
(2): C, 56.33; H, 3.99; N, 10.13. FAB-mass (m/z):Obs. (Calcd)
455.12 (456). Anal. Found (%): C, 68.79; H, 4.85; N, 12.35. Calcd
for C26H22CuN4 (3): C, 68.81; H, 4.87; N, 12.37. FAB-mass (m/z):
Obs. (Calcd) 455.12 (456).
The (19E, 27E)-N1,N2-bis(phenyl(pyridine-2-yl)-methylene)-
ethane-1, 2-diamine Schiff base was synthesized by the condensa-
tion of the 2:1 M ratio of 2- benzoyl pyridine (20.0 mmol, 3.66 g)
with ethane-1, 2-diamine (10 mmol, 0.66 g) dissolved in ethanol
(Scheme 2). The resulting reaction mixture was refluxed on a water
bath for 6 h and then allowed to cool overnight. The colored solid
precipitate of the obtained Schiff base was filtered, washed with
cold ethanol several times and dried in air at room temperature
and finally preserved under reduced pressure in a desiccator. Yield:
75%. Anal. Found (%): C, 79.91; H, 5.63; N, 14.34. Calcd for C26H22N4
(%): C, 79.96; H, 5.66; N, 14.37.
Physical measurements
Elemental analyses were performed on an Elementar Vario EL III
Carlo Erba 1108 analyzer. FAB mass spectra were recorded on a JEOL
SX 102/DA 6000 Mass Spectrometer using argon/xenon (6 kV,
10 mA) as the FAB gas. The accelerating voltage was 10 kV and the
spectra were recorded at room temperature (RT). Magnetic suscep-
tibility measurements were performed on a Gouy balance at RT
using Hg [Co (SCN) 4 as the calibrating agent (xg = 16.44 ꢃ 10ꢁ6 c.g.s.
units). Diamagnetic corrections were appliedin compliancewith the
Pascal constant. The molar conductance measurements were
realized using 10ꢁ3 M solution of the complexes in DMSO on an
Elico-CM 82 conductivity bridge at room temperature. The solid state
electrical conductivity was measured by impedance spectroscopic
method using a HIOKI3532-50LCR Hit ester at a fixed frequency of
1 kHz in the temperature range of 298–400 K. The electronic spectra
Synthesis of complexes
2.3.1 Synthesis of [Cu (L) (H2O)] ClO4 (1), [Cu (L1) (ClO4)]+ (2) and [Cu
(L1)]2+ (3)
Complexes 1–3 was prepared by mixing 50 mL of a 10 mM eth-
anolic solution of Cu (ClO4)2ꢂ6H2O (1.0 mmol, 0.370 g) with 50 mL
of a 10 mM ethanolic solution of the Schiff bases (HL/L1, 0.286
g/0.390 g) in a 1:1(metal–ligand) ratio (Scheme 3). The resulting
mixture was refluxed on a water bath for 5–8 h. A colored product
appeared on standing and cooling the solution. The precipitated
complexes were filtered, washed with ether and recrystallize sev-
eral times from ethanol and dried under reduced pressure over
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M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
Scheme 3. Synthesis of Cu (II) complexes [Cu (L) (H2O)] ClO4 (1), [Cu (L1) (ClO4)]+ (2) and [Cu (L1)]2+ (3).
(in DMSO) were recorded on a Shimadzu UV–Vis spectrophotome-
ter. FT-IR spectra were recorded in KBr disks on a Perkin–Elmer
inhibition of alkaline DMSO mediated reduction of nitrobluetet-
razolium chloride (NBT).
783 spectrophotometer in wave number range 4000–400 cmꢁ1
.
X-band EPR spectra were recorded at room temperature on a Varian
E-line Century Series Spectrometer operating in the X-band region
with 100 kHz modulation frequency, 5 mW microwave power and
1G modulation amplitude was using tetracyano–ethylene (TCNE)
as the internal standard. Cyclic voltammetry was performed with
a BAS-100 Epsilon electrochemical analyzer using a three- electrode
electrochemical cell. Ag/AgCl was used as a reference electrode,
glassy carbon as the working electrode and a platinum wire as the
auxiliary electrode. 0.1 M NaClO4 was used as the supporting elec-
trolyte and DMSO as the solvent. All measurements were performed
at room temperature under a nitrogen atmosphere. The solution was
deoxygenated by purging nitrogen gas.
Antimicrobial activity
The in vitro biological activity of the investigated Schiff bases
(HL/L1) and their metal complexes were tested against the bacteria
Escherichia coli and Salmonella typhi by the disk diffusion method
[27,28] using nutrient agar as the medium and streptomycin as
the control. The antifungal activities of the copper complexes were
also tested by the well diffusion method [29,30] against the fungi
Aspergillus and Penicillium sp., on potato dextrose agar as the
medium and miconazole as the control. Each of the complexes
was dissolved in DMSO and the solutions of the concentrations
i.e. 5–25 mM were prepared separately. In a typical procedure, a well
was made on the agar medium inoculated with micro-organism. The
well was filled with the test solution using a micropipette and the
plate was inoculated 24 h at 37 °C for the bacteria or 72 h at 30 °C
for the fungi. After incubation, the diameter of the clear zone of
inhibition surrounding the sample was taken as a measure of the
inhibitory power of the sample against the particular test organism.
Superoxide dismutase activity
The in vitro SOD activity was measured using alkaline DMSO as
a source of superoxide radical (Oꢁ2 ) and nitrobluetetrazolium chlo-
ride (NBT) as Oꢁ2 scavenger [25,26]. In general, 400
l
l sample to be
assayed was added to a solution containing 2.1 ml of 0.2 M potas-
sium phosphate buffer and 1 ml of 56 M of alkaline DMSO solu-
Single crystal X-ray structure determination
l
tion was added while string. The absorbance was then monitored
at 540 nm against a sample prepared under similar condition
except NaOH was absent in DMSO. A unit of superoxide dismutase
(SOD) activity is concentration of complex, which causes 50%
Single crystal-ray data of complexes (1) and (2) were collected
on a CCD detector based diffractometer (SMART, APEX) from
Bruker-Nonius CAD-4/MACH3, AXs and CrysAlis Pro, Oxford dif-
fractometer using graphite monochromatized Mo K
a radiation
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M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
5
(k ¼ 0:71073 Å). The crystal orientation, cell refinement and inten-
sity measurements were made using the program CAD – 4PC per-
forming – scan measurements. The diffraction data was solved
w
using SIR-92 with GUI control and structure was refined by SHEL-
XL-97 refinement of F2 against all reflections. Non-hydrogen atoms
were refined anisotropically. All the hydrogen atoms were geomet-
rically fixed and allowed to refine using isotropic thermal parame-
ters. Molecular graphics were generated using different software
such as ORTEP-3v2 for WINDOWS, PLATON and Mercury [31–34].
Results and discussion
Syntheses and characterization
In the present paper, the coordination behavior of Schiff bases
(Scheme 1 and 2) derived from the condensation of 5-bromo-2-
hydroxybezaldehyde with N-(2-aminoethyl) ethane-1, 2-diamine
and 2- benzoyl pyridine with ethane- 1, 2-diamine towards Cu
(II) ion is described, which may help in more understanding of
the mode of chelation of ligands towards copper (II) complexes.
The possibly synthetic procedure for complexes (1)–(3) was given
in Scheme 3. All the copper complexes are colored, green for (1),
red for (2) and (3), solid and stable towards air and moisture at
RT. The synthesized 2-(E)-(2-(2-aminoethylamino)methyl)-4-bro-
mophenol (HL) Schiff base ligand (Fig. 1) bound with the Cu (II)
ion in a tetradentate manner, with ON3 donor sites of the pheno-
lic-O, azomethine-N, and two amino-N atoms, whereas the (19E,
27E)-N1,N2-bis(phenyl(pyridine-2-yl)-methyle ne)-ethane-1, 2-dia-
mine (L1) Schiff base ligand (Fig. 2) also coordinated to the metal
ion in a tetradentate manner, with N4 donor sites of the two pyri-
dine-N and two azomethine-N. Such metal complexes may be ste-
reo selective and stereo active in nature and thus applicable in
various catalytic reactions. There were characterized by microanal-
ysis, FAB + spectrometry and then by X-ray single crystal crystal-
lography. The molar conductivity are values in DMSO solution
Fig. 2. Proposed structure of (19E, 27E)-N1, N2-bis (phenyl (pyridine-2-yl)-methy-
lene)-ethane-1, 2-diamine (L1) ligand.
grown from slow evaporation of the reaction mixture at RT and
shown in Figs. 3 and 4. Crystallographic data and crystal refine-
ment parameters are shown in Table 1. Selected bond angles and
bond distances are given in Table 2. The structure of two com-
plexes (1) and (2) are quite similar with square pyramidal (4 + 1)
geometry. Both complexes crystallize in the monoclinic system
of the space group P21/c
c = 8.6517(5)Å, = 90°, b = 108.213(2)°,
a = 9.5019(3)Å, b = 11.3 801(3)Å, c = 25.3168(14)Å,
b = 100.583(4)°, = 90°, and Z = 4 for (2). The molecular structure
,
a = 10.5948(6)Å, b = 19.6164(11)Å,
= 90° and Z = 4 for (1),
= 90°,
a
c
a
c
of (1) and (2) shows that the tetra dentate Schiff base ligands
(HL/L1) occupies the basal plane of pseudo square pyramidal geom-
etry with the H2O of (1) or the ClO4 of (2) occupying the remaining
apical position. The copper atom in the complex (1) is coordinated
by the three N and one O donor atoms of HL ligand and the O (5)
atom of the water molecule located in the apical position of a dis-
torted square pyramid [38]. In the case of complex (2), the copper
atom is coordinated by four N atoms of L1 ligand and to O (1) of the
axially coordinated perchlorate anion to form a distorted square
pyramidal geometry [39]. The ligand in complex (1) is deproto-
nated to behave as an ON3 tetradentate ligand, coordinate via its
phenolic-O, azomethine-N, and two amino-N atoms, thus forming
two five membered [Cu(1)–N(9)–C(10)–C(11)–N(12), Cu(1)–
N(12)–C(13)–C(14)–N(15)] and a six membered chelate rings
[Cu(1)–O(1)–C(2)–C(7)–C(8)–N(9)]. In complex (2), the ligand L1
are very low i. e. 16
X X
ꢁ1 cmꢁ1 molꢁ1 for (1), 18 ꢁ1 cmꢁ1 molꢁ1
for (2) and 12
X
ꢁ1 cmꢁ1 molꢁ1 for (3), indicating the non-electro-
lyte nature [35] of the complexes. All the present complexes are
paramagnetic nature in the solid state at RT as expected from d9
electronic configuration of Cu (II) ion. The observed magnetic
moment values (leff) of these complexes are 1.74 B. M. for (1),
1.76 B.M. for (2) and 1.80 B.M. for (3). These values are quite close
to the values expected for copper (II) complexes [36,37], and is in
fair agreement with the spin only magnetic moment of 1.732
B.M. for an S = ½ system.
is also coordinated in
a tetradentate mode, via its two
azomethine-N and two pyridine-N atoms, thus forming three five
membered chelate rings [Cu(1)–N(4)–C(22)–C(15)–N(3), Cu(1)–
N(3)–C(14)–C(13)–N(2),Cu(1)–N(2)–C(6)–C(5)–N(1)]. In this five
coordinated CuN4O/CuN3O2 chromophore structure [40,41]],
Jahn–Teller effects and non-equivalent nature of the donor atoms
are responsible for considerable variations in bond lengths. So,
Single crystal X-ray structure
Molecular structures of [Cu (L) (H2O)] ClO4 (1) and [Cu (L1)
(ClO4)]+ (2) were confirmed by single crystal X-ray analysis were
Fig. 1. Proposed structure of 2-(E)-(2-(2-aminoethylamino) methyl)-4-bromophenol (HL) ligand.
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6
M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 3. Molecular structure of the complex [Cu (L) (H2O)] ClO4 (1).
Fig. 4. Molecular structure of the complex [Cu (L1) (ClO4)]+ (2).
the ON3/N4 donor Schiff bases occupy the plane is adequate with
bond length of Cu(1)–O(1) = 1.928(3), Cu(1)–N(9) = 1.946(3),
axial Cu–O(1) bond length 2.404 (3) for (1) and Cu–O(1) bond
length 2.334 (19) for (2) is consistent with the trend observed in
other distorted square pyramidal Cu (II) complexes [45]. It is
obvious from the trans N–Cu–N and O–Cu–O bond angles that
the structure is distorted from an ideal square pyramidal. The
largest distortions from the square pyramidal geometry are indi-
cated by O(1)–Cu(1)–N(12) = 173.19(12) and N(9)–Cu(1)–N(15) =
165.30(13) for (1) whereas N(2)–Cu(1)–N(4) = 163.64(8) and
Cu(1)–N(12) = 2.020
(3),
Cu(1)–N(15) = 2.021(3),
Cu(1)–
C(10) = 2.404(3) for (1) and Cu(1)–N(2) = 1.935(2), Cu(1)–
N(3) = 1.939(2), Cu(1)–N(4) = 1.994 (2), Cu(1)–N(1) = 2.011(2),
Cu(1)–O(1) = 2.334(19) for (2), which are close [42] to ꢄ1.9 Å.
The equatorial Cu–O and Cu–N bond lengths are comparable with
square pyramidal CuN3O2/CuN4O coordination sphere [43,44]. The
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M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
7
Table 1
Copper complexes (1) and (2) are five coordinated with a dis-
torted square pyramidal geometry as indicated by structural
Crystal data and structure refinement of complexes [Cu (L) (H2O)] ClO4 (1) and [Cu
(L1) (ClO4)]+ (2).
indexing parameter,
of pentacoordinated geometry. The trigonally index
using the equation = (b– )/60, where and b are the largest coor-
dination angles (for perfect square pyramidal and trigonal bipyra-
midal geometries the value of are zero and unity, respectively).
The value of value is 0.131 for (1) and 0.133 for (2) respectively,
which is indicates distortion in square pyramidal geometry [49].
Comparison of values shows that complex (2) is more distorted
s
which measures the degree of trigonality
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C11H17BrClCuN3O6
466.18
293(2)
1.54178
Monoclinic
P21/c
1
C26H22ClCuN4O4
554.02
120(2)
0.71073
Monoclinic
P21/c
2
s
is calculated
s
a
a
s
s
10.5948(6)
19.6164(11)
8.6517(5)
90
108.213(2)
90°
1708.02(17)
4
1.813
9.5019(3)
11.3801(3)
25.3168(14)
90
100.583(4)
90
2691.00(19)
4
1.612
s
b (Å)
than complex (1). Complexes (1) and (2) show significant hydrogen
bonding interaction. A unit cell packing diagram of complexes (1)
and (2) was shown in Figs. 5 and 6. In complexes (1) and (2),
significant hydrogen bonding occurs, built from N–Hꢂ ꢂ ꢂO and
O–Hꢂ ꢂ ꢂO (intermolecular hydrogen bonding). The relevant hydrogen
bonding distances of copper complexes was given in Table 3. The
uncoordinated perchlorate and water molecule play a significant
role in hydrogen bonding, acting as bridges connecting neighbor-
ing copper (II) dimeric units. Similarly, some more weak hydrogen
bonding (intermolecular) is seen.
c(Å)
a
(0)
b (0)
(0)
c
Volume (Å3)
Z
Dcacl. (Mg/m3)
Absorption coefficient
6.289
1.068
(mmꢁ1
F(000)
)
932
1332
Crystal size (mm3)
h range for data
collection (°)
0.35 ꢃ 0.22 ꢃ 0.15
0.33 ꢃ 0.27 ꢃ 0.22
4.94–65.77
3.04–25.00
Limiting Index
ꢁ12<= h <=12,
ꢁ22<= k <=23,
ꢁ7<= l <=10
22618
2881 [R(int) = 0.0489]
65.77–97.1%
ꢁ11<= h <=11,
ꢁ13<= k <=12,
ꢁ30<= l <=29
IR spectral investigations
Reflections collected
Independent reflections
Completeness to h
18386
The IR spectrum of the complexes were compared with those of
the free ligands in order to determine the involvement of the coor-
dination sites in the chelation. Analysis by FT-IR results in the
absorption spectra in the infrared region and register bands or sig-
nals. IR spectrum of the HL ligand exhibited the most characteristic
4681 [R(int) = 0.0308]
25.00–98.6%
Absorption correction
Semi-empirical from
equivalents
0.3889 and 0.1865
Semi-empirical from
equivalents
0.798 and 0.7194
Max. and min.
transmission
Refinement method
bands at 1628 cmꢁ1
m
(>C = N–, azomethine group), 1270 cmꢁ1
Full-matrix least-
squares on F2
2881/0/208
Full-matrix least-
squares on F2
4681/0/407
m
(>C–O, phenolic moiety) and two amine-N at 3460 cmꢁ1 and
Data/restraints/
parameters
3465 cmꢁ1. The formation of the Schiff base, 2-(E)-(2-(2-aminoeth-
ylamino) methyl)-4-bromophenol was noted from the absence of
C = O peaks in the ligand. The ligand spectrum showed bands at
3150 and 1360 cmꢁ1 due to the stretching and deformation of phe-
nolic OH. These were absent in the spectra of the complex 1. The
(>C = N) band of the ligand at 1628 cmꢁ1 is found to be slightly
shifted to lower energy (1629 cmꢁ1 for 1) in the spectra of complex
(1), indicating the coordination via the azomethine nitrogen(C = N)
to the Cu (II) ion. The phenolic C–O stretching vibration that
appeared at 1270 cmꢁ1 in Schiff base shifted towards higher fre-
quency (25 cmꢁ1) in the complex (1). This suggests deprotonation
of the phenolic OH group after its chelation with the metal ion. The
proposed structure of HL Schiff base ligand is presented in Fig. 1.
Goodness-of-fit on F2
Final R indices
1.107
0.995
R1 = 0.0423,
wR2 = 0.1128
R1 = 0.0445,
wR2 = 0.1152
0.711 and ꢁ0.572
R1 = 0.0326,
wR2 = 0.0817
R1 = 0.0526,
wR2 = 0.0867
0.272 and ꢁ0.263
[I > 2r (I)]
R indices (all data)
Largest diff. peak and
hole (e.Åꢁ3
)
N(3)–Cu(1)–N(1) = 155.65(9) for (2). Such observations has been
made by other workers [46–48] for copper (II) complexes having
distorted square pyramidal geometry.
Table 2
Selected bond lengths (Å) and angles (°) for complexes [Cu (L)(H2O)] ClO4 (1) and [Cu (L1) (ClO4)]+ (2).
[Cu (L) (H2O)]ClO4 (1)
Bond lengths
Cu(1)–O(1)
Cu(1)–N(12)
1.928(3)
2.020(3)
Cu(1)–N(9)
Cu(1)–N(15)
1.946(3)
2.021(3)
Bond angles
O(1)–Cu(1)–N(9)
N(9)–Cu(1)–N(12)
N(9)–Cu(1)–N(15)
O(1)–Cu(1)–O(10)
N(12)–Cu(1)–O(10)
[Cu (L1) (ClO4)]+ (2)
93.37(11)
84.39(13)
165.30(13)
94.95(10)
91.73(11)
O(1)–Cu(1)–N(12)
O(1)–Cu(1)–N(15)
N(12)–Cu(1)–N(15)
N(9)–Cu(1)–O(10)
N(15)–Cu(1)-O(10)
173.19(12)
96.29(11)
84.74(12)
98.01(11)
92.17(12)
Bond lengths
Cu(1)–N(2)
Cu(1)–N(4)
Cu(1)–O(1)
1.935(2)
1.994 (2)
2.3348(19)
Cu(1)–N(3)
Cu(1)–N(1)
Cl(1)–O(2)
1.939(2)
2.011(2)
1.409(2)
Bond angles
N(2)–Cu(1)–N(3)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)-N(1)
N(2)–Cu(1)–O(1)
82.39(8)
81.42(8)
155.65 (9)
102.85(8)
N(2)–Cu(1)–N(4)
N(2)–Cu(1)–N(1)
N(4)–Cu(1)–N(1)
N(3) –Cu(1)-O(1)
163.64 (8)
81.30(8)
113.22(9)
107.62 (9)
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8
M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
The IR spectrum of the L1 ligand exhibited the most character-
istic bands at 1625 cmꢁ1 (>C = N, two azomethine), 1497 cmꢁ1
(>C = N, two pyridine). The formation of the Schiff base, (19E,
m
m
27E)-N1,N2-bis (phenyl (pyridine-2-yl)-methylene)-ethane-1, 2-
diamine was noted from the absence of C = O and NH2 peaks in
the ligand. The (>C = N) band of the ligand at 1625 cmꢁ1 is found
to be slightly shifted to lower energies (1626 cmꢁ1 for
2,1628 cmꢁ1 for 3) in the spectra of complexes (2) and (3), indicat-
ing the coordination via the azomethine nitrogen(C = N) to the
metal ions. This can be explained by the donation of electrons from
nitrogen to the empty d- orbital of the metal atom. Complexes (1)
and (2) showed a broad feature split into three bands at the range
1080, 1110 and 1150 cmꢁ1, is assigned to ionic perchlorate. A med-
ium intensity band at 788 cmꢁ1 (OH rocking) in the spectrum of
complex (1) suggests the presence of coordinated water molecule
in this complex. This band was not observed in the other com-
plexes, indicating the absence of coordinated water molecule in
complexes (2) and (3). In the low frequency region, the band of
weak intensity observed in the spectra of the complexes in the
region 518–525 cmꢁ1 is attributed to Cu–O and in the region
486–491 cmꢁ1 to Cu–N [50–53]. The proposed structure of L1 Schiff
base ligand is presented in Fig. 2. The IR data of ligands and their
copper (II) complexes showed that the Schiff bases (HL/L1) were
coordinated to the metal ion in a tetradetate manner (ON3/N4).
Fig. 5. Perspective view of cell packing in the complex [Cu (L) (H2O)] ClO4 (1).
Electrical conductivity
The temperature dependence of the solid state conductivity (r)
of the copper complexes in their compressed pellet form was mea-
sured at a fixed frequency of 1 kHz in the temperature range 297–
400 K. The value of the solid state electrical conductivity of the
Schiff base and their complexes increased with increasing temper-
ature and deceases upon cooling over the studied temperature
range, indicating their semi-conducting behavior. The general
behavior of electrical conductivity follows the Arrhenius equation:
r
¼ r0expðꢁEa=kTÞ
where Ea is the thermal activation energy of conduction, r0 is the
conductivity constant and k is the Boltzman constant. The plots of
r
vs. 1000/T for all the complexes were found to be linear over
the studied temperature range. The room temperature electrical
conductivity of all the complexes lies in the range 1.231 ꢃ 10ꢁ6
–
2.526 ꢃ 10ꢁ12
X
ꢁ1 cmꢁ1 molꢁ1. These values showed their semi-
conducting nature. The increasing order of the electrical conductivity
at room temperature for the complexes of HL/L1 was (1) > (2) > (3).
The activation energy [54,55] of the copper complexes lies in the
range 0.220–0.677 eV.
Fig. 6. Perspective view of cell packing in the complex [Cu (L1)(ClO4)]+ (2) along a-
axis.
Electron paramagnetic resonance
The EPR spectra of Cu (II) provide information about the extent
of the delocalization of the unpaired electron. The X-band EPR
spectra of the copper (II) complexes were recorded in the polycrys-
talline state at 298 K and in solution at 77 K, using 100 kHz field
modulation and g-factor were quoted relative to the standard
marker TCNE (g = 2.00277). The EPR parameter of the copper com-
plexes are presented in Table 4. Some representative EPR spectra
of complex (1) shown in Fig. 7. The EPR spectrum of complexes
(1)–(3) in polycrystalline state at 298 K displayed three signals
(g values) viz., g1, g2, g3 which, are in complete agreement with
rhombic distortion of the coordination sphere around the Cu (II)
ion. In the spectra with g3 > g2 > g1, rhombic spectral values
R = (g2–g1/g3–g2) may be significant [56]. If R > 1, a predominant
Table 3
Hydrogen bonding interactions for [Cu (L) (H2O)] ClO4 (1) and [Cu (L1) (ClO4)]+ (2) [Å
and (°)].
D–Hꢂ ꢂ ꢂA
d(D–H)
d(Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)
<(D–Hꢂ ꢂ ꢂA)
[Cu (L) (H2O)]ClO4 (1)
O(10)–H(10A)ꢂ ꢂ ꢂO(12)
O(10)–H(10B)ꢂ ꢂ ꢂO(1)#1
N(12)–H(12)ꢂ ꢂ ꢂO(14)
N(15)–H(15B)ꢂ ꢂ ꢂO(13)#2
[Cu(L1)(ClO4)]+ (2)
0.85
0.84
1.00
0.90
2.49
1.90
2.11
2.24
2.940(5)
2.741(3)
2.999(6)
3.117(6)
113.8
170.3
146.5
166.1
1Cl(1)–H(1)ꢂ ꢂ ꢂO(7)b
0.93
0.93
0.93
0.93
2.48
2.45
2.47
2.56
3.240(10)
3.359 (9)
3.380(8)
3.271 (4)
139
164
165
133
1Cl(1)–H(11)ꢂ ꢂ ꢂO(7)C
Intra1Cl(7)–H(17)ꢂ ꢂ ꢂO(6)a
1C(23)–H(23)ꢂ ꢂ ꢂO(4)d
2
2
2
dz ground state is present. If R < 1, a predominant dx
ground
–y
Symmetry transformations used to generate equivalent atoms: #1 ꢁx + 1, ꢁy,ꢁz
#2x, y, zꢁ1 for 1, a = x, y, z; b = ꢁx, ꢁy, ꢁz; c = ꢁx, 1ꢁy, ꢁz; d = ꢁ1 + x, y, z for 2.
state is present and when R = 1, the ground state is approximately
2
2
an equal mixture of dz and dx 2. The rhombic spectra values R
–y
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M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
9
parameters
the covalency of the in-plane
plane bonds respectively. The in-plane
a
2, b2 and c2 which may be regarded as measures of
-bond and the in-plane and out-of-
-bonding parameter a2
Table 4
EPR spectral parameters of the copper (II) complexes 1–3.
r
p
r
Parameters
[Cu (L) (H2O)] ClO4 (1)
[Cu (L1) (ClO4)]+ (2)
[Cu (L1)]2+ (3)
was calculated using the expression of Kivelson and Neiman [58]:
Polycrystalline state (298 K)
g||
G\
giso or gav
DMSO (77 K)
g||
a
2 = (A||/0.036) + (g||ꢁ2.0023) + 3/7 (g\ꢁ2.0023) + 0.04.
2.215
2.087
2.151
2.1696
2.0862
2.127
2.110
2.048
2.079
The orbital reduction factors, K|| = a2 b2 and K\
=
a2 c2 were cal-
culated using the following expression.
K2 ¼ ðg ꢁ 2:0023ÞEdꢁd=8k0
2.285
2.058
160
2.2065
2.0404
155
2.233
2.069
145
jj
jj
g\
A||(G)
G
K2? ¼ ðg? ꢁ 2:0023ÞEdꢁd=2k0
2.51
3.80
2.98
a2
0.790
0.939
0.834
0.776
0.689
142
0.661
0.997
0.862
0.658
0.569
152
0.676
1.044
1.123
0.758
0.705
165
where K|| = a2b2, K\
=
a2c2 and k0 represents the one electron spin–
b2
c2
orbit coupling constant for the free ion, equal to ꢁ828 cmꢁ1. Signifi-
k||
cant information about the nature of
p-bonding in the copper (II)
k\
complexes can be derived from the magnitude of KII and K\. In case
of a pure
-bonding KII ꢅ K\ Ca. 0.77 whereas KII < K\ implies consid-
erable in-plane -bonding while for -out -of plane -bonding KII > K\.
Furthermore,
2, b2 and 2 have value much less than 1 (the value for
f (cmꢁ1
)
r
p
p
a
c
100% ionic bonding, this value decreasing with increasing of the cova-
lent character of the bonding). The orbital reduction factor for copper
complexes (0.776 > 0.689 for 1, 0.658 > 0.569 for 2, 0.758 > 0.705 for
3) showed a relation K|| > K\ which indicates the presence of an out -
of - plane
p
bonding. The empirical factor f = (gII/AII), AII in cmꢁ1 is an
index of tetragonal distortion and its value was found to be in the
range 142, 152, 165 cmꢁ1, respectively, indicating significant distor-
tion from planarity [59].
Electronic absorption spectra
The visible spectra of the complexes were recorded in 100%
DMSO solution at 25 °C. The Cu (II) complexes of HL/L1 (1 and 2
respectively) showed similar electronic spectra consisting of a
broad d–d band at 650 nm for (1) and 680 nm for (2). The complex
has a charge transfer band at 380 for (1) and 370 nm for (2). Pres-
ence of dꢁd band at 700 nm is expected for distorted square pyra-
midal [60–62]. The electronic spectrum of the complex 3 of L1
showed two bands at 15110 and 19456 cmꢁ1, assignable to
2B1g ? 2B2g, and 2B1g ? 2Eg transitions, respectively. The value of
magnetic moment for this complex was 1.80 B.M.; thus, square
planar geometry [63] is suggested for the complex (3).
Fig. 7. EPR spectrum (L.N.T.) in 100% DMSO of the complexes [Cu(L)(H2O)]ClO4(1).
Electrochemical studies
The electrochemical properties of the three complexes of HL/L1
were studied by cyclic voltammetry (CV) under a nitrogen atmo-
sphere in DMSO solution in the potential range ꢁ1.0 to 1.2 V vs.
an Ag/AgCl reference electrode. The Cu (II) complex of HL showed
a reduction peak at Epc = ꢁ619 mV with a corresponding oxidation
peak at Epa = ꢁ426 mV at a scan rate 100 mV sꢁ1. The peak separa-
calculated for the complexes (1)–(3) are found to be less than 1
indicating the presence of dxꢁy ground state.
2
2
EPR spectra of the complexes revealed two g-values (g|| and g\).
Since the g|| and g\ values were closer to 2 and g|| > g\, a tetragonal
distortion around the Cu (II) ion is suggested. The trend g|| > g\ > ge
2
2
(2.0023) shows that the unpaired electron is localized in the dxꢁy
orbital in the ground state of Cu (II) and spectra were characteristic
tion
DEp was 193 mV for this couple. Thus, the cyclic voltammetric
studies gave evidence to a quasi-reversible CuII/CuI couple. The
cyclic voltammogram of the copper complex (2) of L1 exhibited a
one electron quasi-reversible transfer process with a reduction
peak at Epc = ꢁ725 mV with an associated oxidation peak at
Epa = ꢁ442 mV at a scan rate 100 mV sꢁ1 which increased with
of axial symmetry. The value of g|| > 2.3 is characteristic of an ionic
environment and g|| < 2.3 indicates
a covalent environment in
metal–ligand bonding. The g|| values for the complexes were less
than 2.3, suggesting the environment was covalent.
The exchange coupling interaction between two Cu (II) ions is
explained by the Hathaway Expression [57]:
scan rate. The peak separation of this couple (DEp) was 283 mV.
The most significant feature of the Cu (II) complexes was the CuII/
CuI couple. This redox process was consistent with a quasi-revers-
ible process [64,65]. Similar observation found for complex (3). The
difference in CuII/CuI redox potential among these complexes
(1)–(3) demonstrates that the coordination environments around
the Cu (II) ions are different and afford a substantial explanation
for the difference in SOD activity of them. It is known that an
adequate CuII/CuI redox potential for effective catalysis of superox-
ide radical must be required between ꢁ0.405 V vs. SCE for
G ¼ ðgjj ꢁ 2:0023Þ=ðg? ꢁ 2:0023Þ
According to Hathaway, if the value G is greater than 4 (G > 4.0), the
exchange interaction is negligible; whereas when the value of G is
less than 4 (G < 4.0), a considerable exchange coupling is present
in a solid complex. The G values for the complexes were less than
four (2.51 for 1, 3.80 for 2, 2.98 for 3) indicating considerable
exchange interaction in the complexes. The EPR parameters and
d–d transition energies were used to evaluate the bonding
Please cite this article in press as: M. Choudhary et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.018

10
M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
O2/Oꢁ2 + 0.645 V vs. SCE for O2ꢁ/H2O2. Though it is inappropriate to
compare the E° values with the reduction potentials of the three
complexes in DMSO should be in the allowed range of an SOD
mimic, since the obtained results of IC50 show that these have
relatively low activity. These higher values may be due to the
strong ligand field created by the tetradentate Schiff base ligands
(HL/L1) which opposes the interaction of the complexed copper
with the superoxide radical.
Superoxide dismutase activity
SOD mimetic activities of (1)–(3) were measured with an indi-
rect method in which alkaline DMSO served as the source for
superoxide radical. The count fraction causing 50% inhibition of
NBT reduction is called IC50 concentration, equivalent to one unit
of SOD activity (IC50 values), together with the IC50 values of native
SOD are given in Table 5. Some representative SOD activity (IC50
value) of complex (1) was presented in Fig. 8. The chromophore
concentration value required to yield 50% inhibition of the reduc-
tion of NBT (IC50) of the present complexes was found at the range
Fig. 8. Superoxide dismutase activity of [Cu (L) (H2O)] ClO4 (1).
55
3
l
M are higher than the value exhibited by the native
enzyme (IC50 = 0.04
l
mol dmꢁ3) on a molar base (note that the
two selected bacteria E. coli and Salmonella typhi were determined.
These activities were determined at five concentrations i.e. 5–
25 mM of each compound in DMSO and result were compared with
lower concentration of standard antibiotic. Complexes (1) and (2)
have shown excellent antibacterial activity against E. coli compara-
ble to that of Salmonella typhi. The susceptibility of certain strains
of bacteria towards the present copper (II) complexes were
determined by measuring the size of inhibition diameter. Both
the bacteria are pathogens for humans, which causes dysentery
smaller the IC50 value, the higher the SOD activity). The Observed
IC50 values of the present complexes are comparable with the var-
ious reported SOD values for the copper (II) complexes [66,67], but
are less active than the native SOD. The good activities of com-
plexes may be attributed to the flexible HL/L1 ligands which is able
to accommodate the geometrical change from CuII to CuI, which are
proposed to be easily substituted by the substrate Oꢁ2 in the cata-
lytic process, just like the O2ꢁ, in place of H2O bound to copper site
in the mechanism of dismutation of Oꢁ2 by native SOD. Complexes
(1)–(3) showed lower IC50, and exhibits higher SOD activity than
other mononuclear complexes except for two systems including
native SOD so for reported [42,43].
Antimicrobial activities
The in vitro antimicrobial activities of the synthesized Schiff
base ligands and their corresponding metal complexes against
Table 5
Superoxide dismutase activity of some copper (II) complexes.
S.No.
Complexes
IC50
(l
mol dmꢁ3
)
References
1
2
3
4
5
Cu (II)(aspirinate)2(DMSO)2
Cu (II)(aspirinate)2(ImH)2
Cu (II)(aspirinate)2(4-pic)2
Cu (II)(aspirinate)2(salicylate)2
Native SOD
>400
160
100
44
0.04
58
[25]
[25]
[25]
[25]
[25]
[42]
6
[Cu(SAT)(bipy)]
7
[Cu(SAT)(en)]
52
[42]
8
9
[Cu(SAT)(temed)]
[Cu(L)(bipy)]
62
62
[42]
[24]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
[Cu(SAA)(MeImH)]
[Cu(SAA)(EtImH)]
[Cu(SAA)(MebenzImH)]
[Cu(PSBP)(NO3)] (BF4)
[Cu(DAPBMA)2](BF4)2
[Cu(ImH)4(NO3)2]
[Cu(L)(Cl)2]
35
43
52
35
34
25
22
18
132
25
0.79
63
57
61
50
46
48
[43]
[43]
[43]
[8]
[8]
[8]
[67]
[67]
[26]
[26]
[26]
[23]
[23]
[23]
In this study
In this study
In this study
[Cu(L)(Br)2]
[Cu(glygly)].3H2O
[Cu(glygly)(bipy)].3H2O
[Cu(salgly)(phen) (H2O)]
[Cu(L1) (bipy)].2H2O
[Cu(L1) (dmp)].CH3CN
[Cu(L1) (phen)]
[Cu(L)(H2O)]ClO4 (1)
[Cu(L1) ClO4]+ (2)
[Cu(L1)]2+ (3)
Fig. 9. Antibacterial activity of [Cu) (L) (H2O)] ClO4 (1).
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M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
11
Table 6
Antibacterial activity of copper (II) complexes [Cu(L)(H2O)]ClO4 (1) and [Cu(L1)
(ClO4)]+ (2).
Complexes
Diameter of inhibition zone (in mM)
Streptococcus aureus
E. Coli
[Cu(L)(H2O)]ClO4 (1)
5
5
7
10
15
20
25
6
8
16
21
11
12
19
25
[Cu(L1)(ClO4)]+ (2)
5
3
5
10
15
20
25
5
7
13
18
8
10
17
21
Table 7
Antifungal activity of copper (II) complexes [Cu(L)(H2O)]ClO4 (1) and [Cu(L1)(ClO4)]+
(2).
Complexes
% Inhibition of spore germination
Aspergillus sp. (mg mL–1
)
Penicillium sp. (mg mL–1
)
[Cu(L)(H2O)]ClO4 (1)
5
5
8
15
19
22
6
Fig. 10. Antifungal activity of [Cu) (L) (H2O)] ClO4 (1).
10
15
20
25
12
16
20
24
[Cu(L1)(ClO4)]+ (2)
5
10
15
20
25
reduced at a great extent due to the overlap of the ligand orbital
and the partial sharing of the positive charge of the metal ion with
donor groups. Furthermore, it increases the delocalization of the
4
7
10
14
16
5
9
13
17
20
p-electrons over the whole chelating ring and enhances the penetra-
tion of the complexes into lipid membranes and the blocking of the
metal binding sites in the enzyme of micro-organisms. There is
other factor that increases the activity, viz. solubility, lipophilic-
ity/hydrophilicity, conductivity and M-L bond length [72,73].
and typhoid, respectively. They inhibited the bacterial growth up
to 18–25% at 25 mM whereas others have poor antibacterial activ-
ity [68,69]. Both complexes show lower activity than the known
antibiotic with (1) being more active than (2). The antibacterial
activity of complex (1) is graphically presented in Fig. 9 and results
of these antibacterial assessments of complexes are shown in
Table 6. Among fungal species two isolates were taken into consid-
eration and were Aspergillus and Penicillium sp. The zone of inhibi-
tion of these compounds against those fungi was recorded in
Table 7. Similar trends were observed as in the case of bacteria.
Conclusion
[Cu (L) (H2O)] ClO4 (1), [Cu (L1) (ClO4)]+ (2) and [Cu (L1)]2+ (3),
were synthesized and characterized by using different physico-
chemical and spectroscopic techniques. The molecular structures
of (1) and (2) were confirmed by X-ray crystallographic analysis.
The mononuclear complexes (1) and (2) show pentacoordiated
copper (II) ion with distorted square pyramidal coordination
geometry whereas complex (3) have square planar geometry. The
IC50 values of copper complexes are higher than the value exhib-
The area of percent of inhibition of spore germination (mg mL–1
)
is less in the concentration of 5 mM in both fungi and more in
25 mM concentration. It was noted that these complexes are more
effective against Penicillium sp. than Aspergillus sp. Antifungal activ-
ity of complex (1) is graphically presented in Fig 10. It was noted
that Penicillium sp. was highly susceptible against (1). Another
fungi Aspergillus sp. showed least effectiveness against (2); but
comparatively more susceptible towards (1).
On comparing the biological activities of the Schiff base ligands
(HL/L1) and their metal complexes (1) and (2) with those of a stan-
dard bactericide (chloramphenicol) and fungicide (miconazole), it
was shown that the metal complexes had moderate activity as
compared to the standard but both the copper complexes were
more active than their respective ligands. The higher inhibition
zone of the metal complexes than those of the ligands can be
explained based on the Overtone concept [70] and Tweedy’s chela-
tion theory [71]. Upon chelation, the polarity of the metal ions is
ited by the native enzyme (IC50 = 0.04 l
mol dmꢁ3) on a molar base.
Copper (II) complexes display X-band EPR spectra in 100% DMSO at
77 K giving g|| > g\ > 2.0023 indicating dx–y ground state. The solid
2 2
state electrical conductivity data suggested that all the complexes
fall into the semi-conducting rang. The synthesized HL Schiff base
ligand bound with the metal ion in a tetradentate manner, with
ON3 donor sites of the phenolic-O, azomethine-N, and two amino-
N atoms, whereas the L1 ligand also coordinated to the metal ions
in a tetradentate manner, with N4 donor sites of the two azome-
thine-N and two pyridine-N atoms. Copper complexes showed an
irreversible couple corresponding to the Cu (II)/Cu (I) redox process.
The antimicrobial data shows that the copper complexes were more
biologically active compared to the parent Schiff base ligands against
all the tested pathogenic species. Such species may assist in the
search for some novel chemotherapeutic to answer the emerging
problem of drug resistance in health sciences.
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12
M. Choudhary et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
[27] H.B. Gray, J. Ballhausen, J. Am. Chem. Soc. 85 (1963) 260.
Supplementary material
[28] R.K. Jain, A.P. Mishra, J. Serb. Chem. Soc. 77 (2012) 1013.
[29] V.P. Singh, P. Gupta, J. Coord. Chem. 59 (2006) 1483.
[30] V.P. Singh, A. Katiyar, S. Singh, J. Coord. Chem. 62 (2009) 1336.
[31] A. Altomare, G. Cascarno, C. Giacovazzo, A. Gualardi, J. Appl. Cryst. 26 (1993)
343.
CCDC 716024 and 716025, contain the supplementary crystal-
lographic data for complexes 1-2 .These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html/
data request/cif, or from the Cambridge Crystallographic Data Cen-
tre,12 Union Road , Cambridge CB21EZ,UK, Fax: +44 1223 336033,
Email: deposit@ccdc.cam.ac.uk.
[32] G.M. Sheldrick, Acta Cryst. 64 (2008) 112.
[33] C.F. Macrae, P.R. Edington, P. McCabe, E. Pidcock, G.P. Shields, R. Tailor, M.
Towler, J. Van de Streek, J. Appl. Crystallogr. 39 (2006) 453.
[34] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[35] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[36] A. Valent, M. Kotiutova, O. Svajlennova, D. Hudecova, P. Olejni Kova, M. Melnik,
J. Coord. Chem. 57 (2004) 1279.
[37] R.N. Patel, V. P Sondhiya, Dheerendra K. Patel, K.K. Shukla, Dinesh K. Patel, Y.
Singh 52A (2013) 717.
Acknowledgements
Our grateful thanks are due to the National Diffraction Facility,
X-ray Division, and RSIC (SAIF), IIT Mumbai for single crystal data
collection and EPR measurements, respectively. The Head RSIC
(SAIF), Central Drug Research Institute, Lucknow is also thankfully
acknowledged for providing analytical and spectral facilities.
Financial assistance from UGC [RGNF Scheme No.F.16-17/2006
(SA-III)] New Delhi, India is thankfully acknowledged.
[38] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143.
[39] A.D. Naik, P.A.N. Reddy, M. Nethaji, A.R. Chakravarty, Inorg. Chim. Acta 349
(2003) 149.
[40] P.A.N. Reddy, R. Datta, A.R. Chackrvarty, Inorg. Chem. Comm. 3 (2000) 322.
[41] A.M. Thomas, A.D. Naik, M. Nethaji, A.R. Chakravarty, Indian J. Chem. A43
(2004) 691.
[42] R.N. Patel, N. Singh, V.L.N. Gundla, Polyhedron 26 (2007) 757.
[43] R.N. Patel, V.L.N. Gundla, D.K. Patel, Polyhedron 27 (2008) 1054.
[44] R. Pradhan, A.M. Thomas, A. Mukherjee, S. Dhar, M. Nethaji, A.R. Chakravarty,
Indian. J. Chem. A44 (2005) 18.
[45] A. Sreekanth, M.R.P. Kurup, Polyhedron 22 (2003) 3321.
[46] P.A.N. Reddy, M. Nethaji, A.R. Chakravarty, Inorg. Chim. Acta 337 (2003) 450.
[47] M.N. Dhars, A.R. Chakravarty, Inorg. Chim. Acta 358 (2005) 2437.
[48] Fan-Jin. Meng, Heng-Qing Jia, Ning-Hai Hu, Jing-Wei Xu 28 (2013) 41.
[49] A.W. Addison, E. Sinn, Inorg. Chem. 22 (1988) 1225.
[50] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Part, A and B, 5th ed., Wiley, New York, USA, 1998.
[51] A. Garcia-Raso, J.J. Friol, B. Adrover, P. Tauler, A. Pons, I. Mota, E. Espinosa, E.
Molins, Polyhedron 22 (2003) 3255.
[52] K. Sharma, R. Singh, N. Fahmi, R.V. Singh, Spectrochim. Acta A75 (2010) 422.
[53] M. Pragathi, Hussain Reddy, Indian J. Chem. 52A (2013) 845.
[54] M.G. Wahid, H.A. Bayoumi, M.I. Mohamme, Bull. Korean Chem. Soc. 24 (2003)
1313.
[55] J.T. Makode, A.R. Yaul, S.G. Bhadange, A.S. Aswar, Russ. J. Inorg. Chem. 54
(2009) 1372.
[56] V. Philip, V. Suni, M.R.P. Kurup, M. Nethaji, Polyhedron 24 (2005) 1133.
[57] B.J. Hathaway, in: G. Wilkinson (Ed.), Comprehensive Coordination Chemistry,
vol. 5, Pergamon Press, Oxford, 1985. pp. 674.
[58] D. Kivelson, R. Neiman, J. Chem. Soc., Dalton Trans. 35 (1961) 149.
[59] P.F. Rapheal, E. Manoj, M.R.P. Kurup, Polyhedron 26 (2007) 818.
[60] R. Pogni, M.C. Bartoo, A. Diaz, R. Basosi, J. Inorg. Bichem. 79 (2002) 333.
[61] E.K. Efthimiadou, S.H. Thomadaki, C.P. Raptopoulou, N. Katsaros, A. Scorilas, A.
Karaliota, G. Psmass, J. Inorg. Biochem. 64 (2007) 101.
[62] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsever, Amsterdam, 1968.
[63] S. Chandra, A.K. Sharma, Spectrochim. Acta A74 (2009) 271.
[64] S. Praveen, F. Arjmand, Indian J. Chem. A44 (2005) 1151.
[65] R.N. Patel, J. Coord. Chem. 63 (2010) 1207.
References
[1] J. Labuda, L. Fenikova, Z. Durackova, Biochem. Bioenerg. 44 (1997) 31.
[2] E.V. Rybak-Akimova, A.Y. Nazarenko, L. Chen, P.W. Krieger, A.M. Herrera, V.V.
Tarasov, P.D. Robinson, Inorg. Chim. Acta 324 (2001) 1.
[3] A. Nilgun, G.O. Selma, I. Semra, Struct. Chem. 18 (2007) 667.
[4] Z.H. Chohan, A. Munawar, C.T. Supuran, Met.-Based Drugs 8 (2001) 137.
[5] K.M. Khan, M. Khan, M. Ali, M. Taha, S. Rasheed, S. Perveen, M.I. Choudhary,
Bioorg. Med. Chem. 17 (2009) 7795.
[6] M. Joseph, V. Suni, C.R. Nayar, M.R.P. Kurup, H.K. Fun, J. Mol. Struct. 63 (2004)
705.
[7] S. Choubey, S. Roy, K. Bhar, R. Ghosh, P. Mitra, Chia-Her Lin, J. Ribas, B.K. Ghosh,
Polyhedron 55 (2013) 1.
[8] R.N. Patel, K.K. Shukla, Anurag Singh, M. Choudhary, D.K. Patel, J. Niclos-
Guiterrez, J. Coord. Chem. 63 (2010) 3648.
[9] U. Weser, L.M. Schubotz, E. Lengfelder, J. Mol. Catal. 13 (1963) 249.
[10] M.G.B. Drew, M. Mc Cann, S.M. Nelson, J. Chem. Soc., Dalton Trans. 1868
(1981).
[11] C.A. Salta, M.T. Youinou, C.J. Burrows, Inorg. Chem. 30 (1991) 3454.
[12] J.J.R. Frausto da Silva, R.J.P. Williams, The Biological Chemistry of the Elements,
second ed., Oxford University Press, Oxford, 2001 (Chapter1).
[13] J.M. Mc Cord, Biol. Med. 2 (1986) 307.
[14] L.W. Oberley, G.R. Buettner, Cancer Res. 39 (1979) 1141.
[15] I. Fridovich, Annu. Rev. Biochem. 64 (1995) 97.
[16] A.F. Miller, Comments Mol. Cell. Biophys. 9 (1997) 1.
[17] B.J. Hathaway, Struct. Bond. (Berlin) 57 (1984) 55.
[18] J.R. Wasson, Spectrosc. Lett. 9 (1976) 95.
[19] J.R.G. Sorenson, Chem. Ber. 21 (1989) 169.
[20] J.R.G. Sorenson, V. Kishore, A. Pezeshk, L.W. Oberley, S.W.C. Leuthauser, Inorg.
Chim. Acta 91 (1984) 285.
[21] M.N. Patel, C.R. Patel, H.N. Joshi, Inorg. Chem. Comm. 27 (2013) 51.
[22] K. Giannousi, K. Lafazanis, J. Arvanitidis, A. Pantazaki, C. Dendrinon-Samara, J.
Inorg. Biochem. 133 (2014) 24.
[23] M. Choudhary, R.N. Patel, S.P. Rawat, J. Mol. Struct. 1060 (2014) 197.
[24] R.N. Patel, S.P. Rawat, M. Choudhary, V.P. Sondhiya, D.K. Patel, K.K. Shukla, Y.
Singh, R. Pandey, Inorg. Chim. Acta 392 (2012) 283.
[66] R.N. Patel, K.K. Shukla, Anurag Singh, M. Choudhary, D.K. Patel 63 (2010) 586.
[67] R.N. Patel, K.K. Shula, A.Singh.M. Choudhry, U.K. Chauhan, S. Dwivedi, Inorg.
Chim. Acta 362 (2009) 4891.
[68] M.T.H. Tarafder, K.B. Chew, K.A. Crouse, A.M. Ali, B.M. Yasmin, H.K. Fun,
Polyhedron 21 (2002) 2683.
[69] M.A. Ali, A.H. Mirza, R.J. Butcher, M.T.H. Tarafder, Inorg. Chim. Acta 1 (2001)
320.
[70] Y. Anjaneyula, R.P. Rao, Synth. React. Inorg. Met.-Org. Chem. 16 (1986) 257.
[71] B.G. Tweedy, Phytopathology 55 (1964) 910.
[72] V.G. Vidyanathan, B.U. Nair, J. Inorg. Biochem. 93 (2003) 271.
[73] R. Nagar, J. Inorg. Biochem. 40 (1990) 349.
[25] R.G. Bhirud, T.S. Shrivastava, Inorg. Chim. Acta 179 (1991) 125.
[26] R.G. Bhirud, T.S. Shrivastava, Inorg. Chim. Acta 179 (1990) 121.
Please cite this article in press as: M. Choudhary et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.018