Carboxylate-bridged Cu(II) coordination polymeric complex: synthesis, crystal structure, magnetic properties, DNA binding and electrochemical studies

Article abstract of DOI:10.1007/s12039-017-1330-2

Abstract: A novel water-soluble carboxylate-bridged copper(II) coordination polymer, Cu-BIG was formed by the reaction of Cu(ClO4)2·6H2O and tridentate benzimidazole-glycine conjugate ligand, 2-((1H-benzimidazol-2-yl)methylamino) acetic acid, BIGH and its structure has been determined by IR, UV, powder XRD, VSM, CV, TGA, DTA, EPR and single crystal X-ray diffraction. Crystallographic studies indicate it to be a coordination polymer with Pī Space group. The asymmetric unit of complex contains two Cu(II) ions with elongated square pyramid geometry. The axial positions of the Cu(II) atoms are occupied by the carbonyl oxygen of the carboxylate group with the bond distances Cu (1) –O(5)axial,2.28?, and Cu (2) –O(2)axial,2.26?. The two Cu(II) are connected through the carboxylic group present in BIGH, which provides electron mobilisation in the molecule and hence results in the soft ferromagnetic polymer. An in vitro antibacterial activity study of BIGH and Cu-BIG showed moderate activity against Bacillus subtilis. The DNA binding studies showed the interaction of Cu-BIG with CT-DNA. Graphical Abstract: Synopsis: A water soluble ferromagnetic carboxylate-bridged copper(II) coordination polymer, Cu-BIG was formed by the reaction of Cu(ClO4)2·6H2O and tridentate benzimidazole-glycine conjugate ligand, 2-((1H-benzimidazol-2-yl)methylamino) acetic acid. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-017-1330-2

J. Chem. Sci.
© Indian Academy of Sciences
DOI 10.1007/s12039-017-1330-2
REGULAR ARTICLE
Carboxylate-bridged Cu(II) coordination polymeric complex:
synthesis, crystal structure, magnetic properties, DNA binding
and electrochemical studies
SABITHAKALA THATITURIa, BHARGAVI GOVINDUGARIb
and VENKATA RAMANA REDDY CHITTIREDDYa,∗
aDepartment of Chemistry, Jawaharlal Nehru Technological University Hyderabad, Hyderabad,
Telangana 500 085, India
bSchool of Chemistry, University of Hyderabad, Hyderabad, Telangana 500 046, India
E-mail: vrr9@yahoo.com
MS received 12 November 2016; revised 11 May 2017; accepted 18 May 2017
Abstract. A novel water-soluble carboxylate-bridged copper(II) coordination polymer, Cu-BIG was formed by
the reaction of Cu(ClO4)2 ·6H2O and tridentate benzimidazole-glycine conjugate ligand, 2-((1H-benzimidazol-
2-yl)methylamino) acetic acid, BIGH and its structure has been determined by IR, UV, powder XRD, VSM, CV,
TGA, DTA, EPR and single crystal X-ray diffraction. Crystallographic studies indicate it to be a coordination
polymer with P¯ı Space group. The asymmetric unit of complex contains two Cu(II) ions with elongated square
pyramid geometry. Theaxial positions of the Cu(II) atoms areoccupiedbythecarbonyl oxygenof the carboxylate
group with the bond distances Cu(1)–O(5)axial, 2.28 Å, and Cu(2)–O(2)axial, 2.26 Å. The two Cu(II) are
connected through the carboxylic group present in BIGH, which provides electron mobilisation in the molecule
and hence results in the soft ferromagnetic polymer. An in vitro antibacterial activity study of BIGH and Cu-BIG
showed moderate activity against Bacillus subtilis. The DNA binding studies showed the interaction of Cu-BIG
with CT-DNA.
Keywords. Copper(II)polymeric complex; ferromagnetism; electrochemical studies; crystal structure.
1. Introduction
out to synthesize a copper(II) coordination polymer
of benzimidazole-glycine conjugate ligand, 2-((1H-
benzimidazol-2-yl)methylamino) acetic acid, (BIGH),
[{Cu (BIG) (H2O)}2]n (ClO4)2n·3nH2O. TheBIGHcon-
sistsofbenzimidazoleringandcarboxylicacidinitsside
chain, which facilitates the formation of MOCPs.14–18
Owing to its versatile coordination modes, the terminal
carboxylate group acts as a bridge to construct coordina-
tion polymer. The flexible and free carboxylate terminal
in BIGH is conformationally diverse to form a stable
covalent bond with metal ion. The Cu-BIG coordina-
tion polymer is connected through carboxylate group,
[Cu(1)–O–C–O–Cu(2)], which acts as a bridge for elec-
tron mobilization between two copper atoms which in
turn makes a soft ferromagnetic material. The crystal
structure, magnetic properties, antibacterial activity and
DNA binding studies of Cu-BIG have been carried out.
The electron transfer mechanism of copper(II) complex
was investigated by cyclic voltammetry.
The design and synthesis of metal–organic coordina-
tion polymers (MOCPs) is an emerging area in the
field of advanced materials research in recent years.1–4
The study of MOCPs is exciting due to their diverse
structures, properties and compositions. Their easy
customizability in addition to fascinating structural
topologies has further drawn the attention of many
researchers, for their potential application as advanced
functional materials in the fields of catalysis, non-linear
optics, medicine, etc.5–9 Consequently, many efforts
have been devoted to the study of transition metal–
organic coordination polymers. Especially, the MOCPs
based on the N-donor heterocycles have been widely
used as luminescence materials, catalysts, electrical
and magnetic materials.10–13 In view of the interest-
ing applications, the present work has been carried
*
For correspondence
Electronic supplementary material: The online version of this article (doi:10.1007/s12039-017-1330-2) contains supplementary material,
which is available to authorized users.

Sabithakala Thatituri et al.
done as follows. BIGH (0.250 g, 1.12 mmol) was dissolved in
2. Experimental
25 mL water, to which 5 mL aqueous solution of Cu(ClO4)2 ·
6H2O (0.45 g, 1.12 mmol) was added slowly and stirred for
5 min. The resultant dark blue coloured solution was filtered
and kept for crystallization in desiccator over H2SO4. Good
quality blue coloured single crystals obtained were collected
after seven days. Yield: 0.72 g (0.87 mmol, 72%). IR data
(KBr, cm−1): 3435 (bound water), 3249 (N–H), 3228 (Ar-
H), 1615 (C=O), 1285 (C–N).
2.1 Chemicals
All the chemicals such as iminodiacetic acid,
o-phenylenediamine and Copper(II) perchlorate hexahydrate
were used as obtained from Aldrich. All other chemicals and
solvents used for the synthesis were reagent grade.
2.2 Instrumentation
IR spectrum was recorded on a JASCO FT-IR 5300 spec-
trometer. Elemental analysis for C, H and N was done using
a FLASH Ea 1112 SERIES CHNS analyzer. EPR spec-
trum was obtained using BRUKER Xenon EMX-ER073
spectrometer. X-ray powder diffractograms were recorded
on a SMART Bruker D8 advance X-ray diffractometer
using Cu-Kα λ-radiation (λ = 1.5406Å) at 40 kV and 30
mA. Magnetic moments were recorded on Lakeshore VSM
7410. Diffuse reflectance spectra were obtained using a
Shimadzu UV-3100 PC Spectrophotometer. Cyclic voltam-
mograms were recorded using Gamry-600 electrochemi-
cal analyzer and Fluorescence measurements were made
using Perkin Elmer LS45 fluorescence spectrometer. Thermo
gravimetric analysis was made using Exstrar TG DTA
6300.
2.4 X-ray crystal structure determination
X-ray diffraction data were collected for Cu-BIG complex on
a BRUKER-AXS SMART APEX CCD X-ray diffractometer,
α
using graphite-monochromatic Mo K radiation (=0.71073
Å). Data were reduced using SAINTPLUS20 and a multi-scan
absorption correction using SADABS21 was performed. The
structures were solved using SHELXS-9722 and full matrix
least-squares refinements against F2 were carried out using
SHELXL-97.23 Allringhydrogenatoms wereassignedonthe
basis of geometrical considerations and were allowed to ride
upon the respective carbon atoms. All hydrogen atoms were
assigned fixed Uiso values, equal to 1.2Ueq of the parent atom
for ring and 1.5Ueq for methyl hydrogens. Crystallographic
data and structure refinement parameters are presented in
Table 1.
2.3 Synthesis of 2-((1H-benzimidazol-2-yl)methyla
mino)acetic acid (BIGH)
Table 1. Crystal data and structure refinement
details for Cu-BIG.
Iminodiacetic acid (15.98 g, 120.0 mmol) was dissolved in
100 mL of 6N HCl, and o−phenylenediamine (3.25 g, 30.0
mmol) in 20 mL of 4N HCl was added dropwise. The reac-
tion mass was refluxed at 100◦C for about 16 h. To this
solution, o-phenylenediamine (3.25 g, 30.0 mmol) in 20 mL
of 4N HCl was added and the reaction was continued for
72 h. The final green solution was cooled to room tempera-
ture. Green coloured precipitate obtained was filtered (dimer),
and the clear brown coloured filtrate was allowed for solvent
evaporation up to a minimum volume. A white solid formed
was separated and dissolved in 100 mL of water and neu-
tralized with 2N NaOH; above synthesis was done based on
literature procedure.19 Formed precipitate was collected and
leached with cold methanol (80 mL) and dried in the oven.
Formula
C20H30Cl2Cu2N6O17
Formula weight
Crystal system
a(Å)
824.48
Triclinic
7.0044(8)
11.8269(13)
18.495(2)
88.306(2)
85.763(2)
84.972(2)
1521.7(3)
P ¯ı
b(Å)
c(Å)
α(o)
β(o)
γ (o)
V (Å3)
Space group
Z
2
1
Yield: 4.7 g (23 mmol, 42%). M.p. : 205–210◦C; H NMR
T (K)
ρ
298(2)
1.799
1.661
1.10–28.26
–9, 9/ –15, 15/ –24, 24
17733
(400 MHz, DMSO-d6, 25◦C): δ = 7.5 (multiplet, 2H, Ar-
H), 7.15 (multiplet, 2H, Ar-H), 4.1 (singlet, 2H, CH2), 3.3
(singlet, 2H, CH2COO), as shown in Figure S3 (Supplemen-
tary Information). IR data (KBr, cm−1): 3460 (N–H), 1643
(C=O), 1596 (C=C aromatic), 1268 (C–N). Anal. Calcd. (%)
for (BIGH): C, 58.53; H, 5.40; N, 20.48. Found (%): C, 58.42;
H, 5.45; N, 20.36 as shown in Figure S4 (Supplementary
Information).
calcd(g cm−3
)
μ (mm−1
)
θ Range (o)
h/k/l indices
Reflections collected
Unique reflection, Rint 7083, 0.0285
GooF
1.038
0.0509
0.1329
R1[I > 2σ(I)]
wR2 [all data]
ꢀρmax, ꢀρmin(e · Å−3) 1.069, –0.542
2.3a Synthesis of copper(II) complex, Cu-BIG (1):
ꢀ
ꢁ
Synthesis of {Cu (BIG) (H2 O)}2 (ClO4)2n · 3nH2 O was
n

Carboxylate-bridged Cu(II) coordination polymeric complex
are occupied by the secondary amino nitrogen (Cu(1)–
3. Results and Discussion
N(1), 2.01 Å; Cu(2)–N(4), 2.02Å), the imidazole nitro-
gen (Cu(1)–N(2), 1.96Å; Cu(2)–N(4), 1.96 Å) and the
carboxylate oxygen (Cu(1)–O(1), 1.96Å; Cu(2)–O(4),
1.95Å) of the ligand. The fourth position of the basal
plane is occupied by neutral water molecule with the
bond distance, Cu(1)–O(3W), 1.98Å; Cu(2)–O(6W),
1.97Å. The axial positions of the Cu(II) ions are occu-
pied by the carbonyl oxygen of the carboxylate group
with the bond distances Cu(1)–O(5)axial, 2.28 Å; Cu(2)–
O(2)axial, 2.26 Å. The two Cu(II) ions are connected
through the carboxyl oxygen atom of a carboxylic group
and form a dimeric unit. Cu-BIG is freely soluble in an
aqueousmediumduetothedeprotonatedligandiswhich
involved in the polymer formation.
3.1 Crystal structure of [Cu(BIG)(H2O)2]n
(ClO4)2n · 3nH2O
ThereactionofCu(ClO4)2·6H2Owiththetridendatelig-
and, BIGH in 1:1 molar ratio in aqueous medium, upon
crystallization yields blue coloured stable Cu(II) coor-
dination polymeric complex (Scheme 1). Yield 75%.
The ORTEP24 view of the complex with the labeling of
non-hydrogen atoms is shown in Figure 1. The complex,
Cu-BIG crystallizes into the triclinic system with space
group P¯ı. The asymmetric unit of the complex contains
two Cu(II) ions with elongated square pyramid geome-
try. Three of the basal coordination sites of Cu(II) ions
Scheme 1. Schematic representation of the synthesis of Cu-BIG complex.
Figure 1. ORTEP view of the dimeric unit of [{Cu(BIG)(H2O)}2]n(ClO4)2n · 3nH2O. Hydrogen atoms
are omitted for the sake of clarity and the thermal ellipsoids are represented at the 30% probability level.
Symmetry transformation [i = x − 1, y, z].

Sabithakala Thatituri et al.
The dimeric units are translated along the crys- Å than the Cu–O bond lengths in the basal plane.
tallographic a-axis, leading to a polymeric zig-zag The molecular geometry is close to that predicted for
chain (Figure 2). Bond angles in the square plane M(tridentate)(monodentate)2 systems by simple donor
vary from 83.0(1)◦ to 100.8(1)◦. The metal ion lies atom repulsion theory.25 Analysis data of bond length
0.13 Å out of the least-squares basal plane, towards and bond angles are listed in Tables 2 and 3. Neigh-
O(5)axial. The axial Cu–O(5) bond is longer by 0.31 bouring copper ions in the polymer are linked through
Figure 2. Perspective view of zig-zag polymeric chain of [{Cu(BIG)(H2O)}2]n
(ClO4)2n · 3nH2O along the a-axis (i = x–1, y, z). Colour code for atoms: grey C; blue N;
red O; violet Cu(1); brick red Cu(2).
Table 2. Selected bond lengths (Å) and angles (◦) for Cu-BIG complex.
Bond
Bond length(Å)
Bond
Bond length(Å)
Bond
Bond length(Å)
Cu1–O1
Cu1–O3
Cu1–N1
Cu1–N2
Cu1–O5
Cl2–O12
1.962(2)
1.978(2)
2.011(3)
1.963(3)
2.281(2)
1.367(9)
Cu2–O6
Cu2–O4
Cu2–N4
Cu2–N5
Cu2–O2#1
Cl2–O13
1.972(3)
1.949(2)
2.017(3)
1.954(3)
2.254(2)
1.333(4)
Cl1–O7
Cl1–O8
Cl1–O9
Cl1–O10
Cl2–O11
Cl2–O14
1.438(3)
1.421(3)
1.362(5)
1.421(5)
1.438(5)
1.249(5)
Symmetry transformation = #1x + 1, y, z #2x − 1, y, z.
Table 3. Selected bond angles (◦) for Cu-BIG complex.
Angle
Bond angle (◦)
Angle
Bond angle (◦)
Angle
Bond angle (◦)
O1–Cu1–N1
O1–Cu1–N2
O1–Cu1–O3
O1–Cu1–O5
O3–Cu1–N1
O3–Cu1–O5
N2–Cu1–O3
N2–Cu1–N1
N2–Cu1–O5
83.76(11)
159.15(11)
92.85(11)
98.41(10)
176.08(11)
81.67(10)
100.79(11)
83.01(11)
99.11(10)
O4–Cu2–N4
O4–Cu2–06
84.66(10)
93.80(11)
157.51(11)
176.14(12)
96.86(10)
97.50(11)
82.80(11)
110.56(8)
140.62(8)
O4–Cu2–O2#1
N4–Cu2–O2#1
O6–Cu2–O2#1
N5–Cu2–O2#1
O4–Cu2–O2#2
N5–Cu2–O2#2
O6–Cu2–O2#2
101.09(10)
96.44(10)
87.32(11)
98.81(10)
55.68(8)
112.20(8)
65.74(9)
O4–Cu2–N5
O6–Cu2–N4
N1–Cu1–O5
N5–Cu2–O6
N5–Cu2–N4
N4–Cu2–O2#2
O2#1–Cu2–O2#2
Symmetry transformation = #1x + 1, y, z #2x − 1, y, z.

Carboxylate-bridged Cu(II) coordination polymeric complex
of absorption spectroscopy, emission spectroscopy and
by viscosity measurements.
3.3a Absorption spectroscopic studies: The absorp-
tion spectrum of Cu-BIG complex was recorded by
increasingtheDNAconcentration, whichshowedhyper-
chromism (Figure 4a). This is due to the interaction of
the complex with DNA through van der Waals interac-
tions. The magnitude of the hyperchromism depends on
the extent of van der Waals interactions between DNA
and the Cu-BIG Complex.
The concentration of CT-DNA was calculated from
Beer’s law and the ratio of absorbance at 260 and 280
nm is between 1.8 and 1.9, which indicates that the DNA
is free from protein.28 Absorption titration experiment
was carried out with constant complex concentration
(10 μM, cuvette pathlength, 10 mm) with varying DNA
concentration (0–100 μM) in phosphate buffer. Solution
of complex and DNA was incubated at 25◦C for 10 min,
after which absorbance readings were noted. The data
was then fit into van Vleck equation29 to obtain intrinsic
binding constant, Kb:
Figure 3. Powder X-ray diffraction patterns of Cu-BIG.
terminal carboxylate oxygen atoms of the ligand and
form a · · · Cu· · · O–C—O--Cu–O· · · Cu· · · zigzag syn-
anti conformational chain (Figure 3). The closest Cu
· · · Cu distance in this polymeric chain is 5.33 Å.
The polymeric chain is additionally stabilized by the
presence of hydrogen bonds involving the carboxy-
late oxygen, perchlorate and coordinated lattice water
molecules.
ε
ε
ε
ε
ε
ε
[DNA] / [ a − ] = [DNA] / [ − ] +1/ (Kb [ − ])
f
b
f
b
f
(1)
εa
where
is the apparent extinction coefficient
3.2 Infrared spectral analysis
ε
f
(A_obs/[DNA]) for each DNA + complex solution,
is the extinction coefficient of the free complex and
is the extinction coefficient of the fully bound com-
plex with DNA. Kb is the intrinsic binding constant.
ε
b
The IR spectrum of the BIGH shows several IR
absorption frequencies appearing at 3462, 3013, and
2783 cm−1 due to N–H stretching of secondary amine in
the side chain, N–H stretching imidazole ring and O–H
stretching of carboxylic acid, respectively. These fre-
quencies are absent in the IR spectrum of the complex
Cu-BIG. Thus, it confirms the involvement of nitrogen
and oxygen atom in chelation with metal ion. Hence,
a broad band at 3400 cm−1 indicates the presence of a
water molecule in the complex, as shown in Figures S1
and S2 (Supplementary Information).
ε
ε
f
The plot of [DNA]/[ − ] versus [DNA] (Figure 4(b))
a
gave the intrinsic binding constant, Kb as a ratio of
the slope to intercept. The Kb for Cu-BIG complex is
0.125 × 105M−1.
3.3b Ethidiumbromidefluorescencedisplacementexp-
eriments: The apparent binding constants, Kapp of
Cu-BIG complex was calculated by using Stern–Volmer
equation.30 Fluorescence study of ethidium bromide
(EtBr) bound CT DNA in the presence of a competing
Cu-BIG complex in phosphate buffer (pH 7.2) was done
3.3 DNA binding studies
Generally, the DNA shows hyperchromism or at constant (10 μM) concentration of DNA by varying
hypochromism when it reacts with metal complexes. the complex concentration (10–500 μM). Each complex
DNA binding study of the Cu-BIG complex shows and DNA solution was incubated at 25◦C for 10 min,
hyperchromism due to the interaction of the complex after which emission spectra were recorded. Changes
with the base pairs of DNA26 through non-covalent in emission intensity at 600 nm of EtBr bound to DNA
π π
interactions, such as – stacking interactions, groove were recorded with increasing amount of the Cu-BIGH
bindings, electrostatic interactions, hydrogen bonds and complex concentration (Figure 5). In phosphate buffer
van der Waals interactions.27 This is evident from the (pH 7.2), EtBr was non-emissive due to fluorescence
increase in the absorbance with an increase in the DNA quenching of the free EtBr by the solvent molecules.31,32
concentration and these binding interactions of the com- In the presence of DNA, EtBr showed enhanced emis-
plex with the CT-DNA have been studied with the help sion intensity due to its intercalative binding to DNA. A

Sabithakala Thatituri et al.
Figure 4. (a) Absorption spectra of Cu-BIG complex (50 μM, cuvette pathlength, 10 mm) for increasing concentration of
f] versus [DNA]. ( = 19968 M−1 cm−1).
ε
a
ε
ε
DNA in phosphate buffer pH 7.0. (b) Plot of [DNA]/[
−
f
80, 100, 150 μL) solution (0.2 mM), which was intro-
duced into the DNA solution (0.25 mM). Flow time
was measured with a digital stopwatch, each sample
was measured thrice and an average flow time was
calculated and listed in Table S1 (Supplementary Infor-
1/3
η η
mation). Data was presented as ( /
)
versus the
0
ratio of the concentration of Cu-BIG complex to DNA.34
The DNA helixes lengthen as the base pairs are sep-
arated to accommodate the binding molecule, which
leads to the increase of DNA viscosity. The plots of rela-
tive viscosities are shown in Figure S6 (Supplementary
Information), which show an increase in the viscosity
of the complex due to the binding of Cu-BIG with the
DNA through intercalation. However, its binding abil-
ity is less when compared to classical intercalator like
ethidium bromide.
Figure 5. Emission spectra of Cu-BIG Complex, excited at
520 nm, for varying concentrations (10–500μM).
ꢀꢂꢂ
ꢃ
ꢃ
ꢁ
1/3
1/3
η η
( / )
=
tcomplex − t0 /t0 / ((tcontrol − t0) /t0)
0
(3)
competitive binding of the copper complex to CT DNA
resulted in the displacement of the bound EtBr, decreas-
ing its emission intensity. The apparent binding constant
(Kapp) was calculated from the following equation:33
η
η0
Here,
= (tComplex − t0)/t0,
= (tControl − t0)/t0,
tComplex = flow time of the complex for each titration
(20, 40, 60, 80, 100, 150 μL), t0 = flow time of the
pure buffer (192 s) and tcontrol = flow time of the CT
DNA solution (211 s).
ꢀ
ꢁ
K
EtBr [EtBr] = Kapp complex
(2)
where KEtBr is 1×107 M−1, EtBr concentration is 10μM
and [complex] is the concentration of the BIGH com-
plex, for reduction of the emission intensity of−E1 tBr by
50%. The Kapp value for Cu-BIG is 2 × 105 M .
3.4 Magnetic properties
The magnetic properties of the polymeric complex,
Cu-BIG have been studied using a vibrating sample
3.3c Viscosity measurements: Viscosity measure- magnetometer (VSM). The VSM spectrum (M–H) of
ments were carried out using Oswald viscometer. Titra- magnetization (μ emu/g) versus magnetic field (G) was
tions were performed for Cu-BIG complex (20, 40, 60, recorded. The M–H measurement area35,36 and the curve

Carboxylate-bridged Cu(II) coordination polymeric complex
show that it is ferromagnetic in nature with low hystere- hysteresis loop implies that the compound is soft fer-
sis loss. Variation of magnetization with applied field of romagnetic and easier to magnetize and demagnetize
Cu-BIG at 20 K and at room temperature are shown in in low fields. The corresponding parameters, saturation
the Figures 6 and 7, respectively, which show hystere- magnetization (Ms), retentivity and coercivity values
sis loops of the compound measured by sweeping the obtained from the hysteresis loops are listed in Table 4.
external field between –1500 and 1500 G. The hysteresis Low temperature measurements using VSM show that
loops are found to be extremely narrow. The squareness saturation magnetization increases with a decrease in
ratio for the particles is also extremely small. Narrow temperature. The saturation magnetization at room tem-
Figure 6. Variation of magnetization with applied field of Cu-BIG complex at 20 K.
Figure 7. Variation of magnetization with applied field of Cu-BIG complex at room temperature.
Table 4. Magnetic data of Cu-BIG complex.
Temperature
Sat.Mag (Ms) emu/g
Coercivity (G)
Retentivity (Mr) emu/g
Squareness (Mr/Ms)
20 K
Room temperature
0.0189
265.15
310.79
0.365 × 10−3
0.0571 × 10−3
0.0193
0.0743
0.769 × 10−3

Sabithakala Thatituri et al.
Figure 8. Magnetization versus temperature (M–T) plot of
Cu-BIG (1) at H = 100 Oe.
Figure 9. EPR spectrum of Cu-BIG complex.
perature is 0.769 × 10−3 emu/g, which increases to
0.0189 emu/g at 20 K and also shows an increase in coer-
civity with increase in temperature. As the temperature
reaches the room temperature from 20 K, soft ferromag-
netic nature shifts slowly to hard ferromagnetic due to
an increase in hopping length.
The magnetization as a function of temperature and
magnetic field of Cu-BIG (1) was studied using a
superconducting quantum interference device (SQUID)
magnetometer. Field-cooled (FC) and zero-field cooled
(ZFC) magnetizations with temperature are shown
in Figure 8.
Magnetic measurements of the compound were made
at room temperature on a Gouy Balance. The effective
magnetic moment (μeff ) of 1 was found to be 2.088 BM.
Magnetic moment of square planar Cu(II) complexes
lies in the range of 1.70–1.90 BM.The higher value indi-
cates distortion from square planar geometry,37 which
can be inferred from the crystal structure.
200 mV s−1 shows only one redox peak in the stud-
ied potential range, at +0.73 V for the oxidation in
the forward scan and at +0.296 V for the reduction
peak in the reverse scan. The peak potential separation,
ꢀE = (Epa − Epc), between the anodic and cathodic
peaks is 434 mV. This large peak separation suggests
that the reaction is quasi-reversible. The oxidation and
reduction peak currents increase with the increase in
scan rate. The effect of scan rate on the peak potential
for the complex was also investigated by increasing the
scan rate and the results are listed in Table S2 (Supple-
mentary Information); the anodic peak potentials shift
to more negative values and the cathodic peak potentials
shift to more positive values. The increase in separation
between the peak potentials, ꢀE, by increasing the scan
rate is a characteristic behaviour of a quasi-reversible
system.
3.7 Thermal analysis
Thermal behaviour of the complex was studied by ther-
mogravimetric analysis (TGA) and differential thermal
analysis (DTA) recorded at 0–800◦C, as shown in Fig-
ure 10. Thermogram of the complex shows only one
stage of weight loss between 250 and 275◦C which cor-
responds to the decomposition of the complex and the
same is evident from the exothermic DTA curve. An
initial endothermic peak in DTA curve at 59–65◦C cor-
responds to phase transition of the compound, second
endothermic peak at 110–120◦C corresponds to the loss
of coordinated water molecule.40
3.5 EPR studies
The EPR spectrum of the complex was recorded at room
temperature and presented in Figure 9. EPR spectrum of
the complex exhibits an isotropic spectrum with giso
=
2.121.
3.6 Electrochemical studies
The redox properties of the complex were monitored
by cyclic voltammetry. Cyclic voltammograms were
recorded (Figures S7 and S8, in Supplementary Infor-
mation) in aqueous solution with Ag/AgCl reference
electrode at the potential range, −1.2 to +1.2 V in the
3.8 Antibacterial activity
presence of 0.1 M KCl as a supporting electrolyte.38,39 In vitro antibacterial activities of BIGH and Cu-BIG
The cyclic voltammogram of 1 M aqueous solution at were tested by the well-diffusion method under standard

Carboxylate-bridged Cu(II) coordination polymeric complex
Figure 10. Thermogram of Cu-BIG complex.
conditions.41 The strains chosen were G(+) binding constant (Kb) of Cu-BIG were found to be
Staphylococcus aureus, Bacillus subtilis and 2 × 105 M−1 and 0.125 × 105 M−1, respectively. The
G(−)Escherichia coli and Pseudomonas aeruginosa. cyclic voltammetric study shows that the Cu-BIG com-
Bacterial subculture medium was autoclaved for 20 min plex undergoes quasi-reversible reaction. The in vitro
before inoculation. Later, the bacteria were cultured for antibacterial activity study of Cu-BIG indicates that it
24 h in an incubator at 37◦C. Nutrient agar media plates is active against Bacillus subtilis with 2.9 cm zone of
were prepared and each plate was seeded with a pure inhibition.
test cultures by spread plate technique. Wells were bored
Supplementary Information (SI)
into the media using a sterile tip and 20 μL of the test
compounds (γ = 1 mg/mL) was inoculated into the
well by micropipette. Then the plates were incubated
at 37◦C. The width of the growth inhibition zone was
measured after 24 h of incubation. The results (Table
S3 in SI) show that the Cu-BIG complex and BIGH are
active against Bacillus subtilis and inactive against the
other species. Further, the study evidently indicates that
the antibacterial activity of the BIGH increased when
coordinated to the Cu(II) ions. This is due to the greater
lipophilic nature of the metal complex (Cu-BIG) than
the free ligand (BIGH).
CCDC 1442822 contains the supplementary crystallographic
data for this paper. This data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or from the Cambridge Crystallographic Data Center, 12
Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223 336
033; or E-mail: deposit@ccdc.cam.ac.uk. The IR spectra of
BIGH and Cu-BIG, NMR, CHNS of BIGH, UV spectrum
of Cu-BIG, Relative viscosity of Cu-BIG, Cyclic voltammo-
grams and Crystal structure with a clear view of coordinated
water (Figures S1–S9) and viscosity data of Cu-BIG, Cyclic
voltammetric data for Cu-BIG and at different scan rates and
in vitro antimicrobial activity of BIGH and its copper complex
(Tables S1–S3) are available in Supplementary Information
at www.ias.ac.in/chemsci.
4. Conclusions
The Cu(II) coordination polymeric complex of
benzimidazole-glycine conjugate ligand, Cu-BIG was
synthesized under green conditions. Though there is
no direct linkage between Cu–Cu in the polymeric
complex, in Cu-BIG they are linked through carboxy-
late group of BIGH. The delocalized electron cloud
of carboxylate group of BIGH induces indirect mag-
netic couple moments between copper ions, whereby it
exhibits ferromagnetism. From the DNA binding stud-
ies, the apparent binding constant (Kapp) and intrinsic
Acknowledgements
The authors are thankful to JNTU, Hyderabad and UGC net-
working resource centre, University of Hyderabad, India for
providing necessary facilities to carry out this work.
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