2-Benzoylpyridine and copper(II) ion in basic medium: Hydroxide nucleophilic addition stabilized by metal complexation, reactivity, crystal structure, DNA binding study and magnetic behavior

Article abstract of DOI:10.1016/j.ica.2010.11.012

On reaction of 2-benzoylpyridine (Bzpy) with copper(II) ion, different types of copper(II) complexes have been isolated in pure form depending upon the counter anion of the copper(II) salts used as reactant and the pH of the medium. Mono-nuclear copper(II

Full text of DOI:10.1016/j.ica.2010.11.012

Inorganica Chimica Acta 367 (2011) 1–8
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
2-Benzoylpyridine and copper(II) ion in basic medium: Hydroxide nucleophilic
addition stabilized by metal complexation, reactivity, crystal structure, DNA
binding study and magnetic behavior
Sourav Dey a, Sandipan Sarkar a, Ennio Zangrando b, Helen Stoeckli Evans c, Jean-Pascal Sutter d,
Pabitra Chattopadhyay a,
⇑
a Department of Chemistry, Burdwan University, Golapbag, Burdwan 713104, India
b Dipartimento di Scienze Chimiche, Via Licio Giorgieri 1, 34127 Trieste, Italy
c Institute of Physics, University of Neuchâtel, Rue Emile-Argand 11, CP 158, CH-2009 Neuchâtel, Switzerland
d CNRS, Laboratoire de Chimie de Coordination, 205, Route de Narbonne, F-31077 Toulouse, France
a r t i c l e i n f o
a b s t r a c t
Article history:
On reaction of 2-benzoylpyridine (Bzpy) with copper(II) ion, different types of copper(II) complexes have
been isolated in pure form depending upon the counter anion of the copper(II) salts used as reactant
and the pH of the medium. Mono-nuclear copper(II) complexes of formula [Cu(Bzpy)2(ClO4)2] (1) and
[Cu(Bzpy)2(H2O)2](NO3)2 (2) were formed with copper(II) perchlorate and nitrate, respectively. On the
other hand, following a similar reaction type in presence of alkali, we obtained the dinuclear copper(II)
complex [Cu2(Bzpy)2{BzOpy}2(H2O)](ClO4)2 (3) containing the hydroxy-2-pyridylphenylmethanolato
(BzOpy)ꢀ anion, achieved through the nucleophilic addition of the hydroxide to the carbonyl group of
Bzpy, which is stabilized by metal complexation. However, this behavior was not recorded with
copper(II) nitrate. The complexes were characterized by physicochemical and spectroscopic tools along
with structural characterization by single crystal X-ray diffraction analysis. The interaction of dinuclear
copper(II) complex 3 with calf thymus DNA (CT-DNA) has been investigated by using absorption and
emission spectral studies and the binding constant (Kb) and the linear Stern–Volmer quenching constant
(Ksv) have been determined. Complex 3 was active to oxidize the catechol to the corresponding quinone
in MeCN medium via complex-catechol intermediate. Magnetic behavior for 3 is typical for uncorrelated
spins down even up to 2 K.
Received 21 May 2010
Received in revised form 15 September
2010
Accepted 12 November 2010
Available online 25 November 2010
Keywords:
2-Benzoylpyridine
Copper(II) ion
Nucleophilic addition on ketone
Crystal structure
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
complexes for metalloenzymes that mimics the oxygenase activity
is therefore of great promise for the development of new and effi-
The design of binuclear metal complexes incorporating suitable
bridging ligands has attracted considerable research interest in re-
cent years [1–4], primarily due to their relevance for biological pro-
cesses, molecular electronics and for theoretical studies of electron
transfer processes [5–9]. In addition binuclear copper(II) com-
plexes are of interest for availing magnetostructural correlations
and as useful model systems for catalysis. As far as biochemistry
is concerned, catechol oxidases are ubiquitous plant enzymes,
belonging to the oxidoreductase class and containing a dinuclear
copper center, which catalyse the two-electron oxidation of a
broad range of o-diphenols (catechol) to the corresponding
quinones coupled with the reduction of molecular oxygen to water
[10]. The synthesis and investigation of functional model
cient catalysts for oxidation reactions [11]. Moreover, compounds
showing the property of cleaving double stranded DNA under
physiological conditions are of importance since these could be
used as diagnostic agents in medicinal and genomic research
[12]. Several efficient cleaving agents have been developed over
the course of time, however, most of the studies deal with macro-
cyclic mononuclear copper(II) complexes [13–15] indicating
greater DNA cleaving efficiency of the macrocyclic binuclear
copper(II) complexes than mononuclear ones [16].
Considering the above fact, with the use of 2-benzoyl pyridine
(Bzpy) as ligand moiety we have synthesized the mononuclear
copper(II) complexes [Cu(Bzpy)2(ClO4)2] (1) and [Cu(Bzpy)2(H2O)2]
(NO3)2 (2), and one dinuclear copper(II) complex, [Cu2(Bzpy)2(BzO-
py)2(H2O)](ClO4)2 (3) in alkali medium. The dinuclear one (3)
contains the hydroxy-2-pyridylphenylmethanolato (BzOpy)ꢀ
monoanion in situ formed through the nucleophilic addition of
the hydroxide to the ketone group of the 2-benzoyl pyridine. The
⇑
Corresponding author.
E-mail address: pabitracc@yahoo.com (P. Chattopadhyay).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.11.012

2
S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
new ligand results stabilized upon coordination and to the best of
our knowledge it represents the first structurally characterized
report of this species. The interaction of complex 3 with DNA
(CT-DNA) along with the oxidation of catechol to its corresponding
quinone via complex-catechol intermediate has been investigated
using spectral studies. The magnetic properties of complex 3 are
also reported, here.
(3): Anal. Calc. for C48H40Cl2Cu2N4O15: C, 51.72; H, 3.68; N, 4.98,
Cu, 11.32. Found: C, 51.88; H, 3.63; N, 5.04, Cu, 11.45%. IR (cmꢀ1):
m
C@O, 1750; mClO , 1084.
4
2.3. X-ray crystal structure analyses
Diffraction data were collected at room temperature on a Non-
ius DIP-1030H system (complex 1) and at 173 K on a Stoe Mark II-
Image Plate Diffraction System [18] equipped with a two-circle
2. Experimental
goniometer for complex 3. The radiation used was Mo Ka graphite
monochromatized (k = 0.71073 Å) in both cases. Cell refinement,
indexing and scaling of the data sets were performed using pro-
grams Denzo, Scalepack [19] and CrysAlis [20]. An empirical
absorption correction was applied to the data of compound 3 using
the MULscan ABS routine in PLATON [21].
The structures were solved by direct methods [22] and subse-
quent Fourier analyses and refined by the full-matrix least-squares
method [22] based on F2 with all reflections. The H-atoms were in-
cluded at calculated positions and treated as riding atoms using
SHELXL default parameters, those of the coordinated water in 3 were
2.1. Materials and physical measurements
All chemicals and reagents were obtained from commercial
sources and used as received. Solvents were distilled from an
appropriate drying agent. Tris–HCl buffer solution and CT-DNA
were purchased from Bangalore-Genie, ethidium bromide (EB)
from Sigma. Microanalyses were performed with the use of a
Perkin–Elmer 2400 CHN elemental analyzer. Copper analyses were
carried out by Varian atomic absorption spectrophotometer (AAS)
model-AA55B, GTA using graphite furnace. Infrared spectra were
obtained by a JASCO FT-IR model 420 using KBr disk. Electronic
spectra were recorded on the JASCO UV–Vis/NIR model V-570.
located on
DF map. In compound 3 the two perchlorate anions are
positionally disordered with large thermal displacement parame-
ters. Oxygen atoms of Cl(1) are disordered over two positions
(occupancies 0.72/0.28), while the other anion is located over
two positions (0.6/0.4) sharing two O atoms. Moreover two adja-
cent residuals were interpreted as partially occupied water mole-
cules (occupancy of 0.2 each). In the final cycles of refinement
the perchlorate anions and the water molecules were held fixed.
All the calculations were performed using the WinGX System,
Ver. 1.80.05 [23]. Crystal data and details of data collection and
refinement for the structures reported are summarized in Table 1.
Magnetic moments (l, B.M.) were obtained from vibrating sample
magnetometer PAR 155 model. The magnetic measurements were
carried out with a Quantum design MPMS-5S SQUID susceptome-
ter. Molar magnetic susceptibility was recorded between 300 and
2 K with an applied field of 1 kOe. Data have been corrected for
the sample holder and for the diamagnetic contribution of all
atoms by using Pascal’s tables [17]. The field dependence of the
magnetization was recorded at 2 K up to 50 kOe. All measurements
have been performed on crushed crystals, the powder (46.5 mg)
was mixed to grease and hold in a gelatin capsule.
2.4. DNA binding experiments
2.2. Reactions of 2-benzoylpyridine with copper(II) ion
The Tris–HCl buffer solution (pH 8.0), used in all the experi-
ments involving CT-DNA, was prepared by using deionized and
sonicated HPLC grade water (Merck). The CT-DNA was sufficiently
free from protein, being the ratio of UV absorbance of the DNA in
2.2.1. Synthesis of [Cu(Bzpy)2(ClO4)2] (1)
To
a methanolic solution of 2-benzoyl pyridine (2 mmol,
366 mg) copper(II) perchlorate hexahydrate (1 mmol, 370 mg) in
methanol was added dropwise and the mixture was stirred for
4 h at ambient temperature. Then the reaction mixture was filtered
off and the green single crystals, suitable for X-ray diffraction, were
obtained from the filtrate through slow evaporation at room tem-
perature. Yield: 80–85%.
Tris–HCl solution at 260 and 280 nm (K260/K280) of ca. 1.9 [24].
Table 1
Crystal data and details of structure refinement for complex 1 and 3.
1
3ꢁ0.4(H2O)
(1): Anal. Calc. for C24H18Cl2CuN2O10: C, 45.78; H, 2.74; N, 4.48;
Cu, 10.37. Found: C, 45.82; H, 2.89; N, 4.45; Cu, 10.11%. IR (cmꢀ1):
m
Formula
Formula weight
Crystal system
Space group
a (Å)
C
24H18Cl2CuN2O10 C48H40Cl2Cu2N4O15ꢁ0.4(H2O)
628.84
monoclinic
P21/n
6.848(3)
13.889(4)
13.211(4)
92.98(3)
1254.8(8)
1.664
1118.03
monoclinic
P21/n
C@N, 1472; mð3ÞClO , 1135, 1060. Magnetic moment (l, B.M.): 1.71.
4
2.2.2. Synthesis of [Cu(Bzpy)2(H2O)2](NO3)2 (2)
It was prepared following a similar procedure as for 1 by replac-
ing only the copper(II) perchlorate with the nitrate salt.
18.6204(13)
14.1696(8)
18.7372(13)
102.195(5)
4832.1(6)
1.536
b (Å)
c (Å)
b (°)
(2): Anal. Calc. for C24H22CuN4O10: C, 25.78; H, 1.60; N, 2.48; Cu,
V (Å3)
10.97. Found: C, 48.84; H, 3.76; N, 9.50; Cu, 10.77%. IR (cmꢀ1):
qcalc (g/cm3)
Z
m
C@N, 1473;
m
, 1379. Magnetic moment (l, B.M.): 1.74.
NO3
2
638
4
F(0 0 0)
2288
h Range (°)
l
2.13–23.25
1.146
1.4–25.70
1.066
2.2.3. Synthesis of [Cu2(Bzpy)2(BzOpy)2(H2O)](ClO4)2 (3)
(Mo Ka )
) (mmꢀ1
To a methanolic solution of 2-benzoyl pyridine (2.0 mmol
366 mg) copper(II) perchlorate hexahydrate (1.0 mmol, 370 mg)
was added dropwise and the mixture was stirred for 4 h at ambient
temperature. Then KOH (1.0 mmol, 56 mg) in methanol was added
and the final mixture was stirred for another 2 h. The solution was
kept aside and after a few days, deep green colored crystalline
complex was obtained by filtration followed by washing with
water, methanol and dried in a vacuum arrangement. Single
crystals suitable for X-ray diffraction were also obtained from this
solution. Yield: 70–75%.
Reflections collected
Independent reflections
5693
1752
65 242
9143
(Rint
)
R merge
Reflections I > 2r(I)
0.0973
781
0.798
0.0502
7198
1.037
Goodness-of-fit (GOF)
on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0440
wR2 = 0.0898
R1 = 0.1098
wR2 = 0.1008
R1 = 0.0461
wR2 = 0.1155
R1 = 0.0630
wR2 = 0.1231
R indices (all data)

S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
3
The concentration of DNA was determined with the help of its
extinction coefficient
of 6600 L molꢀ1 cmꢀ1 at 260 nm [25]. Stock
e
N
O
Cu(ClO4)2.6H2O
solution of DNA was always stored at 4 °C and used within 4 days.
Concentrated stock solution of complex 3 was prepared by dissolv-
ing the copper(II) complex in DMSO and diluting suitably with
Tris–HCl buffer to the required concentration for all the experi-
ments. Absorption spectral titration experiment was performed
by keeping constant the concentration of the copper(II) complex
with varying the CT-DNA concentration. To eliminate the absor-
bance of DNA itself, equal solution of CT-DNA was added either
to the copper(II) complex solution and to the reference one. In
the fluorescence displacement experiment with ethidium bromide
(EB), 5.0 mL of EB solution (1.0 mmol Lꢀ1) in Tris–HCl were added
to 1.0 mL of DNA solution at saturated binding levels [26], and
stored in the dark for 2.0 h. The copper(II) complex solution was ti-
trated into the DNA/EB mixture and then diluted in Tris–HCl buffer
to 5.0 mL, making the solutions with the varied mole ratio of the
copper(II) complex to CT-DNA. Prior to measurements, the mixture
was shaken up and incubated at room temperature for 30 min. The
fluorescence spectra of EB bound to DNA were obtained at an emis-
sion wavelength of 584 nm.
Cu(NO3)2.3H2O
[Cu(Bzpy)2(ClO4)2] (1)
Bzpy
Cu(ClO4)
.
6H2O
2
[Cu(Bzpy)2(H2O)2](NO3)2 (2)
Mixture
KOH / Stir
OH
KOH / Stir
KOH / Stir
Or
KOH / ClO4- / Stir
Ph
Ph
O
O
N
Ph
O
O
N
N
Cu
(ClO )
2
4
Cu
OH2
Ph
N
OH
[Cu2(Bzpy)2(BzOpy)2(H2O)](ClO4)2 (3)
Scheme 1. Reactions of 2-benzoylpyridine with copper(II) ion.
2.5. Reactivity of complex 3: oxidation of catechol
3.2. Structural description of complexes
To record the reactivity of complex 3 towards stable organic
compound, the oxidation of catechol to the corresponding quinone
under dinitrogen atmosphere has been studied by treating an
appropriate amount of 10ꢀ4 mol dmꢀ3 solutions of 3 in acetonitrile
with 10ꢀ2 mol dmꢀ3 (100 eq.) of catechol and recording the UV–Vis
spectra.
The ORTEP view of complex [Cu(Bzpy)2(ClO4)2] (1) with the
atom numbering schemes is illustrated in Fig. 1 and a selection
of bond distances and angles is reported in Table 2. The molecular
structure of the complex is centrosymmetric with the N, O chelat-
ing Bzpy ligands located in the equatorial plane (Cu–O and Cu–N
bond distances of 1.988(4) and 1.956(4) Å, respectively) and com-
pleting the coordination sphere by two perchlorate ions at consid-
erably longer distance (Cu–O(4) = 2.451(4) Å) as expected for the
Jahn–Teller distortion. The chelating angle N–Cu–O angle is
82.08(18)°. The crystal packing shows complex molecules well
separated that do not exhibit short contacts.
3. Results and discussion
3.1. Synthesis and characterization
The copper(II) complexes 1–3 were obtained in good yield by
the reaction of the corresponding copper(II) salts with 2-benzoyl-
pyridine in methanol. The dinuclear complex [Cu2(Bzpy)2(BzO-
py)2(H2O)](ClO4)2 (3) was collected to stir the reaction mixture
(obtained from the reaction of copper(II) perchlorate and 2-benzo-
ylpyridine in 1:2 M ratio) in alkaline (KOH) medium. It is notewor-
thy that the complex 3 was also obtained if the methanolic
solution of complex, 1 was stirred in alkaline KOH medium as gi-
ven in Scheme 1. The probable reaction path has been shown in
Scheme 2. This may be taken place due to the presence of the
two large perchlorate ions in the axial position of the octahedral
coordination sphere of copper(II) ion in complex 1 (supported by
the crystal structure described in Section 3.2). This is an unusual
situation for copper(II) ion to accommodate two perchlorate ions
in the coordination sphere. And as a result of sterically hindered
condition, this was occurred in case of the complex 1, but similar
phenomena was not observed in case of complex 2 where two
water molecules was comfortably present in the coordination
sphere of copper(II) ion as usual.
The molecular structure of complex 2 consists of centrosym-
metric [Cu(Bzpy)2(H2O)2]2+ cations and nitrate ions. Since its
structural characterization has been already reported [27], it is
not discussed in detail. The Cu–O and Cu–N bond distances of
the chelating Bzpy ligands are 2.068(2), and 1.965(2) Å, respec-
tively. The former being longer than the value measured in 1,
but conversely the axial Cu–OH2 is significantly shorter
(2.256(3) Å).
The molecular structure of complex 3 together with the atom
numbering is illustrated in Fig. 2 and the crystal packing in Fig. 3.
A selection of bond distances and angles are listed in Table 2. The
X-ray structural determination confirms the presence in the dinu-
clear complex [Cu2(Bzpy)2{BzOpy}2(H2O)]2+ of the (BzOpy)ꢀ anion
formed by the nucleophilic addition of the hydroxide to the ketone
group of Bzpy.
The formation of the (BzOpy)ꢀ anion was rather unexpected,
although a similar reaction is frequently observed for the di-2-pyr-
idylketone [(2-py)2CO]. In fact when this ligand is coordinated to a
number of metal ions, its carbonyl group easily undergoes addition
of various nucleophiles, including water and methanol, forming the
gem-diol [(2-py)2C(OH)2] and the hemiacetal form [(2-py)2C(OR)
(OH)], respectively. The former can function either as mono- or
di-anionic and the presence of deprotonated hydroxy group(s)
leads to a great coordinative flexibility [28–32]. The cited refer-
ences report some selected examples of copper complexes, but
hundreds of complexes containing other transition metal ions have
been reported. On the other hand, structural result of 3 represents
at our best knowledge the first report of the (BzOpy)ꢀ species
stabilized upon coordination to the metal.
All the complexes are soluble in methanol, DMF and DMSO. In
the solid state the complex is fairly stable in air so as to allow
performing physical measurements. The room temperature mag-
netic moment (l) of complex 1 and 2 are 1.71 and 1.74 B.M.,
equivalent to one unpaired electron. In case of the complex 3,
[Cu2(Bzpy)2(BzOpy)2(H2O)](ClO4)2, two Cu(Bzpy) fragments are
bridged by oxygen of the new hydroxy-methanolato ligand formed
by nucleophilic addition of hydroxide to carbonyl group. The vari-
able temperature magnetic moment of 3 was measured and will
discuss in details at Section 3.6.

4
S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
O
O
Ph
Cl
O
O
O
OH
Ph
KOH
N
Complex 1
-
- ClO4
N
Ph
Cu
N
O
O
Cu
O
-OH
O
O
Ph
N
O
Cl
O
O
O
Cl
O
O
H2O
+
Ph
Ph
O
+
O
OH
Ph
N
H2O
N
Cu
N
Ph
-
Cu
HO
Ph
-ClO4
HO
Ph
O
N
N
Rearrangement
O
O
Cu
N
O
H2O
O
O
O
O
+
Ph
OH
H2O
Cu
Cl
H2O
N
O
N
O
Ph
OH
Ph
Ph
- H O
2
O
O
Ph
(ClO4)2
O
N
N
Cu
Cu
OH2
Ph
N
O
N
OH
[Cu2(Bzpy)2(BzOpy)2(H2O)](ClO4)2 (3)
Scheme 2. Probable reaction path to form complex 3.
Fig. 1. ORTEP view (ellipsoids at 35% probability) of complex 1 with labeling scheme of independent atoms.
In complex 3 the metal ions Cu(1) and Cu(2) show an octahedral
oxygen acts as bridging donor towards the two Cu(Bzpy) fragments
with Cu–O distances in between 1.916(2)–1.960(2) Å. These bridg-
ing oxygens, which form the Cu2O2 core of the complex, figure out
Cu–O–Cu bond angles of 102.71(9)° and 103.58(10)°, and separate
the metals at 3.028 Å.
and a square pyramidal coordination geometry, respectively. In
fact each (BzOpy)ꢀ anion is mono-coordinated to one copper ion
through the pyridine N donor (Cu–N distances of 1.989(3) and
1.977(3) Å in Cu(1) Cu(2), respectively), whereas the methanolate

S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
5
Table 2
Selected coordination bond lengths (Å) and angles (°) for 1 and 3.
Complex 1
Cu–N(1)
Cu–O(4)
1.956(4)
2.451(4)
Cu–O(1)
1.988(4)
N(1)–Cu–O(1)#1
N(1)–Cu–O(1)
N(1)–Cu–O(4)#1
N(1)–Cu–O(4)
97.92(18)
82.08(18)
95.51(15)
84.49(15)
O(1)–Cu–O(4)
O(1)–Cu–O(4)#1
C(6)–O(1)–Cu
89.76(16)
90.24(16)
113.5(4)
Complex 3
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–O(1)
Cu(1)–O(4)
Cu(1)–O(1w)
Cu(1)–O(6)
1.989(3)
2.016(2)
1.960(2)
1.928(2)
2.450(2)
2.499(2)
Cu(2)–N(1)
Cu(2)–N(2)
Cu(2)–O(1)
Cu(2)–O(4)
Cu(2)–O(3)
1.977(3)
1.991(2)
1.916(2)
1.925(2)
2.391(2)
N(3)–Cu(1)–N(4)
O(1)–Cu(1)–O(1w)
O(1)–Cu(1)–O(4)
O(1)–Cu(1)–O(6)
O(1)–Cu(1)–N(3)
O(1)–Cu(1)–N(4)
O(1w)–Cu(1)–O(4)
O(1w)–Cu(1)–O(6)
O(1w)–Cu(1)–N(3)
O(1w)–Cu(1)–N(4)
O(4)–Cu(1)–O(6)
O(4)–Cu(1)–N(3)
O(4)–Cu(1)–N(4)
102.38(10)
88.79(9)
76.22(9)
O(6)–Cu(1)–N(3)
O(6)–Cu(1)–N(4)
N(1)–Cu(2)–N(2)
O(1)–Cu(2)–O(3)
O(1)–Cu(2)–O(4)
O(1)–Cu(2)–N(1)
O(1)–Cu(2)–N(2)
O(3)–Cu(2)–O(4)
O(3)–Cu(2)–N(1)
O(3)–Cu(2)–N(2)
O(4)–Cu(2)–N(1)
O(4)–Cu(2)–N(2)
88.82(9)
73.01(9)
100.64(10)
105.99(8)
77.33(9)
82.24(10)
176.87(10)
102.15(8)
88.56(9)
75.44(9)
158.86(10)
99.68(9)
97.49(9)
157.47(10)
100.16(9)
91.83(8)
165.83(9)
90.17(9)
93.43(9)
101.99(8)
81.32(10)
173.56(9)
Fig. 3. Side view of complex 3 showing the hydrogen bond interactions with the
perchlorate anions. Only oxygen atoms at higher occupancy (0.72) are shown for
Cl(1) anion, while perchlorate Cl(2) is splitted over two positions (0.60/0.40).
of the complex, form hydrogen bonds with the perchlorate counte-
rions giving rise to a discrete entity (Fig. 3). The positional disorder
detected for the counter anions (see Section 2) could be a require-
ment to ensure these interactions, but due to this crystallographic
feature a detailed analysis is meaningless.
3.3. Spectral characterization
In IR spectra, the point of interest for 1 and 3 is the band due to
perchlorate. The perchlorate m3 vibration of 1 splits into two
stretching frequencies at 1135 and 1060 cmꢀ1, suggesting the uni-
ꢀ
dentate function of the ClO4 ligand to Cu(II) ion in the solid state
[33,34] and it is also supported by the X-ray crystallographic struc-
ture. But in the IR spectrum of complex 3 an intense absorption
band at 1085 cmꢀ1 along with a weak band at ca. 623 cmꢀ1 due
to the symmetric (ms(C104)) and asymmetric (mas(C104)) stretching
vibration of non-coordinated perchlorate ion, respectively were
observed. In addition to the characteristic band at ca. 1750 cmꢀ1
assignable to mC@O observed in the IR spectra of 1 and 3, a weak
band around 3350 cmꢀ1 attributable to mOH was observed only in
the IR spectrum of complex 3. The presence of an intense band at
Fig. 2. ORTEP view (ellipsoids at 50% probability) of complex 3, C atoms not labeled
for sake of clarity.
Here the N, O chelating Bzpy ligands have the oxygen located at
one axial position of the octahedral coordination sphere of Cu(1)
and at the apical site of the square pyramid of Cu(2). Thus Cu–
O(Bzpy) bond lengths of 2.499(2) Å (Cu(1)–O(6)) and 2.391(2) Å
(Cu(2)–O(3)) are significantly elongated with respect the value
measured in 1, while the Cu(1)–N(4) and Cu(2)–N(2) are only sen-
sibly longer (2.016(2) and 1.991(2) Å, respectively). The octahedral
geometry of Cu(1) is completed by an aqua ligand with Cu(1)–
O(1w) bond length of 2.450(2) Å.
Excluding the coordinated water molecule at Cu(1), the com-
plex has an approximately 2-fold axis with the pseudo symmetry
axis passing in between the metals, approximately normal to
Fig. 2. The chiral C atoms in the (BzOpy)ꢀ anions of each complex
have the same configuration.
around 1379 cmꢀ1 (corresponding to mNO ) in the IR spectrum of
3
complex 2 confirm the existence of the nitrate ion as counter an-
ion; besides those observed in the range 1469–1478 cmꢀ1 for
mNO . Band attributable to m(Cu–N) at ca. 455 is present in IR spectra
3
of the three complexes present.
The electronic spectra of 1 and 3 were recorded in acetonitrile
at room temperature. The intraligand absorptions <400 nm are as-
signed to
224 nm,
= 7123 dm3 molꢀ1 cmꢀ1 for
p ? e
p⁄ (226 nm, = 17,687 dm3 molꢀ1 cmꢀ1 for 1 and
e
= 16 902 dm3 molꢀ1 cmꢀ1 for 3) and n ? p⁄ (258 nm,
and 261 nm,
= 6453 dm3 mol
e
1
e
ꢀ1 cmꢀ1 for 3) transitions. The complex 1 exhibit the characteristic
broad d–d absorption band at 540 nm (438 dm3 molꢀ1 cmꢀ1) with
a shoulder at low energy at ca. 695 nm (112 dm3 molꢀ1 cmꢀ1) in
solution along with an intense demonstrates square planar
geometry around the copper ion in the solution state [35]. A
characteristic broad d–d absorption band at ca. 597 nm
The coordinated water molecule O(1w) and the hydroxyl
groups, which are located on the same side of the equatorial plane

6
S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
(398 dm3 molꢀ1 cmꢀ1) observed in the electronic spectra of the
complex 3 demonstrates the square pyramidal geometry around
the copper ion in the solution state and it is assignable to assigned
1.2x10-10
1.2x10-10
1.1x10-10
1.1x10-10
1.0x10-10
1.0x10-10
9.5x10-11
to the envelope of 2B1g ? 2A1g 2B2g and 2Eg transitions [36].
,
3.4. DNA-binding studies
3.4.1. Electronic absorption titration
The absorption spectra of complex 3 in the absence and pres-
ence of CT-DNA help to examine the binding mode of the copper
complex with DNA helix. As shown in Fig. 4, when titrated by
the CT-DNA, the copper complex showed a significant hyperchro-
mism effect centered at the 270 nm absorption maximum, sug-
gesting that
a strong interaction is operative between the
copper(II) complex and DNA. The observed spectral changes of
the complex in the presence of CT-DNA might be indicative of
groove binding mode interaction [37]. The literature survey shows
that the interaction of the molecules having unfused aromatic ring
systems linked by bonds that guarantee torsional freedom with
DNA, allows the molecules to adopt appropriate conformation to
closely match the helical turn of DNA grooves [38]. Here, the aro-
matic rings of the ligands in the copper(II) complex are likely to
facilitate the formation of van der Waals contacts within the walls
of groove or hydrogen bonds in DNA grooves. These spectral data
helped us to calculate the intrinsic binding constant Kb of 3 with
CT-DNA using the following equation [39] from the slope to inter-
2.0x10-6
4.0x10-6
6.0x10-6
8.0x10-6
[DNA]
Fig. 5. Plot of [DNA]/(ea–ef) vs. [DNA] for the titration of 3 with CT-DNA in Tris–HCl
buffer. Binding constant (Kb) = 3.8 ꢃ 104 Mꢀ1 (R = 0.99866). PABITRA if you report
Plot of [DNA]/(ea
–
e
f) ꢃ 10ꢀ10 vs. [DNA] ꢃ 10ꢀ6, CORRECT it would be more clear
(just a suggestion).
of EB/DNA system is observed at 584 nm with the increasing con-
centration of 3 as reported in Fig. 6. The present observation leads
us to guess that the copper complex may interact with DNA
through a groove binding mode, releasing some EB molecules from
the EB–DNA system. The quenching of EB bound to DNA due to the
presence of the complex can be interpreted with the linear Stern–
Volmer equation [43]:
cept ratio of the graph obtained by plotting the [DNA]/(ea–ef) ver-
sus [DNA] (Fig. 5).
½DNAꢂ=ðea
ꢀ
ef Þ ¼ ½DNAꢂ=ðeb
ꢀ
ef Þ þ 1=½Kbðeb
ꢀ ef Þꢂ
where [DNA] is the DNA concentration, ea
,
eb and ef symbolizes the
extinction coefficient for each addition of DNA to the copper(II)
complex, for the copper complex in the fully bound form and for
the free copper complex, respectively. This binding constant Kb of
3 with CT-DNA was found to be 3.8 ꢃ 104 Mꢀ1 (R = 0.99866, four
regression points). This value compares well with that of the
well-established groove binding agent [40].
I0=I ¼ 1 þ Ksv½Qꢂ
where I0 and I represent the fluorescence intensities in the absence
and presence of quencher, respectively. Ksv is the linear Stern–Vol-
mer quenching constant and Q is the concentration of quencher.
From the slope to intercept ratio in the plot of I0/I versus [complex]
(Fig. 7), the Ksv value was found to be 0.5 ꢃ 104 (R = 0.98775 for five
points), which indicates a strong affinity of the copper(II) complex
to CT-DNA.
3.4.2. Ethidium bromide fluorescence displacement experiments
The ethidium bromide (EB) fluorescence displacement experi-
ments were also performed to investigate the interaction mode
of 3 with CT-DNA. EB has been used to probe the interaction of me-
tal complexes with DNA as the fluorescence intensity of EB is en-
hanced for its intercalation into the DNA and is quenched by the
addition of another molecule being displaced in this case from
DNA [41,42]. A significant decrease of the fluorescence intensity
3.5. UV–Vis spectroscopic study of reaction of complex 3 with catechol
First of all, the UV–Vis activities of pure catechol, dicopper(II)
complexes and o-quinone in acetonitrile have been investigated.
400
a
300
0.6
0.4
0.2
0.0
e
a
200
e
100
0
550
600
650
700
750
240
270
300
Wave length (nm)
Wave length (nm)
Fig. 6. Emission spectra of the titration of the CT-DNA–EB system with complex 3
Fig. 4. Electronic spectral titration of 3 with CT-DNA at 270 nm in Tris–HCl buffer;
[complex] = 5.16 ꢃ 10ꢀ5; [DNA] ꢃ 10ꢀ6: (a) 0.0, (b) 0.94, (c) 2.00, (d) 4.82, and (e)
7.76 mol Lꢀ1. The arrow indicates the increase of DNA concentration.
in Tris–HCl buffer. kex = 522 nm; [EB] = 0.96 ꢃ 10ꢀ6 mol Lꢀ1; [DNA] = 2.07 ꢃ 10ꢀ5
;
[complex] ꢃ 10ꢀ6: (a) 0.0, (b) 0.82, (c) 1.64, (d) 2.46, and (e) 3.28 mol Lꢀ1. The arrow
indicates the increase of complex concentration.

S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
7
1.0
1.20
1.15
1.10
1.05
0.90
0.80
0.70
0.60
1.0x10-5
2.0x10-5
3.0x10-5
0.50
[complex]
0
50
100
150
200
250
300
T (K)
Fig. 7. Plot of I0/I vs. [complex] for the titration of 3 to the CT-DNA–EB system using
spectrofluorimeter; linear Stern–Volmer quenching constant Ksv = 0.5 ꢃ 104;
(R = 0.98775, five regression points).
Fig. 9. Plot of
vMT vs. T for complex 3.
in good agreement with two non-interacting S = ½ spin with
g = 2.06. This value remains unchanged for lower temperatures
with a slight decrease below 70 K to reach 0.78 cm3 molꢀ1 K for
2 K. This behavior is typical for uncorrelated spins.
5
This behavior is rather surprising when the compound’s
structure is considered. Indeed, for two Cu(II) bridged by two
alkoxo-oxygens sitting in equatorial position for both ions, with a
Cu–O–Cu angle of ca. 103°, one would expect substantial antiferro-
magnetic interactions [44,45]. In the lack of any salient structural
feature that may be invoked to account for the absence of exchange
coupling, this behavior remains puzzling. More examples of related
Cu dimers involving this bridging ligand will be required to
conclude on the role of this peculiar ligand.
4
Ortho quinone
3
Complex
2
Catechol
1
4. Conclusion
0
The reaction of 2-benzoylpyridine (Bzpy) with copper(II) salts
leads to octahedral mononuclear complexes [Cu(Bzpy)2(ClO4)2]
(1) and [Cu(Bzpy)2(H2O)2](NO3)2 (2) By stirring the methanolic
solution of complex 1 in alkaline medium or the by allowing a
reaction with the reaction mixture of copper(II) perchlorate and
Bzpy (1:2 M ratio) in alkaline medium a dinuclear complex,
[Cu2(Bzpy)2{BzOpy}2(H2O)](ClO4)2, was obtained. The latter in-
cludes the monoanionic ligand BzOpy, obtained through the addi-
tion of a hydroxide to carbonyl group of Bzpy, which results
stabilized upon metal coordination. This phenomenon of occurring
the dinuclear copper(II) complexes 3 may be due to the presence of
two perchlorate ions in the coordination sphere with a steric inter-
actions. The dinuclear complex shows a biological activity, since it
oxidizes the catechol to the corresponding quinone in MeCN med-
ium and interacts with calf thymus DNA (CT-DNA) through a
groove binding mode interaction.
300
400
500
600
Wave length (nm)
Fig. 8. Changes in UV–Vis spectra of catechol upon addition of complex 3.
Catechol is observed to be silent in the range of 350–800 nm,
where o-quinone exhibits a band at 370 nm. To study the reaction
of the dicopper(II) complex with catechol in acetonitrile medium,
5 ꢃ 10ꢀ5 mol dm3 solution of 3 was treated with 5 ꢃ 10ꢀ3 mol
dmꢀ3 (100 eq.) of catechol under aerobic condition. Immediately
after the addition of the complex, the colorless solution becomes
yellow. Then UV–Vis spectroscopic study (Fig. 8) was performed
on this mixture. Change in intensity and band position was
observed taking reading at intervals of 20 min during 2 h of the
reaction course. No further change in intensity was detected after
2 h of the reaction completion. This result proves the oxidation of
catechol to quinone catalyzed by complex 3.
Acknowledgments
½CuIIðBzpyÞ ðBzOpyÞ ðH2OÞꢂðClO4Þ þ catechol
2
2
2
2
Financial support from Department of Science and Technology
(DST), New Delhi, India is gratefully acknowledged. S.S. Would like
to acknowledge CSIR, New Delhi, India for Senior Research Fellow-
ship. E.Z. thanks MIUR-Rome for financial support (PRIN No.
2007HMTJWP_002).
! ½CuI ðBzpyÞ ðBzOpyÞ ðH2OÞꢂ þ orthoquinone
2
2
2
3.6. Temperature dependence of magnetic susceptibility of complex 2
The temperature dependence of the molar magnetic suscepti-
Appendix A. Supplementary material
bility,
range of 2–300 K. Results are plotted in the form of
in Fig. 9. The value for
MT at 300 K is 0.80 cm3 molꢀ1 K, which is
v
M, of complex 3 has been measured in the temperature
vMT versus T
CCDC 773466 and 773465 contain the supplementary crystallo-
graphic data for 1 and 3. These data can be obtained free of charge
v

8
S. Dey et al. / Inorganica Chimica Acta 367 (2011) 1–8
[23] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[24] J. Marmur, J. Mol. Biol. 3 (1961) 208.
[25] M.E. Reichmann, S.A. Rice, C.A. Thomas, P.J. Doty, J. Am. Chem. Soc. 76 (1954)
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif. Supplementary data associated with
this article can be found, in the online version, at doi:10.1016/
j.ica.2010.11.012.
3047.
[26] J.K. Barton, J.M. Goldberg, C.V. Kumar, N.J. Turro, J. Am. Chem. Soc. 108 (1986)
2081.
[27] M.A.S. Goher, Ru-Ji Wang, T.C.W. Mak, J. Crystallogr. Spectrosc. Res. 20 (1990)
265.
References
ˇ
[28] C.G. Efthymiou, C.P. Raptopoulou, A. Terzis, R. Boca, M. Korabic, J. Mrozinski,
[1] W. Kaim, A. Klein, M. Glöckle, Acc. Chem. Res. 33 (2000) 755.
[2] K.D. Demandis, C.M. Hartshorn, T.J. Meyer, Chem. Rev. 101 (2001) 2655.
[3] W.R. Browne, R. Hage, J.G. Vos, Coord. Chem. Rev. 250 (2006) 1653.
[4] W. Kaim, B. Sarkar, Coord. Chem. Rev. 251 (2007) 584.
[5] E.I. Solomon, T.C. Brunold, M.I. Davis, J.N. Kemsley, S.K. Lee, N. Lehnert, F.
Neese, A.J. Skulan, Y.S. Yang, J. Zhou, Chem. Rev. 100 (2000) 235.
[6] B.S. Brunschwig, N. Sutin, Coord. Chem. Rev. 187 (1999) 33.
[7] F. Paul, C. Lapinte, Coord. Chem. Rev. 431 (1998) 178.
[8] A. Bencini, I. Ciofini, C.A. Daul, A. Ferretti, J. Am. Chem. Soc. 121 (1999) 11418.
[9] M.D. Ward, Chem. Ind. (1997) 640.
S.P. Perlepes, E.G. Bakalbassis, Eur. J. Inorg. Chem. (2006) 2236.
[29] S.-L. Wang, J.W. Richardson Jr., S.J. Briggs, R.A. Jacobson, W.P. Jensen, Inorg.
Chim. Acta 111 (1986) 67.
[30] D.R. Turner, S.R. Batten, Cryst. Eng. Commun. 10 (2008) 170.
[31] S.R. Breeze, S. Wang, J.E. Greedan, N.P. Raju, Inorg. Chem. 35 (1996) 6944.
[32] T.C. Stamatatos, V. Tangoulis, C.P. Raptopoulou, A. Terzis, G.S. Papaefstathiou,
S.P. Perlepes, Inorg. Chem. 47 (2008) 7969.
[33] S. Yamanaka, H. Okawa, K. Motoda, M. Yonemura, D.E. Fenton, M. Ebadi, A.B.P.
Lever, Inorg. Chem. 38 (1999) 1825.
[34] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Part B: Applications in Coordination, Organometallic, and
[10] N.A. Rey, A. Neves, A. Bortoluzzi, C.T. Pich, H. Terenzi, Inorg. Chem. 46 (2007)
348.
Bioinorganic Chemistry, fifth ed.,
A Wiley-Interscience Publication, John
[11] P. Gentschev, N. Moller, B. Krebs, Inorg. Chim. Acta 300 (2000) 442.
[12] D. Koushik, J. Ratha, M. Manassero, X.-Y. Wang, S. Gao, P. Banerjee, J. Inorg.
Biochem. 101 (2007) 95.
Wiley and Sons Inc., New York, 1997.
[35] P.K. Dhara, S. Pramanik, T.-H. Lu, M.G.B. Drew, P. Chattopadhyay, Polyhedron
24 (2004) 2357.
[13] E.L. Hegg, J.N. Burstyn, Inorg. Chem. 35 (1996) 7474.
[14] E.L. Hegg, K.A. Deal, L.L. Kiessling, J.N. Burstyn, Inorg. Chem. 36 (1997) 1715.
[15] Y.G. Fang, J. Zhang, S.Y. Chen, N. Jiang, H.H. Lin, Y. Zhang, X.-Q. Yu, Bioorg. Med.
Chem. 15 (2007) 696.
[36] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed., Elsevier,
Amsterdam, 1984.
[37] R. Vijayalakshmi, M. Kanthimathi, V. Subramanian, B.U. Nair, Biochem.
Biophys. Acta 157 (2000) 1475.
[16] M.C.B. Oliveira, M.S.R. Couto, P.C. Severino, T. Foppa, G.T.S. Martins, B.
Szpoganicz, R.A. Peralta, A. Neves, H. Terenzi, Polyhedron 24 (2005) 495.
[17] O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993.
[18] X-Area V1.35 and X-RED32 V1.31 Software, Stoe and Cie GmbH, Darmstadt,
Germany, Stoe and Cie, 2006.
[19] Z. Otwinowski, W. Minor, Processing of X-ray diffraction data collected in
oscillation mode, methods in enzymology, in: C.W. Carter Jr., R.M. Sweet (Eds.),
Macromolecular Crystallography, Part A, vol. 276, Academic Press, New York,
1997, p. 307.
[38] L. Strekowski, B. Wilson, Mutat. Res. 3 (2007) 623.
[39] A. Wolfe, G.H. Shimer, T. Meehan, Biochemistry 26 (1987) 6392.
[40] L. Strekowski, D.B. Harden, R.L. Wydra, K.D. Stewart, W.D. Wilson, J. Mol.
Recognit. 2 (1989) 158.
[41] R. Indumathy, S. Radhika, M. Kanthimathi, T. Weyhermuller, B.U. Nair, J. Inorg.
Biochem. 101 (2007) 434.
[42] D.L. Boger, B.E. Fink, S.R. Brunette, W.C. Tse, M.P. Hedrick, J. Am. Chem. Soc. 123
(2001) 5878.
[43] O. Stern, M. Volmer, Z. Phys. 20 (1919) 183.
[44] L. Merz, W. Haase, Dalton Trans. (1980) 875.
[45] M. Handa, N. Koga, S. Kida, Bull. Chem. Soc. Jpn. 61 (1988) 3853.
[20] CrysAlis, v32.24 Oxford Diffraction, 2008.
[21] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
[22] G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112.