Structure and spectral characterisation of copper(II) meclofenamate complexes

Article abstract of DOI:10.1016/j.poly.2008.08.017

The synthesis and characterisation of Cu(meclof)₂H₂O and Cu(meclof)₂L₂ (meclof = meclofenamate; L = 2-pyridylcarbinol (2-pyca), 3-pyridylcarbinol (3-pyca), nicotinamide (na), N,N-diethylnicotinamide (dena) are reported. The characterisation of the compounds were based on elemental analyses, electronic, IR and EPR spectra. The carboxyl group of the meclofenamate anions coordinates to the Cu(II) atom as an unidentate or as a chelating ligand. The crystal and molecular structures of one of the products, namely Cu(meclof)₂(2-pyca)₂ were measured. The EPR spectra of the studied complexes show they are monomeric, except for Cu(meclof)₂ · H₂O which shows triplet state feature. On the basis of the spectroscopic parameters observed, a monomeric structure with a tetragonally Jahn-Teller distorted octahedron around the Cu(II) atom is deduced for Cu(meclof)₂L₂ and for Cu(meclof)₂ · H₂O a dimeric structure is proposed. The degree of distortion in the series of the Cu(meclof)₂L₂ complexes increases in the order of L: na < 2-pyca < 3-pyca < dena.

Full text of DOI:10.1016/j.poly.2008.08.017

Polyhedron 27 (2008) 3545–3548
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structure and spectral characterisation of copper(II) meclofenamate complexes
*
Štefan Lörinc, Jozef Švorec, Milan Melník, Marian Koman
Department of Inorganic Chemistry, Slovak Technical University, Radlinského 9, SK-812 37 Bratislava, Slovak Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and characterisation of Cu(meclof)2H2O and Cu(meclof)2L2 (meclof = meclofenamate; L = 2-
pyridylcarbinol (2-pyca), 3-pyridylcarbinol (3-pyca), nicotinamide (na), N,N-diethylnicotinamide (dena)
are reported. The characterisation of the compounds were based on elemental analyses, electronic, IR
and EPR spectra. The carboxyl group of the meclofenamate anions coordinates to the Cu(II) atom as an
unidentate or as a chelating ligand. The crystal and molecular structures of one of the products, namely
Cu(meclof)2(2-pyca)2 were measured. The EPR spectra of the studied complexes show they are mono-
meric, except for Cu(meclof)2 ꢀ H2O which shows triplet state feature. On the basis of the spectroscopic
parameters observed, a monomeric structure with a tetragonally Jahn–Teller distorted octahedron
around the Cu(II) atom is deduced for Cu(meclof)2L2 and for Cu(meclof)2 ꢀ H2O a dimeric structure is pro-
posed. The degree of distortion in the series of the Cu(meclof)2L2 complexes increases in the order of L:
na < 2-pyca < 3-pyca < dena.
Received 29 April 2008
Accepted 18 August 2008
Available online 4 October 2008
Keywords:
Copper(II)
Meclofenamate
Structure
Spectra
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental
The chemistry of copper complexes has been extensively inves-
tigated and the relationship between the structure and reactivity,
ranging from industrial catalysis to biomedical activity, is of major
importance. Meclofenamic acid (N-(2,6-dichloro-3-methylphenyl)
anthranilic acid) and some similar derivatives of N-phenylanthra-
nilic acid are biologically active substances. This compound group
is called fenamates and some of its members are used as non-ste-
roidal anti-inflammatory drugs. The activity of this drug type is of-
ten enhanced if they are used in the form of their copper(II)
complexes [1]. It is known that some drugs act via chelating or
via inhibition of metalloenzymes, but little is known about the
modification of the activities of most drugs that are potential
ligands.
In this paper, we report as a part of our investigation of metal
ion–drug interactions the complexation of meclofenamate in the
presence of water, 2-pyridylcarbinol (2-pyca), 3-pyridylcarbinol
(3-pyca), nicotinamide (na) and N,N-diethylnicotinamide (dena).
The crystal and molecular structures of one of the complexes,
namely Cu(meclof)2(2-pyca)2, has been solved. Based on the
molecular structure, the electronic, infrared and EPR data are dis-
cussed, and the stereochemistry as well as the mode for ligand
coordination in the five new solid complexes have been
determined.
2.1. Chemical reagents, analysis and physical measurements
All the chemicals used were of reagent grade (Aldrich or Sigma)
and were used without further purification. The copper content
was determined by electrolysis after mineralisation of the com-
plexes; carbon, hydrogen and nitrogen were determined by micro-
analytical methods (Carlo Erba Instruments EA 1180). Electronic
spectra of the powdered samples in Nujol mulls were recorded at
room temperature (r.t.) with a Specord 200. IR spectra in the region
of 400–4000 cmꢁ1 were recorded on a Magna 750 spectrometer at
r.t. Spectra of the solid samples were obtained in Nujol mulls and
KBr pellets (1 wt%).
The EPR spectra were measured using either a Bruker ER 200E
SRC with an internal marker for the determining the frequency
or a Bruker EMX series with an ER 035 NMR gaussmeter and a Sys-
tem Donner EMX frequency counter. The spectrum of Cu(tolf)2(de-
na)2(H2O)2 was simulated using the shareware program Simfonia
developed by Bruker. The EPR spectra were measured in the poly-
crystalline form at r.t.
2.2. Crystallography
Intensity data for Cu(meclof)2(2-pyca)2 were collected using a
Siemens P4 diffractometer with graphite monochromated Mo K
a
radiation at 293 K [2]. The diffraction intensities were corrected
for Lorentz and polarization effects [3]. Absorption corrections
were applied using the program XEMP [4]. The structures were
solved by direct methods using the program SHELXS-97 and refined
* Corresponding author.
E-mail address: marian.koman@stuba.sk (M. Koman).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.08.017

3546
Š. Lörinc et al. / Polyhedron 27 (2008) 3545–3548
by the full-matrix least-squares method on all F2 data using the
program SHELXL-97 [5]. Geometrical analysis was performed using
SHELXL-97. The structures were drawn by ORTEP-3 for Windows.
The single crystal suite WINGX was used as an integrated system
for all crystallographic programs and software for preparing the
material for publication [6]. Crystal data and conditions of data col-
lection and refinement are reported in Table 1.
Cu(meclof)2(na)2: Calc. for C40H32N6O6Cl4Cu: C, 53.50; H, 3.59;
N, 9.36; Cu, 7.08. Found: C, 51.59; H, 4.07; N, 9.45; Cu, 7.14%.
UV–Vis spectrum: 640 nm (band I) and 330 nm (band II).
Cu(meclof)2(dena)2(H2O)2: Calc. for C48H52N6O8Cl4Cu: C, 55.10;
H, 5.01; N, 8.03; Cu, 6.07. Found: C, 53.95; H, 5.17; N, 8.19; Cu,
6.08%. UV–Vis spectrum: 605 nm (band I) and 325 nm (band II).
3. Results and discussion
2.3. Preparation of the complexes
An ORTEP plot of Cu(meclof)2(2-pyca)2 is shown in Fig. 1, and
selected bond distances and angles are given in Table 2. In the
structure of the complex, the Cu(II) atom is six-coordinated and
the coordination polyhedron can be described as a tetragonally dis-
torted octahedron. Two equatorial positions are occupied by two
oxygen atoms [Cu1–O1 1.968(3) Å] from the carboxyl groups of
two meclofenamate anions, which are coordinated to the central
atom in an unidentate manner. Two heterobidentate (O, N) 2-pyr-
idylcarbinol ligands, which span the equatorial plane [Cu1–N1
2.021(5) Å] and the axial positions [Cu1–O3 2.387(4) Å], complete
the distorted tetragonal bipyramidal arrangement. The value of the
2.3.1. Cu(meclof)2H2O
To an aqueous solution of copper(II) sulfate (5 mmol), an aque-
ous solution of meclofenamate and an equimolar quantity of so-
dium hydroxide (10 mmol) were added, and the reaction mixture
was refluxed for 30 min. The blue green precipitate that formed
was filtered off and dried at ambient temperature.
Elemental Anal. Calc. for C28H22N2O5Cl4Cu: C, 50.06; H, 3.30; N,
4.17; Cu, 9.46. Found: C, 49.84; H, 3.32; N, 4.68; Cu, 9.48%. UV–Vis
spectrum: 675 nm (band I) and 375 nm (band II).
Cu(meclof)2L2 (L = 2-pyridylcarbinol (2-pyca), 3-pyridylcarbinol
(3-pyca), nicotinamide (na) and N,N-diethylnicotinamide (dena)).
A solution of L (10 mmol) in methanol (20 ml) was added to a
solution of Cu(meclof)2H2O (5 mmol) in methanol (50 ml). The
resulting solution was heated and left to stand at ambient temper-
ature. The blue precipitate that formed was collected by filtration,
washed with cold methanol and finally dried at ambient tempera-
ture (the yield of the complexes was ꢂ70%).
angle which is part of the five-membered metallocycles (N1(eq)
Cu1–O3(ax)) of 76.8(2)°) is about 7.87° smaller than those of
(O1(eq)–Cu1–O3(ax)) 84.67(14)°. However, the (N1(eq)–Cu1–O3(ax)
–
)
angle from the cis-angles is the most open, with a value of
103.2(2)°. All the trans L–Cu–L angles are linear (180.0°).
The structural chemistry for over 600 coordinated monomeric
copper(II) compounds has been reviewed by us [7]. From the three
principal forms of distortion of the octahedron, all of which occur
in the chemistry of Cu(II) to varying degrees, the tetragonal distor-
Elemental Anal. Cu(meclof)2(2-pyca)2: Calc. for C40H34N4O6Cl4-
Cu(%): C, 55.09; H, 3.93; N, 6.42; Cu, 7.29. Found: C, 54.32; H,
4.11; N, 6.67; Cu, 7.31%. UV–Vis spectrum: 615 nm (band I) and
330 nm (band II).
Cu(meclof)2(3-pyca)2: Calc. for C40H34N4O6Cl4Cu: C, 55.09; H,
3.93; N, 6.42; Cu, 7.29. Found: C, 54.76; H, 4.03; N, 6.65; Cu,
7.35%. UV–Vis spectrum: 615 nm (band I) and 330 nm (band II).
Table 1
Crystal data and structure refinement for the complex Cu(meclof)2(2-pyca)2
Internal index
Compound
mk16
[Cu2(meclof)2(2-pyca)2]
C40H34O6N4Cl4Cu
872.05
0.71073
monoclinic, C2/c
Empirical formula
Formula weight
Wavelength (Å)
Crystal system, space group
Unit cell dimensions
a (Å)
10.723(1)
b (Å)
15.333(1)
c (Å)
18.721(2)
a
(°)
90
b (°)
108.434(6)
c
(°)
90
3978.2(8)
4, 1.456
Volume (Å3)
Z, Dcalc (Mg mꢁ3
)
Absorption coefficient (mmꢁ1), F(000)
Crystal size (mm)
1.100, 1452
0.126 ꢃ 0.26 ꢃ 0.52
2.48–25.23
ꢁ1 6 h 6 40,
ꢁ1 6 k 6 11,
ꢁ24 6 l 6 22
4238/3479 (0.0481)
96.8
h Range for data collection (°)
Limiting indices
Reflections collected/unique (Rint
Completeness to h = 25.23 (%)
Absorption correction
)
psi-scan
Refinement method
full-matrix least-squares on F2
5720/84/236
0.903
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0706, wR2 = 0.1465
R = 0.1723, wR2 = 0.1780
0.624 and ꢁ0.282
685931
Largest difference in peak and hole (e Åꢁ3
CCDC
)
Fig. 1. ORTEP-plot of Cu(meclof)2(2-pyca)2. Thermal ellipsoids are drawn at the 30%
probability level.

Š. Lörinc et al. / Polyhedron 27 (2008) 3545–3548
3547
Table 2
Selected distances (Å) and angles (°) for complex the Cu(meclof)2(2-pyca)2
Table 4
IR-data (cmꢁ1
)
Cu1–O1
Cu1–N1
Cu1–O3
O1–C1
O2–C1
C1–C2
1.973(3)
2.018(5)
2.386(4)
1.278(6)
1.245(7)
1.467(8)
1.438(7)
1.329(7)
O1–Cu1–O3
O1–Cu1–N1
N1–Cu1–O3
Cu1–O3–C14
O3–C14–C15
C14–C15–N1
C15–N1–Cu1
Cu1–O1–C1
O1–C1–O2
84.89(2)
89.62()
L
Carboxylic groups
Dv
Vas(COOꢁ)
Vs(COOꢁ)
76.89(2)
103.7(4)
115.7(6)
117.4(6)
120.1(4)
127.2(4)
123.9(5)
dena
3-pyca
2-pyca
na
1624, 1613
1612
1609
1457, 1426
1448
1364
ꢂ177
164
245
1615
1427
188
O3–C14
N1–C15
Table 5
Electronic spectra (nm)
tion most commonly involves an elongation of one C4 axis. There
are some examples of the general formula CuX2(2-pyca)2
(X = mefanamate, clofibriate, salicylate, 2-bromopropionate and
meclofenamate) and selected data of these complexes are given
in Table 3. The value of the T (T = RS/RL) parameter for CuX2(2-
pyca)2, indicating the degree of the tetragonal distortion about
the Cu(II) centers, decreases in the order: X = salicylate
0.850 > meclofenamate 0.835 > clofibriate 0.832 > 2-bromopropio-
nate 0.829 > mefanamate 0.819.
L
Band I
Band II
325
dena
3-pyca
2-pyca
na
605
615
615
640
330
330
The EPR spectrum of a powdered sample of Cu(meclof)2 ꢀ H2O
was made at room temperature. The spectrum exhibit feature typ-
ical of those for dimeric carboxylate copper(II) complexes [16],
absorption at low and high field (HZ1 ꢂ 300 G and HZ2 ꢂ 6000 G,
respectively) and line H\2 ꢂ about 4700 G. Absorption at about
3200 G (g = 2100) confirms monomeric impurities in measured
powered sample of ꢂ2.6%. The EPR spectrum was interpreted by
using the effective spin Hamiltonian [17] for a randomly oriented
triplet state, S = 1:
The IR spectrum of Cu(meclof)2H2O shows two absorption
bands at 3308 and 3248 cmꢁ1. These bands correspond to the anti-
symmetric and symmetric OH stretch and confirm the presence of
water in the complex. Moreover, the IR spectrum exhibits charac-
teristic bands at approximately 850 and 550 cmꢁ1 assigned to the
rocking and wagging mode of the coordinated water molecule [12].
Each complex showed carboxylate stretching frequencies,
Vas(COOꢁ) and Vs(COOꢁ), which are in the expected region (Table
4). The broad bands at about 1610 cmꢁ1 (assigned to the asymmet-
ric stretch Vas(COOꢁ)) are overlapped with the stretching vibration
of C@N of the pyridine ring. The difference between the asymmet-
ꢀ
ꢀ2
ꢀ2 ꢀ2
H ¼ gbHS þ DSz þ EðSx ꢁ Sy Þ ꢁ 2=3 ꢀ D
where D and E are the axial and rhombic zero-field splitting param-
eters, and x, y, z are the principal axes of a coordinated system fixed
with respect to the Cu–Cu bond. The obtained parameters are
ric and symmetric stretching vibration
(
D
v = Vas(COOꢁ) ꢁ
Vs(COOꢁ)) (Table 4), which gives information on the carboxylate
bonding mode, especially for Cu(meclof)2 ꢀ H2O, could not be deter-
mined accurately. However, splitting of the bands assigned to
Vs(COOꢁ) indicates that the meclofenamate anion as a ligand in
Cu(meclof)2 ꢀ H2O is coordinated as a bidentate bridging carboxyl
group (see electronic and EPR spectra). The difference
g\ = 2.090,
g|| = 2.397,
.
gav = 2.192,
|D| = 0.331 cmꢁ1
and
E = 0.003 cmꢁ1
The EPR spectra of all the remainding complexes exhibit a
monomeric type of signal and have either axial (complexes
Cu(meclof)2 ꢀ L2, L = 2-pyca, 3-pyca and na) or rhombic symmetry
(Cu(meclof)2dena2) with g\ < g||. This indicates that the unpaired
D
v = 245 cmꢁ1 for Cu(meclof)2 ꢀ (2-pyca)2 is typical for a uniden-
tately bonded carboxylic group of meclofenamate (see the crystal
structure). The smaller
electron is located mostly on the dx2
orbital of the copper(II)
ꢁy2
D
values from 164 to 188 cmꢁ1 for the com-
atom. The values of the g factors are summarized in Table 6. Com-
plexes Cu(meclof)2 ꢀ L2 (L = 3-pyca and dena) also exhibit well-re-
solved parallel hyperfine splitting with A|| values of 166 and
157 G, respectively.
plexes Cu(meclof)2 ꢀ L2 (L = 3-pyca, na, dena) indicate that the mec-
lofenamate anions are coordinated as asymmetrically bidentate
chelating carboxylic groups.
The electronic spectrum of Cu(meclof)2 ꢀ H2O shows a broad
On the basis of the spectral data observed, a dimeric structure
for Cu(meclof)2 ꢀ H2O can be proposed, in which two copper(II)
atoms are held together by four bidentate meclofenamate anions
in a syn–syn arrangement. Each Cu(II) atom is penta-coordinated
with four oxygen atoms of four different meclofenamate anions
assuming the basal positions in a tetragonal pyramidal arrange-
ment and molecule water occupying an apical position.
For Cu(meclof)2 ꢀ L2 (L = 3-pyca, na and dena) we proposed, on
the basis of the spectroscopic data observed, a monomeric struc-
ture with a tetragonal bipyramidal geometry around the Cu(II)
atom. We propose that meclofenamate use both carboxylate
absorption band (band I) in the visible region at 675 nm, which
could be assigned to the dxz;yz ! dx2 transition [13]. Moreover,
y2
the spectrum displays a shoulder at 375 nm (band II). Band II has
been assigned to a charge transfer LMCT absorption [14] and is be-
lieved to be indicative of a dimeric structure [15]. The electronic
spectra of all the remaining Cu(meclof)2 ꢀ L2 complexes exhibit a
broad asymmetrical ligand field band with a maximum in the
range 605–610 nm (Table 5). For complexes Cu(meclof)2 ꢀ L2
(L = 3-pyca, na and dena) there is also a charge transfer band at
about 330 nm.
Table 3
Selected lengths (Å) and angles (°) for the CuX2(2-pyca)2 complexes
Mefanamate [8]
Clofibriate [9]
Salicylate [10]
2-Bromopropionate [11]
Meclofenamate, this work
Cu–Oeq
Cu–Neq
Cu–Oax
Neq–Cu–Oax
Neq–Cu–Oax
1.966(2)
1.990(3)
2.415(3)
75.82(1)
96.26(9)
1.997(2)
1.978(2)
2.388(2)
76.83(7)
94.19(6)
1.981(1)
1.981(1)
2.331(2)
77.62(7)
95.13(5)
2.003(2)
1.984(2)
2.404(2)
76.97(7)
96.15(7)
1.968(3)
2.021(5)
2.387(4)
76.79(2)
90.38(3)

3548
Š. Lörinc et al. / Polyhedron 27 (2008) 3545–3548
Table 6
EPR-data
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2008.08.017.
L
g\
g||
gav
g1
g2
dena
3-pyca
2-pyca
na
2.029
2.066
2.303
2.178
2.290
2.301
3.133
2.137
2.142
2.154
2.066
2.068
2.080
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[3] Siemens, Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA,
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bipyramid. The mean g-values of the complexes (Table 6) slightly
decrease in the order: 2.154 (L = na) > 2.142 (2-pyca) > 2.137 (3-
pyca) > 2.133 (dena), which seems to be associated with a lowering
of the symmetry of coordination geometry in the given order.
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[9] J. Moncol, B. Kalinaková, J. Švorec, M. Kleinová, M. Koman, D. Hudecová, M.
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Appendix A. Supplementary data
ˇ
ˇ ˇ
CCDC 685931 contains supplementary crystallographic data for
Cu(meclof)2(2-pyca)2. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
[17] A. Abragan, B. Bleaney, Electron Paramagnetic Resonance of Transition Ions,
Clarendon Press, Oxford, 1971.