Synthesis, spectral and magnetic properties of two different 2-nitrobenzoatocopper(II) complexes containing N,N-diethylnicotinamide

Article abstract of DOI:10.1016/j.poly.2007.12.030

Two structurally different complexes, [Cu₂(2-NO₂Bz)₄(denia)₁]_n (1) and [Cu(2-NO₂Bz)₂(denia)₂(H₂O)₂] (2), were prepared from the same reaction (where 2-NO₂Bz = 2-nitrobenzoate, denia = N,N-diethylnicotinamide) and they are reported together with [Cu₂(2-NO₂Bz)₄(DMF)₂] (3) (DMF = N,N-dimethylformamide). The compounds under study were characterized by elemental analysis, electronic, IR and EPR spectra, magnetic measurements over the temperature range of 1.8-300 K and X-ray analysis. The molecular structure of (1) is polymeric, (2) is monomeric and (3) is dimeric. In the polymeric chain of (1), the denia molecules serve as bridges between dimeric Cu₂(2-NO₂bz)₄ units. Each Cu(II) atom has a square-pyramidal arrangement with different chromophores, Cu¹O₄O′ and Cu²O₄N. The Cu-Cu distances are 2.699(1) ? in the dimeric unit and 7.980(3) ? between the dimeric units. In (2) the Cu(II) atom has a tetragonal-bipyramidal environment CuO₂N₂O′₂. In (3) two Cu(II) atoms are bridged by four carboxylate groups of four 2-NO₂bz anions in a syn-syn arrangement which create a square base about each Cu(II) atom and an apical position is occupied by the O atom of a DMF molecule (CuO₄O′). The Cu-Cu distance of 2.633(1) ? is somewhat shorter than in (1). Spectral and magnetic data of the complexes are discussed with their structures.

Full text of DOI:10.1016/j.poly.2007.12.030

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 1333–1342
www.elsevier.com/locate/poly
Synthesis, spectral and magnetic properties of two different
2-nitrobenzoatocopper(II) complexes containing
N,N-diethylnicotinamide
a
b
a
a
c
b
J. Kavalırova , M. Korabik , P. Stachova , J. Moncol , R. Sillanpaa , T. Lis , D. Miklos ,
ˇ a
´
´
´
¨ ¨
a
b
a,
*
´
´
M. Melnık , J. Mrozinski , D. Valigura
a Department of Inorganic Chemistry, Slovak Technical University, Radlinske´ho 9, 812 37 Bratislava, Slovakia
b Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland
c Department of Chemistry, University of Jyva¨skyla¨, 40351 Jyva¨skyla¨, Finland
Received 16 November 2007; accepted 24 December 2007
Available online 4 March 2008
Abstract
Two structurally different complexes, [Cu2(2-NO2Bz)4(denia)1]n (1) and [Cu(2-NO2Bz)2(denia)2(H2O)2] (2), were prepared from the
same reaction (where 2-NO2Bz = 2-nitrobenzoate, denia = N,N-diethylnicotinamide) and they are reported together with [Cu2(2-
NO2Bz)4(DMF)2] (3) (DMF = N,N-dimethylformamide). The compounds under study were characterized by elemental analysis, elec-
tronic, IR and EPR spectra, magnetic measurements over the temperature range of 1.8–300 K and X-ray analysis. The molecular struc-
ture of (1) is polymeric, (2) is monomeric and (3) is dimeric. In the polymeric chain of (1), the denia molecules serve as bridges between
dimeric Cu2(2-NO2bz)4 units. Each Cu(II) atom has a square-pyramidal arrangement with different chromophores, Cu1O4O0 and
2
˚
˚
Cu O4N. The Cu–Cu distances are 2.699(1) A in the dimeric unit and 7.980(3) A between the dimeric units. In (2) the Cu(II) atom
has a tetragonal-bipyramidal environment CuO2N2O02. In (3) two Cu(II) atoms are bridged by four carboxylate groups of four 2-NO2bz
anions in a syn–syn arrangement which create a square base about each Cu(II) atom and an apical position is occupied by the O atom of
0
˚
a DMF molecule (CuO4O ). The Cu–Cu distance of 2.633(1) A is somewhat shorter than in (1). Spectral and magnetic data of the com-
plexes are discussed with their structures.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Copper(II); Carboxylate; 2-Nitrobenzoate; Crystal structure; Spectra; Magnetism
1. Introduction
atom and the other possible donor atoms for coordination
bonds are less preferred. This preferential bonding can be
seen on the basis of structural data found in the CSD data-
base [4]. There are 43 structures of metal complexes con-
taining the denia moiety bonded to a metal atom via the
pyridine nitrogen donor atom and only seven of those
structures contain denia as a bridging ligand bonded to
the metal atom by carbonyl oxygen donor atoms too. There
is no example with the amide nitrogen atom involved in
coordination. The monodentate bonding mode of the denia
ligand is even more dominant for carboxylatocopper(II)
complexes and there are two main stoichiometries within
this group of complexes with the denia ligand. The 1:1
N,N-Diethylnicotinamide (denia) [1] is an important
respiratory stimulant. It is metabolized rapidly to nicotin-
amide, one of metabolite of vitamin B3 – niacin. Denia is
a toxic agent, but coordinated in the form of complexes it
shows different biological activity [2,3]. The coordination
of the denia ligand occurs via the pyridine ring nitrogen
*
Corresponding author. Tel.: +421 2 593 25 726; fax: +421 2 524 93
198.
E-mail address: dusan.valigura@stuba.sk (D. Valigura).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.12.030

1334
J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
stoichiometry is found for the acetate type [Cu2(RCOO)4-
(denia)2] dimeric complexes [3–7]. The 1:2 stoichiometry
can be found in monomeric complexes of Cu(RCOO)2-
(denia)2(H2O)x, where x = 0, [8–10], x = 2 [11–15], x = 4
[16] or in Cu(RCOO)2(denia)2(CH3OH) [17], and in all those
complexes the denia molecules are unidentate N donor
ligands. Recently the first polymeric complex with bridging
denia molecules, of the composition [Cu2(ClCH2COO)4-
(denia)1]n, has been structurally characterized [18]. In this
paper we report on the preparation, spectral and magnetic
properties, and X-ray structures of two new copper(II)
complexes containing the denia ligand – one is a polymeric
complex of an unusual stoichiometry containing denia
bridges, [Cu2(2-NO2Bz)4(denia)1]n (1), and its molecular
counterpart with the same 2-nitrobenzoato-ligand showing
the usual and most frequent stoichiometry, [Cu(2-NO2Bz)2-
(denia)2(H2O)2] (2), together with the complex [Cu2-
(2-NO2Bz)4(DMF)2] (3), that was obtained as a byproduct
by recrystallization of (1) using dimethylformamide solvent.
2.1.3. Preparation of[Cu2(2-NO2Bz)4(DMF)2] (3)
Crystals for X-ray structure determination were obtained
by recrystallization of (1) from dimethylformamide.
Calc. for C34H30N6O18Cu2: Cu, 13.22; C, 44.96; H, 3.14;
N, 8.74. Found: Cu, 13.00; C, 44.90; H, 3.20; N, 8.95%.
2.2. Analytical measurements
Carbon, hydrogen and nitrogen analysis were carried
out on a CHNSO FlashEA 1112 (ThermoFinnigan) ele-
mental analyzer. Copper was determined by electrolysis
of a water solution obtained by sample mineralization
with a mixture of sulfuric acid and potassium peroxodi-
sulfate.
2.3. Physical measurements
Electronic spectra (190–1100 nm) of the complexes were
measured in Nujol suspensions with a SPECORD 200
(Carl Zeiss Jena) spectrophotometer, and infrared spectra
in the region 4000–100 cmꢀ1 were measured with a Nicolet
MAGNA 750 IR spectrometer using both KBr pellet and
Nujol suspension techniques for the 4000–400 cmꢀ1 region
and polyethylene pellets for the 400–100 cmꢀ1 region.
EPR spectra of powdered samples were recorded at
room temperature and at 77 K, on a Bruker ESP 300 spec-
trometer, operating at the X-band and equipped with an
ER 035M Bruker NMR gaussmeter and a HP 5350B Hew-
lett Packard microwave frequency counter.
Data collection and cell refinement of complex (1) were
carried out using a Siemens P4 diffractometer [19], data
for complex (2) were collected using a Nonius kappaCCD
diffractometer [20], and for complex (3) using an Xcalibur
PX kappa-geometry diffractometer with a CCD Onyx
camera with graphite monochromated Mo Ka radiation,
using the CRYSALIS software package [21]. Intensity data
were corrected for Lorenz and polarization factors and
absorption corrections of (1) were made [22]. The struc-
tures were solved by the direct atom method with SHEL-
XS-97 [23], and refined by the full-matrix least squares
procedure with SHELXL-97 [24]. Geometrical analyses were
performed using SHELXL-97 [24] and the structures were
drawn using the ORTEP-3 for Windows program [25]. Final
crystal data and structure refinement parameters are given
in Table 1.
2. Experimental
2.1. Synthesis
Both complexes (1) and (2) could be obtained from the
same reaction mixture at different temperatures.
2.1.1. Preparation of [Cu2(2-NO2Bz)4(denia)1]n (1)
An ethanolic solution of copper(II) acetate (1 mmol in
cca 20 mL of ethanol) was stirred with N,N-diethylnicoti-
namide (2 mmol), then 2-nitrobenzoic acid (2 mmol) was
added and the reaction mixture was stirred until the precip-
itation of the green product finished (about 20 min). The
microcrystalline green product (1) was filtered off, washed
with a small portion of ethanol and dried at ambient tem-
perature. The light blue mother liquid obtained after filtra-
tion was left for crystallization. Blue crystals of complex (2)
were obtained from mother liquid. Crystals of (1) suitable
for X-ray structure determination were obtained by recrys-
tallization of (1) from an ethanolic solution.
Calc. for C38H30N6O17Cu2 Cu, 13.10; C, 47.06; H, 3.12;
N, 8.67. Found: Cu, 13.37; C, 46.86; H, 3.21; N, 9.41%.
2.1.2. Preparation of[Cu(2-NO2Bz)2(denia)2(H2O)2] (2)
An ethanolic solution of copper(II) acetate (1 mmol in
cca 20 mL of ethanol) was stirred with N,N-diethylnico-
tinamide (2 mmol), then 2-nitrobenzoic acid (2 mmol)
was added and the reaction mixture was stirred under
heating until the green microcrystalline solid dissolved
and a dark blue solution was obtained. The obtained
solution was left to stand for slow crystallization and
the obtained blue crystalline product (including crystals
suitable for X-ray structure determination) was filtered
off, washed with a small amount of ethanol and dried
at ambient temperature.
Magnetization measurements of all the samples in the
temperature range 1.8–300 K were carried out on pow-
dered samples of the complexes, at a magnetic field of
5 kG, using a Quantum Design SQUID Magnetometer
(type MPMS-XL5). Corrections for diamagnetism of the
constituent atoms were calculated using Pascal constants
[26], the value of 60 ꢁ 10ꢀ6 cm3 molꢀ1 was used as the tem-
perature-independent paramagnetism of the Cu2+ ion. The
effective magnetic moments were calculated from the
expression:
Calc. for C34H44N6O12Cu: Cu, 8.06; C, 51.81; H, 5.12;
N, 10.66. Found: Cu, 8.82; C, 51.99; H, 5.24; N, 11.71%.
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
leff ¼ 2:83 vcmorr ꢂ T ðB:M:Þ

J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
1335
Table 1
Crystal data and structure refinement for complexes 1, 2 and 3
3. Results and discussion
1
2
3
3.1. Complex preparation
Chemical
formula
Mr
C38H30Cu2N6O17 C34H40CuN6O12 C34H30Cu2N6O18
The present study of N,N-diethylnicotinamidecopper(II)
complexes with 2-nitrobenzoate anions is based on a
knowledge that the 2-nitrobenzoate anion in comparison
to other isomeric nitrobenzoate anions exhibits variable
bonding modes, due to the presence of a nitro-substituent
in the ortho-position. The formation of a dimeric complex,
[Cu2(2-NO2bz)4(H2O)2] ꢂ 2H2O, has been observed [27]. On
the other hand, [Cu(2-NO2bz)2(3-pyme)2(H2O)2] (where 3-
pyme=3-pyridylmethanol) is the first complex with the 3-
pyme ligand that exhibits a molecular monomeric structure
[28], while all other carboxylatocopper(II) complexes with
the 3-pyme ligand have a polymeric structure with 3-pyme
as a bridging ligand. A monomeric structure was also
observed in the [Cu(2-NO2bz)2(nia)2(H2O)2] complex [29].
However, the reaction conditions (solvent used, stoichiom-
etry and temperature) can play a significant role in such
syntheses, and therefore we performed the syntheses under
different conditions. The reactions done in water solutions
gave [Cu2(2-NO2Bz)4(denia)1]n (1) only at lower cop-
per(II):denia molar ratios (1:0.5 or 1:1), whilst with cop-
per(II):denia ratios higher than 1:1 blue solutions were
obtained and blue crystals of [Cu(2-NO2Bz)2(de-
nia)2(H2O)2] (2) crystallized after solvent evaporation. Less
polar solvents that shift equilibria towards dimeric species
969.76
788.26
937.72
Crystal system monoclinic
Space group
monoclinic
P21/n
monoclinic
P21/n
P21/n
T (K)
298(2)
173(2)
100(2)
˚
a (A)
10.685(3)
21.913(5)
17.094(4)
92.25(2)
3999.3(17)
4
12.5476(2)
10.7613(2)
14.5198(3)
110.972(1)
1830.71(6)
2
10.196(3)
10.562(3)
17.638(5)
95.86(3)
1889.5(9)
2
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
Z
Dx (Mg mꢀ3
)
1.611
1.430
1.648
Radiation type Mo Ka
Mo Ka
0.67
Mo Ka
1.21
l (mmꢀ1
)
1.15
Crystal form,
colour
Crystal size
(mm)
prism, green
block, blue
parallelepiped,
blue
0.50 ꢁ 0.35 ꢁ
0.30
0.26 ꢁ
0.20 ꢁ 0.20 ꢁ
0.24 ꢁ 0.16
ꢀ14,14/
0.15
h/k/l
ꢀ1,13/ꢀ1,27/
ꢀ16,15/ꢀ17,13/
ꢀ21,21
ꢀ12,11/ꢀ17,17 ꢀ28,28
Data/restrains/ 8170/76/604
parameters
F(000)
h Range (°)
R, wR
S
3111/3/249
5481/0/273
1976
822
956
2.12–26.5
0.058, 0.150
1.06
3.00–24.7
0.032, 0.077
1.07
4.84–35.0
0.048, 0.080
1.01
Dqmax,ꢀD3qmin
0.70, ꢀ0.67
0.24, ꢀ0.29
0.72, ꢀ0.39
˚
(e A
)
Fig. 1. Perspective view of [Cu2(2-NO2bz)4(denia)1]n (1) with the non-hydrogen atom numbering scheme. The disordered ethyl groups of the complex are
drawn in open dashed lines.

1336
J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
in solution (acetone and/or toluene) give preferential com-
plex (1) formation even at copper(II):denia molar ratios of
1:2 or 1:4. However, recrystallizations from different sol-
vents have shown that the acidity of the reaction mixture
(presence of acetic acid) after the reaction probably plays
a significant role in transformation of [Cu2(2-NO2Bz)4(de-
nia)1]n (1) to [Cu(2-NO2Bz)2(denia)2(H2O)2] (2) during
heating of the reaction mixture.
plane towards the apical nitrogen atom in comparison to
that towards the apical O-donor [30]. The distance between
the Cu atoms bridged by the denia molecule, Cu2ꢂ ꢂ ꢂCu1ii
˚
[(ii) = x + 0.5, ꢀ y + 0.5, z ꢀ 0.5], is 7.980(3) A.
An interesting feature of this structure is that all four 2-
nitrobenzoato anions are crystallographically independent,
thus all of them exhibit different space orientations. The
dihedral angles between the Cu2O2C plane (bridging car-
boxylato group with both copper atoms) and the corre-
sponding phenyl ring plane are 40.4° for the C12–C17
ring, 69.1° for the C22–C27 ring, 61.6° in the case of the
C32–C37 ring and finally 35.2 for the C42–C47 ring. Con-
sequently these different space orientations of the phenyl
rings lead to the conclusion that to name this structure as
a ‘‘paddle-wheel” like structure is inadequate because the
C12–C17 phenyl ring shows an opposite space orientation
in comparison to the three other rings. Similarly different
values were found for the ‘‘nitro group-to-benzene ring”
with a dihedral angle of 49.4° for the C12–C17 ring,
14.3° for the C22–C27 ring, 26.0° for the C32–C37 ring
and 52.2° for the C42–C47 ring.
The published structure of [Cu2(ClCH2COO)4(denia)]n,
the only one containing a bridging denia ligand [18], differs
from our one by having an ‘‘antiparallel denia bridge orien-
tation” which results in alternation of two different dimeric
units {–[Cu2(RCOO)4]–N(l-denia)O–[Cu2(RCOO)4]–O(l-
denia)N–}n, while the ‘‘similar denia bridge orientation” in
our case leads to the formation of dimeric units with two dif-
ferent apical donor atoms. It should be stressed that this is
the second example in which two Cu(II) atoms within one
dimeric unit are different from each other by their coordina-
tion polyhedra (Cu1O4O0 and Cu2O4N). The first one was
the [Cu2(Cl3CCOO)4(caf)]n ꢂ 2n(CH3C6H5) polymeric com-
plex [31] with a caffeine molecule as the bridging ligand
between the dimeric units. Similarly, different chromoph-
ores were observed [32] for the molecular complex
[Cu2(fluf)4(caf)(H2O)] where caf = caffeine and fluf = flufe-
namate. On the other hand, the alternation of two different
dimeric units were found for the [Cu2(CH3COO)4(nia)] [33]
(where nia = nicotinamide) and [Cu2(Me3CCOO)4(NIT-
pPY)]n complexes [34] (where NITpPY = 2-(3-pyridyl)-
3.2. Structure, spectral and magnetic properties of [Cu2(2-
NO2Bz)4(denia)1]n (1)
The principal structural features and atom numbering
scheme of complex (1) are depicted in Fig. 1 and selected
bond distances and angles are listed in Table 2. The inde-
pendent part of the structure consists of the dimeric
Cu2(2-NO2Bz)4 unit and one molecule of a denia ligand
that is bonded to the Cu2 atom of the dimeric unit via
the pyridine N5 nitrogen atom (with a Cu2–N5 distance
˚
of 2.145(4) A) and bonded via the carbonyl O1 oxygen
atom to the Cu1ii [(ii) = x + 0.5, ꢀy + 0.5, z ꢀ 0.5] atom
of a neighbouring dimeric unit (with a Cu1–O1 distance
˚
of 2.137(4) A), thus forming a zig-zag chain parallel to
the ac plane. The square-pyramidal coordination polyhe-
dron of the Cu1 atom has the base formed by the O11,
O21, O31 and O41 atoms of carboxylate groups (average
˚
Cu1–Obase distance 1.968 A) and the O1 atom of the bridg-
ing denia molecule in the apical position. Similarly, the
square pyramid of the Cu2 atom consists of O12, O22,
O32 and O42 oxygen atoms (average Cu2–Obase distance
˚
1.972 A) within the basal plane and the N5 nitrogen atom
in the apical position. The Cu1ꢂ ꢂ ꢂCu2 distance within the
˚
dimeric Cu2(2-NO2bz)4 unit is 2.6990(9) A and both copper
atoms are shifted from the basal planes towards the apical
position, showing a Cu1–O4(basal plane) distance of
˚
˚
0.209 A and Cu2–O4(basal plane) distance of 0.238 A, con-
firming the greater shift of the copper atom from the basal
Table 2
´
˚
Selected distances (A) and angles (°) for complex 1
4,4,5,5-tetramethyl-1H-imidazolyl-1-oxyl-3-oxide).
The
Cu1–O11
Cu1–O31
Cu1–O1i
Cu2–O12
Cu2–O32
Cu2–N5
1.943(3)
1.943(3)
2.137(4)
2.022(3)
1.995(3)
2.145(4)
Cu1–O21
Cu1–O41
Cu1ꢂ ꢂ ꢂCu2
Cu2–O22
Cu2–O42
O1–Cu1ii
1.986(3)
1.998(3)
2.6990(9)
1.947(3)
1.953(3)
2.137(4)
polymeric chains of complexes [Cu2(2-O2Nbz)4(denia)]n (a)
and [Cu2(ClCH2COO)4(denia)]n (b) are given in Fig. S1 in
the Supplementary material.
Both magnetic susceptibility measurements, Fig. 2, and
EPR spectra, Fig. 3, have proved the presence of a dimeric
moiety within the crystal structure of [Cu2(2-NO2Bz)4(de-
nia)1]n (1). Magnetic susceptibility, measured in the temper-
ature range 1.8–300 K, has shown that complex (1) is
diamagnetic in the temperature region 1.8–75 K, then the
magnetic susceptibility increases systematically with
increasing temperature, from 80 K to 300 K, and a reaches
maximum at about room temperature. At 300 K the
observed value of the effective magnetic moment is equal
to 1.33 B.M. and at a temperature of 80 K leff ffi 0.08 B.M.
This trend indicates an exchange antiferromagnetic interac-
O11–Cu1–O21
O11–Cu1–O41
O21–Cu1–O41
O11–Cu1–O1i
O31–Cu1–O1i
O12–Cu2–O22
O12–Cu2–O42
O22–Cu2–O42
O12–Cu2–N5
O32–Cu2–N5
90.20(15)
89.06(14)
161.61(14)
89.44(15)
96.05(15)
88.45(15)
90.76(15)
172.51(15)
94.15(14)
105.92(14)
O11–Cu1–O31
O21–Cu1–O31
O31–Cu1–O41
O21–Cu1–O1i
O41–Cu1–O1i
O12–Cu2–O32
O22–Cu2–O32
O32–Cu2–O42
O22–Cu2–N5
O42–Cu2–N5
174.11(14)
90.12(15)
88.78(15)
108.18(16)
90.19(15)
159.92(14)
89.38(15)
88.81(15)
95.81(15)
91.68(15)
Symmetry codes: (i) x ꢀ 1/2, ꢀy + 1/2, z + 1/2; (ii) x + 1/2, ꢀy + 1/2,
z ꢀ 1/2.

J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
1337
The best fitting parameters: singlet–triplet energy gap
2J = ꢀ340 cmꢀ1, zJ0 = ꢀ0.1 cmꢀ1, g = 2.20, were obtained
with a good agreement factor R = 1.99 10ꢀ4, R is the agree-
ment factor, defined by
0.0008
0.0006
0.0004
0.0002
0
0.25
0.2
0.15
0.1
P
n
2
i¼1ðviexpT ꢀ vci alcTÞ
0.05
0
R ¼
P
n
2
i¼1ðvei xpTÞ
0
100
200
300
400
The results are presented in Fig. 2. The calculation proce-
dure shows that the main factor determining the magnetic
properties of the polymeric complex 1 is the antiferromag-
netic coupling between the Cu2+ ions in the dimeric
subunits. The magnetic interactions through diethylnicoti-
namide are very weak (zJ0 = ꢀ0.1 cmꢀ1), comparable to
nicotinamide bridges [38]. The 2J value exceeding
300 cmꢀ1 is in good relation [39] to the coplanarity of
all four carboxylato groups with the corresponding Cu2O2
planes. The greatest deviation from coplanarity was found
between the O11–C11–O12 plane and the corresponding
O11–Cu1–Cu2–O12 plane, where the ubend dihedral angle
is 2.90°.
T(K)
Fig. 2. The plot of vm (ꢃ) and the vmT (ꢄ) product vs. temperature for
complex (1) (vm – the molar magnetic susceptibility calculated per one
copper(II) center). The solid line was generated from the best-fit magnetic
parameters, g = 2.20, 2J = ꢀ340 cmꢀ1 zJ0 = ꢀ0.10 cmꢀ1
,
R = 2.00 ꢁ
10ꢀ4
.
RT
The EPR spectra, Fig. 3, of complex (1) shows the typ-
ical features of dimeric ‘‘acetate type” copper(II) com-
plexes. The signal of complex (1) is very weak at liquid
nitrogen temperature and that is consistent with the mag-
netic susceptibility measurements and raising a singlet state
population with decreasing temperature. It is worth noting
that no signal of a paramagnetic monomeric impurity is
observed in this case, thus the dimeric units are connected
and form a polymeric structure.
LNT
0
1000
2000
3000
4000
5000
6000
7000
B / Gauss
This structural observation is also supported by the IR
spectrum data. The spectrum of complex (1) contains peaks
of COOꢀ vibrations at 1579 (mas) and 1411 cmꢀ1 (ms). The
Dm value (Dm = mas ꢀ ms) of 168 cmꢀ1 is consistent with a
bridging mode of bonding of the 2-NO2-benzoate anion
[40] and our previous results [27]. The electronic spectrum
of (1) exhibits a broad asymmetric band with a maximum
at 733 nm, that could be assigned to a d d transition,
and a shoulder at about 375 nm, which is typical for a
dimeric ‘‘acetate type” structure.
Fig. 3. EPR spectra of a powdered sample of complex (1) at room (RT)
and at liquid nitrogen temperature (LNT). Parameters obtained from the
spectra: g\ = 2.07, gk ¼ 2:35, D = 0.380 cmꢀ1
.
tion between the copper(II) magnetic centers like in the
other dimeric CuII tetracarboxylates [35,36]. Similar mag-
netic properties were observed in the dihydrate tetrakis(2-
nitrobenzoato)di(aqua)dicopper(II) complex [27]. The
magnetic data of the complex were fitted to a susceptibility
equation derived from the spin Hamiltonian H = ꢀ
2JS1S2, with the Bleaney–Bowers equation [37], to charac-
terize the intradimer interaction:
3.3. Structure, spectral and magnetic properties of [Cu(2-
NO2Bz)2(denia)2(H2O)2] (2)
ꢂ
ꢀ
ꢁꢃ
ꢀ1 þ Na
Nb2g2
3kT
1
1 þ exp
3
ꢀ2J
vCu
¼
The structure of (2) consists of centrosymmetric mole-
cules, Figs. 4 and 5, with an elongated tetragonal-bipyra-
midal coordination polyhedron around the Cu atom
(Table 3). The coordination sphere of the copper(II) atom
in the trans-basal plane is formed by two 2-nitrobenzoate
anions bonded via O1 atoms (the Cu–O1 distance is
kT
(where N is the Avogadro number, g – the spectroscopic
splitting factor, b – the Bohr magneton, k – the Boltz-
mann constant and J – the exchange parameter), together
with the application of a molecular field model for the
calculation of the present magnetic data of complex (1)
to obtain characteristics of the interdimer magnetic inter-
actions, the zJ0 parameter (z is the number of nearest
neighbours) [42].
˚
1.958(2) A) and two denia molecules bonded via N2 atoms
˚
(the Cu–N2 distance is 2.042(2) A), and in the apical posi-
tions are two water molecules (the Cu–O1W distance is
˚
2.462(2) A). The water molecules, due to an intramolecular
hydrogen bond (O1W–H2Wꢂ ꢂ ꢂO2iii with O1Wꢂ ꢂ ꢂO2iii
vm
vcmorr
¼
2zJ0vm
Ng2b2
[symmetry code: (iii) ꢀx + 1, ꢀy, ꢀz] at a distance of
1 ꢀ
˚
2.770(2) A) are slightly shifted from a precise apical posi-

1338
J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
Fig. 4. Perspective view of [Cu(2-NO2bz)2(denia)2(H2O)2] (2) with the non-hydrogen atom numbering scheme.
Fig. 5. View of the two-dimensional sheet of complex (2). Dashed lines indicate O–Hꢂ ꢂ ꢂO hydrogen bonds. The 2-nitrophenyl groups are omitted for
clarity.
O1W–H1Wꢂ ꢂ ꢂO5iv [symmetry code: (iv) x + 3/2, y1/2,
Table 3
z + 1/2] hydrogen bonds with a O1Wꢂ ꢂ ꢂO5iv distance of
˚
Selected distances (A) and angles (°) for complex 2
˚
2.810(2) A into 2-D hydrogen bonding sheets with a
Cu–O1
Cu–N2
Cu–O1W
1.9579(13)
2.0415(16)
2.4622(16)
O1–Cu–O1W
O1–Cu–N2
N2–Cu–O1W
86.52(6)
92.17(6)
87.46(6)
˚
Cuꢂ ꢂ ꢂCu distance of 9.403(3) A (Fig. 5).
The structure of (2) can be compared to other complexes
of the general formula [Cu(RCOO)2(denia)2(H2O)2] [11–
15]. The Cu–O distances (Cu–Oeq where Oeq is the oxygen
of a carboxylate group, and Cu–Oax where Oax stands for
water oxygen) for complex (2) were found within the range
tion towards the uncoordinated O2 carboxylato oxygen
atom and the O1–Cu–O1W angle is 86.52(6)° (Table 4).
The molecules of (2) are linked to adjacent molecules by

J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
1339
Table 4
monomeric complex [Cu(2-NO2Bz)2(nia)2(H2O)2] [29].
This similarity is probably based on similar weak intermo-
lecular hydrogen bonds (Table 4) in the crystal lattice. The
p–p stacking between the aromatic rings of complex 1 mol-
ecules was not observed in the crystal structure. In order to
obtain a value of the exchange interactions parameter, the
present magnetic data of (2) have been fitted using mag-
netic centers (S = 1/2) in the molecular field model of mag-
netic interactions [42]:
˚
Parameters in (A) and (°) of hydrogen bonds within the structure of
complex 2
D–Hꢂ ꢂ ꢂO
d(Dꢂ ꢂ ꢂO) \(DHO) Symmetry code
O1W–H1Wꢂ ꢂ ꢂO5iv 2.810 (2) 168 (4)
ꢀx + 3/2, y ꢀ 1/2, ꢀz + 1/2
O1W–H2Wꢂ ꢂ ꢂO2iii 2.770 (2) 155 (4)
ꢀx + 1, ꢀy, ꢀz
of those distances for other known complexes 1.936(3) and
2.557(3) A for RCOO = mefenamate [11], 1.961(2) and
2.449(2) A for RCOO = flufenamate [12], 1.959(2) and
2.485(2) A for RCOO = 4-nitrobenzoate [13], 1.965(2)
and 2.503(2) A for RCOO = 2-chloronicotinate [14] and
1.960(1) and 2.440(2) A for RCOO = 2-chlorobenzoate
[15]. On the other hand, the Cu–Neq distance (Neq is the
pyridine nitrogen atom of the denia ligand) for complex
(2) is the longest one in comparison to 2.027(3) A for
˚
˚
˚
Nb2g2
3kT
vm
vm ¼
SðS þ 1Þ; vcmorr
¼
2zJ0vm
1 ꢀ
Ng2b2
˚
where zJ0 is the molecular exchange parameter, z is number
of the nearest neighbours. The R is the agreement factor
defined as
˚
˚
2
n
exp
ðvi T ꢀ vci alcTÞ
X
˚
R ¼
:
RCOO = mefenamate [11], 2.001(2) A for RCOO = flufe-
namate [12], 2.019(2) A for RCOO = 4-nitrobenzoate
[13], 2.015(2) A for RCOO = 2-chloronicotinate [14] and
2
ðvei xpTÞ
˚
i¼1
˚
The magnitude of the magnetic exchange between the ions
2.031(2) for RCOO = 2-chlorobenzoate [15]. The value of
the s parameter (s = RS/RL), indicating [41] the degree of
tetragonal elongation of the octahedron, increases in the
order 0.775 (mefenamate) [11] <0.795 (2-chloronicotinate)
[14] <0.800 (4-nitrobenzoate) [13] <0.809 (flufenamate)
[12] <0.813 for complex (2) <0.818 (2-chlorobenzoate)
[15]. All the complexes [Cu(RCOO)2(denia)2(H2O)2] have
a similar molecular structure, but only [Cu(2-ClBz)2(de-
nia)2(H2O)2] [15] is isostructural with complex (2).
The magnetic data of Cu(2-NO2bz)2(denia)2(H2O)2 are
shown in Fig. 6. At 300 K vmT is equal to 0.417 cm3
K molꢀ1 (leff = 1.83 B.M.) and it is characteristic for
non-coupled, S = 1/2 CuII centers. With a lowering of a
temperature, the vmT value and the magnetic moment
smoothly, but systematically, increase to vmT = 0.431
cm3 K molꢀ1 (leff = 1.86 B.M.) at 1.8 K. It suggests a very
weak ferromagnetic interaction between the CuII centers,
similar to those observed for the polymeric, [Cu{3,5-
(NO2)2bz}2(ron)2]n complex [28]. Very weak but antiferro-
magnetic interactions were also observed in the similar
obtained from these calculations, zJ0 = 0.05 cmꢀ1
,
R = 4.99 ꢂ 10ꢀ5 confirm only very weak ferromagnetic
interactions in the crystal lattice of complex 2.
The EPR spectrum, Fig. 7, of complex (2) is different
from the previous one and is of the axial type with hyper-
fine splitting in the parallel area that was detected at room
and even at liquid nitrogen temperature. Hyperfine split-
ting of polycrystalline samples of Cu(II) complexes is
observed when the copper centers are isolated in the crystal
lattice [29], in this case by 2-nitrobenzoate anions and denia
molecules.
This conclusion is supported by the IR spectrum of
Cu(2-NO2Bz)2(denia)2(H2O)2 where the COOꢀ vibrations
at 1607 (mas), and 1375 cmꢀ1 (ms), giving a difference
between asymmetric and symmetric vibration of
232 cmꢀ1, confirms the monodentate bonding mode of
the 2-NO2-benzoate anion [40]. The electronic spectrum
of this monomeric complex also differs from the dimeric
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.5
0.4
0.3
0.2
0.1
0.0
0
100
200
300
400
T(K)
2000
2500
3000
3500
4000
Fig. 6. Plots of the magnetic data versus temperature; vm (d), vm ꢂ T (s)
for complex (2). Solid lines present calculated curves using magnetic
centers (S = 1/2) in the molecular field model of the magnetic interactions
(parameters in the text).
B / Gauss
Fig. 7. The EPR spectrum of a powdered sample of complex (2) at room
temperature: g\ = 2.05, g ¼ 2:30, A ¼ 160 G.
k
k

1340
J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
Fig. 8. Perspective view of [Cu2(2-NO2bz)4(DMF)2] (3) with the non-hydrogen atom numbering scheme.
ones and the d d transition for complex (2) was found at
bridging ligand nature1, because the apical ligands are
DMF. Similarly, the Cu–DMF distances vary from 2.097
634 nm as a broad asymmetric band.
˚
to 2.207 A and there is a very weak relationship between
3.4. Structure, spectral and magnetic properties of [Cu2(2-
NO2Bz)4(DMF)2] (3)
this distance and the displacement of the copper atom from
the basal plane. Comparison of similar complexes contain-
ing the moiety [Cu2(2-NO2bz)4(L)2] (where L = H2O [27]
or L = DMSO [54]) with complex (3) shows that the nature
of the apical ligand exhibits a greater influence on all the
Cuꢂ ꢂ ꢂCu, the Cu–basal plane and Cu–Oapic distances.
The magnetic properties of complex (3) (Fig. 9) are
The molecular structure and the numbering scheme are
shown in Fig. 8. The structure consists of the centrosym-
metric dimeric molecule [Cu2(2-NO2bz)4(DMF)2], in which
two copper(II) atoms are bridged via four carboxylato
anions thus forming a square base of four oxygen atoms
(Table 5) around each copper (the average Cu–O distance
shown as plots of vm and the vmT product versus T (vm
–
the molar magnetic susceptibility calculated per one cop-
per(II) center). The magnetic susceptibility reaches a max-
imum at room temperature and the value of vmT
continuously decreases on lowering of the temperature.
At 300 K the observed value of vmT is 0.238 cm3 K molꢀ1
and the effective magnetic moment is equal to 1.38 B.M.
At the temperature 50 K, vmT reaches a minimum (about
0.002 cm3 K molꢀ1, which corresponds to leff ffi 0.13 B.M).
This trend indicates an antiferromagnetic exchange interac-
tion between the two copper(II) magnetic centers of the
dimeric unit and depopulation of the excited triplet
(S = 1) state. Further temperature decreasing results in an
increase of vmT, probably due to the presence of mono-
˚
is 1.97(2) A). The apical position of the square-pyramidal
coordination polyhedron is occupied by the oxygen atom
O9 of
a DMF molecule (the Cu–O9 distance is
˚
2.127(2) A). The copper atoms are displaced from the
respective basal planes towards the apical oxygen atoms
by 0.19(1) A, and the Cu–Cu separation within the dimer
˚
˚
was found to be 2.633(1) A. The crystal structure of (3)
can be compared with the other dimeric copper(II)
aromatic carboxylates with DMF ligands in apical posi-
tions [43–53]. It is interesting that the Cuꢂ ꢂ ꢂCu intradimer
distances vary within a narrow region from 2.598 to
˚
2.641 A, and this variation is caused mainly by moving
the copper atom from the basal plane towards the apical
ligand (correlation coefficient R = 0.90, Table S1 and
Fig. S2), and this movement must be related to the anionic
1
For data see Supplementary material Table S1.

J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
1341
Table 5
Selected distances (A) and angles (°) for complex 3
´
˚
Cu–O1
Cu–O5
Cu–O9
1.9702(12)
1.9666(12)
2.1272(12)
Cu–O2v
Cu–O6v
Cu–Cuv
1.9797(12)
1.9690(12)
2.6334(7)
RT
O1–Cu–O2v
O1–Cu–O6v
O2v–Cu–O6v
O1–Cu–O9
O5–Cu–O9
168.89(4)
O1–Cu–O5
O2v–Cu–O5
O5–Cu–O6v
O2v–Cu–O9
O6v–Cu–O9
89.19(5)
90.53(5)
168.93(5)
92.55(5)
92.86(5)
89.66(5)
88.49(5)
98.48(5)
98.20(5)
LNT
Symmetry codes: (v) ꢀx + 1, ꢀy + 1, ꢀz + 1.
0
1000
2000
3000
4000
5000
6000
7000
0.001
0.0008
0.0006
0.0004
0.0002
0
0.25
0.2
0.15
0.1
0.05
0
B / Gauss
Fig. 10. EPR spectra of a powdered sample of complex (3) at room (RT)
and at liquid nitrogen temperature (LNT). The amount of monomeric
impurity, calculated from magnetic measurements equal ꢆ0.4%, and 7
lines observed at Hz1 lines correspond to A = 65 G. Remaining EPR
parameters are: g\ = 2.06, gk ¼ 2:28, D = 0,346 cmꢀ1, gmon = 2.06.
-10
90
190
290
390
T(K)
plexes, absorptions at low and high field (at room temper-
ature Hz1 ꢅ 415 G and Hz2 ꢅ 6280 G, respectively) and
the line H\2 ꢅ 4900 G. At liquid nitrogen temperature
the signal of the dimeric species becomes weaker, but
hyperfine splitting was observed in the Hz1 region
(Fig. 10). At room temperature as well as at liquid nitro-
gen temperature a monomeric impurity was observed at
about 3380 G.
Fig. 9. The plot of vm and the vmT product vs. temperature for complex
(3) (vm – the molar magnetic susceptibility calculated per one copper(II)
center). The solid line was generated from the best-fit parameters
gdim = 2.20, gmon = 2.16, 2J = ꢀ320 cmꢀ1, R = 9.97 ꢁ 10ꢀ6
.
meric impurities present in this sample. The magnetic data
of the complex were fitting using the modified Bleaney–
Bower’s equation [42]:
The spectrum of (3) contains peaks of COOꢀ vibrations
at 1577 (mas) and 1412 cmꢀ1 (ms), and the Dm value
(Dm = mas ꢀ ms) of 168 cmꢀ1 is similar to that for complex
(1). Similarly the electronic spectrum of (3) exhibits a broad
asymmetric band with a maximum at 718 nm (d d tran-
sition) and a shoulder at about 400 nm.
(
)
ꢂ
ꢃꢀ1
ꢀ
ꢁ
Ng2dimb2
3kT
1
Ng2monb2
4kT
vm ¼
1 þ ðeꢀ2J=kT
Þ
ð1 ꢀ xÞ þ
x
3
where x is the mole fraction of the monomeric form, and
gmon and gdim are spectroscopic splitting factors of the
monomer and dimer forms, respectively, and the other
symbols have their usual meaning. The magnetic parame-
ters: gdim = 2.20, gmon = 2.16, 2J = ꢀ320 cmꢀ1 and mono-
meric impurities at the 0.38% level were obtained,
R = 9.97 ꢁ 10ꢀ6
Acknowledgements
We thank the Scientific Grant Agency of the Ministry of
Education of Slovak Republic and the Slovak Academy of
Sciences (1/2452/05), Research and Development Support
Agency (APVT-20-005504) and the Polish Ministry of Sci-
ence and Higher Education – Grant No. 1T09A 12430, for
financial support.
2
n
exp
ðvi T ꢀ vci alcTÞ
X
R ¼
2
ðvei xpTÞ
i¼1
The ‘‘normal‘‘ ꢀ2J value for complex (3) is a proof of the
mutual relation between the ꢀ2J value and the ubend angle.
Both structurally independent bridges are nearly planar
and exhibit small values of the ubend angle 1.1(2)° and
3.2(2)°. The orientation of the benzene rings with respect
to the carboxylate bridge probably has no influence on
the magnetic interaction between the copper centers.
The EPR spectra of the powdered sample of complex
(3) were measured at room temperature and liquid nitro-
gen temperature (Fig. 10). The spectra exhibit features
typical of those for dimeric carboxylatocopper(II) com-
Appendix A. Supplementary material
CCDC 667553, 667554 and 667555 contain the supple-
mentary crystallographic data for 1, 2 and 3. These data
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge 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.2007.12.030.

1342
J. Kavalı´rova´ et al. / Polyhedron 27 (2008) 1333–1342
[26] E. Ko}nig, Magnetic Properties of Coordination and Organometallic
Transition Metal Compounds, Springer, Berlin, 1996.
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}