Synthesis, crystal structure and magnetism of three novel copper(II) complexes with pyrazole-based ligands

Article abstract of DOI:10.1016/j.molstruc.2011.12.036

In this work we present the synthesis, crystal structure and magnetic properties of three copper(II) pyrazole-based complexes. These compounds were prepared by reactions between the ligands (L1 = 5-amino-1-phenyl-1H-pyrazole-4- carbonitrile, L2 = 5-amino-1-(4'metoxiphenyl)-1H-pyrazole-4-carbonitrile and L3 = Ethyl 5-amino-1-phenyl-1H-pyrazole-4-carboxylate) and CuCl₂· 2H₂O using an appropriate solvent. The crystalline structures of [Cu(L1)₂Cl₂] (1), [Cu(L2)₂Cl₂] (2) and [Cu(L3)₂Cl₂] (3) showed that copper ion is coordinated by two pirazolic ligands through pyridinic nitrogen atom and two chloride ions in a distorted square-planar geometry. The magnetic measurements revealed a paramagnetic behavior for (1) and weak antiferromagnetic coupling between copper(II) ions in (2) and (3). Due to the presence of labile chloride ions in the structures, these monomeric copper(II) complexes may be used as building blocks in the synthesis of molecular magnetic compounds.

Full text of DOI:10.1016/j.molstruc.2011.12.036

Journal of Molecular Structure 1011 (2012) 99–104
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, crystal structure and magnetism of three novel copper(II) complexes
with pyrazole-based ligands
1
⇑
Igor F. Santos, Guilherme P. Guedes , Luiza A. Mercante, Alice M.R. Bernardino, Maria G.F. Vaz
Universidade Federal Fluminense, Instituto de Química, 24020-141 Niterói, Rio de Janeiro, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work we present the synthesis, crystal structure and magnetic properties of three copper(II) pyr-
azole-based complexes. These compounds were prepared by reactions between the ligands (L1 = 5-
amino-1-phenyl-1H-pyrazole-4-carbonitrile, L2 = 5-amino-1-(4’metoxiphenyl)-1H-pyrazole-4-carboni-
trile and L3 = Ethyl 5-amino-1-phenyl-1H-pyrazole-4-carboxylate) and CuCl2ꢀ2H2O using an appropriate
solvent. The crystalline structures of [Cu(L1)2Cl2] (1), [Cu(L2)2Cl2] (2) and [Cu(L3)2Cl2] (3) showed that
copper ion is coordinated by two pirazolic ligands through pyridinic nitrogen atom and two chloride ions
in a distorted square-planar geometry. The magnetic measurements revealed a paramagnetic behavior
for (1) and weak antiferromagnetic coupling between copper(II) ions in (2) and (3). Due to the presence
of labile chloride ions in the structures, these monomeric copper(II) complexes may be used as building
blocks in the synthesis of molecular magnetic compounds.
Received 4 November 2011
Received in revised form 22 December 2011
Accepted 23 December 2011
Available online 3 January 2012
Keywords:
Molecular magnetism
Pyrazole
Copper(II) complex
Crystal structure
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
materials in which the peculiar properties of compounds can be
tuned through modification in the organic ligand [6]. The investiga-
Pyrazoles and their derivatives are aromatic systems that have
strong electron donor ability due to two chemically different nitro-
gen atoms (N-pyrrole and N-pyridine) [1]. Previously reports
showed that this difference allows the interaction of the nitrogen
atoms with specific proteins leading to distinct pharmacological
activities. Due to this fact pyrazole and its derivatives are an
important class of compounds that attracted widespread attention
and are widely used in medicinal chemistry [2]. Besides, pyrazole is
also a versatile ligand in coordination chemistry, since it exhibits
twenty-two distinct coordination modes [3]. Complexes containing
this kind of ligand are known since 1889 with the discovery by
Büchner of an Ag(I) complex, [Ag(pz)]n, where pz stands for pyra-
zole [4]. However, a new interest in these compounds arose in
the 1980s with the publication of Trofimenko’s work, which high-
lighted a rich coordination chemistry of pyrazole-based ligands [5].
Although several coordination modes of the transition metals to
pyrazole, the synthesis of polynuclear compounds with pyrazole-
substituted ligands is not trivial and the formation of mononuclear
complexes is favored. Furthermore, monomeric complexes have at-
tracted the interest of many research groups in order to develop
tion of these complexes has become an interesting research field
due to their relevance in bioinorganic chemistry [7], catalysis [8]
and luminescent materials [9]. In addition, monomeric compounds
havealsobeenstudiedinthemolecularmagnetismfieldbecausethey
can act as building blocks for supramolecular architectures [10]. In
order to obtain molecular magnetic compounds there are several
widespread strategies [11]. One of them consists on the synthesis of
coordination compounds in which a labile ligand is coordinated to
the metal, allowing its replacement by other ligand or preformed
coordination compound [12]. This methodology is useful to connect
discrete molecules turning them into a polynuclear structure. The
magneticinteractionoccursbetween the spincarriers ofeach module
through an organic binder. One of the interesting aspects of this
methodology is the possibility to control connectivity and final archi-
tecture by choosing appropriate molecular bricks [13]. Therefore, the
knowledge of crystal structure and magnetic properties of these
building blocks is important for designing complex structures. Here
we report the syntheses, crystal structures and magnetic properties
of three novel copper(II) pyrazole-basedcomplexes, which are poten-
tialcandidatesasbuildingblocksformolecularmagneticcompounds.
⇑
Corresponding author. Address: Universidade Federal Fluminense, Instituto de
Química, Outeiro de São João Batista, s/n, CEP 24020-150 Niterói, Rio de Janeiro,
Brazil. Tel.: +55 21 2629 2354; fax: +55 21 2629 2129.
2. Experimental
2.1. Materials and methods
E-mail address: mariavaz@vm.uff.br (M.G.F. Vaz).
Permanent address: Universidade Federal Rural do Rio de Janeiro, Instituto de
1
Analytical grade reagents were purchased from different
sources and used without further purification. The melting points
Ciências Exatas, Departamento de Química, BR 465 – km 47, 23070-200 Seropédica,
RJ, Brazil.
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.12.036

100
I.F. Santos et al. / Journal of Molecular Structure 1011 (2012) 99–104
1658–1512 (C@C/C@N); 1257 (CAO). 1H NMR (ppm): 7.60 (s,
1H); 7.38 (d, J 9.0 Hz, 2H); 7.00 (d, J 9.0 Hz, 2H); 3.8 (s, 3H). L3
[16]: Yield: 80%. mp = 100 °C. IR (KBr, cmꢁ1): 3394 (
as(NH2));
3263 s(NH2)); 1682 (C@O); 1627–1550 (C@C/C@N); 1280
as(CAO)); 1111 (
s(CAO)). 1H NMR (ppm): 7.85 (s, 1H); 7.40–
m
(m
(m
m
7.55 (m, 5H); 4.8 (br, 2H); 4.31 (q, J 7.2 Hz, 2H); 1.36 (t, J 7.2 Hz,
3H).
2.2.2. Preparation of the complexes
The reaction between CuCl2ꢀ2H2O with the ligands
5-amino-1-phenyl-1H-pyrazole-4-carbonitrile (L1), 5-amino-1-
(40metoxiphenyl)-1H-pyrazole-4-carbonitrile (L2) and ethyl
5-amino-1-phenyl-1H-pyrazole-4-carboxylate (L3) lead to the
formation of monomeric copper complexes, namely [Cu(L1)2Cl2]
(1), [Cu(L2)2Cl2] (2) and [Cu(L3)2Cl2] (3).
Fig. 1. Pyrazole-based ligands with N-donor substituents (nitriles and amines).
were determined in Fisatom digital device model 430. Elemental
analyses were determined on a Perkin–Elmer 2400 CHN Elemental
Analyzer. Nuclear magnetic resonance (NMR) spectrum was ob-
tained at room temperature on a Varian Unity spectrometer oper-
ating at 500 MHz. The infrared spectrum was taken on a Spectrum
2.2.2.1. Preparation of compound (1). An ethanolic solution (20 mL)
of CuCl2ꢀ2H2O (0.187 g, 1.1 mmol) was added slowly onto a solu-
tion containing 0.405 g (2.2 mmol) of L1 in 10 mL of ethanol. The
resulting solution was stored at 8 °C and red crystals were obtained
after one week. Yield: 43%. mp = 167 °C. Anal. Calc. for
[Cu(L1)2Cl2]: C = 46.24%; H = 3.58%; N = 20.84%. Found C = 46.12%;
One Perkin–Elmer spectrometer in the range of 4000–500 cmꢁ1
,
using KBr pellets. Magnetic measurements were performed on a
Cryogenic SX-600 SQUID magnetometer in a range of 2–290 K with
an applied field of 0.1 T. The sample was placed in a gelatin capsule
and data were corrected for the diamagnetism and sample holder.
H = 3.48%; N = 21.41%. IR (KBr, cmꢁ1): 3329 (
s(NH2)); 2227 ( s(CN)).
mas(NH2)); 3234
(m
m
2.2. Syntheses
2.2.2.2. Preparation of compound (2). A solution prepared by stirring
0.187 g (1.1 mmol) of CuCl2ꢀ2H2O in 20 mL acetonitrile was added
slowly onto a solution containing 0.471 g (2.2 mmol) of L2 in
10 mL of the same solvent. The resulting solution was stored at
8 °C and yellow crystals were obtained after four days. Yield 44%.
mp = 215 °C. Anal. Calc. for [Cu(L2)2Cl2]: C = 47.12%; H = 3.68%;
N = 19.55%. Found C = 46.94%; H = 3.58%; N = 19.91%. IR (KBr,
2.2.1. Preparation of the ligands L1–L3
The ligands L1–L3 (Fig. 1) were synthesized following the pro-
cedures previously reported [14]. L1 [15]: Yield: 90%. mp = 139–
140 °C. IR (KBr, cmꢁ1): 3325 (
m
as(NH2)); 3225 (
ms(NH2)); 2222
(m
s(CN)); 1643–1535 (C@C/C@N). 1H NMR (ppm): 7.63 (s, 1H);
7.41–7.57 (m, 5H); 4.5 (br, 2H). L2: Yield: 75%. mp = 144–145 °C.
cmꢁ1): 3313 (
(ms(OCH3)).
mas(NH2)); 3240 (ms(NH2)); 2222 (ms(CN)); 1250
IR (KBr, cmꢁ1): 3359 (
m
as(NH2)); 3180 (
ms(NH2)); 2214 (
ms(CN));
Table 1
Summary of the crystal structure, data collection and refinement for compounds 1–3.
Identification
(1)
(2)
(3)
Formula
C
20H18Cl2CuN8O
C22H20Cl2CuN8O2
562.90
293
0.71073
Triclinic
P-1
7.4025(15)
8.7411(17)
10.546(2)
66.60(3)
79.55(3)
67.67(3)
578.9(2)
1
C24H26Cl2CuN6O4
596.96
293
1.54180
Monoclinic
C2/c
7.92190(10)
17.7558(2)
18.9725(3)
90.0
97.0310(10)
90.00
2648.60(6)
4
1.497
Molecular weight (g molꢁ1
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
)
520.87
293
1.54180
Monoclinic
P21/n
7.5174(2)
16.7682(15)
17.7966(10)
90.0
95.133(3)
90.0
2234.3(2)
4
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Volume (Å3)
Z
Dcalc (g cmꢁ3
)
1.548
3.84
1.615
1.21
l
(mmꢁ1
)
3.38
F (000)
Crystal size (mm)
h Range for data collection (°)
Reflections collected
1060
287
1228
0.26 ꢂ 0.16 ꢂ 0.07
2.5–62.7
6882
0.04 ꢂ 0.02 ꢂ 0.01
3.3–25.0
14993
0.30 ꢂ 0.23 ꢂ 0.11
2.4–62.4
17,344
Independent reflections/Rint
Data/restraints/parameters
Goodness-of-fit on F2
3585/0.025
3948/2/297
1.01
2044/0.074
2044/2/168
1.08
2102/0.032
2085/0/176
1.05
Final R indices [I > 2
r
(I)]
R1 = 0.038
wR2 = 0.106
R1 = 0.053
wR2 = 0.097
0.45/ꢁ0.34
R1 = 0.049
wR2 = 0.133
R1 = 0.067
wR2 = 0.1225
0.48/ꢁ0.61
R1 = 0.030
wR2 = 0.082
R1 = 0.0364
wR2 = 0.783
0.50/ꢁ0.43
R indices (all data)
Max peak/hole (e Åꢁ3
)
For compound (1): w = 1/[
r
2(Fo2) + (0.0608P)2 + 1.725P]; (2): w = 1/[
r
2(Fo2) + (0.055P)2 + 1.386P], (3): 1/[ 2(Fo2) + (0.0391P)2 + 4.2304P], where
r
P = (Fo2 + 2Fc2)/3.

I.F. Santos et al. / Journal of Molecular Structure 1011 (2012) 99–104
101
2.2.2.3. Preparation of compound (3). Compound (3) was synthe-
sized under same conditions as (1), using the L3 ligand. Red single crys-
tals were obtained after one week. Yield: 45%. mp = 184 °C. Anal. Calc.
for [Cu(L3)2Cl2]: C = 48.29%; H = 4.39%; N = 14.08%. Found C = 48.14%;
Details of data collection and structure refinement for compounds
1–3 are summarized in Table 1. Selected distances and angles are
given in Tables 2 and 3.
H = 4.36%; N = 13.95%. IR (KBr, cmꢁ1): 3441 (
1705 ( s(C@O)); 1257 ( as(CAO)); 1111 (
mas(NH2)); 3333 (ms(NH2));
m
m
ms(CAO)).
2.3. X-ray crystallographic data
Single crystal X-ray diffraction data for compounds (1) and (3)
were obtained on a Oxford GEMINI A Ultra with CCD diffractome-
ter with CuKa radiation (k = 1.54180 Å) at room temperature. Data
collection, reduction and cell refinement were performed by
CrysAlis RED program [17]. A multiscan absorption correction
was applied [18]. The crystallographic data for (2) were collected
on an Enraf Nonius Bruker KAPPA CCD diffractometer, using graph-
ite monochromatic MoKa radiation (k = 0.71069 Å). Final unit cell
parameters were based on the fitting of all reflections positions
using DIRAX [19]. Collected reflections were integrated using the
EVALCCD program [20]. Empirical multiscan absorption correc-
tions using equivalent reflections were performed with the
SADABS program [21]. The structure solutions and full-matrix
least-squares refinements based on F2 were performed with the
SHELXS-97 and SHELXL-97 program packages [22]. All atoms ex-
cept hydrogen were refined anisotropically. Hydrogen atoms were
treated by a mixture of independent and constrained refinement.
Fig. 2. ORTEP view of the molecular unit of compound 1. Ellipsoids are at 50%
probability.
Table 2
Selected experimental bond distances (Å) and bond angles (°).
Compounds Bond distance (Å)
Bond angle (°)
(1)
(2)
(3)
Cu1AN5
Cu1AN1
Cu1ACl1
Cu1ACl2
1.979(3)
2.011(2)
2.2021(9)
2.2316(9)
N5ACu1AN1
N5ACu1ACl1
N1ACu1ACl1
N5ACu1ACl2
N1ACu1ACl2
Cl1ACu1ACl2
96.00(10)
148.17(8)
92.62(7)
94.19(7)
141.79(8)
97.77(4)
Cu1AN2
Cu1AN2i
CuACl1i
CuACl1
1.967(3)
1.968(3)
N2ACu1AN2i
N2ACu1ACl1i
180
90.57(11)
89.43(11)
89.43(11)
90.57(11)
180
2.2557(14) N2iACu1ACl1i
2.2558(14) N2ACu1ACl1
N2iACu1ACl1
Cl1iACu1ACl1
Cu1AN2
Cu1AN2ii
Cu1ACl1
Cu1ACl1ii
2.0124(18) N2ACu1AN2ii
2.0124(18) N2ACu1ACl1
2.2358(6)
2.2358(6)
92.30(11)
157.17(6)
91.89(5)
91.89(5)
N2iACu1ACl1
N2ACu1ACl1ii
N2iACu1ACl1ii 157.17(6)
Cl1ACu1ACl1ii 92.90(3)
Fig. 3. ORTEP view of the molecular unit of compound 2. Ellipsoids are at 50%
probability.
Symmetry codes: (i) ꢁx, ꢁy, ꢁz; (ii) ꢁx + 1, y, ꢁz + 1/2.
Table 3
Intermolecular interactions geometry.
Compounds
DAHꢀ ꢀ ꢀA
DAH
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
DAHꢀ ꢀ ꢀA
(1)
N3AH3Bꢀ ꢀ ꢀO1w
0.86
0.86
0.81(2)
0.82(2)
0.86
2.32
2.23
2.81(4)
2.51(3)
2.37
2.985(4)
3.081(4)
3.456(3)
3.278(4)
2.962(4)
2.972(4)
134
173
138(5)
156(6)
126
N3AH3Aꢀ ꢀ ꢀN8i
O1wAH1wꢀ ꢀ ꢀCl1ii
O1wAH2wꢀ ꢀ ꢀCl2ii
N7AH7Aꢀ ꢀ ꢀO1wiii
N7AH7Bꢀ ꢀ ꢀN4iv
0.86
2.13
168
(2)
(3)
N3AH3ꢀ ꢀ ꢀCl1v
0.861(10)
0.863(10)
2.64(3)
2.239(17)
3.380(5)
3.080(6)
145(4)
165(5)
N3AH2ꢀ ꢀ ꢀN4vi
N3AH3Bꢀ ꢀ ꢀCl1vii
N3AH3Aꢀ ꢀ ꢀO1
0.87(3)
0.80(3)
0.80(3)
2.78(3)
2.35(3)
2.92(3)
3.509(2)
2.936(3)
3.475(2)
142(2)
131(3)
128(3)
N3AH3Aꢀ ꢀ ꢀCl1viii
Symmetry codes: (i) x ꢁ 1/2, ꢁy + 3/2, z + 1/2; (ii) ꢁx ꢁ 1/2, y + 1/2, ꢁz + 1/2; (iii) x + 1, y, z; (iv) x + 1/2, ꢁy + 3/2, z ꢁ 1/2; (v) x + 1, y, z; (vi) ꢁx + 1, ꢁy + 1, ꢁz ꢁ 1; (vii) xꢁ1/2,
y ꢁ 1/2, z; (viii) ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2.

102
I.F. Santos et al. / Journal of Molecular Structure 1011 (2012) 99–104
Fig. 4. ORTEP view of the molecular unit of compound 3. Ellipsoids are at 50% probability.
Fig. 5. Crystal packing of compound 1. Hydrogen atoms were omitted for clarity.
[23]. The substituent groups in the 4 and 5 positions of the pyraz-
3. Results and discussion
olic ring (amino and cyano for L1 and L2, and amino and ester, for
L3) have an important role in the crystal packing of the compounds
1–3 due to the establishment of a hydrogen bonded supramolecu-
lar network. Intermolecular short contacts parameters are given in
Table 3. In the compound (1) the crystal packing is stabilized by
intermolecular hydrogen bonds between the amino group and
the lattice water molecule, with distance of 2.985(4) Å
(O1wꢀ ꢀ ꢀN3) and 2.962(4) Å (O1w(x + 1, y, z)ꢀ ꢀ ꢀN7). In addition,
intermolecular interactions between water hydrogen atoms and
chloride ions with distances 3.456(3) Å (O1wꢀ ꢀ ꢀCl1(x ꢁ
1/2, y + 1/2, ꢁz + 1/2)) and 3.278(4) Å (O1wꢀ ꢀ ꢀCl2(ꢁx ꢁ 1/2, y + 1/
2, ꢁz + 1/2)) probably lead to a cis configuration on the complex.
3.1. Structure descriptions
The molecular units of compounds 1–3 are shown in Figs. 2–4.
In the three complexes, the copper(II) ion lies on a distorted square
planar geometry, coordinated to two chloride ions and two ligand
molecules through the pyridinic nitrogen atom of pyrazolic ring in
a neutral monodentate mode [3]. In compounds (1) and (3) the
copper(II) ion displays a cis geometry while in compound (2) the
metal ion is in a trans geometry. The CuAN and CuACl bond
lengths are typical when compared with those previously reported
The crystal packing of (1) shows
a supramolecular zig-zag
Fig. 7. Intramolecular hydrogen bond between the amino and carbonyl groups in
compound 3. The hydrogen atoms except those involved in hydrogen bonding were
omitted for clarity.
Fig. 6. Intermolecular hydrogen bonds in compound 2. The hydrogen atoms except
those involved in hydrogen bonding were omitted for clarity.

I.F. Santos et al. / Journal of Molecular Structure 1011 (2012) 99–104
103
chain-like structure as result of hydrogen bonds between amino
and cyano groups (Fig. 5).
Hydrogen bonds between amine and cyano groups are also present
in this complex (Fig. 6). In the compound (3), the copper(II) ion dis-
plays a cis geometry as observed in (1). Weak interactions between
chloride and amino group hydrogen atoms N3AH(3b)ꢀ ꢀ ꢀCl1(x ꢁ 1/
2, y ꢁ 1/2, z) (2.78(3) Å) and N3AH(3a)ꢀ ꢀ ꢀCl1(ꢁx + 1/2, y ꢁ 1/2,
ꢁz + 1/2) (2.92(3) Å) stabilize the crystal packing. Besides, intramo-
lecular hydrogen bond interactions between amino and ester
groups in 4 and 5 positions with distance of 2.350(5) Å (N3ꢀ ꢀ ꢀO1)
form a stable six members ring (Fig. 7). It is important to highlight
that lattice water molecule and the substituent in the para position
of the benzene ring play a key role in the crystal packing and prob-
ably are the main factors to lead to a trans geometry in compound
(2), spite of the cis conformation of (1) and (3). In addition, the
shortest intermolecular distances between copper ions are
8.401(7) Å (1), 7.4030(2) Å (2) and 7.922(4) Å (3).
The X-ray structure of compound (2) shows that the copper(II)
ion is coordinated to two L2 ligands, which has a methoxide sub-
stituent in the para position of the benzene ring. Intermolecular
interaction between amine group and chloride ion with distance
of 3.380(5) Å (N3ꢀ ꢀ ꢀCl1(x + 1, y, z)) is responsible to the trans con-
figuration establishment in contrast to compounds (1) and (3).
3.2. Magnetic properties
The temperature dependences of the
vMT products are dis-
played in Fig. 8. The experimental
vMT values for compounds 1–3
at 290 K are 0.40 (1), 0.39 (2) and 0.41 cm3 K molꢁ1 (3), close to
the calculated one for S = 1/2 ion, with g = 2.00 (0.375 cm3
K molꢁ1). These values remain constant from 290 to 8 K (1), 290
to 22 K (2) and 290 to 23 K (3) indicating a paramagnetic behavior
in these temperature ranges. Upon cooling,
vMT values decrease
abruptly due to antiferromagnetic interactions. The reciprocal sus-
ceptibility versus temperature can be nicely fitted to the Curie–
Weiss law (
v
M = C/(T ꢁ h)) (insets Fig. 8). This analysis gives a Curie
and Weiss constants of C = 0.40 emu molꢁ1 and h = ꢁ0.02 K for (1),
C = 0.39 emu molꢁ1 and h = ꢁ0.61 K for (2), and C = 0.40 emu molꢁ1
and h = ꢁ0.42 K for (3). The negative Weiss constants indicate the
existence of a very weak antiferromagnetic coupling due to the
intermolecular interactions, which connect the molecular units in
the crystal lattice [24]. In order to taking into account the values
of the magnetic coupling constant, the susceptibility magnetic data
for (2) and (3) were reproduced considering a mean field approxi-
mation accordingly with the following expressions:
Nb2g2
3kT
vm
vm
¼
SðS þ 1Þ vMmF
¼
1 ꢁ zJ0vm
where zJ0 is the intermolecular magnetic coupling constant. The best
fit parameters were g = 2.04 and zJ0 = ꢁ1.70 cmꢁ1 for compound (2)
and g = 2.08 and zJ0 = ꢁ1.45 cmꢁ1 for compound (3). Magneto-struc-
tural correlation for compounds 1–3 showed that the values of
Weiss constant and the intermolecular magnetic coupling constant
decrease as the distance between the copper ions increases, as ex-
pected. Compound (1) displays the longest distance between these
ions, thus the lowest Weiss constant was obtained. Due to the para-
magnetic behavior until 8 K, the magnetic data were not fitted as for
(2) and (3). The comparison between compounds (2) and (3) shows
the same tendency for the intermolecular magnetic coupling; in
compound (2) the distance between copper ions is the shortest
one, thus the intermolecular magnetic interactions are stronger
when compared with compound (3).
4. Conclusion
In this work the syntheses, crystal structure and magnetic prop-
erties of three novel monomeric copper(II) pyrazole-based com-
plexes were presented. Intermolecular and intramolecular
interactions involving cyano, amine and ester groups play an
important role for establishing a supramolecular network of
hydrogen bonds in the compounds. We also showed that the
change of the substituent in the para position of phenyl group
bound to the 1-position of the pyrazole ring probably is the main
Fig. 8. Temperature dependences of
(c). Solid lines in (b and c) represent the magnetic data fits. Insets: 1/vM data as a
function of the temperature fitted to the Curie–Weiss law (solid line).
vMT products of compounds 1 (a), 2 (b) and 3

104
I.F. Santos et al. / Journal of Molecular Structure 1011 (2012) 99–104
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reason that lead to the trans conformation of (2). Magnetic mea-
surements revealed paramagnetic behavior for (1) and weak anti-
ferromagnetic interactions for (2) and (3). This weak
antiferromagnetic coupling can arise due the pathway provided
by intermolecular interactions that connect the molecular units.
ˇ
ˇ
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Supplementary material
CCDC ID: 851371 (1), 851372 (2), 851373 (3), contain the sup-
plementary crystallographic data for this compound. These data
can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgements
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Financial support from CAPES, FAPERJ, CNPq are kindly
acknowledged. The authors also acknowledge the LDRX (Univer-
sidade Federal Fluminense), LabCri (Universidade Federal de Minas
Gerais) for use of crystallographic facilities as well as Dr. Jackson
A.L.C Resende for data collection of compound (2). We also thank
Prof. Miguel A. Novak for the magnetic measurements.
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