Synthesis, crystal structure, magnetism and specific heat of a new copper(II) compound with p-aminobenzoic acid

Article abstract of DOI:10.1016/j.ica.2011.08.035

In this work we present the synthesis, crystal structure, magnetic and specific heat measurements of a new monomeric copper(II) compound, in which the metal ion is coordinated to two p-aminobenzoic acid (PABA) molecules and two chloride ions. This compound with formula [CuCl₂(C₇H ₇NO₂)₂] presents a peculiar crystalline structure packing, showing hydrogen-bonds between carboxylic acid groups and short N-H...Cl contacts resulting in a polymeric character in two dimensions. In the third direction, Cu...Cl close contacts between neighboring molecules are responsible for a chain-like magnetic behavior. Considering the simplicity of the molecular unit, the magnetic properties show surprising results: below 6.4 K a hysteresis cycle appears in the magnetization curves as well as a splitting between low field ZFC-FC measurements. No phase transition to a long-range order was observed by specific heat measurement.

Full text of DOI:10.1016/j.ica.2011.08.035

Inorganica Chimica Acta 378 (2011) 134–139
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, crystal structure, magnetism and specific heat of a new copper(II)
compound with p-aminobenzoic acid
Guilherme P. Guedes a,1, Fernanda F. Farias b, Miguel A. Novak b, Fernando L. de A. Machado c,
Maria G.F. Vaz a,
⇑
a Universidade Federal Fluminense – Instituto de Química, Outeiro de São João Batista, s/n, Niterói – Rio de Janeiro, CEP 24.020-150, Brazil
b Universidade Federal do Rio de Janeiro – Instituto de Física, Av. Athos da Silveira Ramos, 149 – Rio de Janeiro, CEP 21.941-972, Brazil
c
´
´
Universidade Federal de Pernambuco – Departamento de Fisica, Av. Professor Luiz Freire, s/n, Cidade Universitaria, Recife – Pernambuco, CEP 50.670-901, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 April 2011
Received in revised form 12 August 2011
Accepted 17 August 2011
Available online 26 August 2011
In this work we present the synthesis, crystal structure, magnetic and specific heat measurements of a
new monomeric copper(II) compound, in which the metal ion is coordinated to two p-aminobenzoic acid
(PABA) molecules and two chloride ions. This compound with formula [CuCl2(C7H7NO2)2] presents a
peculiar crystalline structure packing, showing hydrogen-bonds between carboxylic acid groups and
short N–Hꢀ ꢀ ꢀCl contacts resulting in a polymeric character in two dimensions. In the third direction,
Cuꢀ ꢀ ꢀCl close contacts between neighboring molecules are responsible for a chain-like magnetic behavior.
Considering the simplicity of the molecular unit, the magnetic properties show surprising results: below
6.4 K a hysteresis cycle appears in the magnetization curves as well as a splitting between low field ZFC–
FC measurements. No phase transition to a long-range order was observed by specific heat measurement.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Copper(II) complex
Molecular magnetism
p-aminobenzoic acid
Specific heat measurement
1. Introduction
because copper(II) is the simplest transition magnetic metal ion,
which can be theoretically treated by S = 1/2 Heisenberg models,
Several strategies have been used to synthesize molecule-based
magnetic compounds [1–3], among which the assembly of metal
ions and organic molecules is the most popular. Monomers, di-
mers, trimers or more complex structures with magnetic dimensi-
onalities greater than zero, such as chains, planes and three
dimensional systems can be obtained depending on the choice of
the organic ligand. The magnetic properties of these compounds
are strongly correlated with the crystal structure, which is essen-
tial to understand the possible ways in which the magnetic
coupling occurs [4]. Covalent bonds are not the only possible
pathways for these magnetic couplings; weak intermolecular
interactions have also been considered a key to understand and
explain the magnetic behavior in molecular compounds [5–7].
Chemists can modify these intermolecular interactions by using
different ligands and molecular moieties [8–11].
such as one- and two-dimensional structures with ferromagnetic
or antiferromagnetic interactions [15–17]. Magneto-structural
correlations in these compounds highlighted the importance of
hydrogen bonds and the halide–halide interactions for the under-
standing of the magnetic properties [18]. The p-aminobenzoic acid
(PABA) is a well known and versatile ligand which can generate
intermolecular interactions through hydrogen bonds and
p–p
stacking interactions. In addition, different coordination com-
pounds have been obtained as result of its ability to coordinate
either by carboxylate or amine groups [19–21]. In this work we
present the synthesis, crystalline structure, magnetic and specific
heat measurements of a new copper(II) complex with molecular
formula [CuCl2(C7H7NO2)2], which displays unusual magnetic
properties for this class of coordination compounds.
Many examples of coordination compounds with general
molecular formula [CuX2(L)2]n, where L stands for an amine ligand
and X for a halide ion are known [12–14]. They have been studied
2. Experimental
2.1. General
⇑
Corresponding author. Tel.: +55 21 2629 2354; fax: +55 21 2629 2129.
E-mail address: mariavaz@vm.uff.br (M.G.F. Vaz).
Permanent address: Universidade Federal Rural do Rio de Janeiro, Instituto de
Anhydrous CuCl2 and PABA (C7H7NO2), methanol and absolute
ethanol were purchased from commercial sources and used with-
out further purification. Elemental analysis (CHN) was carried
out in a Perkin–Elmer CHN 2400 spectrometer. Infrared spectrum
1
Ciências Exatas – Departamento de Química, BR 465, km 47, Seropédica – Rio de
Janeiro, CEP 23.070-200, Brazil. Tel.: +55 21 2682-2807.
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.08.035

G.P. Guedes et al. / Inorganica Chimica Acta 378 (2011) 134–139
135
was recorded from KBr pellets in 4000–500 cmꢁ1 range on a Spec-
Table 2
Selected bond distances (Å) and bond angles (°) for [CuCl2(PABA)2].
trum One Perkin–Elmer spectrometer.
Bond lengths
Bond angles
Cu1–N1
Cu1–N1i
Cu1–Cl1
Cu1–Cl1i
2.044(2)
2.044(2)
2.2645(7)
2.2645(7)
N1–Cu1–N1i
N1–Cu1–Cl1
N1i–Cu1–Cl
N1–Cu1–Cl1i
Cl1–Cu1–Cl1i
O1–H1ꢀ ꢀ ꢀO2ii
N1–H1b–Cl1iii
180.00(10)
2.2. Synthesis of [CuCl2(C7H7NO2)2]
88.62(7)
191.38(7)
91.6(3)
To a solution of p-aminobenzoic acid (222 mg, 16.2 mmol) in
25 mL of absolute ethanol, CuCl2 (105 mg, 0.79 mmol) was added
slowly under constant stirring. The color of the solution changed
from pale yellow to green and a dark-brown microcrystalline pre-
cipitate appeared. The reaction mixture was left under constant
stirring for 2 h. The precipitate was isolated by filtration and
washed with cooled absolute ethanol. Ten milligrams of the micro-
crystalline powder were dissolved in 15 mL of methanol and
through slow evaporation, single rhombohedra crystals were ob-
tained. Yield: 196 mg (61% based on copper chloride). Selected IR
Hydrogen bonds (D–Hꢀ ꢀ ꢀA)
180.0
172.2
170.5
O1–H1ꢀ ꢀ ꢀO2ii
O1ꢀ ꢀ ꢀO2ii
1.82
2.631(3)
2.62
N1–H1bꢀ ꢀ ꢀCl1iii
N1ꢀ ꢀ ꢀCl1iii
3.510(2)
Symmetry codes: (i) ꢁx + 1, ꢁy + 1, ꢁz + 1; (ii) ꢁx + 3, ꢁy + 2, ꢁz; (iii) ꢁx + 1, ꢁy + 2,
ꢁz + 1.
data (cmꢁ1): 3438 (
C@O) and 1606, 1580, 1512 (
m
O–H), 3254 and 3142 (
m N–H), 1808 (m
2.4. Magnetic measurements
m
C@C). Anal. Calc. for C14H14Cl2Cu-
N2O4: C, 41.28; H, 3.47; N, 6.88. Found: C, 41.45; H, 3.63; N, 6.82%.
Magnetization curves versus temperature or applied field were
measured using a Cryogenic SX-600 SQUID magnetometer on
27.2 mg of a polycrystalline sample. Zero-field cooled (ZFC) and
field cooled (FC) were performed between 2.5 and 300 K. The sam-
ple was placed in a gelatin capsule and data were corrected for the
diamagnetism and sample holder. Ac susceptibility measurements
were carried out in a Quantum Design PPMS (Physical Properties
Measurement System) model 6000 with frequencies ranging be-
tween 10 Hz and 10 kHz and constant magnetic field of 12 Oe.
2.3. X-ray diffraction data
Single-crystal X-ray measurements were carried out on a Bru-
ker KAPPA CCD diffractometer using graphite-monochromated
MoKa radiation (k = 0.71073 Å). The final unit cell parameters
were determined from all reflections obtained with DIRAX program
[22]. The integration of the collected reflections was performed
using the EVALCCD program [23]. The absorption correction using
equivalent reflections was performed with the SADABS program
[24]. The structure solutions and full-matrix least-squares refine-
2.5. Specific heat measurement
ments based on F2 were performed with the SHELXS-97 and SHELXL
-
Heat capacity measurements were performed by using a micro-
calorimeter probe of a PPMS (Physical Properties Measurement
System made by Quantum Design), for temperatures in the range
1.8–30 K at zero applied magnetic field. 2.1 mg of the sample
was mixed to 2.0 mg of Apiezon N-grease and attached to the cal-
orimeter. This procedure is necessary to improve the sample-calo-
rimeter thermal contact. The heat capacity of the sample was then
obtained by properly subtracting the addenda (calorimeter plus N-
grease) heat capacity [26].
97 program packages, respectively [25]. Non-hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen atoms
were set in calculated positions and refined as riding atoms. Crys-
tallographic data and processing parameters are given in Table 1.
Selected bond lengths and angles are listed in Table 2.
Table 1
Summary of the crystal structure, data collection and refinement for [CuCl2(PABA)2].
Empirical formula
Formula weight (g molꢁ1
T (K)
C14H14Cl2CuN2O4
408.71
298(2)
3. Results and discussions
)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
3.1. Structure description
triclinic
ꢀ
P1
The structure of [CuCl2(PABA)2] is shown in Fig. 1. The cop-
per(II) ion lies in a square planar environment, coordinated to
nitrogen atoms from two trans PABA molecules and two chloride
ions. The Cu–N1 and Cu–Cl1 bond lengths are typical when com-
pared with other complexes containing amine and chloride ligands
[16,17,27]. The bonds angles N1–Cu–N10 and C11–Cu–C110 are
180°. Each [CuCl2(PABA)2] molecule is linked to another one
through hydrogen bonds between their carboxylic groups, leading
to a hydrogen-bonded layer. The bond lengths H1ꢀ ꢀ ꢀO2 and
O1ꢀ ꢀ ꢀO2 (Table 2) are slightly longer than similar supramolecular
synthons of double hydrogen-bonded carboxylic groups [28–30].
The carboxylic groups are important to the structural packing of
the compound, being responsible for a polymeric character estab-
lished by units linked by pairs of hydrogen bonds. In addition,
weak interactions between hydrogen and chloride of neighboring
molecules lead to a two dimensional network. The H1bꢀ ꢀ ꢀCl1 dis-
tance and N1–H1bꢀ ꢀ ꢀCl1 bond angle are similar to others described
in the literature [21,31,32].
4.6719(7)
5.9916(4)
14.0625(13)
86.942(7)
88.683(11)
88.115(9)
392.72(7)
1
1.728
1.75
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Calculated density (Mg mꢁ3
)
Absorption coefficient ( mmꢁ1
F(000)
)
207
h Range for data colletion (°)
Index ranges
3.63–27.5
ꢁ6 6 h 6 6, ꢁ7 6 k 6 7,
ꢁ18 6 l 6 17
5138
1780 (0.041)
1780/0/106
1.05
R1 = 0.033, wR2 = 0.076
R1 = 0.049, wR2 = 0.099
0.34 and ꢁ0.33
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
)
r
(I)]
Largest difference peak and hole
The shortest distance between copper(II) ions is 4.672 Å, deter-
mined by a translation operation over the a axis (Fig. 2a). At this
point, it is important to highlight that chloride and copper(II) ions
(e Åꢁ3
)
For [CuCl2(PABA)2], w = 1/[
r
2(Fo2) + (0.0309P)2 + 0.1659P] where P = (Fo2 + 2Fc2)/3.

136
G.P. Guedes et al. / Inorganica Chimica Acta 378 (2011) 134–139
Fig. 1. ORTEP view of the molecular unit of compound [CuCl2(PABA)2]. Ellipsoids are at 50% probability.
Fig. 2. Crystal packing of [CuCl2(PABA)2]: (a) ---- intermolecular interaction between chloride and copper(II) ions. (b) Hydrogen bond and weak interactions N–Hꢀ ꢀ ꢀCl.
from neighboring molecules are separated by a distance of 3.563 Å,
which is too long to be considered a di- -chloro bridge [27,33]. The
3.2. Magnetic properties
l
copper ions are separated by a distance of 5.992 Å along the b axis,
where the molecular units are connected by weak N–Hꢀ ꢀ ꢀCl inter-
molecular interactions (Fig. 2b). The longest one, through the
hydrogen bonds formed by the carboxylic acid group is 17.596 Å.
The dihedral angle between the equatorial plane containing the
copper ion and the p-aminobenzoic acid phenyl ring is 69.23°. All
planes of the phenyl rings are quasi parallel to each other, with a
centroid distance between molecular units of 4.667 Å.
3.2.1. DC magnetic measurements
The thermal dependence of the vMT product measured with an
applied field of 1000 Oe (0.1 T) is shown in Fig. 3. In the tempera-
ture range 280–100 K, MT has constant value of
0.37 cm3 K molꢁ1, as expected for a paramagnetic S = ½ ion, with
g = 2.00 (0.375 cm3 K molꢁ1). Upon cooling, the
MT value de-
v
a
v
creases indicating the presence of antiferromagnetic interactions
between the copper ions. Between 15 and 8 K a ‘‘shoulder’’ appears

G.P. Guedes et al. / Inorganica Chimica Acta 378 (2011) 134–139
137
Fig. 3. Thermal dependence of
vMT product measured at H = 1 kOe. The solid line is
Fig. 4. Thermal dependence of vMT product measured at H = 30 Oe.
the best fit by Eq. (1). Inset: plot of
vMT vs. T in temperature range 2–35 K.
explain the results but is ruled out by the presence of an inversion
center between the copper(II) ions [38,39].
(inset Fig. 3) and below that the vMT value decreases continuously
to zero, suggesting an antiferromagnetic ground state.
The deviation of the experimental results with
vMT values
In compound [CuCl2(4-Et(py))2] (4-Et(py) = 4-ethylpyridine)
[34], chloride ions from neighboring molecules occupy the out-
of-plane positions above and below the square quadratic plane
with a distance of 3.22 Å. Due to the out-of-plane stacking, the
compound was considered a chloride-bridged 1D linear chain. In
[CuCl2(PABA)2], the copper environment presents the same charac-
teristics, with the distance between chloride and copper(II) ions of
3.563 Å along the a axis (Fig. 2a), which is slightly longer than in
above the 1D chain behavior suggests that ferromagnetic interac-
tions between copper(II) ions of neighboring chains are present.
The enhancement of the observed behavior in low field suggests
that these interactions should be weak. Ferromagnetic interchain
coupling is expected by considering H1bꢀ ꢀ ꢀCl1 short contact in
the b direction, as shown in Fig. 6. It is important to emphasize that
the magnetic coupling between copper ions separated by the
molecular synthons was neglected due to the large distance be-
tween these ions (ꢃ17 Å). It is clear that the full description of
the magnetic properties cannot be explained by a simple 1D or
1D plus mean field corrections models.
[CuCl2(4-Et(py))2]. Therefore, considering a regular chain 1D Hei-
P
senberg model, with Hamiltonian H ¼ ꢁ2J nꢁ1SA ꢀ SA , we used
i¼1
i
iþ1
the following empirical expression that reproduce Bonner Fisher’s
numerical calculation [35,36] to fit the magnetic data of
[CuCl2(PABA)2]:
3.2.2. AC magnetic measurements
The alternating current magnetic susceptibility of [CuCl2(PA-
BA)2] compound presented a peak at the same temperature as
the low field magnetization (ꢃ6.4 K) that does not change with fre-
quency. The out-phase component (v00) is very small with small in-
crease below 7 K (Fig. S2, Supplementary information). There is a
weak frequency dependence on both components below 7 K. These
results indicated that [CuCl2(PABA)2] compound does not present
slow magnetization relaxation or glassy behavior as found on sin-
gle molecule magnets or single chain magnets [40], but suggest
some kind of ordering.
Ng2b2½0:25 þ 0:14995x þ 0:30094x2ꢂ
vT ¼
ð1Þ
k½1 þ 1:9862x þ 0:68854x2 þ 6:0626x3ꢂ
where x ¼ jJj=kT.
This 1D model describes the magnetic data in the fitted temper-
ature range 280–15 K (solid line – Fig. 3) with the best fit leading to
|J|/k = 4.9 K (3.4 cmꢁ1) and Landée factor of 2.02. The coupling con-
stant value is of the same order of magnitude when compared with
those obtained for chloride-bridged 1D linear chain analogs of gen-
eral molecular formula [CuX2(L)2] (L is a ligand containing the
amine function) [32]. The fitted
vMT curve was extrapolated below
3.3. Specific heat
15 K and shows clearly that this 1D model is not enough to
describe the low temperature data, where other magnetic interac-
tions have to be taken into account. We thus tried to use a first-or-
der molecular field correction [12] to account for the magnetic
path through the short contact between H1bꢀ ꢀ ꢀCl1 (Fig. 2b). No
acceptable fit could be obtained below 15 K. This unusual behavior
becomes more apparent when the field cooled (FC) magnetization
measurement is carried out under a lower magnetic field (30 Oe),
The specific heat versus T data showed a continuous increase
without any sharp peak that would indicate a phase transition to
a long range order as suggested by the AC magnetic measurements
(Fig. S3, Supplementary information). The overall specific heat data
showed a T-dependence that is described by a lattice term and a
magnetic contribution. Unfortunately we could not synthesize a
nonmagnetic analog compound by substitution of copper(II) by
zinc(II), so it was not possible to determine the lattice specific heat
beyond the Debye approximation. Therefore we used this approx-
as shown in Fig. 4, displaying an increase in the vMT value around
8 K. In addition the low field zero field cooled (ZFC) and FC magne-
tization curves show a magnetic irreversibility, below the maxi-
mum at 6.4 K (Fig. 5a). The irreversibility between the ZFC–FC
curves decreases when the magnetic field intensity was increased
from 20 to 100 Oe (Fig. S1, Supplementary information). As ex-
pected, this compound also displays a hysteresis cycle in the range
250 Oe at 1.8 K (Fig. 5b), suggesting a ferromagnetic like behavior.
Spin canting and the related weak ferromagnetism [37] could also
imation cautiously, and the 1D Heisenberg chain model, with
P
H ¼ ꢁ2J nꢁ1SA ꢀ SA , to calculate the specific heat in the temper-
i¼1
i
iþ1
ature range 8–15 K using Eq. (2). The magnetic contribution in Eq.
(2), cmag(T), is a polynomial expression that reproduces the Fabri-
cius’ numerical calculations [41,42]. The term LT3 in Eq. (2) is the
lattice contribution to the total specific heat in the Debye
approximation.

138
G.P. Guedes et al. / Inorganica Chimica Acta 378 (2011) 134–139
Fig. 5. (a) ZFC and FC measures performed under applied field of 20 Oe. (b) Hysteresis cycle at 1.8 K in magnetic field range 250 Oe.
Fig. 6. Spin topology in [CuCl2(PABA)2] compound.
cðTÞ ¼ cmagðTÞ þ LT3
ð2Þ
Fig. 7. Temperature dependence of total specific heat of [CuCl2(PABA)2] (open
circles). Dash-dot and solid lines represent the lattice contribution and the fit by Eq.
(2), respectively. Dashed line is the extrapolated 1D behavior below 8 K. Inset:
magnetic contribution to total specific heat.
with
!
x þ Ax2 þ Bx3
cmagðxÞ ¼ R
3 þ Cx þ Dx2 þ Ex3 þ Fx4 þ Gx5
where
interactions between copper(II) ions and can be modeled, in first
approximation, by a 1D Heisenberg antiferromagnetic chain mod-
el. At low temperatures, a deviation from this model and an unu-
sual magnetic irreversibility was observed, suggesting the
presence of weak ferromagnetic interactions. No phase transition
was evidenced by specific heat measurements, but an excess con-
tribution due to additional interactions is responsible to the devi-
ation from a simple chain model as also seen in the magnetic
measurements. Further work such as EPR, X-ray diffraction at
low temperature and simulation should be pursued in order to ex-
plain the observed low temperature behavior.
x ¼ kT=jJj
and the A–G parameter values were obtained from Ref. [41].
The results are shown in Fig. 7, where it can be seen that the 1D
chain model accounts for the data reasonably in the temperature
range 8–15 K. The best fit was achieved with |J|/k = 11.1 K
(7.7 cmꢁ1), which is higher than the obtained from magnetic data.
The lattice contribution term, from which we estimated the Debye
temperature hD = 78 K, was L = 4.1 mJ molꢁ1 K4. This value is of the
same order as previously reported for a similar mononuclear cop-
per(II) compound [43]. Inset in Fig. 7 represents the magnetic con-
tribution, obtained by subtracting the lattice contribution from
total specific heat. The calculated ctotal was extrapolated below
8 K and an excess contribution becomes apparent, attributed to
other interactions not taken into account by this simple 1D model.
Acknowledgments
Financial support by CAPES, FAPERJ, CNPq and FACEPE is kindly
acknowledged. The authors also acknowledge the LDRX-UFF.
4. Conclusion
Appendix A. Supplementary material
In this work we presented the synthesis, structure, magnetic
and specific heat measurements of the [CuCl2(PABA)2] compound.
Intermolecular interactions act as pathways for the main magnetic
CCDC 784624 contains the supplementary crystallographic data
for this compound. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-

G.P. Guedes et al. / Inorganica Chimica Acta 378 (2011) 134–139
139
[16] R.T. Butcher, J.J. Novoa, J. Ribas-Ariño, A.W. Sandvik, M.M. Turnbull, C.P.
Landee, B.M. Wells, F.F. Awwadi, Chem. Commun. (2009) 1359.
[17] T. Lancaster, S.J. Blundell, M.L. Brooks, P.J. Baker, F.L. Pratt, J.L. Manson, M.M.
Conner, F. Xiao, C.P. Landee, F.A. Chaves, S. Soriano, M.A. Novak, T.P.
Papageorgiou, A.D. Bianchi, T. Herrmannsdörfer, J. Wosnitza, J.A. Schlueter,
Phys. Rev. B: Condens. Matter Mater. Phys. B 75 (2007) 094421.
[18] R.D. Willett, C. Galeriu, C.P. Landee, M.M. Turnbull, B. Twamley, Inorg. Chem.
43 (2004) 3804.
c.uk/data_request/cif. Figure S1 displays ZFC and FC measures per-
formed under applied field of 100 Oe. The temperature dependence
of in-phase and out-phase components of the ac susceptibility are
shown in Figure S2. The thermal dependence of total specific heat
is depicted in Figure S3. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.ica.2011.08.035. These data include MOL files and InChiKeys of
the most important compounds described in this article.
[19] D.-H. Hu, W. Huang, S.-H. Gou, J.-L. Fang, H.-K. Fun, Polyhedron 22 (2003)
2661.
[20] H.-J. Chen, X.-M. Chen, Inorg. Chim. Acta 329 (2002) 13.
[21] M.-L. Tong, S.-L. Zheng, X.-M. Chen, Polyhedron 19 (2000) 1809.
[22] A.J.M. Duisenberg, J. Appl. Crystallogr. 25 (1992) 92.
[23] A.J.M. Duisenberg, L.M.J. Kroon-Batenburg, A.M.M. Schreurs, J. Appl.
Crystallogr. 36 (2003) 220.
References
[24] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area
Detector Data, University of Göttingen, Germany, 1996.
[25] G.M. Sheldrick, T.R. Schneider, Methods Enzymol. 277 (1997) 319.
[26] F.L.A. Machado, W.G. Clark, Rev. Sci. Instrum. 59 (1988) 1176.
[27] S. Mukherjee, C. Basu, S. Chowdhury, A.P. Chattopadhyay, A. Ghorai, U. Ghosh,
H. Stoeckli-Evans, Inorg. Chim. Acta 363 (2010) 2752.
[28] G. Yang, H.-G. Zhu, B.-H. Liang, X.-M. Chen, J. Chem. Soc., Dalton Trans. (2001)
580.
[29] M. Baskett, P.M. Lahti, Polyhedron 24 (2005) 2645.
[30] T. Inabe, J. Mater. Chem. 15 (2005) 1317.
[31] T. Ghosh, S. Das, S. Pal, Polyhedron 29 (2010) 3074.
[32] K.C. Shortsleeves, L.N. Dawe, C.P. Landee, M.M. Turnbull, Inorg. Chim. Acta 362
(2009) 1859.
[33] C.-H. Ge, H.-Z. Kou, Z.-H. Ni, Y.-B. Jiang, A.-L. Cui, Inorg. Chim. Acta 359 (2006)
541.
[34] V.H. Crawford, W.E. Hatfield, Inorg. Chem. 16 (1977) 1336.
[35] J.C. Bonner, M.E. Fisher, Phys. Rev. 135 (1964) A640.
[36] W.E. Hatfield, R.R. Weller, J.W. Hall, Inorg. Chem. 19 (1980) 3825.
[37] B.-P. Yang, A.V. Prosvirin, Y.-Q. Guo, J.-G. Mao, Inorg. Chem. 47 (2008) 1453.
[38] J.-Y. Zhang, C.-M. Liu, D.-Q. Zhang, S. Gao, D.-B. Zhu, Inorg. Chem. Commun. 10
(2007) 897.
[39] B. Zhang, Z. Wang, Y. Zhang, K. Takahashi, Y. Okano, H. Cui, H. Kobayashi, K.
Inoue, M. Kurmoo, F.L. Pratt, D. Zhu, Inorg. Chem. 45 (2006) 3275.
[40] M.A. Novak, J. Magn. Magn. Mater. 272–276 (2004) E707.
[41] R.E. Rapp, E.P. Souza, H. Godfrin, R. Calvo, J. Phys.: Condens. Matter. 7 (1995)
9595.
[1] V. Tangoulis, D. Panagoulis, C.P. Raptopoulou, C. Dendrinou-Samara, Dalton
Trans. (2008) 1752.
[2] O. Cador, M.G.F. Vaz, H.O. Stumpf, C. Mathonière, O. Kahn, Synth. Met. 122
(2001) 559.
[3] A. Dei, D. Gatteschi, C. Sangregorio, L. Sorace, M.G.F. Vaz, Chem. Phys. Lett. 368
(2003) 162.
[4] M. Vázquez, A. Taglietti, D. Gatteschi, L. Sorace, C. Sangregorio, A.M. González,
M. Maneiro, R.M. Pedrido, M.R. Bermejo, Chem. Commun. 15 (2003) 1840.
[5] M.G.F. Vaz, E.F. Pedroso, N.L. Speziali, M.A. Novak, A.F.C. Alcântara, H.O.
Stumpf, Inorg. Chim. Acta 326 (2001) 65.
[6] J.-P. Costes, F. Dahan, B. Donnadieu, M.-J.R. Douton, M.-I.F. Garcia, A.
Bousseksou, J.-P. Tuchagues, Inorg. Chem. 43 (2004) 2736.
[7] S.-W. Hung, F.-A. Yang, J.-H. Chen, S.-S. Wang, J.-Y. Tung, Inorg. Chem. 47
(2008) 7202.
[8] C.B. Aakeröy, A.M. Beatty, K.R. Lorimer, J. Chem. Soc., Dalton Trans. (2000)
3869.
[9] A. Bencini, A. Caneschi, A. Dei, D. Gatteschi, C. Sangregorio, D. Shultz, L. Sorace,
M.G.F. Vaz, C. R. Chim. 6 (2003) 663.
[10] Y.-F. Han, M. Li, T.-W. Wang, Y.-Z. Li, Z. Shen, Y. Song, X.-Z. You, Inorg. Chem.
Commun. 11 (2008) 945.
[11] M. Perec, R.F. Baggio, O. Peña, R.P. Sartoris, R. Calvo, Inorg. Chim. Acta 373
(2011) 117.
[12] W.E. Estes, D.P. Gavel, W.E. Hatfield, D.J. Hodgson, Inorg. Chem. 17 (1978)
1415.
[13] M. Hernández-Molina, J. González-Platas, C. Ruiz-Pérez, F. Lloret, M. Julve,
Inorg. Chim. Acta 284 (1999) 258.
[14] M.F. Primik, S. Göschl, M.A. Jakupec, A. Roller, B.K. Keppler, V.B. Arion, Inorg.
Chem. 49 (2010) 11084.
[42] K. Fabricius, U. Low, K.-H. Mutter, P. Ueberholz, Phys. Rev. B 44 (1991) 7476.
[43] P.R. Hammar, M.B. Stone, D.H. Reich, C. Broholm, P.J. Gibson, M.M. Turnbull,
C.P. Landee, M. Oshikawa, Phys. Rev. B: Condens. Matter Mater. Phys. 59
(1999) 1008.
[15] G.A. van Albada, S. Tanase, I. Mutikainen, U. Turpeinen, J. Reedijk, Inorg. Chim.
Acta 361 (2008) 1463.