Mild Hydrothermal Synthesis of Cu(SeO3).2H2O: Structural Characterization, Thermal, Spectroscopic and Magnetic Studies

Article abstract of DOI:10.1016/j.saa.2008.10.032

Cu(SeO₃).2H₂O has been synthesized by hydrothermal technique under autogeneous pressure. The compound crystallizes in the P2₁2₁2₁ orthorhombic space group. The unit cell parameters are a = 6.672(1), b

Full text of DOI:10.1016/j.saa.2008.10.032

Spectrochimica Acta Part A 72 (2009) 356–360
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Mild Hydrothermal Synthesis of Cu(SeO3).2H2O: Structural Characterization,
Thermal, Spectroscopic and Magnetic Studies
Aitor Larran˜agaa, José L. Mesab,∗, Luis Lezamab, María I. Arriortuaa, Teófilo Rojob
a Departamento de Mineralogía y Petrología, Facultad de Ciencia y Tecnología. Universidad del País Vasco/EHU, Apdo. 644, E-48080 Bilbao. Spain
b Departamento de Química Inorgánica, Facultad de Ciencia y Tecnología. Universidad del País Vasco/EHU, Apdo. 644, E-48080 Bilbao. Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 April 2008
Received in revised form 19 August 2008
Accepted 9 October 2008
Cu(SeO3).2H2O has been synthesized by hydrothermal technique under autogeneous pressure. The com-
pound crystallizes in the P212121 orthorhombic space group. The unit cell parameters are a = 6.672(1),
b = 9.167(1) and c = 7.372(1) Å with Z = 4. The crystal structure has been refined using the Rietveld method.
The limit of thermal stability is 130 ◦C, temperature at which the water content is lost. Above 470 ◦C
the compound decomposes in SeO2(g) and CuO(s). The IR spectrum shows the characteristic bands of
the (SeO3)2− oxoanion and water molecules. An intense absorption band characteristic of Cu(II) cations
in five-coordination is observed in the diffuse reflectance spectrum. The ESR spectra are isotropic from
room temperature to 4.2 K, with g = 2.13(1). Magnetic measurements confirm the existence of a global
antiferromagnetic behavior with a spin canting phenomenon detected at, approximately, 30 K.
© 2008 Elsevier B.V. All rights reserved.
Keywords:
Hydrothermal synthesis
Cu(II) selenite
Thermal study
IR and UV-Vis spectroscopies
ESR
Magnetism
1. Introduction
structural chemistry in transition metal selenites. In this way, in the
Mn4(H2O)3(SeO4)3 and Mn3(H2O)(SeO3) phases [8], which exhibit
An important area in materials science is the design of com-
pounds with condensed frameworks, which can give rise to original
physical properties with potential practical applications such as ion
exchange, surface absorption chemistry, conductivity, etc., due to
the great number of different cations and arrangement that they
can exhibit [1,2]. In this way, the crystal chemistry of selenium(IV)
oxo compounds shows abundant structural versatility expressed by
the significant number of different compounds [3]. The transition
metal-selenium-oxygen system has been the subject of many pre-
vious investigations. Several phases have been reported in which
selenium is found in an oxidation state IV. Depending on the con-
ditions in solution [4] transition-metal compounds with (HSeO3)−,
(SeO3)2− or (Se2O5)2− oxoanions are known [5–7]. The electronic
configuration of the selenium(IV) oxoanion promotes the formation
of three bonding electrons pairs with the oxygen atoms. Further-
more, the presence of an active lone-pair of electrons on the Se(IV)
centers can play an important role in the crystalline architecture of
this family of compounds [3], affected by the requirement of empty
space to accommodate the selenium lone-pair electrons. Thus, it
can be predicted that the combination of the inherently asymme-
try of (SeO3)2− with various transition metals will result in a rich
a three-dimensional crystal structure constructed by chains, there
exist cavities delimited by the MnO6 octahedra, and SeO3 trigo-
nal pyramids, with the lone pair, in an sp3 hybrid orbital, pointing
towards the center of the cavities. Similarly, the two Mn(SeO3) poly-
morps [9] also exhibit a three-dimensional crystal structure formed
by chains that give rise to hexagonal channels with the lone elec-
tronic pair directed towards the center of these channels. Recently,
a few amine-templated metal selenites have also been synthesized
under hydrothermal/solvothermal conditions in the presence of
organic amines as templates. These systems have open-framework
structures [10].
V.G. Gattow synthesized the Cu(SeO3).2H2O, and crystal struc-
ture was solved from single-crystal X-ray diffraction [11]. The
crystal structure of Cu(SeO3).2H2O consists of a not very compact
three-dimensional framework constructed by one CuO5 polyhe-
dron with square pyramidal geometry and one SeO3 trigonal
pyramid, both of them crystallografically independent (Fig. 1). In
the CuO5 polyhedra, the copper(II) ions are coordinated to five
oxygen atoms at a mean bond distance of 2.05(1) Å and semi-
coordinated to other oxygen ones at approximately 3 Å [12,13].
Furthermore, the CuO5 polyhedra are not linked amongst them-
selves, but they share three vertices with three selenite groups. The
un-shared oxygen atoms belong to the water molecules. This inor-
ganic skeleton is extended along the three spatial directions, giving
rise to the three-dimensional crystal structure.
∗
Corresponding author. Tel.: +34 946015523; fax: +34 946013500.
E-mail address: joseluis.mesa@ehu.es (J.L. Mesa).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.10.032

A. Larra˜naga et al. / Spectrochimica Acta Part A 72 (2009) 356–360
357
Table 1
Summary of crystallographic data and least-squares refinement for Cu(SeO3).2H2O.
Compound
Cu(SeO3).2H2O
226.53
Orthorhombic
P212121 (no. 19)
6.672(1)
9.167(1)
7.372(1)
450.9(1)
273
M/gmol−1
Crystal system
Space group
a/Å
b/Å
b/Å
Volume/Å3
T/K
␭(CuK␣)
1.5418
4
3.34
Z
Dc/gcm−3
2␪ range/◦
5-90
2␪ step-scan increment/◦
Time per step/s
No. of reflections, independent
No. of structural parameters
No. of profile parameters
No. of atoms refined
RBragg, Rf/%
0.02
10
466, 234
21
11
7
Fig. 1. Polyhedral view of the of the crystal structure of Cu(SeO3).2H2O.
12.6, 10.4
8.09, 10.3
1.70
Rp, Rwp/%
␹2/%
On the other hand, mild hydrothermal synthesis can be used
to obtain, as chemically pure phases, not very condensed tran-
sition metal selenites, that only exist over narrow stabilization
ranges [14]. This allows the study of their physical properties. In the
present work, we report on the mild hydrothermal synthesis, struc-
tural characterization, and the thermal, spectroscopic and magnetic
properties of Cu(SeO3).2H2O.
and the bond distances and angles, obtained from the Rietveld
refinement, are very similar to those reported by Gattow [11]. So
the same three-dimensional crystal structure is maintained (see
Supplementary Material).
2.3. Physicochemical Characterization Techniques
2. Experimental
The thermogravimetric analysis was carried out under oxygen
in a SDC 2960 Simultaneous DSC-TGA TA Instrument, at 5 ◦C.min−1
in the temperature range 30-800 ◦C. A crucible containing ca. 20 mg
of sample was used. The X-ray thermodiffractometry in air was
performed on a PHILIPS X’PERT automatic diffrcatometer (Cu-K␣
radiation) equipped with a variable-temperature stage (Paar Phys-
ica TCU2000) with a Pt sample holder. The IR spectrum (KBr pellet)
was obtained with a Nicolet FT-IR 740 spectrophotometer in the
spectral range 4000-400 cm−1. The diffuse reflectance spectrum
was registered at room temperature on a Cary 5000 spectrometer
in the spectral range 2000-210 nm. A Bruker ESP 300 spectrometer
was used to record the polycrystalline ESR spectra. The tempera-
ture was stabilized with an Oxford Instrument (ITC 4) regulator.
The magnetic field was measured with a Bruker BNM 200 gauss-
meter and the frequency inside the cavity was determined using
a Hewlett-Packard 5352B microwave frequency counter. Magnetic
measurements on a powdered sample were performed in the tem-
2.1. Synthesis and Characterization
Cu(SeO3).2H2O has been synthezised by mild hydrothermal
conditions in 20 mL of water and starting from SeO2 (9 mmol)
and CuCl2.2H2O (1 mmol). The pH of the resulting solution
was increased up to 6.0 by addition of NH4OH. The mixture
was maintained in a politetrafluoroethylene reactor at 100 ◦C
for 3 days. Blue single-crystals were obtained, with dimensions
0.3 × 0.2 × 0.15 mm, which were isolated by filtration and washed
with water and acetone and dried over P2O5 for 6 hrs. The yield,
approximately 80%, was estimated taking into account the max-
imum amount to obtain considering that the CuCl2.2H2O acts as
limiting reagent.
The metal ion and selenium contents were confirmed by induc-
tively coupled plasma atomic emission spectroscopy (ICP-AES),
performed with an RL Fisons 3410 spectrometer. Found: Se, 34.5;
Cu, 28.0. Cu(SeO3).2H2O requires: Se, 34.9; Cu, 28.1. The density
was measured by picnometry using kerosene. The value obtained
is 3.4(1) g.cm−3
.
2.2. X-ray Powder Diffraction Characterization
The X-ray powder diffraction (PXD) characterization of
Cu(SeO3).2H2O has been carried out using a PHILPIS X’PERT auto-
matic diffractometer with the Cu-K␣ radiation. Table 1 gives the
experimental conditions in which the powder diffraction pattern
was recorded, along with the final values of the residual indices of
the refinement.
The FULLPROF program was used to perform the profile refine-
ment of the diffractogram without structural model (pattern
matching routine) [15]. The structural refinement was carried out
using the refined unit-cell parameters and the atomic coordi-
nates given in the literature for the Cu(SeO3).2H2O phase [11].
The observed, calculated and difference PXD patterns are shown
in Fig. 2. The refined unit cell parameters, the atomic coordinates
Fig. 2. Observed, calculated and difference X-ray powder diffraction patterns of
Cu(SeO3).2H2O.

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A. Larra˜naga et al. / Spectrochimica Acta Part A 72 (2009) 356–360
Fig. 3. Thermodifractograms of Cu(SeO3).2H2O.
perature range 5-300 K, using a Quantum Desing MPMS-7 SQUID
magnetometer. The magnetic field was 0.1 T, a value within the
range of linear dependence of magnetization vs. magnetic, field
even at 5 K.
The thermal behavior of this selenite has been also studied
by time-resolved X-ray thermodiffractometry. The patterns were
recorded in 2␪ steps of 0.02◦ in the range 5-40◦, counting for 2 s
per step and increasing the temperature at 5 ◦C.min−1. The results
are given in Fig. 3. Cu(SeO3).2H2O is stable up to, approximately,
130 ◦C. Above this temperature an amorphous phase is formed,
which recrystallizes between 400 and 485 ◦C, giving rise to the
Cu2O(SeO3) phase [space group, P213; a = 8.925 Å] [16b]. Finally, at
temperatures higher than 485 ◦C the decomposition of the selenite
starts, and subsequent formation of CuO as an inorganic residue is
obtained at 800 ◦C. This later result is similar to that obtained in the
thermogravimetric study.
3. Results and discussion
3.1. Thermal Behaviour
The thermal decomposition curve of Cu(SeO3).2H2O shows an
initial mass loss of, approximately, 1%, in the 25-130 ◦C range, which
has been assigned to the elimination of the water absorbed by
the sample. From 130 to 280 ◦C the elimination of the water takes
place (exp. 18%; calc. 16%). Finally, in the 470-570 ◦C range the
decomposition of the (SeO3)2− anion to SeO2 gas (exp. 49.3; calc.
48.9%) occurs. The X-ray powder diffraction pattern of the inorganic
residue obtained at 800 ◦C shows the presence of CuO (s) [Space
group, Cc; a = 4.694, b = 3.428, c = 5.137 Å, ␤ = 99.546◦] [16a]. The
proposed decomposition reaction is: Cu(SeO3).2H2O (s) → 2H2O
(g) + SeO2 (g) + CuO (s).
3.2. Infrared and UV-Vis Spectroscopies
The infrared spectrum of Cu(SeO3).2H2O shows the bands
corresponding to the vibrational modes of the water molecules
and selenite oxoanion. For the H2O molecule, the stretching and
deformation modes appear in the 3335-2850 cm−1 range and at
1590 cm−1, respectively. For the (SeO3)2− oxoanion, the symmetric
Fig. 4. Thermal evolution of the intensity and line width of the ESR signals of Cu(SeO3).2H2O.

A. Larra˜naga et al. / Spectrochimica Acta Part A 72 (2009) 356–360
359
Fig. 5. Thermal variation of the ␹ and ␹mT curves for Cu(SeO3).2H2O, at 1000 G.
m
Fig. 7. Remnant magnetization measured at 100 G for Cu(SeO3).2H2O.
and antisymmetric stretching vibrations, ␯s(SeO3), ␯as(SeO3) and
the deformation mode, ␦(SeO3), appear at 1045, 800-615, and 530,
485 cm−1, respectively. The position observed for these bands are
in good agreement with those expected for this kind of compound
and are similar to those found in the literature for other selenite
phases [17].
In the diffuse reflectance spectrum of Cu(SeO3).2H2O an intense
absorption band centred at, approximately, 750 nm, is observed,
which is characteristic of a five-coordinated environment for the
Cu(II) cation with a square pyramidal geometry [18]. An estima-
The thermal evolution of the intensity of the signals is shown
in Fig. 4b. The intensity slightly increases from room temperature
to 80 K, temperature at which the intensity reaches its maximum
value. From this temperature the intensity decreases continuously
until 5.0 K. These results are in good agreement with the exis-
tence of a global antiferromagnetic ordering. However, from Fig. 4c,
it can be observed as the intensity of the ESR signals increases
from 5 to 30 K, suggesting a ferromagnetic transition at this later
temperature. Signals with low intensity are observed at low tem-
peratures, which show small variations in both intensity and line
width (Fig. 4d), in comparison with those obtained at higher tem-
peratures (Fig. 4a and b). The thermal variation of the line width
remains practically unchanged from 300 to 70 K; below this tem-
perature the line width increases vigorously, probably due to a spin
correlation (Fig. 4b) [20].
tion of the “band gap”, from the position a half-height of the more
∼
energetic band observed in the diffuse reflectance spectrum (
=
28000 cm−1, see Supplementary Material), gives a value of 3.47 eV.
3.3. Magnetic behavior
3.3.1. ESR Measurements
The ESR spectra of Cu(SeO3).2H2O were performed at the X-
band on a powdered sample from room temperature to 4.2 K. The
spectra exhibit isotropic signals due to the presence of magneti-
cally coupled Cu(II) cations [19] (Fig. 4a). The signals are centred at,
approximately, 3150 Gauss. They were fitted to Lorentzian curves
obtaining a value for g = 2.13(1), which is in the characteristic range
of the d9-Cu(II) ion [19]. The ESR signals do not show variation
with decreasing temperature from 300 to 70 K; however, below this
temperature, the signal broadens and loses intensity (Fig. 4a).
3.3.2. Magnetic Measurements
Magnetic susceptibility measurements were carried out on a
powdered sample from 5.0 K to room temperature at a magnetic
field of 1000 Gauss in the Zero Field Cooling (ZFC) and Field Cooling
Fig. 6. Thermal variation of the ␹m and ␹mT curves for Cu(SeO3).2H2O, measured at
different magnetic fields.
Fig. 8. Hysteresis loops carried out at 5 K for Cu(SeO3).2H2O.

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A. Larra˜naga et al. / Spectrochimica Acta Part A 72 (2009) 356–360
Table 2
rio de Ciencia y Tecnología” and “Fondo Social Europeo” (FSE), for
the magnetic and the X-ray diffraction measurements, respectively.
Values (◦) of the Se-O-Cu bond angles for Cu(SeO3).2H2O.
Cu-O(1)-Se
Cu-O(3)-Se
Cu-O(5)-Se
136.9(1)
127.7(1)
68.5(1)
Cu-O(2)-Se
Cu-O(4)-Se
114.0(1)
65.6(1)
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.saa.2008.10.032.
(FC) modes. The thermal evolution of the molar magnetic suscep-
tibility, ␹m, and the ␹mT product is shown in Fig. 5. The molar
magnetic susceptibility, which shows an abrupt increase at approx-
imately 30 K probably due to a canting spin phenomenon, follows
the Curie-Weiss law in the 300-100 K range. The values of the
Curie and Curie-Weiss temperature are Cm = 0.40 cm3K/mol and
␪ = -73.5 K.
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Acknowledgements
This work has been financially supported by the “Ministerio de
Educación y Ciencia” (MAT2007-60400) and the “Gobierno Vasco”
(IT-177-07 and IT-312-07). The authors thank the technicians of
SGIker, Dr. I. Orue and Dr. F.J. Sangüesa, financed by the National
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