Syntheses, crystal structures, and properties of three new metal selenites Na2Co2(SeO3)3, Na2Co 1.67Ni0.33(SeO3)3, and Na 2Ni2(SeO3)3

Article abstract of DOI:10.1016/j.jssc.2010.06.020

Three new sodium cobalt (nickel) selenite compounds, namely, Na ₂Co₂(SeO₃)₃, Na₂Co _1.67Ni_0.33(SeO₃)₃, and Na ₂Ni₂(SeO₃)₃ have been hydro-/solvothermally synthesized in the mixed solvents of acetonitrile and water. Single-crystal X-ray diffraction analyses reveal that these isostructural compounds belong to the orthorhombic Cmcm space group and their structures feature three-dimensional open frameworks constructed by the two-dimensional layers of [MSeO₃] pillared by the [SeO₃]^2- groups. The two different types of Na ions reside in the intersecting two-dimensional channels parallel to the a- and c-axes, respectively. Their thermal properties have been investigated via TGADSC. The magnetic measurements indicate the existence of the antiferromagnetic interactions in these compounds.

Full text of DOI:10.1016/j.jssc.2010.06.020

Journal of Solid State Chemistry 183 (2010) 1955–1961
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Syntheses, crystal structures, and properties of three new metal selenites
Na Co (SeO ) , Na Co1.67Ni0.33(SeO ) , and Na Ni (SeO )
2
2
3 3
2
3 3
2
2
3 3
a,b
a,n
a,b
a,n
Xiao-Qing Yuan , Mei-Ling Feng , Jian-Rong Li , Xiao-Ying Huang
a
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
Graduate School of the Chinese Academy of Sciences, Beijing 100049, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new sodium cobalt (nickel) selenite compounds, namely, Na Co (SeO ) , Na Co1.67Ni0.33(SeO ) ,
2
2
3 3
2
3 3
Received 1 May 2010
Received in revised form
2 2 3 3
and Na Ni (SeO ) have been hydro-/solvothermally synthesized in the mixed solvents of acetonitrile
and water. Single-crystal X-ray diffraction analyses reveal that these isostructural compounds belong to
2
5 June 2010
the orthorhombic Cmcm space group and their structures feature three-dimensional open frameworks
Accepted 28 June 2010
Available online 16 July 2010
2ꢀ
constructed by the two-dimensional layers of [MSeO
3
] pillared by the [SeO
3
]
groups. The two
+
different types of Na ions reside in the intersecting two-dimensional channels parallel to the a- and
c-axes, respectively. Their thermal properties have been investigated via TGA–DSC. The magnetic
measurements indicate the existence of the antiferromagnetic interactions in these compounds.
Keywords:
Cobalt
Nickel
&
2010 Elsevier Inc. All rights reserved.
Selenite
Hydro-/solvothermal
Magnetic properties
1
. Introduction
obtained three new inorganic transition metal selenite compounds
containing the sodium ions, namely, Na Co2ꢀxNi (SeO (x¼0 (1),
0.33 (2), (3)). Herein we report their syntheses, crystal
structures, and thermal and magnetic properties.
2
x
3 3
)
Metal selenites have received considerable attention in the past
2
two decades, in which selenium is found in a formal oxidation
state of IV. Depending on the different conditions in solutions
[
1,2], selenium(IV) may exist in various forms such as H
2
SeO
[3–6]. Of particularly interesting is
, in which the Se ion with stereochemically active lone
pair of electrons adopts the asymmetric coordination geometry of
-SeO , which may lead to noncentrosymmetric structures with
3
,
ꢀ
2ꢀ
2ꢀ
HSeO
SeO
3
ꢀ
, SeO
3
, and Se
2 5
4+
O
2. Experimental section
2
3
2.1. Materials and methods
c
3
consequent interesting physical properties, such as nonlinear
optical second harmonic generation (SHG) [7–10]. The transition
metal selenites are of special interest due to their unique magnetic
properties. The transition metal selenites incorporating alkali (or
alkaline earth) metal ions have been reported mostly by Giester
CoCl
pyrazinedicarboxylic acid (98%), pyridine-3,5-dicarboxylic acid
98%), 1,10-phenanthroline (99%), and acetonitrile (99%) were
2
ꢁ 6 H
2 2 2 2 3
O (99%), NiCl d6H O (98%), Na SeO (98%), 2,3-
(
used. All of the chemical reagents were obtained from commercial
sources and used without future purification. Co, Ni, Na,
Se analyses were carried out with an ICPQ-100 spectrometer.
Energy dispersive X-ray spectroscopy (EDX) was measured by
JEOL-6700F scanning electron microscope. IR spectra were
recorded with a Magna 750FT-IR spectrometer using KBr pellets
and Wildner, formulated as A
x
B
y
(SeO
3
)
2
(A¼alkali metals or
(SeO
[25–28], and A
3 8
) [25], respectively. A variety of lanthanide selenites and
alkaline earth metals, B¼transition metals) [5,11–17], A
B
x y
3 3
)
[
(
18–23], A B (SeO )
x y 3 4
SeO
[17,23,24], A
x y
B (SeO
)
3 6
x y
B
actinide selenites have also been studied [29–32]. In addition,
organic–inorganic hybrid materials by incorporating organic
carboxylate ligands into metal selenite moieties have been
described [33,34]. In our attempt to synthesize the organic–
inorganic hybrid transition metal selenites, we unexpectedly
ꢀ1
in the range 4000–400 cm . Simultaneous thermogravimetric
analysis and differential scanning calorimetry (TGA–DSC) were
carried out with a NETZSCH STA 449F3 unit at a heating rate of
10 1C/min under a nitrogen atmosphere. The powder X-ray
diffraction patterns were collected in the angular range of
2
y¼10–801 with a step size of 0.021 on the Rigaku MiniFlexII
n
X-ray diffractometer. The variable-temperature magnetic suscept-
ibilities (2–300 K) were measured with a model MPMS60000
superconducting extraction sample magnetometer under a field
Corresponding author. Fax: +86 591 83793727.
E-mail addresses: fml@fjirsm.ac.cn (M.-L. Feng),
xyhuang@fjirsm.ac.cn (X.-Y. Huang).
0022-4596/$ - see front matter & 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2010.06.020

1
956
X.-Q. Yuan et al. / Journal of Solid State Chemistry 183 (2010) 1955–1961
of 1000 Oe with the crystalline samples kept in a capsule for
weighing.
1617 (s), 1384 (m), 1018 (w), 818 (w), 722 (m), 726 (m), 622 (s),
475 (m).
The pure powders of 1 and 3 could also be synthesized by the
same reactions in the absence of organic reagents.
2.2. Syntheses of compounds 1, 2, and 3
Compounds 1, 2, and 3 were synthesized by employing the
2.3. Determination of crystal structures
hydro-/solvothermal methods in similar reaction conditions and
isolation procedures. A mixture of reactants in a mixed solvent of
The single crystal X-ray diffraction studies were performed on
a Rigaku SCX-mini CCD diffractometer for compounds 1 and 2,
and on a Rigaku Saturn724 CCD diffractometer for compound 3
3
mL acetonitrile and 3 mL distilled water was stirred to assure
homogeneity and sealed in an autoclave equipped with a Teflon
liner (28 mL). After 7 days of reaction at 140 1C, the crystals were
isolated by filtration and washed with distilled water. The powder
X-ray diffraction study for the compounds indicated that all of the
three compounds are single-phased.
equipped with graphite monochromated MoK
a radiation
¼0.71073 A˚ ). Intensity data were collected by the narrow
(l
frame method at room temperature and corrected for Lorentz and
polarization effects as well as for absorption by the SADABS
program. All the structures were solved by direct methods and
refined by full-matrix least-squares cycles in SHELX-97 [35]. The
crystallographic data and structural refinement parameters for
the three compounds are summarized in Table 1. The atomic
coordinates are listed in Table 2 for compounds 1, 2, and 3.
2
.2.1. Preparation of Na
The reagents are CoCl
0.173 g, 1 mmol), and 2,3-pyrazinedicarboxylic acid (0.088 g,
.52 mmol). The dark purple crystals of 1 were isolated in 49.62%
2
Co
2
(SeO
3
)
3
(1)
2
ꢁ 6H
2
O (0.118 g, 0.5 mmol), Na
2 3
SeO
(
0
ꢀ
1
yield (0.067 g) calculated based on Co. IR (KBr, cm ): 2920 (vw),
849 (vw), 1636 (v), 1617 (s), 1384 (s), 1356 (w), 1021 (w), 715
br), 619 (m), 527 (w), 476 (w).
2
(
3. Results and discussion
3
.1. Synthesis
2
.2.2. Preparation of Na
The reagents are CoCl
0.049 g, 0.2 mmol), Na
2
Co1.67Ni0.33(SeO
3
)
3
(2)
O (0.071 g, 0.3 mmol), NiCl
(0.177 g, 1.02 mmol), and 2,3-
2
d6H
SeO
2
2 2
d6H O
The title compounds were synthesized hydro-/solvothermally
(
2
3
in the mixed solvents of acetonitrile and distilled water in a
volume proportion of 1:1. It is noteworthy that the presence of
organic carboxylic acids in the reactions is important not only for
the phase purity but also for the crystallinity, although they did
not enter the structures of final products. For instance, we could
obtain the crystals of compounds 1 and 3 in the presence of
organic acids, while the pure phases of compounds 1 and 3 in
powder form were formed in the same synthetic conditions but
without adding any kind of organic acids. Note that the pH values
for the reactant mixtures were ꢂ6 with organic acids and ꢂ9
without adding organic acids, respectively. It is likely the pH
values also influence the formation of the crystals of compounds 1
and 3. More interestingly, the crystals of 1 and 3 were grown in
the presence of 2,3-pyrazinedicarboxylic acid and pyridine-3,5-
pyrazinedicarboxylic acid (0.089 g, 0.52 mmol ). The green
crystals of 2 were obtained in 40.14% yield (0.055 g) (based on
ꢀ
1
Co). IR (KBr, cm ): 2924 (vw), 2827 (vw), 2346 (m), 1606 (s),
384 (s), 1109 (w), 1016 (w), 763 (w), 712 (w), 660 (w), 472 (w).
1
The ratio of Co and Ni were established as 1.67:0.33 by EDX
measurements.
2
.2.3. Preparation of Na
The reagents are NiCl
0.173 g, 1 mmol), pyridine-3,5-dicarboxylic acid (0.084 g,
.5 mmol), and 1,10-phenanthroline (0.106 g, 0.59 mmol). The
green crystals of 3 were obtained in 35.29% yield (0.048 g) (based
2
Ni
2
(SeO
3 3
) (3)
2
ꢁ 6H O (0.119 g, 0.5 mmol), Na
2
2 3
SeO
(
0
ꢀ
1
on Ni). IR (KBr, cm ): 2920 (vw), 2029 (w), 1772 (vw), 1637 (s),
Table 1
Summary of the crystal data and structure refinements for compounds 1, 2, and 3.
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
T/K
Na
2
Co
2
O
9
Se
3
Na
2
Co1.67Ni0.33
O
9
Se
3
2 2 9 3
Na Ni O Se
544.72
544.65
544.28
orthorhombic
Cmcm
orthorhombic
Cmcm
orthorhombic
Cmcm
293
293
293
0
7
1
1
.71073
0.71073
0.71073
l
/A˚
a/A˚
b/A˚
.551(5)
1.147(8)
0.270(8)
7.5156(16)
11.107(3)
10.2320(14)
854.1(3)
7.464(4)
11.055(5)
10.180(5)
840.0(7)
c/A˚
V/ A˚ 3
864.4(11)
Z
4
4
4
ꢀ
3
D
c
/g cm
4.186
4.236
4.304
ꢀ
1
m
/mm
16.602
1000
16.888
1001
17.616
1008
F(0 0 0)
Measured refls.
Independent refls.
No. of parameters
GOF
3302
3230
3596
561
556
550
59
59
59
1.079
1.071
1.079
R indices [I42
R indices (all data): R1, wR2
s
(I)]: R1, wR2
0.0300, 0.0999
0.0312, 0.1008
4,21,690
0.0316, 0.0956
0.0337, 0.0972
4,21,692
0.0320, 0.0758
0.0353, 0.0777
4,21,691
ICSD no.
R1¼P99Fo9–9Fc99/P9Fo9, wR2¼{P
P
2
2
2
2 2 1/2
w[(Fo) ꢀ(Fc) ] / w[(Fo) ] }
.

X.-Q. Yuan et al. / Journal of Solid State Chemistry 183 (2010) 1955–1961
1957
dicarboxylic acid, respectively, while using 2,3-pyrazinedicar-
3.2. Crystal structures
boxylic acid instead of pyridine-3,5-dicarboxylic acid in the
synthesis of compound 3 resulted in an unidentified powder
only. Therefore, the different dicarboxylic acids have some
influence in the formation of final products. Also note that the
Single crystal X-ray analyses reveal that compounds 1, 2, and 3
crystallize in the space group Cmcm and they are isostructural.
Therefore, only the structure of compound 1 as a representative is
described in detail. The asymmetric unit of compound 1 contains
compounds K
2
Co
2
(SeO
3
)
3
[20], K
2
[Co
2
(SeO
3
)
3
] ꢁ 2H
2 2 2
O, and K [Ni
2
+
2ꢀ
2ꢀ
(
SeO ]d2H O [18] have the same formula of anionic parts but
3
)
3
2
half a Co
ion, half a Se(1)O
group, a quarter of Se(2)O3
3
+
+
totally different structures compared to the title compounds,
however, in their preparation no organic acid was added, and the
reactions were carried out at higher temperature. Unluckily, we
group, a quarter of Na(1) ion, and a quarter of Na(2) ion,
respectively. The Co
from four Se(1)O
2
+
ion is coordinated by six oxygen atoms
2
3
ꢀ
2ꢀ
groups and two Se(2)O3 groups in an
+
+
tried to use the K reagent instead of Na to synthesize the
isostructural potassium-transition metal selenites in similar
reaction conditions but failed.
unidentate fashion, respectively (Fig. 1a). The CoꢀO bond lengths
range from 2.069(4) to 2.175(5) A˚ and the OꢀCoꢀO angles are in
the range 75.7(3)ꢀ 167.35(17)1. Two CoO octahedra share two
6
2
ꢀ
O(1) and one O(3) to form a Co
2
O
9
dimer. The Se(1)O
3
and
ions,
2
ꢀ
2+
Se(2)O
3
groups are tetradentate and bridge four Co
2
3
ꢀ
respectively. The O(1) atom from Se(1)O
group and O(3) atom
2
3
ꢀ
from Se(2)O
group are bidentate metal linkers whereas the two
Table 2
2ꢀ
4
O(2) atoms from Se(1)O
3
group and the two O(4) atoms from
group are unidentate, respectively. The disordered
group is randomly distributed on one of the two
Atomic coordinates ( ꢃ 10 ) for compounds 1, 2, and 3.
2
3
ꢀ
Se(2)O
Se(2)O
Atoms
x
y
z
3
2
ꢀ
positions [20]. The SeO
3
trigonal pyramids exhibit bond
1
˚
lengths with a mean value of 1.696 A, which is in good agree-
ment with the values observed for related selenite compounds
Se(1)
Se(2)
Co(1)
O(1)
O(2)
O(3)
O(4)
Na(1)
Na(2)
0
2346(1)
5299(1)
1999(2)
2500
0
1934(2)
0
5155(1)
2430(1)
1638(5)
1663(4)
3811(9)
5812(7)
ꢀ211(5)
0
2
+
2ꢀ
[18,20]. The interconnections of Co ions by bridging Se(1)O
groups result in a two-dimensional layer (2D) of [CoSe(1)O
along the ac plane, Fig. 2. Four-membered Co rings and eight-
membered Co–(O–Se(1)–O) –Co rings are evident in the 2D layer.
The CoyCo separation within a Co four-membered ring is
3
3813(6)
6050(4)
3
]
1714(6)
0
2 2
O
2770(11)
2762(11)
2500
2
ꢀ1736(11)
0
2 2
O
2697(12)
5000
2
Se(1)
Se(2)
M
0
2353(1)
5155(1)
2428(1)
1643(5)
1668(4)
3792(8)
5815(7)
ꢀ208(5)
0
5301(1)
1992(2)
2500
0
1922(1)
0
O(1)
O(2)
O(3)
O(4)
Na(1)
Na(2)
3811(5)
6052(4)
2779(8)
2753(10)
2500
1727(6)
0
ꢀ1750(10)
0
2708(11)
5000
3
Se(1)
Se(2)
Ni(1)
O(1)
O(2)
O(3)
O(4)
Na(1)
Na(2)
0
2367(1)
5152(1)
2426(1)
1637(4)
1674(3)
3806(7)
5811(5)
ꢀ214(3)
0
5305(1)
1976(1)
2500
0
1898(1)
0
3814(4)
6067(3)
2773(9)
2758(8)
2500
1732(4)
0
ꢀ1766(7)
0
2702(8)
5000
M¼0.835 Co+0.165 Ni.
3
Fig. 2. The two-dimensional layer of [CoSe(1)O ] in structure 1 along the ac plane.
Fig. 1. The coordination environments of Co ion (a), Na(1) ion (b), and Na(2) ion (c) in structure 1.

1
958
X.-Q. Yuan et al. / Journal of Solid State Chemistry 183 (2010) 1955–1961
˚
2
.928 A. The CoSe(1)O
3
layers are further cross-linked by Se(2)O
3
4 2 7
(Fig. 4a), whereas the 14-membered Co Se(1)Se(2) O rings
˚
groups into a pillared layered architecture, Fig. 3a. It is interesting
that compound 1 reveals intersecting two-dimensional channels
parallel to the a- and c-axis, respectively. A rough square cross
comprising a rough elliptical cross section of 5.7 ꢃ 7.5 A are
present parallel to the c-axis (Fig. 4b). The lone pair electrons of
4
+
the Se ions are oriented toward the interior of channels. The
+
+
+
˚
section of 4.1 ꢃ 5.7 A constructed by 16-membered Co
4
Se(1)
2
Na(1) ions and Na(2) ions are located in the channels. Na(1)
ion is surrounded by eight oxygen atoms to form a Na(1)O
polyhedron; six of them are from four different Se(1)O groups,
while the other two oxygen atoms are from two different Se(2)O
Se(2)
2
O
8
ring is evident for the channels parallel to the a-axis
8
3
3
+
groups (Fig. 1b). The Na(2) ion is surrounded by six oxygen
atoms to form a Na(2)O polyhedron; four of them are from two
different Se(1)O groups, while the other two oxygen atoms are
from two different Se(2)O groups (Fig. 1c). The Na–O distances
range from 2.269(5) to 2.995(8) A. In each channel parallel to the
6
3
3
˚
+
+
c-axis, the Na(1) ions are in the middle and the Na(2) ions are in
the two sides of the channel, Fig. 3b. In fact, the reported
compounds, namely K
[Ni (SeO O [18] contain the same anionic moiety of
] ꢁ 2H
(SeO
(M¼Co, Ni) as the title compounds, however, their
structures are different. The compound K Co (SeO crystallizing
in the space group P6 /mmc features a two-dimensional double-
layer structure of Co
Se(1)O to form a single layer of cobalt selenite with the 12-
membered Co Se(1) rings along the ab plane. Two single layers
of the cobalt selenite are further linked by Se(2)O groups to give
rise to a two-dimensional double-layer of Co (SeO
Whereas the structures of K [M (SeO ]d2H
2
Co
2
(SeO
3
)
3
[20], K
2
[Co
2
(SeO
3
)
3
] ꢁ 2H
2
O, and
K
M
2
2
3
ꢀ
)
3
2
2
2
3 3
)
2
2
3 3
)
3
2
3 3
ꢀ
2+
2
(SeO ) . The Co ions are connected by
3
3
3 6
O
3
2
3
ꢀ
2
3
)
(Fig. S6).
2
2
3
)
3
2
O (M¼Co, Ni)
feature three-dimensional open frameworks with one-dimen-
sional honeycomb-like channels along the c-axis constructed by
6 6
24 membered Co Se O12 rings, which are quite different from that
of the title compounds (Fig. S7).
4. Characterizations and properties
4.1. IR spectra
The IR spectra of the title compounds were studied in the
ꢀ
1
range 4000–400 cm . Three different groups of bands attributed
to the vibrational modes of the selenite anions were observed
[
1
36]. The symmetric
016–1021 cm , however, the asymmetric as(Se–O) stretching
n
s
(Se–O) stretching bands are detected at
ꢀ
1
n
2
ꢀ
bands are split, due to the inherently asymmetric SeO
and appears as a group of bands around 818–712 cm . Finally,
those from 470–660 cm
vibrations of (O–Se–O). The obtained results are similar with
those of the other related metal selenite compounds [37,38].
3
anion
ꢀ
1
ꢀ
1
originated from the deformation
Fig. 3. (a) View of the three-dimensional (3D) framework of compound 1 along
the a-axis and (b) polyhedral view of the 3D framework of compound 1 along the
c-axis.
d
Fig. 4. (a) A rough square cross section of 4.1 ꢃ 5.7 A˚ parallel to the a-axis constructed by 16-membered Co
2 2 8
Se(1) Se(2) O ring in compound 1; (b) the 14-membered
4
4
Co Se(1)Se(2)
2 7
O
rings comprising a rough elliptical cross section of 5.7 ꢃ 7.5 A˚ parallel to the c-axis in compound 1.

X.-Q. Yuan et al. / Journal of Solid State Chemistry 183 (2010) 1955–1961
1959
Fig. 5. The TGA and DSC curves for compounds 1 (a), 2 (b), and 3 (c).
4
.2. Thermal stability studies
calculated values (46.6%). On the DSC curve of compound 2, there
was one weak accompanying exothermic signal at 631 1C.
However, the TGA curves of compound 3 showed only one main
step of weight loss which corresponds to the loss of two SeO2
molecules. The observed weight loss of 41.18% for 3 was in good
agreement with the calculated values (40.7%). And there was one
main exothermic signal at 664 1C for 3 on the DSC curve. The
residual solids contain CoO for 1, NiO for 3, Co0.83Ni0.17O for 2, and
unidentified phases.
The thermal stabilities of compounds 1–3 were examined by
2
TGA–DSC in a N atmosphere from 25 to 1000 1C. As shown in
Fig. 5, the TGA curves indicated that compounds 1 and 2 displayed
two steps of weight losses, while compound 3 showed one main
step of weight loss. Compound 1 was stable up to 320 1C, and then
there was a stepwise weight loss of one O
weight loss corresponded to the release of two SeO
2
at first. The subsequent
molecules.
2
The total observed weight loss of 44.56% was in good agreement
with the calculated values (46.6%). There was one sharp
accompanying exothermic signal at 636 1C on the DSC curve.
4.3. Magnetic measurements
2 2
Compound 2 released one O and one SeO [39] for the first step
from around 320 to 650 1C with the weight loss of 24.02% (the
theoretical value is 26.2%). The second step weight loss
The results for the temperature-dependent magnetic measure-
ments of compounds 1, 2, and 3 are shown in Fig. 6 in the
temperature range 2–300 K at 1000 Oe applied field. For the three
compounds, the thermal evolution of the molar magnetic
corresponds to the release of another SeO
2
molecule. The total
observed weight loss of 45.26% was in good agreement with the

1
960
X.-Q. Yuan et al. / Journal of Solid State Chemistry 183 (2010) 1955–1961
shows the maximum at 19 K, and below that temperature the
susceptibility decreases continuously until 6 K. After that there is
M
a little jump increase at 2 K. It reveals a room-temperature w T
3
ꢀ1
value of 5.40 cm K mol . For 3, the thermal evolution of the
molar magnetic susceptibility shows the maximum at 35 K,
w
M
and below that temperature the susceptibility decreases
continuously until 9 K. But there is a continuously increase until
3
ꢀ1
2
K. The value of
lower than the above three. As shown in Fig. 6, upon lowering
the temperature, all of the three decreases slowly
between 300 and 100 K, and then rapidly decreases to the
w
M
T is 2.30 cm K mol , which is much
M
w T
3
ꢀ1
3
ꢀ1
minimum of 0.16 cm K mol for 1, 0.14 cm K mol
for 2,
3
ꢀ1
and 0.04 cm K mol for
3
at 2 K, indicating an overall
antiferromagnetic coupling [41,42]. For 1, the molar magnetic
susceptibility higher than 14 K follows the Curie–Weiss law
3
ꢀ1
(
y
w
M
¼C/(Tꢀ
y
)) with C¼8.08 cm K mol
,
and
a
negative
¼ ꢀ61.47 K, Fig. 6a. These features confirm the existence of
the antiferromagnetic interactions and the effect of the spin–orbit
coupling known for octahedral Co ions [43–45]. For 2, the molar
magnetic susceptibility higher than 22 K follows the Curie–Weiss
3
ꢀ1
law (
y
w
M
¼C/(Tꢀ
y
)) with C¼6.32 cm K mol , and a negative
¼ ꢀ53.38 K, Fig. 6b. For 3, the molar magnetic susceptibility
higher than 40 K follows the Curie–Weiss law (
w
M
¼C/(Tꢀ )) with
y
3
ꢀ1
C¼2.73 cm K mol
,
and
a
negative
y
¼ ꢀ52.65 K, Fig. 6c.
Furthermore, the large negative
y value suggests a dominant
antiferromagnetic coupling [46] between the adjacent Ni(II) ions
47,48] for 3.
[
5. Conclusion
Three new isostructural transition metal selenites, namely
Na
2
Co2-xNi
x
(SeO
3
)
3
(x¼0 (1), 0.33 (2), 2 (3)) have been synthe-
sized under mild hydro-/solvothermal conditions. Their crystal
structures feature three-dimensional open frameworks of
2
ꢀ
2ꢀ
[M
2
(SeO
3
)
3
]
(M¼Co, Co/Ni, Ni) constructed by the [SeO
]. The
3
]
groups bridging the two-dimensional layers of [MSeO
3
+
intersecting two-dimensional channels are occupied by Na ions.
The thermal properties and the magnetic properties of com-
pounds 1–3 have been investigated. The magnetic measurements
indicate the existence of the antiferromagnetic interactions in
compounds 1–3.
Acknowledgments
This work was supported by grants from the NNSF of China
(
2
Nos. 20873149, 20803081), and the NSF of Fujian Province (No.
008J0174).
Appendix A. Supporting Materials
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.jssc.2010.06.020.
Fig. 6. Temperature dependence of
w
M
T,
M
w for compounds 1 (a), 2 (b), and 3 (c).
ꢀ
1
The insets show the
M
v versus T.
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