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sharing vanadium polyhedra [38]. Interestingly, in structure of 2,
these eight-membered rings share edges to form a ladder-like
chain. In other words, each [VO6] unit shares three oxygen atoms
with adjacent Se atoms, while each SeO3 unit shares three oxygen
atoms with adjacent V atoms in 2. The connectivity of the alternat-
ing [VO6] and SeO3 units create a ladder motif. Adjacent chains are
interlinked by the oxalate ligands, creating a 2D brick-wall struc-
ture, as shown in Fig. 2b. The oxalate ligand acting in a chelating
mode, as found in related compounds [39,40], bridges two neigh-
boring chain vanadium atoms. This formation of the chain is also
found in related structures [22,26,27]. In 2, SeO3 units serve as a
(Found: 36.7%, Calc: 39.9%) in the temperature range of 228–
800 °C is observed, contributed the sublimation of SeO2. The
remaining weight of 34.8% corresponds to the percentage 32.7%
of V and O components, indicating that the final product is V2O5.
Compound 2 shows a weight loss (Found: 31.9%, Calc: 31.0%) in
the range of 288–363 °C, corresponding to the release of the pipe
molecules and oxalate molecules and the sublimation of SeO2 with
the decomposition of the framework. Another successive weight
loss (Found: 38.5%, Calc: 39.5%) in the range of 363–800 °C corre-
sponds to the sublimation of SeO2. The remaining weight of
28.6% corresponds to the percentage of 29.5% V and O components,
indicating that the final product is VO2.
l3 bridge linking the vanadium–oxygen polyhedra, similar to those
found in comparable structures [DABCOH2]0.5[(VO)(HSeO3)
(SeO3)]ꢀH2O, [(VO)(H2O)2(SeO3)]2[(H2piperazidine)(SO4)], (2,20-
bipyridine)(VSeO4) and (4,40-bipyridine)(V2Se2O8) [22,26]. More
interestingly, the neutral chain of [(VO)(H2O)2(SeO3)]2 found in
[(VO)(H2O)2(SeO3)]2[(H2piperazidine)(SO4)], similar to that fund
in 2 can further extends higher dimensional structures and consid-
ered to be a secondary building block in V/Se/O system (See
Scheme 1) In this chain, the coordinated water molecules coordi-
nated to vanadium centers can be replaced by others species to form
new phase of vanadium selenites. In (2,20-bipyridine)VSeO4, 2,20-
bipyridine ligands replace the coordinated waters to form herring-
bone chains; if these coordinated water molecules are replaced by
4, 40-bipyridine, two-dimensional neutral sheets are obtained [26];
in [DABCOH2]0.5[(VO)(HSeO3)(SeO3)]ꢀH2O, the coordinated water
molecules are replaced by [HSeO3] groups to form a brick-wall struc-
ture [22]. In the structure of 2, these coordinated water molecules
are replaced by oxalate ligands, creating a novel brick-wall vanadyl
selenite, which is firstly observed in V/Se/O system. These interest-
ing results excite us. We expect that each vanadium–oxygen polyhe-
dron can share five or six SeO3 units to form 3D networks. We have
successfully obtained a target compound with 3D channels in the
presence of N1,N10-(ethane-1,2-diyl)diethane-1,2-diamine, in
which each VO6 unit is bridged by five SeO3 units. Unfortunately,
the organic amine is severely disordered in the channel, but the inor-
ganic framework can be clearly observed.
4. Conclusion
In conclusion, two novel vanadium selenites are prepared in the
presence of organic amine, DABCO and piperazidine, respectively.
Depending on the mode of connectivity between the SeO3 unit and
vanadium–oxygen polyhedra, the vanadium selenites show a rich
variety of architectures. In structures of 1 and 2, the SeO3 group acts
as a l3 bridge linking the vanadium–oxygen polyhedra, while in
comparable structures, The SeO3 group can act as a l2 as well as a
l3 bridge via corner-sharing mode [21,22]. The association of the
[VO6] units and SeO3 units into extended structures is an interesting
aspect of the structures described above. Interestingly, the struc-
tures of many of selenites are close to those of the phosphates. There
is a secondary building unit for the selenites similar to the eight-
membered ring structures in the case of open-framework phos-
phates [18]. In structure of 1, an unprecedented [V2Se2O12] basic
building block is observed in V/Se/O system. These building blocks
are arranged in perpendicular direction, and connected by SeO3
groups via corner-sharing mode to form a grid structure. In com-
pound 2, an important basic building block comprised of
[V2Se2O14] (eight-membered ring) is observed. Scheme 1 illustrates
the assembly pattern found in the related vanadium selenites (j:
stands for VO6 unit; : stands for V2O6 unit; D: stands for SeO3 unit;
d: stands for bridging ligand). The mode I is found in b-(enH2)[(VO)
(SeO3)2] [25]. Mode II is (2,20-bipyridine) [(V4O8)(SeO3)2] [28]. Mode
III is found in K(VO)(SeO3)H [38]. Mode IV is found in
[DABCOH2]0.5[(VO)(HSeO3)(SeO3)]ꢀH2O [22], [(VO)(H2O)2(SeO3)]2-
[(H2piperazidine)(SO4)] [27], (2,20-bipyridine)(VSeO4) and (4,40-
bipyridine)(V2Se2O8) as well as compound 2 [26]. This formation of
the chain as mode IV can be viewed as an important secondary build-
ing block in V/Se/O system, which can further form two or three-
dimensionalstructuresasfoundinmodeV. Thesechainscanbeinter-
linked by [SeO3] groups as well as 4,40-bipy ligands to result in layers.
In the present work, the formation of the chain is bridged by oxalate
ligands resulting in 2D brick-wall structure. Further work to investi-
gate the effects of various reaction parameters on the formation of
these materials will be discussed in more detail in the future.
In 2, organic layers and inorganic layers are also alternately
packed, similar to those found in 1, and interact with each other
via hydrogen bonds to creating 3D networks, as shown in Fig. 2c.
3.3. IR spectroscopy of compounds 1 and 2
The FT-IR spectra of 1 and 2 exhibit broad absorptions in the re-
gions 3460–2530 cmꢁ1 occurring because of the existence of water
molecules or NH groups in the structures. The FT-IR spectra of 2
display the typical stretching bands of carboxylate groups between
1580 and 1660 cmꢁ1
. The absorptions in the region 1180–
1470 cmꢁ1 in 1 and 2 are due to stretching mode of CAN and
CAH. The FT-IR spectra of 1 and 2 show peaks at 928 and
966 cmꢁ1 are assigned to symmetric stretching mode of the SeO3
group; peaks at 852 to 839 cmꢁ1 are assigned to the symmetric
stretching mode of the VO6; peaks at 708 to 776 cmꢁ1are due to
asymmetric stretching mode of the VO62;ꢁ peaks at 493 and
537 cmꢁ1 are likely associated with the SeO3 anion.
5. Supplementary materials
Crystallographic data (excluding structure factors) for the struc-
tures 1 and 2 in this paper have been deposited with Cambridge
Crystallographic Data Centre as supplementary, publication, No.
CCDC 695599 for compound 1, and 695598 for compound 2. Copies
of the data can be obtained free of charge, on application to CCDC,
12 Union Road Cambridge CB21 EZ, UK (fax: +44 12 23 60 33 or
Email: deposit@ccdc.cam.ac.uk).
3.4. Thermal analysis of compounds 1 and 2
To examine the thermal stability of the two compounds and
their structural variation as function of the temperature, thermo
gravimetric analyses (TGA) were performed on single-phase poly-
crystalline samples of these materials. The TGA of compound 1
show a successive weight loss of the lattice water molecules in
the temperature range of 80–204 °C (Calc: 4.0%, Found: 4.2%),
and another weigh loss of 24.3% (Calc: 20.5%) at 228 °C, contrib-
uted by the release of DABCO. Another successive weight loss
Acknowledgment
The work was financially supported by the Natural Science
Foundation of Henan Institute of Science and Technology (No.
06038 and 7031).