Abstract. The new arsenato polyxoxvanadate (NH4)4[V12As8O40(H2O)]·4H2O (1) was obtained under solvothermal conditions using either a mixture of ethyl ether/H2O or ethanol/H2O acting as reducing agents. Compound 1 crystallizes in the orthorhombic space group Pnnm with a = 13.6740(3), b = 12.7378(5), c = 13.0580(3) Å, V = 2274.40(11) Å3, Z = 2. The central structural motif features an anionic cluster shell, which can be derived from the {V18O42} archetype cluster by replacing VO5 polyhedra by As2O5 units and omitting two VO5 square pyramids. The electronic situation of the cluster anion can be best described by the formula [V8IVV4VAs8IIIO40(H2O)]4–. The charge neutrality of the compound is achieved by NH4+ cations which occupy the free space between the clusters together with crystal H2O molecules. Thermal investigation shows a complex decomposition process occurring in at least three steps. Determination of the optical band gap classifies 1 as a semiconductor with a band gap of 2.8 eV. Solubility studies accompanied by IR spectroscopy, ESI‐MS, X‐ray powder diffractometry and elemental analysis demonstrate that the cluster is partially dissolved.
The title compound is prepared by solvothermal reaction of NH4VO3 and As2O3 in a 1:1 mixture of Et2O (or EtOH) and H2O (pH 6.5, 80 °C, closed glass tube, 7 d, 20% yield).
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