The quadruple chains of SbO6 octahedra in Sb2Te2O9: an example of low extent of aggregation of pentavalent antimony polyhedra

Abstract

Single crystals of Sb₂Te₂O₉ have been grown by transport methods, and the crystal structure determined by X-ray single-crystal techniques. The results have been confirmed by a neutron powder diffraction refinement. The compound crystallizes in the monoclinic system, space group P2₁/c, Z= 8, with unit-cell parameters a= 21.79(1), b= 4.849(1), c= 14.574(9)Å and β= 109.21 (3)°. The structure consists of infinite quadruple chains of vertex-sharing Sb^VO₆ octahedra, running along the b axis, bridged by (Te₆O₂₆)_∞ strings parallel to the [0 0 1] direction and by isolated Te₂O₁₀ groups. The Te^IV is five- and six-co-ordinated by oxygen, in very irregular environments making room for the free electron pairs. This structure is discussed in the framework of other pentavalent antimony complex oxides and contrasted with those of the known oxides in the M₂O₅–TeO₂(M = V, Nb or Ta) systems.