Preparation, properties, and crystal structure of RuSn6[(Al1/3-xSi3x/4)O-4](2) (0 <= x <= 1/3) - an oxide with isolated RnSn6 octahedra

RuSn6[(Al1/3-xSi3x/4)O-4](2) is obtained by the solid state reaction of RuO 2, SnO2, Sn and Si in an Al2O3-crucible at 1273 to 1373 K. The compound is cubic with the space group Fm (3) over bar m (a = 9.941(1) Angstrom, Z = 4, R-1 = 0.0277, wR(2) = 0.0619), a semiconductor and stable in air. Results of Mossbauer measurements as well as bond length-bond strength calculations justify the ionic formulation Ru2+Sn62+[(Al1/3-x3+Si3x/44+)O-4(2-)](2). Th e central motif of the crystal structure are separated RuSn6-octahedrea. Th ese are interconnected by oxygen atoms, arranged tetrahedrely above the sur faces of the RuSn6-octahedrea and partialy filled with Al and Si, respectiv ely. Because of these features the compound can be considered as a variant of the crystal structure type of pentlandite.