Mixed-valent 1:1 oxidotellurates(IV/VI) of Na, K and Rb: superstructure and three-dimensional disorder

Abstract

Single crystals of three mixed-valent oxidotellurates(IV/VI) with general formula M2TeIVTeVIO6 (H2O) x (M = Na, K, Rb) were grown under hydrothermal conditions at 210 °C from M2CO3, TeO2 and Te(OH)6 in a 4:1:1 molar ratio. Na2Te2O6·11/8H2O (where TeIVTeVI is abbreviated as Te2) crystallizes as a monoclinic eightfold superstructure with occupational modulation of the water molecules. The structure is built of diperiodic corrugated [Te2O6]2- networks interleaved by the Na atoms and H2O molecules. The hexagonal crystal structures of M2Te2O4(OH)4 (M = K, Rb; x = 2) with P63/mmc symmetry are made up of [Te2O4(OH)4]2- rods extending in the [001] direction. The rods are connected by the M atoms. The [TeIVO2(OH)2] units are disordered about the threefold axis, resulting in pronounced three-dimensional diffuse scattering.