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

Single crystals of three mixed-valent oxidotellurates(IV/VI) with general formula (M2TeTeO6)-Te-IV-O-VI (H2O)( x ) (M = Na, K, Rb) were grown under hydrothermal conditions at 210 degrees C from M2CO3, TeO2 and Te(OH)(6) in a 4:1:1 molar ratio. Na2Te2O6 center dot 11/8H(2)O (where (TeTeVI)-Te-IV is abbreviated as Te-2) 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 P6(3)/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 [(TeO2)-O-IV(OH)(2)] units are disordered about the threefold axis, resulting in pronounced three-dimensional diffuse scattering.