High-temperature phase transitions, spectroscopic properties, and dimensionality reduction in rubidium thorium molybdate family.

Four new rubidium thorium molybdates have been synthesized by high-temperature solid-state reactions. The crystal structures of Rb8Th(MoO4)6, Rb2Th(MoO4)3, Rb4Th(MoO4)4, and Rb4Th5(MoO4)12 were determined using single-crystal X-ray diffraction. All these compounds construct from MoO4 tetrahedra and ThO8 square antiprisms. The studied compounds adopt the whole range of possible structure dimensionalities from zero-dimensional (0D) to three-dimensional (3D): finite clusters, chains, sheets, and frameworks. Rb8Th(MoO4)6 crystallizes in 0D containing clusters of Th(MoO4)6. The crystal structure of Rb2Th(MoO4)3 is based upon one-dimensional chains with configuration units of Th(MoO4)3. Two-dimensional sheets occur in compound Rb4Th(MoO4)4, and a 3D framework with channels formed by thorium and molybdate polyhedra has been observed in Rb4Th5(MoO4)12. The Raman and IR spectroscopic properties of these compounds are reported. Temperature-depended phase transition effects were observed in Rb2Th(MoO4)3 and Rb4Th(MoO4)4 using thermogravimetry-differential scanning calorimetry analysis and high-temperature powder diffraction methods.