Crystal structure of Rb{sub 2}[Ti(VO{sub 2}){sub 3}(PO{sub 4}){sub 3}]

The crystal structure of the new compound Rb{sub 2}[Ti(VO{sub 2}){sub 3}(PO{sub 4}){sub 3}] obtained by hydrothermal synthesis in the RbCl-TiPO{sub 4}-V{sub 2}O{sub 5}-B{sub 2}O{sub 3}-H{sub 2}O system (a = 13.604(2) A, c = 9.386(2) A, sp. gr. P6cc, Z = 4, {rho}{sub calcd} = 3.32 g/cm{sup 3}) has been studied by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.038). It is shown that the isotypism of Rb{sub 2}[Ti(VO{sub 2}){sub 3}(PO{sub 4}){sub 3}] and Cs{sub 2}[Ti(VO{sub 2}){sub 3}(PO{sub 4}){sub 3}] is caused by the flexibility of a mixed anionic framework composed of phosphorus tetrahedra, vanadium five-vertex polyhedra, and titanium octahedra (bases of the crystal structures of these compounds). The topological correlations between the structures of titanium-vanadyl phosphates and benitoite and beryl silicates are analyzed.