High temperature synthesis of two open-framework uranyl silicates with ten-ring channels: Cs2(UO2)2Si8O19 and Rb2(UO2)2Si5O13

The uranyl silicates Cs2(UO2)2Si8O19 and Rb2(UO2)2Si5O13 were obtained by mixing stoichiometric amounts of uranium metal, tellurium dioxide, silicon dioxide, and an excess of correspondent alkali metal halide flux. These compounds crystallize in the orthorhombic space groups Pnma and C222 with eight and two units per unit cell, respectively. Their crystal structures are dominated by zippered pentagonal bipyramidal chains of UO7 and silicates layer that are further connected into 3D frameworks. The cesium compound has silicate double layers while rubidium has a single layer. Six-ring voids and ten-ring channels are found in both compounds.