New Microporous Framework in the Structure of (K0.67Rb0.33)2[(UO2)2(Si5O13)](H2O)

A new uranyl silicate (K0.67Rb0.33)2[(UO2)2(Si5O13)](H2O) (1) is prepared from the melt in a sealed quartz ampoule. The new compound is orthorhombic, Pbca, a = 14.1909(4), b = 14.0406(5), c = 17.9151(7) Å, V = 3569.6(2) Å3, R1 = 0.03. The [Si5O13]6– layers and chains of uranium polyhedra form a microporous heteropolyhedral framework with 9.63×3.34 Å channels containing mixed-occupied sites of alkali metal cations. The structure of the new compound is compared with those of related uranyl silicate compounds and minerals.