Hydrothermal synthesis and structures of the new open-framework uranyl silicates Rb4(UO2)2(Si8O20) (USH-2Rb), Rb2(UO2)(Si2O6)·H2O (USH-4Rb) and A2(UO2)(Si2O6)·0.5H2O (USH-5A; A = Rb, Cs)

Abstract

Four new open-framework alkali metal uranyl silicates, Rb₄(UO₂)₂(Si₈O₂₀) (USH-2Rb), Rb₂(UO₂)(Si₂O₆)·H₂O (USH-4Rb), and A₂(UO₂)(Si₂O₆)·0.5H₂O (USH-5A; A = Rb, Cs), have been prepared hydrothermally at 245 °C. The structures of USH-2, -4, and -5 contain UO₆ tetragonal bipyramidal units connected by double chains, 4-membered rings, and single chains of SiO₄ tetrahedra, respectively. The compounds have been characterized by single crystal X-ray diffraction, scanning electron microscopy, UV-vis and infrared spectroscopy, and thermogravimetric analysis.