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)

Four new open-framework alkali metal uranyl silicates, Rb-4(UO2)(2) (Si8O20) (USH-2Rb), Rb-2 (UO2)(Si2O6).H2O (USH-4Rb), and A(2) (UO2)(Si2O6).0.5H(2)O (USH-5A; A = Rb, Cs), have been prepared hydrothermally at 245 degreesC. 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.