Syntheses, Structures, and Characterization of Open-Framework Uranyl Germanates

Three uranyl germanates, Cs2[(UO2)(Ge2O6)](H2O) (1), Ag[(UO2)2(HGe2O7)](H2O) (2), and Ag2[(UO2)3(GeO4)2](H2O)2 (3) were synthesized under hydrothermal conditions, and their structures were determined by single crystal X-ray diffraction. Compound 1 crystallizes in space group P21/n, a = 7.9159(2) Å, b = 21.5949(5) Å, c = 12.4659(3) Å, β = 96.964(1)°, V = 2115.24(9) Å3, Z = 8; 2 is orthorhombic Ama2, a = 7.124(1) Å, b = 10.771(2) Å, c = 14.024(1) Å, V = 1076.2(4) Å3, Z = 4; 3 is orthorhombic Pnma, a = 10.0462(6) Å, b = 7.4699(5) Å, c = 17.776(1) Å, V = 1334.0(2) Å3, Z = 4. These compounds are frameworks of uranyl square (1) or pentagonal (2, 3) bipyramids and four-membered rings of germanate tetrahedra (1), dimers of germanate tetrahedra (2), or chains of GeO5 triangular bipyramids (3). There are channels through each of the frameworks that contain the low-valence cations and the H2O groups. Compound 1 dehydrates upon heating, but the framework remains intact to at least 900 °C.