A New Uranyl Sulfate Chain in the Structure of Uranopilite

The structure of uranopilite, [(UO2)6(SO4)O2(OH)6(H2O)6](H2O)8, space group P1̄, a 8.896(2), b 14.029(3), c 14.339(3) Å, 96.610(4), 98.472(4), 99.802(4)°, V 1726.1(4) Å3, Z = 2, has been solved and refined on the basis of F2 for all unique data collected with monochromatic MoK X-radiation and a CCD-based detector to an agreement factor (R1) of 7.0%, calculated using 3907 unique observed reflections (Fo ≥ 4 F). The structure contains six symmetrically distinct U6+ cations, each of which is part of an approximately linear (UO2) uranyl ion (Ur). The uranyl ions are each coordinated by five ligands arranged at the equatorial vertices of Ur 5 [ : O2–, (OH)–, H2O] pentagonal bipyramids that are capped by OUr atoms. The single symmetrically unique S6+ cation is coordinated by four O atoms in a tetrahedral arrangement. The Ur 5 pentagonal bipyramids share vertices and edges, resulting in a cluster of composition [(UO2)6O6(OH)6(H2O)6]. These clusters are linked through SO4 tetrahedra, which share each of their vertices with different Ur 5 pentagonal bipyramids, resulting in electroneutral uranyl sulfate chains of composition [(UO2)6(SO4)O2(OH)6(H2O)6] that extend along [100]. The uranyl sulfate chains are linked to form the extended structure by hydrogen bonds bridging directly between the chains and to interstitial H2O groups. The uranyl sulfate chain in uranopilite is novel in minerals and synthetic compounds.