The synthesis and crystal structure of U₇O₂Se ₁₂

The new compound U₇O₂Se₁₂ was synthesized at 1173 K as a result of both unintentional and intentional oxygen contamination. The composition balances with formal charges of +4, -2, and -2 for U, O, and Se, respectively. U₇O₂Se₁₂ crystallizes with one formula unit in space group C¹ _3h-P6̄ of the hexagonal system in a cell of dimensions a = 11.3222(4) Å, c = 4.1362(1) Å. The structure of U₇O ₂Se₁₂ closely resembles that of the An₇Te ₁₂ (An = Th, U) compounds, but contains cavities, in which oxygen atoms are coordinated to three uranium atoms in a trigonal planar arrangement. It is not known if other members of the An₇Q₁₂ family (An = Th, U; Q = S, Se, Te) are actually An₇O₂Q₁₂ compounds.