Single Crystal Growth and Structural Characterization of a Novel Mixed-Valent Ternary Uranium Oxide, K8U7O24

Abstract

Single crystals of K8U7O24 (K8U7.04O24) were grown out of a reactive potassium fluoride flux and characterized by single crystal X-ray diffraction. The reaction was carried out in a sealed copper tube. The title compound crystallizes in the cubic space group Im-3m with a = 8.65050(10) A. The material exhibits an ordered perovskite structure type that is a 2 × 2 × 2 cubic superstructure of the CaTiO3 perovskite type. Six of the uranium atoms in the composition are in the +6 oxidation state, while the seventh one is +4. The uranium(VI) atom is located in a distorted UO6 octahedral coordination environment containing two short, 1.966(5) A, and four long, 2.16260(10) A, U–O bonds, consistent with the uranyl cation, UO2 2+. The uranium(IV) atom is in a regular octahedral environment with U–O bonds of 2.359(5) A. The synthesis and crystal structure are reported for K8U7O24, a new complex uranium(IV/VI) oxide.