Single crystals of K 8 U 7 O 24 (K 8 U 7.04 O 24 ) 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) Å . The material exhibits an ordered perovskite structure type that is a 2 9 2 9 2 cubic superstructure of the CaTiO 3 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 UO 6 octahedral coordination environment containing two short, 1.966(5) Å , and four long, 2.16260(10) Å , U-O bonds, consistent with the uranyl cation, UO 2 2? . The uranium(IV) atom is in a regular octahedral environment with U-O bonds of 2.359(5) Å .