Tetrapotassium dicarbonatodioxoperoxouranium(VI) 2.5-hydrate, K4[U(CO3)2O2(O2)].2.5H2O.

The title compound was obtained by reacting UO2 powder in 2 M K2CO3 with hydrogen peroxide. The compound contains individual [U(CO3)2O2(O2)]4- ions, which are linked via an extended network of K atoms and hydrogen bonding. The U atom is coordinated to two trans-axial O atoms and six O atoms in the equatorial plane, forming distorted hexagonal bipyramids. The carbonate ligands are bound to the U center in a bidentate manner, with U-O bond distances ranging from 2.438 (5) to 2.488 (5) A. The peroxo group forms a three-membered ring with the U atom, with U-O bond distances of 2.256 (6) and 2.240 (6) A. The U=O bond distances of 1.806 (5) and 1.817 (5) A, and an O-U-O angle of 175.3 (3) degrees are characteristic of the linear uranyl(VI) unit.