Pentavalent Uranium Oxide via Reduction of [UO2]2+ Under Hydrothermal Reaction Conditions

The synthesis, crystal structure, and spectroscopic characterization of [U-V(H2O)(2)((UO2)-O-VI)(2)O-4(OH)](H2O)(4) (1), a mixed-valent U-V/U-VI oxide material, are reported. The hydrothermal reaction of UO22+ with Zn and hydrazine at 120 degrees C for three days yields 1 in the form of a dark red crystalline solid. Compound 1 has been characterized by a combination of single-crystal and powder X-ray diffraction (XRD), elemental analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The structure consists of an extended sheet of edge and corner shared U-VI pentagonal bipyramids that are further connected by edge sharing to square bipyramidal U-V units. The overall topology is similar to the mineral ianthinite. The uranium L-III-edge XAS revealed features consistent with those observed by single-crystal X-ray diffraction. High resolution XPS data analysis of the U4f region confirmed the oxidation states of U as originally assigned from XRD analysis and bond valence summations.