Reactions of Neptunium(V) in Alkali-Metal Hydroxides.

The preparation of two new neptunium hydroxide compounds synthesized in concentrated potassium and rubidium hydroxide is reported. The phases K[(NpO)(OH)]·4HO and Rb[(NpO)(OH)]·2HO were prepared and their chemical structures determined using single-crystal X-ray diffraction. Raman spectra of the compounds are also presented. The newly synthesized phases are structurally related to NpO and Na[NpO(OH)]. The potassium-containing phase reported here consists of infinite chains of edge-sharing neptunium hydroxide polyhedra but lacking the cation-cation interactions (CCIs) observed in NpO and Na[NpO(OH)]. Rb[(NpO)(OH)]·2HO is a an expanded three-dimensional framework based on NpO CCIs like those observed in NpO and Na[NpO(OH)]. Together these complexes begin to develop a structural series of neptunium(V) oxides and hydroxides of varying dimensionalities within the alkali-metal series. The potential roles of the alkali-metal cations and neptunyl(V) CCIs in directing the resulting structures are discussed.