Structure and Some Properties of a Double Neptunyl(V) Cesium Molybdate, Cs[NpO₂MoO₄(H₂O)]

Abstract

A double neptunyl(V) cesium molybdate, Cs[NpO₂MoO₄(H₂O)], was studied by single crystal X-ray diffraction. Crystal data: rhombic system, a = 9.478(2), b = 7.900(1), c = 10.499(2) Å; space group Pnna, Z = 4, d = 5.05 g cm⁻³, R = 0.030. The compound has a framework structure; the coordination polyhedron of the Np atom is a distorted pentagonal bipyramid with the equatorial positions occupied by four O atoms of four molybdate groups and an O atom of the coordinated water molecule. The IR and visible absorption spectra of this compound and of Cs₂[(NpO₂)₂Mo₂O₈] whose structure had been determined previously were measured. The NpO ⁺₂ stretching vibration frequencies in the IR spectra of these compounds virtually coincide. Incorporation of the O atom of the Mo-O-Mo bridge into the first coordination sphere of the neptunyl(V) ion in Cs₂[(NpO₂)₂Mo₂O₈] exerts the same disturbing effect on the electronic absorption spectrum as does the cation-cation interaction with one of the O atoms acting as a bridge between two Np atoms.