Sulfate compounds of hexavalent neptunium and plutonium

Several techniques, X-ray diffraction, thermogravimetry, IR and optical spe ctroscopy were applied to study the formation of solid Np(VI) and Pu(VI) co mpounds with SO42- oxoanions. In case of solutions containing equimolar amo unts of NpO22+ and cesium sulfate only one compound Cs-2(NpO2)(2)(SO4)(3) w as obtained in crystalline form. But in solutions containing NpO22+ (PuO22) sulfates with a molar ratio [Cs]:[Np](Pu) higher than 2:1, Cs2NpO2(SO4)(2 ) as well as Cs2PuO2(SO4)(2) were precipitated. The crystal structure of Cs 2NpO2(SO4)(2) is of layered type and is built up by anionic layers [NpO2(SO 4)(2)](n)(2n-) linked together by Cs' ions. Each Np atom in the anionic lay er is linked via the sulfateions to three other atoms by such a manner that the bonds form an hexagonal net. Attempts to synthesize hydrated sulfate c ompounds of Np(VI) and Pu(VI) with cesium via the slow solution evaporation procedure were unsuccessful.