Structural and thermal investigations of tetrasulphate complexes of uranium(IV) and plutonium(IV)

Abstract Solid sulphate complexes with the formula M 4 I M IV (SO 4 ) 4 · 2H 2 O, where M I ≡ K or Rb and M IV ≡ U or Pu, were prepared and characterized by IR, thermal and X-ray methods. The X-ray data show that the crystals are monoclinic, space group P 2 1 / c , with the unit cells containing four formula units. The IR spectra suggest the presence of bidentate sulphate groups some of which are of the chelating type. The thermal decomposition to the diuranates M 2 U 2 O 7 in the case of uranium complexes proceeds through the formation of uranyl trisulphates. The oxidation of uranium(IV) to the hexavalent intermediate takes place even if the thermal decomposition is carried out in a helium atmosphere. The thermal decomposition of the plutonium complexes gives PuO 2 . All the intermediate products were also characterized.