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Pu(SO 4 ) 2  · 4 H 2 O has been prepared in two polymorphic forms,  α - and  β -. The  α -form crystals are orthorhombic, space group  Fddd , with eight formula units in a cell of dimensions  a  = 26.527(19),  b  = 11.995(9) and  c  = 5.687(4) Å. The  β -form crystals are also orthorhombic, space group  Pnma  with four formula units in a cell of dimensions  a  = 14.544(10),  b  = 10.980(8) and  c  = 5.667(3) Å. The structure of the  β -form has been determined from three dimensional X-ray data obtained on Weissenberg films. Least-squares refinement has led to a value of the conventional  R  index of 0.089 for 476 observed reflections. The coordination geometry about the Pu(IV) ion is an archemedian square – antiprism formed by oxygen atoms from four sulphate groups and four water molecules. Each sulphate group is shared by two Pu(IV) ions. Hydrogen bonds operate between the water molecules and sulphate oxygen atoms not bonded to plutonium. The structure of the  α -form derived from powder data shows that it differs from the  β -structure only in the functional nature of the hydrogen bonds. The  α - to  β -transformation can be achieved by slow heating upto 120°C.

The crystal structures of α - and β -forms of plutonium(IV) sulphate tetrahydrate