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

Abstract

Pu(S0 4 ) 2 • 4 H 2 0 has been prepared in two polymorphic forms, a-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) Â. The ß-form crystals are also orthorhombic, space group Prima with four formula-units in a cell of dimensions a = 14.544(10), b = 10.980(8) and c = 5.667(3) Λ. The structure of the ß-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 ^-structure only in the functional nature of the hydrogen bonds. The a-to ^-transformation can be achieved by slow heating upto 120°C.

Two Ce(SO4)2·4H2O polymorphs: Crystal structure and thermal behavior

“…As expected, the infrared spectra of the a-and b-Pu(SO 4 ) 2 Á 4H 2 O did not exhibit substantial differences [24]. The differences between the a-and b-structure have been discussed by Singer and Cromer [13] and by Jayadevan et al [24]. Singer and Cromer [13] have suggested the operation necessary to relate the Fddd structure of Zr(SO 4 ) 2 Á 4H 2 O to the Pnma structure of U(SO 4 ) 2 Á 4H 2 O, resulting in a puckering of the flat layers of the Fddd-structure, shown in Figs.…”

“…Indexed powder data [12d,24] confirm the existence of the orthorhombic modification with space group Fddd, which is isomorphic with the structure of Zr(SO 4 ) 2 Á 4H 2 O, as shown by Jayadevan et al [24], and to the structure of a-Ce(SO 4 ) 2 Á 4H 2 O. As expected, the infrared spectra of the a-and b-Pu(SO 4 ) 2 Á 4H 2 O did not exhibit substantial differences [24]. The differences between the a-and b-structure have been discussed by Singer and Cromer [13] and by Jayadevan et al [24].…”

“…The b-Pu(SO 4 ) 2 Á 4H 2 O can be obtained by very slow heating of the a-Pu(SO 4 ) 2 Á 4H 2 O to 120 1C [24]. This a-b transformation can also be achieved by hydrothermal equilibration [24] similarly to the a-b transformation of Ce(SO 4 ) 2 Á 4H 2 O.…”

“…Pu(SO 4 ) 2 Á 4H 2 O is the only compound apart from Ce(SO 4 ) 2 Á 4H 2 O that has proven to crystallize in both the orthorhombic space groups, Fddd and Pnma. The structure of b-Pu(SO 4 ) 2 Á 4H 2 O, space group Pnma, has been determined [24] and it is isomorphic with the structure of b-Ce(SO 4 ) 2 Á 4H 2 O and even the hydrogen bonding patterns are the same within these two structures. Indexed powder data [12d,24] confirm the existence of the orthorhombic modification with space group Fddd, which is isomorphic with the structure of Zr(SO 4 ) 2 Á 4H 2 O, as shown by Jayadevan et al [24], and to the structure of a-Ce(SO 4 ) 2 Á 4H 2 O.…”

“…The structure of b-Pu(SO 4 ) 2 Á 4H 2 O, space group Pnma, has been determined [24] and it is isomorphic with the structure of b-Ce(SO 4 ) 2 Á 4H 2 O and even the hydrogen bonding patterns are the same within these two structures. Indexed powder data [12d,24] confirm the existence of the orthorhombic modification with space group Fddd, which is isomorphic with the structure of Zr(SO 4 ) 2 Á 4H 2 O, as shown by Jayadevan et al [24], and to the structure of a-Ce(SO 4 ) 2 Á 4H 2 O. As expected, the infrared spectra of the a-and b-Pu(SO 4 ) 2 Á 4H 2 O did not exhibit substantial differences [24].…”