Yttrium Selenates

Structural Studies.—The structures of some compounds of scandium and yttrium, in addition to those of some of the lanthanides and actinides, have been reviewed. The crystal structure of scandium selenate pentahydrate, Sc(Se04)3,5H20, has been determined by single-crystal JT-ray diffraction. The scandium atoms were shown to be octahedrally co-ordinated by the oxygen atoms of the selenate groups and water molecules. The mean Sc—O distances in the scandium co-ordination polyhedra vary from 2.08 to 2.10 A and the mean Sc—O bond lengths in the selenate groups vary from 1.61 to 1.64 A. Two formula units were found in each cell. 

The double alkali sulfates are used in separating tho yttrium and cent groups. The ethyl sulfates are very useful in certain separations, but th are rather difficult to form and they must be handled very carefully becai they decompose easily, even at room temperature. Sulfites, thiosulfat dithionates, selenites, and selenates of most of tho metals have been p pared. 

Johansson et al. (1985) and Johansson and Wakita (1985) have studied the selenate and perchlorate systems using isomorphous substitution by yttrium to remove the ambiguities involved in the interpretation of the experimental data. The results indicate that selenate ions are monodentate ligands to R " while the perchlorate ions show no inner-sphere complex formation even at high concentrations. The coordination number was found in all systems to be invariably 8 0.3. This is the same value as Wertz and coworkers have assumed to be valid in concentrated chloride and bromide solutions. On the other hand, the neutron diffraction study by Narten and Hahn (1982) using isotopic substitution gave 8.5 0.2 for 2.85MNdCl3. 

---