Stereochemistry of Thorium in Oxygen-Containing Compounds

Voronoi-Dirichlet (VD) polyhedra and the method of intersecting spheres have been used to perform analysis of coordination of 198 types of crystallographically different Th(IV) atoms in the crystal structures of oxygen-containing compounds characterized with R <= 0.05. The volumes of VD polyhedra have been determined for the thorium atoms forming ThOn complexes in which the Th-O bond lengths (2.14-2.91 ) are roughly independent of the CN (n), varying from 4 to 12. It has been found that the phase transition of thorianite ThO2 at elevated pressure is accompanied by a considerable distortion of the thorium VD polyhedra because of the appearance of faces corresponding to Th-Th contacts in which the interatomic distances are shorter than in thorium metal. It has been demonstrated that the baric phase transitions in thorium metal and thorianite are accompanied by similar changes in characteristics of Th VD polyhedra, which are tentatively believed to be a result of appearance of bonding 5f interactions between thorium atoms.