The EuOn coordination polyhedra in crystal structures

The Voronoi-Dirichlet polyhedra (VDP) and the method of intersecting sphere s were used to perform crystal-chemical analysis of the compounds studied t o date containing EuOn polyhedra. The Eu(III) and Eu(II) atoms were found t o have coordination numbers (C.N.s) from 6 to 12 with respect to oxygen. Th e Eu(III) --> Eu(II) transition entails an increase in the VDP volume by, o n average, 4 Angstrom (3). For a constant valence state of europium, the VD P volume barely depends on the C.N., although the Eu-O interatomic distance s change by 0.72 Angstrom for Eu(III)-containing structures and by 0.59 Ang strom for Eu(II)-containing structures.