The SmOn Coordination Polyhedra in Crystal Structures

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Crystal-chemical analysis of all compounds studied to date and containing SmOn coordination polyhedra was performed using the methods of Voronoi–Dirichlet polyhedra (VDP) and intersecting spheres. It was shown that the coordination number (CN) of Sm(III) atoms with respect to oxygen varies from 4 to 12 and the CN of Sm(II) is 5, 7, or 9. The Sm(III) → Sm(II) transition was found to entail an increase in the VDP volume by, on average, 2.8 Å3, whereas for a constant oxidation state of Sm, the VDP volume barely depends on the CN, although the Sm–O interatomic distances vary by 0.83 Å for Sm(III)-containing crystals and by 0.39 Å for Sm(II)-containing crystals. The results of analysis of the topology of [SmaOb] groups in the crystal structure are presented.

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