Coordination polyhedrons ScXn (X = F, Cl, Br, I) in crystal structures

The Voronoi-Dirichlet (VD) polyhedrons and the method of intersecting spher es were used to carry out the crystallochemical analysis of all hitherto st udied compounds containing Sc atoms in the coordination polyhedrons of the type ScXn (X = F, Cl, Br, and I). It is established that fluorides contain only Sc(III) atoms; chlorides contain Sc(III), Sc(II), and Sc(I); bromides contain Sc(III); and iodides contain Sc(II). Some of the scandium atoms in compounds with X = Cl, Br, and I exist in the noninteger and uncertain oxid ation state and are capable of forming not only Sc-X but also Sc-Sc bonds. The volume of VD polyhedron of the Sc atom in the (ScFn)-F-III complexes do es not depend on the metal coordination number, although the interatomic Sc -F distances vary over wide limits from 1.94 to 2.15 Angstrom. The characte ristics of the Sc VD polyhedrons and the ability of Sc atoms to form Sc-Sc bonds in the [Sc(XnScm)] (X = Cl, Br, or I; n = 3-6, and m = 0, 3, 4, and 5 ) complexes are found to depend both on the valence state of the metal and on the nature of the halogen atom.