Coordination polyhedra PtXn (X = F, Cl, Pr, or I) in crystal structures

The Voronoi-Dirichlet polyhedra and the method of intersecting spheres are used to carry out crystallochemical analysis of the coordination modes for 156 sorts of Pt atoms in the structures of halogen-containing compounds. It is established that the coordination number (C.N.) of Pt(IV or V) with res pect to the fluorine atoms is only 6, whereas the C.N; of the Pt(II or IV) atoms in chlorides, bromides, and iodides is 4, 5, or 6. It is found that, in going from the (PtX6)-X-IV octahedra to the (PtX4)-X-II squares, a simul taneous decrease in the degree of oxidation and the C.N. of Pt atoms is acc ompanied by the shortening (by 0.02-0.08 Angstrom) of the Pt-X distances fo r any X (Cl, Br, and I). Some of the compositional and structural features of the PtXn complexes are explained in terms of the 18-electron rule.