HgXn coordination polyhedra (X = F, Cl, Br, and I) in crystal structures

The crystallochemical analysis of 188 structures containing 252 crystallogr aphic kinds of Hg(II) atoms in HgXn coordination polyhedra (X = F, Cl, Br, and I) has been performed by the method of intersecting spheres with the us e of Voronoi-Dirichlet polyhedra. It was found that halogen atoms surrounde d by Hg(II) atoms are characterized by the coordination numbers from 3 to 8 . It was demonstrated that, at the unvarying nature of the X atoms, the ave rage Hg-X interatomic distance increases by 0.13-0.57 Angstrom with an incr ease of the coordination number, whereas the average radius of spheres with the volume equal to that of the Voronoi-Dirichlet polyhedron of a Hg atom is either independent of the coordination number (at X = F) or varies with it only by about 0.02-0.07 Angstrom (at X = Cl, Br, and I). This allows the approximation of mercury atoms in the crystal structures by soft (deformab le) spheres of a constant volume. Some results obtained in the analysis of the topology and the geometry of [HgmXn](z-)-complexes in crystal structure s are also presented. (C) 2001 MAIK "Nauka/Interperiodica".