Russian Journal of Inorganic Chemistry, Vol. 42, No. 12, 1997, pp. 18711910. Translated from Zhurnal Neorganicheskoi Khimii, Vol. 42, No. 12, 1997, pp. 20362077. Original Russian Text Copyright 1997 by Serezhkin, Mikhailov, Buslaev. English Translation Copyright 1997 Interperiodica Publishing (Russia).

V. N. Serezhkin*, Yu. N. Mikhailov**, and Yu. A. Buslaev**

** Kurnakov Institute of General and Inorganic Chemistry, Leninskii pr. 31, Moscow, 117907 Russia

Received May 15, 1997

AbstractA new method of determining the coordination numbers (CNs) of atoms in crystal structures is sug-gested. The method is based on the interatomic interaction model in which each atom is approximated by two spheres (of radii r_S and R_SD) with the common center at the atomic nucleus. One of the spheres characterizes a conventionally isolated (chemically nonbonded) atom, and its radius is a constant equal to the quasi-orbital Slater radius for the atoms of a given chemical type in any structure. The other sphere of radius R_SD characterizes a chemically bonded atom and represents the sphere whose volume is equal to the volume of the VoronoiDirichlet polyhedron of the corresponding atom in a certain crystal structure. The simultaneous occurrence of two (O₂), three (O₃), or all four (O₄) possible pairwise intersections of the above spheres of two atoms is accepted as a criterion for the formation of a strong chemical bond (covalent, ionic, or metallic) between these atoms in the structure of a compound. The overlap of only the external spheres (O₁) of atoms is considered to be evidence for van der Waals interaction and is ignored when determining the CNs. The validity of this method for determining the CNs of atoms in the structures of both elements and chemical compounds is shown by a number of examples. The CNs obtained by this method correspond well with the commonly accepted CNs of atoms for the crystals in question. A number of fundamental advantages of the new method over the classical method of assessment of CNs are demonstrated.