Crystal chemistry of divalent lead: characteristics of Pb-Ox-Cly-polyhedra

Abstract

Size and shape of a coordination polyhedron built up by its appertaining atoms (in the special case a central lead atom coordinated by oxygen and chlorine atoms) is defined by its space filling polyhedron based in an arbitrary manner on the ratio of the radii with Pb:O:Cl=1:1:1. As a consequence, the faces of each polyhedron cut the distance between central atom and coordinating atom in half [1]. Rather typical for formally divalent lead is the frequent occurrence of one-sided coordination polyhedra. Crystal chemical calculations concerning the coordination polyhedra of divalent lead, in which both the two elements oxygen and chlorine are involved, show two interesting features. The two features in the geometric arrangement are: (1) The irregularity of the coordination polyhedra, which can be deduced from the configuration of the electrons, especially of the lone pair 6s electrons of divalent lead. (2) A tendency of O and Cl atoms to be arranged in different hemispheres around the central lead atom [2]. The following values are further results of statistic investigations of the distances: In Pb-O-polyhedra the mean distance measures 2.5 A, in Pb-Cl-polyhedra 2.9 A. If both ligands participate, the distances are ≈ 2.4 A and ≈ 3.2 A. These calculations and statistic investigations confirm the more or less sophisticated bond valences determined from bond lengths.