Ligand association/dissociation paths and ill-defined coordination numbers.

The continuous shape measures approach provides a means for handling the common situation in which a metal atom presents an ill-defined coordination number. Those cases are characterized by the presence of secondary interactions to Lewis bases at distances significantly longer than those expected for a chemical bond. Systematic ways of analyzing ligand association/dissociation pathways that describe such structures and their application to a variety of specific cases are presented. The concepts and methodology presented here apply to molecules and extended solids as well and provide, when needed, a more flexible and precise stereochemical description of the metal coordination sphere than that of an integer coordination number and the associated polyhedral shape.