Charge distribution as a tool to investigate structural details. II. Extension to hydrogen bonds, distorted and hetero-ligand polyhedra

It is shown that one of the main reasons for most failures of the methods f or calculating distance-dependent bond strengths is related to the distorti on of the coordination polyhedra. The charge distribution (CD) method which depends on only one universal empirical parameter (contraction parameter) is modified to include: (i) an iterative calculation of the effective coord ination number (ECoN), to deal with structures containing very distorted co ordination polyhedra; (ii) a specific contraction parameter to treat struct ures containing any type of hydrogen bond; (iii) scale factors for coordina tion subshells, to treat structures with hetero-ligand polyhedra. The contr action parameter for the hydrogen bonds was obtained from 119 well refined structures based on neutron diffraction data. Examples of the application o f the iterative charge distribution (CD-IT) are presented to show the effic iency of the new method in dealing with distorted (including hydrogen bondi ng) and hetero-ligand polyhedra. In particular, analysis of a series of 74 structures with pentacoordinated cations shows that deviations from overall trends are related to structure instability. The possible failure of the m ethod with polyionic structures and 'dynamic' structures is discussed.