LCP theory

In chemistry, ligand close packing theory (LCP theory), sometimes called the ligand close packing model describes how ligand – ligand repulsions affect the geometry around a central atom. It has been developed by R. J. Gillespie and others from 1997 onwards and is said to sit alongside VSEPR which was originally developed by R. J. Gillespie and R Nyholm. The inter-ligand distances in a wide range of molecules have been determined. The example below shows a series of related molecules:

The consistency of the interligand distances (F-F and O-F) in the above molecules is striking and this phenomenon is repeated across a wide range of molecules and forms the basis for LCP theory.

Ligand radius

From a study of known structural data a series of inter-ligand distances has been determined and it has been found that there is a constant inter-ligand radius for a given central atom. The table below shows the inter-ligand radius (pm) for some of the period 2 elements:

The ligand radius should not be confused with the ionic radius.