Ligand close-packing model molecules

Gillespie, R.J. Robinson, E.A. (1998). Molecular geometry of "ionic" molecules A ligand close packing model. Advances in Molecular Structure and Resonance, 4, 1-41. 

MOLECULAR GEOMETRY OF "IONIC" MOLECULES A LIGAND CLOSE-PACKING MODEL Ronald J. Cillespie and Edward A. Robinson... 

Before discussing the AIM theory, we describe in Chapters 4 and 5 two simple models, the valence shell electron pair (VSEPR) model and the ligand close-packing (LCP) model of molecular geometry. These models are based on a simple qualitative picture of the electron distribution in a molecule, particularly as it influenced by the Pauli principle. 

IV. THE LIGAND CLOSE-PACKING (LCP) MODEL FOR PREDOMINANTLY IONIC MOLECULES... 

For AX molecules with no lone pairs in the valence shell of A, both the VSEPR model and the LCP model predict the same geometries, namely AX2 linear, AX3 equilateral triangular, AX4 tetrahedral, AX5 trigonal bipyramidal, and AX octahedral. Indeed Bent s tangent sphere model can be used equally as a model of the packing of spherical electron pair domains and as a model of the close packing of spherical ligands around the core of the central atom. 

Close-packing (LCP) model. The LCP model considers the ligand ligand repulsion in molecules rather than bond pair-bond pair repulsion. The starting point of the LCP model was the observation that the inter-ligand distances of atoms X, which are bonded to a common central atom E, exhibit very nearly constant values X- -X in related molecules EX L where L is another ligand group or atom. Examples for X = F are shown in Table 19. 

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