Local geometry effects ionic bonding

If the electronegativity of the ligands X is much less than the electronegativity of the central atom A, the electrons in the valence shell of A are not well localized into pairs and therefore have a small or zero effect on the geometry. In such molecules the bonds are very ionic in the sense A X+, and the central atom A is essentially an anion with a spherical electron density distribution. In this case the VSEPR model is not valid, and the geometry of the molecule is determined by ligand-ligand repulsions. 

The main difference between them is that the delocalisation of the orbitals mimics the effects of ionic structures, giving stronger bonds in the molecule. This allows us to study the effect of the bond-strength in the 7i-system on the geometry. The local orbitals allow a description closer to the Pauling picture [47], since the orbitals lack freedom. 

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