VSEPR theory
The chemical inertness of the s electrons in the lower oxidation state is not always married to steric inertness (where steric inertness means that the presence of the s-electron lone pair has little or no influence on the geometry of the molecule or crystal). A simple example of steric activity is that of SnCl2, which is bent in accordance with VSEPR theory. Some examples where the lone pair appears to be inactive are bismuth(III) iodide, BiI3, and the anion. In both of these the central Bi atom is octahedrally coordinated with little or no distortion, in contravention to VSEPR theory.