According to valence bond theory, there are two types of octahedral complexes are possible, namely, inner orbital complexes and outer orbital complexes.
When a transition or inner transition metals with a specific oxidation state forms octahedral complexes, then some of complexes are inner orbital and some of complexes are outer orbital.

Valence bond theory explained this matter on the basis of hybridization of metal ion. Now, in case of [Fe (H 2O) 6] 2+ion, the