Question

Why some coordination compounds form sp3d2 and some form d2sp3?

Answer 1

In sp3d2, the s, p and d orbitals which are hybridized all come from the same energy level, for instance, it has been taught that when sulfur combines with six fluorine atoms to make SF6 that the 3s, 3p and two 3d orbitals hybridize to make the sp3d2 hybrid orbital set.

But d2sp3 is different. In this case the d-orbitals come from the n-1 energy level. Transition metals may exhibit d2sp3 hybridization where the d orbitals are from the 3d and the s and p orbitals are the 4s and 3d.