Consider a complex [Fe(CN)6]−3
CN is a powerful field ligand and uses inner 3d-orbitals to form a low spin complex. Because there are 6 ligands, it has octahedral geometry. So the hybridization of the complex is d2sp3.
The electronic configuration of central metal ion Fe is
Fe (26) = [Ar] 4s2 3d6
Fe3+ = [Ar] 3d5 4s0