(i) Bonding in complexes are explained in terms of hybridisation. If the hybridisation of central metal atom/ion involves the use of (n-1) d, ns and np orbitals, then d2sp3 hybridisation is possible for octahedral complexes. Complexes formed by d2sp3 hybridisation of the central metal atom or ion is known as inner orbital complex. [Fe(CN)6]-4, [Fe(CN)6]-3, [Cr(NH3)6]+3 are examples of inner orbital complexes.
(ii) If the hybridisation of the metal ion involved the ns, np and nd orbitals and for octahedral complexes sp3d2 hybridisation involved, the complex formed is known as outer orbital complex. [CoF6]-3 is an example for outer orbital complex.
