Explain `[Co(NH_3)_6]^(3+)` is an inner orbital complex whereas `[Ni(NH_3))6]^(2+)` is an outer orbital complex.

Explanation

The electronic configuration of cobalt is `[Ar] 3d^7 4s^2` as shhown below :

In the influence of `NH_3` molecules, all the electrons in d-orbitals of `Co^(3+)` ion get pair up. The two vacant 3d-orbitals, one vancant 4s -orbital and three vacant 4p-orbitals hybridise to give six vacant `d^2sp^3` hybrid orbitals. Now six vacant `d^2sp^3` hybrid orbitals are occupied by six pairs of electrons given by six `NH_3` molecules. Hence, octahedral complex is formed. It is diamagnetic in nature because it has no unpaired electrons. Since it involves inner d-orbital. Hence it is an inner orbiral complex.