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

Explanation

In `[Co(NH_3)_6]^(3+), Co` is in +3 state and its configuration is `3d^6`. In the presence of `NH_3`, the 3d electrons get paired leaving behind two empty d-orbitals. Hence, `d^2sp^3` hybridization takes place and an inner-orbital complex is formed. In `[Ni(NH_3)_6]^(2+), Ni` is in +2 state and its configuraton is `d^8`. Although the ligand is same, the 3d-electrns do not get paired. In this case, `sp^3d^2` hybridization takes place leading to the formation of an outer orbital complex. It is the difference in configuraton of d-orbitals that makes the difference.