Explain the following:
(i) All the octahedral complexes of `Ni^(2+)` must be outer orbital complexes.
(ii) `[CoF_(6)]^(3-)` is paramgnetic but `[Co(CN)_(6)]^(3-)` is diamagnetic .

Explanation

(i) `Ni^(2+)` configuration
During rearrangement only one 3d-orbital may be made available for pairing of the electrons.
Thus, `d^(2)sp^(3)` hybridization is not possible. So only `sp^(3)d^(2)` (outer) hybridization can occur.
(ii) In `[CoF_(6)]^(3-), Co^(3+)` undergoes `sp^(3)d^(2)` hybridization. Four d-orbitals are singly occupied. Hence, it is paramagnetic .
` [CoF_(6)]^(3-) (##RES_CHM_CC_S01_007_S02.png" width="80%">
In `[Co(CN)_(6)]^(3-),Co^(3+)` undergoes `d^(2)sp^(3)` hybridization. All electrons are paired and thus it is diamagnetic.
`[Co(CN)_(6)]^(3-) (##RES_CHM_CC_S01_007_S03.png" width="80%">