Explain why a knowledge of magnetic suceptilbility of a complex is often necessary for a correct assignment of the electronic conifiguration according to valence bond theory
(b) Draw valence bond representations of the electronic structures of (i) `[CoF_(6)]^(3-)` (paramagnetic) and (ii) `[Co(CN)_(6)]^(3-)` (diamagnetic) .

Explanation

Inner orbital complexes in which inner orbitals are involved `d^(2)sp^(3)` or `dsp^(2)` or `dsp^(3)` electrons pairing is necessary in some cases The change in magnetic susceptibility moment is an indication of what orbitals are being used
(b) (i) Valence bond representation of `[CoF_(6)]^(3-)`
paramagetic Co is `Co^(3+)` ion in `[CoF_(6)]^(3-)`
`[Co(Z =27)implies 3d^(7) 4s^(2),Co^(3+)implies3d^(6)]`

Since `[CoF_(6)]^(3-)` is paramagntic electron Partiring will not take place and `Co^(3+)` ion will be `sp^(2)d^(2)` hybridised forming outer orbital complex
(ii) Valence bond representation of `[Co(CN)_(6)]^(3-)` (diamagntic)
In `[Co(CN)_(6)]^(3-)` Co is present `Co^(3+)`

Since the complex ion is diamagnetic pairing of electrons takes place resulting in `Co^(3+)` ion in `[Co(CN)_(6)]^(3-)` complex ion be to `d^(2)sp^(3)` hybridised and hence forms inner orbital complex .