Using valence bond theory, explain the following in relation to the complexes given below
`[Mn(CN)_(6)]^(3-), [Co(NH_(3))_(6)]^(3+), [Cr(H_(2)O)_(6)]^(3+), [FeCl_(6)]^(4-)`
(a) type of hybridisation
(b) Inner or outer orbital complex
(c) Magnetic behaviour
(d) Spin only magnetic moment value.

Explanation

`[Mn(CN)_(6)]^(3-)` : The element Mn is in `+3` oxidation state. As `CN^(-)` ion is a strong field ligand, the electron pairing is possible in this case.

i) The hybridisation is of `d^(2)sp^(3)` type.
ii) It is an inner orbital complex.
iii) Paramagnetic in nature.
iv) Spin only magnetic moment `(mu) = sqrt(n(n+2)) = sqrt(2(2+2) = sqrt(8) = 2.87 BM`
`[Co(NH_(3))_(6)]^(3+)`: The element Co is in `+3` oxidation state. As `NH_(3)` is a strong field ligand, electron pairing is possible is this case:

i) The hybridisation is of `d^(2)sp^(3)` type.
ii) It is an inner orbital complex.
iii) Diamagnetic in nature.
iv) Spin only magnetic moment `(mu)` = zero.
`[Cr(H_(2)O)_(6)]^(3+)` : The element Cr is in `+3` oxidation state. As `H_(2)O` is a weak field ligand, electron pairing is not possible in this case:

i) The hybridisation is of `d^(2)sp^(3)` type.
ii) It is an inner orbital complex.
iii) Paramagnetic in nature.
iv) Spin only magnetic moment `(mu) = sqrt(n(n+2)) = sqrt(3(3+2) = sqrt(15) = 3.87 BM`
`[FeCl_(6)]^(4-)` : The element Fe is `+2` oxidation state. As `Cl^(-)` is a weak ligand, electron is not possible in this case.

i) The hybridisation of `sp^(3)d^(2)` type.
ii) It is an outer orbital complex.
iii) Paramagnetic in nature.
iv) Spin only magnetic moment `(mu)` = `sqrt(n(n+2)) = sqrt(4(4+2)) = sqrt(24) = 4.9 BM`