Using crystal field theory, draw energy level diagram, write electronic configuration of the central metal atom/ion and determine the magnetic moment value in the following
(a) `[CoF_(6)]^(3-), [Co(H_(2)O)_(6)]^(2+), [Co(CN)_(6)]^(3-)`
(b) `FeF_(6)^(3-), [Fe(H_(2)O)_(6)]^(2+), [Fe(CN)_(6)]^(4-)`

Explanation

The magnetic moment value is linked with the number of unpaired which depends upon the position of the ligands. In the electrochemical series i.e., whether it is a weak field ligand or strong field ligand. Ini the light of the above observation, the magnetic moment values of the compounds are calculated:
i) `[CoF_(6)]^(3-)`: `F^(-)` ion is a weak field ligand. The value of `Delta_(0)` is small `(Pgt Delta_(0))`. Electron pairing is not possible.

Number of unpaired electrons = 4
Magnetic moment = `sqrt(n(n+2))=sqrt(4(4+2)) = sqrt(24)= 4.9BM`
ii) `[Co(H_(2)O)_(6)]^(2+)`: `H_(2)O` is a weak field ligand. The value of `Delta_(0)` is small (Pgt`Delta_(0))`. Electron pairing is not possible.
ltbr. Number of electrons = 3
`sqrt(n(n+2))=sqrt(3(3+2)) = sqrt(15)= 3.87BM`
iii) `[Co(CN)_(6)]^(3-)` : `CN^(-)` is a strong field ligand. The value of `Delta_(0)` is large (P lt`Delta_(0))`. Electron pairing is not possible.

Number of unpaired electrons = Zero.
Since there are no unpaired electrons present, the complex is diamagnetic in nature.
`[FeF_(6)]^(3-)` : `F^(-)` ion is a weak ligand. The value of `Delta_(0)` is small `(P gt Delta_(0))`. Electrons pairing is not possible.

Number of unpaired electrons = 5
`sqrt(n(n+2))=sqrt(5(5+2)) = sqrt(35)= 5.92BM`
v) `[Fe(H_(2)O)_(6)]^(2+)` : `H_(2)O` is a weak field ligand. The value of `Delta_(0)` is small `(Pgt Delta_(0))`. Electrons pairing is not possible.

Number of unpaired electrons = 4
Magnetic moment = `sqrt(n(n+2))=sqrt(4(4+2)) = sqrt(24)= 4.9BM`
`[Fe(CN)_(6)]^(4-)` : `CN^(-)` ion is a strong field ligand. The value of `Delta_(0)` is large `(P lt Delta_(0))`. Electron pairing is possible.

Number of unpaired electrons= zero.
Since there are no unpaired electrons present, the complex is diamagnetic in nature.