Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory.
`[Fe(CN)_(6)]^(4-)`

Explanation

`[Fe(CN)_(6)]^(4-)` In this complex, Fe is present as `Fe^(2+)`.
`Fe=[Ar]3d^(6)4s^(2)`
Outer electronic configuration of `Fe^(2+)=3d^(6)4s^(0)`

`CN^(-)` being strong field ligand, pair up the unpaired d-electrons. Thus, two 3d-orbitals are now available for `CN^(-)` inos.
`[Fe(CN)_(6)]^(4-)=`

Since, all the eelctrons are paired, the complex is diamagnetic. Moreover, (n - 1) d-orbitals are involved in bonding. So, it is an inner orbital or low spin complex.