Onthe basis of valence bond theory explain the structure and magnetic nature of `[Fe(CN)_6]^(3_) complex ion.

Explanation

The electronic configuration of iron (Z = 26) in its ground state is `[Ar] 3d^6 4s^2 4p^0`. It loses three electrons to acquire +3 oxidation state. Now its electronic configuration is given as below :

Now, when `CN^(-)` ions approach `Fe^(3+)` ion, then electron in d- orbitals are pair up leaving two 3d-orbitals vacant. These vacant 3d - orbitals get hybridised with one 4s - orbital and three 4p - orbitals. THe resulting hybridisation is `d^2sp^3`. Now six pairs of electrons will occupy six vancant hybridised orbitas. Hence formed complex `[Fe(CN)_6]^(3-)` has octahedral geometry. It is paramagnetic in nature because there is one unpair.e~ electron in 3d-orbital.