Explain why `[Fe(H_(2)O)_(6)]^(3+)` has magnetic moment value of 5.92 BM whereas `[Fe(CN)_(6)]^(3-)` has a value of only 1.74 BM ?

Explanation

Both have `Fe^(3+)(3d^(5)=3d^(1)3d^(1)3d^(1)3d^(1)3d^(1)).H_(2)O` is weak ligand. Electrons do not pair up. Hybridisation is `sp^(3)d^(2)`. As `n=5, mu=sqrt(5(5+2))=5.92BM`
`CN^(-)` is a strong ligand. Electrons pair up to give `3d^(2)3d^(2)3d^(1)3d^(0)3d^(0)`
Hybridisation is `d^(2)sp^(3)`. As `n=1, mu=sqrt(1(1+2))=1.73 BM`