Question

For the octahedral complexes of $Fe^{3+}$ in $SCN^{-}$ (thiocyanato-S) and in $CN^{-}$ ligand environments, the difference between the spin-only magnetic moments in Bohr Magneton (when approximated to the nearest integer) is -
[Atomic number of Fe = 26]

Answer 1

$Fe^{+3 }+ SCN^{-} → \left[Fe\left(SCN\right)_{6}\right]^{3-}$
$Fe^{+3} ⇒ \left[Ar\right] 3d^{5}$
Number of unpaired electrons $= 5$
$μ = 5.9$
$Fe^{+3} + CN^{-} → \left[Fe\left(CN\right)_{6}\right]^{3-}$
$Fe^{+3} = \left[Ar\right]3d^{5}$
Number of unpaired electrons $= 1$
$μ = 1.732$
Difference $= 5.91 - 1.73 = 4.18$
$\simeq 4$