Question

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

Answer 1

$F{e}^{3+}$ has $3d^5$ outer electronic electronic configuration.

$C{N}^{-}$ ion is a strong field ligand. It produces low spin complex with 1 unpaired electron having a magnetic moment.

${\mu }_{eff}=\sqrt{n(n+2)}=\sqrt{1(1+2)}=\sqrt{3}=1.73B.M.$

$SC{N}^{-}$ ion is a weak field ligand. It produces high spin complex with 5 unpaired electrons having a magnetic moment.

${\mu }_{eff}=\sqrt{n(n+2)}=\sqrt{5(5+2)}=\sqrt{35}=5.92B.M.$

Hence, the difference in the magnetic moment is $5.92B.M.-1.73B.M.=4.19B.M.\simeq 4B.M.$