Question

For the octahedral complexes of $F{e}^{3+}$in $SCN$ (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

Answer: 4

$Fe\left(26\right)\to {\left[Ar\right]}_{18}3d^{6}4s^2$
$F{e}^{3+}\to {\left[Ar\right]}_{18}3d^{5}4s^0$
$SC{N}^{-}$ is weak field ligand hence pairing will not occur.
$\therefore F{e}^{3+}\to$
Unpaired electrons. $n=5$
$\therefore {\mu }_1=\sqrt{n\left(n+2\right)}B.M=\sqrt{35}B.M$
For strong field ligand, $C{N}^{-}$,pairing will occur.
$\therefore F{e}^{3+}\to$
Hence, unpaired, $n=1$
$\therefore {\mu }_2=\sqrt{n\left(n+2\right)}=\sqrt{3}B.M$
$\therefore$ Difference in magnetic moment
$\left({\mu }_1-{\mu }_2\right)=\sqrt{35}-\sqrt{3}=4$