Question

The spin only magnetic moment of $Co$ in the compound $Hg\left[Co\right(SCN{)}_4]$ is:
(where $SC{N}^{-}$ is a weak ligand)

• A. $\sqrt{3}$
• B. $\sqrt{8}$
• C. $\sqrt{15}$
• D. $\sqrt{24}$

Answer 1

The correct option is C $\sqrt{15}$

The spin only magnetic moment is given by $\sqrt{n(n+2)}$, where n is the number of unpaired electrons.
In $Hg\left[Co\right(SCN{)}_4]$, $Co$ is in +2 oxidation state. Since $SCN$ is a week field ligand, the electronic configuration of
$C{o}^{+2}=t_{2g}^5{e}_g^2$. So, the number of unpaired electrons - n = 3. Hence, the magnetic moment $\mu =\sqrt{15}$ BM.