Question

A complex ${\left[{MF}_6\right]}^{-x}$ has magnetic moment of $4.91B.M$ whereas ${\left[M{\left(CN\right)}_6\right]}^{-x}$ has zero magnetic moment, metal ion can be :

• A. ${Co}^{+2}$
• B. ${Mn}^{+2}$
• C. ${Fe}^{+2}$
• D. ${Fe}^{+3}$

Answer 1

The correct option is C ${Fe}^{+2}$

The magnetic moment 4.91BM denotes 4 unpaired electron in the complex and 0 BM magnetic moment denotes 0 unpaired electron in the compound. in the case of M=$F{e}^{2+}$, then the configuration will be $3d^{6}4s^2$. For the complex $[M{F}_6{]}^{-x}$ here the fluorine as a ligand is a weak field ligand which will not be able to pair the 4 unpaired electron and hence magnetic moment comes to be 4.91 B.M and in complex $\left[M\right(CN{)}_6{]}^{-6}$ CN is a strong field ligand and hence will pair up the 4 unpaired electrons into a pair of 2 and therefore there are 0 unpaired electrons left which implies 0 BM magnetic moment. Hence C is the correct option.