Question
Which one of the following cyano complexes would exhibit the lowest value of paramagnetic behaviour?
$$\left( {{\text{At}}\,{\text{Nos}}:\,Cr = 24,\,Mn = 25,\,Fe = 26,\,Co = 27} \right)$$
A.
$${\left[ {Co{{\left( {CN} \right)}_6}} \right]^{3 - }}$$
B.
$${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }}$$
C.
$${\left[ {Mn{{\left( {CN} \right)}_6}} \right]^{3 - }}$$
D.
$${\left[ {Cr{{\left( {CN} \right)}_6}} \right]^{3 - }}$$
Answer :
$${\left[ {Co{{\left( {CN} \right)}_6}} \right]^{3 - }}$$
Solution :
$$\eqalign{
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{No}}{\text{. of unpaired electron }} \cr
& \left( {\text{A}} \right)C{o^{3 + }}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,4 \cr
& \left( {\text{B}} \right)F{e^{3 + }}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1 \cr
& \left( {\text{C}} \right)M{n^{3 + }}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,4 \cr
& \left( {\text{D}} \right)C{r^{3 + }}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,3 \cr} $$
The effective magnetic moment is given by the number of unpaired electrons in a substance, the lesser the number of unpaired electrons lower is its magnetic moment in Bohr — Magneton and lower shall be its paramagnetism