Question

Which one of the following complexes is an outer orbital complex ?
(Atomic number of $Mn=25,Fe=26,Co=27,Ni=28$ )

• A. ${\left[Fe{\left(CN\right)}_6\right]}^{4-}$
• B. ${\left[Mn{\left(CN\right)}_6\right]}^{4-}$
• C. ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$
• D. ${\left[Ni{\left(N{H}_3\right)}_6\right]}^{2+}$

Answer 1

Answer: (D)

In this case, $N{H}_3$ is a strong ligand but electrons remain unpaired since only one orbital is left vacant in $3d$. Thus,