Question

Which complex ion has no $d$-electron in the central metal atom?

• A. ${\left[Mn{O}_4\right]}^{-}$
• B. ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$
• C. ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$
• D. ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{3+}$

Answer 1

The correct option is A ${\left[Mn{O}_4\right]}^{-}$

The complex ion ${\left[Mn{O}_4\right]}^{-}$ has no $d$-electron in the central metal atom.

The electronic configuration of Mn is $\left[Ar\right]3d^{5}4s^2$. In $Mn{O}_4^{-}$, oxidation number of $Mn$ is $+7$ i.e. all the $3d$ and $4s$ electrons are lost to form ${\left[Mn{O}_4\right]}^{-}$ complex. Hence, it has no $d$-electron.

The electronic configuration of Mn(VII) is $\left[Ar\right]3d^{0}4s^0$.

The complex ions ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$, ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$ and ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{3+}$ have 6, 5 and 3 $d$-electrons respectively in the central metal atom.