Question

Which of the following molecule does not obey 18 electron rule?

• A. $\left[Mn\right(CO{)}_6]$
• B. $Fe(CO{)}_5$
• C. $[PtC{l}_6{]}^{2-}$
• D. $\left[Ni\right(CO{)}_4]$

Answer 1

The correct option is A $\left[Mn\right(CO{)}_6]$

According to $18e^{-}$ rule, in a complex the sum of valence electrons and the electrons donated by the ligands equals to 18. It provides a closed and stable configuration, $n{s}^2(n-1)d^{10}n{p}^6$

$\left(i\right).\left[Mn\right(CO{)}_6]\to 7+(6\times 2)=19(ii).[Fe(CO{)}_5\to 8+(5\times 2)=18(iii).[Pt(Cl{)}_6{]}^{2-}\to 6+(6\times 2)=18(iv).[Ni\left(CO{)}_4\right]\to 10+(4\times 2)=18$

Hence, compound (a) does not obeys $18e^{-}$ rule.