Question

Which of the following carbonyls will have the strongest $C-O$ bond?

• A. $\left[Fe\right(CO{)}_5]$
• B. $\left[Mn\right(CO{)}_6{]}^{+}$
  
• C. $\left[Cr\right(CO{)}_6]$
• D. $\left[V\right(CO{)}_6{]}^{-}$
  

Answer 1

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


We know that $CO$ is a $\pi -$ accepting ligand. In $\left[Fe\right(CO{)}_5]$, $\left[Mn\right(CO{)}_6{]}^{+}$, $\left[Cr\right(CO{)}_6]$ and $\left[V\right(CO{)}_6{]}^{-}$, oxidation state of $Fe$, $Mn$, $Cr$ and $V$ are $0,+1,0,-1$ respectively. Since $Mn$ has positive oxidation state, thus it is not easy for $Mn$ to donate its electrons to the antibonding orbital of $CO$. Due to the absence of synergic bond in $\left[Mn\right(CO{)}_6{]}^{+}$, it has the strongest $C-O$ bond.