Question

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

• A. $Fe\left(CO\right)_{5}$
• B. $Mn(CO)_6^+$
• C. $Cr(CO)_{6}$
• D. $V\left(CO\right)_{6}^{-}$

Answer 1

Answer: (B)

The presence of a positive charge on the metal carbonyl would resist the flow of the metal electron to $\pi ^{\star}$ orbitals of $CO$ . THis would increase the $CO$ bond order and hence $CO$ in a metal carbonyl will absorb at a higher frequency compared to its absorption in a neutral metal carbonyl.