Question

The correct order of metal-carbon bond strength in the given metal carbonyls is:

• A. $\left[Fe\right(CO{)}_4{]}^{2-}>\left[Co\right(CO{)}_4{]}^{-}>\left[Ni\right(CO{)}_4]$
• B. $\left[Ni\right(CO{)}_4]>[Co(CO{)}_4{]}^{-}>[Fe(CO{)}_4{]}^{2-}$
• C. $\left[Fe\right(CO{)}_4{]}^{2-}>\left[Ni\right(CO{)}_4]>[Co(CO{)}_4{]}^{-}$
• D. $\left[Ni\right(CO{)}_4]=[Co(CO{)}_4{]}^{-}=[Fe(CO{)}_4{]}^{2-}$

Answer 1

The correct option is A $\left[Fe\right(CO{)}_4{]}^{2-}>\left[Co\right(CO{)}_4{]}^{-}>\left[Ni\right(CO{)}_4]$

This can be explained on the basis of metal to ligand electron tranfser (back bonding). If the central metal of the complex is an electron rich one, there is a higher possibility of back bonding and metal donates to the ${\pi }^{\ast }$ oribital of $CO$, which weakens the $C-O$ bond and makes the metal-carbon bond stronger. Thus, the correct order of metal-carbon bond strength in given metal carbonyls is $\left[Fe\right(CO{)}_4{]}^{2-}>\left[Co\right(CO{)}_4{]}^{-}>\left[Ni\right(CO{)}_4]$