Question

Which of the following statement is true about back bonding in metal carbonyls, $\left[M\right(CO{)}_x]$?

• A. Bond order of $M-C$ and $C-O$ increases
• B. Bond order of $M-C$ increases and $C-O$ decreases
• C. Bond order of $M-C$ decreases and $C-O$ increases
• D. Bond order of $M-C$ and $C-O$ decreases

Answer 1

The correct option is B Bond order of $M-C$ increases and $C-O$ decreases

Synergic bonding interactions are present in metal carbonyls. The sigma bond is formed when lone pair of electrons of carbonyl carbon is donated to vacant orbital of metal. To form a pi bond, an electron pair donated from filled metal d -orbital to vacant anti-bonding pi orbital of $CO$. This involves lateral overlap of orbitals. Due to this bond order of $CO$ decreases. Thus, the bond order of $M-C$ increases and bond order of $CO$ decreases.