Question

Due to the back bonding in metal carbonyls:

• A. Strength of metal-carbon bond decreases.
• B. Strength of carbon-oxygen bond increases.
• C. Strength of all bonds is unaffected.
• D. Strength of carbon-oxygen bond decreases.

Answer 1

The correct option is D Strength of carbon-oxygen bond 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 is donated from filled metal d orbital to vacant anti bonding pi orbital of CO. This involves lateral overlap of orbitals. Due to this the electron density in the bonding pi orbitals of CO decreases and antibonding pi orbitals increases. This decreases the bond order. Hence the strength of carbon-oxygen bond decreases.
The strenght of metal carbon bond increases.