Question

Which is not true about metal carbonyls?

• A. Here CO acts as a Lewis base as well as Lewis acid
• B. Here metal acts as Lewis base as well as Lewis acid
• C. Here $d\pi -p\pi$ back bonding takes place
• D. Here $p\pi -p\pi$ back bonding takes place

Answer 1

The correct option is D Here $p\pi -p\pi$ back bonding takes place

In metal carbonyls, both metal and CO acts as Lewis acid as well as base.
carbon of CO donates electron pair to the empty orbital of metal and in return, metal donates electron pari to CO which involves $d\pi -p\pi$ back bonding, i.e., sideways overlap of a filled orbital on the metal with empty antibonding ${\pi }_{2py}^{\ast }$ orbital of CO.