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 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

Answer: (D)

CO is called $\pi$ -acid ligand. In metal carbonyl complexes, there is donation of an electron pair from carbon to the empty orbital of metal and then simultaneously a back $\pi$ -bonding is formed by sideways overlap of a filled orbital on the metal with empty anti-bonding ${\pi }_{2py}^{\ast }$ orbital of CO.