Question

The ligand called $\pi$-acid is:

• A. $CO$
• B. $N{H}_3$
• C. $C_2{O}_4^{2-}$
• D. ethylene diamine

Answer 1

The correct option is A $CO$

A example of a pi acid ligand is carbon monoxide(CO). CO is a good pi acceptor (lewis acid) due to empty pi orbitals and a good sigma donor (lewis acid). When bonding to a metal the ligand (in this case CO) sigma donates to an empty d-orbital and the filled d-orbitals of the metal donates to the empty pi* orbitals of CO, back donation.