Question

CO is stronger ligand than NH₃ for many metals. Explain giving appropriate reason.

Answer 1

Ligands such as CO, CN^–, NO⁺ have empty π orbitals which overlap with the filled d orbitals (t_2g) of transition metals forming π bonds (back bonding). These π interactions increase the value of Δ_o. This account for the position of these ligands as strong ligand. NH₃ cannot form π bonds by back bonding.