Question

CO is a stronger ligand than NH3 for many metals why?

Answer 1

According to Ligand field theory;the π-acceptor ligands are the stronger ligand & the π-donating ligand is weak field ligand,Here we know that NH3 is aπ-donor in composition to the CO which is a π-acceptor ligand.

Answer 2

Explanation:

A CO molecule is able to form a $\sigma$ bond with the metal atoms by donating lone pair of electrons.

As well as CO is able to form a $\pi$ electron by accepting electrons from filled metal orbitals.

Whereas a $NH_{3}$ molecule can only form a $\sigma$ by donating lone pair of electrons. But it cannot form back bonding by accepting electrons from metal orbitals.

That is why, CO is a stronger ligand than $NH_{3}$ for many metals.