Question

Why CO is stronge ligand?

Answer 1

CO forms a coordination bond that has both sigma and pi properties. A non-bonding orbital on the CO will form the primary bond, and an anti-bonding orbital forms a bond as well. Because of this multiple coordination bond, the carbonyl-metal bond is very strong, and the energy splitting is very high. A ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligand."