Chemistry

The nature of bonding in Ni (CO)? includes synergic bonding. The synergic bonding in metal carbonyls like nickel tetracarbonyl is due to two-way interaction of metal and carbonyl ligand electron density donation.

The synergic bonding is best explained thorugh Molecular Orbital Theory (MOT), which explains the donation of electron density from the filled d-orbitals of nickel (Ni) into the antibonding? * orbitals of the carbon monoxide (CO) ligand.

The synergic bonding can be described as a combination of? -bond formation due to donation of lone pair to metal center, and? back-bond formation due to donation of lone pair to CO ligand. 

The metal-carbon bonds (M-C) in metal carbonyls are due to the synergic interaction between the metal and carbonyl group. There are two types of bonding between metal and carbonyl group. 

? -bond in Metal Carbonyls: The Carbonyl (CO) ligand donates a lone pair of electrons to the metal center to fill its empty d-filled orbital. This electron density donation is called? -donation.

? -back bond in Metal Carbonyls: This is the case of back bonding. The already filled d-orbitals return the electron density into the empty? * (antibonding) orbital of CO. This electron density donation by the metal is called? -back donation.

Both these combined? -bonding and? -back bonding are called synergic bonding.