Question

Is there both sigma and pi bonding between metal carbonyl bonding?

Answer 1

Answer:

Carbon monoxide is a common ligand in transition metal chemistry, in part due to the synergistic nature of its bonding to transition metals. ... The more sigma donation by the carbonyl (or other sigma-donors on the metal center), the stronger the pi-backbonding interaction...

thats why it is not necessary but it happens sometime!!

hope it is helpful