In metal carbonyls, there is synergic bonding interaction between metal and carbon monoxide. This leads to increase in strength of metal ligands bond and decrease in bond order of CO in carbonyl complex as compared to bond order in carbon monoxide. Simple carbonyls are invariably spin-paired complexes except for vanadium metal. The increase in bond length in CO as compared to carbon monoxide is due to :

In metal carbonyls, there is synergic bonding interaction between meta

1.	In metal carbonyls, there is synergic bonding interaction between metal and carbon monoxide. This leads to increase in strength of metal ligands bond and decrease in bond order of CO in carbonyl complex as compared to bond order in carbon monoxide. Simple carbonyls are invariably spin-paired complexes except for vanadium metal. The increase in bond length in CO as compared to carbon monoxide is due to :
Answer» the donation of lone pair of electrons on the carbon into a VACANT ORBITAL of the metla atom. the donation of a pair of electrons form a filled d-orbital of metal into the vacant antibonding `PI^(**)` orbital of carbon MONOXIDE. (a) and (b) both none. Solution :Cr' has greater electron density than 'W' due to small size. Hence Cr is a BETTER `pi`-donor.