Question

In how many of the following synergic bonding is present 

(i) [Mn(CO)₅]

(ii) [Mn₂(CO)₁₀]

(iii) [Cr(CO)₆]

Answer 1

(3)

The M-Cπ bond is formed by the donation of a pair of electrons from a filled d orbital of metal into the vacant antibonding π* orbital of carbon monoxide. Thus carbon monoxide acts as a donor (OC → M) and a π acceptor (OC← M), with the two interactions creating a synergic effect which strengthens the bond between CO and the metal as shown in figure.