Question

In metal–carbonyl complexes, the $\pi$-back bonding is

• A. pπ – dπ type
• B. dπ – dπ type
• C. dπ – π* type
• D. dπ – σ* type

Hint:

Metal → CO back-donation always involves metal dπ orbitals and CO π* orbitals.

Answer 1

The Correct Option is C

Step 1: Understand metal–CO bonding.
In metal carbonyls, CO donates its lone pair from carbon to the metal (σ-bond). Simultaneously, the metal donates electron density back into the empty π* antibonding orbital of CO. This is known as π-back-bonding.
Step 2: Identify orbitals involved.
The metal uses its filled dπ orbital, while CO uses its empty π* orbital. Thus, back bonding is of the dπ → π* type.
Step 3: Conclusion.
The correct description of π-back bonding is given in option (C).