Question

Metal carbonyls are stable due to

• A. $\sigma$-back bonding
• B. synergic bonding
• C. either (a) or (b)
• D. neither (a) nor (b).

Answer 1

Answer: (B)

synergic bonding

Answer 2

The metal-carbon bond in metal carbonyls possesses both $\sigma$ and $\pi$-characters. The ligand to metal is $\sigma$-bond and metal to ligand is back bonding through $\pi$-dative bond. This unique synergic bonding provides stability to metal carbonyls.