Question

Which of the following is not true for metal carbonyls?

• A. The oxidation state of the metal in the carbonyls is zero
• B. dπ - π* MO back bonding is present from M → CO
• C. Metal carbonyls are singly bonded species
• D. pπ- pπ overlap is observed in metal carbonyls

Answer 1

Answer: (C)

Metal carbonyls are singly bonded species

Answer 2

Metal carbonyls exhibit synergic bonding involving σ donation from CO to metal and π back-donation from metal to CO. This back-bonding imparts significant partial double bond character to the M-C bond. Therefore, stating that metal carbonyls are "singly bonded species" is incorrect. Other options (a) zero oxidation state of metal, (b) dπ - π* back bonding, and (d) pπ-pπ overlap (if referring to C-O bond within CO, or dπ-pπ* if referring to M-C bond) are generally correct or describe aspects of the bonding.