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Question:

Which of the following carbonyls will have the strongest C-O bond?

V(CO)6

Fe(CO)5

Cr(CO)6

Mn(CO)+6

Solution:

As the positive charge on the central metal atom increases, the less readily the metal can donate electron density into the π* orbitals of CO ligand to weaken the C-O bond. Due to this, the strength of the C-O bond increases. The charge on the central metal atom is highest in Mn(CO)+6. Hence the C-O bond would be strongest in Mn(CO)+6. Thus Mn(CO)+6 will have the strongest C-O bond. Therefore, the correct option is A.