Which of the following has the longest C-O bond length? (C-O bond length of CO is 1.128 `A`)

Options

A. `[Fe(CO)_(4)]^(2-)`
B. `[Mn(CO)_(6)]^(+)`
C. `Ni(CO)_(4)`
D. `[Co(CO)_(4)]^(-)`

Answer

A

Explanation

Please note that greater the magnitude of negative charge on the carbonyl complex easier will be for the metal atom to make available its electrons to participate in the black bonding. Consequently higher would be the bond order and smaller would be the bond length. Under the circumstances the complex `[Fe(CO)_4]^(2-)` has minimum charge and as a result, C-O bond length would be the maximum.