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

Options

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

Answer

D

Explanation

With increase in the probability of back bonding between metal and carbon atom, the bond length of `C-O` increases.
Again, with increase in the `-ve` charge on the central metal ion, the probability of backbonding increases. So, in this case, the `C-O` bond length in `[Fe(CO)_(4)]^(2-)` is maximum.