Among the following metal carbonyls, the `C-O` bond order is lowest in

Options

A. `[Mn(CO)_(6)]^(+)`
B. `[Fe(CO)_(6)^(2+)]`
C. `[Cr(CO)_(6)]`
D. `[V(CO)_(6)]^(-)`

Answer

D

Explanation

`Mn^(+) = 3 d^(5) 4s^(1)` in presence of CO effective configuration `= 3d^(6) 4s^(0)`, three lone pair for back bonding with vacant orbitals of C in CO
`Fe^(2+) = 3d^(6) 4s^(0)` in presence of CO effective configuration `= 3d^(6)` four lone pair for back bonding with CO.
`Cr^(0) = 3 d^(5) 4s^(1)`, effective configuration `= 3d^(6)`, three lone pair for back bonding with CO.
`V^(-) = 3 d^(4) 4s^(2)`, effective configuration `= 3d^(6)`, three lone pair for back bonding with CO.
Maximum back bonding is present in `[V(CO)_(6)]^(-)` therefore C - O bond order is lowest here.