Among the following metal carbonyls, the 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

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