Among the following metal carbonyls, the bond order is lowest in :

Options

A. `[Mn(CO)_(6)]^(o+)`
B. `[Fe(CO)_(5)]`
C. `[Cr(CO)_(6)]`
D. `[V(CO)_(6)]^(Θ)`

Answer

b

Explanation

`Mn^(o+) =3d^(5)4s^(1)` In presence of `CO` effective condguration is `3d^(6)4s^(0)implies3` lone pair (lp) for back bnding with vacant orbital of CinCO
(b) `Fe^(0) =3d^(6)` In presence of `CO` effective configuration is `3d^(8)implies4lp` for back bonding with `CO`
(c ) `cr^(0) =3d^(5) 4s^(1)` effective configuration `=3d^(6)implieslp` for back bonding with `CO`
(d) `V =3d^(3) 4s^(2),V^(o+) =3d^(4) 3d^(4) 4s^(2)` effective configuration `=3d^(6)implies3` lp for back bonding with `CO`
Thus, maximum back -bonding in `[Fe(CO)_(5],` therfore `CO` bond order is lowest here .