Question

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

• A. $\left[Mn\right(CO{)}_6{]}^{+}$
• B. $\left[Fe\right(CO{)}_5]$
• C. $\left[Cr\right(CO{)}_6]$
• D. $\left[V\right(CO{)}_6{]}^{-}$

Answer 1

The correct option is D $\left[V\right(CO{)}_6{]}^{-}$

$C-Obondlength\propto \frac{1}{bondorder}$

In this case, vanadium is already electron rich and so the extent of synergic bonding will be maximum for $\left[V\right(CO{)}_6{]}^{-}$. Hence $CO$ bond length will be maximum and the bond order will be minimum for $\left[V\right(CO{)}_6{]}^{-}$.