In the isoelectronic series of metal carbonyl, the CO bond length is expected to increase in the order
[V(CO)6]- < [Cr(CO)6] < [Mn(CO)6]+
Kindly explain
Hint: Refer to the theory on Synergic bonding. The M-C bond has donation going on the both ways that is C to M and M to C. This effect strengthens the bond between M and CO. The lack of this behaviour would weaken the bond between M and CO and would strengthen the CO bond.