The IR stretchin frequencies of free `CO`, and CO `[V(CO)_(6)]^(-),[Cr(CO)_(6)]^(-) and [Mn(CO)_(6)]^(-)` are 2143`cm^(-1),1860cm^-1),2000cm^(-1) and 2090cm^(-1)`, respectively. Then correct statemet about metal carbonyl is:

Options

A. C-O' bond is strongest in the cation and weakest in the anion.
B. C-O' bond is weakest in the cation and strongest in the anion
C. C-O' bond is longer in the cation than in the anion
D. M-C' pi bonding is higher in the cation

Answer

B

Explanation

In metal carbonyls:
Higher the negative oxidation state of central metal: `prop `Bond length of C-O
`:prop(1)/("Bond order of CO")`
: Bond order of M-C bond.