If in the mixed carbonyl the other ligand is also `pi` acceptor it would compete with the ligand `CO` for gaining the metal `d_(pi)` electron charge The higher is the extent of back donation in `CO` , the lesser will be the stretching vibration frequency for `C-O` bond If `PP_(3)` is better pi-acceptor than `CO` then answer the following
Select the correct order of `M-C` bond order in the following molecule and ions .
(I) `[Ni(CO)_(4)]`
(II) `[Co(CO)_(4)]^(Θ)`
(III) `[Fe(CO)_(4)]^(2-)`
(a) `IgtIIgtIII`
(b) `I=II=III`
(c) `IIgtIIIgtI`
(d) `IltIIltIII` .

Answer

D

Explanation

Higher the negative oxidation state of central metal the higher will be back donation from `M underset(underset(pi)to)(overset(sigma)larr) C-=O`
hence `M-C` bond order will increase .