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Metal carbonyls – synergic bonding
Concepts tested here
- back-bonding-co-bond-length
All Questions
2016 1 question
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Which of the following has longest C–O bond length? (Free C–O bond length in CO is 1.128 Å.)
More negative charge on the metal → more back bonding → longer C–O.
The interaction between a filled metal orbital and a vacant orbital of CO is known as back bonding.
When the metal in a metal carbonyl complex carries a negative charge, back bonding increases; the M–C bond length decreases and the C–O bond length increases.
So $[Fe(CO)_4]^{2-}$ has the longest C–O bond: $[Mn(CO)_6]^+ < Ni(CO)_4 < [Co(CO)_4]^- < [Fe(CO)_4]^{2-}$