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Coordination Compounds

Question
CBSEENCH12011050

Which of the following has longest C-O bond length? (free C-O bond length in CO is 1.128 A0)

  • [Co(CO)4]-

  • [Fe(CO)4]-2

  • [Mn(CO)6]+

  • Ni(CO)4

Solution

B.

[Fe(CO)4]-2

As the negative charge on metal carbonyl complex increases back pi bonding increases and hence the bond length of C-O bond increases while the bond length of metal-carbon bond decreases. Hence,[Fe(CO)4]2- has longest C-O bond length among the given complexes.
The correct order of bond length of the given complexes is
[Mn(CO)6]+<[Ni(CO)4]<[Co(CO)4]-<[Fe(CO)4]2-