question_answer 31)

  [Fe(CN)6]4– and [Fe(H2O)6]2+ are of different colours in dilute solutions. Why?

Answer:

Ans.       In both the complexes, Fe is in +2 state with the configuration 3d6, i.e., it has four unpaired electrons. In presence of the weak H2O ligand, they don't pair up. In presence of strong ligand, they pair up leaving no unpaired electron. Because of the difference in the number of unpaired electrons, they have different colours.