. [Fe(CN)6]4– and [Fe(H2O6]2+ are of different colours

[Fe(CN)6]4– and [Fe(H2O6]2+ are of different colours in dilute solutions. Why?

Best Answer

In both the complex compounds, Fe is in +2 oxidation state with configuration 3d6, i.e., it has four  unpaired electrons. In the presence of weak H2O ligands, the unpaired electrons do not pair up. But in the presence of strong ligand CN, they get paired up. Then no unpaired electron is left. Due to this difference in the number of unpaired electrons, both complex ions have different colours

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