\[{{[\mathbf{Fe}{{\left( \mathbf{CN} \right)}_{\mathbf{6}}}]}^{\mathbf{4}}}~\mathbf{and}\text{ }{{[\mathbf{Fe}{{({{\mathbf{H}}_{\mathbf{2}}}\mathbf{O})}_{\mathbf{6}}}]}^{\mathbf{2}+}}~\] are of different colours in dilute solutions. Why?

are of different colours in dilute solutions. Why?

Vinay

3 years ago

[Fe( H2O)₆ ]²⁺ and [ Fe( CN)₆ ]²⁺ have H₂O and CN^– ligands respectively. CN^– has a higher CFSE (crystal field splitting energy) than water because it is a strong field ligand. As a result, different wavelengths of light are absorbed and returned by the d-d transitions. As a result, they have various colours in a solution.