In an actual, fully sodiated Prussian blue based system (e.g. Na 2 Fe[Fe(CN) 6 ]), both Fe atoms are in the +2 oxidation state. Nevertheless, they are distinguishable because of the differences in their chemical (ligand) environment. The iron coordinated to the carbon atom of the cyanide ligand experiences a strong field due to the carbon site of the cyanide ligand being a strong π-acceptor. This causes a large splitting of the d-orbitals, which results in a low spin configuration of the carbon-coordinated Fe atoms. Contrary, the iron atoms that are coordinated to the nitrogen are exposed to an effective π-donor, wherefore they experience a weak field and stabilize in a high spin configuration. While the splitting of the d-orbitals for the high spin Fe is only slightly beneficial in energy, there is a large energy gain due to all electrons of the low spin Fe being lowered in an octahedral crystal environment.