Figure 8: Structure of Prussian Blue analog, that is, metal hexacyanoferrates (MeHCFs). Fe and Me atoms are in the corner of each cube, occupying the 4a and 4b crystallographic sites of the Fm3m space group (soluble structure). Countercations as well as water are placed in the interstitial 8c position (violet) and can be mobile, giving rise to a wide variety of applications. The insoluble structure is formed when Fe(CN)6 vacancies are present, and the N empty sites are occupied by O of coordinated water.