FeCN63FeCN64

FeCN63FeCN64 is a shorthand notation used in materials chemistry to denote a mixed-valence iron-cyanide framework that incorporates both ferricyanide and ferrocyanide units. In this representation, ferricyanide corresponds to [Fe(CN)6]3− and ferrocyanide to [Fe(CN)6]4−, indicating iron centers in two oxidation states linked by cyanide ligands within a three-dimensional network. The concept is closely related to Prussian blue and its analogues, which are iron–cyanide coordination polymers.

Structure and composition

Materials described as FeCN63FeCN64 are typically interpreted as extended networks containing Fe3+ centers connected to Fe2+ centers through CN− bridges. A common empirical formulation for related Prussian blue analogues is Fe4[Fe(CN)6]3·xH2O, though exact stoichiometry varies with vacancies, hydration, and synthesis conditions. The alternating or mixed-valence arrangement enables electronic communication between iron centers across cyanide linkages, contributing to characteristic optical and magnetic properties.

Properties

These materials are known for their deep blue color, magnetic interactions such as ferrimagnetism or antiferromagnetism depending on composition, and potential electronic conductivity. They also exhibit redox activity at the iron centers and can participate in ion intercalation, making them of interest for electrochemical applications. The presence of vacancies and hydration levels can markedly influence porosity, stability, and transport properties.

Synthesis and applications

FeCN63FeCN64-type materials are typically formed by co-precipitating iron salts with ferrocyanide or ferricyanide sources under controlled pH and temperature. They are studied as Prussian blue analogues for use in energy storage electrodes, electrochromic devices, catalysis, sensing, and ion-exchange applications, with research focusing on tuning composition, vacancy content, and hydration to optimize performance.