Interactions between the [Fe(CN)6]3- Complex and Monovalent Group IA A+ Ions (A+ = H+, Li+, Na+, K+, Rb+, and Cs+) in A3[Fe(CN)6] Model Compounds and Their Influence on the Formation and Properties of CoFe Prussian Blue Analogues

Abstract

The successful preparation of the Rb₃[Fe(CN)₆] and Cs₃[Fe(CN)₆] single crystals enabled us to compare the environment of the monovalent cation for all the nonradioactive elements in group IA of the periodic table in A₃[Fe(CN)₆] single crystals (A⁺ = H⁺, Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺). Three different coordination modes between the monovalent cation and [Fe(CN)₆]^3- complexes were identified and discussed throughout the series. These were then compared to the expected binding modes for all of the cation sites surrounding the Fe(CN)₆ units in Prussian blue analogues (PBA). CoFe PBAs were prepared from Co(NO₃)₂ and A₃[Fe(CN)₆] aqueous solutions. The resulting powders were studied by X-ray diffraction, infrared spectroscopy, and magnetic measurements. The electronic structure of all the powders and the switching properties of most of them can be explained by the effect of the number of interstitial A⁺ cations per unit cell on the redox potentials of the transition metal ions. However, the weak or nonexistent switching properties of the powders containing H⁺ and Rb⁺ cations suggest that a better knowledge of the location of interstitial cations within the PBA structure is also important for a full understanding of their properties.