Electron transfer in the CsÌ{Mn4Fe4} cubic switch: a soluble molecular model of the MnFe Prussian Blue Analogs (PBAs).

A mixed-valence {(Mn3MnFe2Fe2III)-Mn-II-Fe-III-Fe-II} cyanide-bridged molecular cube hosting a caesium cation, Cs subset of{Mn4Fe4}, was synthesized and structurally characterized by X-ray diffraction. Cyclic-voltammetry measurements show that its electronic state can be switched between five different redox states, which results in a remarkable electrochromic effect. Magnetic measurements on fresh samples point to the occurrence of a spin-state change near room temperature, which could be ascribed to a metal-to-metal electron transfer converting the {Fe-II-CN-Mn-III} pair into a {Fe-III-CN-Mn-II} pair. This feature was only previously observed in the polymeric MnFe Prussian-blue analogues (PBAs). Moreover, this novel switchable molecule proved to be soluble and stable in organic solvents, paving the way for its integration into advanced materials.