Building a molecular PrussianBlueAnalogue FeII/CoIII cube around a Cs+ ion; a preferred, tight, robust, water soluble, and kinetically inert encapsulator

Abstract

The preparation of a caesium inclusion complex of the molecular cube [{CoIII(Me3-tacn)}4{FeII(CN)6}4]}]4–, a mixed valent molecular Prussian Blue Analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process in aqueous solution. The assembly has been shown to be Cs-preferred as, even in the presence of Na+ in solution, no Na-encapsulated have been found in the assembled product when Cs+ is present in the reaction medium. Even so, the tightness of the system produces large amounts of a void cubic structure whenever not large excesses of Cs+ are present. The species is robust, extremely soluble in aqueous media, pH-stable in the 1–13 range, and redox inactive between −400 and 600 mV. The molecular species has been characterised by UV–vis, ICP, multinuclear NMR spectroscopy, and electrochemistry. As expected from previous data reported, the complex in aqueous solution is totally inert to cation exchange, the leaching of the encapsulated Cs+ being hampered by the small size of the cube portal.