Self-Assembly and Properties of a Discrete Water-Soluble Prussian Blue Analogue Fe II /Co III Cube: Confinement of a Water Molecule in Aqueous Solution

Novel types of water-soluble anionic cubic cages, K [{Co (Me -Tacn)} {Fe (CN) } ] and Na [{Co (Me -Tacn)} {Fe (CN) } ] (Me -Tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), were prepared by means of a mechanistically designed self-assembly process between [Co(Me -Tacn)Cl ] and A [Fe (CN) ] (M = Na or K), consisting of a rate-limiting outer-sphere redox step, followed by a fast substitution/inner-sphere redox reaction sequence. These compounds show remarkable stability in aqueous solution at different pH ranges, displaying neat protonation processes and reversible oxidation with peroxodisulfate to its neutral {Fe Co } form. Furthermore, the cages behave as a robust and water-soluble molecular Prussian Blue analogue capable of encapsulating {Na-OH } pairs and K cations in aqueous solution, with the cubic structure of the complex being preserved. Substitution of the {Na-OH } pairs by K is easily accomplished, and the electrochemical properties of the sodium and potassium salts of the new cages have been found to be dramatically dependent on the encapsulated units.