Electrochemically Triggered Double Translocation of Two Different Metal Ions with a Ditopic Calix[6]arene Ligand

A ditopic ligand based on a calix[6]arene with three imidazoles (Im) appended at the small rim and three triazoles (Tria) at the large one is able to form selectively two stable heterodinuclear complexes with Zn(II)(Im)/Cu(I)(Tria) and Cu(II)(Im)/Zn(II)(Tria). In the Cu(I) case, the zinc cation is preferentially coordinated at the Im site while the copper is bound at the Tria site. The situation is the opposite when Cu(II) is used. The position of the two cations within the complex can be electrochemically switched via the oxidation-reduction of the copper cation between oxidation states +I and +II. The presence of the zinc cation is crucial (i) to control the bistability of the system by an allosteric structuring role and (ii) to promote the metal switch since the monocopper complex exhibits reversible behavior with Cu located at the imidazole site in both oxidation states. This represents the first example of a double translocation of two different metal cations.