Carboxylate Fullerene Derivatives in Redox-Reversible Bimetallic Assemblies

Supramolecular assemblies containing bimetallic units displaying paddlewheel motifs are well known, especially Zn₂ and Cu₂.  However, assemblies containing stable, electrochemically active and reversible bimetallic units are scarce, and their physicochemical properties are not well studied. These bimetallic units (e.g. Cr₂, Mo₂, Ru₂ and W₂) possess very rich electrochemical properties and exhibit multiple bonding between the metal atoms. Fullerenes containing carboxylic acid addends are excellent candidates to complement the bimetallic units due to their rich and stable redox properties. We successfully synthesized and characterized three different carboxylate fullerene derivatives. After we preassembled a Secondary Building Unit (SBU) using labile bridging ligands such as formamidinates, carboxylates  and acetonitriles, we prepared a series of new discrete molecular systems containing the synthesized fullerene derivatives (See image below) and studied their electrochemical properties. Of particular interest is the degree of electronic coupling between the fullerenes and through the metallic centers via the carboxylate connections. In the future, discrete bimetallic assemblies will  be extended to form Metal Organic Frameworks (MOFs).