Infrared Spectroelectrochemical Insights into Rhenium-Based Supramolecular Assemblies for Electron Storage and Transfer

Three supramolecular square assemblies featuring Re(CO)3Cl nodes and monodentate pyridyl linkers [4,4’-bipyridine, (1a), pyrazine (2a), and 1,2-di(4-pyridyl)ethylene (3a), where a denotes the ground state] were synthesized and studied via infrared spectroelectrochemistry (IR-SEC). IR-SEC revealed that the length of the bridging ligand and degree of electronic coupling in rhenium squares greatly impacts the reduction pathway in both inert and CO2 atmospheres; notably, the squares are capable of interacting with CO2 after only ligand-reduction, thereby avoiding the need for a second reductive event to generate the rhenium anion. This mechanism differs from mononuclear complexes, highlighting how unique redox properties can be endowed by electronic coupling in supramolecular systems.