Investigating Electron Transfer in Macromolecular Ruthenium Tris(bipyridyl) Complexes Using Collection Experiments at a Rotating Ring–Disk Electrode

Abstract

Three transition metal complexes, based on the ruthenium tris-bipyridyl unit and containing two, three, and four metal centers, were synthesized and investigated with electrochemical techniques. While the bimetallic complex exhibited very similar properties to the parent ruthenium tris-bipyridine, the two larger complexes behaved differently. During cyclic voltammetry, upon the second ligand-based reduction, both the tri- and the tetra-metallic complex precipitated and adsorbed to the electrode surface, as evidenced by the characteristic voltammetric stripping wave observed both upon further reduction and upon reoxidation. Further, when these complexes were investigated with collection experiments at a rotating ring–disk electrode, anomalously low values of the collection efficiency were measured. This effect is attributed to the size of the molecules, which prevents all of the redox centers from being able to simultaneously access the electrode surface, leading to only a portion of the redox active sites...