Electronic Influence of the 2,2'-Bipyridine-6,6'-dicarboxylate Ligand in Ru-Based Molecular Water Oxidation Catalysts.

Water provides an ideal source for the production of protons and electrons required for generation of renewable fuels. Among the most-prominent electrocatalysts capable of water oxidation at low overpotentials are Ru(bda)L2-type catalysts. Although many studies were dedicated to the investigation of the influence of structural variations, the true implication of the bda backbone on catalysis remains mostly unclarified. In this work, we further investigated if electronic effects are contributing to catalysis by Ru(bda)(pic)2 or if the intrinsic catalytic activity mainly originates from the structural features of the ligand. Through introduction of pyrazines in the bda backbone, forming Ru(N1-bda)(pic)2 and Ru(N2-bda)(pic)2, electronic differences were maximized while minimizing changes in the geometry and other intermolecular interactions. Through a combination of electrochemical analysis, chemical oxygen evolution, and density functional theory calculations, we reveal that the catalytic activity is unaffected by the electronic features of the backbone and that the unique bimolecular reactivity of the Ru(bda)L2 family of catalysts thus purely depends on the spatial geometry of the ligand.