3d–4f {CoII 3Ln(OR)4} Cubanes as Bio-Inspired Water Oxidation Catalysts

Although the {CaMn4O5} oxygen evolving complex (OEC) of photosystem II is a major paradigm for water oxidation catalyst (WOC) development, the comprehensive translation of its key features into active molecular WOCs remains challenging. The [CoII 3Ln­(hmp)4(OAc)5H2O] ({CoII 3Ln­(OR)4}; Ln = Ho–Yb, hmp = 2-(hydroxymethyl)­pyridine) cubane WOC series is introduced as a new springboard to address crucial design parameters, ranging from nuclearity and redox-inactive promoters to operational stability and ligand exchange properties. The {CoII 3Ln­(OR)4} cubanes promote bioinspired WOC design by newly combining Ln3+ centers as redox-inactive Ca2+ analogues with flexible aqua-/acetate ligands into active and stable WOCs (max. TON/TOF values of 211/9 s–1). Furthermore, they open up the important family of 3d–4f complexes for photocatalytic applications. The stability of the {CoII 3Ln­(OR)4} WOCs under photocatalytic conditions is demonstrated with a comprehensive analytical strategy including trace metal analyses and solution-based X-ray absorption spectroscopy (XAS) investigations. The productive influence of the Ln3+ centers is linked to favorable ligand mobility, and the experimental trends are substantiated with Born–Oppenheimer molecular dynamics studies.