Water-Oxidizing Complex in Photosystem II through a Chemist’s Lens: from Natural Structure to Artificial Models

High Resolution Image Download MS PowerPoint Slide Mn-based catalysts are central to artificial photosynthesis because manganese forms the redox-active core of the water-oxidizing complex in Photosystem II. This perspective considers Mn water-oxidation chemistry through the relationship between natural Mn 4 CaO 5 function, biomimetic molecular models, and reconstructed Mn oxide catalysts. A key conclusion is that many Mn complexes, salts, and even preformed oxides do not remain structurally intact under water-oxidation conditions. Instead, ligand oxidation, hydrolysis, Mn leaching, Mn(III) instability, and redeposition frequently generate mixed-valence MnO x phases, often disordered or layered birnessite-like materials. These reconstructed phases may be the true catalytic entities, making catalyst identity, stability, and operando verification essential for mechanistic claims. The perspective also highlights lessons from photosystem II, including stepwise charge accumulation, proton-coupled electron transfer, second-sphere organization, water and proton channels, Ca/Sr effects, spin-state control, and repair or regulation strategies. Rather than treating reconstruction as simple degradation, the work frames it as a design parameter for producing hydrated, defect-rich, mixed-valent Mn oxide active states. Future catalyst development should combine bioinspired structural principles with rigorous benchmarking, direct oxygen quantification, impurity control, mass-balance analysis, and in situ or operando structural characterization.