Closer to photosystem II: a Co4O4 cubane catalyst with flexible ligand architecture.

We introduce the novel Co4O4 complex [Co(II)4(hmp)4(μ-OAc)2(μ2-OAc)2(H2O)2] (1) (hmp = 2-(hydroxymethyl)pyridine) as the first Co(II)-based cubane water oxidation catalyst. Monodentate acetate and aqua ligands lend the flexible environment of 1 closest resemblance to photosystem II among its tetranuclear mimics to date. Visible-light-driven catalytic activity of 1 increases with pH value through aqua ligand deprotonation. The Co(II) core combines robustness and stability with flexibility through a new type of water-oxidation mechanism via mobile ligands.