Thermal stability of [Mn(III)(O)2Mn(IV)(H2O)2(Terpy)2](NO3)3 (Terpy = 2,2′:6′,2″-terpyridine) in aqueous solution

► Mn(III/IV)-oxo dimer is a PS II functional model and thermally unstable in solution. ► Mn(III/IV)-oxo oligomer is thermally stable and highly active in water oxidation. ► Mn(III/IV)-oxo compounds are unique catalytic materials in solar fuel production.