DFT characterization on the effect of redox-inactive cation Ca2+ on water oxidation by CoII-based cuboidal catalyst

The activity of the biomimetic CoII-based cuboidal water oxidation catalyst (WOC) [CoII4(hmp)4(μ-OAc)2(μ2-OAc)2(H2O)] ([CoII4O4]) and its Ca2+-substitute [CoII3CaO4] were theoretically investigated to evaluate the effect of redox-inactive Ca2+ on water oxidation by CoII-based cuboidal catalyst. Compared with [CoII4O4], the smaller redox potential of [CoII3CaO4] results in the more efficient oxidation-equivalents accumulation for water oxidation. By contrast, the water oxidation by [CoII3CaO4] is identified to be more thermodynamically superior than that for [CoII4O4]. The energy barrier of key O O bond formation step in water oxidation by [CoII3CaO4] is 22.0 kcal/mol and lower than that found for [CoII4O4] (25.0 kcal/mol).