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

Abstract The activity of the biomimetic Co II -based cuboidal water oxidation catalyst (WOC) [Co II 4 (hmp) 4 ( μ -OAc) 2 ( μ 2 -OAc) 2 (H 2 O)] ([Co II 4 O 4 ]) and its Ca 2+ -substitute [Co II 3 CaO 4 ] were theoretically investigated to evaluate the effect of redox-inactive Ca 2+ on water oxidation by Co II -based cuboidal catalyst. Compared with [Co II 4 O 4 ], the smaller redox potential of [Co II 3 CaO 4 ] results in the more efficient oxidation-equivalents accumulation for water oxidation. By contrast, the water oxidation by [Co II 3 CaO 4 ] is identified to be more thermodynamically superior than that for [Co II 4 O 4 ]. The energy barrier of key O O bond formation step in water oxidation by [Co II 3 CaO 4 ] is 22.0 kcal/mol and lower than that found for [Co II 4 O 4 ] (25.0 kcal/mol).