note that intramolecular electron transfer from the hexacoordinated Fe ions in the triangular core to iron ions at the apical position results in the formation of Fe=o units at the triangular core . the o - o bond formation can proceed between the co -facial oxo groups in B to afford the peroxo species in fig . 3 )without spin rearrangement and with an estimated reaction barrier of less than 10 kcal mol .for details , see supplementary information