New diMn(III) complexes of general formula [Mn2L(mu-OR)(mu-OAc)]BPh4 (H3L = 1,5-bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino]pentan-3-ol, 1: X = H, R = Me, 2: X = OMe, R = Me, 3: X = Br, R = Me, 4: X = Br, R = Et) have been prepared and structurally characterized. The synthesized complexes possess a triply bridged (mu-alkoxo)2(mu-acetato)Mn-2(3+) core, a short intermetallic distance of 2.95/6 angstrom modulated by the aliphatic spacers between the central alcoholato and N-amino donor sites, and the remaining coordination sites of the two Mn-III centers occupied by the six donor atoms of the polydentate ligand. In dimethylformamide, complexes 1-3 are able to disproportionate more than 1500 equiv of H2O2 without significant decomposition, with first-order dependence on catalyst and saturation kinetic on [H2O2]. Spectroscopic monitoring of the reaction mixtures revealed that the catalyst converts into [Mn-2(III)(mu-O)(mu-OAc)L], which is the major active form during cycling. Overall, kinetics and spectroscopic studies of H2O2 dismutation by these complexes converge at a catalytic cycle between Mn-2(III) and Mn-2(II) oxidation levels. Comparison to other alkoxo-bridged complexes suggests that the binding mode of peroxide to the metal center of the Mn-2(III) form of the catalyst is a key factor for tuning the Mn oxidation states involved in the H2O2 dismutation mechanism.