The reaction of 2,5-bis[N,N'-bis(2-pyridyl-aminomethyl)aminomethyl]-p-hydroquinone (H(2)bpymah) with VO2+ salts in acetonitrile or water at a low pH (2.2-3.5) results' in the isolation of [{V-IV(O)(Cl)}(2)(mu-bpymah)], the p-semiquinonate complex [{V-IV(O)(Cl)}(2)(mu-bpymas)] (OH); the cyclic mixed-valent hexanuclear compound [{V-V(O)(mu-O)V-IV(O)}(mu-bpymah)](3), and [((VO2)-O-V)(2)(mu-bpymah)]. [{V-IV(O)(Cl)}(2) (mu-bpymas)] (OH) is an intermediate of the radical-mediated oxidation of [{V-IV(O)(Cl)}(2)(mu-bpymah)] from O-2. At lower pH values (2.2), a reversible intramolecular electron transfer from the metal to the ligand of [{V-IV(O)(Cl)}(2)(mu-bpymas)] (OH) is induced with the concurrent substitution of chlorine atoms by the oxygen-bridging atoms, resulting in the formation of [{V-V(O)(mu-O)V-IV(O)}(mu-bpymah)](3). The metal complexes were fully characterized by X-ray crystallography, infrared (IR) spectroscopy, and magnetic measurements in the solid state, as well as by conductivity measurements, UV-vis spectroscopy, and electrochemical measurements in solution. The oxidation states of the metal ions and ligands were determined by the crystallographic data. The [{V-IV(O)(Cl)}(2)(mu-bpymah)]-[{V-IV(O)(Cl)}(2) (mu-bpymas)] (OH) redox process is electrochemically reversible. The V-IV ion in the semiquinonate compound exhibits a surprisingly low oxophilicity, resulting in the stabilization of OH- counterions at acidic pH values. An investigation of the mechanism of this reaction reveals that these complexes induce the reduction of O-2 to H2O2 mimicking the activity of enzymes incorporating two redox-active centers (metal-organic) in the active site.