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Title: Aerial Oxidation of a VIV-Iminopyridine Hydroquinonate Complex: A Trap for the VIV-Semiquinonate Radical Intermediate
Authors: Stylianou, Marios 
Drouza, Chryssoula 
Giapintzakis, John 
Athanasopoulos, Georgios I. 
Keramidas, Anastasios D. 
Keywords: Bis(2-methylpyridyl)amine;Paraformaldehyde;Sodium vanadate;NMR Spectroscopies
Category: Chemical Sciences
Field: Natural Sciences
Issue Date: 3-Aug-2015
Publisher: American Chemical Society
Source: Inorganic Chemistry, 2015, Volume 54, Issue 15, Pages 7218-7229
DOI: 10.1021/acs.inorgchem.5b00571
Journal: Inorganic Chemistry 
Abstract: The reaction of 2,5-bis[N,N′-bis(2-pyridyl-aminomethyl)aminomethyl]-p-hydroquinone (H2bpymah) with VO2+ salts in acetonitrile or water at a low pH (2.2-3.5) results in the isolation of [{VIV(O)(Cl)}2(μ-bpymah)], the p-semiquinonate complex [{VIV(O)(Cl)}2(μ-bpymas)](OH), the cyclic mixed-valent hexanuclear compound [{VV(O)(μ-O)VIV(O)}(μ-bpymah)]3, and [(VVO2)2(μ-bpymah)]. [{VIV(O)(Cl)}2(μ-bpymas)](OH) is an intermediate of the radical-mediated oxidation of [{VIV(O)(Cl)}2(μ-bpymah)] from O2. At lower pH values (2.2), a reversible intramolecular electron transfer from the metal to the ligand of [{VIV(O)(Cl)}2(μ-bpymas)](OH) is induced with the concurrent substitution of chlorine atoms by the oxygen-bridging atoms, resulting in the formation of [{VV(O)(μ-O)VIV(O)}(μ-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 [{VIV(O)(Cl)}2(μ-bpymah)]-[{VIV(O)(Cl)}2(μ-bpymas)](OH) redox process is electrochemically reversible. The VIV 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 O2 to H2O2, mimicking the activity of enzymes incorporating two redox-active centers (metal-organic) in the active site.
ISSN: 1520-510X
DOI: 10.1021/acs.inorgchem.5b00571
Rights: © 2015 American Chemical Society.
Type: Article
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