Complex Formation of Iron(II/III) with [15]aneN4 in Aqueous Solution. Kinetics of the Oxidation of FeII([15]aneN4) by Dioxygen
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Antje Schrodt
Abstract
The stability constants of the Fe(II) and Fe(III) complexes of the macrocyclic ligand [15]aneN4, were determined potentiometrically at 25.0 °C and ionic strength 0.10 Μ (NaClO4). The protonation constants of the free ligand were found to be in good agreement with available literature data. On the basis of these data, a kinetic study of the oxidation of Fe11(L), L = [15]aneN4, by dioxygen as a function of [Fe11(L)], [O2], pH and temperature was undertaken. The oxidation of FeII(L) was found to be very pH dependent, and due to stability and solubility limitations could only be studied in the pH range 7.0-8.0. The oxidation reaction was found to occur in one step, but the observed first-order rate constant in the presence of an excess of FeII(L) exhibited a first- and second-order dependence on the FeII(L) concentration, viz. kobs = k1[FeII(L)] + k2[FeII(L)]2. The activation entropies for k1 and k2 were found to be strongly negative, viz. -110 and -95 J K-1 mol-1 respectively, whereas the activation enthalpies were found to be relatively small, viz. 32 and 15kj mol-1, respectively. Some kinetic experiments were also performed in an excess of dioxygen and the results are in good agreement with those obtained in the presence of an excess FeII(L). The suggested reaction mechanism consists of the subsequent formation of a monomelic Fe(III) superoxo complex and a dimeric Fe(III) peroxo complex. Some experiments were also performed with H2O2 and an excess of the Fe(II) complex. The data could be fitted with a single exponential function and exhibited a first- order dependence on the FeII(L) concentration.The second-order rate constant of 47.0 ± 0.5 Μ-1 s-1 is significantly faster than in the case of the reaction with dioxygen. The results are compared and discussed in reference to related Fe(II) and Co(II) systems in the literature.
© 2014 by Walter de Gruyter Berlin/Boston
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- Dedicated to Ralph G. Wilkins
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- Oxidation of Thiol-containing Substrates by the Pentaamminechromatocobalt(III) Complex Ion
- Complex Formation of Iron(II/III) with [15]aneN4 in Aqueous Solution. Kinetics of the Oxidation of FeII([15]aneN4) by Dioxygen
- Hydrogen Atom Abstraction by Methyl Radicals from tert-Butyl Hydroperoxide in a Modified Fenton Reaction
- The Rate of Electron Self-Exchange in the System [CuIL]+/[CuIIL]2+ with L = 2,2′-Bis(3-(2-pyridyl)-l-methyltriazolyl)biphenyl
- Notes for Contributors Inorganic Reaction Mechanisms
- Disk Specifications
- Journal Order Form
Articles in the same Issue
- Editorial
- Dedicated to Ralph G. Wilkins
- Kinetic Studies of Water Exchange and Substitution by NCS– on the Sulphur-capped Triangular Ion [Μο3(μ3-S)(μ-O)3(ΟΗ2)9]4+
- A Kinetic Study of the Photolysis of Ethylferrocene in Chloroform
- Oxidation of Thioglycolic Acid by Nickel(IV) Oxime-Imine Complexes - A Kinetic and Mechanistic Approach
- The Copper(II)-2,2′-Dipyridylamine Catalysed Hydrolysis of the Phosphotriester 2,4-Dinitrophenyl Diethyl Phosphate and O-isopropyl Methylfluorophosphonate (Sarin)
- Oxidation of Thiol-containing Substrates by the Pentaamminechromatocobalt(III) Complex Ion
- Complex Formation of Iron(II/III) with [15]aneN4 in Aqueous Solution. Kinetics of the Oxidation of FeII([15]aneN4) by Dioxygen
- Hydrogen Atom Abstraction by Methyl Radicals from tert-Butyl Hydroperoxide in a Modified Fenton Reaction
- The Rate of Electron Self-Exchange in the System [CuIL]+/[CuIIL]2+ with L = 2,2′-Bis(3-(2-pyridyl)-l-methyltriazolyl)biphenyl
- Notes for Contributors Inorganic Reaction Mechanisms
- Disk Specifications
- Journal Order Form
