The reactions of a dinuclear ferric complex (oxo) di-iron(III) triethylenetetraamminehexaacetate, Fe2O(ttha), with oxidizing and reducing free radicals. A pulse radiolysis study |
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Authors: | James D Rush Diane E Cabelli |
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Institution: | Chemistry Department, Brookhaven National Laboratory, Upton, New York, NY 11973, U.S.A. |
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Abstract: | The rate constants at which oxidizing and reducing radicals react with the dinuclear iron(III) complex Fe2O(ttha)2− were measured in neutral aqueous solution. The rate constants for reduction of the complex by ·CO2.− CH3.CHOH and O2.− were found to be comparable with rate constants previously measured in mononuclear iron(III) polyaminocarboxylate systems. Fe2O(ttha)2− reacts slowly with O2.− (k8 = (1.2 ± 0.2) × 104 dm3 mol−1 s−1) and, hence, is a relatively poor catalyst for the dismutation of superoxide radical. The hydrated electron reduces the complex at a diffusion-controlled rate in a process which consumes one proton: eaq− + Fe2O(ttha)2− → Fe2III,IIO(ttha)3− The reduction by carbon-centered radicals produces a (III,II) mixed-valence complex with an absorption spectrum different from that of the Fe2(II,III) species produced from reduction by the hydrated electron. The oxidizing radicals .OH and ·CO3− appear to act as reductants of the complex via ligand oxidation rather than by oxidation of the Fe2IIIO core to Fe2III,IVO. In the former case ligand attack appears to occur mainly at the methylene carbon of a glycinate group. The decarboxylation product, CO2, was detected by its aquation reaction in the presence of a pH sensitive dye, bromthymol blue. |
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