Mossbauer investigation of peroxo species in the iron(III)-EDTA-H2O2 system
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abstract
The reaction of a diiron(III)-EDTA complex with H2O2 in alkaline medium is studied by Mssbauer spectroscopy in conjunction with the rapid-freeze/quench technique in order to identify possible intermediate species during the formation and decomposition of the purple (EDTA)Fe III(2-O2)3- complex ion. Starting from the six-coordinate [FeIIIEDTA]- species at acidic pH, it is demonstrated that mononuclear complexes formed at a pH of about 1 are convert into the diiron(III)-EDTA complex [(EDTA)FeIII-O- FeIII(EDTA)]4- upon raising the pH to around 10.4. H 2O2 reacts with the diiron(III) complex to give peroxide/hydroperoxide related adducts. Initially, the reaction tears apart the dimers to form a peroxo adduct, namely the seven-coordinate mononuclear [(EDTA)FeIII(2-O2)]3-, which is stable only at very high pH. The decomposition of this peroxo adduct gives two new species, which are reported for the first time. The Mssbauer parameters of these species suggest a six-coordinate -peroxodiiron(III) complex [(EDTA)FeIII-(OO)-FeIII(EDTA)]4- and a seven-coordinate -hydroxo--peroxodiiron(III) complex [(EDTA)Fe III-(OO)(OH)-FeIII(EDTA)]5-. A badly resolved, extremely broad component is observed in the Mssbauer spectra during the conversion of the monomer to dimeric peroxo species, which may be attributed to the short-lived [(EDTA)FeIII-OO]3- or [(EDTA)Fe III-OOH]2- intermediate species. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
