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Photochemistry of the Fe(III)–EDTA complexes: A mechanistic study

Paper ID Volume ID Publish Year Pages File Format Full-Text
28749 44089 2006 8 PDF Available
Title
Photochemistry of the Fe(III)–EDTA complexes: A mechanistic study
Abstract

The Fe(III) photoreduction in the EDTA complexes studied by pulse photolysis and continuous irradiation revealed that LMCT excitation is followed by reaction of the primary photoproduct with the parent complex, generating intermediate species formulated as [(H2O)(EDTA+)FeII(μ-OHx)FeIIIEDTA]x − 4. The presence of molecular oxygen is of crucial relevance for the intermediate life time and pathway of decay. In deoxygenated media, the intermediate is relatively long-lived (kobs ∼1 × 10−3 s−1) and its degradation proceeds by the back electron transfer regenerating the parent complex and by the second inner-sphere electron transfer producing Fe(II) species and EDTA oxidation products. In this case the product ratio of the Fe(II) to (EDTA)ox should be 2:1, consistent with the previous reports.In the presence of molecular oxygen, the intermediate dimer decomposes much faster (kobs ∼1.4 × 102 s−1), presumably via outer-sphere two-electron oxidation of the dangling CH2COO group and the Fe(II) centre, yielding [FeIIIEDTA]−, [FeIIIED3A] and EDTA oxidation products. Formation of the [FeIIIED3A] complex was recorded only when Fe(III)–EDTA was irradiated in the presence of O2. Under prolonged irradiation, it undergoes photoredox reaction resulting in oxidation of successive EDTA fragments and Feaq3+ production. Thus, in aerated media EDTA is oxidized by O2 in the photocatalytic process, in which Fe(III) species plays a role of photocatalyst.Quantum yields of the Fe(III)–EDTA decay depend on the irradiation wavelengths and solution pH; in deoxygenated media, the post-irradiation substrate regeneration makes the measured quantum yields apparently dependent on measurement time (ϕ0 ≈ 4–5ϕ∞).

Keywords
Fe(III)EDTA; EDTA photodegradation; LMCT photoreduction; Photoinduced electron transfer; Post-irradiation effect
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Photochemistry of the Fe(III)–EDTA complexes: A mechanistic study
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 179, Issues 1–2, 1 April 2006, Pages 176–183
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
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