Photochemistry of Fe III Polycarhoxylate Complexes

As discussed above, the first step in photochemical reactions of Fe(III) carboxylate complexes has been thought to involve ligand to metal charge transfer [224,225] as a concerted inner sphere electron transfer, and the subsequent separation of the photofragments into the bulk solution. It can be written in simplified form as 

However, it could be argued that, despite the discovery of the new transient, the net chemical products are identical with those in (24). Possible reactions of the long lived radical complex are poorly characterized but they will most likely influence the quantum yield and product formation depending on the reaction conditions and available reaction partners. In laboratory systems such reactions could involve dissolved O2, other Fe(III) species, or back-electron transfer reaction paths in the atmospheric aqueous phase would be less restricted. 

After the radical complex decays, R-COO will decarboxylate instantaneously (kR27 10 -10 s ) [231-233]  

Subsequent reactions of R and R02 can be specific depending on the type of ligand and its substitution. The scheme in Fig. 11 presents a critical evaluation of possible reactions following complex photolysis proposed by Faust and Zepp (1993). The main channels are electron transfer reactions of the alkyl radical R with Fe(Ill) species and the formation of peroxyl radicals RO2.  

Peroxyl radical formation has been suggested, for example, in the photolysis of Fe (III) acetate [242] and Fe(III) malate [243]. According to the known pathways of peroxyl radical chemistry in solution [234], formation of H2O2, H02, and stable organic end products will occur. Consequently, 02 can be produced indirectly via H02 elimination in some cases. 

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