The iron complexes found in the systems FeC1,-phenol, FeC1,-catechol, FeCI,-2,3-dihydroxybenzaldehyde, FeC13-2,3-dihydroxybenzoic acid, and FeCI,-salicylic acid have been investigated by pH and conductance titrations together with Mossbauer spectroscopy. On the basis of further studies using ascorbic acid and salicylaldehyde, a mechanism for the reduction of Fe"' to FeII and the reverse oxidation via a phenolic or catecholic radical is discussed. The properties of enterobactin are explored in the light of the chemistry of the model systems.The Mossbauer spectra of frozen aqueous solutions of hydroxybenzene compounds containing iron cations show that those complexes that are green or blue a t acid pH contain Fe'I, whereas those that are purple or red contain Fe"'.It is proposed that these results make the colour of the complex a good indication of the oxidation state of the iron in phenolic and catecholic systems.

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Mittels pH‐ und konduktometrischer Titrationen sowie Mößbauerspektroskopie werden die sich in den Systemen FeCl3/Phenol, FeC13/Brenzcatechin, FeC13/2,B‐Dihydroxybenzaldehyd, FeC13/2,3‐Dihydroxybenzoesäure und FeCl3 /Salicylsäure bildenden Fe‐Komplexe untersucht.