Examination of Activation Parameters for the Dissociation of Iron(m) Complexes as a means of Assessing Mechanistic Ambiguities: Data for Phenolic Complexes

Abstract

Activation parameters for the dissociation (aquation) of iron(III) monophenolate complexes in aqueous solution have been estimated at ionic strength 0.1 mol dm–3 by the temperature-jump method and examined together with those of other iron(III) complexes. The activation entropies for the pathways involving the FeOH2+ species in the transition state appear to be markedly higher than those for the pathways involving Fe3+. The correponding differences in the activation enthalpies are generally less significant. The dissociation activation parameters (ΔS*d much better than ΔH*d) can be considered a useful tool, in both the complex formation and dissociation processes, for establishing the actual reaction path for the two kinetically indistinguishable reactions Fe(H2O)3+6+ A–⇌(H2O)5FeA2++ H2O and Fe(H2O)5OH2++ HA ⇌(H2O)5FeA2++ H2O.