Volumes of activation for dissociation of the cations of [tris-2,2′-bipyridyl]iron(II), [tris-1,10- phenanthroline]iron(II) and of other diimine iron(II) complexes in aqueous solution

Abstract

The kinetics of dissociation of several iron(II) diimine complexes by aqueous hydroxide ions have been studied spectrophotometrically at atmospheric pressure and elevated pressures, at 298.2 K. Values of Δ V * are between + 10 and + 16 cm 3 mol −1, and are interpreted as arising from a significant loss of electrostricted water from the hydroxide ion as it reacts with the iron(II) complex associatively. Dissociation of the [Fe(5NO 2phen) 3] 2+ and [Fe(5Brphen) 3] 2+ complexes in the presence of aqueous EDTA is reported. For both, Δ V * is + 22 cm 3 mol −1. These values can be understood by considering the reaction as a process comparable to aquation in acidic medium, a dissociative process. Activation enthalpy data support this idea.