Kinetics and mechanism of formation of binuclear complexes of iron(III) with malonatopentaaminecobalt(lll) and <i>trans-</i>bis(Hmalonato)bis-(ethylenediamine)cobalt(III) ions in aqueous solution

Abstract

125-129The kinetics of formation of binuclear complexes between iron (III) and malonatopentaaminecobalt(lll) and trans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) have been studied using stopped-flow technique in the concentration ranges [H+]=0.050-0.30, [Fe(Ill)]=0.005-0.03, and I= 0.5 mol dm-3 and over the temperature range 15.0 to 30.0°C. A general mechanism is proposed which accounts for the available data on the formation of binuclear species involving mainly the reactions of Fe3+ and FeOH2+ with the undissociated form of the cobalt(III) substrates. The rate data for the various paths for transbis(Hmalonato)bis(ethylenediamine)cobalt(III) are slightly higher than those for the corresponding pen-taamine analogues. The activation parameters for the various paths are also reported