Iron(III)‐Complexes Engaged in the Biochemical Processes in Seawater. II. Voltammetry of Fe(III)‐Malate Complexes in Model Aqueous Solution

Abstract

AbstractCharacteristics of iron(III) complexes with malic acid in 0.55 mol L−1 NaCl were investigated by voltammetric techniques. Three iron(III)‐malate redox processes were detected in the pH range from 4.5 to 11: first one at −0.11 V, second at −0.35 V and third at −0.60 V. First process was reversible, so stability constants of iron(III) and iron(II) complexes were calculated: log K1(FeIII(mal))=12.66±0.33, log β2(FeIII(mal)2)=15.21±0.25, log K1(FeII(mal))=2.25±0.36, and log β2(FeII(mal)2)=3.18±0.32. In the case of second and third reduction process, conditional cumulative stability constants of the involved complexes were determined using the competition method: log β(Fe(mal)2(OH)x)=15.28±0.10 and log β(Fe(mal)2(OH)y)=27.20±0.09.