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

Fe 3+ complexes with succinic acid, a ligand naturally present in seawater, were investigated in aqueous solutions by square‐wave and cyclic voltammetry. [Fe(suc) 2 (OH) 2 ] and [Fe(suc) 3 ] were detected at potentials −0.22 and −0.37 V, depending on C suc in the ranges from 0.01 to 0.07 and 0.1 to 0.5 mol L −1 , respectively. Redox processes were irreversible, first with reactant adsorption and second diffusion controlled, both accompanied by chemical step. By UV/Vis spectra formation of these complexes was confirmed and equilibrium constant Fe(suc) 2 (OH) 2 ⇌Fe(suc) 3 calculated (log K 2−3 =(1.14±0.15) mol −1 L), as well as their perceptible stoichiometry. With NTA as competing ligand, conditional stability constant of [Fe(suc) 2 (OH) 2 ] complex was calculated (β cond   Fe(suc)   2 [OH]   2=(3.1±1.3)×10 22 mol −1 L).