Speciation in the ternary system Iron(III)-nitrilotrimethylphosphonic acid-1,3-dicarboxypropane-1-iminodiacetic acid

The interaction of iron(III) ions with nitrilotrimethylphosphonic acid and 1,3-dicarboxypro-pane-1-iminodiacetic acid in aqueous solutions has been studied by spectrophotometry. It has been shown that complex formation in the system is complicated by protonation, hydrolysis, and precipitation. Homoligand 1: 1 complexes of different proton composition have been identified. The stability constants of the iron(III) complexonates and their fractional distribution as a function of pH (T = 20 ± 2°C, I = 0.1) have been determined. Conditions that make it possible to prevent the precipitation of iron(III) nitrilotrimethylphosphonates in the presence of 1,3-dicarboxypropane-1-iminodiacetic acid have been selected.