Effect of anion-exchange resin on the formation of iron(III)-Tiron complexes

A comparison between iron(III)-Tiron complexes in solution and in the presence of a finely divided anion-exchange resin suspension (ARS) was studied. The effects of the ARS on the acid dissociation constants of Tiron (Ka1 and Ka2) and on the stepwise stability constants (K1, K2 and K3) of iron(III)-Tiron complexes (FeL, FeL2 and FeL3) were investigated. Instead of the three complexes formed in solution at different pH values, only two complexes (FeL2 and FeL3) were found to be fixed on the ARS. Although the ARS did not affect the acid dissociation constants of Tiron, the stability constants of FeL2 and FeL3 were considerably improved. The stepwise stability constants were 20.0, 18.5 and 15.0, respectively, compared with reported values in solution of 20.4, 15.1 and 10.8, respectively.