Complex formation equilibria between 1-hydroxy-7-sulpho-2-naphthoic or 1-hydroxy-4,7-disulpho-2-naphthoic acid and iron(III) in 0.1M NaClO4 medium

The equilibria for formation of iron(III) complexes with 1-hydroxy-7-sulpho-2-naphthoic and 1-hydroxy-4,7-disulpho-2-naphthoic acids in aqueous 0.1M sodium perchlorate medium at 25 degrees have been studied by spectrophotometric and potentiometric methods. The data are well described in terms of a series of stepwise complexes, FeL((3-rn)+)(r) in both systems (L(n-) denotes the unprotonated ligand anion).