COMPLEXES OF AL(III) WITH HYDROXYAROMATIC LIGANDS

In order to assess the aluminium binding ability of humic and fulvic a cids, important organic soil constituents, a pH-potentiometric study w as made of the proton and aluminium(III) complexes of various bi-, tri - and tetradentate catechol and salicylic acid derivatives at 25-degre es-C and at an ionic strength of 0.20 mol dm-3 (KCl). The stability da ta revealed that at low pH the salicylate function, and at high pH the catecholate function, is preferentially bound to the aluminium ion. I n the intermediate pH range, mixed hydroxo complexes and other di/olig omeric species are also formed. With an increase of the number of avai lable coordinating sites in the molecule, the tendency to oligomeric c omplex formation increases, while the tendency to metal ion hydrolysis decreases.