Novel polydentate phosphonic acids: Protonation and stability constants of complexes with Fe(III) and Cu(II) in aqueous medium

Abstract

The acido-basic and the complexation properties of di-, tri-, and tetra-phosphonic acids (H6L1, H8L2, and H10L3) toward Fe(III) and Cu(II) were determined by potentiometric titration in aqueousmedia at 25.0 ± 0.1°Cwith constant ionic strength (0.1 M, NaClO4). We have determined six, ten, and eight pKa values for the di, tri, and tetra-phosphonic acids, respectively. In acidic conditions, e.g., 0 ≤ pH ≤ 5; iron and copper presented a high affinity toward these ligands to give complex species. With the ligand H10L3, [FeL3H7], and [CuL3H6]2-were easily obtained at pH 1.8 and 2.7, respectively. We have determined ten stability constants for the H10L3/Fe system and nine for the H10L3/Cu one; six and four in the cases of H8L2/Fe and H8L2/Cu systems, respectively. Finally, five stability constants were calculated for the H 6L1/Fe system and four for the H6L1/Cu one. We have not observed any insoluble species in these complexes in acidic medium as well as in alkaline solutions. © 2010 Wiley Periodicals, Inc.