Complexes of beryllium(II) in aqueous solution with 3-phosphonopropionic acid

Recent studies in aqueous solution on the coordinating ability of beryllium (II) with ligands containing phosphonate groups show that these ligands for m more stable complexes than ligands with carboxylate groups. Phosphonoacet ic acid (H(3)pa) forms beryllium(II) complexes containing six-membered chel ate rings. For comparison purposes in this work the reactions in aqueous so lution between beryllium(II) and 3-phosphonopropionic acid (H(3)pp), which should give rise to seven-membered chelate complexes, have been studied usi ng both potentiometry and multinuclear magnetic resonance spectroscopy. The protonation constants of the 3-phosphonopropionate ligand (pp(3-)) were de termined at 298 K at 0.5 mol dm(-3) ionic strength made up with NaClO4 and [(CH3)(4)N]Cl. Five phosphonopropionate complexes Be(Hpp), Be(pp)(-), Be(OH )(pp)(2-), Be(Hpp)(2)(2-) and Be-3(OH)(3)(pp) have been identified as the m ajor complexes species present at the equilibrium. The corresponding format ion constants were determined at 298 K at 0.5 mol dm(-3) ionic strength (Na ClO4 and [(CH3)(4)N]Cl). Beryllium(II) phosphonoacetate complexes, containi ng six-membered chelate rings, are more stable than the corresponding phosp honopropionate complexes, as expected. (C) 1999 Elsevier Science Ltd. All r ights reserved.