Interaction of beryllium(II) in aqueous solution with bidentate ligands containing phosphonate groups

The complexes formed by beryllium(II) with ligands derived from phosphonoac etic acid (H(3)pa) and methylenediphosphonic acid (H(4)mdp) have born inves tigated in aqueous solution using both potentiometric and multinuclear magn etic resonance measurements, The protonation constants of the two ligands w ere determined at 298 K at ionic strength 0.5 mol dm(-3) made up with NaClO 4 and [(CH3)(4)N]Cl. Seven phosphonoacetate complexes [Be(pa)](-), [Be(pa)( 2)](4-). [Be(Hpa)], [Be(Hpa)(pa)](3-), [Be(Hpa)(2)](2-), [Be-3(OH)(3)(pa)] and [Be-3(OH)(3)(pa)(3)](6-) and seven methylenediphosphonate complexes, [B e(mdp)](2-), [Be(mdp)(2)](6-), [Be(Hmdp)](-), [Be(H(2)mdp)], [Be(Hmdp)(mdp) ](5-)[Be(Hmdp)(2)](4-) and [Be(H(2)mdp)](2-), have been assumed to be prese nt as major complex species. The corresponding formation constants were det ermined at 25 degrees C at ionic strength 0.5 mol dm(-3) (NaClO4). In gener al, mdp complexes are more stable than the pa complexes having comparable s toichiometry. Phosphonate is able to displace water from [Be(H2O)(4)](2+) w ithout the assistance of a chelate effect, even at very low pH values. The complexes [BeL2](n-),(L = pa, n = 3; L = mdp, n = 6), are the most predomin ant species at physiological pH values; the mdp derivative is more stable t han the pa one which, in turn, is much more stable than the corresponding m alonate complex. The complex K-2[Be(H(2)mdp)(2)]. 2H(2)O was isolated in th e solid state from reaction of Be(OH)(2) with H(4)mdp and KOH, in aqueous s olution, at pH 2.60 and its composition has been confirmed through ESMS spe ctra. (C) 1999 Elsevier Science S.A. All rights reserved.