Abstract
The deprotonations of 2-hydroxynicotinic acid (H 2nic) and 3-hydroxypicolinic acid (H 2pic) and the complexation of these molecules with Ga 3+ were studied by 1H NMR, UV-Vis spectrophotometry and potentiometric titration. Both ligands bind Ga 3+ at very low pH; the ligand binds in the monodeprotonated form. The stability constants of the [Ga(HL) n (3- n)+ (L = nic or pic; n = 1,2, or 3) complexes were measured at 25°C, 1.0 M NaCl (for β 1) and 0.16 M NaCl (for β 2 and β 3); for H 2nic (H 2pic), log β 1 = 6.78 (7.04), log β 2 = 12.43 (13.09) and log β 3 = 16.20 (17.74). At higher pH, polynuclear mixed ligand-hydroxo species form, although their composition and stability could not be determined. These complexes undergo hydrolysis to form [Ga(OH) 4 − above pH 7.
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