Formation and stability of Sc(III), La (III), Dy(III), Pr(III) and Y(III) complexes with hydroxypyridine-carboxylic acids in aqueous solution
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https://doi.org/10.54939/1859-1043.j.mst.109.2026.87-94Keywords:
Rare-earth metals; Hydroxypyridine carboxylic acids; Metal complexes; Spectrophotometric titration; Potentiometric titration.Abstract
The complexation of three hydroxy-substituted pyridine carboxylic acids: 2-hydroxypicolinic acid (L1), 3-hydroxynicotinic acid (L2), and 2-hydroxy-6-methylnicotinic acid (L3) - with Sc³⁺, Y³⁺, La³⁺, Pr³⁺, and Dy³⁺ was systematically studied using spectrophotometric and potentiometric titrations. Stepwise ligand deprotonation allowed determination of complex stoichiometries and formation constants (log β = 4.63 - 11.51), revealing a strong dependence on metal ionic radius, charge density, and donor atom type. Oxygen-donor ligands L1 and L3 preferentially stabilize small, charge-dense cations (Sc³⁺, Dy³⁺), whereas the nitrogen-donor ligand L2 favors larger ions (Y³⁺, La³⁺). The 6-methyl substituent in L3 introduces steric hindrance that reduces complex stability for larger cations. These results demonstrate the combined influence of donor atom identity, steric effects, and metal-ion properties on rare-earth complex stability, providing a quantitative basis for the rational design of selective ligands and functional coordination materials.
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