Stabilities of proton, binary and ternary lanthanide complexes of 2-methyl-8-hydroxyquinoline-5-sulphonic acid in various aquo-organic solvents

Proton-ligand formation constants of 2-methyl-8-hydroxyquinoline 5-sulphonic acid have been measured in water and other aquo-organic media containing dioxane, isopropanol, ethanol and methanol as cosolvents. The trends of sup(P)Ksub(n)sup(H) are interpreted in terms of the dielectric constants of the media and proton-solvent interactions. Stabilities of binary complexes of the ligand with La, Pr, Nd, Sm, Gd, Tb, Dy have also been calculated in different media and the trends are discussed in terms of dielectric constants of the media and the ionic radii of the metal ions. Stepwise constants for ternary complex formation with NTA or EDTA as primary ligands have also been computed. The ternary complexes with NTA are more stable than those with EDTA. Thermodynamic parameters of ternary complex formation have also been evaluated. (author). 4 tables, 12 refs