pH-metric studies on formation constants of the complexes of substituted pyrazoles with some lanthanide metal ions and the influence of ionic strengths on complex equilibria in a 70% dioxane-water mixture

The pKa values of N-heterocyclic compounds (substituted pyrazoles) in a 70% (v/v) dioxane-water mixture have been determined using pH-metric measurements. The stability constants of the complexes of Dy(III), Nd(III), Sm(III), and Tb(III) with 3-(2-hydroxyphenyl)-5-methylpyrazole, l-phenyl-3-(2-hydimyphenyl)-5-methylpyrazole 3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole, and l-phenyl-3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole have been determined by the pH-metric method at ( 300 ± 0.1) K. The effect of ionic strengths on the complexes of Sm3+ and Pr3+ ions with pyrazole has been investigated in the internal from 0.02 to 0.1 mol dm−3 (sodium perchlorate) in the pH range 2–3.