Stability constants and thermodynamic parameters of Mn~(2+), Co~(2+), Ni~(2+), Cu~(2+), Zn~(2+), Cd~(2+), UO_2~(2+), Th~(4+), Ce~(3+) and Pr~(3+)-complexes with some schiff base hydrazones containing the pyrimidine moiety

摘要

Proton-ligand dissociation and metal-ligand formation constants of 2-amino-4-chloro-6-[alpha-(phenyl)ethylidenehydrazino]pyrimidine; (AHP) and its p-chloro (ClAHP) and p-methoxy (OMeAHP) derivatives (Str. I & II) with Mn~(2+), Co~(2+), Ni~(2+), Cu~(2+), Zn~(2+), Cd~(2+), UO_2~(2+), Th~(4+), Ce~(3+) and Pr~(3+) ions have been evaluated potentiometrically in 75% (v/v) dioxane-water and 0.1 mol dm~(-3) KNO_3. The thermodynamic functions (DELTAG, DELTAH and DELTAS) for the complexation of OMeAHP were evaluated and discussed. The effect of the temperature, dielectric constant of the solvents, mole fraction of dioxane and ionic strength of the medium on the stability of Pr~(3+) - complexes show that the stability of the chelates increases by increasing both the electron repelling property of the substituents and the organic solvent content, and by decreasing the temperature, the ionic strength and the dielectric constant of the medium.