Potentiometry is not limited to aqueous solutions, even with the use of the glass electrode. For all practical purposes these alcohol-water or dioxanewater solvents can be treated just like aqueous solutions for potentiometric purposes [1]. In this work the protonation constants of 1,3,5-triazine-2,4,6- triamine (tata) and pyridine-2,6-bis (monothiocarboxylate) (pdtc), the building blocks of the proton-transfer systems (tata) and (pdtc) the stability constants of these systems were determined by potentiometric studies in a dioxane/H2O (1:1 v/v) mixture. The stoichiometry and the formation stability constants of complexes formed on reacting pdtc/tata 1:1 molar mixtures with the UO2 2+ ion in dioxane/H2O (1:1 v/v) were investigated by potentiometric pH titration methods. Ligand protonation constants and stability constants of protontransfer systems and their complexes with uranyl cation were evaluated using the program BEST described by Martell and Motekaitis [2] The value of the autoprotolysis constant for dioxane/H2O (1:1 v/v) solution (Ks = [H+][OH-]) was calculated according to the literature[2]. For pdtc (L) and tata (Q) – UO2 systems, the most likely species are: UO2L, UO2L2, UO2Q2, UO2Q2H2 and UO2QH-1 respectively. The pdtc-tata-UO2 system the predominant species is: (UO2)2L2QH3. The results of solution study was compared with the obtained of solid state.

Keywords