Complexation between the 2,9-dihydroxy-1,10-diphenoxy-4,7-dithiadecane (DHDPDTD) ligand and La3+, UO2 2+, Ce3+, and Y3+ cations has been studied by means of conductometry in acetonitrile–ethyl acetate binary mixtures over a range of temperature. Formation of the 1 : 1 complexes has been confirmed, and the complexes stability constants have been determined taking advantage of GENPLOT software. The complexes stability is affected by the metal ion nature and the solvent composition. The ligand selectivity towards metal ions depends on the solvent composition. In detail, the complexes stability decreases in the Ce3+ ≈ UO2 2+ > Y3+ > La3+ series in pure acetonitrile at 15°C, whereas the stability series in pure ethyl acetate at the same temperature is as follows: UO2 2+ > La3+ ≈Y3+ > Ce3+. Standard thermodynamic parameters of the complexation reaction (ΔcH0 and ΔcS0) have been determined and found to be affected by the metal ion nature and the binary solvent composition.

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