The complexation process between Y3+ cation and kryptofix 22DD was studied in ethyl acetate– dimethylformamide (EtOAc–DMF), ethyl acetate–methanol (EtOAc–MeOH), ethyl acetate–nitromethane (EtOAc–NM) and ethyl acetate–dimethylsulfoxide (EtOAc–DMSO) binary mixtures at different temperatures by using conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between the macrocyclic ligand and the Y3+ cation is 1 : 1 [ML]. But in some systems such as, in the case of EtOAc–DMSO (90 mol % DMSO) binary solvent solution, in addition to formation of a 1 : 1 (ML) complex, a 1 : 2 (ML2) complex is formed in solution, which shows that the stoichoimetry of complexes may be changed by the nature of the medium. The stability order of (kryptofix 22DD · Y)3+complex in the studied binary solvent solutions at 25°C was found to be: EtOAc–MeOH > EtOAc–DMF > EtOAc–DMSO and in the case of pure non-aqueous solvents at 25°C it was: EtOAc > MeOH > DMF ∼ NM. A density functional theory (DFT) study of the interaction of yttrium(III) cation with kryptofix 22DD in the liquid phase for the pure organic solvents was performed. The results are in reasonably good agreement with the experimental data. A non-linear behavior was observed for changes of log Kf of (kryptofix 22DD · Y)3+ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the preferential solvation of the species involved in the complexation reaction.

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