Stabilities in water and transfer activity coefficients between nonaqueoussolvents and water of 1 : 1 complexes of 15,15-dimethyl-16-crown-5 with metal ions

The stability constants of 1:1 complexes of 15,15-dimethyl-16-crown-5 (DM16 C5) with Li+, Na+, K+, Ag+, Tl+, Sr2+, Ba2+, and Pb2+ and of 16-crown-5 (16 C5) with Li+ have been determined by conductometry in water at 25 degreesC. The transfer activity coefficients ((s)y(H2O)) of the alkali metal ion com plexes between nonaqueous solvents (s: acetonitrile, propylene carbonate, a nd methanol) and water have been calculated. These values have been compare d with the literature values for 16C5 and 15-(2,5-dioxahexyl)-15-methyI-16- crown-5 (L16C5). In water, 16C5 and DM16C5 selectively complex Li+ over Na and K+. The complexing ability of DM16C5 for a given metal ion is generall y lower than that of 16C5 and L16C5. The alkali metal ion complexes of all the crown ethers are much less stable in water than in s, and the selectivi ty and the substituent effects also depend upon the solvent. The (s)y(H2O) values provide the following information: the alkali metal ion and the ethe r oxygen atoms are greatly dehydrated upon complexation in water; the dehyd ration is most drastic for Na+; the dehydration for Na+ is hindered by the methyl groups of DM16C5 and facilitated by the electron-donating side arm o f L16C5. The solvent effects upon complexation are explained in terms of so lute-solvent interactions.