摘要：

Stability constants of (2,1,1), (2,2,1), and (2,2,2) cryptates of alkali-metal cations, Ag+ and Ca2+, have been measured in several solvents, both protic and aprotic. There is a large variation with solvent of the stability constants, but qualitatively the same selectivity pattern is observed in all solvents. Free energies of transfer of MCry+I- between the solvents have been obtained by combining measured stability constants with free energies of transfer of the corresponding MI salts. For transfer from water to nonaqueous solvents, (2,2,2) cryptates show distinct minima corresponding to transfer of the K(2,2,2)+ cryptate. Similar behavior is observed for (2,2,1) and (2,1,1) cryptates, but as the size of the ligand decreases, transfer of cryptates containing the smaller cations becomes progressively favored. Free energies of transfer of cryptate salts between nonaqueous solvents are essentially independent of the included cation. The implications of the results for the extraction of alkali-metal salts from water into nonaqueous media by cryptands and related ligands are discussed.

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