THERMODYNAMIC STUDIES OF CROWN-ETHER COMP LEXES WITH ALKALI-METAL ANDAMMONIUM-IONS IN VARIOUS SOLVENTS

Thermodynamic studies on the 18-crown-6 and 12-crown-4 complexes with alkali-metal and ammonium ions in various solvents were conducted. The difference in the solvation of 18-crown-6 and 12-crown-4 in various s olvents was investigated by measuring the heats of solution in order t o obtain the enthalpies of transfer of the ethers from water to variou s aprotic solvents. The complexation of 18-crown-6 and 12-crown-4 with alkali-metal and ammonium ions in acetonitrile (MeCN), propylene carb onate (PC), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and pyridine (PY), as well as in water for 12-crown-4 was investigated by precise titration calcoimetry. Also, the reaction enthalpies and entr opies of the complexation were determined. Using the thus-obtained the rmodynamic parameters the enthalpies of transfer of [M(18-crown-6)](+) (M = Na+, K+, Rb+, Cs+, NH4+) complexes from water to various solvent s and [M(12-crown-4)](+) (M = Na+, K+, Rb+, Cs+, NH4+) complexes from PC to various solvents were obtained. The Na-23 chemical shift of [Na( 18-crown-6)](+) was measured in nitromethane, MeCN, PC, DMF, PY and wa ter. Based on these data, a detailed discussion of the solvent effect on the complexation of 18-crown-6 and 12-crown-4 is given.