STABILITIES IN WATER OF 1 1 LARIAT 16-CROWN-5 COMPLEXES WITH METAL-IONS - TRANSFER ACTIVITY-COEFFICIENTS FROM PROTIC TO APROTIC-SOLVENTS OF1/1 COMPLEXES OF LARIAT AND SUBSTITUTED 16-CROWN-5 DERIVATIVES WITH METAL-IONS/

Stability constants (K-ML) of 1:1 complexes of 15-(2,5-dioxahexyl)-15- methyl-16-crown-5 (L16C5) with metal ions have been determined in wate r at 25 degrees C by conductometry and potentiometry with ion-selectiv e electrodes. The selectivity order of L16C5 to monovalent and bivalen t metal ions are Ag+ > Na+ > Tl+ > K+ and Sr2+ > Ba2+ > Pb2+, respecti vely. The selectivity is not altered by the side chains. The stability of the L16C5-metal ion complex in water is much lower than might be e xpected on the basis of the solvation power of water for the metal ion (i.e. the relative solubility of the metal ion). Transfer activity co efficients (gamma) of L16C5-Na+ and -K+ complexes from water to aceton itrile, propylene carbonate and methanol [(s) gamma(H2O)(ML(+))] were calculated from the (s) gamma(H2O)(L16C5) and K-ML values determined i n this study and the literature values; s, M(+) and L denote a solvent , a monovalent metal ion, and a crown ether, respectively. (s) gamma(H 2O)(ML(+)) of L16C5 is larger than (s) gamma(H2O)(L16C5) and the corre sponding (s) gamma(H2O)(M(+)) values. The unexpectedly low stabilities of the L16C5-Na+ and -K+ complexes in water are due to strong hydroge n bonding between the uncomplexed L16C5 and water.