COMPLEXATION OF ALKALI METAL AND SILVER IONS WITH UNSUBSTITUTED AND DICYCLOHEXANO-SUBSTITUTED 3m-CROWN-m ETHERS IN DIPOLAR APROTIC SOLVENTS AND ALCOHOLS

摘要

Formation constants, K~f(LM~+), of the 1:1 complexes of 3m-crown-ni (m =4,5,6) with Li~+ were estimated in acetonitrile (AN) using a cation selective electrode. Here L refers to the ligand and M~+ to the metal ion. Those of 3m-crown-m (m =7,8,9, 10) ligands and their dicyclohexano-substituted analogs with Na~+, K~+ and Rb~+ were found from the solubility of the halide or picrate salt in the presence of excess ligand. Solvents were methanol, isopropanol, n-butanol, AN, acetone and propylene carbonate. The maximum stability of 3m-crown-mM~+ in AN occurs at m =5 for Li~+ and Na~+, and at m = 6 for K~+ and Rb~+, corresponding to a close fit of ring hole size and ionic radius. A shallow plateau was observed at m =8 for Na~+ and probably at m = 10 for K~+ due to a wrap around" complex. Extensive salvation of the latter has been inferred from its low ionic mobility, which is discussed in terms of the Zwanzig theory of ionic conductivity. Solubility data of sodium iodate in the presence of dibenzo- 18-crown-6 in tetraethylammonium perchlorate (0.04 mol L~(-1)) in methanol yield K~f(Lna~+) close to that at low ionic strength. Electrochemical methods for estimation of K~f(LM~+) are therefore suitable in the presence of a high concentration of inert electrolyte.