Critical evaluation of stability constants and thermodynamic functions of metal complexes of crown ethers: (IUPAC technical report)

Abstract

Stability constants and thermodynamic functions of metal complexes of crown ethers in various solvents published between 1971 and the beginning of 2000 have been critically evaluated. The most studied crown ethers have been selected: 1,4,7,10-tetraoxacyclododecane (12C4), 1,4,7,10,13-pentaoxacyclopentadecane (15C5), and 1,4,7,10,13,16-hexaoxacyclooctadecane (18C6). The metal ions chosen are: alkali and alkaline earth metal ions, Ag+, Tl+, Cd2+, and Pb2+. The solvents considered are: water, methanol, ethanol, and their mixtures, as well as acetonitrile, N,N′-dimethylformamide, dimethylsulfoxide, and propylene carbonate. The published data have been examined and grouped into two categories, "accepted" and "rejected". The "accepted" values were considered as: (i) recommended (R), when the standard deviations (s.d.) on the constant K or on ΔrH were ≤0.05 lg unit or ≤1 kJ mol-1, respectively; (ii) provisional (P), when 0.05 < s.d. ≤ 0.2 for lg K or 1 < s.d. ≤ 2 kJ mol-1 for ΔrH; (iii) recommended 1 (R1), if the values were obtained by a single research group, but were considered reliable in comparison with related systems, and considering that the research team usually presents R-level values for other similar systems.