Abstract
Proton NMR spectroscopy was used to study the complexation reaction of 18-crown-6 (18C6) with K+, Rb+ and Tl+ ions in a number of binary dimethyl sulfoxide-nitrobenzene mixtures. In all cases, the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average 1H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of dimethyl sulfoxide in the mixed solvent. It was found that, in all solvent mixtures used, Rb+ ion forms the most stable complex with 18-crown-6 in the series.
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