On the nature of the interaction between potassium ions and bis(crown ether) derivatives as revealed by low-temperature carbon-13 nuclear magnetic resonance spectroscopy
Abstract
Bis(benzo-crown ether) derivatives linked by HN(CH2)nNH chains where n= 2–6, 8 or 10 have been prepared and their interaction with potassium ions examined. In multinuclear NMR studies it was shown that the structure in solution was a rapidly exchanging series of several different complexes of 1 : 1 composition. Some of these exchange processes are characterised by NMR kinetics. A quantitative mass spectroscopic evaluation of the competition between pairs of bis(crowns) for a single cation (potassium, rubidium or caesium ion) was made. In 1H, 13C NMR and in FAB mass spectroscopic studies the crown where n= 3 in the series showed the most extreme behaviour, suggestive of stronger complexation and/or a different conformation.
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