ON THE NATURE OF THE INTERACTION BETWEEN POTASSIUM-IONS AND BIS(CROWNETHER) DERIVATIVES AS REVEALED BY LOW-TEMPERATURE C-13 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Bis(benzo-crown ether) derivatives linked by HN(CH2)(n)NH chains where n = 2-6, 8 or 10 have been prepared and their interaction with potass ium ions examined. In multinuclear NMR studies it was shown that the s tructure in solution was a rapidly exchanging series of several differ ent complexes of 1:1 composition. Some of these exchange processes are characterised by NMR kinetics. A quantitative mass spectroscopic eval uation of the competition between pairs of bis(crowns) for a single ca tion (potassium, rubidium or caesium ion) was made. In H-1, C-13 NMR a nd in FAB mass spectroscopic studies the crown where n = 3 in the seri es showed the most extreme behaviour, suggestive of stronger complexat ion and/or a different conformation.