Solid-state NMR studies of alkali metal ion complexes of p-tertbutyl-calixarenes

Calixarenes of different molecular sizes form complexes with alkali metal c ations but have different affinities for small cations (Li+ and Na+) and la rge cations (Rb+ and Cs+). p-tert-Butyl-calix[4]arene easily forms complexe s with the small cations by virtue of steric recognition. In p-tert-butyl-c alix[8]arene, the sites next to the oxygens are more accessible to large ca tions because of the more extensive hydrogen-bonding network. The character istic behaviour of p-tert-butyl-calix[6]arene in the complexation of Rb+ an d Cs+ is caused by its 'pinched' conformation. (C) 1999 Elsevier Science B. V. All rights reserved.