Structural aspects of cesium ion selectivity by tetrabenzo-24-crown-8

The structural origins of the selectivity of the cesium ion over other alka li metal ions by tetrabenzo-24-crown-8 are investigated using molecular mec hanics and single crystal X-ray diffraction. The structures containing Csand Rb+ are the first reported for these ions with any 24-crown-8 ether. Th e same crown conformation is observed for Cs+, Rb+ and acetonitrile as gues ts, suggesting that this binding conformation is relatively low energy and inflexible. A different, higher energy, crown conformation is observed in t he Na+ structure. (C) 1999 Published by Elsevier Science S.A. All rights re served.