1,3‐Dialkoxycalix[4]arenecrowns‐6 in 1,3‐Alternate Conformation: Cesium‐Selective Ligands that Exploit Cation‐Arene Interactions

Abstract

Exceptionally high selectivity for cesium ions (α(Cs/Na) > 33000) is displayed by calix[4]arenecrowns-6 in the 1,3-alternate conformation. They also remove 137Cs quantitatively (>96%) from radioactive waste that is 1 M in HNO3. The complexation properties result from the simultaneous operation of several effects: the size of the crown ether ring, the polarity of the calix conformation, and the strength of the cation/π-electron interactions. The latter interaction was evident in the X-ray crystal structure of the cesium complex (shown on the right).