Further insight to selectivity issues in halide binding in a tiny octaazacryptand

Abstract

The crystal structure of the hexahydrochloride salt of the tiny azacryptand, 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane, reveals a chloride ion inside the tiny bicyclic cavity; 1H NMR studies indicate that while only fluoride binds strongly in the pH range 5.5–2.5, a dramatic increase in the affinity for chloride occurs at pH ≲ 2.5.