Cone Calix[4]arene Diethyl Ester Strapped Calix[4]pyrrole: A Selective Receptor for the Fluoride Anion

A calix[4]­pyrrole
strapped by a bulky calix[4]­arene diester locked
in its cone conformation has been prepared. On the basis of 1H NMR spectroscopic analyses carried out in CDCl3, it
is concluded that this hybrid system, receptor 2, binds
only the fluoride anion and does so with remarkably high affinity
even in the presence of an excess of various potentially competing
environmentally and biologically ubiquitous anions (studied as the
tetra­butyl­ammonium, cesium, or lithium salts). Solid state
structural analyses provide support for the notion that receptor 2 interacts well with the fluoride anion in the solid state.