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 (1)H 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.