Capture and displacement-based release of the bicarbonate anion by calix[4]pyrroles with small rigid straps.

Two-phenoxy walled calix[4]pyrroles and strapped with small rigid linkers containing pyridine and benzene, respectively, have been synthesized. H NMR spectroscopic analyses carried out in CDCl revealed that both of receptors and recognize only F and HCO among various test anions with high preference for HCO (as the tetraethylammonium, TEA salt) relative to F (as the TBA salt). The bound HCO anion was completely released out of the receptors upon the addition of F (as the tetrabutylammonium, TBA salt) as a result of significantly enhanced affinities and selectivities of the receptors for F once converted to the TEAHCO complexes. Consequently, relatively stable TEAF complexes of receptors and were formed anion metathesis occurring within the receptor cavities. By contrast, the direct addition of TEAF to receptors and produces different complexation products initially, although eventually the same TEAF complexes are produced as sequential TEAHCO and TBAF addition. These findings are rationalized in terms of the formation of different ion pair complexes involving interactions both inside and outside of the core receptor framework.