Capping the calix: how toluene completes cesium(I) coordination with calix[4] pyrrole

The role of solvent in molecular recognition systems is under-researched and often ignored, especially when the solvent is considered non-interacting''. This study concerns the role of toluene solvent in cesium(I) recognition by calix[4] pyrrole. We show that pi-donor interactions bind toluene molecules onto the open face of the cation-receptor complex, thus capping the calix.'' By characterizing this unusual aromatically-saturated complex, we show how non-interacting'' aromatic solvents can directly coordinate receptor-bound cations and thus influence recognition.