Interaction of cesium ions with calix[2]furan[4]pyrrole and its fluoride complex

Binding of Cs+ ions to calix[2]furan[4]pyrrole (1) and its complex with fluoride ions (1·F−) was studied in acetonitrile-d3 using 133Cs NMR and quantum-chemical DFT calculations. The measured equilibrium constants K are 114 mol−1 L−1 for Cs+·1 and 1302 mol−1 L−1 for Cs+·1·F− at 300 K. The correlation times of exchange between free and bound Cs+ ions are 2.64 × 10−6 s in the former case and 1.31 × 10−5 s in the latter. In accord with NMR, the DFT calculations predict a much stronger binding of Cs+ to the fluoride complex of 1, the ions being more embedded into the ring and interacting both with the electron donating groups of 1 and the bound fluoride ion.