Binding of Cs+ ions to calix[2]furan[4]pyrrole (1) and its complex with fluoride ions (1.F) was studied in acetonitrile-d(3) using Cs-133 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 x 10 (6) s in the former case and 1.31 x 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. (C) 2012 Elsevier B. V. All rights reserved.