Selective Inclusion of Fluoride within the Cavity of a Two-Wall Bis-calix[4]pyrrole.

We report what to our knowledge is the smallest bis-calix[4]pyrrole (2). It proved capable of trapping fluoride anions exclusively relative to other anions (Cl-, Br-, SCN-, NO3-, H2PO4-, HSO4-, SO42-, and HP2O73-; tetrabutylammonium salts), as confirmed by 1H NMR spectroscopy (CDCl3), X-ray diffraction analysis, DFT calculations, and molecular dynamics simulations. The F- selectivity is ascribed to the small size of the cavity in 2.