Anion cryptates: Synthesis, crystal structures, and complexation constants of fluoride and chloride inclusion complexes of polyammonium macrobicyclic ligands

Abstract

Three macrobicyclic octamines 1-3 and the macrotricyclic hexadecamine 14 have been synthesized. The octamines 1-3 bind anionic substrates when protonated. The stability constants of the complexes between the protonated forms of the macrobicyclic polyamines and halide anions have been determined by pH-metric measurements. The stability constants in H2O are very high, 1 in its hexaprotonated form binds F- with high selectivity (selectivity F-/Cl- > 108), while 3 exhibits strong stability constants for both F- and Cl-. Three X-ray structures have been obtained, one where F- is held inside the cavity of 1·6H+, one where Cl- is included in 3·6H+, and 3·6H+ where the cavity is empty.