Selective encapsulation of chloride ions within novel cage host complexes in the presence of equimolar amounts of chloride and bromide ions

Four macrotricyclic cage hosts which feature four positive binding sites or iented toward the center of the intramolecular cavity are presented as prom ising candidates for anion receptors and they have been expected to play a important role in the selective encapsulation of the halide ion Cl- or Br-. The complementarity between a macrotricyclic quaternary ammonium ion and C l- was achieved by fine-tuning of the four ammonium nitrogen atoms and the endocyclic methylene groups. The cage hosts [R4N4(C5H10)(4)(C6H12)(2)](4+) (abbreviated as [556]) showed perfect encapsulation of all chloride ions in acetonitrile at 0 < r = ([Cl-](o)/[[556]](o)) less than or equal to 1 with in the sensitivity of the H-1 NMR spectra in combination with a rather slow chemical exchange of the Cl- ion in an encapsulation/decapsulation equilib rium with [556]. Further, the selective encapsulation of all the chloride i ons into [556] cage occurs unambiguously at r = 1 in the presence of equimo lar amounts of Br-. The structural complementarity of the newly designed [5 56] host prevails over the Hofmeister-series restraints determined by diffe rences in Gibbs free energy of halide anion solvation.