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 ) showed perfect encapsulation of all chloride ions in
acetonitrile at 0 < r = ([Cl-](o)/[](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 . Further, the selective encapsulation of all the chloride i
ons into  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.