Tricyclic Host for Linear Anions

A tricyclic host for anions consisting of two tetraamide monocycles attached by two ethylene chains was designed and synthesized. Structural and binding results indicate that the receptor is selective for linear triatomic anions. Crystallographic data for two hydrated free bases, along with FHF−, N3−, and SO42− complexes indicate that there are at least two preferred gross conformations for the host, one of which possesses pseudo-D2 symmetry and the other pseudo-C2h symmetry. Both FHF− and N3− are encapsulated in the pseudo-D2 symmetric complex, bridging the two tetraamido macrocyclic halves. The pseudo-C2h octahydrate structure shows an ice-like H-bonded (H2O)6 array of water molecules embedded in the host cavity. The SO42− structure has a nearly superimposable host conformation to the octahydrate but with the SO42− anions lying outside the host. Binding studies in DMSO-d6 indicate selectivity for FHF−, with lesser affinity for other inorganic anions.