A Halogen-Bonding Bis-triazolium Rotaxane for Halide-Selective Anion Recognition

A systematic study on the anion-binding properties of acyclic halogen-and hydrogen-bonding bis-triazolium carbazole receptors is described. The halide-binding potency of halogen-bonding bis-iodotriazolium carbazole receptors was found to be far superior to their hydrogen-bonding bis-triazolium-based analogues. This led to the synthesis of a mixed halogen-and hydrogen-bonding rotaxane host containing a bis-iodotriazolium carbazole axle component. The rotaxane's anion recognition properties, determined by H-1 NMR titration experiments in a competitive aqueous solvent mixture, demonstrated the preorganised halogen-bonding interlocked host cavity to be halide-selective, with a strong binding affinity for bromide.