Bromide is best: The first [2]rotaxane incorporating the triazolium anion-binding motif is prepared using bromide anion templation. Preliminary anion-binding investigations reveal that the rotaxane exhibits the rare selectivity preference for bromide over chloride ions.

The anion-templated synthesis of three novel halogen-bonding 5-halo-1,2,3-triazolium axle containing [2]rotaxanes is described, and the effects of altering the nature of the halogen-bond donor atom together with the degree of inter-component preorganisation on the anion-recognition properties of the interlocked host investigated. The ability of the bromotriazolium motif to direct the halide-anion-templated assembly of interpenetrated [2]pseudorotaxanes was studied initially; bromide was found to be the most effective template. As a consequence, bromide anion templation was used to synthesise the first bromotriazolium axle containing [2]rotaxane, the anion-binding properties of which, determined by (1) H NMR spectroscopic titration experiments, revealed enhanced bromide and iodide recognition relative to a hydrogen-bonding protic triazolium rotaxane analogue. Two halogen-bonding [2]rotaxanes with bromo- and iodotriazolium motifs integrated into shortened axles designed to increase inter-component preorganisation were also synthesised. Anion (1) H NMR spectroscopic titration experiments demonstrated that these rotaxanes were able to bind halide anions even more strongly, with the iodotriazolium axle integrated rotaxane capable of recognising halides in aqueous solvent media. Importantly, these observations suggest that a halogen-bonding interlocked host binding domain, in combination with increased inter-component preorganisation, are requisite design features for a potent anion receptor.

A mixed halogen- and hydrogen-bonding hetero-[2]catenane has been synthesised via anion templation and demonstrated to bind and sense oxoanions.

Four pyridine N-oxide axle containing [2]rotaxanes have been synthesised via an anion templated threading-followed-by-stoppering strategy and shown to be the first examples of neutral interlocked host systems capable of recognising halide anions in aqueous solvent mixtures.