The ubiquity of anions in biological and environmental systems has motivated the development of many novel anion receptors and sensors over the past two decades. Optical anion sensors, which undergo...

The first examples of halogen bonding (XB) heteroditopic homo [2]catenanes were prepared by discrete Na + template-directed assembly of oligo(ethylene glycol) units derived from XB donor-containing macrocycles and acyclic bis-azide precursors, followed by a Cu I -mediated azide-alkyne cycloaddition macrocyclisation reaction. Extensive 1 H NMR spectroscopic studies show the [2]catenane hosts exhibit positive cooperative ion-pair recognition behaviour, wherein XB-mediated halide recognition is enhanced by alkali metal cation pre-complexation. Notably, subtle changes in the catenanes' oligo(ethylene glycol) chain length dramatically alters their ion-binding affinity, stoichiometry, complexation mode, and conformational dynamics. Solutionphase and single-crystal X-ray diffraction studies provide evidence for competing host-separated and directcontact ion-pair binding modes. We further demonstrate the [2]catenanes are capable of extracting solid alkalimetal halide salts into organic media.

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Exceptionally strong halogen bonding (XB) donor-chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroarylfunctionalised axle components, including a remarkably potent novel 4,6-dinitro-1,3-bis-iodotriazole motif. Halide anion recognition properties in aqueous-organic media, determined via extensive 1 H NMR halide anion titration experiments, reveal the rotaxane host systems exhibit dramatically enhanced affinities for hydrophilic Cl À and Br À , but conversely diminished affinities for hydrophobic I À , relative to their non-interlocked axle counterparts. Crucially, this mechanical bond effect induces a binding selectivity which directly opposes Hofmeister bias. Free-energy analysis of this mechanical bond enhancement demonstrates anion recognition by neutral XB interlocked host systems as a rare and general strategy to engineer anti-Hofmeister bias anion selectivity in synthetic receptor design.

Chirality is a key aspect of amino acids and essential for life. Here, a chiral metal-organic framework, S-Mg2dobpdc, is used to determine the chirality of three BOC protected amino acids...