This feature article highlights recent approaches to anion recognition with a focus on aryl CH hydrogen bonds.

Despite competing trends and computational predictions to the contrary, three bis-urea receptors bind disparate oxoanions (ClO4−, HSO4−, H2PO4−) with equal affinities in a non-polar solvent; in a more polar solvent the trend in association constants for one receptor matches that of the pKb of the guest, as expected for H-bond donating hosts.

Selective tuning of arylethynyl urea scaffolds for anionic guests requires an understanding of preferred binding motifs of the host–guest interaction. To investigate the binding preference of receptors without a pre-organized binding pocket, two electron-deficient phenylacetylene receptors with a single urea moiety have been prepared and were found to bind halides as 2:1 host–guest complexes that feature key CH–anion or anion–π interactions. These supporting interactions also appear to influence the mechanism of the 2:1 binding event.