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

The short C–H⋯S contacts found in available structural data for both small molecules and larger biomolecular systems suggest that such contacts are an often overlooked yet important stabilizing interaction.

Supramolecular anion receptors can be used to study the molecular recognition properties of the reactive yet biologically critical hydrochalcogenide anions (HCh–). Achieving selectivity for HCh– over the halides is challenging but necessary for not only developing future supramolecular probes for HCh– binding and detection, but also for understanding the fundamental properties that govern these binding and recognition events. Here we demonstrate that linear free energy relationships (LFERs)including Hammett and Swain–Lupton plotsreveal a clear difference in sensitivity to the polarity of an aryl C–H hydrogen bond (HB) donor for HS– over other HCh– and halides. Analysis using electrostatic potential maps highlights that this difference in sensitivity results from a preference of the aryl C–H HB donor for HS– in this host scaffold. From this study, we demonstrate that LFERs are a powerful tool to gain interpretative insight into motif design for future anion-selective supramolecular receptors and highlight the importance of C–H HB donors for HS– recognition. From our results, we suggest that aryl C–H HB donors should be investigated in the next generation of HS– selective receptors based on the enhanced HS– selectivity over other competing anions in this system.

Synthetic supramolecular receptors have been widely used to study reversible solution binding of anions; however, few systems target highly-reactive species.