Simultaneous Selective Recognition of Two Different Anions within a Hydrogen/Halogen-Bonding Cage

The search for selective anion receptors that can function in water is a longstanding challenge in supramolecular chemistry, motivated by anions’ fundamental roles (and potential applications) in biological, environmental, and industrial processes. Here, we incorporate halogen and hydrogen bond donors into an easy-to-prepare organic cage molecule and demonstrate that this can bind anions at either or both of a halogen-bonding pocket and hydrogen-bonding pockets depending on the nature of the anions and the solvent. The halogen-bonding pocket comprising six bromopyridinium donors is a potent host for iodide anions and can selectively bind this guest in water as strongly as biological iodide binders (Ka = 43,000 M–1 measured by 1H NMR spectroscopy) with the exclusion of other halide anions. In DMSO/water mixtures, the hydrogen-bonding pockets are able to recognize chloride anions, resulting in the formation of mixed anion iodide/chloride complexes with an iodide bound in the center of the cage and chlorides in the peripheral binding sites. This demonstrates the exquisite selectivity afforded by halogen-bonding systems and reveals a general route to a range of supramolecular anion hosts that bind multiple guests in different locations.