A Hexapodal Capsule for the Recognition of Anions.

We herein describe the preparation, characterization, and recognition characteristics of novel hexapodal capsule 1 composed of two benzenes joined by six hydrogen bonding (HB) groups to encircle space. This barrel-shaped host was obtained by reversible imine condensation of hexakis-aldehyde 2 and hexakis-amine 3 in the presence of oxyanions or halides acting as templates. Fascinatingly, capsule 1 includes 18 HB donating (Csp2-H and N-H) and 12 HB accepting groups (C═O and C═N) surrounding a binding pocket (78 Å3). In this regard, the complexation of fluoride, chloride, carbonate, sulfate, and hydrogen phosphate was probed by NMR spectroscopy (DMSO) and X-ray diffraction analysis to disclose the adaptive nature of 1 undergoing an adjustment of its conformation to complement each anionic guest. Furthermore, the rate by which encapsulated chloride was substituted by sulfate or hydrogen phosphate was slow (>7 days) while the stability of [SO4⊂1]2- was greatest in the series with Ka > 107 M-1 in highly competitive DMSO. With facile access to 1, the stage is set to probe this modular, polyvalent, and novel host to further improve the extraction of tetrahedral oxyanions from waste and the environment or control their chemistry in living systems.