Host–Guest Chemistry: Oxoanion Recognition Based on Combined Charge-Assisted C¢H or Halogen-Bonding Interactions and Anion···Anion Interactions Mediated by Hydrogen Bonds
Several bis-triazolium-based receptors have been synthesized and their anion-recognition capabilities have been studied. The central chiral 1,1′-bi-2-naphthol (BINOL) core features either two aryl or ferrocenyl end-capped side arms with central halogen- or hydrogen-bonding triazolium receptors. NMR spectroscopic data indicate the simultaneous occurrence of several charge-assisted aliphatic and heteroaromatic C−H noncovalent interactions and combinations of C−H hydrogen and halogen bonding. The receptors are able to selectively interact with HP2O73−, H2PO4−, and SO42− anions, and the value of the association constant follows the sequence: HP2O73−>SO42−>H2PO4−. The ferrocenyl end-capped 72+⋅2 BF4− receptor allows recognition and differentiation of H2PO4− and HP2O73− anions by using different channels: H2PO4− is selectively detected through absorption and emission methods and HP2O73− by using electrochemical techniques. Significant structural results are the observation of an anion⋅⋅⋅anion interaction in the solid state (2:2 complex, 62+⋅[H2P2O7]2−), and a short C−I⋅⋅⋅O contact is observed in the structure of the complex [82+][SO4]0.5[BF4].