N-Alkyl Ammonium Resorcinarene Salts as High-Affinity Tetravalent Chloride Receptors

N-Alkyl ammonium resorcinarene salts (NARYs, Y=triflate, picrate, nitrate, trifluoroacetates and NARBr) as tetravalent receptors, are shown to have a strong affinity for chlorides. The high affinity for chlorides was confirmed from a multitude of exchange experiments in solution (NMR and UV/Vis), gas phase (mass spectrometry), and solid-state (X-ray crystallography). A new tetra-iodide resorcinarene salt (NARI) was isolated and fully characterized from exchange experiments in the solid-state. Competition experiments with a known monovalent bis-urea receptor (5) with strong affinity for chloride, reveals these receptors to have a much higher affinity for the first two chlorides, a similar affinity as 5 for the third chloride, and lower affinity for the fourth chloride. The receptors affinity toward chloride follows the trend K₁蠑K₂蠑K₃≈5>K₄, with K_a=5011 m^-1 for 5 in 9:1 CDCl₃/[D₆]DMSO. Completing the circle: N-Alkyl ammonium resorcinarene salts (NARYs) are high-affinity tetravalent chloride receptors. Competition experiments including multiple ¹H NMR titration experiments reveal that NARYs have a higher affinity towards the first two Cl^- ions, comparable affinity for the third Cl^-, and lower affinity for the fourth Cl^- compared to a known bis-urea receptor.