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≫K2≫K3≈5>K4, with Ka=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.