N-tert-Butyl Sulfinyl Squaramide Receptors for Anion Recognition through Assisted tert-Butyl C–H Hydrogen Bonding

A series of novel N-tert-butyl sulfinyl squaramide receptors have been designed and synthesized. Their interactions with a range of inorganic anions were studied in solution by 1H NMR spectroscopy. This new type of squaramide displayed better anion-binding abilities over conventional diphenyl squaramides. The single crystal analysis and DFT calulations implied the role of the tert-butyl C–H protons in binding Cl–. The energies of C–H···Cl– interactions were estimated to be 1.4–1.6 kcal/mol in solution.