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 H-1 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 C1(-). The energies of C-H center dot center dot center dot C1(-) interactions were estimated to be 1.4-1.6 kcal/mol in solution.