Anion and cation binding by a new indole/pyridine/amine-based ion-pair receptor

A new ion-pair receptor bis(3-bromoindol-2-ylmethyl)(2-pyridylmethyl)amine (1) was synthesized and studied for its anion and cation binding behavior using ESI-MS and 1H NMR spectroscopy. Among halides, 1 exhibits the strongest binding with Cl− to form a 1:1 adduct (Ka = 1042 ± 21 in CD3CN). Among alkali metal ions, Li+ and Na+ showed the strongest binding in the formation of a 1·M+ complex. The simultaneous binding of Cl− and Li+ to 1 was confirmed by 1H NMR titration of a 1:1 mixture of 1 and Cl− with LiPF6 in 83:17 v/v mixture of CDCl3 and DMSO-d6. DFT-optimized structures of 1·Cl−, 1·Li+, and 1·Li+·Cl− are consistent with the chemical shift changes observed in 1H NMR studies.