Molecular engineering. Part 7. Cavitands having four aromatic sp2 nitrogens as salt binding ligands

Nine new salt binders built on resorcin[4]arene or calix[4]arene and having four aromatic sp2 nitrogens as salt binding ligands were designed and characterized. Structurally rigid cavitands based on resorcin[4]arene showed much higher affinities toward metal cations compared to those based on flexible calix[4]arene. In particular, imidazolylcavitand 7 showed high affinity for alkali metal cations (−ΔG° = 7.0–10.9 kcal mol−1) and pyrazolylcavitand 8 showed unusually high selectivity for silver cations, which are presumably due to their different binding modes, nesting vs. inclusion fashion, respectively.