New P-bridgehead urea-based tripodal anion receptors for H2PO4− recognition

A series of new P-bridgehead tripodal urea-based anion receptors 1–3 bearing phosphine oxide (PO) were synthesized and characterized. Their anion-binding ability was examined by UV–vis, 1H NMR, 31P NMR, and ESI-MS. The results revealed that receptors 1–3 showed good sensitivity, selectivity, and binding affinity for H2PO4− over NO3− and Br−, and among them receptor 2 showed the best binding affinity for H2PO4− over F−, Br−, CH3COO−, HSO4−, and NO3−. The Job plot experiments indicated that receptors 1–3 formed 1:1 stoichiometric complex with H2PO4−.