Conformationally flexible arylethynyl bis-urea receptors bind disparate oxoanions with similar, high affinities†
Conformationally flexible hosts with relatively small binding pockets are seldom shown to bind oxoanions preferentially over other guests. Herein, we disclose the binding of diprotic, monoprotic, and aprotic tetrahedral oxoanions with three different pyridylethynyl bis-urea scaffolds. In less polar solvent, the trend in association constants appears to be heavily influenced by solvation and entropic effects. However, in a more polar solvent, the trend in association constants matches that of the pKa of the conjugate acid of the anionic guest, as expected for H-bond donating hosts.