Anion‐receptor molecules: Macrocyclic and macrobicyclic effects on anion binding by polyammonium receptor molecules

The stability constants for anion binding by the acyclic hexaamine 1, its macrocyclic analogue 2, and the bicyclic compound 3 in their protonated forms are reported. Compound 3 forms stable and selective complexes with halide ions, the stability sequence being I− > Br− > Cl−. Compound 2 forms more stable complexes with sulfate, oxalate, and malonate dianions than its acyclic analogue 1 and shows a better selectivity pattern. Compound 3 forms stronger complexes with oxalate2− than 2 and shows a remarkably high binding selectivity between oxalate2− and malonate2−. The comparison of the ability of 1–3 to complex anions demonstrates the macrocyclic and macrobicyclic effects on anion binding stability and selectivity.