A Self‐Assembled Cage Binding Iodide Anions over Other Halide Ions in Water

Abstract

A triangular‐prism shaped cage was self‐assembled by the formation of a dynamic covalent bond, namely a hydrazone, in acidic aqueous solution. The hexacationic host bears a number of relatively acidic protons pointing inside the cage cavity, which is able to accommodate an iodide anion selectively in water over other halide anions such as F−, Cl−, and Br−, which are more hydrated. As a comparison, a macrocycle analogue bearing fewer positive charges and fewer hydrogen bond donors shows no anion binding ability. As inferred from the single‐crystal structure and theoretical calculations, the ability of the cage to selectively recognize iodide anions results from the combination of electrostatic forces, C−H⋅⋅⋅I− hydrogen bonds, and the hydrophobic effect.