Anion-Driven Assembly of Water Clusters in Polyamide Macrocyclic Host

Water assembly within macrocyclic environments is critically influenced by the presence and nature of the guest anions. Using a previously reported pincer-type macrocyclic receptor (E-1), known for its strong selectivity toward dihydrogen phosphate (H2PO4–) over chloride (Cl–) and acetate (MeCO2–) anions, we systematically explored how anion binding strength affects water cluster formation. Depending on the presence and binding strength of the anion, the crystallization of E-1 yielded three distinct E-1/water assemblies: a simple discrete solvate in the absence of anions, a dimer-bridged structure in the presence of H2PO4– anions, and a sophisticated infinite water tape formed exclusively in the presence of MeCO2– anions. The latter structure features repeating tetrameric water clusters interconnected by six water chains, with additional single-water chains extending from the tetramers─a novel motif in water cluster chemistry. These findings provide new insights into anion-mediated modulation of water organization and suggest potential strategies for designing supramolecular systems with controlled water structuring.