Anion-Coordination-Driven Assembly of Chiral Quadruple and Single Helices Controlled by Countercations

Enantiopure helical assemblies were constructed by chiral C₂-symmetric bis-bis(urea) ligands (L^S/R) with phosphate or hydrogen phosphate anion, which is dictated by the countercation. In the presence of smaller cations (TMA⁺ or TEA⁺), the chiral ligands coordinate to dihydrated phosphate to form homochiral quadruple helicates (TMA)₆[(PO₄·2H₂O)₂L^S/R ₄]. However, when larger cations (TPA⁺ or TBA⁺) were used, the ligand tends to assemble with monohydrated hydrogen phosphate ions into infinite single helices (TPA)_2n[(HPO₄·H₂O)L^S/R]_n or (TBA)_2n[(HPO₄·H₂O)L^S/R]_n. The predisposed point chirality next to the anion binding center in the ligands has a profound impact on the resulting assemblies, and their chirality is manipulated in a predictable manner.