Multiple Transformations among Anion-based A_2<i>n</i>L_3<i>n</i> Assemblies: Bicapped Trigonal Antiprism A₈L₁₂, Tetrahedron A₄L₆, and Triple Helicate A₂L₃ (A = Anion)

Abstract

The construction of sophisticated, high-nuclearity polyhedral cages is an attractive yet challenging task in supramolecular chemistry. Herein we report the anion-coordination-driven assembly (ACDA) of a series of A_2<i>n</i>L_3<i>n</i> architectures ("A" denotes anion, L is ligand, <i>n</i> = 1, 2, 4) with a biphenylene-spaced <i>bis</i>-<i>bis</i>(urea) ligand including triple helicate A₂L₃ (<b>H</b>), tetrahedron A₄L₆ (<b>T</b>), and the octanuclear, bicapped trigonal antiprism (or parallelepiped) A₈L₁₂ (<b>P</b>). Among them, <b>P</b> is held by 96 hydrogen bonds, the largest number ever reported in a discrete polyhedron, and encapsulates multiple guests (three tetramethylammonium cations) in three compartments. Remarkably, multiple reversible transformations of these dynamic assemblies have been realized by alternation of the template guest, solvent, and concentration. Furthermore, a chiral ligand (<b>L</b>^{<b>2</b><i>S</i>}) with carbon stereocenters at both termini of the <i>bis</i>-<i>bis</i>(urea) backbone was designed and assembled with phosphate to form the enantio-pure triple helicate or tetrahedron. The chiral amplification effect in the tetrahedral complex is significantly larger than that in the triple helicate as a function of the point chirality.