Multiple Transformations among Anion-based A_(2n)L_(3n) Assemblies: Bicapped Trigonal Antiprism A_8L_(12), Tetrahedron A_4L_6, and Triple Helicate A_2L_3 (A = Anion)

摘要

The construction of sophisticated, high-nuclearity polyhedral cages is an attractive yet challenging task in supra-molecular chemistry. Herein we report the anion-coordination-driven assembly (ACDA) of a series of A_(2n)L_(3n) architectures ("A" denotes anion, L is ligand, n = 1, 2, 4) with a biphenylene-spaced bis-bis(urea) ligand including triple helicate A_2L_3 (H), tetrahedron A_4L_6 (T), and the octanuclear, bicapped trigonal antiprism (or parallelepiped) A_8L_(12) (P). Among them, P 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 (L~(2s)) with carbon stereocenters at both termini of the bis-bis(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.