Peripheral Control of the Assembly and Chirality of Anion-Based Octanuclear Cubes by Cation-π Networks.

Self-assembly of sophisticated polyhedral cages has drawn much attention because of their elaborate structures and potential applications. Herein, we report the anion-coordination-driven assembly of the first AL (A = anion, L = ligand) octanuclear cubic structures from phosphate anion and -xylylene-spaced bis-bis(urea) ligands via peripheral templating of countercations (TEA or TPA). By attaching terminal aryl rings (phenyl or naphthyl) to the ligand through a flexible (methylene) linker, these aryls actively participate in the formation of plenty of "aromatic pockets" for guest cation binding. As a result, multiple peripheral guests (up to 22) of suitable size are bound on the faces and vertices of the cube, forming a network of cation-π interactions to stabilize the cube structure. More interestingly, when chiral ligands were used, either diastereomers of mixed Λ- and Δ-configurations (with TEA countercation) for the phosphate coordination centers or enantiopure cubes (with TPA) were formed. Thus, the assembly and chirality of the cube can be modulated by remote terminal groups and peripheral templating tetraalkylammonium cations.