Steric control over inter-ligand dihedrals and splay leads to the formation of FeII6L6 and FeII8L8 antiprisms

Macrocycles have found uses in guest capture, sensing and porous materials, motivating the development of new methods for their synthesis. Here we report the construction of two types of barrel-shaped macrocyclic assemblies, with trigonal antiprismatic Fe^II₆L₆ and square antiprismatic Fe^II₈L₈ architectures, from Fe^II and boron-containing tritopic ligands. Two factors, the steric hindrance of ligands and the preferred coordination angles at different vertices, were observed to regulate the dihedral angles between adjacent ligands, leading to the formation of the structures observed. The effects of ligand steric hindrance led to the formation of a Fe^II₆L₆ trigonal antiprism, which efficiently encapsulated persistent environmental pollutant perfluorosulfonate anions. In contrast with the iminopyridine chelating groups of the Fe^II₆L₆ structure, the incorporation of azopyridine moieties coordinated to the Fe^II centres not only increased the vertex opening angle, resulting in the construction of a Fe^II₈L₈ square antiprism, but also enabled the redox-driven reversible disassembly of this structure. The design strategies that have enabled the construction of these antiprismatic macrocycles may provide insight into the design principles governing the formation of more complex functional assemblies.

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