A molecular meccano kit

Abstract

A range of secondary dialkylammonium (R₂NH₂⁺) ions has been shown to thread through the cavities of appropriately-sized crown ether compounds to afford interwoven complexes. X-Ray crystallographic investigations to probe the solid-state properties of these supermolecules have revealed that many subtle factors—e.g., solvent of crystallisation, crown ether conformation and anion interactions—can influence the nature of the overall three-dimensional superstructures. Nonetheless, a family of building blocks—namely R₂NH₂⁺ ions and crown ethers—can be generated, which constitute a molecular meccano kit. By mixing and matching these modules in different ways, intricate interwoven supramolecular architectures can be constructed. From relatively simple beginnings—where one R₂NH₂⁺ ion is threaded through one monotopic crown ether (dibenzo[24]crown-8)—the designed evolution of the building blocks in the molecular meccano kit has led to more elaborate multiply encircled and/or multiply threaded superstructures. The effects of crown ether constitution, macroring size, and both crown ether as well as R₂NH₂⁺ ion substitution, upon the solid-state behaviour of these interwoven complexes have also been examined. A statistical analysis of the hydrogen bonding interactions observed in these systems has been carried out. It reveals that a reasonable correlation exists between N⁺–H⋯O bond angle and H⋯O bond length. The correlation between C–H⋯O bond angle and H⋯O distance is poor, suggesting that C–H⋯O hydrogen bonding interactions are of secondary importance in determining the co-conformations adopted by these supermolecules.