Topological Control of Metallosupramolecular Assemblies

Supervisors: Associate Professor Kathleen Mullen & Professor John McMurtrie

Metallosupramolecular chemistry is a field of study which encompasses the variety of two- and three-dimensional architectures formed through the self-assembly of metal ions with organic ligands. This field is inspired by nature, where non-symmetric, highly complex architectures are used to perform a wide range of complex functions such as enzyme catalysis-like, synthetic metalloenzyme function and signal transduction. However, to date most reported cages are highly symmetrical. In order to improve the functionality of synthetic metallosupramolecular systems the complexity and non-symmetric nature of these metallo-supramolecular systems should be explored.

This project aimed to successfully synthesise and characterise a series of M₄L₆ tetrahedral cages with (bis)benzimidazole ligands. Benzimidazole was chosen as the coordination moiety of choice for this project given its established use in drug discovery, polymer chemistry, and supramolecular chemistry. Their ability to be easily modified has allowed for the formation of coordination polymers, metal-organic frameworks, and metallosupramolecular cages. Self-assembly of cages with these ligands in the presence of a range of metal ions with varying counter anions was then conducted and the formation of cages evaluated using ion-mobility mass spectrometry (IM-MS) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy.

For this project the metal ions investigated were iron (Fe) and zinc (Zn) with counter-ions including NTF₂, TfO, and BF₄. Preliminary IM-MS results suggest that a dynamic mixture of M2L3 helicate, M4L6 tetrahedron and uncomplexed ligand exists at the concentrations used for the mass spectrometry studies. It is clear that the nature of the metal, and ligand influence the relative proportions of these two metallosupramolecular assemblies, however more work is needed to fully understand the trends observed.