Self-Assembly of Tetra-Anilines into Metal-Organic Architectures
The internal cavities of supramolecular capsules can be used to bind and sense guests, stabilize reactive molecules and catalyse chemical transformations. To improve the selectivity and scope of substrates for the aforementioned applications, design rules for capsules that extend beyond those of high-symmetry and moderate size are required. The work presented in this thesis aims to explore design strategies for the formation of new or under-explored structure types of metal-organic architectures. The structure types targeted are expected to provide interior spaces distinct from those provided by the current generation of metal-organic capsules with well-understood design principles. Previously under-explored rigid rectangular ligand panels provide the cornerstone for this work. In particular, the subcomponent self-assembly of tetra-aniline subcomponents with 2-formylpyridine and Zn(II) cations. First, it will be demonstrated that rectangular tetra-anilines, even those with relatively high aspect ratios (i.e. they show significant deviation from a square), can assemble into Zn₈L₆ pseudo-cubes. There are myriad possible diastereomeric configurations that could be adopted; however, remarkable diastereoselectivity is observed for each of the six tetra-anilines investigated. A thorough analysis of the solid state structures allowed the elucidation of guiding principles for the formation of Zn₈L₆ pseudo-cubes. The observed stereochemical configuration for each structure was rationalised by considering subcomponent aspect ratio and conformational flexibility. The second project presents the impact of incorporating a twist into the tetra-aniline subcomponent upon the product of self-assembly. A Zn₈L₆ pseudo-cube is a kinetic self-assembly product, while a much larger Zn₁₆L₁₂ tetrahedral capsule is the thermodynamically favoured product. The third project places the geometric design rules elucidated in project one in the context of heteroleptic (i.e. mixed-ligand) self-assembly. This work demonstrates that by selecting combinations of two-dimensional subcomponents with well-matched side lengths, mixed-ligand assemblies can be selectively prepared. Design rules underpinning the formation of heteroleptic prismatic architectures are explored. A Zn₆L₃L’₂ triangular prismatic structure type assembles from the combination of tetra- and tri-topic subcomponents, while mixing two different tetratopic subcomponents constructs a Zn₈L₂L’₄ tetragonal prism. Taken together, the presented work provides an insight into the potential of using geometry-based design strategies for the construction of new structure types of metal-organic architectures.
Chemistry, Supramolecular chemistry, Self-assembly, Coordination cages, Stereochemistry
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