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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.

Metal-organic coordination cages can be assembled from simple building blocks to form a wide range of structure types such as Platonic and Archimedean solids. Such architectures are able to encapsulate a diverse array of molecular guests in the solution state, from both organic and aqueous media. This thesis investigates the application of metal-organic coordination cages in the solid-supported physisorbed and neat liquid states and the host-guest chemistry of the resulting materials. This thesis is divided into three main sections are these are outlined below: Chapter 1 presents a brief introduction to the history and development of supramolecular chemistry and metal-organic architectures. A particular emphasis is placed on the formation of coordination cages and the factors unpinning their guest encapsulation properties. Chapter 3, the first research chapter, investigates the adsorption of coordination cages on to alumina supports, via solution depletion, from water and acetonitrile. The adsorbed cages are analysed spectroscopically and their host-guest chemistry is probed via a series of guest displacement experiments under flow conditions. Finally, it is demonstrated that adsorbed cages can be used to store reactive molecular guests for subsequent release and reaction. Chapter 4, the second research chapter, presents the current progress towards the development of a new generation of porous liquids based on coordination cage scaffolds peripherally-functionalised with polymer chains. The first section explores the use of a coordination cage ion metathesis reaction in the formation of a cage salt. The second section investigates the effect of the peripheral chain length on the thermal properties of the resulting cage materials.

Directed transport of materials against chemical potential gradients is a fundamental feature of living systems, underpinning processes that range from transport through cell membranes to neurotransmission. The development of artificial active cargo transport could enable new modes of chemical purification and pumping. Coordination cages with inner cavities are able to encapsulate and release guest molecules based on their size and shape complementarity, providing a new technological basis to transport molecular cargoes. This thesis presents systems using coordination cages to transport materials, targeting chemical separation and material shifted away from equilibrium. In these systems, coordination cages cross liquid phase boundaries upon exposing to heat stimuli or diffuse within aqueous membrane layers to promote the passage of materials. The first system employs a thermoresponsive cage, FeII4L4, to transport encapsulated cargo across multiple phase boundaries, allowing for longer-distance transport than would be possible using a single pair of phases. The system constitutes a novel class of heat engine when thermal energy drives the material transport over a distance. The second system introduces aqueous membranes consist of coordination cages, FeII4L6 or CoII4L4, to separate chemical compounds from organic phases. The coordination cages diffuse within the membrane and selectively encapsulate the target compounds from stock mixtures at room temperature. The studies demonstrate the potential applications of cages for chemical purification without heating requires. Finally, the aqueous cage membranes are further developed to drive flows of materials away from the initial equilibrium when irradiated to light, making the system analogous to Maxwell's demon. The thesis demonstrates that coordination cages will be useful means for chemical separation and material transport independently to chemical gradients.

Coordination cages formed by supramolecular self-assembly are excellent candidates for the selective encapsulation of molecules and sheltering these guests from their environment after uptake. The easily tuneable nature of these 3D-structures can make them versatile carriers in applications such as drug delivery. However, to achieve this, the capsules need to be converted into biocompatible vehicles by the conjugation of biomolecules onto the cages' surface for example. This thesis describes initial efforts towards this goal. Firstly, the compatibility and influence of coordination cages on a simple biomaterial was studied by the incorporation of tetrahedral cages in a peptide-based supramolecular gel. Rheological changes of the macroscopic material were observed while the host-guest properties of the cages remained unchanged, enabling the chemical segregation of guests. Secondly, bioconjugation of single amino acids and a tripeptide gelator onto coordination cages were investigated, showing that the properties of the peptide such as chirality and gelation were transferred to the whole system. Addition of a photoacid generator to the organo-gel formed triggered the reversible gel-sol transition of the material under alternating cycles of light irradiation and darkness. Finally, a water-soluble cage was synthesised using N-acetylatedgalactoamine building blocks. The geometry and organisation of the sugar biotags were engineered to allow ligation of the cage onto the asialoglycoprotein receptor of hepatocytes with the goal of realising the cellular internalisation of the complex and its cargo. In synthetic supramolecular systems, molecules can interact in different ways to yield complex self-assembled libraries. Multiple components combined can result in the integrative formation of single products or, most often, multiple self-assembled products. Deciphering the self-assembly rules within such systems involves new characterisation challenges: dynamic, low-symmetry products are difficult to detect and identify by NMR spectroscopy and labile species can re-equilibrate after chromatographic separation. Hence, in this thesis the potential to assess individual outcomes of self-sorting experiments by mass spectrometric techniques was investigated in three case-studies. A new methodology to calculate the relative energies of heteroleptic structures compared to the more stable homoleptic was developed, allowing for the quantification of each ligand's structural preferences. Following a similar approach, the effect of anion binding on a dynamic library of self-assembled tetrahedra was probed. Finally, quantitative information on speciation within mixtures was obtained for a complex system of self-assembled scalenohedra and pseudo-octahedra.

The first chapter of this thesis introduces the fundamental concepts governing the design and synthesis of supramolecular complexes. By illustrating the synthesis of several coordination cages reported in the literature, the principles underlying the construction of coordination cages by subcomponent self-assembly are elucidated. Ionic liquids are then proposed as solvents for cage systems; general methods for the preparation and synthesis of these solvents are described. The second chapter explores the use of ionic liquids as solvents for existing coordination cages. Potential methods of characterising these cages in ionic liquids are discussed; cages are demonstrated to be stable and capable of encapsulating guests in these ionic environments; and systems in which cages have good solubility in ionic liquids are designed. Building upon these observations, a triphasic sorting system is presented such that each of three different host-guest complexes are soluble in only one of three immiscible liquid phases. In contrast to the static triphasic system described in the second chapter, the third chapter explores directed phase transfer of coordination cages and their cargos from water, across a phase interface, and into an ionic liquid phase. The host-guest complex can then be recycled from the ionic liquid layer back into water after several additional steps. Furthermore, phase transfer of cationic cages is used to separate a mixture of cationic and anionic host-guest complexes. In the fourth chapter, fully reversible phase transfer of coordination cages is developed. Using anion exchange to modulate the solubility of three different cationic cages, reversible transport between water and ethyl acetate is demonstrated. Sequential phase transfer can also be achieved such that, from a mixture of cubic (+16) and tetrahedral (+8) cages, the cubic cage transfers from water to ethyl acetate before the tetrahedral cage. This process is fully reversible; upon the addition of a hydrophilic anion, the tetrahedral cage returns from ethyl acetate to water before the cubic cage.

A major function assessed by Nature is the transport of a cargo between two different media, such as anions through cell membranes. Mimicking this function using complex systems is one of the biggest challenge of supramolecular chemistry. Metallo-organic cages are an important breakthrough in the encapsulation and transport of small molecules, providing a crucial platform for the development of systems chemistry. Binding a network member within a tetrahedral cage allows it to be hidden and then revealed upon receipt of a release signal, or transported as a cargo between spatially distant parts of a network. Larger capsules may also isolate subsystems from each other in the manner of vesicles. These dynamic architectures are synthesised by self-assembly, which involves the simultaneous formation of multiple coordinative and dynamic covalent linkages during the same overall synthetic process. Their shape and binding properties can be tuned by changing the subcomponents such as metals or ligands. Great progress has been reported in recent years in the development of three-dimensional cages that can interact with specific guest species, but there are limitations associated with the transport of these systems. Recent work by Nitschke et al. have successfully addressed practical separations problems by transporting a tetrahedral cage and its cargo from water into an ionic liquid layer. However, this system is not ideal as the process is triggered by an anion exchange not by a direct stimulus. This thesis reports the synthesis of an ionic liquid inspired tetrahedral system achieving reversible transport between water and an immiscible organic solvent driven by a change in temperature. Once the switchable capsules were obtained and characterised, their ability to move between different solvent phases upon heating was investigated. A capsule-mediated transport system as developed that is both directional and reversible. The flow of the capsule and its encapsulated cargo is directed using stimuli such as temperature modification. Ultimately an apparatus that allows the switchable capsules to move along a channel has been developed.