Subcomponent self-assembly of cages and mechanically interlocked molecules

Abstract

The self-assembly of metal ions and organic subcomponents has enabled the construction of a wide range of discrete cages, often containing internal cavities, that have potential applications in sensing, catalysis and molecular purifications. The geometry of the cage can be controlled by the choice of metal ion and ligands. PdII and PtII are commonly used to achieve square planar coordination motifs, whilst FeII and CoII are used to form octahedral motifs. The use of other metal ions with less welldefined coordination geometries, such as ZnII and AgI, has led to the formation of a range of unusual, non-platonic architectures. A few studies have demonstrated that CuI can also form unusual architectures, however, CuI remains underexplored due to its air sensitivity and propensity to form low nuclearity structures. Alternatively, the use of reduced-symmetry ligands can also be used to access metal-organic cages with unusual geometries. Chapter 2 explores the formation of a CuI₆L₄ pseudo-octahedral cage, which exists as a mixture of diastereomers at room temperature. Cooling the sample to 253 K results in the selective formation of the S₄-symmetric CuI₆L₄ diastereomer. Changing the solvent from MeCN to DMSO gives a mixture of the S₄-symmetric and T-symmetric diastereomers at room temperature, whilst addition of tetrahedral guest molecules in MeCN forms the T-symmetric diastereomer with one equivalent of guest encapsulated within the cage. For a guest with elongated arms, the host-guest complex formed can be considered a type of mechanically interlocked molecule. At 253 K, the CuI₆L₄ cages were found to externally interact with fluorinated steroids but not non-fluorinated steroids. Chapter 3 investigates how the substitution pattern of the 2-formylpyridine subcomponent affects the self-assembled structure formed. Assemblies with 2-formylpyridine, 5-methyl-2-formylpyridine, 5-hydroxy-2-formylpyridine and 5-methoxy-2-formylpyridine gave S₄-symmetric [2]catenane-type structures with the formula CuI₁₂L₈. Use of 3-methyl-2-formylpyridine gave an S₄-symmetric, CuI₆L₄ cage at 253 K at low concentrations, but a large, more complex structure at higher concentrations. The identity of this structure is not currently known, but it is hypothesised to be an isomer of a [2]catenane. 4-methyl-2-formylpyridine gives an apparent mixture of products. Overall, substituents on the 3- and 4-positions prevent the exclusive formation of the S₄-symmetric [2]catenane, whilst substituents on the 5- position do not prevent the formation of the [2]catenane. Chapter 4 discusses the formation of a reduced-symmetry Zn₄L₄ cage formed from reduced-symmetry tri-aniline panels. The cage was found to bind bicycles over spherical guest molecules. In the presence of oxygen partial subcomponent oxidation occurred, leading to the formation of a Zn₁₀L₆(picolinate)6(H₂O)₂ species.