Browsing by Author "Loots, Leigh-Anne"
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- ItemInvestigation of the co-crystallisation of N-heterocycles(Stellenbosch : University of Stellenbosch, 2009-03) Loots, Leigh-Anne; Barbour, Leonard J.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.Co-crystals are excellent materials for studying intermolecular interactions in the solid-state and can be used to further our knowledge of the balance between strong and weak intermolecular interactions. The O–H∙∙∙∙∙∙Narom synthon was chosen as the focus of this investigation of hydrogen bonding motifs. The starting materials selected all have two hydrogen bond donor and/or acceptor sites for the formation of extended networks. All molecules are also aromatic such that the influence of weaker π∙∙∙∙∙∙π interactions can be included in the study. Two 3x3 grids of related co-crystals were produced from these starting materials and are reported in this thesis as part of an ongoing investigation into a broader set of co-crystals. A part of the work describes the investigation of co-crystals prepared by the combination of related benzenediol and diazine isomers taken from a 3x3 grid. The solid-state structures of each of the six starting materials are discussed briefly to describe the nature of intermolecular interactions involved in the single component crystals. Trends in hydrogen-bonding patterns as well as the weaker interactions identified in the starting materials, can be used to recognise those in the subsequent multi-component crystals. Thirteen co-crystal compounds were obtained, of which twelve structures are novel. Each of these co-crystal structures is discussed in terms of intermolecular interactions and packing in the solid state. Hydrogen-bonding patterns and structural similarities are highlighted in related co-crystal structures as well as between co-crystals and their respective starting materials. The combination of benzenediol isomers with benzodiazine isomers yielded seven novel co-crystal structures in a second 33 grid is reported. The structure of phthalazine, which has not yet been reported, is included in addition to these co-crystals, while the structures of quinazoline and quinoxaline that were retrieved from the CSD are discussed briefly. Co-crystal structures are discussed individually, focusing on the intermolecular interactions that are significant to the structural architecture of the compound. Certain co-crystals that display structural similarities with structures of the 3x3 grid, as well as with co-crystals presented in Chapter 3, are discussed in the relevant sections. Lastly, two extended pyridyl diyne ligands that were synthesised for use in future co-crystallisation studies similar to those reported earlier are briefly highlighted. The crystal structures of the pure compounds and of a hydrate of one of the ligands were obtained and discussed briefly. To date only one of these structures has been reported in the literature.
- ItemThe structural analysis of imidazole-functionalised metallocycles(Stellenbosch : Stellenbosch University, 2012-12) Loots, Leigh-Anne; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The primary objective of this study was to synthesise novel metallocyclic compounds and analyse their crystal structures. To this end seven novel imidazole-functionalised ligands were synthesised and reacted with a variety of transition-metal halide salts. In addition to this study a new, simple, yet robust methodology for the analysis of π···π packing motifs in aromatic molecules is described. Seventeen homeotypic metallocyclic compounds were obtained with a ligand containing a dimethoxyphenyl spacer between imidazole functionalities. These compounds form reliably from a number of solvent systems involving acetonitrile and they all include acetonitrile molecules as part of their host assembly. In each case a second guest molecule is enclosed within the walls of the metallocycles. These compounds are compared by means of thermal analysis, calculated powder X-ray diffraction patterns as well as crystal packing similarity calculations. Metallocycles prepared from a phenanthrene-based ligand form an unprecedented infinite π···π stack, which induces the assembly of an infinite catenane. This catenane forms concomitantly with its topological isomer, which consists of unlinked metallocycles. The intermolecular interactions responsible for the two topologically unique structures were investigated. Finally, a further twelve metallocycles were prepared from four novel imidazolefunctionalised ligands and their structures were analysed for any similarities and/or differences. A few of these crystals showed the release of solvent guest molecules as singlecrystal to single-crystal transformations.