Browsing by Author "Du Plessis, Marike"

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    Guest uptake in porous metallocyclic host compounds
    (Stellenbosch : Stellenbosch University, 2020-01) Du Plessis, Marike; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: The general aim of the work discussed in this dissertation is to contribute to scientific knowledge, thereby broadening our understanding of the relationships between the structure of a solid, crystalline material and its properties. Only when we truly understand the principles of supramolecular chemistry might we be able to design crystals for targeted applications at will. Metallocycles are a sub-class of supramolecular materials studied by the Barbour group for their potential porosity. In this regard, we selected three previously reported metallocycles, known to be porous, with the specific aim of further probing their porosity by means of guest exchange experiments. The first metallocycle studied is a silver-based acetonitrile solvate with the formula [Ag2L12](BF4)2•2CH3CN, where L1 is the ligand 1,4-bis(2-methylimidazol-1-ylmethyl)benzene; we refer to this metallocycle asMC1•2CH3CN. It was shown that the acetonitrile guest molecules can be replaced by other small guest molecules, specifically acetone, dichloromethane, benzene, p-difluorobenzene and toluene by immersing the as-synthesised crystals in the liquid of the target guest. The second is a Cu-based metallocycle with dimethylsulfoxide (DMSO) coordinated to the metal centre. The formula for this metallocycle (referred to as MC2S2) is [Cu2Cl4L12S2], where S is the coordinated solvent. The coordination bond can be cleaved by replacing the DMSO with acetonitrile in a solvent exchange process. We have shown that, by exposing the acetonitrile inclusion compound (MC2•2CH3CN) to vapours of solids, inclusion compounds with pyrazine, p-benzoquinone, p-dichlorobenzene and naphthalene can be obtained. While MC1•2CH3CN and MC2S2 are constructed using the same ligand, the third metallocycle, [Cu2L22Cl4] or MC3, contains the ligand 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L2). Guest exchange experiments were carried out with MC3 and the three isomers of xylene. We have shown that p-xylene is selectively included from a mixture of the xylene isomers and that this metallocycle can be used to purify commercially pure o-xylene by extracting p-xylene impurities. All of the guest exchanges occurred as single-crystal to single-crystal transformations, allowing us to obtain crystal structures of the new inclusion compounds using single-crystal X-ray diffraction techniques. The crystal structures were analysed and insights gained from the crystal structures as well as supporting techniques such as thermogravimetric analysis, powder X-ray diffraction, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, vapour sorption, gas chromatography and nuclear magnetic resonance spectroscopy are discussed in this dissertation.
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    Structural characterisation of coordination compounds incorporating Imidazole-based ligands
    (Stellenbosch : Stellenbosch University, 2012-03) Du Plessis, Marike; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Crystal engineering is a relatively new and fast growing branch of science. It emanates from the field of supramolecular chemistry and involves the self assembly of molecular and/or ionic “building blocks” to form a crystal – i.e. a “supermolecule”. Ultimately, a crystal with a predetermined structure and properties may result from a shrewd choice of building blocks. The main objective of this study was to investigate the architectures formed by flexible imidazole derived ligands when combined with a range of transition metal salts. The specific architecture that we aim to obtain with these building blocks is the “doughnut”-shaped metallocycle. Stacking of metallocycles to form columns in the crystal is a design strategy for creating porous materials and it has proven to be successful on several occasions. The following organic ligands were synthesised as part of this work: - 1,4-bis(benzimidazol-1-ylmethyl)benzene - 4,4'-bis(benzimidazol-1-ylmethyl)biphenyl - 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene - 1,4-bis(benzimidazol-1-ylmethyl)tetrafluorobenzene - 1,4-bis-(2-methylimidazol-1-ylmethyl)benzene - 1,4-bis-(2-methylimidazol-1-ylmethyl)tetrafluorobenzene The coordination compounds that were obtained during the course of this study were mainly analysed using single-crystal X-ray diffraction (SCD). A total of 40 novel crystal structures were obtained, of which 13 are metallocycles, 26 are either 1D or 2D coordination polymers and one is a salt. Of the 13 metallocycles, seven have the conventional doughnut shape. However, the property of porosity was limited by certain factors, which are discussed. Preliminary results show that two of these metallocycles are potential candidates for porosity studies. Many of the crystal structures also provide excellent examples of isostructurality, solvatomorphism and supramolecular isomerism – i.e. different crystal forms. The latter terms refer to similarities in the packing arrangements of molecules in the solid state or different packing arrangements of the same molecules or building blocks, both common phenomena in supramolecular chemistry. In the context of crystal engineering, we are still far from being able to predict and control the outcome of a crystallisation experiment to obtain a specific crystal form.