Browsing by Author "Kutama, Aluwani"

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    Guest inclusion in porous metal-organic crystals and high-pressure single-crystal X-ray diffraction analysis at low temperatures
    (Stellenbosch : Stellenbosch University, 2024-03) Kutama, Aluwani; Barbour, Leonard James; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Porous metal-organic materials are an intriguing class of compounds that are capable of adsorbing guest molecules, such as gases, into their cavities. This ability of these materials has stimulated research across various domains, including purification, gas storage, separation, and drug delivery. In this study, we analyzed two well-known porous metal-organic compounds namely, [Zn2(L1)(OBA)2] and [Cu2(L2)2(Cl)4]. The metal-organic framework (MOF), [Zn2(L1)(OBA)2], was successfully synthesized and fully characterized in preparation for gas sorption studies. This characterization included single crystal Xray diffraction (SCXRD), thermogravimetric analysis (TGA), and Fourier-transform infrared (FT-IR) spectroscopy. Gas sorption studies were thereafter carried out using volumetric sorption analysis and pressure-ramped differential scanning calorimetry (P-DSC) up to 50 bar using CO2 and C2H4. The sorption profiles with CO2 indicated the presence of shape memory, while the sorption profiles with C2H4 were indicative of Type 1 isotherms. In addition, the metallocycle [Cu2(L2)2(Cl)4], was synthesized using a layering methodology that required the use of three solvents (namely EtOAc, DMF and EtOH), and further studies revealed that EtOAc was the solvent that was included in the crystal structure and hence responsible for the structural channel formation. The characterization of [Cu2(L2)2(Cl)4] involved using powder X-ray diffraction, SCXRD, TGA, FT-IR, and thereafter the activated crystals were pressurized up to 20 bar with CO2 and characterized using, gravimetric sorption analysis and P-DSC. In this work a novel method for obtaining high-pressure SCXRD data at low temperatures is also described for the first time and utilized primarily to reduce the thermal motion of the included guest molecules for structural modelling purposes. This was carried out with CO2 (20 bar) and Xe (10 bar). The results revealed acceptable molecular geometrical parameters for the included CO2 guest molecule, and that the cavity of [Cu2(L2)2(Cl)4] increased in volume to accommodate the large Xe molecule, indicating the flexible nature of this metallocycle.