Crystal engineering of mixed-ligand metal-organic frameworks based on simple carboxylate and bipyridyl ligands

• Main Author: Mutti, Marcello
• Other Authors: Oliver, Clive
• Format: Dissertation
• Language: English
• Published: University of Cape Town 2019
• Subjects: Chemistry
• Online Access: http://hdl.handle.net/11427/29726

Over the last few decades research in supramolecular chemistry and crystal engineering have seen an exponential growth. The synthesis of metal-organic frameworks (MOFs) has attracted much interest worldwide due to the possibility of obtaining a large variety of structures with a wide range of applications in fields pertaining to storage, separation and catalysis. This work focuses on the crystal engineering of MOFs based on mixed ligands which may ultimately be used in the gas storage of pollutants, greenhouse gases or fuel. Two novel 2D mixed-ligand MOFs, both based on manganese, 4,4’-bipyridine and 1,3,5- benzenetricarboxylic acid, have been prepared and fully characterized. The employment of dimethylformamide or dimethylacetamide, as the solvent, results in two isostructural MOFs. Another novel MOF, similar in structure to the previous two, with 5-nitroisophthalic acid instead of 1,3,5-benzenetricarboxylic acid has been also prepared and characterized. This MOF has the same metal and ligand combination as, and is largely isostructural to, a literature example, but differs in method of preparation and solvent content. These Mnbased MOFs have potential voids in the structure making them candidates for gas sorption experiments. A novel 2D mixed-ligand MOF based on cobalt, 4,4’-bipyridine and 5-nitroisophthalic acid has been synthesized and fully characterized. Its structure is the same of another MOF, based on manganese, present in this work and like its manganese analogue it exhibits potential void spaces in the framework that make it a candidate for gas sorption experiments. Finally, a novel 2D MOF based on 1,3,5-benzenetricarboxylic acid and cadmium bromide has been synthesized and fully characterized. Dehydration and rehydration studies performed by combining powder X-ray diffraction with thermogravimetric analysis show that it can lose coordinated water, that comes from the reaction solvent, upon heating, and reabsorb water from the atmosphere, ultimately regaining its original structure. All MOFs were synthesized via the solvothermal method and characterized with X-ray diffraction (single crystal and powder) and thermal analyses (hot stage microscopy, differential scanning calorimetry and thermogravimetric analysis).