Abstract
The use of s-block metals in the synthesis of metal-organic frameworks (MOFs) remains an under explored area of MOF chemistry. The work in this thesis details the design and synthesis of mixed-donor ligands for the synthesis of MOFs with a focus on using s-block metals and the study of their structure, gas sorption capabilities and other functionalities of the frameworks.
Chapter 1 introduces a brief history and the key terminology of MOFs. This is then followed an overview of linker design and use of metal ions in the construction of MOFs. Finally, the applications and functionalities are discussed with a focus on preparation of materials, gas adsorption and the behaviour of flexible MOFs.
Chapter 2 of this thesis details the synthesis of two linear mixed donor carboxylate-phenanthroline ligands HL1 and HL2 using the three component Debus-Radziszewski reaction. Using these linkers and the alkaline earth metal ions Mg(II), Ca(II) and Ba(II) as well as Zn(II), series of diamondoid MOFs Mg.L2-dia, Ca.L2-dia, Ba.L2-dia and Zn.L2-dia were synthesised. The properties of these MOFs were investigated with nitrogen and carbon dioxide gas adsorption measurements. From the gas adsorption measurements Ca.L2-dia was shown to be a flexible framework with seven of phases of Ca.L2-dia being identified using SCXRD. The flexible behaviour of Ca.L2-dia was further investigated using in situ PXRD measurements during gas adsorption and during the loading of high pressures of gases. From the in situ PXRD data, in conjunction with the SCXRD phases, the flexible behaviour, phase transitions and mechanism of flexibility were determined.
Chapter 3 covers the modular alteration of the linkers synthesised using the Debus-Radziszewski reaction. Beginning with the synthesis of the HL3 ligand with the incorporation of a triazole ring and investigating potential frameworks with Zn(II) and Ca(II) metal ions. The four component Debus-Radziszewski reaction was then used to install an additional pendent group at the ‘1’ position of the imidazole ring. From this approach, a series of four new ligands HL4, H2L5, H2L6 and H3L7 were designed and synthesised with the tuning of the linker’s intermolecular interactions and alteration of the topicity. Using the linear HL4 ligand new MOFs Mg.L4-pcu and Ca.L4-pcu were synthesised using Mg(II) and Ca(II) metal ions respectively. The tritopic linkers H2L5, H2L6 resulted in the 2D sheet Cu.L5-1 or the 3D framework Ca.L6-1 with the Cu(II) and Ca(II) ions, respectively. The tetratopic linker H3L7 was able to form MOFs with a variety of metal ions, namely Gd(III), Ba(II) and Ca(II). In addition, with H3L7 and H2BDC as an auxiliary linker, a mixed linker Ca(II) MOF, Ca.L7.BDC, was synthesised with the framework with accessible cage structure. The properties of Mg.L4-pcu, Ca.L4-pcu and Ca.L7.BDC MOFs were investigated with nitrogen and carbon dioxide gas adsorption measurements. In addition, Ca.L7.BDC was shown to be able uptake aromatic guests from solution; the guests were shown to occupy the cage cavity by SCXRD and supported by NMR spectroscopy.
Chapter 4 focuses on the use of alkali metals in the synthesis of MOFs. Using the HL1 ligand and the Na(I) ion the framework Na.L1-1 was synthesised. In investigating the formation of lithium MOFs with the HL1 ligand and either H2BDC or H2TDC as a secondary linker, the frameworks Li.BDC-hex and Li.TDC-H2O, which only incorporated the secondary linker were synthesised. Na.L1-1, Li.BDC-hex and Li.TDC-H2O were investigated with nitrogen and carbon dioxide gas adsorption measurements. The gas adsorption measurements show that Li.TDC-H2O is a flexible framework. The flexibility of Li.TDC-H2O was further investigated using VT-PXRD, which showed a phase change during heating. Further investigating the phase change observed in the PXRD data led to the identification of new phases of Li.TDC-H2O using SCXRD giving insight into its flexible behaviour.
Chapter 5 concludes the work discussed in this thesis. as well as providing future experiments and directions for this project.
Chapter 6 covers the experimental details for this thesis.
Then finally Appendix A provides additional X-ray diffraction data and Appendix B provides details of the collected SCXRD structures.