Pyrimidyl isophthalate metal organic frameworks for gas storage

This thesis focuses on the syntheses and gas sorption studies of a series of novel metal-organic frameworks constructed from Cu(II) paddlewheels and pyrimidyl isophthalate ligands. The effects of ligand extension and functionalisation on the framework structures and properties are investigated and discussed under respective chapters. Chapter 1 introduces metal-organic frameworks (MOFs), places the thesis in its scientific context, and discusses the syntheses of the ligands and MOFs with emphasis on the design of pyrimidyl isophthalate MOFs as having no open metal sites. Chapter 2 describes the syntheses of two porous phenyl-based pyrimidyl isophthalate frameworks to investigate the effect of extending linker length on the MOF structure, surface area and gas uptake capacities. Chapter 3 discusses the concept of pore functionalisation of the pyrimidyl isophthalate MOFs with amide pendant groups. Chapter 4 centres on the incorporation of alkyne groups in the ligand design and the impact on the pore characteristics and gas uptake properties. Chapter 5 is an overview of the experimental results and includes comparisons of the different ligands, the crystal structures of the MOFs and their gas uptake capabilities. The conclusions for the thesis and resulting future research perspectives are stated in Chapter 6. According to the results, all the pyrimidyl isophthalate MOFs investigated in this work are isostructural having the same trigonal crystal system with an eea topology but with slight differences in space groups. Moreover, all display similar trends in their gas uptake behaviour, showing higher uptake and selectivity for CO2 relative to CH4 and N2, with the amide-functionalised MOFs showing the highest values. The results also show that, as anticipated, ligand expansion increases surface area, pore volume and gas uptake capacities. However, the effect of this difference in ligand length is more pronounced in the amide-based MOFs than in phenyl-based ones. The amide MOFs exhibit not only the highest CO2 gravimetric adsorption values when compared with the phenyl and alkyne-based ones but also perform well against MOFs reported in the literature, especially in respect of CO2 uptake capacity under similar conditions. Based on these results, it is concluded that these new Cu(II) pyrimidyl isophthalate frameworks, particularly those with amide pendant groups, are good candidates for CO2 capture and sequestration. Further research is suggested, including the use of metals other that Cu with these ligands and further advanced analyses with neutron powder diffraction and other techniques: these are the first few examples of such materials and need to be thoroughly investigated in order to establish how widely applicable our observations are