Adamantane: A Versatile Core for Accessing Non-Default Topologies

Abstract

This research addresses the main concerns of design and synthesis of the robust non-interpenetrated mesoporous MOFs with well-defined pores, by accessing non-default topologies which are more resilient towards interpenetration. Chapter 1 provides a general introduction and a literature review for the currently employed strategies to prevent interpenetration in MOFs. To this end, eight adamantane-based ligands were synthesised by functionalising two- to four-bridgeheads of the adamantane core and were characterised by single crystal X-ray crystallography and other analytical techniques. Chapter 2 discusses the strategy of utilisation of the rigid adamantane core to design and synthesise these eight ligands for the purpose of constructing the robust non-interpenetrated MOFs. Chapter 3 describes the reticular synthesis strategy of combining a simple rigid tetrahedral ligand, tetrakis(4-cyanophenyl)adamantane, with a Ag(I) metal ion, at room temperature and atmospheric pressure, to result in both Lonsdaleite (lon) and diamondoid (dia) MOFs and associated 2D honeycomb networks. In total, four new networks each of lon- and dia-MOFs and two 2D honeycomb (hcb) networks were synthesised and characterised. The effect of counteranion and (or) solvent molecules in templating the formation of these networks is established. Interestingly, lon networks are considered to be resilient to interpenetration were found to be three-fold interpenetrated. Additionally, the nanoindentation studies and Cremer-Pople puckering analyses to quantify the topologies are presented. Studies indicated the dia-MOFs were harder than the lon-MOFs while the latter were thermally more stable. Chapter 4 describes the study of the templating effect of anion and solvent in the formation of Ag-MOFs isoreticular to lon, dia and 2D networks. Isoreticulations of the dia-MOFs and hcb network were achieved by the successful syntheses of two dia networks and a 2D hcb net. Furthermore, five more networks possessing rare Kagomé dual (kgd), herringbone and square lattice (sql) network topologies were also synthesised and characterised. This chapter presents the complication of solvent in polymorphism and interpenetration in thwarting the goals of isoreticulation. Chapter 5 presents three non-interpenetrated carboxylate-MOFs which were synthesised by employing Pb(II), Cu(II) and Li(I) cations. The Pb- and Cu-MOFs were synthesised by employing a rigid tetrahedral ligand, tetrakis(4-carboxyphenyl) adamantane while the Li-MOFs were synthesised by employing a rigid angular ligand, bis(4-carboxyphenyl)adamantane. The Cu-MOF was achieved by accessing PtS topology while the Pb- and Li-MOFs were achieved by accessing the topologies which possessed high connectivity M-O clusters and rods. The Pb-MOF possessed a pseudo Pb-O mesh-like networks which blocked the microporous network in the ab plane while the network was accessible along the other two crystallographic axes. A series of isostructural Li-MOFs was constructed by employing different anti-solvents. These Li-MOFs possessed 1D mesoporous channels running along a crystallographic axis while being impermeable through the other two axes. The resultant MOF possessed double-walled network, mesoporous cavities and low-density. This MOF could withstand the guest removal without the collapse of the framework and possessed extremely high thermal stability. The unidirectional 1D channels in this MOF displayed uniaxial crystallographic changes upon guest removal. These subtle crystallographic changes are studied by SC-SC transformations over a period of 315 days using laboratory diffractometer. The effect of these transformations on the porosity and stability of this material has been established. The gas adsorption studies revealed that the Li-MOF displayed high affinity towards gases such as CO2 and H2, slight affinity towards CH4 and N2. At room temperature and low pressure, this MOF selectively preferred CO2 over N2 and CH4. This thesis concludes with a summary of the design of two unique systems namely the lon-MOFs and the Li-MOF, along with Cu-MOF and draws attention to the potential applications of these materials. The future directions on this project have been included.