title: Synthesis, characterisation and properties of flexible metal-organic frameworks
Creators: name: Perkins, Catherine
Publisher: name: University of Liverpool Repository
Year: 2014

description: In this thesis the synthesis, characterisation and analysis of new Metal-Organic Frameworks (MOFs) are presented. Introduction: Chapter 1 includes an overview of recent literature focusing on the potential application of porous MOFs. Synthetic and Experimental Techniques: Chapter 2 contains information regarding the synthesis of the organic ligand, tetrakis-(4-carboxyphenyl)-benzene (H4TCPB) and solvothermal MOF synthesis. Characterisation techniques used in this thesis are also explained. Mixed Carboxylate-Imidazole Based Metal-Organic Frameworks: In chapter 3, the synthesis of MOFs containing ligands with both imidazole and carboxylate functionality are presented. The MOFs produced are based on metal-carboxylate coordination networks with imidazole coordinated as a terminal, neutral ligand in all cases. An investigation into how reagent ratio and addition of base affects the product of reaction with the combination of Co(II), 1,3,5-benzene tricarboxylate and imidazole yields three different frameworks from the same three reagents. The main compound discussed has the formula Co3(BTB)1.5(IM)1.35(O)0.5(OH)0.5(H2O)1.65·guests and is based on a novel Co6 building unit which comprises neutral imidazole, oxo, hydroxo and carboxylate coordination. This Co6 unit is the basis of a 2D tri-layer, stacked into a 3D porous arrangement via π···π stacking interactions between 1,3,5-benzene tribenzoate ligands. This material was characterised to be permanently porosity towards N2, CO2 and CH4, however the material is sensitive to activation conditions, presumably due to the reliance on weak π···π stacking interactions between imidazole ligands to retain the void space. A Cerium-Based Metal-Organic Framework: Structure, Sorption and Structural Transformations upon Desolvation: In chapter 4, a 3D framework based on Ce(III) and H4TPCB with the formula Ce(HTCPB)"guests is presented. A variable temperature single crystal x-ray diffraction experiment allowed four structures to be determined from the same parent material: The as-made structure, the partially desolvated structure in which all channel and coordainted H2O has been removed but coordinated EtOH remains, the fully desolvated structure and the structure following re-exposure of the desolvated phase to air. Powder x-ray diffraction confirms that the phase changes observed occur in both the single crystal and bulk crystalline phases. A gas cell experiment on the rearranged phase shows that the material can reversibly uptake Xe into the channels. This investigation highlights the structural stability and flexibility of 11. ii! ! Ce(HTCPB) for Xylene Separation and Analysis of Uptake of Aromatic Guests: In chapter 5, Ce(HTCPB) is investigated for its potential in xylene separation and shows para-/meta-xylene (pX/mX) selectivity in line with the highest performing MOF and zeolite materials. Analysis of the para-, meta-, ortho-xylene (oX) and ethylbenzene (EB) loaded single crystal structures provides an insight into the preference of the material for pX over the other isomers. The framework relaxes favourably around the pX isomer, which forms C-H···π and C-H···O interactions with the channel walls, forming an almost perfect pX pocket. Such interactions are formed to a lesser extent with the other less streamlined guests. Single crystals of Ce(HTCPB) are also loaded with benzene and toluene in for comparison with the pX loaded structure. A Series of Isostructural Lanthanide-Based MOFs for Xylene Separation and A Framework using a Smaller Lanthanide: In chapter 6, a series of compounds isostructural with Ce(HTPCB) are presented with the formula Ln(HTPCB), where Ln = La, Ce, Pr, Nd and Sm. The single crystal structures of the desolvated and rearranged phases were also determined to be isostructural with the corresponding Ce(HTCPB) phases. These compounds were investigated for their pX/mX selectivities, with Pr, Nd and Sm(HTCPB) producing selectivities around 50 % higher than any reported MOF or zeolite material. Analysis of the pX and mX loaded single crystal structures of this series of compounds provided an understanding of the trend in selectivity observed. Also in this chapter, combination of H4TCPB with a smaller lanthanide, Yb, produced a new framework.