X-ray studies of novel metal-organic frameworks

Abstract

MOFs (Metal-organic frameworks) are a series of record-breaking materials that have been developed rapidly, in terms of variety, functionality, popularity and understanding, over the past quarter of a century. MOFs are defined not only by their inclusion of inorganic SBUs (Secondary building units) held together by organic linkers, but also by their potential for containing void space within their structures. MOFs quickly became the most porous materials in the world, surpassing the previous record holders, zeolites. Interest in these materials began with their ability to store and separate different gasses efficiently. It is however, their unique tunability that makes these materials so exciting, and they have since been put to work solving innumerable problems throughout the chemical and materials fields.

The majority of MOFs use anionic, polydentate linkers, such as carboxylates, because they result in neutral MOFs with large SBUs, which retain their porosity upon solvent removal. It was found early on that using just neutral, N-donor linkers results in cationic frameworks which collapse upon guest removal. The work in this thesis explores the use of both N- and O-donor linkers in the same system, with the aim of synthesizing novel structures with unique topologies and physical properties.

The first two chapters of this work will briefly introduce the history and theory behind crystallography and diffraction techniques, then MOFs and some of the associated characterisation techniques and structural features.

The main chapter of this work will then detail the structural characterisation of 18 novel mixed N/O-donor MOFs synthesized by the author or by Reza Abazari's group at Tarbiat Modares University, Iran. The materials produced spanned a range of dimensionalities, and the geometrical and topological features of these new compounds are discussed and compared with analogues in the literature. Unique SBUs were achieved in some of these structures, resulting in three new MOF topologies.

The two chapters following this will describe some additional MOFs which, despite failing to incorporate the N-donor linkers, are still new structures. The first of these two chapters focuses mainly on transition metal structures, with some examples of SBU modification by N-donor ligands to produce rare topologies. The second of these chapters focuses solely on new lanthanoid MOFs.

The penultimate chapter contains the experimental procedures involved in synthesizing and characterizing the MOFs in this work. The final chapter is an additional structures section, depicting some of the other new structures run and solved by the author. The Supplementary information can be found at the end of this volume and contains a SC-XRD experimental table for each structure presented in this work.