An Exploration Into the Self-Assembly of Metal-Organic Materials and Their Host-Guest Chemistry

Abstract

Metal-organic materials describe a vast array of structures, from simple metal complexes to infinite networks. The choice of architecture targeted therefore influences the synthesis routes and the material's application. This thesis will focus on the ability of metal-organic materials to entrap species within their structure, referred to as host-guest chemistry. Exploiting an architecture's ability to immobilise guests has allowed applications including catalysis, separation, sensing and protection of guests to be investigated. An introduction surrounding metal-organic materials is given in Chapter One, with emphasis on specific concepts touched upon in this thesis. Biomimetic mineralisation has been developed as a mild preparation technique for metal-organic frameworks, where nucleation is induced by a biomolecule that is encapsulated within the final network. Immobilisation of biomolecules within a solid support allows for their use in environments which would usually result in denaturation. A limited number of metal-organic frameworks have been prepared through biomimetic mineralisation and demonstrated retention of protein function following encapsulation. In particular, ZIF-8 has shown great potential as a protective structure for biomolecules. Chapter Two describes the attempts to prepare metal-organic frameworks using dicarboxylic acid linkers via biomimetic mineralisation, with the goal being to identify materials capable of displaying comparable protein protection to ZIF-8. Ultimately the Chapter established ZIF-8 as a unique framework for biomolecule encapsulation, and describes the challenges associated with biomolecule@MOF preparation. Discrete metal-organic cages can immobilise small molecules and be used and analysed in solution in comparison to porous solid supports, which are heterogeneous in nature. The self-assembly of mono- and bimetallic trigonal bipyramid architectures from a heteroditopic ligand and tris(2-aminoethyl)amine is explored in Chapter Three. Investigations into the host-guest chemistry of a family of trigonal bipyramids was carried out, with a focus on variation of the guest molecules and efforts to examine the potential catalytic activity exhibited by an Fe(II)2Cu(I)3 architecture. The immobilisation of metal-organic cages within solid supports is a new concept with a limited number of reports in recent years. Similar to concepts explored in Chapter Two, the encapsulation of metal-organic cages via biomimetic mineralisation could allow use of the discrete architectures within the solid state whilst maintaining their desired host-guest properties. Chapter Four investigates the immobilisation of a water-soluble Fe4L6 cage within ZIF-8 and details attempts to evaluate any changes in the host-guest chemistry of the incorporated cage. The capture of two other metal-organic materials within ZIF-8 is also explored. Chapter Five summarises findings in Chapters Two to Four and elaborates on any potential future work that could be carried out.

Date of Award	30 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Imogen Riddell (Supervisor) & David Collison (Supervisor)