Potent Chelators with Intrinsic Intermolecular Affinity

Abstract

This thesis, entitled 'Potent Chelators with Intrinsic Intermolecular Affinity', investigates the development of unsymmetrically substituted 6-carboxy-4-aryl-2,2'-bipyridine (bpy) scaffolds for incorporation into coordination polymers and supramolecular materials, and the structural and mechanical properties governing their formation. The aim is to exploit the synthetic versatility of this moiety, to install additional binding sites and to then examine the resultant structural chemistry with d- and f-block metal ions. The knowledge obtained from single crystal X-ray data of the coordination environment of these systems will provide fundamental knowledge that will then be used in the design and engineering of complex, higher order metallosupramolecular assemblies. A library of functionalised 2,2'-bipyridine compounds were synthesised and over 60 metal complexes were obtained; reported in this study are specific examples which demonstrate an understanding of the coordination environment. While this study is primarily concerned with solid-state structural chemistry of 2,2'-bipyridine derivatives, attention is paid where appropriate to solution-based measurements such as UV/Visible absorption spectroscopy and 1H NMR studies and the pertinent behaviour of functional materials, such as thermogravimetric analysis (TGA) for solvated species, scanning electron microscopy (SEM) for soft materials, and gas uptake studies for stable void-containing materials. Chapter 1 introduces the central tenets of supramolecular chemistry and crystal engineering, with examples of discrete and infinite assemblies, specifically in the context of functionalised bipyridine derivatives. The focus of Chapter 2 is primarily on the preparation of a ligand family in which the functional group on the terminal phenyl ring is varied as a function of the synthetic procedure. The structural properties of the coordination complexes (mononuclear, trinuclear and one- and two-dimensional polymeric) obtained are examined in the solid-state. The coordination chemistry investigated in this chapter provides the background for the development of this highly modular building block as a robust coordinating tecton for use in generating larger, more complex metallosupramolecular assemblies. Chapter 3 investigates the preparation of a new pyrazine-pyridine hybrid ligand family, formed by installing an additional binding site ? the pyrazin-4-yl nitrogen atom – on the bipyridyl ring. The reaction of this ligand family with Cu(II) ions resulted in the formation of a soft material which then underwent a transition to a discrete complex. Reactions with Ag(I) ions demonstrates the importance of the regiochemistry employed. The 3-isomer forms a three-dimensional polymer, while the change in the geometric substitution to the 4-isomer results in the formation of an octanucelar macrocycle, which showed fully reversible guest uptake and exchange. Chapter 4 presents an extension of this work to include the preparation of the amino-substituted pyrazine-pyridine hybrid ligands and a Schiff-base containing ligand species. These ligands are analysed in the solid state, and their properties in solution upon titration with Fe(II) and Cu(II) ions are examined. Investigations into the soft materials formed with these systems is also discussed. Chapter 5 introduces the synthesis of three new rigid aromatic scaffolds with examples of dipyridyl and dicarboxylic acid functionalities. The pyridyl scaffolds are reacted with a variety of palladium salts in an attempt to form supramolecular cages in solution, and when in the presence of a carboxylic acid co-ligand produces crystalline MOF material. The reaction of the dicarboxylic acid functionalised bpy ligand with d-metal ions also produces a porous coordination network capable of guest adsorption and evacuation. The conclusions are presented in Chapter 6, while Chapter 7 describes the experimental details of the work presented herein. The combined references for this thesis are found in Chapter 8. Additional information, such as characterisation, and supplementary data for each chapter are shown in the appendix. Crystallographic information files (.cif) for each crystal structure reported can be found on the accompanying USB to this thesis.