School of Chemistry - Theses
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ItemMetal-anilate coordination polymers( 2018)Crystalline coordination polymers are a class of materials which hold promise as adsorbents, sensors, electronic materials and magnets, as catalysts and separation matrices, or as batteries and electro-catalysts. Many of these applications depend on materials which offer an unusual combination of properties, resulting from the combination of a ligand and metal in a periodic lattice. These properties include stability and permanent porosity upon desolvation, crystallinity, monodisperse pores, open metal sites, flexibility, uptake of and interaction with guest molecules. Coordination polymers derived from redox-active ‘anilate’ ligands such as 2,5-dihydroxy-p-benzoquinone (H2dhbq) and chloranilic acid (H2can) have been studied as a possible mechanism for the introduction of electroactive properties into coordination polymers. No systematic study of the coordination polymers derived from substituted anilate ligands has previously been undertaken. In Chapter 2, the syntheses and crystal structures of novel anilate molecules and derived mononuclear and dinuclear compounds are reported. Ligand syntheses are achieved in one or two steps from commercially available starting materials, achieving sufficient purity upon recrystallisation, and many are observed to form isostructural dinuclear metal complexes. The bond distances within these compounds and similar compounds in the literature are observed to be dependent on oxidation state, and are independent of metal coordination geometry, allowing for the assignment of oxidation state from crystallographic data. In Chapter 3, a number of novel one-dimensional coordination polymers are described with metal centres linked by anilate ligands. These one-dimensional chains are shown to have a few different shapes, dependent on the relative coordination geometries around sequential metal centres in a chain. Two strategies for the formation of porous materials by cross-linking of one-dimensional chains are described, but synthetic attempts ultimately resulted in the formation of non-porous materials. In Chapter 4, structures are shown in which each metal centre links to three bridging anilate ligands, forming two- and three-dimensional coordination polymers, the majority of which showed a two-dimensional hexagonal grid network structure. Of these compounds, anionic coordination polymers of the form [M2(anilate)3]2- were found to show open-type structure, and were investigated for host-guest properties via gas adsorption. Reversible, gas-specific structural transformations were observed with the loading of CO2 and N2O into some of these compounds; by changing the cation, the structure was rigidified and did not collapse on desolvation. Compounds containing iron exhibited metal-to-ligand charge transfer, resulting in enhanced conductivity. This MLCT was found to be a temperature-dependent process in some cases. In Chapter 5, structures are shown in which each metal centre links to four bridging anilate ligands, forming two- dimensional square-grid coordination polymers and three-dimensional diamond-type coordination polymers. The square grid compound (Et4N)[Y(can)2] is shown to maintain structure on loss of solvent, and is investigated for interactions with solid, liquid and gaseous intercalants. Particularly strong interactions with hydrogen, methane and CO2 are investigated further via in situ crystallographic methods. Finally, this thesis is concluded, and these individual results are examined as a whole, including commentary on the limitations of this work and potential future work in this area. Appendices 1–5 contain additional data that supplement the thesis.