Lunn, Richard David James; (2021) Using Metal-Organic Frameworks to Determine the Crystal Structures of Non-Crystalline Compounds via the Crystalline Sponge Method. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Crystalline Sponge Method has been expanded to the structural elucidation of hydrophilic and non-aromatic compounds through the study of new potential crystalline sponges and a range of novel host-guest inclusion complexes have been presented. First, it was important to reliably synthesise high quality single crystals of the original crystalline sponge {[(ZnI2)3(TPT)2].x(solvent)}n and its ZnBr2 and ZnCl2 variants. Then crystals of these metal-organic frameworks could be used in guest encapsulation experiments. Initial encapsulation experiments focused on improving on work performed previously in the Carmalt group on the encapsulation of 2,6-diphenylphenol; this was successful resulting in the structural elucidation of a fully refined crystal structure of 2,6-diphenylphenol. The crystalline sponge {[(ZnI2)3(TPT)2].x(solvent)}n and its ZnBr2 variant were used to obtain crystal structures of the liquid agrochemical active ingredients metalaxyl-M and S-metolachlor. The encapsulation of three model compounds with similar chemical fragments to metalaxyl-M and S-metolachlor were also studied allowing for the effect of guest size on the position of the pores the guests occupy to be investigated. Additionally, the effect of changing the ZnX2 (X = I or Br) nodes of the host metal-organic framework on the pore positions the guest molecules prefer to occupy and the effect of increasing the incubation temperature on guest inclusion was also studied. Further to this, studies were performed into the use of alternative metal-organic frameworks as crystalline sponges. This work was performed with the aim of mitigating the limitations of the original crystalline sponge and increasing the range of compounds that can have their structures elucidated via the crystalline sponge method. Several novel guest inclusion complexes have been presented using the metal-organic frameworks NOTT-125 and RUM-2. This demonstrated the ability of these frameworks to successfully order and elucidate the structures of guest compounds. It was observed that the framework RUM-2 was capable of elucidating the structures of both hydrophilic and hydrophobic structures, expanding the scope of the crystalline sponge method to a larger range of potent guest molecules. Additionally, an analysis of the host-guest interactions formed was performed when using RUM-2 as a crystalline sponge. It was observed that stronger covalent host-guest interactions were formed with guest molecules containing Lewis basic functional groups. These bonds were observed to allow for increased guest occupancy and improve guest ordering in comparison to that observed when solely non-covalent interactions were formed. Furthermore, experiments were performed to test the applicability of RUM-2 to the structural elucidation of agrochemical active ingredients. The successful structural elucidation of the herbicide active ingredient molinate in addition to the successful encapsulation of metalaxyl-M into {[(ZnI2)3(TPT)2].x(solvent)}n and its ZnBr2 variant demonstrated the potential of the crystalline sponge method in the structural elucidation of hard to crystallise compounds in the research and development of new agrochemical products.

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