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RESEARCH PRODUCT

Préparation et spéciation d’oxo-clusters de métaux du bloc p

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The main subject of this thesis is the use of Pair Distribution Function (PDF) analysis for solution phase speciation during metal-cluster growth. The PDF method allows the extraction of structural information from a sample in the form of an atom-atom distance distribution via Fourier transform of synchrotron X-ray scattering data. The growth mechanisms of two solution-based systems are analysed in this thesis. Precursor materials are synthesized through a mechanochemical method that was developed and shown to be able to access a wide range of related systems.Mechanochemical routes of synthesizing bismuth Active Pharmaceutical Ingredients (APIs) were investigated and optimised. Samples were analysed using a range of techniques, including powder X-ray diffraction (PXRD), thermogravi-metric analysis (TGA) and Raman spectroscopy. Various milling conditions were explored, resulting in optimised routes to bismuth (III) gallate and bismuth (III) citrate, as well as improving the literature syntheses of bismuth (III) di- and trisalicylate. All reactions used Bi2O3 and the corresponding organic acids. Significantly, a water dependent structural transformation of mechanochemically activated bismuth citrate was discovered, suggesting an origami-like folded structure that expands when filled with water to reveal a highly porous framework of the cubic crystal system.The first solution-phase metal-oxo cluster studied was [Bi38O44], a "magic-size" Keplerate-shaped molecule. Using bismuth (III) disalicylate as a precursor, it was found to grow in a multistep reaction with initial formation of the smaller [Bi9O7] cluster. The growth occurs in multiple solvents, including acetone cyclohexanone, pentanone, methyl ethyl ketone and dimethylformamide. The growth mechanism is shown to be influenced by the solvent choice and water content. The PDF method observations were confirmed by spectroscopy and Dynamic Light Scattering (DLS).The second system studied was the formation of the ε-[Al13] cluster from an aqueous AlCl3 solution. Two mutually exclusive growth mechanisms are proposed for this system in the literature. A gradual polymerization model involving an array of intermediate oligomers and an immediate self-assembly model in which the growth occurs from small Al1–Al3 species. The PDF method indicated that the immediate self-assembly model is correct. Experimental X-ray scattering data was exclusively used to describe and analyse the ε-[Al13] cluster growth with the aid of computational methods such as Principle Component Analysis.