Ammonolyse von Uranhalogeniden und Beiträge zur Chemie der Platinfluoride
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Philipps-Universität Marburg
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The importance of uranium mononitride as a fuel for future nuclear reactors and the promising properties of uranium compounds in regard to catalysis, caused growing interest in the research on uranium-nitrogen compounds over the past 20 years. Recently, uranium-element multiple bonds came into the focus, as the nature of such bonds remains unclear and the high reactivity of compounds, containing such bonds, makes their synthesis a challenging task for the preparative chemist.
In this thesis, reactions of the uranium halides in liquid ammonia were investigated. Synthetic requirements and a legal pecularity, specific for Germany, made it necessary to first develop methods for the synthesis of the pure uranium halides, especially free from oxidic impurities, starting from basic materials like oxides, uranium hexafluoride or uranium metal. For the uranium tetrahalides, a metathesis reaction of uranium dioxide and the respective aluminium halide was elaborated, which by an in situ chemical vapor transport reaction leads to products in the form of large crystals. Silicon was found to be a proper reducing agent for these tetrahalides to prepare the uranium trihalides. A chemical transport reaction was used to remove impurities. The common synthesis of UBr5 from the elements was conducted in a flame sealed extraction apparatus for thorough exclusion of air and moisture. The high purity and good crystal quality achieved by these methods enabled the redetermination of the crystal structures of UI3 and UBr4 as well as the discovery of a hitherto unknown modification of uranium pentabromide. Reactions of uranium halides in neutral ammonia resulted in a series of ammine complexes, which crystallized in the form of ammoniates. It was shown that uranium trihalides form nonaammine complexes, [U(NH3)9]3+, while the heavier uranium tetrahalides form decaammine complexes, [U(NH3)10]4+. The
lighter halide ions are stronger Lewis bases and coordinate stronger towards the uranium cation, such that [UCl(NH3)8]3+ and [UF4(NH3)4] were obtained. By increasing the pH value, single steps of the ammonolysis reaction could be observed on the basis of a variety of crystallized complex compounds, starting with
the mononuclear amido complex [U(NH2)(NH3)8]3+, followed by the dinuclear, amide-bridged complex [(NH3)6U(μ-NH2)3U(NH3)6]5+ and higher oligomers,
towards mixed-anionic, complex amide nitrides. The disproportionation of uranium pentahalides in liquid ammonia yielded complexes of a molecular uranium dinitride for the first time outside of an argon matrix in the form of the ammoniate [(NH3)8U(μ-N)(NH3)5U(μ-N)U(NH3)8]Br8·26NH3 and a chloride of similar molecular structure. Additionally, the reactivity of the uranium halides in liquid ammonia was investigated regarding their hydrolysis, redox and ligand exchange reactions, for example with cyanide ions. This resulted in a series of oxido and cyanido complexes. Anhydrous hydrogen cyanide was established as a solvent for the attempted synthesis of uranium cyanides, which enabled the structural characterization of formonitrile complexes of uranium, [UCl4(HCN)4] and [UF4/1F2/2(HCN)2/1], for the first time. All compounds were crystallographically characterized. Infrared and Raman spectroscopy were used supplementary. In some cases, thermal and elemental analyses were applied. The development of an apparatus for opening pressurized glass ampoules under cooling and strict exclusion of moisture and air was crucial for the successful study of the ammonolysis studies. Without this tool, the isolation of the mostly air and temperature sensitive crystals was not possible. For further analyses several pieces of glassware had to be designed, such as tools for the charging of cuvettes for neutron diffraction using schlenk technique, for the condensation of gases into X-ray capillaries and for the preparation of samples for Raman spectroscopy under cooling.
A second field of research covered the fluorides of platinum. An attempt to synthesize a platinum oxidefluoride led to a facile synthesis of O2PtF6 in well crystallized form. For this purpose, a cooling finger for the sublimation in a stream of fluorine was developed. The residue of the fluorination of commercially available platinum oxide hydrate contained Na2PtF6, which was subsequently synthesized in a pure state and crystallized for the elaboration of its crystal structure. Additionally, novel hexafluoridoplatinate(V) salts were synthesized by reactions of O2PtF6 with alkali metal fluorides.
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Created: 2019Issued: 2020-04-06Updated: 2020-04-06
Faculty
Fachbereich Chemie
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Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
Bomb tubeDioxygenylChloridPlatinumAmminkomplexChlorideFluorineDioxygenylFluorIodidAmidBombenrohrNitrideIodideNitridBromidUranBromideAmmineUraniumAmideAmmoniakPlatinAmmonia
DDC-Numbers
540
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Rudel, Stefan Sebastian: Ammonolyse von Uranhalogeniden und Beiträge zur Chemie der Platinfluoride. : Philipps-Universität Marburg 2020-04-06. DOI: https://doi.org/10.17192/z2019.0487.
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This item has been published with the following license: In Copyright