No description available.

Experimentally measuring how ligand modifications affect metal-ligand bonding and electronic structure is an important goal with relevance to diverse fields such as transition metal catalysis and f-element separations. X-ray absorption spectroscopy (XAS) is an excellent technique for investigating structure/function relationships in metal complexes because it can be used to quantify variations in covalent metal-ligand bonding and electronic structure. Here I describe a series of XAS investigations aimed at elucidating how ligand and structural changes affect chemical bonding and properties in transition metal and uranium complexes. The synthesis and characterization of several new classes of f-element complexes are also discussed. Diphosphines are very important ligands in homogeneous catalysis because they can be used to tune reaction rates, the electronic properties of transition metals, and the stereochemistry of catalytic products. P K-edge XAS studies on solid Ni and Pd diphosphine compounds have shown that M-P covalency is not exclusively dependent on the P-M-P angle (i.e. bite angle), which changes as a function of differing linker groups on the diphosphine backbone. Building on these studies, I show how changes in diphosphine bite angle influence Pd-P covalency in solution and when phenyl substituents attached to phosphorus are replaced with alkyl substituents. This work required the development of an improved solid energy calibration standard for routine energy referencing of P K-edge XAS spectra. I discuss the limitations of P K-edge XAS energy standards used previously and propose tetraphenylphosphonium bromide as a new energy calibration standard for future P K-edge XAS work. The use of nuclear power has resulted in critical challenges surrounding the long-term storage and remediation of nuclear waste. Advanced nuclear fuel cycles can address the scientific challenges of nuclear waste, but require the difficult separation of minor actinides and lanthanides. A multi-donor ligand containing a thioether appendage was prepared to determine if it would bind differently to lanthanide and actinide metals, thereby resulting in metal complexes that could be separated due to differing solubilities. In a related study, a new class of homoleptic lanthanide and actinide borohydride complexes called phosphinodiboranates were prepared. I discuss how the differing solution structures of f-element phosphinodiboranates may offer potential for f-element separations. A series of polyoxovanadate alkoxide clusters was synthesized to investigate the underlying electronic properties that make them useful in catalysis and small-molecule activation. The clusters can access four discrete pseudo-reversible one-electron transfer reactions. V K-edge XAS studies were performed to elucidate variations in electronic structure and bonding in the clusters as a function of redox events, and the results indicate that covalency plays a significant role in the one-electron transfer reactions. These results inspired the synthesis and characterization of an actinide polyoxovanadate compound. Activation and functionalization of the oxo bond in UO22+ is important for understanding the fundamental chemistry of uranium and for developing metal separation processes. A novel uranyl polyoxovanadate compound was studied with V K-edge XAS to determine if covalent interactions between the uranium and vanadium metal centers exist (similar to those observed for the polyoxovanadate alkoxide clusters), and if such interactions could be exploited for activation of the oxo bond in the uranyl dication. Results indicate, however, that the U-O bond remains inactivated.

The aim of this work is to predict the influence of phonon modulations (Kozina et al. 2019 [1]) on the x-ray absorption near-edge fine structure of the Ti-L2,3-edge (Yamaguchi et al. 1982 [2], Thole et al. 1985 [3], De Groot 1990 [4]) in cubic SrTiO3. Employing Density Functional Theory in combination with Multiplet Ligand Field Theory (Haverkort et al. 2012 [5], Luder et al. 2017 [6]), previous experimental and theoretical data on the octahedrally symmetric structure are reproduced with good agreement. Phonon modulations with a maximum atomic displacement of 5% of the lattice parameter are shown to cause polarization-dependent changes in the x-ray absorption spectra just within reach of experimental resolution. This is suggested to reflect the strong susceptibility of the electronic structure to collective lattice excitations in SrTiO3.

No description available.

Bi-annual report on the activities at the ROssendorf BeamLine (ROBL) at the ESRF in Grenoble. The report contains selected contributions on actual research topics, a list of all scheduled experiments, and short experimental reports.

No description available.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23286号 / 人博第1001号 / 新制||人||236(附属図書館) / 2020||人博||1001(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 高木 紀明 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20391号 / 工博第4328号 / 新制||工||1671(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 中村 正治, 教授 辻 康之, 教授 小澤 文幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第21433号 / 人博第871号 / 2018||人博||871(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 吉田 寿雄, 准教授 戸﨑 充男 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

Developing highly active and durable oxygen reduction reaction (ORR) catalysts is crucial to reduce the cost of polymer electrolyte fuel cells (PEFCs). To meet those requirements, unsupported Pt-Cu alloy nanochains (aerogels) were synthesized by a simple co-reduction route in aqueous solution and their structure was characterized by X-ray absorption spectroscopy and STEM-EDX. These catalysts exceeded the ORR activity of commercial Pt/C catalysts by more than 100 % in RDE experiments and met the US DOE targets, thereby qualifying as very promising materials. The behavior of Pt-Cu aerogels under PEFC operation conditions was mimicked by acid washing experiments which showed that the Cu content in the alloy phase and ORR activity decrease through this step. Comparing composition, structure and ORR activity for various specimens, the Cu content in the alloy phase was identified as the main descriptor of ORR activity. An almost linear correlation was found between those two parameters and complemented by supporting data from the literature.