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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Structural and thermogravimetric studies of alkali metal amides and imides

Lowton, Rebecca L. January 1999 (has links)
This work presents an in-depth study of the crystal structures and hydrogen sorption potential of the Li - N - H and Li - Na - N - H systems. The structures of the materials have been studied using X-ray and neutron diffraction, Raman spectroscopy and inelastic neutron scattering. The behavior of the materials during heating was studied using variable temperature X-ray diffraction, intelligent gravimetric analysis in conjunction with neutron diffraction, intelligent gravimetric analysis combined with mass spectrometry and differential scanning calorimetry. The role of cation disorder in the Li - N - H (D) system has been explored, indicating that crystallographic ordering of the Li<sup>+</sup> ions within lithium amide and lithium imide significantly affects the hydrogen sorption properties of the materials. Order-disorder transitions were observed both during hydrogen desorption from ordered LiNH<sub>2</sub> and during deuterium adsorption on ordered Li<sub>2</sub>ND. Such transitions were not observed in disordered samples of the materials. The intrinsic disorder and the stoichiometry of Li - N - H(D) materials was shown to depend strongly on the techniques used during their synthesis. Studies regarding the synthesis, crystal chemistry and decomposition properties of the mixed Li / Na amides are presented. Two distinct mixed Li / Na amides of formulae Li<sub>3</sub>Na(NH<sub>2</sub>)<sub>4</sub> and LiNa<sub>2</sub>(NH<sub>2</sub>)<sub>3</sub> were observed in the LiNH<sub>2</sub> / NaNH<sub>2</sub> phase space. Na was also seen to be soluble in LiNH<sub>2</sub>, forming sodium-doped LiNH<sub>2</sub> . Li<sub>3</sub>Na(NH<sub>2</sub>)<sub>4</sub> and Na-doped LiNH<sub>2</sub> were found to exhibit significant cation non-stoichiometry, whereas LiNa<sub>2</sub>(NH<sub>2</sub>)<sub>4</sub> was shown to exist as a line phase material. Thermogravimetric and calorimetric studies of the mixed Li / Na amides suggested that these materials decompose primarily with loss of H<sub>2</sub>.
2

Computational Studies of C–H/C–C Manipulation Utilizing Transition Metal Complexes

Pardue, Daniel B. 05 1900 (has links)
Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. Finally, the amination and aziridination of C–H and C=C bonds, respectively, by a CuI reagent was studied. The mechanism was investigated using DFT calculations. Presently, these mechanisms involving the use of coinage metals are debated. Our DFT simulations shed some insight into how these transformations occur and ultimately how they can be manipulated.

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