Theses and Dissertations at Montana State University (MSU)
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Item Multi-edge X-ray absorption near-edge spectroscopic analysis of palladium complexes in II, III and IV oxidation states(Montana State University - Bozeman, College of Letters & Science, 2013) Barton, Rhonda Lee Hoffert; Chairperson, Graduate Committee: Robert K. SzilagyiPalladium-based complexes have profoundly impact on the synthetic tools of organic chemists due to their importance as catalysts in a myriad of chemical transformations. Palladium in the 0, II, III and IV oxidation states have all been experimentally observed to have catalytic activity in carbon-carbon bond coupling reactions. A common organometallic research aim is to improve catalytic activity of these complexes by designing and optimizing new ligand systems to access more difficult transformations. In order to understand the electronic effects that ligand systems have on reactivity, X-ray absorption spectroscopy is used to characterize the electronic structure of the ligand and metal components of pre-catalysts and palladium model complexes. The multi-edge X-ray absorption near-edge absorption spectroscopic technique (XANES) is an element specific technique that excites core electrons of the 1s (K-edge) and 2p (L-edge) orbitals to frontier unoccupied molecular orbitals, providing a ground state picture of a complex's ligand and metal electronic structure. This thisis will describe a comparative analysis between homoleptic chloropalladium complexes and interesting heteroleptic palladium based complexes of II, III and IV oxidation states to understand the stabilizing effects of a unique ligand environment. Furthermore, it will emphasize the benefits of using multi-edge XANES technique in rationalized catalyst design.Item Development of the molecular level descripton for nickel(II)-based ligand-exchange thermochromism(Montana State University - Bozeman, College of Letters & Science, 2014) Queen, Matthew Scott; Co-chairpersons, Graduate Committee: Patrick R. Callis and Robert K. Szilagyi; Bradley D. Towey, Kevin A. Murray, Brad S. Veldkamp, Harlan J. Byker and Robert K. Szilagyi were co-authors of the article, 'Electronic structure of [Ni(II)S 4] complexes from S K-edge X-ray absorption spectroscopy' in the journal 'Coordination chemistry reviews' which is contained within this thesis.; Farideh Jalilehvand and Robert K. Szilagyi were co-authors of the article, 'Electronic structure of Ni(II), Co(II), and Zn(II) thiourea complexes from sulfur K-edge X-ray absorption spectroscopy' submitted to the journal 'Canadian journal of chemistry' which is contained within this thesis.Coordination compound-based nickel(II) thermochromic systems rely on a temperature-dependent equilibrium shift between different coordination environments of the central nickel ion. These systems are found in thermochromic "smart windows" that tint reversibly in response to temperature increases in their environment providing the benefit of energy savings in commercial and private buildings. Despite the stoichiometrically simple equilibrium for these ligand exchange systems, there is a complex and delicate network of chemical interactions that determine the color, and thermodynamic performance. Accurate computational modeling of nickel(II) ligand exchange thermochromic systems is an important first step in the direction of understanding the parameter space that determines whether a given metal ligand system is thermochromic, the color of the high and low temperature species, the temperature at which the system will change color. The research presented in this dissertation uses experimental results to evaluate theoretical models. Core and valence electronic spectroscopies probe the ground and excited state electronic structures of high temperature nickel(II) thermochromic chromophores which range from the very covalent nickel tetrathiocyclotetradecane thiocrownether to the highly ionic nickel dibromodi(1-pentylbenzimidazole)nickel(II). The experimental electronic structures of these high temperature species combined with experimental ligand exchange thermodynamics are used to guide the evaluation of computational modeling methods in search of methods that reproduces the experimental observables. It is found that commercially relevant nickel(II) thermochromism takes place on an extremely flat potential energy surface governed by ion pairing, hydrogen bonding and dispersion interactions. The modeling of these surfaces requires the explicit consideration of ion pairing and solvent-solute interactions.