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  Partner: UNT Libraries
 Decade: 2010-2019
 Degree Discipline: Chemistry
 Collection: UNT Theses and Dissertations
Applications of Single Reference Methods to Multi-Reference Problems

Applications of Single Reference Methods to Multi-Reference Problems

Date: May 2015
Creator: Jeffrey, Chris C.
Description: Density functional theory is an efficient and useful method of solving single-reference computational chemistry problems, however it struggles with multi-reference systems. Modifications have been developed in order to improve the capabilities of density functional theory. In this work, density functional theory has been successfully applied to solve multi-reference systems with large amounts of non-dynamical correlation by use of modifications. It has also been successfully applied for geometry optimizations for lanthanide trifluorides.
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Characterization of Ionic Liquid As a Charge Carrier for the Detection of Neutral Organometallic Complexes Using Electrospray Ionization Mass Spectrometry

Characterization of Ionic Liquid As a Charge Carrier for the Detection of Neutral Organometallic Complexes Using Electrospray Ionization Mass Spectrometry

Date: August 2012
Creator: Joshi, Ubisha
Description: A novel application of ionic liquid as a charge carrier for the analysis and detection of neutral organometallic complexes using a mass spectrometer has been presented. The mass spectrometer detects only charged compounds which raise a difficulty in analyzing a neutral molecule that lacks a basic site to associate with charge. Therefore, an effective way of providing charge has always been an area of keen interest in the field of mass spectrometry. Ionic liquids have a very fascinating property of forming a cation-? interaction with other molecules to give a charged complex. In order to take advantage of this, it is important to know the geometric structure of the complex. Advanced methodologies like hydrogen-deuterium exchange and computational calculations have been used assisting in better understanding of the structure of the ionic liquid complexes.
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Computational Studies of C–h/c–c Manipulation Utilizing Transition Metal Complexes

Computational Studies of C–h/c–c Manipulation Utilizing Transition Metal Complexes

Date: May 2015
Creator: Pardue, Daniel B.
Description: 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. ...
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Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Date: May 2010
Creator: Pierpont, Aaron
Description: Methane and dinitrogen are abundant precursors to numerous valuable chemicals such as methanol and ammonia, respectively. However, given the robustness of these substrates, catalytically circumventing the high temperatures and pressures required for such transformations has been a challenging task for chemists. In this work, computational studies of various transition metal catalysts for methane C-H activation and N2 activation have been carried out. For methane C-H activation, catalysts of the form LnM=E are studied, where Ln is the supporting ligand (dihydrophosphinoethane or β-diketiminate), E the activating ligand (O, NCH3, NCF3) at which C-H activation takes place, and M the late transition metal (Fe,Co,Ni,Cu). A hydrogen atom abstraction (HAA) / radical rebound (RR) mechanism is assumed for methane functionalization (CH4 à CH3EH). Since the best energetics are found for (β-diket)Ni=O and (β-diket)Cu=O catalysts, with or without CF3 substituents around the supporting ligand periphery, complete methane-to-methanol cycles were studied for such systems, for which N2O was used as oxygen atom transfer (OAT) reagent. Both monometallic and bimetallic OAT pathways are addressed. Monometallic Fe-N2 complexes of various supporting ligands (LnFe-N2) are studied at the beginning of the N2 activation chapter, where the effect of ligand on N2 activation in end-on vs. side-on N2 isomers ...
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Effect of Fluorine and Hydrogen Radical Species on Modified Oxidized Ni(pt)si

Effect of Fluorine and Hydrogen Radical Species on Modified Oxidized Ni(pt)si

Date: May 2010
Creator: Gaddam, Sneha Sen
Description: NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NFx+F and NHx+H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the ...
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Investigating Molecular Structures: Rapidly Examining Molecular Fingerprints Through Fast Passage Broadband Fourier Transform Microwave Spectroscopy

Investigating Molecular Structures: Rapidly Examining Molecular Fingerprints Through Fast Passage Broadband Fourier Transform Microwave Spectroscopy

Date: May 2011
Creator: Grubbs, Garry Smith, II
Description: Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of Molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ≤1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation o, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (≤10 s) than the molecular relaxation (≈100 s). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, ...
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Kinetic Investigation of the Gas Phase Atomic Sulfur and Nitrogen Dioxide Reaction

Kinetic Investigation of the Gas Phase Atomic Sulfur and Nitrogen Dioxide Reaction

Date: May 2011
Creator: Thompson, Kristopher Michael
Description: The kinetics of the reaction of atomic sulfur and nitrogen dioxide have been investigated over the temperature range 298 to 650 K and pressures from 14 - 405 mbar using the laser flash photolysis - resonance fluorescence technique. The overall bimolecular rate expression k (T) = (1.88 ± 0.49) x10-11 exp-(4.14 ± 0.10 kJ mol-1)/RT cm3 molecule-1 s-1 is derived. Ab initio calculations were performed at the CCSD(T)/CBS level of theory and a potential energy surface has been derived. RRKM theory calculations were performed on the system. It is found that an initially formed SNO2 is vibrationally excited and the rate of collisional stabilization is slower than the rate of dissociation to SO + NO products by a factor of 100 - 1000, under the experimental conditions.
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Microwave-Assisted Synthesis, Characterization, and Photophysical Properties of New Rhenium(I) Pyrazolyl-Triazine Complexes

Microwave-Assisted Synthesis, Characterization, and Photophysical Properties of New Rhenium(I) Pyrazolyl-Triazine Complexes

Date: May 2010
Creator: Salazar Garza, Gustavo Adolfo
Description: The reaction of the chelating ligand 4-[4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazin-2-yl]-N,N-diethyl-benzenamine, L, with pentacarbonylchlororhenium by conventional heating method produces the complexes fac-[ReL(CO)3Cl2] and fac-[Re2L(CO)6Cl2] in a period of 48 hours. The use of microwaves as the source of heat and the increase in the equivalents of one of the reactants leads to a more selective reaction and also decreases the reaction time to 1 hour. After proper purification, the photophysical properties of fac-[ReL(CO)3Cl] were analyzed. The solid-state photoluminescence analysis showed an emission band at 628 nm independent of temperature. However, in the solution studies, the emission band shifted from 550 nm in frozen media to 610 nm when the matrix became fluid. These results confirm that this complex possess a phenomenon known as rigidochromism.
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The Pure Rotational Spectra of Diatomics and Halogen-Addition Benzene Measured by Microwave and Radio Frequency Spectrometers

The Pure Rotational Spectra of Diatomics and Halogen-Addition Benzene Measured by Microwave and Radio Frequency Spectrometers

Date: August 2010
Creator: Etchison, Kerry C.
Description: Two aluminum spherical mirrors with radii of 203.2 mm and radii of curvature also of 203.2 mm have been used to construct a tunable Fabry-Perót type resonator operational at frequencies as low as 500 MHz. The resonator has been incorporated into a pulsed nozzle, Fourier transform, Balle-Flygare spectrometer. The spectrometer is of use in recording low J transitions of large asymmetric molecules where the spectra are often greatly simplified compared to higher frequency regions. The resonators use is illustrated by recording the rotational spectra of bromobenzene and iodobenzene. In related experiments, using similar equipment, the pure rotational spectra of four isotopomers of SrS and all three naturally occurring isotopomers of the actinide-containing compound thorium monoxide have been recorded between 6 and 26 GHz. The data have been thoroughly analyzed to produce information pertaining to bond lengths and electronic structures.
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Rational Design of Metal-organic Electronic Devices: a Computational Perspective

Rational Design of Metal-organic Electronic Devices: a Computational Perspective

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Date: December 2012
Creator: Chilukuri, Bhaskar
Description: Organic and organometallic electronic materials continue to attract considerable attention among researchers due to their cost effectiveness, high flexibility, low temperature processing conditions and the continuous emergence of new semiconducting materials with tailored electronic properties. In addition, organic semiconductors can be used in a variety of important technological devices such as solar cells, field-effect transistors (FETs), flash memory, radio frequency identification (RFID) tags, light emitting diodes (LEDs), etc. However, organic materials have thus far not achieved the reliability and carrier mobility obtainable with inorganic silicon-based devices. Hence, there is a need for finding alternative electronic materials other than organic semiconductors to overcome the problems of inferior stability and performance. In this dissertation, I research the development of new transition metal based electronic materials which due to the presence of metal-metal, metal-?, and ?-? interactions may give rise to superior electronic and chemical properties versus their organic counterparts. Specifically, I performed computational modeling studies on platinum based charge transfer complexes and d10 cyclo-[M(?-L)]3 trimers (M = Ag, Au and L = monoanionic bidentate bridging (C/N~C/N) ligand). The research done is aimed to guide experimental chemists to make rational choices of metals, ligands, substituents in synthesizing novel organometallic electronic materials. Furthermore, the ...
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