Browsing by Subject "organometallics"
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Item Atomistic Simulations of Bonding, Thermodynamics, and Surface Passivation in Nanoscale Solid Propellant Materials(2012-10-19) Williams, KristenEngineering new solid propellant materials requires optimization of several factors, to include energy density, burn rate, sensitivity, and environmental impact. Equally important is the need for materials that will maintain their mechanical properties and thermal stability during long periods of storage. The nanoscale materials considered in this dissertation are proposed metal additives that may enhance energy density and improve combustion in a composite rocket motor. Density Functional Theory methods are used to determine cluster geometries, bond strengths, and energy densities. The ground-state geometries and electron affinities (EAs) for MnxO?: x = 3, 4, y = 1, 2 clusters were calculated with GGA, and estimates for the vertical detachment energies compare well with experimental results. It was found that the presence of oxygen influences the overall cluster moment and spin configuration, stabilizing ferrimagnetic and antiferromagnetic isomers. The calculated EAs range from 1.29-1.84 eV, which is considerably lower than the 3.0-5.0 eV EAs characteristic of current propellant oxidizers. Their use as solid propellant additives is limited. The structures and bonding of a range of Al-cyclopentadienyl cluster compounds were studied with multilayer quantum mechanics/molecular mechanics (QM:MM) methods. The organometallic Al-ligand bonds are generally 55-85 kcal/mol and are much stronger than Al-Al interactions. This suggests that thermal decomposition in these clusters will proceed via the loss of surface metal-ligand units. The energy density of the large clusters is calculated to be nearly 60% that of pure aluminum. These organometallic cluster systems may provide a route to extremely rapid Al combustion in solid rocket motors. Lastly, the properties of COOH-terminated passivating agents were modeled with the GPW method. It is confirmed that fluorinated polymers bind to both Al(111) and Al(100) at two Al surface sites. The oligomers HCOOH, CH3CH2COOH, and CF3CF2COOH chemisorb onto Al(111) with adsorption energies of 10-45 kcal/mol. The preferred contact angle for the organic chains is 65-85 degrees, and adsorption energy weakens slightly with increasing chain length. Despite their relatively weak adsorption energies, fluorinated polymers have elevated melting temperatures, making them good passivation materials for micron-scale Al fuel particles.Item Designing phase selective soluble polymers for applications in organic chemistry(Texas A&M University, 2004-09-30) Li, ChunmeiSoluble polymers as supports are gaining more attention now. Developing new polymers, new reagents and catalysts, new separation systems are thus of great interest as these sorts of materials' applications in synthesis and catalysis increase. The work described in the succeeding chapters describes my efforts to synthesize new catalysts that can be attached to polymer supports, to study their catalytic activity and to study separation efficiency. Most of the work focus is on polyacrylamide polymers. Both organometallic catalysts and organic catalysts have been studied. Liquid/liquid separation was the technique mainly investigated. In addition, a new separation scheme called latent biphasic system which is a new liquid/liquid separation method is described. Finally, studies with the Cremer group where the LCST behavior of polyacrylamides was studied using dark field methods are also discussed.Item Synthesis and Characterization of Novel Pincer Ligands and Triarylaminium Oxidants(2014-12-15) Davidson, Jillian JordanDiarylamido-based tridentate pincer ligands have become an important archetype in transition-metal chemistry and their reactivity has been widely explored. The diarylamido backbone offers rigidity and can be easily tuned to change the steric and electronic properties of the ligand. Motivated by previous successes, efforts were made to expand the scope of pincer ligands developed within the Ozerov group, which historically have been limited to C2V symmetric ligands bearing either two phosphine donor arms or two imine donor arms. New ligands synthesized for this purpose include CS symmetric ligands PNP and PNN ligands. In an effort to categorize pincer ligands commonly employed in the Ozerov group we set out to compare the redox properties of the ligands and their donor ability towards a metal center. This was a two part endeavor where we (a) obtained cyclic voltammograms for (pincer)MCl compounds of Group 10 metals and (b) measured the IR stretching frequencies of (pincer)RhCO compounds. Our underlying assumptions were that the cyclic voltammograms report on how easy it is to oxidize the ligand (approximates the electron-richness of the ligand) and that the IR stretching frequencies give insight into the ?electron-richness? of the metal center (a reflection on the basicity of the pincer ligand). The results of this study suggest that changes to the ligand framework directly affect the level of conjugation and in turn affect the redox potentials and the ?(CO) values in a nearly linear fashion. The more electron-rich a ligand is, (due to direct conjugation from donor substituents on the diarylamido-backbone and from the influence of the donor arms) the more readily it is oxidized and the stronger donor it becomes. Chemical oxidations have become a rising field of interest. Triarylaminium oxidants are advantageous since they boast modest oxidation potentials and generate chemically neutral amines upon reduction. Our goal was to expand the scope of triarylaminium oxidants bearing non-coordinating carborane anions. A series of oxidizing triarylaminium radical cations were synthesized and isolated as [NAr3]^+[CRB11Cl11]^? salts (R = H, CH3). These salts were prepared by treatment of a neutral amine, Me3SiX (X = OTf, Cl), and Na[CRB11Cl11] (R = H, CH3) with half an equivalent of PhI(OAc)2.