UA cloudflare authentication

Browsing by Author "Mikulas, Tanya C."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Boron-Substituted 1,3-Dihydro-1,3-azaborines: Synthesis, Structure, and Evaluation of Aromaticity
    (Wiley-VCH, 2013) Xu, Senmiao; Mikulas, Tanya C.; Zakharov, Lev N.; Dixon, David A.; Liu, Shih-Yuan; University of Oregon; University of Alabama Tuscaloosa
  • Thumbnail Image
    Item
    Electronic structure investigations of titanium oxide nanoclusters, boron-nitrogen heterocycles, and reaction products of lanthanides with oxygen difluoride and lanthanides with water
    (University of Alabama Libraries, 2015) Mikulas, Tanya C.; Dixon, David A.; University of Alabama Tuscaloosa
    Advanced electronic structure methods on high performance computers have been used to predict the reactions of lanthanides, properties of liquid chemical hydrogen storage systems, and Fe doped TiO2 nanoclusters. Chapter 2 describes a detailed experimental matrix isolation and computational study of the reactions of lanthanide atoms with F2O. The experimental data is analyzed in terms of the results of density functional theory and CCSD(T) calculations. The products OlnF and OLnF2 are observed, with most Ln in the +III oxidation state for both products. The bonding in these molecules is strongly dependent on the oxidation state of the lanthanide. The coupling of the spin on the O with that on the Ln is important in determining the Ln-O frequency. Chapter 3 describes the reactions of the lanthanides with H2O. The dominant products are LnO + H2 and HLnOH with the Ln in the +II oxidation state. The difference in the reactions of F2O and H2O are due to the differences in the reactant and product bond strengths. Chapter 4 describes combined experimental and computational studies of the liquid chemical hydrogen storage systems based on substituting a C-C with a B-N. Experimental structural analysis and high level electronic structure calculations suggest that the aromaticity of the 1,3-dihydro-1,3-azaborine heterocycle is intermediate between that of benzene and that of 1,2-dihydro-1,2-azaborine. The development of the first reported parental BN isostere of cyclohexane featuring two BN units is thermally stable up to 150 °C with a H2 storage capacity of 4.7 weight% is described. High level computations have been used to predict the reaction energetics of the formation of two cage compounds from the H2 desorption reactions. The photophysical properties resulting from BN/CC isosterism for 10 1,2-azaborine-based BN isosteres of stilbenes have been explained by using high level electronic structure calculations. Chapter 5 describes computational and experimental evidence for facile charge transfer from the transition metal ion Fe(II) to titanium sites in nanoscale TiO2 and its oxynitride, TiO2-xNx. The transfer has been characterized through core level and valance band photoelectron spectroscopies and detailed electronic structure calculations.
  • Thumbnail Image
    Item
    The Synthesis, Characterization and Dehydrogenation of Sigma-Complexes of BN-Cyclohexanes
    (Wiley-VCH, 2016) Kumar, Amit; Ishibashi, Jacob S. A.; Hooper, Thomas N.; Mikulas, Tanya C.; Dixon, David A.; Liu, Shih-Yuan; Weller, Andrew S.; University of Oxford; Boston College; University of Alabama Tuscaloosa
    The coordination chemistry of the 1,2-BN-cyclohexanes 2,2-R-2-1,2-B,N-C4H10 (R-2=HH, MeH, Me-2) with Ir and Rh metal fragments has been studied. This led to the solution (NMR spectroscopy) and solid-state (X-ray diffraction) characterization of [Ir(PCy3)(2)(H)(2)(eta(2)eta(2)-H2BNR2C4H8)][BAr4F] (NR2=NH2, NMeH) and [Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(eta(2)eta(2)-H2BNR2C4H8)][ BAr4F] (NR2=NH2, NMeH, NMe2). For NR2=NH2 subsequent metal-promoted, dehydrocoupling shows the eventual formation of the cyclic tricyclic borazine [BNC4H8](3), via amino-borane and, tentatively characterized using DFT/GIAO chemical shift calculations, cycloborazane intermediates. For NR2=NMeH the final product is the cyclic amino-borane HBNMeC4H8. The mechanism of dehydrogenation of 2,2-H,Me-1,2-B,N-C4H10 using the {Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))}+ catalyst has been probed. Catalytic experiments indicate the rapid formation of a dimeric species, [Rh-2(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(2)H-5][BAr4F]. Using the initial rate method starting from this dimer, a first-order relationship to [amine-borane], but half-order to [Rh] is established, which is suggested to be due to a rapid dimer-monomer equilibrium operating.