R-3 Repository :: Browsing by Author "Whitmire, Kenton H."

Browsing by Author "Whitmire, Kenton H."

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A multi-scale approach to study silicate dissolution: Kinetic Monte Carlo simulations and experimental observations
(2013-08-14) Kurganskaya, Inna; Luttge, Andreas; Dasgupta, Rajdeep; Whitmire, Kenton H.; Sawyer, Dale S.
Dissolution of silicate minerals is an important part of many geological processes taking place on Earth’s surface as well as in the deep crust. Weathering of rocks and soil formation, metasomatic rock alteration by hydrothermal fluids, and diagenetic transformation of sediments are controlled by dissolution reactions. Secondary pore space of natural reservoirs can be significantly altered by dissolution and the subsequent precipitation of clay minerals. As a consequence, the potential storage capacity of natural fuels, carbon dioxide, or radioactive waste, can be affected. In addition, the stability of rocks hosting potentially hazardous materials largely depends on their dissolution rates. The development of computational ab initio and Molecular Dynamics techniques drives the interest to study dissolution reactions at the molecular scale. At the same time, advanced microscopic techniques allow us to study dissolution process at the nm to micron scale and investigate spatio-temporal variations of surface reactivity. The combination of these methods has great potential for tackling fundamental questions of the mechanisms of mineral dissolution. My thesis work presents an integrated multiscale approach to studying the dissolution of silicates. The work consists of three main parts: experimental studies of the dissolving mineral surface at the micron scale, Kinetic Monte Carlo (KMC) simulations at the nanometer scale, and the parametrization of KMC models by ab initio derived activation energies. Muscovite mica and quartz were chosen as template study objects. These two minerals represent “2-dimentional” (phyllosilicates) and 3-dimentional (tectosilicates) crystal structures of silicates as well as “complex” and “simple” chemical bond networks. The first part of my muscovite dissolution studies is based on experimental observations of the reacted surface with vertical scanning interferometry. We quantified the distribution of surface reactivity in terms of surface roughness and mean height levels and also measured the dissolution rate. Additional investigations of the detailed surface structure were done by using atomic force microscopy. KMC simulations of muscovite dissolution constitute the second part of this work. We developed KMC models that simulate the dissolution of mica structures. We varied the number of the basic reaction types in the system and achieved a satisfying match between modeling results and experimental observations. Also, we showed how KMC methods can be used as a tool for testing my hypotheses regarding the role of surface reactions on the overall reaction mechanism. The third part of the work is dedicated to the problems of complexity and parametrization of KMC models. Here, we present four KMC models of quartz dissolution that vary by their complexity level. The capabilities of the models to predict experimentally observed dissolution features were shown for prism, rhombohedral, and pinacoid quartz faces. The simulation results demonstrate the role of the topological state in the recognition of key surface sites. From this study we derived basic dissolution mechanisms for the three faces.
A TiO2/FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution
(American Chemical Society, 2017) Schipper, Desmond E.; Zhao, Zhenhuan; Leitner, Andrew P.; Xie, Lixin; Qin, Fan; Alam, Md Kamrul; Chen, Shuo; Wang, Dezhi; Ren, Zhifeng; Wang, Zhiming; Bao, Jiming; Whitmire, Kenton H.
A variety of catalysts have recently been developed for electrocatalytic oxygen evolution, but very few of them can be readily integrated with semiconducting light absorbers for photoelectrochemical or photocatalytic water splitting. Here, we demonstrate an efficient core/shell photoanode with a highly active oxygen evolution electrocatalyst shell (FeMnP) and semiconductor core (rutile TiO2) for photoelectrochemical oxygen evolution reaction. Metal–organic chemical vapor deposition from a single-source precursor was used to ensure good contact between the FeMnP and the TiO2. The TiO2/FeMnP core/shell photoanode reaches the theoretical photocurrent density for rutile TiO2 of 1.8 mA cm–2 at 1.23 V vs reversible hydrogen electrode under simulated 100 mW cm–2 (1 sun) irradiation. The dramatic enhancement is a result of the synergistic effects of the high oxygen evolution reaction activity of FeMnP (delivering an overpotential of 300 mV with a Tafel slope of 65 mV dec–1 in 1 M KOH) and the conductive interlayer between the surface active sites and semiconductor core which boosts the interfacial charge transfer and photocarrier collection. The facile fabrication of the TiO2/FeMnP core/shell nanorod array photoanode offers a compelling strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.
Advanced transition metal phosphide materials from single-source molecular precursors
(2012) Colson, Adam Caleb; Whitmire, Kenton H.
In this thesis, the feasibility of employing organometallic single-source precursors in the preparation of advanced transition metal pnictide materials such as colloidal nanoparticles and films has been investigated. In particular, the ternary FeMnP phase was targeted as a model for preparing advanced heterobimetallic phosphide materials, and the iron-rich Fe 3 P phase was targeted due to its favorable ferromagnetic properties as well as the fact that the preparation of advanced Fe 3 P materials has been elusive by commonly used methods. Progress towards the synthesis of advanced Fe 2-x Mn x P nanomaterials and films was facilitated by the synthesis of the novel heterobimetallic complexes FeMn(CO) 8 (μ-PR 1 R 2 ) (R 1 = H, R 2 = H or R 1 = H, R 2 = Ph), which contain the relatively rare μ-PH2 and μ-PPhH functionalities. Iron rich Fe 2-x Mn x P nanoparticles were obtained by thermal decomposition of FeMn(CO) 8 (μ-PH 2 ) using solution-based synthetic methods, and empirical evidence suggested that oleic acid was responsible for manganese depletion. Films containing Fe, Mn, and P with the desired stoichiometric ratio of 1:1:1 were prepared using FeMn(CO) 8 (μ-PH 2 ) in a simple low-pressure metal-organic chemical vapor deposition (MOCVD) apparatus. Although the elemental composition of the precursor was conserved in the deposited film material, spectroscopic evidence indicated that the films were not composed of pure-phase FeMnP, but were actually mixtures of crystalline FeMnP and amorphous FeP and Mn x O y . A new method for the preparation of phase-pure ferromagnetic Fe 3 P films on quartz substrates has also been developed. This approach involved the thermal decomposition of the single-source precursors H 2 Fe 3 (CO) 9 PR (R = t Bu or Ph) at 400 °C. The films were deposited using a simple home-built MOCVD apparatus and were characterized using a variety of analytical methods. The films exhibited excellent phase purity, as evidenced by X-ray diffraction, X-ray photoelectron spectroscopy, and field-dependent magnetization measurements, the results of which were all in good agreement with measurements obtained from bulk Fe 3 P. As-deposited Fe 3 P films were found to be amorphous, and little or no magnetic hysteresis was observed in plots of magnetization versus applied field. Annealing the Fe 3 P films at 550 °C resulted in improved crystallinity as well as the observation of magnetic hysteresis.
Aminopolycarboxylate Bismuth(III)-Based Heterometallic Compounds as Single-Source Molecular Precursors for Bi4V2O11 and Bi2CuO4 Mixed Oxides
(American Chemical Society, 2014) Bulimestru, Ion; Shova, Sergiu; Popa, Nelea; Roussel, Pascal; Capet, Frederic; Vannier, Rose-Noelle; Djelal, Nora; Burylo, Laurence; Wignacourt, Jean-Pierre; Gulea, Aurelian; Whitmire, Kenton H.
Five heterometallic complexes of general formula M(L)y{Bi(APC)}2·nH2O [M = VO2+, Cu2+; APC = aminopolycarboxylate, in this work ethylenediaminetetraacetate (edta4–) or 1,2 cyclohexanediaminetetraacetate (cdta4–); L = 2,2′-bipyridine; y = 0, 1, or 2; n = 5–16] have been synthesized. The crystal structures of four of them have been determined from single-crystal X-ray diffraction data. The compounds have been probed as single-source molecular precursors for Bi4V2O11 and Bi2CuO4 mixed oxides. Temperature-controlled X-ray powder diffraction was used to monitor the phase transitions during the thermolysis of the precursors. The influence of the ligand type and intermetallic distances in the precursors, heating rate, and the atmosphere have been investigated. The best candidates to yield pure Bi4V2O11 and Bi2CuO4 are complexes with separations between heterometals of ∼4 Å containing ∼29–30% of carbon. The optimal working conditions under which the precursors can be smoothly converted to the corresponding heterometallic oxides are heating at low rates under air flow. The precursors containing ∼29–30% of carbon yield smaller grains and more homogeneous morphology of the residues than the analogues with lower or higher carbon amount. The advantage of the APC-based molecular precursor method is compared to previously reported procedures to produce bimetallic oxides.
Anionic Bismuth Oxido Clusters with Pendant Silver Cations: Synthesis and Structures of {[Bi4(µ3-O)2(TFA)9Ag(tol)2]2} and {Bi4(µ3-O)2(TFA)10(AgPPh3)2}n
(Wiley, 2017) Andleeb, Sohaila; Donaldson, Samantha L.; Schipper, Desmond E.; Fernandez, Ismael I. Loera; ud Dean, Imtiaz; Whitmire, Kenton H.
Anionic Bismuth-Oxido Carboxylate Clusters with Transition Metal Countercations
(American Chemical Society, 2016) Fernandez, Ismael I. Loera; Donaldson, Samantha L.; Schipper, Desmond E.; Andleeb, Sohaila; Whitmire, Kenton H.
Six new anionic bismuth-oxido clusters containing trifluoroacetate ligands were prepared. These include two new Bi6O8 clusters: [M(NCMe)2(H2O)4]3[Bi6(μ3-O)4(μ3-OH)4(CF3CO2)12] with an octahedral Bi6O4(OH)4 core (M = Ni, 1a; Co, 1b) and four Bi4O2 clusters, {[Co(NCMe)6][Bi4(μ3-O)2(CF3CO2)10]}n (2a), {[Co{HC(MeCO)2(MeCNH)}2][Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2]·2[CF3CO2H]·2[H2O]}n (2b), {[Cu(NCMe)4]2[Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2c), and {[Me4N]2[Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2d). These are among the first bismuth-oxido anionic clusters synthesized, and the first to have transition metal countercations. The Bi6O8 anion in 1a and 1b is a high-symmetry octahedron. Additionally, two of the new Bi4O2 clusters are arranged in 1D polymeric structures via bridging carboxylate ligands. The cation in compound 2c had not been previously characterized and was also observed in the synthesis of [Co{HC(MeCO)2(MeCNH)}2][Bi(NO3)6] (3). The new compounds were characterized using single crystal X-ray crystallography and elemental analysis.
Applications of chalcogen containing iron carbonyl clusters: Examination of self-assembled films and homogeneous carbonylation catalysis of methanol
(2002) Guzman-Jimenez, Ilse Yolanda; Whitmire, Kenton H.
Thin films have been prepared via the solution-phase-self-assembly of organometallic chalcogen-containing cluster compounds onto the surface of gold and characterized. The following anionic complexes were used as thin films precursors: [Fe3(CO)9E]2- and [HFe3(CO)9E]-, where E = S, Se, Te. The films were generated by adsorption from organic solvents (e.g., methanol, acetonitrile, acetone, and dichloromethane) onto evaporated gold and were characterized by ellipsometry, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), X-ray diffraction (XRD), atomic force microscopy (AFM), quartz crystal microbalance (QCM), and X-ray photoelectron spectroscopy (XPS). [Et4N]2[Fe3(CO)9E] catalyzes the carbonylation of methanol to form methyl formate under moderate CO pressures (600--1200 psi) between 50 and 90°C. A detailed kinetic analysis of this system is reported. [Fe3(CO)9E]- selectively carbonylates methanol to methyl formate in a homogeneus reaction which first order dependent in cluster concentration, quasi second order dependent in pressure of CO. The reaction appears to be almost independent of the [OCH 3-]total at values of [OCH3 -]total ≤ 3 x 10-3 M, but at higher concentrations it appears to be first order dependence in [OCH3-]total. This system affords the opportunity to compare the effects of different main group heteroatoms in a homogeneous series.
Bifunctional metal phosphide FeMnP films from single source metal organic chemical vapor deposition for efficient overall water splitting
(Elsevier, 2017) Zhao, Zhenhuan; Schipper, Desmond E.; Leitner, Andrew P.; Thirumalai, Hari; Chen, Jing-Han; Xie, Lixin; Qin, Fan; Alam, Md Kamrul; Grabow, Lars C.; Chen, Shuo; Wang, Dezhi; Ren, Zhifeng; Wang, Zhiming; Whitmire, Kenton H.; Bao, Jiming
Developing stable and efficient bifunctional catalysts for overall water splitting into hydrogen and oxygen is a critical step in the realization of several clean-energy technologies. Here we report a robust and highly active electrocatalyst that is constructed by deposition of the ternary metal phosphide FeMnP onto graphene-protected nickel foam by metal-organic chemical vapor deposition from a single source precursor. FeMnP exhibits high electrocatalytic activity toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Utilizing FeMnP/GNF as both the anode and the cathode for overall water splitting, a current density of 10 mA cm−2 is achieved at a cell voltage of as low as 1.55 V with excellent stability. Complementary density functional theory (DFT) calculations suggest that facets exposing both Fe and Mn sites are necessary to achieve high HER activity. The present work provides a facile strategy for fabricating highly efficient electrocatalysts from earth-abundant materials for overall water splitting.
Catalytic applications of cluster compounds: Synthesis, characterization, catalytic activity and solution dynamics of heavy main group-transition metal carbonyl clusters
(1997) van Hal, Jaap Willem; Whitmire, Kenton H.
Alkylation of the compounds (PPN) $\sb2\lbrack$EFe$\rm\sb3(CO)\sb9\rbrack$ (E = S, Se, Te) was performed using methyl triflate and methyl iodide. The S-cluster yielded the novel compound (PPN) (Fe$\sb3$(CO)$\sb9$SMe), whereas the Se and Te-cluster alkylated at the Fe$\sb3$-base yielding (PPN) (MeFe$\sb3$(CO)$\sb9$E). For comparison, the clusters (PPN) $\sb2\lbrack$HE$\rm\{Fe(CO)\sb4\}\sb3\rbrack$ (E = Sb, As) were alkylated as well. Reaction of the Sb-cluster with MeI yielded (PPN) (MeSb(I)$\rm\{Fe(CO)\sb4\}\rbrack,$ whereas the reaction with EtI yielded (PPN) $\sb2\lbrack$ISb$\rm\{Fe(CO)\sb4\}\sb3\rbrack$ and ethane. The possibility of a radical chain reaction for the latter was ruled out by performing the reaction in the presence of a radical scavenger as well as in the dark. The compounds $\rm\lbrack Cat\rbrack\sb{2-x}\lbrack H\sb{x}M\sb3(CO)\sb9E\rbrack\ (cat=Et\sb4N\sp+,\ PPN\sp+;$ x = 0, 1; M = Fe, Ru; E = S, Se, Te) were shown to mediate the catalytic formation of methyl formate from methanol and CO. The reaction is pseudo first order in catalyst and the initial rate is independent of the pressure. NaAsO$\sb2$ reacts with Mo(CO)$\sb6$ in refluxing methanol or ethanol to form $\rm\lbrack Et\sb4N\rbrack\sb2\lbrack(OC)\sb5MoAsMo\sb3(CO)\sb9(\mu\sb3$-$\rm OR)\sb3Mo(CO)\sb3\rbrack$ (R=Me, Et). The compounds are electron rich, and extended Huckel calculations have shown that the extra electron pair resides in an a$\sb2$ orbital, equally delocalized over three molybdenum atoms. A $\sp{205}$Tl NMR study has been conducted on the following compounds with Tl-transition metal bonds: $\rm Tl\{CO(CO)\sb4\}\sb3,\ \lbrack BnMe\sb3N\rbrack\sb3\lbrack Tl\{Fe(CO)\sb4\}\sb3\rbrack,\ Tl\{M(CO)\sb3Cp\}\sb3$ (M = Cr, Mo, W), TlFp$\sb3,$ Fp = CpFe(CO)$\rm\sb2),\ \lbrack PPN\rbrack\sb2\lbrack Tl\sb2Fe\sb6(CO)\sb{24}\rbrack,\ \lbrack Et\sb4N\rbrack\sb2\lbrack Tl\sb2Fe\sb4(CO)\sb{16}\rbrack,\ \lbrack Et\sb4N\rbrack\lbrack LTl\{Fe(CO)\sb4\}\sb2\rbrack$ (L = bipy, en, phen, tmeda, dien), and $\rm\lbrack Et\sb4N\rbrack\sb4\lbrack Tl\sb4Fe\sb8(CO)\sb{30}\rbrack,$ as well as $\rm TlCo(CO)\sb4.$ The possibility of formation of carbonylate anion adducts was also investigated by $\sp{205}$Tl NMR. This technique was used to probe the dynamic behavior of the Tl-metal cluster complexes in solution, and it was shown that most larger Tl-Fe clusters dissociate into simpler fragments in solution.
Cobalt carbonyl clusters incorporating heavy main-group elements: Structure and reactivity
(1989) Leigh, John Scott; Whitmire, Kenton H.
Treating $\rm SbCl\sb3,\ SnCl\sb4.5H\sb2O,\ or\ Pb(OAc)\sb2.3H\sb2O$ with NaCo(CO)$\sb4$ forms the open complexes $\rm Sb\{Co(CO)\sb4\}\sb3,\ Sn\{Co(CO)\sb4\}\sb4$, and Pb$\rm \{$Co(CO)$\sb4\}\sb4$, respectively. The unstable antimony complex was determined to be Sb$\rm \{Co(CO)\sb4\}\sb3$ by the similarity of its infrared spectrum with that of known $\rm Bi\{Co(CO)\sb4\}\sb3$. Isostructural $\rm Sn\{Co(CO)\sb4\}\sb4$ and $\rm Pb\{Co(CO)\sb4\}\sb4$ were characterized by single crystal X-ray diffraction. Each contains a Group 14 element tetrahedrally surrounded by four trigonal bipyramidal Co(CO)$\sb4$ groups. Heating solutions of $\rm Bi\{Co(CO)\sb4\}\sb3$ forms BiCo$\sb3$(CO)$\sb9$, which contains a closed cobalt triangle capped by a bismuth atom. A bridging carbonyl lies along each Co-Co bond. The thermal decomposition is reversible, and a kinetic study of the carbonylation of BiCo$\sb3$(CO)$\sb9$ indicates this transformation to be first-order with respect to (BiCo$\sb3$(CO)$\sb9$) and P(CO) in n-hexane (500-900 psi, 50-65 C), with an activation energy of 68+/$-$2 kJ.mol$\sp{-1}$. Reducing $\rm Bi\{Co(CO)\sb4\}\sb3\ forms\ \lbrack Bi\{Co(CO)\sb4\}\sb4\rbrack \sp-$. This complex is isostructural to Sn$\rm \{Co(CO)\sb4\}\sb4\ and\ Pb\{Co(CO)\sb4\}\sb4$, but it is not isoelectronic, as the bismuth is a hypervalent 10-electron center. Reducing BiCo$\sb3$(CO)$\sb9$ produces (Bi$\sb2$Co$\sb4$(CO)$\sb{11}$) $\sp-$ and (Co(CO)$\sb4\rbrack \sp-$. Single crystal X-ray analysis (Cp$\sb2$Co$\sp+$ salt) determined the core structure of the bismuth anion to consist of a Bi$\sb2$Co$\sb2$ tetrahedron with Co(CO)$\sb3$ units capping the two Bi$\sb2$Co triangular faces. X-ray analyses of (PPN) (Sb$\sb2$Co$\sb4$(CO)$\sb{11}$) and (PPN) $\sb2$ (Sb$\sb2$Co$\sb4$(CO)$\sb{11}$) showed these complexes to have nearly identical frameworks, which are isostructural and isoelectronic to their bismuth homologues. These complexes are electron rich and do not conform to conventional bonding formalisms. Extended Huckel calculations agree with observed structural changes that upon reduction of the monoanion, the added electron enters an antibonding orbital primarily localized between two cobalt atoms bridged by a carbonyl. Treatment of BiCo$\sb3$(CO)$\sb9$ with PPh$\sb3$ gives $\rm Bi\{Co(CO)\sb3PPh\sb3\}\sb3.$ $\rm Bi\{Co(CO)\sb4\}\sb3, BiCo\sb3(CO)\sb9$, and $\rm Sb\{Co(CO)\sb4\}\sb3$ all react with PhC$\sb2$Ph through an apparent radical mechanism to form Co$\sb2$(CO)$\sb6\{$PhC$\sb2$Ph$\}$ as the only infrared observable product.
Crystal Dissolution Kinetics: Linking Surface Processes at the Solid-Solution Interface over Multiple Length-Scales
(2007) Vinson, Michael David; Luttge, Andreas; Sawyer, Dale S.; Lee, Cin-Ty A.; Whitmire, Kenton H.
This thesis presents a multiple-scale experimental study of mineral dissolution kinetics, utilizing direct measurement of crystal surface morphology in great detail to determine rates and mechanisms acting at the reactive solid-solution interface. The overall approach uses primarily vertical scanning interferometry (VSI) to analyze threedimensional crystal surface morphological change and quantify rates of dissolution. Integration of VSI with atomic force microscopy (AFM), theoretical kinetic models, and thermodynamic calculations has permitted the recognition of rate-controlling processes and mechanisms, thus strengthening our ability to link dissolution kinetics over a broad range of length and time scales. The motivation for this thesis arises from an incomplete understanding of how molecular-scale surface processes, acting at the solid-solution interface, control large-scale natural dissolution phenomena. Mineral dissolution is a fundamental geologic process that exerts control over a number of significant geochemical events which can affect both man and the environment over a broad range of spatial and temporal scales. At the Earth surface, rates of dissolution are largely surface-controlled, and thus influenced by the threedimensional nature of the crystal surface. The goals of this thesis involve improving overall understanding of dissolution rate-scaling issues by investigation of crystal surface dissolution kinetics, identification ofrate-controlling mechanisms. This thesis reports investigations into the dissolution kinetics of calcite, rhyolite and uraninite over a range of far-from-equilibrium laboratory conditions. The results presented within this work demonstrate that: 1. Monomolecular "rough" step retreat controls the overall rate of calcite crystal dissolution, which in turn can be inhibited by impurity adsorption at a level dependent on the physical and chemical properties of the adsorbing impurity and the presence of carbonate in solution. 2. Heterogeneous retreat of volcanic glass phases control overall rhyolite dissolution rate and the steady-sate release of ions into solution, which in turn may be influenced by the formation of a surface reprecipitation phase. 3. Dissolved carbon species influence the steady-state dissolution uraninite, although this dissolution fails to produce resolvable surface-normal retreat. In total, this original work constructs a clearer understanding of the kinetics at the reactive solid-solution interface and reveals how dissolution phenomena can scale across time and space.
Effects of Catalyst Phase on the Hydrogen Evolution Reaction of Water Splitting: Preparation of Phase-Pure Films of FeP, Fe2P, and Fe3P and Their Relative Catalytic Activities
(American Chemical Society, 2018) Schipper, Desmond E.; Zhao, Zhenhuan; Thirumalai, Hari; Leitner, Andrew P.; Donaldson, Samantha L.; Kumar, Arvind; Qin, Fan; Wang, Zhiming; Grabow, Lars C.; Bao, Jiming; Whitmire, Kenton H.
The comparative catalytic activities of iron phosphides, FexP (xﾠ= 1ﾖ3), have been established with phase-pure material grown by chemical vapor deposition (CVD) from single-source organometallic precursors. This is the first report of the preparation of phase-pure thin films of FeP and Fe2P, and their identity was established with scanning-electron microscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction. All materials were deposited on fluorine-doped tin oxide (FTO) for evaluation of their activities toward the hydrogen evolution reaction (HER) of water splitting in 0.5 M H2SO4. HER activity follows the trend Fe3P > Fe2P > FeP, with Fe3P having the lowest overpotential of 49 mV at a current density of 10 mA cmﾖ2. Density functional theory (DFT) calculations are congruent with the observed activity trend with hydrogen binding favoring the iron-rich terminating surfaces of Fe3P and Fe2P over the iron-poor terminating surfaces of FeP. The results present a clear trend of activity with iron-rich phosphide phases outperforming phosphorus rich phases for hydrogen evolution. The films of Fe2P were grown using Fe(CO)4PH3ﾠ(1), while the films of FeP were prepared using either Fe(CO)4PtBuH2ﾠ(2) or the new molecule {Fe(CO)4P(H)tBu}2ﾠ(3) on quartz and FTO. Compoundﾠ3ﾠwas prepared from the reaction of PCl2tBu with a mixture of Na[HFe(CO)4] and Na2[Fe(CO)4] and characterized by single-crystal X-ray diffraction, ESI-MS, elemental analysis, andﾠ31P/1H NMR spectroscopies. Films of Fe3P were prepared as previously described from H2Fe3(CO)9PtBu (4).
Facile one-pot synthesis of triphenylbismuth (V) bis(carboxylate) complexes
(American Chemical Society, 2014) Kumar, Ish; Bhattacharya, Prateek; Whitmire, Kenton H.
Triphenylbismuth(V) bis(carboxylates), Ph3Bi(O2CR)2 (R = 5-Br-2-OH-C6H3- (1), 2-OH-C6H4-(2), 2,6-(OH)2-C6H3- (3); 3-Me-2-NH2-C6H3- (4); Ph- (5) and Me- (6)) were obtained from the reaction of triphenylbismuth with hydrogen peroxide and excess carboxylic acid in wet 2-propanol. The synthesis avoids the use of halogens as oxidants and the products crystallize directly from the solution as pure compounds. They crystallize from solution without further need of purification. The structures of 1 - 5 were confirmed by single crystal X-ray diffraction. Compounds 2 and 5 exhibit a different polymorph than that previously reported in the literature. While all of the Bi(V) compounds adopt a trans-axial trigonal-bipyramidal configuration with the carboxylates in the axial positions, there is considerable variation in the coordination of the carboxylate that ranges from simple monohapto to the mixture of mono- and bidentate chelating bonding modes.
Gold coated iron phosphide core–shell structures
(Royal Society of Chemistry, 2017) Kelly, Anna T.; Filgueira, Carly S.; Schipper, Desmond E.; Halas, Naomi J.; Whitmire, Kenton H.
Core–shell particles Fe2P@Au have been prepared beginning with Fe2P nanorods, nanocrosses and nanobundles prepared from the solvothermal decomposition of H2Fe3(CO)9(μ3-PtBu). Iron phosphide structures can be produced from a single-source organometallic precursor with morphological control by varying the surfactant conditions to yield fiber bundles and dumbbell-shaped bundles ranging from nanometers to microns. Derivatization of the surfaces with γ-aminobutyric acid was used to attach Au nanoparticle seeds to the surface of the Fe2P nanoparticles followed by completion of the Au shell by reduction with formaldehyde or aqueous HAuCl4/CO, with the latter giving somewhat better results. Shell thickness ranged from an incomplete, partially coated Au shell to a thickness of 65 ± 21 nm by varying the amount of gold decorated precursor particles. Increasing the thicknesses of the Au shells produced a redshift in the plasmonic resonance of the resulting structures as was observed previously for FeOx@Au.
High-Performance Hybrid Bismuth–Carbon Nanotube Based Contrast Agent for X-ray CT Imaging
(American Chemical Society, 2017) Hernández-Rivera, Mayra; Kumar, Ish; Cho, Stephen Y.; Cheong, Benjamin Y.; Pulikkathara, Merlyn X.; Moghaddam, Sakineh E.; Whitmire, Kenton H.; Wilson, Lon J.
Carbon nanotubes (CNTs) have been used for a plethora of biomedical applications, including their use as delivery vehicles for drugs, imaging agents, proteins, DNA, and other materials. Here, we describe the synthesis and characterization of a new CNT-based contrast agent (CA) for X-ray computed tomography (CT) imaging. The CA is a hybrid material derived from ultrashort single-walled carbon nanotubes (20–80 nm long, US-tubes) and Bi(III) oxo-salicylate clusters with four Bi(III) ions per cluster (Bi4C). The element bismuth was chosen over iodine, which is the conventional element used for CT CAs in the clinic today due to its high X-ray attenuation capability and its low toxicity, which makes bismuth a more-promising element for new CT CA design. The new CA contains 20% by weight bismuth with no detectable release of bismuth after a 48 h challenge by various biological media at 37 °C, demonstrating the presence of a strong interaction between the two components of the hybrid material. The performance of the new Bi4C@US-tubes solid material as a CT CA has been assessed using a clinical scanner and found to possess an X-ray attenuation ability of >2000 Hounsfield units (HU).
In pursuit of advanced materials from single-source precursors based on metal carbonyls
(Royal Society of Chemistry, 2019) Whitmire, Kenton H.; Schipper, Desmond E.
In this perspective, the development of single-source precursors and their relative advantages over multiple source approaches for the synthesis of metal pnictide solid state materials is explored. Particular efforts in the selective production of iron phosphide materials for catalytic applications are discussed, especially directed towards the hydrogen evolution and oxygen evolution reactions of water splitting.
Iron carbonyl clusters with ECl2 units (E = P, As)
(Elsevier, 2017) Schipper, Desmond E.; Chen, Jing-Han; Whitmire, Kenton H.
Reaction of [PPN][HFe(CO)4] (PPN = bis(triphenylphosphine)iminium) with PCl3 in a 1:1 ratio produced small amounts of [PPN][P{Fe(CO)4}2Cl2] ([PPN][Ia]). Reaction of [Et4N][HFe(CO)4] with AsCl3 in a 1:0.75 ratio in THF at −78 °C produced [Et4N][As{Fe(CO)4}2Cl2] ([PPN][Ib]) as the majority product. The compound [PPN][(CO)4FePCl2O] ([PPN][II]) was obtained from the reaction of Fe2(CO)9 with PCl3 in THF. In contrast, [Et4N][HFe(CO)4] reacted with PCl3 at −78 °C in a 2:1 ratio to yield [Et4N][Fe2(CO)6{(μ4-PFe(CO)4)2(μ-CO)}{μ-PCl2}] ([Et4N][III]) as the majority product. The compounds were characterized spectroscopically and by single-crystal X-ray diffraction analyses.
New Main-Group-Element-Rich nido-Octahedral Cluster System: Synthesis and Characterization of [Et4N][Fe2(CO)6(μ3-As){μ3-EFe(CO)4}2]
(American Chemical Society, 2016) Schipper, Desmond E.; Ikhlef, Djamila; Khalal, Samila; Saillard, Jean-Yves; Whitmire, Kenton H.
A series of clusters of the form [Et4N][Fe2(CO)6(μ3-As)}(μ3-EFe(CO)4)], where E is either P or As, were synthesized from [Et4N]2[HAs{Fe(CO)4}3] and ECl3. AsCl3 gives the As-only compound; PCl3 produces compounds having two As atoms with one P atom, or one As atom and two P atoms, and they can exist as two possible isomers, one of which is chiral. The As2P and AsP2clusters cocrystallize, and their structure as determined by single-crystal X-ray diffraction is given along with the structure of the As-only cluster. Analytical data as well as density functional theory calculations support the formation and geometries of the new molecules.
Rock Salt vs. Wurtzite Phases of Co1-xMnxO: Control of Crystal Lattice and Morphology at the Nanoscale
(2013-07-24) Walsh, Sean; Whitmire, Kenton H.; Wilson, Lon J.; Wong, Michael S.
Diamond cuboid-, rhombohedron- and hexagon-shaped nanocrystals as well as branched rods of the solid solution Co1-xMnxO have been synthesized via a solvothermal synthetic route from manganese formate and cobalt acetate at elevated temperature. Rhombohedra and hexagons have dimensions no larger than 50 nm on the longest axis, rods have branches up to 150 nm long and cuboids grow up to 250 nm on a side. X-ray and electron diffraction and transmission electron microscopy analyses show that these nanoparticles are single crystals of wurtzite-type and rock salt-type Co1-xMnxO. Varying the surfactant, water and precursor ratios allows control of particle size, morphology and stoichiometry. Extending growth time at high temperatures (>370°C) leads to the disappearance of the wurtzite phase due to Ostwald ripening. Longer reaction times at temperatures between 345-365°C lead to more crystalline wurtzite-lattice particles. These results show that nanoparticle morphologies and crystal lattices arise from crystal growth and Ostwald ripening at different rates selecting for either small, smooth-surfaced wurtzite lattice particles or large, dendritically-grown rock salt lattice particles.
Structural chemistry of fluoride and oxofluoride complexes of titanium(IV)
(Elsevier, 2015) Davidovich, Ruven L.; Marinin, Dmitry V.; Stavila, Vitalie; Whitmire, Kenton H.
The crystal structures of 119 fluoride and oxofluoride complexes of titanium(IV) (88 fluoride and 31 oxofluoride compounds) published to date have been analyzed and reviewed. Depending on the degree and nature of the association of structural units, the analyzed structures can be divided into monomeric, dimeric, oligomeric, and polymeric, including chain and layered polymeric structures. The manuscript describes the occurrence of various structural motifs, the coordination and geometry of complex anions and cations, as well as the driving forces behind supramolecular crystal assembly. A comprehensive table is compiled to provide details about composition, values of terminal and bridging TiF and TiO bonds, as well as the corresponding references. A table of crystallographic data for the investigated fluoride and oxofluoride complexes of titanium(IV) is presented in the Appendix.

Browsing by Author "Whitmire, Kenton H."

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