A5006857139- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Metal-Catalyzed Oxygenation Mechanisms
- Magnetism in coordination complexes
- Crystallography and molecular interactions
- Organometallic Complex Synthesis and Catalysis
- Metalloenzymes and iron-sulfur proteins
- Metal complexes synthesis and properties
- CO2 Reduction Techniques and Catalysts
- Photosynthetic Processes and Mechanisms
- Hemoglobin structure and function
- Porphyrin and Phthalocyanine Chemistry
- Microbial Fuel Cells and Bioremediation
- Inorganic Fluorides and Related Compounds
- Metal-Organic Frameworks: Synthesis and Applications
- Electrocatalysts for Energy Conversion
- Ammonia Synthesis and Nitrogen Reduction
- X-ray Spectroscopy and Fluorescence Analysis
- Lanthanide and Transition Metal Complexes
- Wastewater Treatment and Nitrogen Removal
- Microbial Community Ecology and Physiology
- Nitric Oxide and Endothelin Effects
- Catalytic Cross-Coupling Reactions
- Inorganic Chemistry and Materials
- Catalytic C–H Functionalization Methods
Cornell University
2016-2025
Ithaca College
2015-2020
Stanford University
2020
SLAC National Accelerator Laboratory
2020
Stanford Synchrotron Radiation Lightsource
2020
University of Hawaii System
2020
Weatherford College
2018
California Institute of Technology
2008-2012
Pomona College
2005
A central light atom in a cofactor at the nitrogenase active site is identified as carbon.
Significance The enzymatic reactions that occur during nitrification are nature’s means to use ammonia as cellular fuel. Complete understanding of and related processes vital sustainable agriculture renewable energy technologies. prevailing view the first phase is oxidizing bacteria two enzymes, monooxygenase hydroxylamine oxidoreductase, oxidize nitrite via an obligate intermediate. Our work reveals nitric oxide additional presented findings necessitate revision a key biogeochemical...
Seventeen Cu complexes with formal oxidation states ranging from CuI to CuIII are investigated through the use of multiedge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Analysis reveals that metal–ligand bonding in high-valent, formally species is extremely covalent, resulting K-edge L2,3-edge spectra whose features have energies complicate physical state assignment. Covalency analysis data all significantly diminished d-character their lowest...
Significance Nitrous oxide (N 2 O) is a potent ozone-depleting greenhouse gas. This work identifies means by which N O generated during nitrification, or biological ammonia oxidation. Fertilizer use in agriculture stimulates thus increasing the volume of emissions worldwide. The results presented herein will inform models and strategies toward optimized, sustainable agriculture. Moreover, these highlight rare example N–N bond formation.
Catching a copper nitrene Nitrogen typically forms three bonds in its stable compounds. If only one bond is available, the resultant electron-deficient can react rapidly with hydrocarbons to fill out valence shell. Metal-stabilized nitrenes have been widely implicated carbon-nitrogen bond-forming reactions, but putative intermediates rarely synthesized directly. Carsch et al. now report preparation of complex from an azide precursor. X-ray absorption and diffraction studies support triplet...
We report a mild and efficient electrochemical protocol to access variety of vicinally C–O C–N difunctionalized compounds from simple alkenes. Detailed mechanistic studies revealed distinct reaction pathway those previously reported for TEMPO-mediated reactions. In this mechanism, electrochemically generated oxoammonium ion facilitates the formation azidyl radical via charge-transfer complex with azide, TEMPO–N3. DFT calculations together spectroscopic characterization provided tentative...
A multitude of organic transformations catalyzed by dirhodium(II) (Rh2) complexes are thought to proceed via the intermediacy highly reactive, electrophilic carbenoid intermediates that have eluded direct observation. Herein, we report generation a metastable Rh2-carbenoid intermediate supported donor-acceptor carbene fragment. This is stable for period ~20 hours in chloroform solution at 0°C, allowing an exploration its physical and chemical properties. The Rh=C bond, characterized...
Femto- to picosecond excited-state dynamics of the complexes [Re(L)(CO)(3)(N,N)](n) (N,N = bpy, phen, 4,7-dimethyl-phen (dmp); L Cl, n 0; imidazole, 1+) were investigated using fluorescence up-conversion, transient absorption in 650-285 nm range (using broad-band UV probe pulses around 300 nm) and time-resolved IR (TRIR) spectroscopy region CO stretching vibrations. Optically populated singlet charge-transfer (CT) state(s) undergo femtosecond intersystem crossing at least two hot triplet...
The molecular and electronic structures of the four members, [Cr(tpy)2](PF6)n (n = 3–0; complexes 1–4; tpy 2,2′:6′,2″-terpyridine), electron transfer series [Cr(tpy)2]n+ have been determined experimentally by single-crystal X-ray crystallography, their electro- magnetochemistry, following spectroscopies: absorption, absorption (XAS), paramagnetic resonance (EPR). monoanion this series, [Cr(tpy)2]1–, has prepared in situ reduction with KC8 its EPR spectrum recorded. 2, 3, 4, 5, 6, where...
The contested electronic structure of [Cu(CF3)4]1– is investigated with UV/visible/near IR spectroscopy, Cu K-edge X-ray absorption and 1s2p resonant inelastic scattering. These data, supported by density functional theory, multiplet multireference calculations, support a ground state configuration in which the lowest unoccupied orbital predominantly trifluoromethyl character. consensus 3d10 features an inverted ligand field all five metal-localized molecular orbitals are located at lower...
Reduction of previously reported iminyl radical (
Dirhodium-catalyzed C-H amination is hypothesized to proceed via Rh2-nitrene intermediates in either the Rh2(II,II) or Rh2(II,III) redox state. Herein, we report joint theoretical and experimental studies of ground electronic state (GES), potentials, [Rh2(II,III)(O2CCH3)4(L)n](+) (1_L) (L = none, Cl(-), H2O), [Rh2(esp)2](+) (2), Rh2(espn)2Cl (3) (esp α,α,α',α'-tetramethyl-1,3-benzenedipropanoate espn α,α,α',α'-tetramethyl-1,3-benzenedipropanamidate). CASSCF calculations on 1_L yield a wave...
Bimetallic (Et4N)2[Co2(L)2], (Et4N)2[1] (where (L)(3-) = (N(o-PhNC(O)(i)Pr)2)(3-)) reacts with 2 equiv of O2 to form the monometallic species (Et4N)[Co(L)O2], (Et4N)[3]. A crystallographically characterized analog (Et4N)2[Co(L)CN], (Et4N)2[2], gives insight into structure [3](1-). Magnetic measurements indicate [2](2-) be an unusual high-spin Co(II)-cyano (S 3/2), while IR, EXAFS, and EPR spectroscopies [3](1-) end-on superoxide complex S 1/2 ground state. By X-ray spectroscopy calculations,...
Nickel K- and L 2,3 -edge X-ray absorption spectra (XAS) are discussed for coordinated nickel centers spanning formal oxidation states from II to IV. The ensuing analysis indicates that a physical “+4” state is untenable Ni.
The iron-molybdenum cofactor (FeMoco) of nitrogenase contains a biologically unprecedented μ(6)-coordinated C(4-) ion. Although the role this interstitial atom in catalysis is unknown, progress understanding its biosynthetic origins has been made. Here we report valence-to-core Fe Kβ X-ray emission spectroscopy data to show that ion present Fe(8)S(9) "L-cluster," which immediate precursor FeMoco prior insertion molybdenum and coordination by homocitrate. These results accord with recent...
Quantum information processing (QIP) could revolutionize how we simulate and understand quantum systems. Any QIP scheme requires both individual units (qubits) that have long phase memories switchable can be placed between the qubits. Here, describe supramolecular systems where {Cr7Ni} rings are used as qubits, linked by redox-switchable {Ru2M} oxo-centered triangles (M = Zn, Ni, or Co). The assemblies been structurally characterized involve two bound to through iso-nicotinate ligands....
The rates of catalytic oxidation cyclohexane and CO are 4 20 times higher, respectively, with Cu supported on a cerium-based metal–organic framework (MOF) than the structurally analogous zirconium material. Both Ce- Zr-based copper catalysts feature uncommon three-coordinate CuII sites bearing different nuclearities, as determined by K-edge extended X-ray absorption fine structure analysis. These results offer molecular-level understanding metal–support interface in MOF establish...
In this perspective, we highlight recent studies that use X-ray spectroscopic methods to identify and elucidate the molecular and/or electronic structures of intermediate resting transition-metal species implicated in homogeneous catalysis. We begin with a brief survey data can be accessed these methods, followed by case showcase advances interpretation data, demonstrate how complement other types spectroscopy, call attention common misconceptions associated techniques. some cases, suggest...
The synthesis and characterization of a Co(II) dithiolato complex Co(Me3TACN)(S2SiMe2) (1) are reported. Reaction 1 with O2 generates rare thiolate-ligated cobalt–superoxo species Co(O2)(Me3TACN)(S2SiMe2) (2) that was characterized spectroscopically structurally by resonance Raman, EPR, X-ray absorption spectroscopies as well density functional theory. Metal–superoxo proposed to S-oxygenate metal-bound thiolate donors in nonheme thiol dioxygenases, but 2 does not lead S-oxygenation the...