54 results on '"Enrique R. Batista"'
Search Results
2. Architector for high-throughput cross-periodic table 3D complex building
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Michael G. Taylor, Daniel J. Burrill, Jan Janssen, Enrique R. Batista, Danny Perez, and Ping Yang
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Multidisciplinary ,General Physics and Astronomy ,General Chemistry ,General Biochemistry, Genetics and Molecular Biology - Abstract
Rare-earth and actinide complexes are critical for a wealth of clean-energy applications. Three-dimensional (3D) structural generation and prediction for these organometallic systems remains a challenge, limiting opportunities for computational chemical discovery. Here, we introduce Architector, a high-throughput in-silico synthesis code for s-, p-, d-, and f-block mononuclear organometallic complexes capable of capturing nearly the full diversity of the known experimental chemical space. Beyond known chemical space, Architector performs in-silico design of new complexes including any chemically accessible metal-ligand combinations. Architector leverages metal-center symmetry, interatomic force fields, and tight binding methods to build many possible 3D conformers from minimal 2D inputs including metal oxidation and spin state. Over a set of more than 6,000 x-ray diffraction (XRD)-determined complexes spanning the periodic table, we demonstrate quantitative agreement between Architector-predicted and experimentally observed structures. Further, we demonstrate out-of-the box conformer generation and energetic rankings of non-minimum energy conformers produced from Architector, which are critical for exploring potential energy surfaces and training force fields. Overall, Architector represents a transformative step towards cross-periodic table computational design of metal complex chemistry.
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- 2023
3. N2-to-NH3 conversion by excess electrons trapped in point vacancies on 5f-element dioxide surfaces
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Gaoxue Wang, Enrique R. Batista, and Ping Yang
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General Chemistry - Abstract
Ammonia (NH3) is one of the basic chemicals in artificial fertilizers and a promising carbon-free energy storage carrier. Its industrial synthesis is typically realized via the Haber−Bosch process using traditional iron-based catalysts. Developing advanced catalysts that can reduce the N2 activation barrier and make NH3 synthesis more efficient is a long-term goal in the field. Most heterogeneous catalysts for N2-to-NH3 conversion are multicomponent systems with singly dispersed metal clusters on supporting materials to activate N2 and H2 molecules. Herein, we report single-component heterogeneous catalysts based on 5f actinide dioxide surfaces (ThO2 and UO2) with oxygen vacancies for N2-to-NH3 conversion. The reaction cycle we propose is enabled by a dual-site mechanism, where N2 and H2 can be activated at different vacancy sites on the same surface; NH3 is subsequently formed by H− migration on the surface via associative pathways. Oxygen vacancies recover to their initial states after the release of two molecules of NH3, making it possible for the catalytic cycle to continue. Our work demonstrates the catalytic activities of oxygen vacancies on 5f actinide dioxide surfaces for N2 activation, which may inspire the search for highly efficient, single-component catalysts that are easy to synthesize and control for NH3 conversion.
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- 2023
4. Pairwise Difference Regression: A Machine Learning Meta-algorithm for Improved Prediction and Uncertainty Quantification in Chemical Search
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Michael Tynes, Enrique R. Batista, Daniel Burrill, Wenhao Gao, Ping Yang, Nicholas Lubbers, and Danny Perez
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Artificial neural network ,Computer science ,business.industry ,Active learning (machine learning) ,General Chemical Engineering ,Uncertainty ,General Chemistry ,Library and Information Sciences ,Machine learning ,computer.software_genre ,Regression ,Computer Science Applications ,Random forest ,Machine Learning ,Data point ,Errors-in-variables models ,Pairwise comparison ,Neural Networks, Computer ,Artificial intelligence ,Uncertainty quantification ,business ,Algorithm ,computer ,Algorithms - Abstract
Machine learning (ML) plays a growing role in the design and discovery of chemicals, aiming to reduce the need to perform expensive experiments and simulations. ML for such applications is promising but difficult, as models must generalize to vast chemical spaces from small training sets and must have reliable uncertainty quantification metrics to identify and prioritize unexplored regions. Ab initio computational chemistry and chemical intuition alike often take advantage of differences between chemical conditions, rather than their absolute structure or state, to generate more reliable results. We have developed an analogous comparison-based approach for ML regression, called pairwise difference regression (PADRE), which is applicable to arbitrary underlying learning models and operates on pairs of input data points. During training, the model learns to predict differences between all possible pairs of input points. During prediction, the test points are paired with all training set points, giving rise to a set of predictions that can be treated as a distribution of which the mean is treated as a final prediction and the dispersion is treated as an uncertainty measure. Pairwise difference regression was shown to reliably improve the performance of the random forest algorithm across five chemical ML tasks. Additionally, the pair-derived dispersion is both well correlated with model error and performs well in active learning. We also show that this method is competitive with state-of-the-art neural network techniques. Thus, pairwise difference regression is a promising tool for candidate selection algorithms used in chemical discovery.
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- 2021
5. Structural and Spectroscopic Comparison of Soft‐Se vs. Hard‐O Donor Bonding in Trivalent Americium/Neodymium Molecules
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Conrad A. P. Goodwin, Anthony W. Schlimgen, Thomas E. Albrecht‐Schönzart, Enrique R. Batista, Andrew J. Gaunt, Michael T. Janicke, Stosh A. Kozimor, Brian L. Scott, Lauren M. Stevens, Frankie D. White, and Ping Yang
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010405 organic chemistry ,chemistry.chemical_element ,Americium ,General Medicine ,General Chemistry ,Actinide ,010402 general chemistry ,01 natural sciences ,Neodymium ,Catalysis ,0104 chemical sciences ,Crystallography ,chemistry ,Ab initio quantum chemistry methods ,Covalent bond ,Molecule ,Spectroscopy ,Selectivity - Abstract
Covalency is often considered to be an influential factor in driving An3+ vs. Ln3+ selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An3+ /Ln3+ covalency differences prevail and manifest as the f-block is traversed, and the effects of periodic breaks beyond Pu. Herein, two Am complexes, [Am{N(E=PPh2 )2 }3 ] (1-Am, E=Se; 2-Am, E=O) are compared to isoradial [Nd{N(E=PPh2 )2 }3 ] (1-Nd, 2-Nd) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. Through ab initio calculations grounded in UV-vis-NIR spectroscopy and single-crystal X-ray structures, we observe differences in f orbital involvement between Am-Se and Nd-Se bonds, which are not present in O-donor congeners.
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- 2021
6. δ and φ back-donation in AnIV metallacycles
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Morgan P. Kelley, Ping Yang, Julie Jung, Enrique R. Batista, and Ivan A. Popov
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Multidisciplinary ,010405 organic chemistry ,Chemistry ,Ligand ,Science ,General Physics and Astronomy ,General Chemistry ,010402 general chemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,0104 chemical sciences ,Bond length ,Metal ,Crystallography ,Atomic orbital ,Group (periodic table) ,visual_art ,visual_art.visual_art_medium ,lcsh:Q ,lcsh:Science - Abstract
In all known examples of metal–ligand (M–L) δ and φ bonds, the metal orbitals are aligned to the ligand orbitals in a “head-to-head” or “side-to-head” fashion. Here, we report two fundamentally new types of M–L δ and φ interactions; “head-to-side” δ and “side-to-side” φ back-bonding, found in complexes of metallacyclopropenes and metallacyclocumulenes of actinides (Pa–Pu) that makes them distinct from their corresponding Group 4 analogues. In addition to the known Th and U complexes, our calculations include complexes of Pa, Np, and Pu. In contrast with conventional An–C bond decreasing, due to the actinide contraction, the An–C distance increases from Pa to Pu. We demonstrate that the direct L–An σ and π donations combined with the An–L δ or φ back-donations are crucial in explaining this non-classical trend of the An–L bond lengths in both series, underscoring the significance of these δ/φ back-donation interactions, and their importance for complexes of Pa and U in particular.
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- 2020
7. Expanding the potential of redox carriers for flow battery applications
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Ping Yang, Ivan A. Popov, Gabriel A. Andrade, Benjamin L. Davis, Celia R. Federico, Enrique R. Batista, and Rangachary Mukundan
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Materials science ,Renewable Energy, Sustainability and the Environment ,Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Redox ,Flow battery ,0104 chemical sciences ,Metal ,chemistry.chemical_compound ,Nickel ,chemistry ,visual_art ,visual_art.visual_art_medium ,Dimethylformamide ,General Materials Science ,Differential pulse voltammetry ,Solubility ,0210 nano-technology ,Acetonitrile - Abstract
Using theoretical modeling to guide our approach, substituents were selected to improve the negative and positive potentials associated with a representative metal-based redox carrier, a phenyl spaced nickel bispicolinamide complex, [Ni(bpb)], 1. To broaden the cell potential, electron donating groups were selected and installed on the pyridyl moieties, [Ni(bpb-(NMe2)2)], 2, while electron withdrawing groups were incorporated on the phenyl linker, [Ni(bpb-R)] (R = –F, –CF3, and –NO2), 3–5. Our model predicts an increase of ∼300 mV and ∼500 mV for the first and second negative waves of Ni(bpb-NMe2), 2, and up to ∼330 mV and ∼210 mV increase to the first and second positive waves in 3–5. The modeled complexes were synthesized in good yields using a modification of the literature procedure. Due to limited solubility, the differential pulse voltammetry was measured on complexes 2–5 using a drop cast technique. Comparison of the observed and predicted potentials is discussed in acetonitrile (MeCN) and dimethylformamide (DMF) solvents.
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- 2020
8. Comparison of tetravalent cerium and terbium ions in a conserved, homoleptic imidophosphorane ligand field
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Henry S. La Pierre, John Bacsa, Ivan A. Popov, Thaige P. Gompa, Enrique R. Batista, Ping Yang, Arun Ramanathan, Dominic R. Russo, and Natalie T. Rice
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Ligand field theory ,Lanthanide ,Crystallography ,chemistry.chemical_compound ,chemistry ,Covalent bond ,Ligand ,chemistry.chemical_element ,Terbium ,General Chemistry ,Homoleptic ,Isostructural ,Natural bond orbital - Abstract
A redox pair of Ce4+ and Ce3+ complexes has been prepared that is stabilized by the [(NP(1,2-bis-tBu-diamidoethane)(NEt2))]1− ligand. Since these complexes are isostructural to the recently reported isovalent terbium analogs, a detailed structural and spectroscopic comparative analysis was pursued via Voronoi–Dirichlet polyhedra analysis, UV-vis-NIR, L3-edge X-ray absorption near edge spectroscopy (XANES), cyclic voltammetry, and natural transitions orbital (NTO) analysis and natural bond orbital (NBO) analysis. The electrochemical studies confirm previous theoretical studies of the redox properties of the related complex [K][Ce3+(NP(pip)3)4] (pip = piperidinyl), 1-Ce(PN). Complex 1-Ce(PN*) presents the most negative Epc of −2.88 V vs. Fc/Fc+ in THF of any cerium complex studied electrochemically. Likewise 1-Tb(PN*) has the most negative Epc for electrochemically interrogated terbium complexes at −1.79 V vs. Fc/Fc+ in THF. Complexes 1-Ce(PN*) and 2-Ce(PN*) were also studied by L3-edge X-ray absorption near edges spectroscopy (XANES) and a comparison to previously reported spectra for 1-Tb(PN*), 2-Tb(PN*), 1-Ce(PN), and, [Ce4+(NP(pip)3)4], 2-Ce(PN), demonstrates similar nf values for all the tetravalent lanthanide complexes. According to the natural bond orbital analysis, a greater covalent character of the M–L bonds is found in 2-Ce(PN*) than in 1-Ce(PN*), in agreement with the shorter Ce–N bonds in the tetravalent counterpart. The greater contribution of Ce orbitals in the Ce–N bonding and, specifically, the higher participation of 4f electrons accounts for the stronger covalent interactions in 2-Ce(PN*) as compared to 2-Tb(PN*).
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- 2020
9. An Allyl Uranium(IV) Sandwich Complex: Are ϕ Bonding Interactions Possible?
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Ivan A. Popov, Brennan S. Billow, Stephanie H. Carpenter, Enrique R. Batista, James M. Boncella, Aaron M. Tondreau, and Ping Yang
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Organic Chemistry ,General Chemistry ,Catalysis - Abstract
A method to explore head-to-head ϕ back-bonding from uranium f-orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single-crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N-((dimethyl)prop-2-enylsilyl)-2,6-diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI
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- 2022
10. [Am(C 5 Me 4 H) 3 ]: An Organometallic Americium Complex
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Scott R. Daly, Andrew J. Gaunt, Thomas E. Albrecht-Schmitt, William J. Evans, Enrique R. Batista, Stosh A. Kozimor, Brian L. Scott, Stefanie Dehnen, Jing Su, Niels Lichtenberger, Ping Yang, Conrad A. P. Goodwin, and Anastasia V. Blake
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Materials science ,actinides ,organometallic complexes ,structure elucidation ,Near-infrared spectroscopy ,chemistry.chemical_element ,Americium ,General Chemistry ,Actinide ,cyclopentadienyl ligands ,Catalysis ,americium ,chemistry ,Yield (chemistry) ,Physical chemistry ,Density functional theory ,Wave function ,Spectroscopy - Abstract
We report the small-scale synthesis, isolated yield, single-crystal X-ray structure, 1H NMR solution spectroscopy /solid-state UV/Vis-nIR spectroscopy, and density functional theory (DFT)/ab initio wave function theory calculations on an Am3+ organometallic complex, [Am(C5Me4H)3] (1). This constitutes the first quantitative data on Am−C bonding in a molecular species.
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- 2019
11. Soft-donor dipicolinamide derivatives for selective actinide(<scp>iii</scp>)/lanthanide(<scp>iii</scp>) separation: the role of S- vs. O-donor sites
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Teresa M. Eaton, Konstantinos E. Papathanasiou, Christopher J. Dares, Konstantinos Kavallieratos, David Dan, Jiwen Jian, Jing Su, Ping Yang, Ingrid Lehman-Andino, Thomas E. Albrecht-Schmitt, Enrique R. Batista, and John K. Gibson
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chemistry.chemical_classification ,Lanthanide ,Ligand ,Complex formation ,Extraction (chemistry) ,Metals and Alloys ,General Chemistry ,Actinide ,Medicinal chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Selectivity ,Thioamide - Abstract
Selectivity for An(iii) vs. Ln(iii) binding and extraction using dipicolinamide analogs containing the C[double bond, length as m-dash]O vs. C[double bond, length as m-dash]S groups was investigated in solution and the gas-phase, and by DFT calculations. The results show higher selectivity for complex formation and extraction for Am(iii) vs. Eu(iii) for the softer dithioamide vs. the diamide ligand, while in CH3CN the diamide binds more strongly than the thioamide to several Ln(iii), forming 1 : 1 complexes.
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- 2019
12. Solubility model of metal complex in ionic liquids from first principle calculations
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Enrique R. Batista, Anwesa Karmakar, Rangachary Mukundan, and Ping Yang
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Chemistry ,General Chemical Engineering ,Solvation ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Ion ,Solvent ,Metal ,chemistry.chemical_compound ,visual_art ,Ionic liquid ,visual_art.visual_art_medium ,Molecule ,Physical chemistry ,Solubility ,0210 nano-technology ,Acetonitrile - Abstract
A predictive model based on first principles calculations has been proposed to study the solid–liquid equilibria comprising of metal complexes and ionic liquids. The model is based on first principle COSMO calculation followed by post statistical thermodynamical treatment of self-consistent properties of solute and solvent molecules. The metal complex and ionic liquid have been treated as a simple binary mixture. The ionic liquid has been treated here as a single intact molecule. The experimentally observed dual-solute relationship between the ionic liquid and redox active species in presence of a third organic solvent has been established using our model in this work. Within the model, the dual-solute relationship appeared as a simple Gibbs–Duhem relationship between these two species at ambient condition. The dual-solute relationship between the metal complex (V(acac)3, Cr(acac)3 and Mn(acac)3) and ionic liquid ([Tea][BF4]) has been validated by calculating the Gibbs–Duhem relationship, xsolute vs. xsolvent(IL) and 1/γsolute vs. xsolvent(IL) plots. The present model has been applied to a set of ionic liquids, metal complexes and organic solvent (acetonitrile) for which experimental study has been done. The solvation mechanism of the metal complexes in those ionic liquids was obtained using the model. According to our findings, the ionic liquid containing imidazolium cation and [NTf2]− anion is appeared as a suitable solvent for the non-aqueous redox flow cell. We have compared our results with the already reported experimental results where they were available for the non-aqueous solvents.
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- 2019
13. Impact of Ligand Substitutions on Multielectron Redox Properties of Fe Complexes Supported by Nitrogenous Chelates
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Enrique R. Batista, Ivan A. Popov, Benjamin L. Davis, Ping Yang, Nada Mehio, Rangachary Mukundan, and Terry Chu
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High energy ,010405 organic chemistry ,Ligand ,Chemistry ,General Chemical Engineering ,Design elements and principles ,General Chemistry ,Electrolyte ,010402 general chemistry ,01 natural sciences ,Combinatorial chemistry ,Redox ,Article ,0104 chemical sciences ,lcsh:Chemistry ,Solvent ,lcsh:QD1-999 ,Chelation ,Electrochemical window - Abstract
Redox flow batteries (RFBs) have recently been recognized as a potentially viable technology for scalable energy storage. To take full advantage of RFBs, one possible approach for achieving high energy densities is to maximize a number of redox events by utilizing charge carriers capable of multiple one-electron transfers within the electrochemical window of solvent. However, past efforts to develop more efficient electrolytes for nonaqueous RFBs have mostly been empirical. In this manuscript, we shed light on design principles by theoretically investigating the effects of systematically substituting pyridyl moieties with imine ligands within a series of Fe complexes with some experimental validation. We found that such replacement is an effective strategy for reducing the molecular weight-to-charge ratios of these complexes. Simultaneously, calculations suggest that the reduction potentials and ligand-based redox activity of such substituted N-heterocyclic Fe compounds might be maintained within their +4 → -1 charge states. Additionally, by theoretically examining the role of coordination geometry, vis-à-vis reducing the number of redox noninnocent ligands within the first coordination sphere, we have demonstrated that Fe complexes with one such ligand were also capable of supporting multielectron reduction events and exhibited reduction potentials similar to their parent analogs supported by two or three of the same multidentate ligands. However, some differences in redox nature within the lower (+2 → -1) charge states were also noticed. Specifically, complexes containing two bidentate ligands, or one tridentate ligand, exhibited ligand-based reductions, whereas compounds with one bidentate ligand exhibited metal-centered reductions. The current results pave the way toward the design of the next-generation of Fe complexes with lower molecular weights and greater stored energy for redox flow batteries.
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- 2018
14. The duality of electron localization and covalency in lanthanide and actinide metallocenes
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Richard L. Martin, Corwin H. Booth, Stefan G. Minasian, Jason M. Keith, David K. Shuh, David Clark, Tolek Tyliszczak, Enrique R. Batista, S. Chantal E. Stieber, Stosh A. Kozimor, and Danil E. Smiles
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Delocalized electron ,Crystallography ,Chemistry ,Materials science ,Atomic orbital ,Chemical Sciences ,Density functional theory ,Strongly correlated material ,General Chemistry ,Time-dependent density functional theory ,Configuration interaction ,Ground state ,Electron localization function - Abstract
Previous magnetic, spectroscopic, and theoretical studies of cerocene, Ce(C8H8)2, have provided evidence for non-negligible 4f-electron density on Ce and implied that charge transfer from the ligands occurs as a result of covalent bonding. Strong correlations of the localized 4f-electrons to the delocalized ligand π-system result in emergence of Kondo-like behavior and other quantum chemical phenomena that are rarely observed in molecular systems. In this study, Ce(C8H8)2 is analyzed experimentally using carbon K-edge and cerium M5,4-edge X-ray absorption spectroscopies (XAS), and computationally using configuration interaction (CI) calculations and density functional theory (DFT) as well as time-dependent DFT (TDDFT). Both spectroscopic approaches provide strong evidence for ligand → metal electron transfer as a result of Ce 4f and 5d mixing with the occupied C 2p orbitals of the C8H82− ligands. Specifically, the Ce M5,4-edge XAS and CI calculations show that the contribution of the 4f1, or Ce3+, configuration to the ground state of Ce(C8H8)2 is similar to strongly correlated materials such as CeRh3 and significantly larger than observed for other formally Ce4+ compounds including CeO2 and CeCl62−. Pre-edge features in the experimental and TDDFT-simulated C K-edge XAS provide unequivocal evidence for C 2p and Ce 4f covalent orbital mixing in the δ-antibonding orbitals of e2u symmetry, which are the unoccupied counterparts to the occupied, ligand-based δ-bonding e2u orbitals. The C K-edge peak intensities, which can be compared directly to the C 2p and Ce 4f orbital mixing coefficients determined by DFT, show that covalency in Ce(C8H8)2 is comparable in magnitude to values reported previously for U(C8H8)2. An intuitive model is presented to show how similar covalent contributions to the ground state can have different impacts on the overall stability of f-element metallocenes., Unequivocal experimental evidence for carbon 2p and cerium 4f orbital mixing in cerocene, Ce(C8H8)2 is provided from carbon K-edge and Ce M5,4-edge X-ray absorption spectroscopies and corroborated with DFT and configuration interaction calculations.
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- 2020
15. Advancing Chelation Chemistry for Actinium and Other +3 f-Elements, Am, Cm, and La
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Eva R. Birnbaum, Stosh A. Kozimor, Brian L. Scott, Veronika Mocko, Samantha K. Cary, Ping Yang, Kevin D. John, Amanda Morgenstern, Benjamin W. Stein, Maryline G. Ferrier, Enrique R. Batista, Sharon E. Bone, and Juan S. Lezama Pacheco
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Actinium ,Inorganic chemistry ,Binding pocket ,chemistry.chemical_element ,010402 general chemistry ,Ligands ,01 natural sciences ,Biochemistry ,Catalysis ,Coordination complex ,Colloid and Surface Chemistry ,Organophosphorus Compounds ,Coordination Complexes ,Lanthanum ,Molecule ,Chelation ,Chelating Agents ,chemistry.chemical_classification ,Americium ,Extended X-ray absorption fine structure ,Molecular Structure ,Extramural ,General Chemistry ,0104 chemical sciences ,chemistry ,Curium ,Radiopharmaceuticals - Abstract
A major chemical challenge facing implementation of 225Ac in targeted alpha therapy-an emerging technology that has potential for treatment of disease-is identifying an 225Ac chelator that is compatible with in vivo applications. It is unclear how to tailor a chelator for Ac binding because Ac coordination chemistry is poorly defined. Most Ac chemistry is inferred from radiochemical experiments carried out on microscopic scales. Of the few Ac compounds that have been characterized spectroscopically, success has only been reported for simple inorganic ligands. Toward advancing understanding in Ac chelation chemistry, we have developed a method for characterizing Ac complexes that contain highly complex chelating agents using small quantities (μg) of 227Ac. We successfully characterized the chelation of Ac3+ by DOTP8- using EXAFS, NMR, and DFT techniques. To develop confidence and credibility in the Ac results, comparisons with +3 cations (Am, Cm, and La) that could be handled on the mg scale were carried out. We discovered that all M3+ cations (M = Ac, Am, Cm, La) were completely encapsulated within the binding pocket of the DOTP8- macrocycle. The computational results highlighted the stability of the M(DOTP)5- complexes.
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- 2019
16. Identification of the Formal +2 Oxidation State of Neptunium: Synthesis and Structural Characterization of {NpII[C5H3(SiMe3)2]3}1–
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Andrew J. Gaunt, David H. Woen, Stosh A. Kozimor, Michael T. Janicke, Brian L. Scott, William J. Evans, Cory J. Windorff, Jing Su, Enrique R. Batista, and Ping Yang
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010405 organic chemistry ,Chemistry ,Neptunium ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Characterization (materials science) ,Ion ,Crystallography ,Colloid and Surface Chemistry ,Oxidation state ,Density functional theory ,Electron configuration ,Ground state - Abstract
We report a new formal oxidation state for neptunium in a crystallographically characterizable molecular complex, namely Np2+ in [K(crypt)][NpIICp″3] [crypt = 2.2.2-cryptand, Cp″ = C5H3(SiMe3)2]. Density functional theory calculations indicate that the ground state electronic configuration of the Np2+ ion in the complex is 5f46d1.
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- 2018
17. Overcoming the quantum efficiency-lifetime tradeoff of photocathodes by coating with atomically thin two-dimensional nanomaterials
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Ping Yang, Enrique R. Batista, Gaoxue Wang, and Nathan A. Moody
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02 engineering and technology ,engineering.material ,010402 general chemistry ,01 natural sciences ,Photocathode ,Nanomaterials ,law.invention ,lcsh:Chemistry ,Coating ,law ,Monolayer ,lcsh:TA401-492 ,General Materials Science ,Work function ,business.industry ,Graphene ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Cathode ,0104 chemical sciences ,lcsh:QD1-999 ,Mechanics of Materials ,engineering ,Optoelectronics ,Quantum efficiency ,lcsh:Materials of engineering and construction. Mechanics of materials ,0210 nano-technology ,business - Abstract
Photocathodes are key components of electron injectors for X-ray free electron laser and X-ray energy recovery linacs, which generate brilliant, ultrafast, and coherent X-rays for the exploration of matter with ultrahigh resolutions in both space and time. Whereas alkali-based semiconducting photocathodes display a higher quantum efficiency (QE) in the visible light spectrum than their metallic counterparts, their lifetimes are much shorter due to the high reactivity of alkali-based surfaces to the residual gases in the vacuum chamber. Overcoming the tradeoff between QE and lifetimes has been a great challenge in the accelerator community. Herein, based on ab initio density functional calculations, we propose an approach to overcome this tradeoff by coating with atomically thin two-dimensional (2D) nanomaterials. On one hand, the 2D coating layers can enhance the lifetimes of photocathodes by preventing the chemical reactions with the residual gases. On the other hand, the 2D coating layers can effectively engineer the work function of photocathodes, thus controlling their QE. A monolayer of insulating BN reduces the work function, whereas a monolayer of semi-metallic graphene or semiconducting molybdenum disulfide (MoS2) increases the work function. This phenomenon originates from the induced interfacial dipoles. The reduction of work function by BN implies that it is capable of maintaining the high QE of semiconducting photocathodes in addition to enhance their lifetimes. This study advances our understandings on the surface chemistry of coated photocathodes and opens new technological avenues to fabricate photocathodes with high QE and longer lifetimes. Coating alkali-based photocathodes with atomically thin hBN enhance their lifetime whilst improving their quantum efficiency. A team led by Enrique Batista at Los Alamos National Laboratory performed ab initio density functional theory calculations on photocathodes coated with a variety of 2D materials. While monolayers of semi-metallic graphene and semiconducting MoS2 were found to increase the photocathode work function, a monolayer of insulating hBN led to a work function reduction whilst offering protection of the highly reactive photocathode surface from irreversible chemical reactions. Such work function reduction, key to achieving high quantum efficiency, was ascribed to the formation of induced dipole moments at the interface between hBN and the Cs3Sb cathode surface, pointing out of Cs3Sb. hBN monolayers are thus promising coating materials for alkali-based semiconducting photocathodes.
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- 2018
18. Spectroscopic and Computational Characterization of Diethylenetriaminepentaacetic Acid/Transplutonium Chelates: Evidencing Heterogeneity in the Heavy Actinide(III) Series
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Corwin H. Booth, Rebecca J. Abergel, Morgan P. Kelley, Enrique R. Batista, Jing Su, Gauthier J.-P. Deblonde, and Ping Yang
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Lanthanide ,Aqueous solution ,Extended X-ray absorption fine structure ,010405 organic chemistry ,chemistry.chemical_element ,General Chemistry ,Actinide ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Bond length ,Berkelium ,chemistry ,Molecule ,Physical chemistry ,Density functional theory - Abstract
The chemistry of trivalent transplutonium ions (Am3+ , Cm3+ , Bk3+ , Cf3+ , Es3+ …) is usually perceived as monotonic and paralleling that of the trivalent lanthanide series. Herein, we present the first extended X-ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to much shorter metal-oxygen nearest-neighbor bond lengths in the case of Cf3+ . Corroborating those results, density functional theory calculations, extended to Es3+ , suggest that the shorter Cf-O and Es-O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [MIII DTPA(H2 O)]2- (M=Am, Cm, Bk) complexes. Taken together, these experimental and theoretical results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years, and that may also be leveraged for future nuclear waste reprocessing technologies.
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- 2018
19. Revisiting complexation thermodynamics of transplutonium elements up to einsteinium
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Enrique R. Batista, Ping Yang, Sergey I. Sinkov, Jenifer C. Shafer, Jing Su, Morgan P. Kelley, Nathan P. Bessen, Matthew Urban, and Gregg J. Lumetta
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010405 organic chemistry ,Chemistry ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,Actinide ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Computational chemistry ,Einsteinium ,Materials Chemistry ,Ceramics and Composites - Abstract
Literature casts einsteinium as a departure from earlier transplutonium actinides, with a decrease in stability constants with aminopolycarboxylate ligands. This report studies transplutonium chemistry - including Am, Bk, Cf, and Es - with aminopolycarboxylate ligands. Es complexation follows similar thermodynamic and structural trends established by the earlier actinides, consistent with first-principle calculations.
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- 2018
20. Quantitative Evidence for Lanthanide-Oxygen Orbital Mixing in CeO2, PrO2, and TbO2
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Enrique R. Batista, S. Chantal E. Stieber, David Clark, Richard L. Martin, Stefan G. Minasian, Stosh A. Kozimor, Jason M. Keith, David K. Shuh, Xiaodong Wen, Wayne W. Lukens, Corwin H. Booth, and Tolek Tylisczcak
- Subjects
Lanthanide ,X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Ionic bonding ,02 engineering and technology ,General Chemistry ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,Atomic orbital ,Covalent bond ,Physical chemistry ,Density functional theory ,0210 nano-technology - Abstract
© 2017 American Chemical Society. Understanding the nature of covalent (band-like) vs ionic (atomic-like) electrons in metal oxides continues to be at the forefront of research in the physical sciences. In particular, the development of a coherent and quantitative model of bonding and electronic structure for the lanthanide dioxides, LnO2(Ln = Ce, Pr, and Tb), has remained a considerable challenge for both experiment and theory. Herein, relative changes in mixing between the O 2p orbitals and the Ln 4f and 5d orbitals in LnO2are evaluated quantitatively using O K-edge X-ray absorption spectroscopy (XAS) obtained with a scanning transmission X-ray microscope and density functional theory (DFT) calculations. For each LnO2, the results reveal significant amounts of Ln 5d and O 2p mixing in the orbitals of t2g(σ-bonding) and eg(π-bonding) symmetry. The remarkable agreement between experiment and theory also shows that significant mixing with the O 2p orbitals occurs in a band derived from the 4f orbitals of a2usymmetry (σ-bonding) for each compound. However, a large increase in orbital mixing is observed for PrO2that is ascribed to a unique interaction derived from the 4f orbitals of t1usymmetry (σ- and π-bonding). O K-edge XAS and DFT results are compared with complementary L3-edge and M5,4-edge XAS measurements and configuration interaction calculations, which shows that each spectroscopic approach provides evidence for ground state O 2p and Ln 4f orbital mixing despite inducing very different core-hole potentials in the final state.
- Published
- 2017
21. Covalency in Americium(III) Hexachloride
- Author
-
Stosh A. Kozimor, Justin N. Cross, Brian L. Scott, Samantha K. Cary, Ping Yang, Enrique R. Batista, Cory J. Windorff, Benjamin W. Stein, William J. Evans, Jing Su, and Veronika Mocko
- Subjects
X-ray absorption spectroscopy ,Americium ,Absorption spectroscopy ,010405 organic chemistry ,Chemistry ,Extramural ,chemistry.chemical_element ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,Chlorides ,Chemical physics ,Computational chemistry ,Mixing (physics) - Abstract
Developing a better understanding of covalency (or orbital mixing) is of fundamental importance. Covalency occupies a central role in directing chemical and physical properties for almost any given compound or material. Hence, the concept of covalency has potential to generate broad and substantial scientific advances, ranging from biological applications to condensed matter physics. Given the importance of orbital mixing combined with the difficultly in measuring covalency, estimating or inferring covalency often leads to fiery debate. Consider the 60-year controversy sparked by Seaborg and co-workers ( Diamond, R. M.; Street, K., Jr.; Seaborg, G. T. J. Am. Chem. Soc. 1954 , 76 , 1461 ) when it was proposed that covalency from 5f-orbitals contributed to the unique behavior of americium in chloride matrixes. Herein, we describe the use of ligand K-edge X-ray absorption spectroscopy (XAS) and electronic structure calculations to quantify the extent of covalent bonding in-arguably-one of the most difficult systems to study, the Am-Cl interaction within AmCl
- Published
- 2017
22. Synthesis and Characterization of the Actinium Aquo Ion
- Author
-
Kevin D. John, Maryline G. Ferrier, John M. Berg, Lindsay N. Redman, Benjamin W. Stein, Juan S. Lezama Pacheco, Eva R. Birnbaum, Stosh A. Kozimor, Jonathan W. Engle, and Enrique R. Batista
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Chemistry ,General Chemical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,3. Good health ,0104 chemical sciences ,Characterization (materials science) ,Coordination complex ,Ion ,Metal ,lcsh:Chemistry ,Actinium ,lcsh:QD1-999 ,visual_art ,visual_art.visual_art_medium ,Molecule ,Absorption (chemistry) ,Metal aquo complex ,Research Article - Abstract
Metal aquo ions occupy central roles in all equilibria that define metal complexation in natural environments. These complexes are used to establish thermodynamic metrics (i.e., stability constants) for predicting metal binding, which are essential for defining critical parameters associated with aqueous speciation, metal chelation, in vivo transport, and so on. As such, establishing the fundamental chemistry of the actinium(III) aquo ion (Ac-aquo ion, Ac(H2O)x3+) is critical for current efforts to develop 225Ac [t1/2 = 10.0(1) d] as a targeted anticancer therapeutic agent. However, given the limited amount of actinium available for study and its high radioactivity, many aspects of actinium chemistry remain poorly defined. We overcame these challenges using the longer-lived 227Ac [t1/2 = 21.772(3) y] isotope and report the first characterization of this fundamentally important Ac-aquo coordination complex. Our X-ray absorption fine structure study revealed 10.9 ± 0.5 water molecules directly coordinated to the AcIII cation with an Ac–OH2O distance of 2.63(1) Å. This experimentally determined distance was consistent with molecular dynamics density functional theory results that showed (over the course of 8 ps) that AcIII was coordinated by 9 water molecules with Ac–OH2O distances ranging from 2.61 to 2.76 Å. The data is presented in the context of other actinide(III) and lanthanide(III) aquo ions characterized by XAFS and highlights the uniqueness of the large AcIII coordination numbers and long Ac–OH2O bond distances., The actinium aquo complex has been characterized using Ac L3-edge X-ray absorption spectroscopy and molecular dynamics density functional theory.
- Published
- 2017
23. Evaluating the electronic structure of formal LnIIions in LnII(C5H4SiMe3)31−using XANES spectroscopy and DFT calculations
- Author
-
Juan S. Lezama Pacheco, Gregory L. Wagner, Enrique R. Batista, David H. Woen, Jing Su, Austin J. Ryan, Maryline G. Ferrier, Stosh A. Kozimor, Samantha K. Cary, Jonathan W. Engle, Tonya Vitova, Benjamin W. Stein, Ping Yang, Angela C. Olson, William J. Evans, and Megan E. Fieser
- Subjects
Lanthanide ,010405 organic chemistry ,Chemistry ,Transition dipole moment ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,XANES ,0104 chemical sciences ,Ion ,Computational chemistry ,Physical chemistry ,Density functional theory ,Electron configuration ,Spectroscopy - Abstract
The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31- (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4f n 5d1 configurations (not 4f n+1 5d0). In these 4f n 5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d1 electronic configurations lower in energy than the more typical 4f n+1 5d0 configuration.
- Published
- 2017
24. Design, Isolation, and Spectroscopic Analysis of a Tetravalent Terbium Complex
- Author
-
Natalie T. Rice, John Bacsa, Joshua Telser, Enrique R. Batista, Dominic R. Russo, Ping Yang, Henry S. La Pierre, and Ivan A. Popov
- Subjects
Models, Molecular ,Lanthanide ,Ligand field theory ,Phosphoranes ,chemistry.chemical_element ,Terbium ,Ligands ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,law.invention ,Colloid and Surface Chemistry ,Coordination Complexes ,law ,Electron paramagnetic resonance ,X-ray absorption spectroscopy ,Ligand ,Electron Spin Resonance Spectroscopy ,General Chemistry ,Combinatorial chemistry ,0104 chemical sciences ,Characterization (materials science) ,Crystallography ,X-Ray Absorption Spectroscopy ,chemistry ,Covalent bond ,Yield (chemistry) ,Density functional theory - Abstract
Synthetic strategies to yield molecular complexes of high-valent lanthanides, other than the ubiquitous Ce4+ ion, are exceptionally rare, and thorough, detailed characterization in these systems is limited by complex lifetime and reaction and isolation conditions. The synthesis of high-symmetry complexes in high purity with significant lifetimes in solution and solid-state are essential for determining the role of ligand-field splitting, multiconfigurational behavior, and covalency in governing the reactivity and physical properties of these potentially technologically transformative tetravalent ions. We report the synthesis and physical characterization of an S4 symmetric, four-coordinate tetravalent terbium complex, [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (where Et is ethyl and tBu is tert-butyl). The ligand field in this complex is weak and the metal-ligand bonds sufficiently covalent so that the tetravalent terbium ion is stable and accessible via a mild oxidant from the anionic, trivalent, terbium precursor, [(Et2O)K][Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4]. The significant stability of the tetravalent complex enables its thorough characterization. The step-wise development of the supporting ligand points to key ligand control elements for further extending the known tetravalent lanthanide ions in molecular complexes. Magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray absorption near-edge spectroscopy (XAS), and density functional theory studies indicate a 4f7 ground state for [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] with considerable zero-field splitting: demonstrating that magnetic, tetravalent lanthanide ions engage in covalent metal-ligand bonds. This result has significant implications for the use of tetravalent lanthanide ions in magnetic applications since the observed zero-field splitting is intermediate between that observed for the trivalent lanthanides and for the transition metals. The similarity of the multiconfigurational behavior in the ground state of [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (measured by Tb L3-edge XAS) to that observed in TbO2 implicates ligand control of multiconfigurational behavior as a key component of the stability of the complex.
- Published
- 2019
25. Energy-Degeneracy-Driven Covalency in Actinide Bonding
- Author
-
Andrew Kerridge, Steven D. Conradson, Sharon E. Bone, Alex S. Ditter, Samantha K. Cary, Marianne P. Wilkerson, Enrique R. Batista, Richard L. Martin, Stefan G. Minasian, Stosh A. Kozimor, Henry S. La Pierre, Nikolas Kaltsoyannis, Kevin S. Boland, Matthias W. Löble, Veronika Mocko, Jason M. Keith, Laura E. Wolfsberg, David K. Shuh, David Clark, J. A. Bradley, Jing Su, Gerald T. Seidler, and Ping Yang
- Subjects
Chemical substance ,Absorption spectroscopy ,010405 organic chemistry ,Chemistry ,Actinide ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Metal ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,Colloid and Surface Chemistry ,Chemical bond ,Covalent bond ,visual_art ,Chemical Sciences ,visual_art.visual_art_medium ,Physical chemistry ,Dalton Nuclear Institute ,Density functional theory ,Degeneracy (biology) - Abstract
Evaluating the nature of chemical bonding for actinide elements represents one of the most important and long-standing problems in actinide science. We directly address this challenge and contribute a Cl K-edge X-ray absorption spectroscopy and relativistic density functional theory study that quantitatively evaluates An-Cl covalency in AnCl62- (AnIV = Th, U, Np, Pu). The results showed significant mixing between Cl 3p- and AnIV 5f- and 6d-orbitals (t1u*/t2u* and t2 g*/eg *), with the 6d-orbitals showing more pronounced covalent bonding than the 5f-orbitals. Moving from Th to U, Np, and Pu markedly changed the amount of M-Cl orbital mixing, such that AnIV 6d - and Cl 3p-mixing decreased and metal 5f - and Cl 3p-orbital mixing increased across this series.
- Published
- 2018
26. Plutonium coordination and redox chemistry with the CyMe4-BTPhen polydentate N-donor extractant ligand
- Author
-
Frank W. Lewis, Daniel M Whittaker, Clint A. Sharrad, Jason M. Keith, Andrew J. Gaunt, Ping Yang, Laurence M. Harwood, Sean D. Reilly, Enrique R. Batista, Brian L. Scott, Jing Su, and Michael J. Hudson
- Subjects
Denticity ,Inorganic chemistry ,F100 ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Redox ,Catalysis ,Metal ,chemistry.chemical_compound ,Materials Chemistry ,Acetonitrile ,Spectroscopy ,010405 organic chemistry ,Ligand ,Metals and Alloys ,General Chemistry ,Actinide ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Plutonium ,chemistry ,visual_art ,Ceramics and Composites ,visual_art.visual_art_medium - Abstract
Complexation of Pu(IV) with the actinide extractant CyMe4-BTPhen (2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline) was followed by UV/vis spectroscopy in acetonitrile solution. The solid-state structure of the crystallized product suggests that Pu(IV) is reduced to Pu(III) upon complexation. Analysis by DFT modeling is consistent with metal-based rather than ligand-based reduction.
- Published
- 2018
27. Back Cover: Structural and Spectroscopic Comparison of Soft‐Se vs. Hard‐O Donor Bonding in Trivalent Americium/Neodymium Molecules (Angew. Chem. Int. Ed. 17/2021)
- Author
-
Andrew J. Gaunt, Brian L. Scott, Stosh A. Kozimor, Frankie D. White, Michael T. Janicke, Anthony W. Schlimgen, Conrad A. P. Goodwin, Thomas E. Albrecht-Schönzart, Lauren M. Stevens, Ping Yang, and Enrique R. Batista
- Subjects
Materials science ,chemistry ,INT ,Physical chemistry ,chemistry.chemical_element ,Molecule ,Cover (algebra) ,Americium ,General Chemistry ,Actinide ,Spectroscopy ,Neodymium ,Catalysis - Published
- 2021
28. Covalency in Lanthanides. An X-ray Absorption Spectroscopy and Density Functional Theory Study of LnCl6x– (x = 3, 2)
- Author
-
Kevin S. Boland, Matthias W. Löble, Brian L. Scott, Alison B. Altman, Marianne P. Wilkerson, David Clark, Angela C. Olson, Ralph A. Zehnder, Steven D. Conradson, David K. Shuh, Stosh A. Kozimor, Juan S. Lezama Pacheco, Tolek Tyliszczak, Richard L. Martin, Stefan G. Minasian, Enrique R. Batista, S. Chantal E. Stieber, and Jason M. Keith
- Subjects
Lanthanide ,X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Inorganic chemistry ,General Chemistry ,Time-dependent density functional theory ,Configuration interaction ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Oxidation state ,Covalent bond ,Physical chemistry ,Density functional theory - Abstract
Covalency in Ln-Cl bonds of Oh-LnCl6(x-) (x = 3 for Ln = Ce(III), Nd(III), Sm(III), Eu(III), Gd(III); x = 2 for Ln = Ce(IV)) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6(x-) (x = 2, 3). The M5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce(III) and Ce(IV)). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce(III) to Ce(IV) had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl6(3-) (formally Ln(III)), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce(IV) 4f-orbital mixing (t1u* + t2u*) in CeCl6(2-). This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl6(2-) (M = Ti, Zr, Hf, U).
- Published
- 2015
29. Understanding Ketone Hydrodeoxygenation for the Production of Fuels and Feedstocks From Biomass
- Author
-
Andrew D. Sutton, Yong-Hui Tian, Enrique R. Batista, Amanda E. King, and Ty J. Brooks
- Subjects
chemistry.chemical_classification ,Ketone ,Biomass ,Alcohol ,General Chemistry ,Catalysis ,Acetic acid ,chemistry.chemical_compound ,chemistry ,Polyketone ,Organic chemistry ,Hydrodeoxygenation ,Bond cleavage - Abstract
Although we can efficiently convert bioderived furans into linear alkanes, the most energy-intensive step in this approach is the hydrodeoxygenation of the intermediate polyketone. To fully understand this process, we have examined the hydrodeoxygenation of a model compound, 3-pentanone, which allows us to follow this process stepwise using Pd/C, H2 (200 psi), and La(OTf)3 in acetic acid to remove the oxygen atom at temperatures between 25 and 200 °C. We have found that ketone reduction to an alcohol is followed by acetoxylation, which provides a more facile route to C–O bond cleavage relative to the parent alcohol.
- Published
- 2015
30. Origins of the Regioselectivity in the Lutetium Triflate Catalyzed Ketalization of Acetone with Glycerol: A DFT Study
- Author
-
Weizhong Chen, Jin Kyung Kim, Caroline B. Hoyt, Louis A. Silks, Ryszard Michalczyk, Aaron W. Pierpont, Richard L. Martin, John C. Gordon, Ruilian Wu, and Enrique R. Batista
- Subjects
chemistry.chemical_compound ,chemistry ,Solketal ,Acetone ,Glycerol ,Regioselectivity ,Organic chemistry ,General Chemistry ,Lewis acids and bases ,Selectivity ,Trifluoromethanesulfonate ,Catalysis - Abstract
We describe DFT computations that address the regioselective preference toward the five-membered ring product 1,3-dioxolane (solketal) over the six-membered-ring product (1,3-dioxane) during Lu(OTf)3-catalyzed ketalization of acetone with glycerol. When ketalization occurs via the internal (secondary) −OH group of glycerol, only solketal production should be possible due to the symmetry of the intermediates. Ketalization via the terminal −OH group of glycerol is predicted to occur in a different manner than the conventionally proposed ketalization mechanism. A constrained hemiketal intermediate is invoked to explain the selectivity for solketal formation.
- Published
- 2015
31. On the Origin of Covalent Bonding in Heavy Actinides
- Author
-
Matthew Urban, Enrique R. Batista, Jing Su, Ping Yang, Morgan Luckey, Morgan P. Kelley, and Jenifer C. Shafer
- Subjects
010405 organic chemistry ,Chemistry ,Ligand ,Nuclear Theory ,Ionic bonding ,General Chemistry ,Orbital overlap ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Specific orbital energy ,Colloid and Surface Chemistry ,Atomic orbital ,Chemical physics ,Covalent bond ,Condensed Matter::Strongly Correlated Electrons ,Molecular orbital ,Degeneracy (biology) ,Atomic physics ,Nuclear Experiment - Abstract
Recent reports have suggested the late actinides participate in more covalent interactions than the earlier actinides, yet the origin of this shift in chemistry is not understood. This report considers the chemistry of actinide dipicolinate complexes to identify why covalent interactions become more prominent for heavy actinides. A modest increase in measured actinide:dipicolinate stability constants is coincident with a significant increase in An 5f energy degeneracy with the dipicolinate molecular orbitals for Bk and Cf relative to Am and Cm. While the interactions in the actinide-dipicolinate complex are largely ionic, the decrease in 5f orbital energy across the series manifests in orbital-mixing and, hence, covalency driven by energy degeneracy. This observation suggests the origin of covalency in heavy actinide interactions stems from the degeneracy of 5f orbitals with ligand molecular orbitals rather than spatial orbital overlap. These findings suggest that the limiting radial extension of the 5f orbitals later in the actinide series could make the heavy actinides ideal elements to probe and tune effects of energy degeneracy driven covalency.
- Published
- 2017
32. New evidence for 5f covalency in actinocenes determined from carbon K-edge XAS and electronic structure theory
- Author
-
Enrique R. Batista, David Clark, David K. Shuh, Tolek Tyliszczak, Kevin S. Boland, Richard L. Martin, Stefan G. Minasian, Stosh A. Kozimor, and Jason M. Keith
- Subjects
chemistry.chemical_compound ,X-ray absorption spectroscopy ,Uranocene ,K-edge ,chemistry ,Atomic orbital ,Absorption spectroscopy ,Molecule ,Molecular orbital ,General Chemistry ,Electronic structure ,Atomic physics ,Molecular physics - Abstract
Evidence for metal–carbon orbital mixing in thorocene and uranocene was determined from DFT calculations and carbon K-edge X-ray absorption spectra (XAS) collected with a scanning transmission X-ray microscope (STXM). Both the experimental and computational results showed that the 5f orbitals engaged in significant δ-type mixing with the C8H82− ligands, which increased as the 5f orbitals dropped in energy on moving from Th4+ to U4+. The first experimental evidence for extensive ϕ-orbital interactions has been provided by the C K-edge XAS analysis of thorocene; however, ϕ-type covalency in uranocene was negligible. The results highlighted two contrasting trends in orbital mixing from one pair of highly symmetric molecules, and showed that covalency does not increase uniformly for different molecular orbital interactions with later actinides.
- Published
- 2014
33. Back Cover: [Am(C 5 Me 4 H) 3 ]: An Organometallic Americium Complex (Angew. Chem. Int. Ed. 34/2019)
- Author
-
Andrew J. Gaunt, Stefanie Dehnen, Niels Lichtenberger, Ping Yang, Scott R. Daly, Brian L. Scott, Conrad A. P. Goodwin, Stosh A. Kozimor, William J. Evans, Anastasia V. Blake, Enrique R. Batista, Thomas E. Albrecht-Schmitt, and Jing Su
- Subjects
Chemistry ,INT ,Physical chemistry ,chemistry.chemical_element ,Cover (algebra) ,Americium ,General Chemistry ,Catalysis - Published
- 2019
34. Tetrahalide Complexes of the [U(NR)2]2+ Ion: Synthesis, Theory, and Chlorine K-Edge X-ray Absorption Spectroscopy
- Author
-
Trevor W. Hayton, Marianne P. Wilkerson, Kevin S. Boland, Brian L. Scott, Richard L. Martin, Stefan G. Minasian, Ping Yang, David K. Shuh, Robert E. Jilek, Steven D. Conradson, James M. Boncella, Molly M. MacInnes, David Clark, Enrique R. Batista, Stosh A. Kozimor, Angela C. Olson, and Liam P. Spencer
- Subjects
Models, Molecular ,X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Inorganic chemistry ,Halide ,General Chemistry ,Electronic structure ,Time-dependent density functional theory ,Imides ,Biochemistry ,Catalysis ,Ion ,Crystallography ,X-Ray Absorption Spectroscopy ,Colloid and Surface Chemistry ,K-edge ,Organometallic Compounds ,Quantum Theory ,Uranium ,Density functional theory ,Chlorine - Abstract
Synthetic routes to salts containing uranium bis-imido tetrahalide anions [U(NR)(2)X(4)](2-) (X = Cl(-), Br(-)) and non-coordinating NEt(4)(+) and PPh(4)(+) countercations are reported. In general, these compounds can be prepared from U(NR)(2)I(2)(THF)(x) (x = 2 and R = (t)Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl(-), the [U(NMe)(2)](2+) cation also reacts with Br(-) to form stable [NEt(4)](2)[U(NMe)(2)Br(4)] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO(2)](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh(4)](2)[U(N(t)Bu)(2)Cl(4)] and [PPh(4)](2)[UO(2)Cl(4)]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.
- Published
- 2013
35. Spectroscopic and computational investigation of actinium coordination chemistry
- Author
-
Henry S. La Pierre, Eva R. Birnbaum, Justin N. Cross, Enrique R. Batista, S. Chantal E. Stieber, Juan S. Lezama Pacheco, Justin J. Wilson, Maryline G. Ferrier, Jonathan W. Engle, Stosh A. Kozimor, John M. Berg, and Benjamin W. Stein
- Subjects
Lanthanide ,Actinium ,Models, Molecular ,Absorption spectroscopy ,Science ,General Physics and Astronomy ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Coordination complex ,Reactivity (chemistry) ,chemistry.chemical_classification ,Radioisotopes ,X-ray absorption spectroscopy ,Multidisciplinary ,Fourier Analysis ,010405 organic chemistry ,General Chemistry ,Actinide ,3. Good health ,0104 chemical sciences ,Solutions ,X-Ray Absorption Spectroscopy ,chemistry ,Physical chemistry ,Density functional theory - Abstract
Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, AcIII reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac–Cl and Ac − O H 2 O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between AcIII and AmIII in HCl solutions indicate AcIII coordinates more inner-sphere Cl1– ligands (3.2±1.1) than AmIII (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique AcIII chemical behaviour.
- Published
- 2016
36. Sulfur K-edge X-ray Absorption Spectroscopy and Time-Dependent Density Functional Theory of Dithiophosphinate Extractants: Minor Actinide Selectivity and Electronic Structure Correlations
- Author
-
David Clark, Scott R. Daly, Jason M. Keith, Kevin S. Boland, Stosh A. Kozimor, Richard L. Martin, and Enrique R. Batista
- Subjects
Lanthanide ,X-ray absorption spectroscopy ,Absorption spectroscopy ,ved/biology ,Chemistry ,ved/biology.organism_classification_rank.species ,Inorganic chemistry ,General Chemistry ,Time-dependent density functional theory ,Biochemistry ,Catalysis ,Spectral line ,Colloid and Surface Chemistry ,K-edge ,Physical chemistry ,Density functional theory ,Conjugate acid - Abstract
The dithiophosphinic acid HS(2)P(o-CF(3)C(6)H(4))(2) is known to exhibit exceptionally high extraction selectivities for trivalent minor actinides (Am and Cm) in the presence of trivalent lanthanides. To generate insight that may account for this observation, a series of [PPh(4)][S(2)PR(2)] complexes, where R = Me (1), Ph (2), p-CF(3)C(6)H(4) (3), m-CF(3)C(6)H(4) (4), o-CF(3)C(6)H(4) (5), o-MeC(6)H(4) (6), and o-MeOC(6)H(4) (7), have been investigated using sulfur K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT). The experimental analyses show distinct features in the spectrum of S(2)P(o-CF(3)C(6)H(4))(2)(-) (5) that are not present in the spectrum of 4, whose conjugate acid exhibits reduced selectivity, or in the spectra of 2 and 3, which are anticipated to have even lower separation factors based on previous studies. In contrast, the spectrum of 5 is similar to those of 6 and 7, despite the significantly different electron-donating properties associated with the o-CF(3), o-Me, and o-OMe substituents. The TDDFT calculations suggest that the distinct spectral features of 5-7 result from steric interactions due to the presence of the ortho substituents, which force the aryl groups to rotate around the P-C bonds and reduce the molecular symmetry from approximately C(2v) in 2-4 to C(2) in 5-7. As a consequence, the change in aryl group orientation appears to make the ortho-substituted S(2)PR(2)(-) anions "softer" extractants compared with analogous Ph-, p-CF(3)C(6)H(4)-, and m-CF(3)C(6)H(4)-containing ligands (2-4) by raising the energies of the sulfur valence orbitals and enhancing orbital mixing between the S(2)P molecular orbitals and the aryl groups bound to phosphorus. Overall, we report that sulfur K-edge XAS experiments and TDDFT calculations reveal unique electronic properties of the S(2)P(o-CF(3)C(6)H(4))(2)(-) anion in 5. These results correlate with the special extraction properties associated with HS(2)P(o-CF(3)C(6)H(4))(2), and suggest that ligand K-edge XAS and TDDFT can be used to guide separation efforts relevant to advanced fuel cycle development.
- Published
- 2012
37. Uranium(VI) bis(imido) disulfonamide and dihalide complexes: Synthesis density functional theory analysis
- Author
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Ping Yang, James M. Boncella, Brian L. Scott, Enrique R. Batista, and Liam P. Spencer
- Subjects
chemistry.chemical_classification ,Stereochemistry ,General Chemical Engineering ,Iodide ,Ionic bonding ,General Chemistry ,Crystal structure ,Uranyl ,Metathesis ,Medicinal chemistry ,chemistry.chemical_compound ,chemistry ,Amide ,Salt metathesis reaction ,Protonolysis - Abstract
Novel cis- and trans-bis(imido) uranium disulfonamide derivatives have been prepared from iodide metathesis reactions between two equivalents of K[N(Me)(SO2Ar’)] (Ar’ = 4-Me-C6H4) and U(NtBu)2(I)2(L)x (L = OPPh3, x = 2; Me2bpy, x = 1; Me2bpy = 4,4’-dimethyl-2,2’-bipyridyl). These bis(amide) derivatives serve as useful precursors for the synthesis of the trans-diphenolate complex U(NtBu)2(O-2-tBuC6H4)2(OPPh3)2 (5), cis- and trans-dithiolate complexes U(NtBu)2(SPh)2(L)x (L = OPPh3 (6); Me2bpy (7)), and cis- and trans-dihalide complexes with the general formulas U(NtBu)2(X)2(L)x (X = Cl, L = OPPh3 (8), L = Me2bpy (10); X = Br, L = OPPh3 (9), L = Me2bpy (11)). DFT calculations performed on the trans-dihalide series U(NtBu)2(X)2(L)2 and the UO22+ analogues UO2X2(OPPh3)2 suggest that the uranium centers in the [U(NtBu)2]2+ ions possess more covalent character than analogous UO22+ derivatives but that the U-X bonds in the U(NtBu)2X2L2 complexes possess a more ionic nature.
- Published
- 2010
38. Cation-Cation Interactions, Magnetic Communication, and Reactivity of the Pentavalent Uranium Ion [U(NtBu)2]+
- Author
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Brian L. Scott, James M. Boncella, Eric J. Schelter, Joe D. Thompson, Robyn L. Gdula, Enrique R. Batista, Ping Yang, Liam P. Spencer, and Jaqueline L. Kiplinger
- Subjects
chemistry.chemical_compound ,Crystallography ,Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Reactivity (chemistry) ,General Chemistry ,Actinide ,Electronic structure ,Uranium ,Imide ,Catalysis ,Ion - Abstract
Communication is important: The dimeric bis(imido) uranium complex [{U(NtBu)(2)(I)(tBu(2)bpy)}(2)] (see picture; U green, N blue, I red) has cation-cation interactions between [U(NR)(2)](+) ions. This f(1)-f(1) system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.
- Published
- 2009
39. A Linear trans-Bis(imido) Neptunium(V) Actinyl Analog: Np(V)(NDipp)2((t)Bu2bipy)2Cl (Dipp = 2,6-(i)Pr2C6H3)
- Author
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Neil C. Tomson, Jessie L. Brown, James M. Boncella, Brian L. Scott, Enrique R. Batista, Sean D. Reilly, and Andrew J. Gaunt
- Subjects
Neptunium ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Electronic structure ,Uranium ,Biochemistry ,Catalysis ,Bipyridine ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Reagent ,Proton NMR ,Transuranium element - Abstract
The discovery that imido analogs of actinyl dioxo cations can be extended beyond uranium into the transuranic elements is presented. Synthesis of the Np(V) complex, Np(NDipp)2((t)Bu2bipy)2Cl (1), is achieved through treatment of a Np(IV) precursor with a bipyridine coligand and lithium-amide reagent. Complex 1 has been structurally characterized, analyzed by (1)H NMR and UV-vis-NIR spectroscopies, and the electronic structure evaluated by DFT calculations.
- Published
- 2015
40. Diffusion and Island formation on the ice Ih basal plane surface
- Author
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Enrique R. Batista and Hannes Jónsson
- Subjects
Surface diffusion ,Arrhenius equation ,General Computer Science ,Chemistry ,Binding energy ,General Physics and Astronomy ,Ice Ih ,General Chemistry ,Activation energy ,Thermal diffusivity ,Kinetic energy ,Molecular physics ,Mean squared displacement ,Computational Mathematics ,Crystallography ,symbols.namesake ,Mechanics of Materials ,symbols ,General Materials Science - Abstract
We present theoretical calculations of the adsorption, diffusion and island formation of water admolecules on the basal plane surface of an ice Ih crystal. These are preliminary calculations based on the simple TIP4P interaction potential, a pairwise additive potential function based on point charges. At low coverage, we find that an admolecule prefers to sit at non-crystallographic sites on the surface (i.e., sites that do not fit into the ice lattice). Since ice Ih is proton disordered, no two sites are exactly the same and there is a wide range of binding energies. For some local environments the binding energy is of the order of, or even larger than, the cohesive energy. The proton disorder also results in a range of activation energies for diffusion. After mapping out a large number of diffusion barriers using the nudged elastic band method, a kinetic Monte-Carlo calculation of the diffusion at 140 K was performed. At early time, the mean squared displacement has anomalous scaling with time as is common for diffusion on random lattices. But, at longer time the scaling is normal and a diffusion coefficient can be obtained. The diffusivity is slightly larger than a recent experimental upper bound given by Brown and George. The energetics and dynamics of the formation of small islands on the ice surface have also been studied. It is found that islands up to and including pentamer are non-crystallographic, but the hexamer is crystallographic. While the formation of a crystallographic hexamer from a non-crystallographic pentamer and a new admolecule involves a complex concerted motion of all the island molecules and a large relaxation of the substrate, the activation energy for the process is estimated to be quite small, smaller than the admolecule diffusion barrier.
- Published
- 2001
41. Carbon K-edge X-ray absorption spectroscopy and time-dependent density functional theory examination of metal-carbon bonding in metallocene dichlorides
- Author
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Tolek Tyliszczak, Kevin S. Boland, Jason M. Keith, Louis J. Vernon, Enrique R. Batista, David K. Shuh, Richard L. Martin, Stefan G. Minasian, and Stosh A. Kozimor
- Subjects
X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Analytical chemistry ,chemistry.chemical_element ,General Chemistry ,Time-dependent density functional theory ,Antibonding molecular orbital ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Atomic orbital ,K-edge ,Density functional theory ,Carbon - Abstract
Metal-carbon covalence in (C5H5)2MCl2 (M = Ti, Zr, Hf) has been evaluated using carbon K-edge X-ray absorption spectroscopy (XAS) as well as ground-state and time-dependent hybrid density functional theory (DFT and TDDFT). Differences in orbital mixing were determined experimentally using transmission XAS of thin crystalline material with a scanning transmission X-ray microscope (STXM). Moving down the periodic table (Ti to Hf) has a marked effect on the experimental transition intensities associated with the low-lying antibonding 1a1* and 1b2* orbitals. The peak intensities, which are directly related to the M-(C5H5) orbital mixing coefficients, increase from 0.08(1) and 0.26(3) for (C5H5)2TiCl2 to 0.31(3) and 0.75(8) for (C5H5)2ZrCl2, and finally to 0.54(5) and 0.83(8) for (C5H5)2HfCl2. The experimental trend toward increased peak intensity for transitions associated with 1a1* and 1b2* orbitals agrees with the calculated TDDFT oscillator strengths [0.10 and 0.21, (C5H5)2TiCl2; 0.21 and 0.73, (C5H5)2ZrCl2; 0.35 and 0.69, (C5H5)2HfCl2] and with the amount of C 2p character obtained from the Mulliken populations for the antibonding 1a1* and 1b2* orbitals [8.2 and 23.4%, (C5H5)2TiCl2; 15.3 and 39.7%, (C5H5)2ZrCl2; 20.1 and 50.9%, (C5H5)2HfCl2]. The excellent agreement between experiment, theory, and recent Cl K-edge XAS and DFT measurements shows that C 2p orbital mixing is enhanced for the diffuse Hf (5d) and Zr (4d) atomic orbitals in relation to the more localized Ti (3d) orbitals. These results provide insight into how changes in M-Cl orbital mixing within the metallocene wedge are correlated with periodic trends in covalent bonding between the metal and the cyclopentadienide ancillary ligands.
- Published
- 2013
42. Covalency in metal-oxygen multiple bonds evaluated using oxygen K-edge spectroscopy and electronic structure theory
- Author
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J. A. Bradley, David K. Shuh, Enrique R. Batista, Jason M. Keith, Stosh A. Kozimor, Ping Yang, Gregory L. Wagner, Tsu-Chein Weng, Richard L. Martin, Stefan G. Minasian, Dimosthenis Sokaras, Scott R. Daly, Wayne W. Lukens, Dennis Nordlund, Gerald T. Seidler, Tolek Tyliszczak, and Kevin S. Boland
- Subjects
Microscopy, Electron, Scanning Transmission ,Absorption spectroscopy ,Molecular Structure ,Chemistry ,X-Rays ,Electrons ,General Chemistry ,Biochemistry ,Catalysis ,XANES ,Specific orbital energy ,Oxygen ,Colloid and Surface Chemistry ,X-Ray Absorption Spectroscopy ,Transition metal ,Atomic orbital ,K-edge ,Metals, Heavy ,Physical chemistry ,Quantum Theory ,Density functional theory ,Spectroscopy - Abstract
Advancing theories of how metal-oxygen bonding influences metal oxo properties can expose new avenues for innovation in materials science, catalysis, and biochemistry. Historically, spectroscopic analyses of the transition metal MO(4)(x-) anions have formed the basis for new M-O bonding theories. Herein, relative changes in M-O orbital mixing in MO(4)(2-) (M = Cr, Mo, W) and MO(4)(-) (M = Mn, Tc, Re) are evaluated for the first time by nonresonant inelastic X-ray scattering, X-ray absorption spectroscopy using fluorescence and transmission (via a scanning transmission X-ray microscope), and time-dependent density functional theory. The results suggest that moving from Group 6 to Group 7 or down the triads increases M-O e* (π*) mixing; for example, it more than doubles in ReO(4)(-) relative to CrO(4)(2-). Mixing in the t(2)* orbitals (σ* + π*) remains relatively constant within the same Group, but increases on moving from Group 6 to Group 7. These unexpected changes in orbital energy and composition for formally isoelectronic tetraoxometalates are evaluated in terms of periodic trends in d orbital energy and radial extension.
- Published
- 2013
43. Scanning tunneling microscopy and theoretical study of water adsorption on Fe3O4: implications for catalysis
- Author
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Daejin Eom, Maria Flytzani-Stephanopoulos, Xiaodong Wen, Kwang Taeg Rim, Siu-Wai Chan, George W. Flynn, and Enrique R. Batista
- Subjects
chemistry.chemical_element ,General Chemistry ,Hematite ,Biochemistry ,Oxygen ,Catalysis ,Dissociation (chemistry) ,law.invention ,Crystallography ,Colloid and Surface Chemistry ,Adsorption ,chemistry ,Computational chemistry ,law ,visual_art ,visual_art.visual_art_medium ,Molecule ,Scanning tunneling microscope ,Single crystal - Abstract
The reduced surface of a natural Hematite single crystal α-Fe(2)O(3)(0001) sample has multiple surface domains with different terminations, Fe(2)O(3)(0001), FeO(111), and Fe(3)O(4)(111). The adsorption of water on this surface was investigated via Scanning Tunneling Microscopy (STM) and first-principle theoretical simulations. Water species are observed only on the Fe-terminated Fe(3)O(4)(111) surface at temperatures up to 235 K. Between 235 and 245 K we observed a change in the surface species from intact water molecules and hydroxyl groups bound to the surface to only hydroxyl groups atop the surface terminating Fe(III) cations. This indicates a low energy barrier for water dissociation on the surface of Fe(3)O(4) that is supported by our theoretical computations. Our first principles simulations confirm the identity of the surface species proposed from the STM images, finding that the most stable state of a water molecule is the dissociated one (OH + H), with OH atop surface terminating Fe(III) sites and H atop under-coordinated oxygen sites. Attempts to simulate reaction of the surface OH with coadsorbed CO fail because the only binding sites for CO are the surface Fe(III) atoms, which are blocked by the much more strongly bound OH. In order to promote this reaction we simulated a surface decorated with gold atoms. The Au adatoms are found to cap the under-coordinated oxygen sites and dosed CO is found to bind to the Au adatom. This newly created binding site for CO not only allows for coexistence of CO and OH on the surface of Fe(3)O(4) but also provides colocation between the two species. These two factors are likely promoters of catalytic activity on Au/Fe(3)O(4)(111) surfaces.
- Published
- 2012
44. Determining relative f and d orbital contributions to M-Cl covalency in MCl6(2-) (M = Ti, Zr, Hf, U) and UOCl5(-) using Cl K-edge X-ray absorption spectroscopy and time-dependent density functional theory
- Author
-
Kevin S. Boland, Richard L. Martin, Stefan G. Minasian, Stosh A. Kozimor, Gregory L. Wagner, Marianne P. Wilkerson, Jason M. Keith, Daniel E. Schwarz, Laura E. Wolfsberg, Enrique R. Batista, Ping Yang, David K. Shuh, Steven D. Conradson, and David Clark
- Subjects
X-ray absorption spectroscopy ,Valence (chemistry) ,Absorption spectroscopy ,Chemistry ,General Chemistry ,Electronic structure ,Time-dependent density functional theory ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,K-edge ,Atomic orbital ,Physical chemistry ,Density functional theory ,Atomic physics - Abstract
Chlorine K-edge X-ray absorption spectroscopy (XAS) and ground-state and time-dependent hybrid density functional theory (DFT) were used to probe the electronic structures of O(h)-MCl(6)(2-) (M = Ti, Zr, Hf, U) and C(4v)-UOCl(5)(-), and to determine the relative contributions of valence 3d, 4d, 5d, 6d, and 5f orbitals in M-Cl bonding. Spectral interpretations were guided by time-dependent DFT calculated transition energies and oscillator strengths, which agree well with the experimental XAS spectra. The data provide new spectroscopic evidence for the involvement of both 5f and 6d orbitals in actinide-ligand bonding in UCl(6)(2-). For the MCl(6)(2-), where transitions into d orbitals of t(2g) symmetry are spectroscopically resolved for all four complexes, the experimentally determined Cl 3p character per M-Cl bond increases from 8.3(4)% (TiCl(6)(2-)) to 10.3(5)% (ZrCl(6)(2-)), 12(1)% (HfCl(6)(2-)), and 18(1)% (UCl(6)(2-)). Chlorine K-edge XAS spectra of UOCl(5)(-) provide additional insights into the transition assignments by lowering the symmetry to C(4v), where five pre-edge transitions into both 5f and 6d orbitals are observed. For UCl(6)(2-), the XAS data suggest that orbital mixing associated with the U 5f orbitals is considerably lower than that of the U 6d orbitals. For both UCl(6)(2-) and UOCl(5)(-), the ground-state DFT calculations predict a larger 5f contribution to bonding than is determined experimentally. These findings are discussed in the context of conventional theories of covalent bonding for d- and f-block metal complexes.
- Published
- 2012
45. Differences in actinide metal-ligand orbital interactions: comparison of U(IV) and Pu(IV) β-ketoiminate N,O donor complexes
- Author
-
Brian L. Scott, Enrique R. Batista, Iain May, David D. Schnaars, Andrew J. Gaunt, Guang Wu, Trevor W. Hayton, and Sean D. Reilly
- Subjects
Chemistry ,Ligand ,Stereochemistry ,Metals and Alloys ,General Chemistry ,Actinide ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Metal ,Crystallography ,visual_art ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium - Abstract
Syntheses and characterization of UCl(2)((Ar)acnac)(2), UI(2)((Ar)acnac)(2), and PuI(2)((Ar)acnac)(2) are reported ((Ar)acnac denotes a bis-phenyl β-ketoiminate ligand where Ar = 3,5-(t)Bu(2)C(6)H(3)). Structural analyses and computations show significant metal-ligand orbital interaction differences in U(IV) vs. Pu(IV) bonding.
- Published
- 2011
46. Experimental and theoretical comparison of the O K-edge nonresonant inelastic X-ray scattering and X-ray absorption spectra of NaReO4
- Author
-
David Clark, J. A. Bradley, Richard L. Martin, Laura E. Wolfsberg, Kevin S. Boland, Stosh A. Kozimor, Brian L. Scott, Steven D. Conradson, Carol J. Burns, Enrique R. Batista, Ping Yang, David K. Shuh, Tolek Tyliszczak, Marianne P. Wilkerson, and Gerald T. Seidler
- Subjects
X-ray absorption spectroscopy ,Absorption spectroscopy ,Scattering ,Chemistry ,X-ray ,Analytical chemistry ,General Chemistry ,Biochemistry ,Catalysis ,Spectral line ,Colloid and Surface Chemistry ,K-edge ,Microscopy ,Saturation (chemistry) - Abstract
Accurate X-ray absorption spectra (XAS) of first row atoms, e.g., O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation affects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO(4)(1-) and provide methodology for obtaining trustworthy and quantitative data on nonconducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by nonresonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO(4)(1-), TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t(2) molecular orbitals that result from Re 5d and O 2p covalent mixing in T(d) symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time dependent-density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO(4) may serve as a well-defined O K-edge energy and intensity standard for future O K-edge XAS studies.
- Published
- 2010
47. Luminescence in Ce(IV) polyoxometalate [Ce(W5O18)2]8-: a combined experimental and theoretical study
- Author
-
Brian L. Scott, Rico E. Del Sesto, Iain May, Michael W. Blair, Lindsay E. Roy, Denisse Ortiz-Acosta, Richard L. Martin, and Enrique R. Batista
- Subjects
Materials science ,Polyoxometalate ,Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,Density functional theory ,General Chemistry ,Luminescence ,Photochemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Herein we describe the unique luminescent behavior observed in [CeIV(W5O18)2]8− clusters and examine the photophysical properties using density functional theory.
- Published
- 2010
48. Uranium azide photolysis results in C-H bond activation and provides evidence for a terminal uranium nitride
- Author
-
Brian L. Scott, David E. Morris, Enrique R. Batista, Jaqueline L. Kiplinger, Thibault Cantat, and Robert K. Thomson
- Subjects
Azides ,Magnetic Resonance Spectroscopy ,Photolysis ,Spectrophotometry, Infrared ,Ligand ,General Chemical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Actinide ,Uranium ,Triple bond ,Nuclear Energy ,Uranium Compounds ,Mass Spectrometry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Lewis acids and bases ,Azide ,Nitrogen Compounds ,Uranium nitride ,Oxidation-Reduction - Abstract
Uranium nitride [U[triple bond]N](x) is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U[triple bond]N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U[triple bond]N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C(6)F(5))(3). These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.
- Published
- 2010
49. Trends in covalency for d- and f-element metallocene dichlorides identified using chlorine K-edge X-ray absorption spectroscopy and time-dependent density functional theory
- Author
-
Laura E. Wolfsberg, Steven D. Conradson, Richard L. Martin, Stosh A. Kozimor, Enrique R. Batista, Kevin S. Boland, Carol J. Burns, Ping Yang, Marianne P. Wilkerson, and David Clark
- Subjects
X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Inorganic chemistry ,General Chemistry ,Electronic structure ,Time-dependent density functional theory ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,K-edge ,Atomic orbital ,Principal quantum number ,Physical chemistry ,Density functional theory - Abstract
We describe the use of Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT) to probe the electronic structure and determine the degree of orbital mixing in M-Cl bonds for (C(5)Me(5))(2)MCl(2) (M = Ti, 1; Zr, 2; Hf, 3; Th, 4; U, 5), where we can directly compare a class of structurally similar compounds for d- and f-elements. Pre-edge features in the Cl K-edge XAS data for the group IV transition-metals 1-3 provide direct evidence of covalent M-Cl orbital mixing. The amount of Cl 3p character was experimentally determined to be 25%, 23%, and 22% per M-Cl bond for 1-3, respectively. For actinides, we find a pre-edge shoulder for 4 (Th) and distinct and weak pre-edge features for U, 5. The amount of Cl 3p character was determined to be 9% for 5, and we were unable to make an experimental determination for 4. Using hybrid DFT calculations with relativistic effective core potentials, the electronic structures of 1-5 were calculated and used as a guide to interpret the experimental Cl K-edge XAS data. For transition-metal compounds 1-3, the pre-edge features arise due to transitions from Cl 1s electrons into the 3d-, 4d-, and 5d-orbitals, with assignments provided in the text. For Th, 4, we find that 5f- and 6d-orbitals are nearly degenerate and give rise to a single pre-edge shoulder in the XAS. For U, 5, we find the 5f- and 6d-orbitals fall into two distinct energy groupings, and Cl K-edge XAS data are interpreted in terms of Cl 1s transitions into both 5f- and 6d-orbitals. Time-dependent DFT was used to calculate the energies and intensities of Cl 1s transitions into empty metal-based orbitals containing Cl 3p character and provide simulated Cl K-edge XAS spectra for 1-4. For 5, which has two unpaired 5f electrons, simulated spectra were obtained from transition dipole calculations using ground-state Kohn-Sham orbitals. To the best of our knowledge, this represents the first application of Cl K-edge XAS to actinide systems. Overall, this study allows trends in orbital mixing within a well-characterized structural motif to be identified and compared between transition-metals and actinide elements. These results show that the orbital mixing for the d-block compounds slightly decreases in covalency with increasing principal quantum number, in the order Ti > Zr approximately = Hf, and that uranium displays approximately half the covalent orbital mixing of transition elements.
- Published
- 2009
50. Imido exchange in bis(imido) uranium(VI) complexes with aryl isocyanates
- Author
-
James M. Boncella, Liam P. Spencer, Brian L. Scott, Enrique R. Batista, and Ping Yang
- Subjects
Chemistry ,Ligand ,Aryl ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Actinide ,Uranium ,Biochemistry ,Medicinal chemistry ,Isocyanate ,Catalysis ,Cycloaddition ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Transition metal ,Density functional theory - Abstract
Addition of 1 and 2 equiv of ArNCO (ArPh, 2,4,6-Me3C6H2) to U(NtBu)2(I)2(OPPh3)2 yields the aryl−imido complexes U(NAr)(NtBu)(I)2(OPPh3)2 and U(NAr)2(I)2(OPPh3)2, respectively. Unlike analogous transition metal reactions this imido exchange reaction does not proceed through a metal oxo intermediate. Density functional theory calculations and 15N-labeling studies suggest this transformation involves the [2 + 2] cycloaddition of the aryl isocyanate CN bond across the UN imido ligand to form an N,N-bound ureato intermediate.
- Published
- 2008
Catalog
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