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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Enhanced tunability of thermodynamic stability of complex hydrides by the incorporation of H{sup –} anions

First-principles calculations were employed to investigate hypothetical complex hydrides (M,M{sup ′}){sub 4}FeH{sub 8} (M = Na, Li; M{sup ′}=Mg, Zn, Y, Al). Besides complex anion [FeH{sub 6}]{sup 4–}, these materials contain two H{sup –} anions, which raise the total anionic charge state from tetravalent to hexavalent, and thereby significantly increasing the number of combinations of countercations. We have determined that similar to complex hydrides (M,M{sup ′}){sub 2}FeH{sub 6} containing only [FeH{sub 6}]{sup 4–}, the thermodynamic stability is tuned by the average cation electronegativity. Thus, the chemical flexibility provided by incorporating H{sup –} enhances the tunability of thermodynamic stability, which will be beneficial in obtaining optimal stability for hydrogen storage materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Deletion of the cytochrome bc complex from Heliobacterium modesticaldum results in viable but non-phototrophic cells

The heliobacteria, a family of anoxygenic phototrophs, possess the simplest known photosynthetic apparatus. Although they are photoheterotrophs in the light, the heliobacteria can also grow chemotrophically via pyruvate metabolism in the dark. In the heliobacteria, the cytochrome bc complex is responsible for oxidizing menaquinol and reducing cytochrome c 553 in the electron flow cycle used for phototrophy. However, there is no known electron acceptor for the mobile cytochrome c 553 other than the photochemical reaction center. We have, therefore, hypothesized that the cytochrome bc complex is necessary for phototrophy, but unnecessary for chemotrophic growth in the dark. Here, we used a two-step method for CRISPR-based genome editing in Heliobacterium modesticaldum to delete the genes encoding the four major subunits of the cytochrome bc complex. Genotypic analysis verified the deletion of the petCBDA gene cluster encoding the catalytic components of the complex. Spectroscopic studies revealed that re-reduction of cytochrome c 553 after flash-induced photo-oxidation was over 100 times slower in the petCBDA mutant compared to the wild-type. Steady-state levels of oxidized P 800 (the primary donor of the photochemical reaction center) were much higher in the petCBDA mutant at every light level, consistent with a limitation in electron flow to the reaction center. The petCBDA mutant was unable to grow phototrophically on acetate plus CO 2 but could grow chemotrophically on pyruvate as a carbon source similar to the wild-type strain in the dark. The mutants could be complemented by reintroduction of the petCBDA gene cluster on a plasmid expressed from the clostridial eno promoter.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Group 10 complexes containing phosphinomethylamine ligands: Synthesis, structural analysis and electrochemical studies

The reaction of [M(triphos)OTf](OTf) (M = Pd, Pt; triphos = (Ph2PCH2CH2)2PPh; OTf = triflate) with one equivalent of a diphenylphosphinomethylamine ligand (PPh2NPh(R), R = Ph or Me) leads to the formation of the M(II) complexes [Pd(triphos)PPh2NPh(R)](OTf)2 (1a, R = Ph; 1b, R = Me) and [Pt(triphos)PPh2NPh(R)]- (OTf)2 (2a, R = Ph; 2b, R = Me). Complexes 1a, 1b, 2a and 2b were obtained in moderate yields and characterized by elemental analysis, 1H, 13C, 31P NMR and X-ray diffraction. The redox behavior of these complexes shows a reversible reduction wave with half-wave potentials ranging from -1.04 to -1.23 V. Electrocatalytic proton reduction studies demonstrate these complexes function as hydrogen production catalysts with turn over frequencies ranging from 120 to 200 s-1. We thank Research Corporation Cottrell Science Award (7293) and Fort Lewis College for financial support of this project. Pacific Northwest National Laboratory collaborators would like to acknowledge the support of the US Department of Energy Basic Energy Sciences’ Chemical Sciences, Geosciences, and Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

08 HYDROGEN↗
DOE OSTI2013

Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Assessment of TD-DFT and LF-DFT for study of d − d transitions in first row transition metal hexaaqua complexes

Herein, we present the systematic, comparative computational study of the d − d transitions in a series of first row transition metal hexaaqua complexes, [M(H{sub 2}O){sub 6}]{sup n+} (M{sup 2+/3+} = V {sup 2+/3+}, Cr{sup 2+/3+}, Mn{sup 2+/3+}, Fe{sup 2+/3+}, Co{sup 2+/3+}, Ni{sup 2+}) by the means of Time-dependent Density Functional Theory (TD-DFT) and Ligand Field Density Functional Theory (LF-DFT). Influence of various exchange-correlation (XC) approximations have been studied, and results have been compared to the experimental transition energies, as well as, to the previous high-level ab initio calculations. TD-DFT gives satisfactory results in the cases of d{sup 2}, d{sup 4}, and low-spin d{sup 6} complexes, but fails in the cases when transitions depend only on the ligand field splitting, and for states with strong character of double excitation. LF-DFT, as a non-empirical approach to the ligand field theory, takes into account in a balanced way both dynamic and non-dynamic correlation effects and hence accurately describes the multiplets of transition metal complexes, even in difficult cases such as sextet-quartet splitting in d{sup 5} complexes. Use of the XC functionals designed for the accurate description of the spin-state splitting, e.g., OPBE, OPBE0, or SSB-D, is found to be crucial for proper prediction of the spin-forbidden excitations by LF-DFT. It is shown that LF-DFT is a valuable alternative to both TD-DFT and ab initio methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ab-initio calculation study on the formation mechanism of boron-oxygen complexes in c-Si

Boron-oxygen (B-O) complex in crystalline silicon (c-Si) solar cells is responsible for the light-induced efficiency degradation of solar cell. However, the formation mechanism of B-O complex is not clear yet. By Ab-initio calculation, it is found that the stagger-type oxygen dimer (O{sub 2i}{sup st}) should be the component of B-O complex, whose movement occurs through its structure reconfiguration at low temperature, instead of its long-distance diffusion. The O{sub 2i}{sup st} can form two stable “latent centers” with the B{sub s}, which are recombination-inactive. The latent centers can be evolved into the metastable recombination centers via their structure transformation in the presence of excess carriers. These results can well explain the formation behaviors of B-O complexes in c-Si.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Ab initio calculations on the magnetic properties of transition metal complexes

We present a protocol for the ab initio determination of the magnetic properties of mono- and polynuclear transition metal compounds. First, we obtain the low lying electronic states by multireference methods. Then, we include spin-orbit coupling and an external magnetic field for the determination of zero-field splitting and g-tensors. For the polynuclear complexes the magnetic exchange coupling constants are determined by a modified complete active space self consistent field method. Based on the results of the ab initio calculations, magnetic data such as magnetic susceptibility or magnetization are simulated and compared to experimental data. The results obtained for the polynuclear complexes are further analysed by calculations on model complexes where part of the magnetic centers are substituted by diamagnetic ions. The methods are applied to different Co and Ni containing transition metal complexes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Wind Forecasting Improvement Project In Complex Terrain Near the Columbia River Gorge

In 2014 a multi-institution team led by Vaisala, Inc. was selected by the Department of Energy (DOE) to partner with multiple DOE and National Oceanic and Atmospheric Administration (NOAA) laboratories on a project designed to improve the quality of wind power forecasts in areas of complex terrain. This was the second Wind Forecast Improvement Project (WFIP2) funded by DOE and it extended from late 2014 through the middle of 2018. It encompassed an 18-month observational field campaign, numerical weather prediction (NWP) model development, extensive analysis of data and NWP output, and the creation of decision support tool algorithms to convey forecast information to end users in the wind industry. WFIP2 focused on improvements to the representation of near-surface and boundary-layer physics in NOAA’s High-Resolution Rapid Refresh (HRRR) model. Improvements to HRRR, which is run operationally over the continental United States, benefit the wind industry in multiple ways. Forecasts from the operational HRRR are used directly by wind power forecast vendors and the operators of wind plants. In addition, because HRRR is built using the widely-used Weather Research and Forecasting (WRF) model, improvements to its parameterizations become available to commercial and research institutions using WRF for a myriad of purposes. The geographic area studied by WFIP2 was a region of the Columbia River basin located to the east of the Cascade Mountains between Oregon and Washington. Home to over 6 GW of installed capacity for wind energy production, this area also hosts a variety of atmospheric phenomena either unique to or augmented by complex topography. This makes it an attractive test-bed for the analysis of wind forecast in complex terrain, though results found are should be applicable in any area of topographic complexity. WFIP2 succeeded as a collaborative effort, and while this report focuses on the activities of the team led by Vaisala, the work described here is part of a larger whole. The Vaisala team accomplished a number of specific tasks as described in this report, while also contributing to this larger effort.

17 WIND ENERGY↗
DOE OSTI2024

Tailoring Molecular Space to Navigate Phase Complexity in Cs-Based Quasi-2D Perovskites via Gated-Gaussian-Driven High-Throughput Discovery

Cesium-based quasi-2D halide perovskites (HPs) offer promising functionalities and low-temperature manufacturability, suited to stable tandem photovoltaics. However, the chemical interplays between the molecular spacers and the inorganic building blocks during crystallization cause substantial phase complexities in the resulting matrices. To successfully optimize and implement the quasi-2D HP functionalities, a systematic understanding of spacer chemistry, along with the seamless navigation of the inherently discrete molecular space, is necessary. Herein, by utilizing high-throughput automated experimentation, the phase complexities in the molecular space of quasi-2D HPs are explored, thus identifying the chemical roles of the spacer cations on the synthesis and functionalities of the complex materials. Furthermore, a novel active machine learning algorithm leveraging a two-stage decision-making process, called gated Gaussian process Bayesian optimization is introduced, to navigate the discrete ternary chemical space defined with two distinctive spacer molecules. Through simultaneous optimization of photoluminescence intensity and stability that “tailors” the chemistry in the molecular space, a ternary-compositional quasi-2D HP film realizing excellent optoelectronic functionalities is demonstrated. Finally, this work not only provides a pathway for the rational and bespoke design of complex HP materials but also sets the stage for accelerated materials discovery in other multifunctional systems.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The Exceptional Diversity of Homoleptic Uranium–Methyl Complexes

Homoleptic σ-bonded uranium–alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium–methyl complexes. Amongst these complexes, the first example of a homoleptic uranium–alkyl dimer, [Li(THF) 4 ] 2 [U 2 (CH 3 ) 10 ], as well as a seven-coordinate uranium–methyl monomer, {Li(OEt 2 )Li(OEt 2 ) 2 UMe 7 Li} n were both crystallographically identified. We report the diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium–alkyl chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear Pt II →Ge IV Complex

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph 2 P)C 6 H 4 ) 2 Ge IV Cl 2 ]Pt II Cl 2 and [(o-(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt III Cl 3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt I Cl with quantum yields of 1.7 % and 3.2 % for the Ge IV –Pt II and Ge III –Pt III isomers, respectively. Conversion of the Ge IV –Pt II isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Additionally, transient-absorption-spectroscopy studies carried out on the Ge III –Pt III isomer point to a ligand arene–Cl. charge-transfer complex as an intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Formation of a Decanuclear Organometallic Dysprosium Complex via a Radical–Radical Cross–Coupling Reaction

Over the years, polynuclear cyclic or torus complexes have attracted increasing interest due to their unique metal topologies and properties. However, the isolation of polynuclear cyclic organometallic complexes is extremely challenging due to their inherent reactivity, which stems from the labile and reactive metal-carbon bonds. In this study, the pyrazine ligand undergoes a radical-radical cross-coupling reaction leading to the formation of a decanuclear [(Cp*) 20 Dy 10 (L1) 10 ] ⋅ 12(C 7 H 8 ) ( 1 ; where L1 = anion of 2-prop-2-enyl-2 H -pyrazine; Cp* = pentamethylcyclopentadienyl) complex, where all Dy III metal centres are bridged by the anionic L1 ligand. Amongst the family of polynuclear Ln organometallic complexes bearing Cp R 2 Ln x units (Cp R = substituted cyclopentadienyl), 1 features the highest nuclearity obtained to date. In-depth computational studies were conducted to elucidate the proposed reaction mechanism and formation of L1, while probing of the magnetic properties of 1 , revealed slow magnetic relaxation upon application of a static dc field.

cross-coupling↗
DOE OSTI2014

Mononuclear iridium dinitrogen complexes bonded to zeolite HY

In this study, the adsorption of N 2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N 2 in H 2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N 2 . Four supported species formed in various flowing gases: Ir(N 2 ), Ir(N 2 )(N 2 ), Ir(C 2 H 5 )(N 2 ), and Ir(H)(N 2 ). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N 2 , Ir(N 2 ) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N 2 ) formed transiently in flowing CO, and in the presence of H 2 , rather stable iridium hydride complexes formed. Here, four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Matching Complexes of Trees and Applications of the Matching Tree Algorithm

A matching complex of a simple graph G is a simplicial complex with faces given by the matchings of G. The topology of matching complexes is mysterious; there are few graphs for which the homotopy type is known. Marietti and Testa showed that matching complexes of forests are contractible or homotopy equivalent to a wedge of spheres. We study two specific families of trees. For caterpillar graphs, we give explicit formulas for the number of spheres in each dimension and for perfect binary trees we find a strict connectivity bound. We also use a tool from discrete Morse theory called the Matching Tree Algorithm to study the connectivity of honeycomb graphs, partially answering a question raised by Jonsson.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Six-coordinate nitrosyl complex of Co-meso-tetra-p-tolylporphyrin with a trans-1-methylimidazole ligand

Electron absorption and Fourier-transform IR spectroscopy was used to determine that the reaction of 1-methylimidazole (1-MeIm) with a nitrosyl complex of meso-tetra-p-tolylporphyrinate cobalt (Co(TTP)(NO)) at 210—240 K led to the formation of the six-coordinate complex (1-MeIm)Co(TTP)(NO), which was stable at low temperatures both in the solid state and in a solution of toluene. Based on the temperature dependence of the equilibrium constants, the thermodynamic parameters of complexation were calculated, which indicated a weak binding of the 1-methylimidazole ligand with the Co-porphyrin nitrosyl complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Addition of phenylacetylene and camphor to the complex [(dpp-bian)Eu(dme){sub 2}] (dpp-bian is the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene dianion)

The reduction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) with an excess of europium metal in 1,2-dimethoxyethane (dme) produces a divalent europium complex with the dpp-bian dianion, [(dpp-bian)Eu(dme){sub 2}] (1). The reactions of 1 with phenyl-acetylene and camphor proceed via protonation of the diimine ligand to form the monomeric amido-amino complexes of divalent europium — [H(dpp-bian)Eu(C≡CPh)(dme){sub 2}] (2) and [H(dpp-bian)Eu(camphor)(dme){sub 2}] (3), respectively. Compounds 2 and 3 were characterized by IR spectroscopy and elemental analysis. Their molecular structures were determined by X-ray diffraction. Compounds 2 and 3 were shown to be monomeric seven-coordinate europium(II) complexes with terminal phenylethynyl and enol ligands, respectively. According to the IR spectroscopic data, the terminal ligands in complexes 2 and 3 undergo tautomerization involving backward proton transfer from the amido-amino ligand to the substrate. The magnetic moment of compound 2 (8.03 μB) remains constant in the temperature range of 4—300 К and confirms the presence of divalent europium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis and structures of zirconium complexes [Et{sub 2}H{sub 2}N]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–}, [Me{sub 3}NCH{sub 2}Ph]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–}•MeCN, [Ph{sub 3}PC{sub 6}H{sub 4}(CHPh{sub 2}-4)]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–}•2 MeCN, and [Ph{sub 4}Sb]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–}

The complexes [Et{sub 2}H{sub 2}N]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–} (1), [Me{sub 3}NCH{sub 2}Ph]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–}•MeCN (2), [Ph{sub 3}PC{sub 6}H{sub 4}(CHPh{sub 2}-4)]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–}•2 MeCN (3), and [Ph{sub 4}Sb]{sup +}{sub 2}[ZrCl{sub 6}]{sup 2–} (4) were synthesized by the reaction of zirconium tetrachloride with tetraorganylammonium, -phosphonium, and -stibonium chlorides in acetonitrile and structurally characterized. The nitrogen, phosphorus, and antimony atoms in the cations have a distorted tetrahedral geometry. The Zr–Cl distances in the centrosymmetric octahedral [ZrCl{sub 6}]{sup 2−} anions of complexes 1–4 have similar values, the longest bonds being observed in the anion of complex 4. Acetonitrile molecules are involved in the structural organization of the crystals of complex 3via weak hydrogen bonding with phenyl hydrogen atoms of the organylphosphonium cations. In the crystal of 2, no hydrogen bonds between the cations and solvent molecules are observed; acetonitrile molecules fill the cavities formed by cations and anions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Elusive Intermediates in the Breakdown Reactivity Patterns of Prodrug Platinum(IV) Complexes

Kinetically inert platinum(IV) complexes are receiving growing attention as promising candidates in the effort to develop safe and valid alternatives to classical square-planar Pt(II) complexes currently used in antineoplastic therapy. Their antiproliferative activity requires intracellular Pt(IV)–Pt(II) reduction (activation by reduction). In the present work, a set of five Pt(IV) complexes has been assayed using mass spectrometry–based techniques, i.e., collision-induced dissociation (CID), and IR multiple photon dissociation (IRMPD) spectroscopy, together with ab initio theoretical investigations. Breakdown and reduction mechanisms are observed that lead to Pt(II) species. Evidence is found for typically transient Pt(III) intermediates along the dissociation paths of isolated, negatively charged (electron-rich) Pt(IV) prodrug complexes. .

62 RADIOLOGY AND NUCLEAR MEDICINE↗