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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Expanding the Chemistry of Rhenium Metal–Metal Bonded Fluoro Complexes: Facile Preparation and Characterization of Paddlewheel Complexes
Quadruply bonded rhenium(III) dimers with the stoichiometry Re 2 L 4 F 2 (1, L = hexahydro-2H-pyrimido[1,2a]pyrimidinate (hpp – ); 2, L = diphenyl formamidinate (dpf – )) were prepared from the solid-state melt reactions (SSMRs) between (NH 4 ) 2 [Re 2 F 8 ]·2H 2 O and HL. Then those compounds were characterized in the solid state by single-crystal X-ray diffraction and in solution by UV–visible spectroscopy and cyclic voltammetry. The compound [Re 2 (hpp) 4 F 2 ]PF 6 (3) was prepared from the one-electron oxidation of Re 2 (hpp) 4 F 2 with [Cp 2 Fe]PF 6 . Compounds 1–3 are isostructural with the corresponding chloro derivatives. In summation, compound 1 undergoes two one-electron oxidations. Comparison with its higher halogen homologues reveals that Re 2 (hpp) 4 F 2 (1) is more easily oxidized than its chloro and bromo analogues.
Capturing Biologically Complex Tissue-Specific Membranes at Different Levels of Compositional Complexity
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Spin Decoherence in VOPc@graphene Nanoribbon Complexes
Carbon nanoribbons or nanographene qubit arrays can facilitate quantum-to-quantum transduction between light, charge, and spin, making them an excellent testbed for fundamental science in quantum coherent systems and for the construction of higher-level qubit circuits. Here, in this work, we study spin decoherence due to coupling with a surrounding nuclear spin bath of an electronic molecular spin of a vanadyl phthalocyanine (VOPc) molecule integrated onto an armchair-edged graphene nanoribbon (GNR). Density functional theory (DFT) is used to obtain ground-state atomic configurations. Decay of spin coherence in Hahn echo experiments is then simulated using the cluster correlation expansion method with a spin Hamiltonian involving hyperfine and electric field gradient tensors calculated from DFT. We find that the decoherence time T 2 is anisotropic with respect to magnetic field orientation and determined only by the hydrogen nuclear spins on both VOPc and GNR. Large electron spin echo envelope modulation (ESEEM) due to nitrogen and vanadium nuclear spins is present at specific field ranges and can be completely suppressed by tuning the magnetic field. The relation between these field ranges and the hyperfine interactions is analyzed. The effects of interactions with the nuclear quadrupole moments are also studied, validating the applicability and limitations of the spin Hamiltonian when they are disregarded.
HLE17: An Efficient Way To Predict Band Gaps of Complex Materials
The recently developed HLE 17 exchange-correlation functional, which is a local functional with high local exchange, is tested for determining the band gaps of various kinds of semiconductors and insulators, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), perovskites, zeolites, and others. The calculated band gaps are compared to those calculated by more conventional functionals, in particular PBE, PBEsol, PBE+U, and HSE06. The HLE 17 functional is found to be more accurate PBE, PBEsol, and PBE+U and almost as accurate as the much more expensive HSE06. For the MOFs, HLE 17 is as accurate as HSE06 with almost 100 times less computational cost. As a result, the HLE 17 functional is found to be more accurate than the hybrid functional for covalent organic frameworks (COFs), β-GaSe, and BC 3 .
Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex
The efficient and atom-economical hydroboration of alkenes and alkynes using an N-heterocyclic carbene (NHC) copper hydroxide catalyst has been developed here. An equimolar combination of substrate and HBpin allows for the selective Markovnikov hydroboration of alkenes and alkynes. A variety of functional groups were tolerated in good to excellent yield. This system highlights a facile reaction setup, atom economy, high selectivity, and an easily synthesized copper–NHC catalyst.
Discovery of a Hybrid System for Photocatalytic CO 2 Reduction via Attachment of a Molecular Cobalt-Quaterpyridine Complex to a Crystalline Carbon Nitride
While recent reports have demonstrated the attachment of molecular catalysts to amorphous, graphitic carbon nitrides (g-CN) for light-driven CO 2 reduction, approaches to the utilization of crystalline carbon nitrides have remained undiscovered. Herein, a functional hybrid photocatalyst system has been found using a crystalline carbon nitride semiconductor, poly(triazine imide) lithium chloride (PTI-LiCl), with a surface-attached CoCl 2 (qpy-Ph-COOH) catalyst for CO 2 reduction. The molecular catalyst attaches to PTI-LiCl at concentrations from 0.10 to 4.30 wt % and exhibits ∼96% selectivity for CO production in a CO 2 -saturated, aqueous 0.5 M KHCO 3 solution. Optimal loadings were found to be within 0.42–1.04 wt % with rates between 1,400 and 1,550 μmol CO/g·h at an irradiance of 172 mW/cm 2 (λ = 390 nm) and apparent quantum yields of ∼2%. This optimized loading is postulated to represent a balance between maximal turnover frequency (TOF; 300+ h –1 ) and excess catalyst that can limit excited-electron lifetimes, as probed via transient absorption spectroscopy. An increase in the incident irradiance yields a concomitant increase in the TOFs and CO rates only for the higher catalyst loadings, reaching up to 2,149 μmol CO/g·h with a more efficient use of the catalyst surface capacity. The lower catalyst loadings, by comparison, already function at maximal TOFs. Higher surface loadings are also found to help mitigate deactivation of the molecular catalysts during extended catalytic testing (>24 h) owing to the greater net surface capacity for CO 2 reduction, thus representing an effective strategy to extend lifetime. The hybrid particles can be deposited onto an FTO substrate to yield ∼60% Faradaic efficiency for photoelectrochemical CO production at −1.2 V vs Ag/AgCl bias. In conclusion, these results demonstrate the synergistic combination of a crystalline carbon nitride with a molecular catalyst that achieves among the highest known rates in carbon-nitride systems for the light-driven CO 2 reduction to CO in aqueous solution with >95% selectivity.
Selective Electrocatalytic Reduction of Nitrous Oxide to Dinitrogen with an Iron Porphyrin Complex
Nitrous oxide (N 2 O) is the third largest contributor to anthropogenic greenhouse gas emissions and plays a detrimental role in the depletion of ozone. Despite the contribution of N 2 O as an atmospheric pollutant, there are currently only a few examples of electrochemical N 2 O remediation to N 2 . Herein we report the electrocatalytic deoxygenation of N 2 O by iron tetraphenylporphyrin (FeTPP) to form N 2 with quantitative Faradaic efficiency and an observed rate of 1.91 s –1 . No degradation was observed after controlled potential electrolysis. Mechanistic investigation of the proposed catalytic steps determined that hydrogen-bond donors are critical for accelerating N 2 O activation and that proton transfer is involved in the rate-determining step.
Hydrocarbon Oxidation by an Exposed, Multiply Bonded Iron(III) Oxo Complex
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Complexation of a Conjugated Polyelectrolyte and Impact on Optoelectronic Properties
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Ab Initio Evaluation of Complexation Energies for Cyclodextrin-Drug Inclusion Complexes
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Accurate Thermochemistry of Complex Lignin Structures via Density Functional Theory, Group Additivity, and Machine Learning
A molecular-level understanding of lignin structures and bond dissociation energies could facilitate depolymerization technologies. Still, this information is currently limited due to the lack of databases and the simplification of surrogate models. Here, substitution effects on seven common linkages in lignin polymers are systematically investigated. An automated reaction network generator is employed to create a database of structures. A new group additivity (GA) model based on principal component analysis (PCA) descriptors is introduced and trained on gas-phase density functional theory data of 4100 species at the M06-2X/6-311++G(d,p) level. Hydrogen bonds, local steric, and nonaromatic ring contributions are also incorporated. Lastly, we improve the accuracy of the group additivity model to reach the G4 theory by computing a data set of 770 species at this level and using a data fusion approach.
Hydrogen-Transfer Catalysis with Cp*IrIII Complexes: The Influence of the Ancillary Ligands
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