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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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85 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Spectroscopic evidence for intact carbonic acid stabilized by halide anions in the gas phase

Here we show elusive carbonic acid being effectively stabilized in the gas phase by interacting with halide anions X – (X = F, Cl, Br, and I). The formed H 2 CO 3 ·X – complexes, characterized by negative ion photoelectron spectroscopy and ab initio calculations, all contain intact trans – trans carbonic acid binding onto the respective halide via two identical strong ionic O–H...X – hydrogen bonds. For X = Cl, Br, and I, the complex spectra exhibit the corresponding X – signature by simply shifting to the higher binding energy side, while an extremely 2 eV wide broader band is observed for X = F. This spectroscopic evidence indicates that an excess electron is removed from each halide in the former case, while a proton is transferred from carbonic acid to fluoride upon electron detachment for the latter. The above H 2 CO 3 ·X – structures as well as those of the previously studied H 2 SO 4 ·X – along the homologous halogen series cannot be explained using the proton affinity (PA) argument. Instead, a qualitative correlation is found between these structural motifs and the constituent acid p K a values, strongly suggesting that p K a is a more suitable factor to predict correct acid–base chemistry between these diprotic oxyacids and halides.

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

Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(C 5 Me 5 )2(2,6- i Pr 2 C 6 H 3 O)Ce(THF)], 1, were investigated. Based on the electrochemical data, treatment of 1 with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(C 5 Me 5 ) 2 (2,6- i Pr 2 C 6 H 3 O)Ce(X)]. Each complex has been characterized using NMR, IR, and UV−vis spectroscopy as well as structurally determined using X-ray crystallography. Additionally, the treatment of [(C 5 Me 5 ) 2 (2,6- i Pr 2 C 6 H 3 O)Ce(Br)] with AgF results in the formation of the putative [(C 5 Me 5 ) 2 (2,6- i Pr 2 C 6 H 3 O)Ce(F)]. Furthermore, the electronic structure of these Ce(IV)−X complexes was investigated by bond analyses and the Ce(IV)−F moiety using quantum chemistry NMR calculations.

Aromatic compounds↗
DOE OSTI2026

Bond Dissociation Energies of the Actinide Halides AnX, An = Ac–Lr and X = F–I, Utilizing Relativistic Composite Coupled Cluster Approaches

Bond dissociation energies (BDEs) have been calculated for the set of actinide halides AnX with An=Ac, Pa, and Np-Lr and X=F-I. Two composite thermochemistry methods based on the Feller-Peterson-Dixon (FPD) approach have been utilized, one involving spinor-based relativistic CCSD(T) calculations where spin-orbit (SO) was included at the orbital level and another using scalar relativistic CCSD(T) with a posteriori SO contributions based on 2-component multireference configuration interaction calculations. The method that was chosen for a given actinide halide was based on which representation yielded the best single determinant reference determinant for the coupled cluster calculation. The spinor-based method was chosen for all cases except for AmX, CmX, and BkX. Both composite approaches included contributions accounting for basis set truncation, outer-core correlation, the Gaunt interaction, and QED. The scalar FPD results, as well as the spinor-based calculations for AcF, also included higher order electron correlation up through CCSDT(Q). In addition to BDEs, CCSD(T) equilibrium bond lengths, harmonic frequencies, and vibrational anharmonicity constants are reported for all species. Last, the FPD BDEs for the fluorides were used to confirm the trend across the actinide series previously predicted by Gibson using bonding models based atomic promotion energies that provide a single 6d electron for bonding. In particular the local minimum in the BDEs at AmF is confirmed in the present calculations. Furthermore, the BDEs for LrX are predicted to be slightly larger than those of AcX, making them the largest in the actinide halide series.

Actinides↗
DOE OSTI2024

Molecular Origins of Near-Infrared Luminescence in Molybdenum and Tungsten Oxyhalide Perovskites

Materials with near-infrared (near-IR) luminescence are desirable for applications in communications and sensing, as well as biomedical diagnostics and imaging. The most used inorganic near-IR emitters rely on precise doping of host crystal structures with select rare-earth or transition metal ions. Recently, another class of materials with intrinsic near-IR emission has been reported. The compositions of these materials were initially described as vacancy-ordered halide double perovskites Cs 2 MoCl 6 and Cs 2 WCl 6 , but further investigation by some of us on the compound reported as Cs2WCl6 revealed an oxyhalide instead, with a composition Cs 2 WO x Cl 6–x , where 1 < x < 2. Here we demonstrate that the Mo compounds similarly possess the composition Cs 2 MoO x Cl 6–x or Cs 2 MoO x Br 6–x where 1 < x < 2. Preparing the pure halide appears harder for Mo than for W, and we have not succeeded in doing so. The distinctly different composition requires the coordination environment and oxidation state for the Mo and W centers to be reconsidered from what was assumed for the pure halides. In this work, we examine the mechanism for near-IR emission in these materials given their true structures and compositions. We demonstrate that the luminescence is due to the specific d-orbital splitting caused by the presence of oxygen in the distorted [MOX 5 ] 2– octahedra (X is Cl or Br). The fine structure in the emission spectra at low temperatures has been resolved and is attributed to vibronic coupling to the Mo–O and W–O bond stretches. Understanding the true structure and composition of these interesting materials, besides explaining the near-IR luminescence, suggests how this desirable emission can be realized and manipulated.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Enhancing Selective Hydrofluorocarbon Greenhouse Gas Capture via Halogenation of Metal–Organic Frameworks

Hydrofluorocarbons (HFCs) are anthropogenically produced greenhouse gases with longer atmospheric lifetimes and higher global warming potentials than those of carbon dioxide. General strategies to abate their emissions from industrial point sources, such as via adsorptive capture, remain scarce. Herein, we uncover the key structure–property relationships that lead to strong binding of HFCs such as fluoroform (CHF 3 ) and difluoromethane (CH 2 F 2 ) in metal–organic frameworks (MOFs) under the low pressures relevant to flue gas scrubbing. Extensive gas sorption and computational studies support that the Zr-based microporous framework MOF-801-Br or HHU-2-Br (HHU = Heinrich-Heine-University Düsseldorf) strongly binds HFCs due to its synergistic combination of Zr-OH sites on the nodes and bromine sites on the linkers. As such, MOF-801-Br demonstrates a record-setting performance for separating CHF 3 from N 2 under dilute conditions. Our work highlights that the combination of multiple hydrogen-bonding sites in microporous MOFs represents a generalizable strategy for HFC capture, enabling their selective removal from industrial waste streams.

adsorption↗
DOE OSTI2023

Thermodynamic characterization of synthetic lead-arsenate apatites with different halogen substitutions

Abstract Thermodynamic parameters have been measured for synthetic analogs of the mimetite-group minerals Pb5(AsO4)3X (X = OH, Cl, Br, I) belonging to the apatite supergroup. Phases precipitated from aqueous solutions under ambient conditions with well characterized structures and compositions were studied. For each phase, dissolution enthalpy was experimentally determined by oxide melt drop solution calorimetry in a molten solvent of sodium molybdate (3Na2O·4MoO3) at 976 K. The enthalpy of formation from the elements ΔHf,elo was calculated using thermochemical cycles and was −3030.6 ± 11.5, −3026.6 ± 15.8, −2967.6 ± 25.0, and −2993.1 ± 12.2 kJ/mol for Pb5.00(AsO4)3.00OH0.86(CO3)0.07, Pb5.00(AsO4)3.00Cl0.80(CO3)0.10, Pb5.00(AsO4)3.00Br0.80(CO3)0.10, and Pb5.00(AsO4)3.00I0.45OH0.35(CO3)0.10, respectively. These ΔHf,elo values exhibit typical trends for apatites: they increased (were less negative) with the increasing molar mass and ionic radius of X and decreased with the electronegativity and ionization energy of X. The compilation and comparison of data for Ca-, Pb-, P-, and As-apatites revealed correlations indicating that thermodynamic enthalpic stability is largely influenced by chemical factors (e.g., differences in electronegativities of the elements, ionization energy, or ionic characteristics of the bonds) and to a lesser extent by physical and geometric parameters in the crystal structure related to the mass and size of the X anion. Using the correlations, it was possible to estimate the value of hitherto unknown ΔHf,elo for Pb5(AsO4)3F, −3144.3 ± 66.5 kJ/mol. The observed relationships apply to the entire apatite supergroup and can be used to predict the values of ΔHf,elo for phases that have not been studied experimentally. The new data on environmentally significant phases will contribute to the modeling of mineral-water interactions, particularly for potential use in the remediation of soils and wastes contaminated with Pb and As and in the immobilization of radioactive waste containing I-129.

Geochemistry & Geophysics↗
DOE OSTI2024

Enhancing Interlayer Charge Transport of Two-Dimensional Perovskites by Structural Stabilization via Fluorine Substitution

Two-dimensional lead-halide perovskites provide a more robust alternative to three-dimensional perovskites in solar energy and optoelectronic applications due to increased chemical stability afforded by interlayer ligands. At the same time, the ligands create barriers for interlayer charge transport, reducing device performance. Using a recently developed ab initio simulation methodology, we demonstrate that ligand fluorination can enhance both hole and electron mobility by 1–2 orders of magnitude. The simulations show that the enhancement arises primarily from improved structural order and reduced thermal atomic fluctuations in the system rather than increased interlayer electronic coupling. Arising from stronger hydrogen bonding and dipolar interactions, the higher structural stability decreases the reorganization energy that enters the Marcus formula and increases the charge transfer rate. The detailed atomistic insights into the electron and hole transfer in layered perovskites indicate that the use of interlayer ligands that make the overall structure more robust is beneficial simultaneously for chemical stability and charge transport, providing an important guideline for the design of new, efficient materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Structure−Property Relationships in a Series of Hybrid Halopyridinium Ruthenium(IV) Halides

Reported is the synthesis and characterization of a family of hybrid ruthenium halides consisting of haloruthenium octahedra (X = Cl, Br) charge balanced with halopyridinium (XPy; X= H, Cl, Br, I) organic cations which assemble via noncovalent interactions between ion pairs. Diffuse reflectance spectroscopy showed that compounds containing RuBr 6 2- octahedra displayed a lower bandgap (1.05 eV< x < 1.08 eV) compared to compounds with RuCl 6 2- octahedra (1.22 eV < x < 1.43 eV). Additionally, computational density functional theory (DFT) based natural bonding orbital (NBO) analysis and density of state (DOS) methods were used to characterize second-sphere non-covalent interaction strengths and elucidate molecular orbital perturbations to elucidate their influence on Ru-X orbital constructs and in turn rationalize band gap trends. Analyses showed ligand to metal charge transfer is responsible for the small bandgap energies and are unperturbed by second-sphere interactions. Here, this report serves as a platform for probing the relationship between the structural and photophysical properties within the haloruthenium family of low dimensional transition metal halide perovskites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Development, Application, and Mechanistic Interrogation of a Dual Ni Catalysis Approach to Photoredox-Based C(sp 3 )–C(sp 3 ) Cross-Coupling

The installation of alkyl substituents such as methyl groups is a crucial tactic for the synthesis and diversification of medicinal compounds with improved pharmacological profiles. However, strategies that leverage methyl radical for C(sp 3 ) methylation remain underdeveloped due to the challenge of obtaining cross-selectivity between fleeting aliphatic radicals and alkyl electrophiles. Here, we report the development, application, and interrogation of a conceptually novel mechanistic framework for C(sp 3 )–Me bond formation using two distinct Ni catalysts capable of cross-coupling sterically and electronically diverse alkyl halides (chlorides and bromides) with methyl radical generated photocatalytically from benzaldehyde dimethyl acetal. Furthermore, by modifying the alkyl substituents on the acetal coupling partner, we demonstrate cross-couplings beyond methylation to access an array of 1°–1° and 1°–2° alkyl–alkyl bonds. Experimental and computational mechanistic studies provide support for cooperativity between an in situ-generated (bpy)Ni I (X) catalyst that facilitates XAT and inner-sphere C–C bond formation and a (Tp*)Ni II (acac) cocatalyst that captures methyl radical and engages in concurrent outer-sphere S H 2 coupling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Low Frequency Vibrational Modes of Two-Dimensional Lead-Free Metal Halide Double Perovskites

2D layered double perovskites of (S-MPA) 4 AgBiI 8 (MPA-AgBiI 8 ) and (S-MPA) 4 CuBiI 8 (MPA-CuBiI 8 ) (S-MPA, S-β-methylphenethylammonium) were synthesized with a hydrothermal method. The crystal structure of MPA-AgBiI 8 was determined using single-crystal X-ray diffraction (scXRD). Powder XRD (pXRD) data suggest that the crystal structure of MPA-CuBiI 8 is more complex than that of MPA-AgBiI 8 . UV-Vis electronic absorption spectra of these perovskites reveal a bandgap of 2.03 eV for both. Short exciton lifetime from time-resolved photoluminescence (TRPL) results and low PL intensity of the Cu-based perovskite suggest a high density of trap states within the bandgap. Low frequency Raman spectra of both materials show distinct peaks and a slightly higher frequency for the Cu-based perovskite than the Ag-based perovskite. Density functional theory (DFT) calculations were conducted to simulate the low frequency Raman spectra and help explain the different phonon modes, which are collective vibrations of metal halide bond bending and stretching within the Ag- and Cu-centered octahedra coupled with MPA libration and twisting within the inorganic layer. The DFT theory also quantified octahedral distortions in the two perovskites. Furthermore, this combined experimental and computational study provides new insights into the low frequency vibrations of 2D perovskites.

Halogens↗
DOE OSTI2024

All-Atom Molecular Dynamics Simulations of Cationic Polyelectrolyte Brushes in the Presence of Halide Counterions

Understanding the response of the charged polyelectrolyte (PE) brushes and brush-supported water and ions to the changes in the nature of screening counterions is significant in developing strategies for utilizing PE brushes in various applications. In this paper, we employ all-atom molecular dynamics (MD) simulations for studying the behavior of cationic [poly(2-(methacryloyloxy)ethyl) trimethylammonium] (PMETA) brushes and brush-supported water and ions in the presence of different halide (X: I – , Br – , Cl – , and F – ) screening counterions. We find that despite the F– ion having the largest charge density, the extent of binding of the counterions on the PMETAX brushes varies as I – > Br – > Cl – > F – , leading to PMETAX brush height being least with I– counterions and greatest with F – counterions. This trend in the binding of the halide ions matches the previous experimental result and can be explained by identifying the chaotropic nature of the I – and Br – ions that promote a disruption of water structure and a more favorable binding of the ions to the polymer chains. Such a binding trend also ensures that the order of the water molecules around the PMETAX chains or the counterions as well as the number of water–water hydrogen bonds inside the brush layer increases in the following order of the counterion-specific PMETAX brushes: F – > Cl – > Br – > I – . Furthermore, halide-ion-PMETAX-chain binding takes place via both interchain and intrachain bridging: intrachain bridging dominates for the case of counterions that show enhanced binding (I – and Br – ), while interchain bridging is more favored for the case of counterions that show weakened binding (F – and Cl – ). Also, a greater degree of intrachain bridging leads to greater compressibility and flexibility of the brush layer. Lastly, we show that the mobility of the halide ions follows a nonmonotonic trend with the charge density: the mobility decreases as I – < Br – < Cl – (as their binding to the PMETAX chains varies as I – > Br – > Cl – ), but the mobility of F – ions is in between that of I – and Br – ions. We argue that the strongly attached hydration layer and the ensuing friction inside the brush layer lead to such a reduced mobility of the F – ions.

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

Metal Halide Scaffolded Assemblies of Organic Molecules with Enhanced Emission and Room Temperature Phosphorescence

Ionically bonded organic metal halide hybrids have emerged as versatile multicomponent material systems exhibiting unique and useful properties. The unlimited combinations of organic cations and metal halides lead to the tremendous structural diversity of this class of materials, which could unlock many undiscovered properties of both organic cations and metal halides. Here we report the synthesis and characterization of a series benzoquinolinium (BZQ) metal halides with a general formula (BZQ)Pb 2 X 5 (X = Cl, Br), in which metal halides form a unique two-dimensional (2D) structure. These BZQ metal halides are found to exhibit enhanced photoluminescence and stability as compared to the pristine BZQ halides, due to the scaffolding effects of 2D metal halides. Optical characterizations and theoretical calculations reveal that BZQ + cations are responsible for the emissions in these hybrid materials. Changing the halide from Cl to Br introduces heavy atom effects, resulting in yellow room temperature phosphorescence (RTP) from BZQ + cations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using 13C NMR Spectroscopy and Computer Simulations

This work demonstrates the first high-resolution comonomer sequencing of Blocky brominated syndiotactic polystyrene (sPS-co-sPS-Br) copolymers based on pentad assign- ments of the quaternary carbon region of the nuclear magnetic resonance spectrum. Copolymers containing p-bromostyrene (Br-Sty) units were prepared in matched sets using postpolymerization bromination methods carried out in the heterogeneous gel state (Blocky) and homogeneous solution state (Random). Quantitative information from the quaternary carbon spectra, heteronuclear multiple bond correlation spectroscopy, electronic structure calculations, and simulated statistically random copolymers was correlated to confirm the carbon resonance assignments for all 20 possible pentad comonomer sequences. Using the experimental pentad sequence prevalences, a computer code was developed to simulate chains with microstructures typical of each sample as a means to visually represent the copolymer blockiness with quantitative precision. Based on the microstructure and distribution of run lengths in these chains, the simulations revealed that the Blocky copolymers contain a high degree of blockiness. By comparing the run lengths in the simulated chains to the average number of styrene units in a crystalline segment of sPS (found by small-angle X-ray scattering), copolymer crystallizability was predicted. For the simulated Blocky B-21% (21 mol % Br-Sty) chain, the probability of randomly selecting a styrene unit in a crystallizable block was 25.8%, while that in the simulated Random R-18% was zero, in excellent agreement with the experimental crystallization behavior measured by differential scanning calorimetry. Additionally, these predictions confirmed that the simulated chains accurately represent the ensemble of chains in their respective copolymer samples. Furthermore, each simulated Blocky chain contained one or more long sPS blocks that paralleled the measured 38-40 styrene units spanning a crystalline segment within the sPS/CCl4 gel. This finding affirmed that the long sPS segments originated from the precise lamellar structure within the heterogeneous gel morphology (i.e., block length is correlated with lamellar thickness). Overall, the ability to tailor the copolymer microstructure through control of the semicrystalline gel morphology opens the door to synthesizing ordered copolymers by postpolymerization functionalization processes with unprecedented levels of compositional control.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗