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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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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Four-Coordinate Fe N 2 and Imido Complexes Supported by a Hemilabile NNC Heteroscorpionate Ligand

Inspired by mechanistic proposals for N 2 reduction at the nitrogenase FeMo cofactor, we report herein a new, strongly σ-donating heteroscorpionate ligand featuring two weak-field pyrazoles and an alkyl donor. This ligand supports four-coordinate Fe(I)-N 2 , Fe(II)-Cl, and Fe(III)-imido complexes, which we have characterized using a variety of spectroscopic and computational methods. Structural and quantum mechanical analysis reveal the nature of the Fe–C bonds to be essentially invariant between the complexes, with conversion between the (formally) low-valent Fe-N 2 and high-valent Fe-imido complexes mediated by pyrazole hemilability. This presents a useful strategy for substrate reduction at such low-coordinate centers and suggests a mechanism by which FeMoco might accommodate the binding of both π-acidic and π-basic nitrogenous substrates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2019

Coordinated Analysis of an Ion Irradiated Carbonaceous Chondrite Suggests Complex Space Weathering Effects

Surfaces of airless planetary bodies are exposed to micrometeorite bombardment and solar wind irradiation which alter the microstructural, compositional, and optical properties of regoliths over time. These processes are collectively known as space weathering, and they complicate the interpretation of remote sensing data and the subsequent characterization of airless surfaces. Within the next 5 years, NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) and JAXA (Japan Aerospace Exploration Agency)’s Hayabusa2 missions will return samples from C-type asteroids Bennu and Ryugu, respectively. Compared to the Moon and S-type asteroids, our understanding of the space weathering of C-complex asteroids is limited. In order to maximize scientific return from remote sensing data and to prepare for the analysis of returned samples from these missions, we must better understand the effects of space weathering on hydrated, organic-rich materials. We can do so by simulating these processes in the laboratory. In this study, we simulate solar wind exposure through ion irradiation of the CM2 carbonaceous chondrite Murchison - a suitable analog for C-complex asteroids. Here, we present coordinated analyses of a sample before and after ion irradiation.

Laczniak, D. L.↗
DOE OSTI2021

Mechanistic investigation of the aerobic oxidation of 2-pyridylacetate coordinated to a Ru(ii) polypyridyl complex

A new ruthenium polypyridyl complex, [Ru(bpy) 2 (acpy)] + (acpy = 2-pyridylacetate, bpy = 2,2'-bipyridine), was synthesized and fully characterized. Distinct from the previously reported analog, [Ru(bpy) 2 (pic)] + (pic = 2-pyridylcarboxylate), the new complex is unstable under aerobic conditions and undergoes oxidation to yield the corresponding α-keto-2-pyridyl-acetate (acpyoxi) coordinated to the Ru II center. The reaction is one of the few examples of C–H activation at mild conditions using O 2 as the primary oxidant and can provide mechanistic insights with important implications for catalysis. Theoretical and experimental investigations of this aerobic oxidative transformation indicate that it takes place in two steps, first producing the α-hydroxo-2-pyridyl-acetate analog and then the final product. The observed rate constant for the first oxidation was in the order of 10 -2 h -1 . The reaction is hindered in the presence of coordinating solvents indicating the role of the metal center in the process. Theoretical calculations at the M06-L level of theory were performed for multiple reaction pathways in order to gain insights into the most probable mechanism. Our results= indicate that O 2 binding to [Ru(bpy) 2 (acpy)] + is favored by the relative instability of the six-ring chelate formed by the acpy ligand and the resulting Ru III -OO˙- superoxo is stabilized by the carboxylate group in the coordination sphere. C–H activation by this species involves high activation free energies (ΔG ‡ = 41.1 kcal mol -1 ), thus the formation of a diruthenium μ-peroxo intermediate, [(Ru III (bpy) 2 (O-acpy)) 2 O 2 ] 2+ via interaction of a second [Ru(bpy) 2 (acpy)] + was examined as an alternative pathway. The dimer yields two Ru IV =O centers with a low ΔG ‡ of 2.3 kcal mol -1 . The resulting Ru IV =O species can activate C–H bonds in acpy (ΔG ‡ = 23.1 kcal mol -1 ) to produce the coordinated α-hydroxo-2-pyridylacetate. Further oxidation of this intermediate leads to the α-keto-2-pyridyl-acetate product. The findings provide new insights into the mechanism of C–H activation catalyzed by transition-metal complexes using O 2 as the sole oxygen source.

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

Constructing protein polyhedra via orthogonal chemical interactions

Many proteins exist naturally as symmetrical homooligomers or homopolymers. The emergent structural and functional properties of such protein assemblies have inspired extensive efforts in biomolecular design2–5. As synthesized by ribosomes, proteins are inherently asymmetric. Therefore, they must acquire multiple surface patches that selectively associate to generate the different symmetry elements needed to form higher-order architectures—a daunting task for protein design. Here we address this problem using an inorganic chemical approach, whereby multiple modes of protein–protein interactions and symmetry are simultaneously achieved by selective, ‘one-pot’ coordination of soft and hard metal ions. We show that a monomeric protein (protomer) appropriately modified with biologically inspired hydroxamate groups and zinc-binding motifs assembles through concurrent Fe 3+ and Zn 2+ coordination into discrete dodecameric and hexameric cages. Our cages closely resemble natural polyhedral protein architectures and are, to our knowledge, unique among designed systems in that they possess tightly packed shells devoid of large apertures. At the same time, they can assemble and disassemble in response to diverse stimuli, owing to their heterobimetallic construction on minimal interprotein-bonding footprints. With stoichiometries ranging from [2 Fe:9 Zn:6 protomers] to [8 Fe:21 Zn:12 protomers], these protein cages represent some of the compositionally most complex protein assemblies—or inorganic coordination complexes—obtained by design.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Cooperative Lanthanide Solvation in an Ionic Liquid for Critical Materials Separations

Effectively separating critical materials, including intra-lanthanide separations, is crucial for meeting growing application demands. Liquid–liquid extraction (LLE) is the industry standard for lanthanide separations, where the selectivity can depend on small changes in metal coordination. In this work, we investigate representative lanthanide Eu coordination with a neutral malonamide extractant in an imidazolium bistriflimide ionic liquid (IL) solvent. Through systematic titrations of the water and extractant and under extraction conditions, we observe surprising cooperative Eu solvation with the IL anion and extractant. Time-resolved fluorescence spectroscopy measurements show strong extractant coordination in water-saturated IL. Lifetime measurements show no water coordination, and extended X-ray fine structure spectroscopy data provide a coordination number of 10. Molecular dynamics simulations confirm this coordination number and reveal IL anion coordination in the final Eu complex, even though it is ordinarily a significantly weaker ligand compared to water. The lack of water in the final extracted complex and IL anion coordination potentially explain the increased extraction in LLE systems using ILs, as evidenced by higher distribution ratios for cation exchange extraction, despite the energetic cost of cation transfer to the aqueous phase. These results highlight the opportunities for tuning metal coordination to drive extraction in unique solvent systems.

Carr, Amanda J.↗
DOE OSTI2020

Formation of monomeric Sn(ii) and Sn(iv) perfluoropinacolate complexes and their characterization by 119 Sn Mössbauer and 119 Sn NMR spectroscopies

The synthesis and characterization of a series of Sn(II) and Sn(IV) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pinF) ligand are reported herein. Three analogs of [Sn IV (pin F ) 3 ] 2- with NEt 3 H + (1), K + (2), and {K(18C6)} + (3) counter cations and two analogs of [SnII(pinF)2]2- with K+ (4) and {K(15C5) 2 } + (5) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119 Sn Mössbauer and NMR spectroscopies. The six-coordinate SnIV(pinF) complexes display 119 Sn NMR resonances and 119 Sn Mössbauer spectra similar to SnO 2 (cassiterite). In contrast, the four-coordinate SnII(pinF) complexes, featuring a stereochemically-active lone pair, possess low 119 Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn(II) complexes are unreactive towards both Lewis bases (pyridine, NEt 3 ) and acids (BX 3 , Et 3 NH + ). Calculations confirm that the Sn(II) lone pair is localized within the 5s orbital and reveal that the Sn 5p x LUMO is energetically inaccessible, which effectively abates reactivity.

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

Influences of Alkali Metal Cation Interactions on N2 Coordination to Iron(I) Beta-Diketiminate Complexes in Electrolyte Solutions

N2 functionalization reactions often use stable, isolable N2-bound complexes and low temperatures or highly activated reagents. However, little work has focused on systems where N2 binds weakly, and the N2 binding equilibrium can be modulated. Here, we describe analysis of surprising trends in alkali metal cation solvation on the formation of an anionic iron(I) beta-diketiminate complex and the subsequent N2 binding equilibrium. Variable temperature UV-vis spectroscopy shows that increased ionic strength in the coordinating solvent tetrahydrofuran promotes N2 coordination. Additionally, less solvated alkali metal cations in noncoordinating 2-methyltetrahydrofuran (MeTHF) stabilize N2 coordination, likely through the formation of contact ion pairs in solution that have enhanced N2 binding. Ionic strength has little effect on the energetics of N2 coordination to these proposed contact ion pairs in MeTHF. When the electrochemical analysis is done at –78 °C, there is an irreversible reduction of iron(II) and an anodically shifted oxidation, which is attributed to the formation of the spectroscopically observed N2 complex. Finally, bulk electrolysis is used to verify the electrochemical formation of the N2-bound anionic iron(I) complex. These studies demonstrate a new strategy for promoting N2 coordination by changing solution properties, which is relevant to homogeneous electrochemical N2 reduction methods.

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

Inducing Ferrimagnetic Exchange in 1D-FeSe 2 Chains Using Heteroleptic Amine Complexes: [Fe(en)(tren)][FeSe 2 ] 2

[Fe(en)(tren)][FeSe 2 ] 2 (en = ethylenediamine, C 2 H 8 N 2 , tren = tris(2-aminoethyl)amine, C 6 H 18 N 4 ) has been synthesized by a mixed-ligand solvothermal method. Its crystal structure contains heteroleptic [Fe(en)(tren)] 2+ complexes with distorted octahedral coordination, incorporated between 1D-FeSe 2 chains composed of edge–sharing FeSe 4 tetrahedra. The twisted octahedral coordination environment of the Fe–amine complex leads to partial dimerization of Fe–Fe distances in the FeSe 2 chains so that the FeSe 4 polyhedra deviate strongly from the regular tetrahedral geometry. 57 Fe Mössbauer spectroscopy reveals oxidation states of +3 for the Fe chain atoms and +2 for the Fe complex atoms. The close proximity of Fe atoms in the chains promotes ferromagnetic nearest neighbor interactions, as indicated by a positive Weiss constant, θ = +53.8(6) K, derived from the Curie–Weiss fitting. Magnetometry and heat capacity reveal two consecutive magnetic transitions below 10 K. DFT calculations suggest that the ordering observed at 4 K is due to antiferromagnetic intrachain interactions in the 1D-FeSe 2 chains. The combination of two different ligands creates an asymmetric coordination environment that induces changes in the structure of the Fe–Se fragments. Finally, this synthetic strategy opens new ways to explore the effects of ligand field strength on the structure of both Fe-amine complexes and surrounding Fe–Se chains.

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

Structure and Reactivity of a High-Spin, Nonheme Iron(III)- Superoxo Complex Supported by Phosphinimide Ligands

Nonheme iron oxygenases utilize dioxygen to accomplish challenging chemical oxidations. Additionally, a further understanding of the Fe-O 2 intermediates implicated in these processes is challenged by their highly transient nature. To that end, we have developed a ligand platform featuring phosphinimide donors intended to stabilize oxidized, high-spin iron complexes. O 2 exposure of single crystals of a three-coordinate Fe(II) complex of this framework allowed for in crystallo trapping of a terminally bound Fe-O 2 complex suitable for XRD characterization. Spectroscopic and computational studies of this species support a high-spin Fe(III) center antiferromagnetically coupled to a superoxide ligand, similar to that proposed for numerous nonheme iron oxygenases. In addition to the apparent stability of this synthetic Fe-O 2 complex, its ability to engage in a range of stoichiometric and catalytic oxidation processes demonstrates that this iron-phosphinimide system is primed for development in modeling oxidizing bioinorganic intermediates and green oxidation chemistry.

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

Enhanced Hydrogenation of Carbon Dioxide to Methanol by a Ruthenium Complex with a Charged Outer-Coordination Sphere

In this paper, we report the hydrogenation of CO₂ to MeOH by a new Ru(triphos) catalyst containing a cationic tetraalkylammonium moiety in the outer coordination sphere. This new catalyst affords superior TON and TOF values for MeOH in comparison to previously reported isostructural catalysts. Kinetic data from operando NMR spectroscopy studies indicate the improvement in MeOH production arises from a 12-fold enhancement in the rate for hydrogenation of the transient formaldehyde intermediate. These results provide insight into the catalyst characteristics that promote methanol formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Structural and spectroscopic characterization of thorium pyrasal complexes

To explore the coordination chemistry of thorium, the most abundant radioactive element on earth, we examine the synthesis and characterization of two Th (IV)-pyrasal complexes, L1 “pyrasal” ((2,2'-((1E,1'E)-(pyrazine-2,3-diylbis(azaneylylidene))bis(methaneylylidene))diphenol), and L2 “naphthylpyrasal” (1,1'-((1E,1'E)-(pyrazine-2,3-diylbis(azaneylylidene))bis(methaneylylidene))bis(naphthalen-2-ol). These complexes demonstrate little or no fluorescence when compared to similar naphthylsalophen thorium complexes previously published. Each complex was synthesized and characterized by IR, NMR (1H), and mass spectrometry. The photometric properties of the complexes were characterized using UV–Vis and fluorescence spectroscopy and their solid-state molecular structures were established by single-crystal X-ray crystallography. The electron-withdrawing effects of the pyrazine ring creates changes in the thorium coordination environment resulting in a secondary solid-state extended structure that minimizes the pi-pi stacking. Further, this subsequently causes an overall decrease in the intensity of fluorescence demonstrated previously in by naphthylsalophen thorium complexes.

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

Photochemical CO 2 Reduction Using Rhenium(I) Tricarbonyl Complexes with Bipyridyl-Type Ligands with and without Second Coordination Sphere Effects

In this study, the effect of phenyl, phenol, aniline, amino, and CF 3 substituents of the 2,2'-bipyridine ligand in fac-ReCl(L)(CO) 3 (L=2,2'-bipyridine derivative) catalysts on photochemical CO 2 reduction in dimethylacetamide is examined, in order to understand the structure-function relationships and to compare the catalytic activities with the previously published electrochemical results. All complexes including ReCl(bpy)(CO) 3 have similar excited-state lifetimes and emission spectra, but complex 1 with the Ph-NH 2 moiety exhibits a significantly larger molar absorption coefficient for its metal-to-ligand charge transfer (MLCT) band. All complexes we tested produce CO with only a negligible amount of H 2 and formate in self-sensitized systems in the presence of triethanolamine (TEOA) and in some cases, BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazole). The presence of the Ph-NH 2 moiety (complex 1) has a beneficial effect on both electrochemical and photochemical activity, allowing a turnover number (TON) of 32 and 120 for photochemical CO production (without and with BIH, respectively). In the case of the Ph-OH group in the second coordination sphere (complexes 4 and 6), these complexes are active for photochemical CO 2 reduction, despite the formation of a stable 6-coordinate Re-OPh intermediate via reductive deprotonation as previously observed under electrochemical conditions. Overall, BIH accelerates the rate of formation of the one-electron reduced species (OERS) of the Re catalysts and allows higher turnover frequency (TOF) and TON for CO formation. The X-ray structures of complexes 1 and 4 were determined to have distorted octahedral Re centres, and show π-π stacking interactions with neighboring molecules as well as intramolecular hydrogen bonds to the internal chloride ligands. The unusually high absorptivity of the MLCT absorption of complex 1 has been explained by TD-DFT calculations.

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

Coordination-Induced N–H Bond Weakening in a Molybdenum Pyrrolidine Complex: Isotopic Labeling Provides Insight into the Pathway for H 2 Evolution

The synthesis and characterization of a cationic molybdenum pyrrolidine complex is described that exhibits significant coordination-induced N–H bond weakening. Here, the N–H bond dissociation free energy (BDFE) of the coordinated pyrrolidine in [( Ph Tpy)(PPh 2 Me) 2 Mo(NH(pyrr))][BArF 24 ] ([1-NH(pyrr)] + ; PhTpy = 4'-Ph-2,2',6',2''-terpyridine, NH(pyrr) = pyrrolidine, ArF 24 = [C 6 H 3 -3,5-(CF 3 ) 2 ] 4 ) was determined to be between 41–51 kcal mol -1 by thermochemical analysis and supported by a density functional theory (DFT) computed value of 48 kcal mol -1 . The complex [1-NH(pyrr)] + underwent proton-coupled electron transfer (PCET) to 2,4,6-tri-tert-butylphenoxyl radical, as well as spontaneous H 2 evolution upon gentle heating to furnish the corresponding molybdenum pyrrolidide complex, [( Ph Tpy)(PPh 2 Me) 2 Mo(N(pyrr))][BArF 24 ] ([1-N(pyrr)] + ). Thermolysis of the deuterated isotopolog, [1-ND(pyrr)] + still produced H 2 with concomitant incorporation of the isotopic label into the pyrrolidide ligand in the product [(1-N(pyrr-d n )] + (n = 0–2), consistent with an H 2 evolution pathway involving intramolecular H–H bond formation followed by an intermolecular product-forming PCET step. These observations provide context for understanding H 2 evolution in the nonclassical ammine complex [( Ph Tpy)(PPh 2 Me) 2 Mo(NH 3 )][BArF 24 ] ([1-NH 3 ] + ) and are supported by DFT-computed reaction thermochemistry. Overall, these studies offer rare insight into the H 2 formation pathway in nonclassical amine complexes with N–H BDFEs below the thermodynamic threshold for H 2 evolution and inform the development of well-defined, thermody-namically potent PCET reagents.

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

Nickel(ii)-methyl complexes adopting unusual seesaw geometries

Here, we report four-coordinate nickel(II)-methyl complexes of tris-carbene borate ligands which adopt rare seesaw geometries. Experimental and computational results suggest the structural distortion from threefold symmetry results from a combination of electronic stabilization of the singlet state, strong field donors, and constrained angles from the chelating ligand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1979

Prebiotic coordination chemistry: The potential role of transition-metal complexes in the chemical evolution

In approaching the extremely involved and complex problem of the origin of life, consideration of the coordination chemistry appeared not only as a possibility but as a necessity. The first model experiments appear to be promising because of prebiotic-type synthesis by means of transition-metal complexes. It is especially significant that in some instances various types of vitally important substances (nucleic bases, amino acids) are formed simultaneously. There is ground to hope that systematic studies in this field will clarify the role of transition-metal complexes in the organizatorial phase of chemical evolution. It is obvious that researchers working in the fields of the chemistry of cyano and carbonyl complexes, and of the catalytic effect of transition-metal complexes are best suited to study these aspects of the attractive and interesting problem of the origin of life.

Beck, M.↗
DOE OSTI2026

Photodissociation and Infrared Spectroscopy of U + (CO 2 ) n , UO + (CO 2 ) n , and UO 2+ (CO 2 ) n Cation-Molecular Complexes

Laser vaporization of uranium in a pulsed supersonic expansion of carbon dioxide is used to produce complexes of the form U + (CO 2 ) n , UO + (CO 2 ) n , and UO 2+ (CO 2 ) n . These ions are selected in a reflectron time-offlight mass spectrometer and studied with visible laser photodissociation and tunable infrared laser photodissociation spectroscopy in the region of the CO 2 antisymmetric stretch. The dissociation patterns and spectroscopy of these ions indicate that CO 2 ligands are intact molecules. Although reaction products that form oxide-carbonyl or oxalate species are predicted to be stable, there is no direct evidence in the frequency range studied for the formation of these species. There is no clear indication for the coordination numbers for singly charged uranium and its oxide complexes with CO 2 . However, there is strong support in the vibrational patterns for an eight-coordinate complex of the doubly charged UO 2+ species, i.e., UO 2+ (CO 2 ) 8 .

Cluster chemistry↗
DOE OSTI2024

SISGR: The regulation of carbon fixation in plant and green algae: Rubisco activase and the origin of heat inactivation of CO 2 assimilation

Rubisco activase (Rca) is a critical AAA+ ATPase protein complex that remodels and promotes the Rubisco enzyme, a key player in photosynthetic performance and carbon fixation. The assembly and function of the Rca protein complex are regulated by a range of factors, including subunit concentration, nucleotide-binding states, thermal conditions, metal-ion coordination, and post-translational modifications, such as phosphorylation. Despite its importance in photosynthesis, the detailed molecular mechanisms underlying the regulation of plant Rca and how it activates Rubisco remain elusive. This project aims to bridge this knowledge gap by integrating sophisticated enzymology tools with single-molecule methods and high-resolution electron microscopy to elucidate the structure and function of plant Rca. Through these multiple approaches, we have systematically investigated how the activity of plant Rca is impacted by various factors, such as phosphorylation and metal-ion coordination. The Rca complex assembly/disassembly dynamics were captured using anti-Brownian electrokinetic (ABEL) trap-based measurements, providing unprecedented insight into its structural flexibility and diverse assembly states. Furthermore, the structural analysis of Rca through electron crystallography and single-particle cryogenic electron microscopy (cryo-EM) reveals novel assembly states of the spinach Rca, providing insight into the mechanistic action for Rubisco remodeling. By combining cutting-edge tools and approaches, this work uncovers critical aspects of Rca’s regulation and assembly, paving the way for a deeper understanding of its role in photosynthetic efficiency and the potential for enhancing carbon fixation in crops.

59 BASIC BIOLOGICAL SCIENCES↗