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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Hydrated Metal and Metal-Nitrate Complexes in Water: Full Lanthanide(III) Series plus Miscellaneous Metal Ions

This is a dataset of hydrated metal complexes and metal–nitrate hydrated complexes intended for public use, reproducibility, and downstream structural analysis. A key feature is coverage across the full lanthanide(III) series (La–Lu), enabling systematic comparisons of coordination motifs and bonding trends across the entire lanthanide sequence. In addition to the lanthanides, the dataset also includes other metal ions such as UO2(VI), Fe(II), and Fe(III). The dataset provides optimized geometries for hydrated and nitrate-containing hydrated complexes, together with representative ab initio molecular dynamics (AIMD) trajectories saved in standard XYZ formats. The accompanying NWChem input decks enable reproduction of the reported calculations and provide a starting point for extending the simulations to related coordination environments. Computationally, DFT calculations employ the B3LYP functional with DFT-D3BJ dispersion corrections and a COSMO continuum solvent model (dielectric constant 78.4) to represent solvation beyond the explicitly treated first hydration shell. AIMD simulations are performed with the NWChem qmd module at 298 K, integrating nuclear motion with the velocity-Verlet algorithm and controlling temperature using a Nosé–Hoover thermostat. Trajectories are approximately 4.8 ps in length and are used primarily to assess short-time stability of candidate coordination motifs, including (for lanthanides) differences between 8- versus 9-water coordination and comparisons between nitrate-bound and nitrate-free hydrated complexes.

Dinpajooh, Mohammadhasan [Pacific Northwest Nation↗
DOE OSTI2023

Impact of lanthanide ion complexation and temperature on the chemical reactivity of N , N , N ', N '-tetraoctyl diglycolamide (TODGA) with the dodecane radical cation

The impact of trivalent lanthanide ion complexation and temperature on the chemical reactivity of N,N,N',N'-tetraoctyl diglycolamide (TODGA) with the n-dodecane radical cation (RH˙+) has been measured by electron pulse radiolysis and evaluated by quantum mechanical calculations. Additionally, Arrhenius parameters were determined for the reaction of the non-complexed TODGA ligand with the RH˙ + from 10–40 °C, giving the activation energy (E a = 17.43 ± 1.64 kJ mol –1 ) and pre-exponential factor (A = (2.36 ± 0.05) × 10 13 M –1 s –1 ). The complexation of Nd(III), Gd(III), and Yb(III) ions by TODGA yielded [LnIII(TODGA)3(NO3)3] complexes that exhibited significantly increased reactivity (up to 9.3× faster) with the RH˙ + , relative to the non-complexed ligand: k([Ln III (TODGA) 3 (NO 3 ) 3 ] + RH˙ + ) = (8.99 ± 0.93) × 10 10 , (2.88 ± 0.40) × 10 10 , and (1.53 ± 0.34) × 10 10 M –1 s –1 , for Nd(III), Gd(III), and Yb(III) ions, respectively. The rate coefficient enhancement measured for these complexes exhibited a dependence on atomic number, decreasing as the lanthanide series was traversed. Preliminary reaction free energy calculations—based on a model [Ln III (TOGDA)] 3+ complex system—indicate that both electron/hole and proton transfer reactions are energetically unfavorable for complexed TODGA. Furthermore, complementary average local ionization energy calculations showed that the most reactive region of model N,N,N',N'-tetraethyl diglycolamide (TEDGA) complexes, [Ln III (TEGDA) 3 (NO 3 ) 3 ], toward electrophilic attack is for the coordinated nitrate (NO 3 – ) counter anions. Furthermore, it is possible that radical reactions with the complexed NO 3 – counter anions dominate the differences in rates seen for the [Ln III (TODGA) 3 (NO 3 ) 3 ] complexes, and are likely responsible for the reported radioprotection in the presence of TODGA complexes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2026

Deciphering the excited-state landscape of Cr(iii) tris(diimines) using [Cr(phen) 3 ] 3+

Earth-abundant Cr(III) polypyridines chromophores feature long-lived doublet ligand-field excited states. The thermally equilibrated 2 T 1 / 2 E ligand-field excited state manifold produces broad, structured UV-Vis-NIR absorption bands. Although ubiquitous across pseudo-octahedral Cr(III) diimine complexes, the dynamics and individual electronic transitions underlying these spectra have remained elusive. Here, we combine time-resolved spectroscopy and multiconfigurational calculations to assign ground- and excited-state absorption spectra of Cr(III) tris(1,10-phenanthroline), [Cr(phen) 3 ] 3+ , as a prototypical example for this class of complexes. Excited-state kinetics reveal a rapid biexponential decay of the initially prepared intraligand/ligand-to-metal charge transfer [ 4 ( 1 IL)/ 4 LMCT] excited state into the lowest 2 T 1 / 2 E state within 10 picoseconds, assigned to intersystem crossing and vibrational relaxation. Calculations identify broad excited-state absorption features associated with metal-centered ligand-field states ( 2 MC) mixed with intraligand ( 2 IL) transitions within the doublet manifold. These results provide detailed spectral assignments and highlight the need to include multiconfigurational ligand-based orbitals when modeling the spectral properties of Cr(III) coordination complexes.

Barth, Alexandra T. [North Carolina State Universi↗
DOE OSTI2023

Ring-Opening in the Actinide Cyclopropyl Complexes [Cp 3 U(2,2-Diphenylcyclopropyl)] n – ( n = 0, 1)

The reaction of [Cp 3 UCl] with in situ generated 1-lithium-2,2-dipenylcyclopropane results in the formation of [Cp 3 U(2,2-diphenylcyclopropyl)] (1) in good yield. Reduction of 1 with KC 8 , in the presence of 2.2.2-cryptand, results in the formation of a rare U(III) alkyl complex, [K(2.2.2-cryptand)][Cp 3 U(2,2-diphenylcyclopropyl)] (2). Thermolysis or photolysis of 1 for 10 d in toluene results in isomerization to the U(IV) η 1 -allyl complex, [Cp 3 U(η 1 -3,3-diphenylallyl)] (3). Moreover, photolysis of 2 in THF for 9 h at room temperature results in isomerization to the U(III) η 1 -allyl complex, [K(2,2,2-cryptand)][Cp 3 U(η 1 -3,3-diphenylallyl)] (4). Both 3 and 4 were fully characterized. Additionally, selective labeling of the C α positions of 1 and 2 with deuterium revealed that cyclopropyl ring-opening occurs via distal C–C bond cleavage via a hypothesized η 3 -allyl intermediate.

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

Synthesis and Computational Analysis of Uranium(III)-Pnictogen Bonds

In this report, we describe the synthesis and characterization of two novel complexes that contain uranium(III)-pnictogen (P: 1-PMes 2 ; As: 1-AsMes 2 ) bonds to elucidate the degrees of covalency among these bonds. To our knowledge, this is the first reported uranium(III)-arsenic complex to be synthesized and characterized. Analysis of the phosphorus and arsenic bonds reveals a similar electronic environment, assessed by UV–vis NIR, that is comparable to other previously reported uranium(III) complexes. A computational analysis of these compounds and their congeners, N, Sb, and Bi, was performed to identify trends in the overall bonding character of the complexes. This analysis shows that bond covalency decreases as the pnictogen becomes heavier and that overall the interaction energy and its components decrease down the group. Here, this study provides an in-depth analysis and understanding of the nature of bonding between hard actinide and soft pnictogen centers.

Actinides↗
DOE OSTI2020

Electrochemical reduction of europium(iii) using tetra- n -octyl diglycolamide functionalized ordered mesoporous carbon microelectrodes

This work investigates the one-electron reduction of Eu(III) to Eu(II) with ordered mesoporous carbon (OMC) in cavity microelectrode (CME) systems. OMC materials with and without tetra-n-octyl diglycolamide (TODGA) functionalization were subjected to voltammetric measurements and compared with commercial carbon black Vulcan® XC-72. The electrochemical reduction of solution Eu(III) with unfunctionalized OMC, XC-72, and TODGA-functionalized OMC—both within the electrode matrix and on the electrode surface—is reported. The complexation of Eu(III) by TODGA-functionalized OMC prior to electrode preparation incorporates Eu(III) as part of the bulk electrode matrix. Under these conditions, the high capacitance obscures the Eu(III)/Eu(II) redox couple. A signal emerges above the background (capacitive) currents when 2-octanol is added to the TODGA-functionalized OMC as a wetting agent. In contrast, surface Eu(III)–TODGA complexation, when Eu(III) contacts the electrode surface exclusively after electrode preparation, provides a strong response. The addition of 2-octanol to TODGA reduces the capacitance of the electrode and narrows the Eu(III)/Eu(II) redox peak widths. In conclusion, the desorption by reductive stripping of Eu(II) was demonstrated using a 2-octanol modified TODGA OMC CME, opening the possibility for selective separation of Eu from adjacent trivalent lanthanides.

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

Thiocyanate complexes of the lanthanides, Am and Cm

In this work, the synthesis and single crystal structures of Am( III ) and Cm( III ) thiocyanate complexes are reported along with an isostructural series of lanthanide thiocyanate complexes. Because the complexes are isostructural, a comparative study of the metal–thiocyanate bonds was conducted using Raman spectroscopy indicating very similar and electrostatic metal–ligand interactions.

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

A comparison of probabilistic generative frameworks for molecular simulations

Generative artificial intelligence is now a widely used tool in molecular science. Despite the popularity of probabilistic generative models, numerical experiments benchmarking their performance on molecular data are lacking. Here, in this work, we introduce and explain several classes of generative models, broadly sorted into two categories: flow-based models and diffusion models. We select three representative models: neural spline flows, conditional flow matching, and denoising diffusion probabilistic models, and examine their accuracy, computational cost, and generation speed across datasets with tunable dimensionality, complexity, and modal asymmetry. Our findings are varied, with no one framework being the best for all purposes. In a nutshell, (i) neural spline flows do best at capturing mode asymmetry present in low-dimensional data, (ii) conditional flow matching outperforms other models for high-dimensional data with low complexity, and (iii) denoising diffusion probabilistic models appear the best for low-dimensional data with high complexity. Our datasets include a Gaussian mixture model and the dihedral torsion angle distribution of the Aib9 peptide, generated via a molecular dynamics simulation. We hope our taxonomy of probabilistic generative frameworks and numerical results may guide model selection for a wide range of molecular tasks.

Artificial intelligence↗
DOE OSTI2023

Uncovering the 3d and 4d Electronic Interactions in Solvated Ru Complexes with 2p3d Resonant Inelastic X-ray Scattering

The electronic structure and dynamics of ruthenium complexes are widely studied given their use in catalytic and light-harvesting materials. Here we investigate three model Ru complexes, [Ru III (NH 3 ) 6 ] 3+ , [Ru II (bpy) 3 ] 2+ , and [Ru II (CN) 6 ] 4– , with L 3 -edge 2p3d resonant inelastic X-ray scattering (RIXS) to probe unoccupied 4d valence orbitals and occupied 3d orbitals and to gain insight into the interactions between these levels. In this study, the 2p3d RIXS maps contain a higher level of spectral information than the L 3 X-ray absorption near edge structure (XANES). This study provides a direct measure of the 3d spin–orbit splittings of 4.3, 4.0, and 4.1 eV between the 3d 5/2 and 3d 3/2 orbitals of the [Ru III (NH 3 ) 6 ] 3+ , [Ru II (bpy) 3 ] 2+ , and [Ru II (CN) 6 ] 4– complexes, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Alkali Metal Ions Dictate the Structure and Reactivity of an Iron(II) Imido Complex

The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds; however, insight from structure/function relationships is limited. Here, alkali metal reduction of the Fe(III) imido complex [Ph 2 B( t BuIm) 2 Fe=NDipp] (1) provides the series of structurally characterized Fe(II) imido complexes [Ph 2 B( t BuIm) 2 Fe=NDippLi(THF) 2 ] (2), [Ph 2 B( t BuIm) 2 Fe=NDippNa(THF) 3 ] (3), and [Ph 2 B( t BuIm) 2 Fe=NDippK] 2 (4), in which the alkali metal cations coordinate the imido ligand. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe=N bond distance from that in the charge separated complex [Ph 2 B( t BuIm) 2 Fe=NDipp][K(18-C-6)THF 2 ] (5), with the longest bond observed for the smallest alkali metal ion. In contrast to 5, the imido ligands in 2–4 can be protonated and alkylated to afford Fe(II) amido complexes. Combined experimental and computational studies reveal that the alkali metal polarizes the Fe=N bond, and the basicity of imido ligand increases according to 5 < 4 ≈ 3 < 2. The basicity of the imido ligands influences the relative rates of reaction with 1,4-cyclohexadiene, specifically by gating access to complex 5, which is the species that is active for HAT. All complexes 2–4 react with benzophenone form metastable Fe(II) intermediates that subsequently eliminate the metathesis product Ph 2 C=NDipp, with relative rates dependent on the alkali metal ion. By contrast, the same reaction with 5 does not lead to the formation of Ph 2 C=NDipp. Furthermore, these results demonstrate that the coordination of alkali metal ions dictate both the structure and reactivity of the imido ligand and moreover can direct the reactivity of reaction intermediates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Plant-specific features of respiratory supercomplex I + III2 from Vigna radiata

Abstract The last steps of cellular respiration—an essential metabolic process in plants—are carried out by mitochondrial oxidative phosphorylation. This process involves a chain of multi-subunit membrane protein complexes (complexes I–V) that form higher-order assemblies called supercomplexes. Although supercomplexes are the most physiologically relevant form of the oxidative phosphorylation complexes, their functions and structures remain mostly unknown. Here we present the cryogenic electron microscopy structure of the supercomplex I + III 2 from Vigna radiata (mung bean). The structure contains the full subunit complement of complex I, including a newly assigned, plant-specific subunit. It also shows differences in the mitochondrial processing peptidase domain of complex III 2 relative to a previously determined supercomplex with complex IV. The supercomplex interface, while reminiscent of that in other organisms, is plant specific, with a major interface involving complex III 2 ’s mitochondrial processing peptidase domain and no participation of complex I’s bridge domain. The complex I structure suggests that the bridge domain sets the angle between the enzyme’s two arms, limiting large-scale conformational changes. Moreover, complex I’s catalytic loops and its response in active-to-deactive assays suggest that, in V. radiata , the resting complex adopts a non-canonical state and can sample deactive- or open-like conformations even in the presence of substrate. This study widens our understanding of the possible conformations and behaviour of complex I and supercomplex I + III 2 . Further studies of complex I and its supercomplexes in diverse organisms are needed to determine the universal and clade-specific mechanisms of respiration.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Revealing the Configuration and Conformation of Surface Organometallic Catalysts with DNP-Enhanced NMR

Although single-site, supported organometallic catalysts were designed with homogeneity in mind, little is strictly known about their atomic-level structure and uniformity. This is in large part due to the inability of conventional characterization tools to provide structural information with adequate resolution and range for this purpose. In this work, we show that dynamic nuclear polarization (DNP)-enhanced solid-state nuclear magnetic resonance (NMR) enables the measurement of distances between the surface and individual carbons, making it possible to orient complexes and molecules on surfaces. We use this approach to determine the orientation and configuration of naturally 13 C-abundant acetate and supported organoiridium(III) pincer complex, both supported on γ-Al 2 O 3 . By combining solid-state NMR and extended X-ray absorption fine structure spectroscopy (EXAFS) experiments with periodic density functional theory (DFT) calculations, we are able to determine the three-dimensional arrangement of ligands around the metal center and thereby identify the structure of the supported complex at a resolution reminiscent of that associated with single-crystal diffractometry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

In situ beam reduction of Pu(IV) and Bk(IV) as a route to trivalent transuranic coordination complexes with hydroxypyridinone chelators

The solution-state interactions of plutonium and berkelium with the octadentate chelator 3,4,3-LI(1,2-HOPO) (343-HOPO) were investigated and characterized by X-ray absorption spectroscopy, which revealed in situ reductive decomposition of the tetravalent species of both actinide metals to yield Pu(III) and Bk(III) coordination complexes. X-ray absorption near-edge structure (XANES) measurements were the first indication of in situ synchrotron redox chemistry as the Pu threshold and white-line position energies for Pu-343-HOPO were in good agreement with known diagnostic Pu(III) species, whereas Bk-343-HOPO results were found to mirror the XANES behavior of Bk(III)-DTPA. Extended X-ray absorption fine structure results revealed An—O HOPO bond distances of 2.498 (5) and 2.415 (2) Å for Pu and Bk, respectively, which match well with bond distances obtained for trivalent actinides and 343-HOPO via density functional theory calculations. Pu(III)- and Bk(III)-343-HOPO data also provide initial insight into actinide periodicity as they can be compared with previous results with Am(III)-, Cm(III)-, Cf(III)-, and Es(III)-343-HOPO, which indicate there is likely an increase in 5 f covalency and heterogeneity across the actinide series.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

A numerical study of process complexity in permafrost dominated regions

Numerical modeling of permafrost dynamics requires adequate representation of atmospheric and surface processes, a reasonable parameter estimation strategy, and site-specific model development. The three main research objectives of the study are: (i) to propose a novel methodology that determines the required level of surface process complexity of permafrost models by conducting parameter sensitivity and calibration, (ii) to design and compare three numerical models of increasing surface process complexity, and (iii) to calibrate and validate the numerical models at the Yakou catchment on the Qinghai-Tibet Plateau as an exemplary study site. The calibration was carried out by coupling the Advanced Terrestrial Simulator (numerical model) and PEST (calibration tool). Simulation results showed that (i) A simple numerical model that considers only subsurface processes can simulate active layer development with the same accuracy as other more complex models that include surface processes. (ii) Peat and mineral soil layer permeability, Van Genuchten alpha, and porosity are highly sensitive. (iii) Liquid precipitation aids in increasing the rate of permafrost degradation. (iv) Deposition of snow insulated the subsurface during the thaw initiation period. We have developed and released an integrated code that couples the numerical software ATS to the calibration software PEST. The numerical model can be further used to determine the impacts of climate change on permafrost degradation.

Calibration↗
DOE OSTI2020

Second Coordination Sphere Effects in an Evolved Ru Complex Based on Highly Adaptable Ligand Results in Rapid Water Oxidation Catalysis

A new Ru complex containing the deprotonated 2,2':6',2"-terpyridine-6,6"-diphosphonic acid (H 4 tPa) and pyridine (py) of general formula [Ru II (H 3 tPa-κ-N 3 O)(py) 2 ] + , 2 + , has been prepared and thoroughly characterized by means of spectroscopic and electrochemical techniques, X-ray diffraction analysis, and density functional theory (DFT) calculations. Complex 2 + presents a dynamic behavior in the solution that involves the synchronous coordination and the decoordination of the dangling phosphonic groups of the tPa 4– ligand. Yet, at oxidation state IV, complex 2 + becomes seven coordinated with the two phosphonic groups now bonded to the metal center. Further, at this oxidation state at neutral and basic pH, the Ru complex undergoes the coordination of an exogenous OH – group from the solvent that leads to an intramolecular aromatic O atom insertion into the CH bond of one of the pyridyl groups, forming the corresponding phenoxo-phosphonate Ru complex [Ru III (tPaO-κ-N 2 O P O C )(py) 2 ] 2– , 4 2– , where tPaO 5– is the 3-(hydroxo-[2,2':6',2"-terpyridine]-6,6"-diyl)bis(phosphonate) ligand. This new in situ generated Ru complex, 4 2– , has been isolated and spectroscopically and electrochemically characterized. In addition, a crystal structure has been also obtained using single-crystal X-ray diffraction techniques. Complex 4 2– turns out to be an exceptional water oxidation catalyst achieving record maximum turnover frequencies (TOF max ) on the order of 16 000 s –1 . A mechanistic analysis complemented with DFT calculations has further been carried out, showing the critical role of intramolecular second coordination sphere effects exerted by the phosphonate groups in lowering the activation energy at the rate-determining step.

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

Changes in Sedimentary Phosphorus Burial Following Artificial Eutrophication of Lake 227, Experimental Lakes Area, Ontario, Canada

Lake 227 of the Experimental Lakes Area (ELA) in Ontario, Canada has been fertilized with phosphorus (P) since 1969, which resulted in a rapid transition from oligotrophic to eutrophic conditions. Sediment cores collected from the oxygenated epilimnion and the mostly anoxic hypolimnion of this unique lake contain a historical record of the changes in sediment P speciation and burial rates across the trophic transition. To elucidate these changes, results of chemical extractions were combined with 210 Pb sediment dating, and with 31 P NMR, Mössbauer and XANES spectroscopies. Prior to 1969, organic P (P Org ) was the major sedimentary P sink in Lake 227. Eutrophication of the lake coincided with marked increases in the burial rate of total P (TP), as well as in the relative contribution of the NaHCO 3 -extractable P pool (humic-bound P, P Hum ). Together, P Hum and P Org account for ≥70% of total P burial in the sediments deposited since artificial fertilization started. The P Hum fraction likely comprises phosphate complexes with humic substances. The strong linear correlation between P and iron (Fe) extracted by NaHCO 3 implies a close association of the two elements in the humic fraction. Mössbauer and XANES spectra further indicate that most Fe in the post-1969 sediments remained in the Fe(III) oxidation state, which is attributed to the stabilization of reducible Fe by organic matter, in part via the formation of phosphate-Fe(III)-humic complexes. Importantly, our results show that the eutrophication experimentation of Lake 227 caused the accumulation of a large reservoir of reactive sediment P, which may continue to fuel internal P loading to the water column once artificial fertilization is terminated.

54 ENVIRONMENTAL SCIENCES↗