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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Cis-Divacant Octahedral Fe(II) in a Dimensionally Reduced Family of 2-(Pyridin-2-yl)pyrrolide Complexes

Four-coordinate transition metal complexes can adopt a diverse array of coordination geometries, with square planar and tetrahedral coordination being the most prevalent. Previously, we reported the synthesis of a trinuclear Fe(II) complex, Fe 3 TPM 2 , supported by a three-fold symmetric 2-pyridylpyrrolide ligand (i.e., tris(5-(pyridin-2-yl)-1H-pyrrol-2-yl)methane), that featured a rare cis-divacant octahedral (CDO) geometry at each Fe(II) center. Here, a series of truncated 2-pyridylpyrrolide ligands is described that support mono- and binuclear Fe(II) complexes that also exhibit CDO geometries. Metallation of tetradentate ligand bis(5-(pyridin-2-yl)-1H-pyrrol-2-yl)methane (H 2 BPM) in THF results in a binuclear complex Fe 2 (BPM) 2 (THF) 2 in which both Fe(II) ions are octahedrally coordinated. The coordinated THF solvent ligands are labile: THF dissociation leads to Fe 2 (BPM) 2 , which features five-coordinate Fe(II) ions. The Fe–Fe distance in these binuclear complexes can be elongated by ligand methylation. Metalation of bis(5-(6-methylpyridin-2-yl)-1H-pyrrol-2-yl)methane (H 2 BPM Me ) in THF leads to the formation of four-coordinate, CDO Fe(II) centers in Fe(BPM Me ) 2 . Further ligand truncation affords bidentate ligands 2-(1H-pyrrol-2-yl)pyridine (PyrPyrrH) and 2-methyl-6-(1H-pyrrol-2-yl)pyridine (Pyr Me PyrrH). Metalation of these ligands in THF affords six-coordinate complexes Fe(PyrPyrr) 2 (THF) 2 and Fe(Pyr Me Pyrr) 2 (THF) 2 . Dissociation of labile solvent ligands provides access to fourcoordinate Fe(II) complexes. Ligand disproportionation at Fe(PyrPyrr) 2 results in the formation of Fe(PyrPyrr) 3 and Fe(0). Ligand methylation suppresses this disproportionation and enables isolation of Fe(Pyr Me Pyrr) 2 , which is rigorously CDO. Complete ligand truncation, by separating the 2-pyridylpyrrolide ligands into the constituent monodentate pyridyl and pyrrolide donors, affords Fe(Pyr) 2 (Pyrr) 2 in which the Fe(II) is tetrahedrally coordinated. Computational analysis indicates that the potential energy surface that dictates the coordination geometry in this family of four-coordinate complexes is fairly flat in the vicinity of CDO coordination. Furthermore, these synthetic studies provide the structural basis to explore the implications of CDO geometry on Fe-catalyzed reactions.

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

Cubic Crystal Structure Formation and Optical Properties within the Ag–B II –M IV –X (B II = Sr, Pb; M IV = Si, Ge, Sn; X = S, Se) Family of Semiconductors

Quaternary chalcogenide semiconductors are promising materials for energy conversion and nonlinear optical applications, with properties tunable primarily by varying the elemental composition and crystal structure. Here, we first analyze the connections among several cubic crystal structure types, as well as the orthorhombic Ag 2 PbGeS 4 -type structure, reported for select members within the Ag–B II –M IV –X (B II = Sr, Pb; M IV = Si, Ge, Sn; X = S, Se) compositional space. Focusing on the Ag–Pb–Si–S and Ag–Sr–Sn–S systems, we show that one structure type, with the formulas Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , is favored. We have prepared powder and single-crystal samples of Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , showing that each takes on the noncentrosymmetric cubic space group I$\bar{43}$d and is isostructural to the previously reported compound Ag 2 Sr 3 Ge 2 Se 8 . Through hybrid density functional theory calculations, these cubic compounds are demonstrated to be (quasi-)direct band gap semiconductors with high densities of states at the band maxima. Furthermore, the band-gap energies are measured by reflectance spectroscopy as 1.95(3) and 2.66(4) eV for Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , respectively. We further measure the optical properties and show the electronic band structures of three other isostructural A I –B II –M IV –X-type materials, i.e., Ag 2 Sr 3 Si 2 S 8 , Ag 2 Sr 3 Ge 2 S 8 , and Ag 2 Sr 3 Ge 2 Se 8 , showing that the band gaps can be predictably tuned by element substitution. Detailed visual analyses of the different structures and of their relationships with other members of the Ag–B II –M IV –X compositional family provide a basis for a broader understanding of the structure formation and optoelectronic properties within the quaternary chalcogenide semiconductor family.

14 SOLAR ENERGY↗
DOE OSTI2023

Changing Directions: Influence of Ligand Electronics on the Directionality and Kinetics of Photoinduced Charge Transfer in Cu(I)Diimine Complexes

A key challenge to the effective utilization of solar energy is to promote efficient photoinduced charge transfer, specifically avoiding unproductive, circuitous electron-transfer pathways and optimizing the kinetics of charge separation and recombination. We hypothesize that one way to address this challenge is to develop a fundamental understanding of how to initiate and control directional photoinduced charge transfer, particularly for earth-abundant first-row transition-metal coordination complexes, which typically suffer from relatively short excited-state lifetimes. Here, in this paper, we report a series of functionalized heteroleptic copper(I)bis(phenanthroline) complexes, which have allowed us to investigate the directionality of intramolecular photoinduced metal-to-ligand charge transfer (MLCT) as a function of the substituent Hammett parameter. Ultrafast transient absorption suggests a complicated interplay of MLCT localization and solvent interaction with the Cu(II) center of the MLCT state. This work provides a set of design principles for directional charge transfer in earth-abundant complexes and can be used to efficiently design pathways for connecting the molecular modules to catalysts or electrodes and integration into systems for light-driven catalysis.

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

A DFT Comparison of C–C Reductive Coupling from Terminal Cyanido and Cyaphido Complexes of Nickel

The density functional theory study of the thermal C–C reductive coupling from terminal cyanido and hypothetical cyaphido complexes of [Ni(dmpe)] (dmpe = 1,2-bis(dimethylphosphino)ethane) revealed the key reaction intermediate in the reductive C–CP coupling being a σ-CC complex unlike an η 2 -aryl complex in the Ni C–CN system, as already observed in our previous studies. The reaction in THF is endothermic by 4.9 kcal/mol for cyanido with a 32.0 kcal/mol activation barrier and exothermic by 28.5 kcal/mol for cyaphido with an 11.3 kcal/mol activation barrier. To compare our results with the existing experimental data, we chose mesityl as the aryl group and also studied the CP reaction with [Pt(dmpe)] and [Pt(dmpm)] (dmpe = 1,2-bis(dimethylphosphino)methane) fragments. Our findings are consistent with the thermodynamically uphill photolytic C–CP bond activation in phosphaalkynes with Pt and a faster thermal back-reaction with [Pt(dmpe)] compared to that of [Pt(dmpm)]. Furthermore, based on the natural population analysis, when the polarity of the C–C bond is inverted, the sign of ΔG° is also inverted.

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

Electron-Donating para -Substituent (X) Enhances the Water Oxidation Activity of the Catalyst Ru(4'-X-terpyridine)(phenanthroline-SO 3 ) +

Recently, our group has developed a Ru-based water oxidation catalyst (WOC) with pendant sulfonate (1, Ru(4'-X-terpyridine)(phenanthroline-SO 3 )OTf (X = H, 1a) that shows high activity under both sacrificial oxidant (CAN, Ce(NH 4 ) 2 (NO 3 ) 6 , Ce IV ) and electrocatalytic conditions, in both acidic and neutral media. Here, we demonstrate that the functionalization of the 4'-X-terpyridine ligand with an electron-donating substituent X = OEt (1b) makes potentials of Ru II /Ru III redox catalysis more negative, whereas when X = NO 2 (1c) and CF 3 (1d), potentials are more positive. For 1b, full conversion of the sacrificial oxidant Ce IV occurred in 0.4 h (7 h for 1a), with an initial rate of 2.07 μmol O 2 s –1 and a turnover frequency of 7.6 s –1 , which is 30-fold faster than that for 1a at [cat] 0 = 20 μM. Under electrocatalytic conditions, water oxidation by 1b is three times faster than that by the parent catalyst 1a at close to the same potential. Extensive computations have identified differences in the initial PCET steps of the water oxidation by catalysts 1a, 1b, and 1d, and demonstrated the increased probability of the O 2 formation via the oxide relay pathway in the order 1b< 1a < 1d.

14 SOLAR ENERGY↗
DOE OSTI2025

U 4+/5+/6+ in a Conserved Pseudotetrahedral Imidophosphorane Coordination Sphere

While several ligand systems support uranium across a range of oxidation states, spanning more than two oxidation states in a conserved coordination geometry is uncommon among structurally authenticated complexes. Imidophosphorane ligands significantly stabilize high-valent lanthanide and actinide complexes. Here, we report a series of homoleptic uranium imidophosphorane complexes, spanning the +4, +5 and +6 oxidation states in a four-coordinate pseudotetrahedral ligand field. The +6 oxidation state is accessible using a mild ferrocenium oxidant, yielding a rare example of U6+ in a pseudotetrahedral coordination environment. As the formal oxidation state increases, the U–N distances gradually contract, consistent with the Shannon ionic radii of U 4+/5+/6+ . Compared to reported complexes, the short U–N distances observed in the U 6+ complex are more comparable to dianionic imido ligands than monoanionic amido ligands.

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

X-ray Spectroscopy Characterization of Electronic Structure and Metal–Metal Bonding in Dicobalt Complexes

Developing multimetallic complexes with tunable metal–metal interactions has long been a target of synthetic inorganic chemistry efforts due to the unique properties that such compounds can exhibit. However, understanding relationships between metal–metal bonding and chemical properties is challenging due to system-dependent factors that influence metal–metal and metal–ligand interactions, including ligand identity, coordination geometry, and metal–metal distance. In this work, we apply X-ray absorption and emission spectroscopy and quantum chemical calculations to describe electronic structure and bonding in a series of dicobalt complexes. The compounds with silane ligands and pseudo-octahedral coordination geometry exhibit Co–Co σ and multicentered bonding character, which we characterize from both the occupied and vacant perspectives via their contributions to the Co X-ray emission and absorption spectra, respectively. In contrast, the dicobalt complexes with a pseudotetrahedral coordination environment do not exhibit Co–Co bonding due to symmetry constraints on orbital overlap. We extend these insights to the theoretical evaluation of related dicobalt complexes to explain how ligand coordination and symmetry dictate the presence or absence of a Co–Co bond. In conclusion, this work highlights how fundamental insights into electronic structure and bonding through X-ray spectroscopy uncover important factors governing metal–metal interactions and guide the rational design of multimetallic complexes with tunable metal–metal bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Metal–Ligand Cooperativity Promoting Sulfur Atom Transfer in Ferrous Complexes and Isolation of a Sulfurmethylenephosphorane Adduct

Here, the reaction of elemental sulfur with the cis-divacant octahedral complex [(pyrr 2 py)Fe(OEt 2 )] (1; pyrr 2 py 2– = 3,5- t Bu 2 -bis(pyrrolyl)pyridine) yields the iron dimer [(pyrr-1-S-pyrrpy)Fe] 2 (2; pyrr-1-S-pyrrpy 2– = 3,5-( t Bu2-pyrrolyl)(1-S-3,5-tBu2-pyrrolyl)pyridine) resulting from a pyrr 2 py 2– ligand based S-oxidation of one pyrrole arm. Addition of the phosphorus ylide H 2 CPPh 3 to 1 forms the ylide adduct [(pyrr 2 py)Fe(CH 2 PPh 3 )] (3), which upon reaction with elemental sulfur produces a rare example of a sulfurmethylenephosphorane adduct, [(pyrr 2 py)Fe(SCH 2 PPh 3 )] (4). The sulfur-oxidized pyrrole group of the ligand pyrr-1-S-pyrrpy 2– can be reversed, since complex 2 exhibits S atom transferability via the addition of 2 equiv of H 2 CPPh 3 to yield a mixture of compounds 3 and 4. For all complexes reported, the ferrous ion remains S = 2. Complexes 2–4 were characterized by single-crystal X-ray diffraction as well as 1 H NMR spectroscopy, solid and solution magnetic studies, and 57 Fe Mössbauer spectroscopic measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Complex Topologies from Simple Building Blocks: Uranium(IV) Thiophosphates

Six new uranium thiophosphates Cs 5 Na 6 [U(PS 4 ) 4 ](PS 4 ) (1), Rb 5 Na 3 [U(PS 4 ) 4 ] (2), CsNa[U(PS 4 ) 2 ] (3), Cs 1.67 Na 0.52 I 0.19 [U(PS 4 ) 2 ] (4), Cs 1.033 Na 1.343 I 0.376 [U(PS 4 ) 2 ] (5), and Rb 1.35 Na 0.93 I 0.28 [U(PS 4 ) 2 ] (6) were obtained from halide flux reactions and characterized using single crystal X-ray diffraction. The structures of these compounds consist of a pseudo-tetrahedral uranium unit that in combination with a set of PS 4 group coordination modes can result in an isolated [U(PS 4 ) 4 ] 8– unit, a [U(PS 4 ) 2 ] 2– chain, or a [U(PS 4 ) 2 ] 2– slab. Optical and magnetic properties of 3 and 4 were collected. Both compounds exhibit paramagnetic behavior, and CsNa[U(PS 4 ) 2 ] (3) exhibits a magnetic transition at 200–225 K between two paramagnetic states that both have similar effective magnetic moments of 4.13 and 4.19 µ B /F.U., and strong antiferromagnetic interactions with θ = -183 and -172 K, for the high- and low-temperature states, respectively.

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

Nearly Identical but Not Isotypic: Influence of Lanthanide Contraction on Cs 2 NaLn(PS 4 ) 2 (Ln = La–Nd, Sm, and Gd–Ho)

The effect of the lanthanide contraction often results in topological and symmetry changes in compounds with the same compositions as a function of lanthanide cation size. Here we report on the first example of a lanthanide thiophosphate exhibiting a change in the lanthanide cation environment without any topological or symmetry change. A series of new lanthanide thiophosphates with mixed alkali cations was obtained via a flux crystal growth technique using a CsI flux. The obtained compounds Cs 2 NaLn(PS 4 ) 2 (Ln = La–Nd, Sm, Gd–Ho) were grown as large single crystals (~0.1–1 mm 3 ) and characterized using single crystal X-ray diffraction and magnetic susceptibility measurements. Moving across the series, the structural studies revealed a change in the lanthanide coordination environment dependent upon the identity of the lanthanide. Although all compounds in the Cs 2 NaLn(PS 4 ) 2 series crystallize in the same space group and have the same Wyckoff positions of the atoms, a slight size change between Sm 3+ and Gd 3+ causes a subtle change in coordination number from 9 (for Ln = La–Sm) to 8 (for Ln = Gd–Ho), resulting in two distinct but virtually identical structure types. Ab initio calculations were performed, and the observed experimental trend was corroborated computationally. Finally, magnetic measurements performed on the Cs 2 NaLn(PS 4 ) 2 (Ln = Ce, Pr, Nd, Gd, and Tb) compounds revealed paramagnetic behavior.

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

Coupled Cluster Study of the Interactions of AnO 2 , AnO 2 + , and AnO 2 2+ (An = U, Np) with N 2 and CO

We report thermochemical and spectroscopic properties for actinyl complexes involving UO 2 2+/1+/0 and NpO 2 2+/1+/0 with N 2 and CO, together with the UO 2 -O 2 , UO 2 + -O 2 , and UO 2 + -NO complexes, have been studied for the first time using an accurate composite coupled cluster approach. Two general bonding motifs were investigated, end-on (η 1 ) and side-on (η 2 ) relative to the metal center of the actinyls. For end-on CO complexes, both C-coordinated (An-C) and O-coordinated (An-O) structures were examined, with the former always being lower in energy. All of the η 1 complexes were calculated to be stable, with dissociation energies ranging from 2 to 36 kcal/mol, except for that of UO 2 + -O 2 (the η 1 orientation for UO 2 + -NO was not amenable to single reference coupled cluster). In agreement with a previous study, the η 2 structure for UO 2 + -O 2 was calculated to be relatively strongly bound, by 22.3 kcal/mol in this work. The closely related NO complex, however, had a calculated dissociation energy of just 4.0 kcal/mol. The binding energy of O 2 to neutral UO 2 in a η 2 orientation was calculated to be very strong, 75.4 kcal/mol, and strongly resembled a UO 2 + (O 2 – ) complex at equilibrium. The N–N and C–O bonds were found to be somewhat activated for all the side-on (η 2 ) neutral An(IV) complexes, with stretching frequencies of N 2 or CO being red-shifted by as much as 480 cm –1 with a 0.06 Å bond length elongation. Dissociation energies for the η 1 complexes are strongly correlated with the extent of electron transfer from ligand to actinyl. The nature of bonding in the actinyl complexes is examined using natural resonance theory (NRT). The correlation between bonding motif and small molecule activation is in agreement with experiments in condensed phases.

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

The Chemistry Graduate Student Experience: Findings from an ACS Survey

Graduate training is a key element in producing a scientific workforce that reflects the nation’s diversity. This paper examines data from a 2013 American Chemical Society (ACS) survey of 2,544 chemistry masters and doctoral students and reveals barriers to reaching this goal. Multivariate statistical analyses indicate that women reported significantly less supportive relationships with advisors. Women were less likely to plan to finish their degrees, and for PhD students, the discrepancy was larger for students at the start of their graduate program. Women were also less likely to pursue the next level of training, and the gender difference related to postdoctoral plans was greater for those who identified with a racial-ethnic group traditionally underrepresented in chemistry (underrepresented minority, URM). URM students who were beyond the first year of their graduate program reported significantly less supportive relationships with peers. They were also less likely to have funding sufficient to meet their needs and more often used personal resources including loans. Despite these difficulties, URM students were more likely to definitely plan to finish their degrees, and men who identified as URM were more likely to plan to pursue postdoctoral work. Independent of gender and identification as URMs, students in more highly ranked schools reported less advisor support. Extensive open-ended comments indicated that large proportions of the students desired more attention and meaningful feedback from advisors and changes within their programs to promote support for students and advisor accountability. Suggestions for future research are given, and a companion commentary discusses needed directions for change.

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

Improving Data and Prediction Quality of High-Throughput Perovskite Synthesis with Model Fusion

Combinatorial fusion analysis (CFA) is an approach for combining multiple scoring systems using the rank-score characteristic function and cognitive diversity measure. One example is to combine diverse machine learning models to achieve better prediction quality. In this work, we apply CFA to the synthesis of metal halide perovskites containing organic ammonium cations via inverse temperature crystallization. Using a data set generated by high-throughput experimentation, four individual models (support vector machines, random forests, weighted logistic classifier, and gradient boosted trees) were developed. We characterize each of these scoring systems and explore 66 possible combinations of the models. When measured by the precision on predicting crystal formation, the majority of the combination models improves the individual model results. The best combination models outperform the best individual models by 3.9 percentage points in precision. In addition to improving prediction quality, we demonstrate how the fusion models can be used to identify mislabeled input data and address issues of data quality. In particular, we identify example cases where all single models and all fusion models do not give the correct prediction. Experimental replication of these syntheses reveals that these compositions are sensitive to modest temperature variations across the different locations of the heating element that can hinder or enhance the crystallization process. In summary, we demonstrate that model fusion using CFA can not only identify a previously unconsidered influence on reaction outcome but also be used as a form of quality control for high-throughput experimentation.

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

Mass Spectrometry Adduct Calculator

We describe the Mass Spectrometry Adduct Calculator (MSAC), an automated Python tool to calculate the adduct ion masses of a parent molecule. Here, adduct refers to a version of a parent molecule [M] that is charged due to addition or loss of atoms and electrons resulting in a charged ion, e.g. [M+H] + . MSAC includes a database of 2,341 potential ions and their mass-to-charge ratios (m/z) as extracted from the NIST/EPA/NIH Mass Spectral Library (NIST17), the Global Natural Products Social Molecular Networking Public Spectral Libraries (GNPS), and MassBank of North America (MoNA). The calculator relies on user-selected subsets of the combined database to calculate expected m/z for adducts of molecules supplied as formulas This tool is intended to help researchers create identification libraries to collect evidence for the presence of molecules in mass spectrometry data. While the included adduct database focuses on adducts typically detected during liquid chromatography-mass spectrometry analyses, users may supply their own lists of adducts and charge states for calculating expected m/z. We also analyzed statistics on adducts from spectra contained in the three selected mass spectral libraries. MSAC is freely available at https://github.com/pnnl/MSAC.

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

PathTracer Comprehensively Identifies Hypoxia-Induced Dormancy Adaptations in Mycobacterium tuberculosis

Mining large-scale data to discover biologically relevant information remains a challenge despite the rapid development of bioinformatics tools. Here, we have developed a new tool, PathTracer, to identify biologically relevant information flows by mining genome-wide protein–protein interaction networks following integration of gene expression data. PathTracer successfully mines interactions between genes and traces the most perturbed paths of perceived activities under the conditions of the study. Here, we further demonstrated the utility of this tool by identifying adaptation mechanisms of hypoxia-induced dormancy in Mycobacterium tuberculosis (Mtb).

59 BASIC BIOLOGICAL SCIENCES↗