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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Complexation and phase evolution at dimethylformamide-Ag(111) interfaces

The interaction of solvent molecules with metallic surfaces impacts many interfacial chemical processes. We investigate the chemical and structure evolution that follows adsorption of the polar solvent dimethylformamide (DMF) on Ag(111). An Ag(DMF) 2 coordination complex forms spontaneously by DMF etching of Ag(111), yielding mixed films of the complexes and DMF. Utilizing ultrahigh vacuum scanning tunneling microscopy (UHV-STM), in combination with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) computations, we map monolayer phases from the 2-D gas regime, consisting of a binary mixture of DMF and Ag(DMF) 2 , through the saturation monolayer limit, in which these two chemical species phase separate into ordered islands. Structural models for the near-square DMF phase and the chain-like Ag(DMF) 2 phase are presented and supported by DFT computation. Interface evolution is summarized in a surface pressure-composition phase diagram, which allows structure prediction over arbitrary experimental conditions. In conclusion, this work reveals new surface coordination chemistry for an important electrolyte-electrode system, and illustrates how surface pressure can be used to tune monolayer phases.

2-D phases↗
DOE OSTI2016

Surface-modified cyanide-based transition metal compounds

A system, method, and articles of manufacture for a surface-modified transition metal cyanide coordination compound (TMCCC) composition, an improved electrode including the composition, and a manufacturing method for the composition. The composition, compound, device, and uses thereof according to A.sub.xMn.sub.(y-k)M.sup.j.sub.k[Mn.sup.m(CN).sub.(6-p-q)(NC).sub.p(Che).- sup.r.sub.q].sub.z.(Che).sup.r.sub.w(Vac).sub.(1-z).nH.sub.2O (wherein Vac is a Mn(CN).sub.(6-p-q)(NC).sub.p(Che).sup.r.sub.q vacancy); wherein Che is an acid chelating agent; wherein: A=Na, K, Li; and M=Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, Cd, In, Sn, Pb; and wherein 0<j.ltoreq.4; 0.ltoreq.k.ltoreq.0.1; 0.ltoreq.(p+q)<6; 0<x.ltoreq.4; 0.ltoreq.y.ltoreq.1; 0<z.ltoreq.1; 0<w.ltoreq.0.2; 0<n.ltoreq.6; -3.ltoreq.r.ltoreq.3; and wherein: x+2(y-k)+jk+(m+(r+1)q-6)z+wr=0.

Motallebi, Shahrokh↗
DOE OSTI2016

Surface-modified cyanide-based transition metal compounds

A system, method, and articles of manufacture for a surface-modified transition metal cyanide coordination compound (TMCCC) composition, an improved electrode including the composition, and a manufacturing method for the composition. The composition, compound, device, and uses thereof according to A.sub.xMn.sub.(y-k)M.sup.j.sub.k[Mn.sup.m(CN).sub.(6-p-q)(NC).sub.p(Che).- sup.r.sub.q].sub.z. (Che).sup.r.sub.w(Vac).sub.(1-z).nH.sub.2O (wherein Vac is a Mn(CN).sub.(6-p-q)(NC).sub.p(Che).sup.r.sub.q vacancy); wherein Che is an acid chelating agent; wherein: A=Na, K, Li; and M=Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, Cd, In, Sn, Pb; and wherein 0<j.ltoreq.4; 0.ltoreq.k.ltoreq.0.1; 0.ltoreq.(p+q)<6; 0<x.ltoreq.4; 0.ltoreq.y.ltoreq.1; 0<z.ltoreq.1; 0<w.ltoreq.0.2; 0<n.ltoreq.6; -3.ltoreq.r.ltoreq.3; and wherein: x+2(y-k)+jk+(m+(r+1)q-6)z+wr=0.

Motallebi, Shahrokh↗
DOE OSTI2019

Surface-modified cyanide-based transition metal compounds

A system, method, and articles of manufacture for a surface-modified transition metal cyanide coordination compound (TMCCC) composition, an improved electrode including the composition, and a manufacturing method for the composition which may include multiple chelation species (Che_x). The composition, compound, device, and uses thereof according to A.sub.xMn.sub.(y-k)M.sup.j.sub.k[Mn.sup.m(CN).sub.(6-p-q)(NC).sub.p(Che_I- ).sup.r.sub.q].sub.z. CHE_GROUP (Vac).sub.(1-z).nH.sub.2O, wherein CHE_GROUP includes one or more chelation materials selected from the group consisting of (Che_I).sup.r.sub.w, (Che_II).sup.s.sub.v, and combinations thereof, and wherein 0<j.ltoreq.4, 0.ltoreq.k.ltoreq.0.1, 0.ltoreq.(p+q).ltoreq.6, 0<x.ltoreq.4, 0<y.ltoreq.1, 0<z.ltoreq.1, 0<w.ltoreq.0.2; -3.ltoreq.r.ltoreq.3; 0<v.ltoreq.0.2; -3.ltoreq.s.ltoreq.3; and 0.ltoreq.n.ltoreq.6; wherein x+2(y-k)+jk+(m+(r+1)q-6)z+wr+vs=0.

Motallebi, Shahrokh↗
DOE OSTI2020

Surface-modified cyanide-based transition metal compounds

A system, method, and articles of manufacture for a surface-modified transition metal cyanide coordination compound (TMCCC) composition, an improved electrode including the composition, and a manufacturing method for the composition which may include multiple chelation species (Che_x). The composition, compound, device, and uses thereof according to AxMn(y-k)Mjk[Mnm(CN)(6-p-q)(NC)p(Che_I)rq]z.CHE_GROUP (Vac)(1-z).nH2O, wherein CHE_GROUP includes one or more chelation materials selected from the group consisting of (Che_I)rw, (Che_II)sv, and combinations thereof, and wherein 0 < j≤4, 0≤k≤0.1, 0≤(p+q)≤6, 0 < x≤4, 0 < y≤1, 0 < z≤1, 0 < w≤0.2; −3≤r≤3; 0 < v≤0.2; −3≤s≤3; and 0≤n≤6; wherein x+2(y−k)+jk+(m+(r+1)q−6)z+wr+vs=0.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Surface-modified cyanide-based transition metal compounds

A system, method, and articles of manufacture for a surface-modified transition metal cyanide coordination compound (TMCCC) composition, an improved electrode including the composition, and a manufacturing method for the composition which may include multiple chelation species (Che_x). The composition, compound, device, and uses thereof according to AxMn(y-k)Mjk[Mnm(CN)(6-p-q)(NC)p(Che_I)rq]z. CHE_GROUP (Vac)(1-z).nH2O, wherein CHE_GROUP includes one or more chelation materials selected from the group consisting of (Che_I)rw, (Che_II)sv, and combinations thereof, and wherein 0 < j≤4, 0≤k≤0.1, 0≤(p+q)≤6, 0 < x≤4, 0 < y≤1, 0 < z≤1, 0 < w≤0.2; −3≤r≤3; 0 < v≤0.2; −3≤s≤3; and 0≤n≤6; wherein x+2(y−k)+jk+(m+(r+1)q−6)z+wr+vs=0.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Ag/α-Fe{sub 2}O{sub 3} hollow microspheres: Preparation and application for hydrogen peroxide detection

In this paper, we demonstrated a simple approach for preparing α-Fe{sub 2}O{sub 3} hollow spheres by mixing ferric nitrate aqueous and glucose in 180 °C. The glucose was found to act as a soft template in the process of α-Fe{sub 2}O{sub 3} hollow spheres formation. Ag/α-Fe{sub 2}O{sub 3} hollow nanocomposite was obtained under UV irradiation without additional reducing agents or initiators. Synthesized Ag/α-Fe{sub 2}O{sub 3} hollow composites exhibited remarkable catalytic performance toward H{sub 2}O{sub 2} reduction. The electrocatalytic activity mechanism of Ag/α-Fe{sub 2}O{sub 3}/GCE were discussed toward the reduction of H{sub 2}O{sub 2} in this paper. - Graphical abstract: Glucose is carbonized as carbon balls in the 180 °C hydrothermal carbonization process, which plays a role of a soft template. Carbon spherical shell is rich in many hydroxyls, which have good hydrophilicity and surface reactivity. When Fe(NO{sub 3}){sub 3} is added to the aqueous solution of Glucose, the hydrophilic -OH will adsorb Fe{sup 3+} to form coordination compound by coordination bond. α-FeOOH is formed on the surface of carbon balls by hydrothermal reaction. After calcination at 500 °C, carbon spheres react with oxygen to form carbon dioxide, which disappears in the air. Meanwhile α-FeOOH is calcined to form α-Fe{sub 2}O{sub 3} hollow spheres.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Iridium complexes for electrocatalysis

Solution-phase (e.g., homogeneous) or surface-immobilized (e.g., heterogeneous) electrode-driven oxidation catalysts based on iridium coordination compounds which self-assemble upon chemical or electrochemical oxidation of suitable precursors and methods of making and using thereof are. Iridium species such as {[Ir(LX).sub.x(H.sub.2O).sub.y(.mu.-O)].sub.z.sup.m+}.sub.n wherein x, y, m are integers from 0-4, z and n from 1-4 and LX is an oxidation-resistant chelate ligand or ligands, such as such as 2(2-pyridyl)-2-propanolate, form upon oxidation of various molecular iridium complexes, for instance [Cp*Ir(LX)OH] or [(cod)Ir(LX)] (Cp*=pentamethylcyclopentadienyl, cod=cis-cis,1,5-cyclooctadiene) when exposed to oxidative conditions, such as sodium periodate (NaIO.sub.4) in aqueous solution at ambient conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Air- and Water-Resistant Noble Metal Coated Ferromagnetic Cobalt Nanorods

Cobalt nanorods possess ideal magnetic properties for applications requiring magnetically hard nanoparticles. However, their exploitation is undermined by their sensitivity toward oxygen and water, which deteriorates their magnetic properties. The development of a continuous metal shell inert to oxidation could render them stable, opening perspectives not only for already identified applications but also for uses in which contact with air and/or aqueous media is inevitable. However, the direct growth of a conformal noble metal shell on magnetic metals is a challenge. Here, we show that prior treatment of Co nanorods with a tin coordination compound is the crucial step that enables the subsequent growth of a continuous noble metal shell on their surface, rendering,them air- and water-resistant, while conserving the monocrystallity, metallicity and the Magnetic properties of the Co core. Thus, the as-synthesized tore shell ferromagnetic nanorods combine high;Magnetization and strong uniaxial Magnetic anisotropy, even after exposure to air and water, and hold promise for successful implementation in in vitro biodiagnostics requiring probes Of high magnetization and anisotropic shape.

Air- and Water-Resistant Noble Metal Coated Ferrom↗
DOE OSTI2014

A new carboxyl-copper-organic framework and its excellent selective absorbability for proteins

One-pot solvothermal treatments of CuCl{sub 2}·2H{sub 2}O, H{sub 2}L (5-(3-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl) isophthalic acid) and Sm(NO{sub 3}){sub 3}·6H{sub 2}O in water yielded a rare carboxyl-copper-organic framework, [Cu(HL)]{sub n}·nH{sub 2}O (1). The existence of carboxyl groups in compound 1 may be due to the interference of Sm(NO{sub 3}){sub 3}·6H{sub 2}O at the relatively high temperature and autogenous pressure of the reaction. Compound 1 has been characterized by single-crystal X-ray diffraction, PXRD, IR, and elemental analysis. Compound 1 is a 3D coordination polymer, and an xfe-4-Fddd, (4{sup 2}.6.8{sup 3}) topology in 1 is created. In addition, the optical properties have been investigated. Rhodamine B dyeing experiments exhibited that there were residual carboxyl groups on the surface of compound 1. UV–vis results showed that more lysozyme was adsorbed onto the surface of compound 1 than BSA at pH 7.4. At the same time, XPS spectra were also investigated to verify the results. - Graphical abstract: One-pot solvothermal treatments of CuCl{sub 2}·2H{sub 2}O, H2L (5-(3-methyl-5-(pyridin-4-yl)-4H-1, 2, 4-triazol-4-yl) isophthalic acid) and Sm(NO{sub 3}){sub 3}·6H{sub 2}O in water yielded a rare carboxyl-copper-organic framework, [Cu(HL)]n·nH{sub 2}O (1). The existence of carboxyl groups in compound 1 may be due to the interference of Sm(NO{sub 3}){sub 3}·6H{sub 2}O at the relatively high temperature and autogenous pressure of the reaction. Compound 1 has been characterized by single-crystal X-ray diffraction, XRPD, IR, and elemental analysis. Compound 1 is a 3D coordination polymer, and an xfe-4-Fddd, (4{sup 2}.6.8{sup 3}) topology in 1 is created. In addition, the optical properties have been investigated. Rhodamine B dyeing experiments exhibited that there were residual carboxyl groups on the surface of compound 1. UV-vis results showed that more lysozyme was adsorbed onto the surface of compound 1 than that of BSA at pH 7.4. At the same time, XPS spectra were also investigated to verify the results. - Highlights: • A rare carboxyl-copper-organic framework has been hydrothermally synthesized. • An xfe-4-Fddd, (4{sup 2}.6.8{sup 3}) topology in 1 is created. • BSA was significantly less adsorbed onto the carboxylic acid-rich surface than lysozyme. • XPS spectra were also investigated to verify the results of protein adsorption.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A topological screening heuristic for low-energy, high-index surfaces

Robust ab initio investigations of nanoparticle surface properties require a method to identify candidate low-energy surface facets a priori . By assuming that low-energy surfaces are planes with high atomic density, we devise an efficient algorithm to screen for low-energy surface orientations, even if they have high ( hkl ) miller indices. We successfully predict the observed low-energy, high-index {$10\overline{12} $} and {$10\bar{1}4 $} surfaces of hematite α-Fe 2 O 3 , the {311} surfaces of cuprite Cu 2 O, and the {112} surfaces of anatase TiO 2 . We further tabulate candidate low-energy surface orientations for nine of the most common binary oxide structures. Screened surfaces are found to be generally applicable across isostructural compounds with varying chemistries, although relative surface energies between facets may vary based on the preferred coordination of the surface atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A bond-order potential for the Al–Cu–H ternary system

Al-Based Al–Cu alloys have a very high strength to density ratio, and are therefore important materials for transportation systems including vehicles and aircrafts. These alloys also appear to have a high resistance to hydrogen embrittlement, and as a result, are being explored for hydrogen related applications. To enable fundamental studies of mechanical behavior of Al–Cu alloys under hydrogen environments, we have developed an Al–Cu–H bond-order potential according to the formalism implemented in the molecular dynamics code LAMMPS. Our potential not only fits well to properties of a variety of elemental and compound configurations (with coordination varying from 1 to 12) including small clusters, bulk lattices, defects, and surfaces, but also passes stringent molecular dynamics simulation tests that sample chaotic configurations. Careful studies verified that this Al–Cu–H potential predicts structural property trends close to experimental results and quantum-mechanical calculations; in addition, it properly captures Al–Cu, Al–H, and Cu–H phase diagrams and enables simulations of H 2 dissociation, chemisorption, and absorption on Al–Cu surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Synthesis and Structural Characterization of Magnesium Based Coordination Networks in Different Solvents

Three magnesium based metal-organic frameworks, Mg{sub 3}(3,5-PDC){sub 3}(DMF){sub 3} {center_dot} DMF [1], Mg(3,5-PDC)(H{sub 2}O) {center_dot} (H{sub 2}O) [3], and Mg4(3,5-PDC)4(DMF){sub 2}(H{sub 2}O){sub 2} {center_dot} 2DMF {center_dot} 4.5H{sub 2}O [4], and a 2-D coordination polymer, [Mg(3,5-PDC)(H{sub 2}O){sub 2}] [2] [PDC = pyridinedicarboxylate], were synthesized using a combination of DMF, methanol, ethanol, and water. Compound 1 [space group P2{sub 1}/n, a = 12.3475(5) {angstrom}, b = 11.1929(5) {angstrom}, c = 28.6734(12) {angstrom}, {beta} = 98.8160(10){sup o}, V = 3916.0(3) {angstrom}{sup 3}] consists of a combination of isolated and corner-sharing magnesium octahedra connected by the organic linkers to form a 3-D network with a 12.2 {angstrom} x 4.6 {angstrom} 1-D channel. The channel contains coordinated and free DMF molecules. In compound 2 [space group C2/c, a = 9.964(5) {angstrom}, b = 12.0694(6) {angstrom}, c = 7.2763(4) {angstrom}, {beta} = 106.4970(6){sup o}, V = 836.70(6) {angstrom}{sup 3}], PDC connects isolated seven coordinated magnesium polyhedra into a layered structure. Compound 3 [space group P6{sub 1}22, a = 11.479(1) {angstrom}, c = 14.735(3) {angstrom}, V = 1681.7(4) {angstrom}{sup 3}] (previously reported) contains isolated magnesium octahedra connected by the organic linker with each other forming a 3D network. Compound 4 [space group P2{sub 1}/c, a = 13.7442(14) {angstrom}, b = 14.2887(15) {angstrom}, c = 14.1178(14) {angstrom}, {beta} = 104.912(2){sup o}, V = 2679.2(5) {angstrom}{sup 3}] also exhibits a 3D network based on isolated magnesium octahedra with square cavities containing both disordered DMF and water molecules. The structural topologies originate due to the variable coordination ability of solvent molecules with the metal center. Water molecules coordinate with the magnesium metal centers preferably over other polar solvents (DMF, methanol, ethanol) used to synthesize the coordination networks. Despite testing multiple desolvation routes, we were unable to measure BET surface areas greater than 51.9 m{sup 2}/g for compound 1.

Banerjee, Debasis↗
DOE OSTI2025

Reference Correlations for the Density and Viscosity of Molten Alkali and Alkaline Earth Fluoride Salts

While there is a significant body of literature pertaining to thermophysical property measurements of molten salts, there is often a wide degree of variability among independent measurements of the same compounds. As such, the scientific community benefits greatly from an unbiased, independent assessment of duplicate datasets, so that reference correlations which describe these thermophysical properties as functions of temperature can be determined and then commonly used by researchers, scientists, and engineers. With regard to molten fluoride compounds, a significant time has elapsed since density and viscosity reference correlations have been determined; Janz conducted the most recent effort, in 1988, to provide reference correlations for the densities and viscosities of molten fluoride compounds via the National Standard Reference Data System coordinated by the National Bureau of Standards. Since then, new data have been published for molten fluoride compounds, and a new precedent has surfaced for putting forth reference correlations that involve fitting to multiple primary datasets. In this work, reference correlations are put forth for molten alkali and alkaline earth fluoride compounds in an effort to provide updated, improved correlations for general use. For molten alkali fluoride densities, estimated uncertainties with a 95% confidence interval are summarized as follows: LiF (0.63%), NaF (0.48%), KF (0.76%), RbF (0.93%), and CsF (0.75%). For molten alkaline earth fluoride densities, an estimated uncertainty was not able to be quantified for BeF 2 because of limited data; however, estimated uncertainties with a 95% confidence interval are summarized as follows for the remaining alkaline earth fluorides: MgF 2 (1.5%), CaF 2 (0.92%), SrF 2 (1.6%), and BaF 2 (0.23%). For molten alkali fluoride viscosities, uncertainty was not able to be quantified for RbF and CsF because of limited data; however, estimated uncertainties with a 95% confidence interval are summarized as follows for the remaining alkali fluorides: LiF (4.4%), NaF (3.0%), and KF (4.0%). For molten alkaline earth fluoride viscosities, limited consistent data resulted in the recommendation of single datasets (from literature) that are deemed to be the most trustworthy based on the quality of the underlying experimental studies.

Birri, A. [Oak Ridge National Laboratory (ORNL), O↗
DOE OSTI2016

Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order to better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. Furthermore, these findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.

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

X-ray absorption spectroscopy study of Mn reference compounds for Mn speciation in terrestrial surface environments

Abstract X-ray absorption spectroscopy (XAS) offers great potential to identify and quantify Mn species in surface environments by means of linear combination fit (LCF), fingerprint, and shell-fit analyses of bulk Mn XAS spectra. However, these approaches are complicated by the lack of a comprehensive and accessible spectrum library. Additionally, molecular-level information on Mn coordination in some potentially important Mn species occurring in soils and sediments is missing. Therefore, we investigated a suite of 32 natural and synthetic Mn reference compounds, including Mn oxide, oxyhydroxide, carbonate, phosphate, and silicate minerals, as well as organic and adsorbed Mn species, by Mn K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The ability of XAS to infer the average oxidation state (AOS) of Mn was assessed by comparing XANES-derived AOS with the AOS obtained from redox titrations. All reference compounds were studied for their local (<5 Å) Mn coordination environment using EXAFS shell-fit analysis. Statistical analyses were employed to clarify how well and to what extent individual Mn species (groups) can be distinguished by XAS based on spectral uniqueness. Our results show that LCF analysis of normalized XANES spectra can reliably quantify the Mn AOS within ~0.1 v.u. in the range +2 to +4. These spectra are diagnostic for most Mn species investigated, but unsuitable to identify and quantify members of the manganate and Mn(III)-oxyhydroxide groups. First-derivative XANES fingerprinting allows the unique identification of pyrolusite, ramsdellite, and potentially lithiophorite within the manganate group. However, XANES spectra of individual Mn compounds can vary significantly depending on chemical composition and/or crystallinity, which limits the accuracy of XANES-based speciation analyses. In contrast, EXAFS spectra provide a much better discriminatory power to identify and quantify Mn species. Principal component and cluster analyses of k2-weighted EXAFS spectra of Mn reference compounds implied that EXAFS LCF analysis of environmental samples can identify and quantify at least the following primary Mn species groups: (1) Phyllo- and tectomanganates with large tunnel sizes (2 × 2 and larger; hollandite sensu stricto, romanèchite, todorokite); (2) tectomanganates with small tunnel sizes (2 × 2 and smaller; cryptomelane, pyrolusite, ramsdellite); (3) Mn(III)-dominated species (nesosilicates, oxyhydroxides, organic compounds, spinels); (4) Mn(II) species (carbonate, phosphate, and phyllosilicate minerals, adsorbed and organic species); and (5) manganosite. All Mn compounds, except for members of the manganate group (excluding pyrolusite) and adsorbed Mn(II) species, exhibit unique EXAFS spectra that would allow their identification and quantification in mixtures. Therefore, our results highlight the potential of Mn K-edge EXAFS spectroscopy to assess bulk Mn speciation in soils and sediments. A complete XAS-based speciation analysis of bulk Mn in environmental samples should preferably include the determination of Mn valences following the “Combo” method of Manceau et al. (2012), EXAFS LCF analyses based on principal component and target transformation results, as well as EXAFS shell-fit analyses for the validation of LCF results. For this purpose, all 32 XAS reference spectra are provided in the Online Materials1 for further use by the scientific community.

Geochemistry & Geophysics↗
DOE OSTI2024

Structural chemistry of penta- and hexanitrato thorium($\tiny{IV}$) complexes isolated using N–H donors

In this study, a series of fifteen tetravalent thorium phases were prepared. The compounds were isolated from acidic aqueous nitrate solutions using protonated nitrogen heterocycles of varying hydrogen-bond donation strength. Structural analysis via single crystal X-ray diffraction showed that the structures are built from pentanitrato, [Th(NO 3 ) 5 (H 2 O) 2 ] 1- , and hexanitrato, [Th(NO 3 ) 6 ] 2- , molecular units, with the latter being far more prevalent in the solid state. The vibrational properties of the compounds were examined using Raman and IR spectroscopy; the spectra are dominated by stretches characteristic of nitrate and the organic ions. The relative energetics of nitrate complexation was examined using electronic structure theory. These results confirmed that there are clear thermodynamic sinks for the penta- and hexanitrato structural units that were observed experimentally. Additionally, electrostatic surface potentials (ESPs) were calculated in an effort to better understand the counterion stabilization of the complexes. The ESP surfaces showed that the position of the water and nitrate molecules and the coordination geometry of the metal complex had a clear effect on the polarizability of the two structural motifs. Despite limited speciation of the Th–nitrate structural units, the compounds exhibit rich supramolecular chemistry resulting from hydrogen bonding of the Th complexes with the organic N–H donors and π–π stacking interactions from the protonated N-heterocycles.

36 MATERIALS SCIENCE↗