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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Unveiling the covalency of versatile Pu(iii)-N bonds in a unique plutonium(iii) complex

A trivalent plutonium–pyrazinyl–tetrazolate complex Na 2 [Pu(Hdtp)(dtp) 2 (H 2 O) 4 ]·9H 2 O (Pu_dtp, H 2 dtp = 2,3-di-1H-tetrazol-5-ylpyrazine) was synthesized through metathesis reaction of plutonium bromide and Na 2 (dtp)·2H 2 O in water. This structure is particularly notable among complexes formed by trivalent f-elements and the dtp 2− ligand in aqueous media. In contrast to other trivalent f-elements, including all Ln 3+ (with the exception of Pm 3+ ) and Cm 3+ , preferentially coordinated with eight water molecules rather than the nitrogen donors of the dtp 2− ligand, Pu 3+ exhibits a distinct affinity for nitrogen coordination. This observation provides strong evidence that the 5f electrons in Pu 3+ are more delocalized than other studied trivalent f-elements. In Pu_dtp, three distinct Pu(III)–N bonds are present: one Pu(III)–N5 from pyrazinyl, one Pu(III)–N4 from the least electronegative nitrogen in the tetrazolate, and three Pu(III)–N1/N2/N3 from the most electronegative nitrogens in the tetrazolate. Experimental Pu(III)–N bond lengths, Wiberg bond indices (WBI), natural localized molecular orbitals (NLMO), quantum theory of atoms in molecules (QTAIM), and energy decomposition analysis (EDA), reveal a covalency trend: Pu(III)–N from the most electronegative nitrogen in tetrazolate > Pu(III)–N from the least electronegative nitrogen in tetrazolate > Pu(III)–N from pyrazinyl. This trend arises from the increased negative charge on the most electronegative nitrogen atoms in the tetrazolate ring, enhancing electrostatic Pu–N1/N2/N3 interactions. These stronger electrostatic interactions lead to shorter bond lengths, thereby enhancing orbital overlap and greater covalency, compared to the less electronegative nitrogen in tetrazolate (Pu–N4) and the neutral pyrazinyl nitrogen (Pu–N5).

Bai, Zhuanling [Colorado School of Mines, Golden, ↗
DOE OSTI2026

Plutonium(III) versus uranium(III) and samarium(III) in small molecule activation chemistry

We report the PuIII complex, [PuIII(CpMe4)3] (1-Pu), and demonstrate its differences in small molecule reactivity compared to the UIII and SmIII analogs, [UIII(CpMe4)3] (1-U) and [SmIII(CpMe4)3] (1-Sm), respectively. 1-Pu reductively cleaves the small molecule (PhS)2, affording a PuIII complex, [{PuIII(CpMe4)2}2(μ-SPh)2] (2-Pu), while retaining the PuIII center and eliminating (CpMe4)2 as a by-product, a fingerprint of a sterically induced reduction (SIR) reaction. Sm is often used as a surrogate for Pu, but the analogous [SmIII(CpMe4)3], (1-Sm), is unreactive. The (PhS)2 cleavage by 1-U proceeds solely via a metal-based oxidation (i.e., UIII → UIV), to form [UIV(CpMe4)3(SPh)] (3-U). Only 1-U reacts with (PhHN)2, affording the reductive cleavage product, [UIV(CpMe4)3(NHPh)] (4-U). The difference in reactivity of 1-Pu compared to complexes 1-Sm and 1-U was unexpected, and since SIR chemistry can enable complexes to participate in otherwise impossible reductive transformation of substrates, this reinforces the importance of studying small molecule reactivity with the transuranic elements.

Keener, Megan↗
DOE OSTI2026

Synthesis of Cp* Terphenylamido U(III) Iodide Complexes with a Substitutable Iodide Position to Generate Terminal U(III)–(κ 3 -BH 4 ) Complexes

Reaction of Cp*UI 2 (THF) 3 (Cp* = pentamethylcyclopentadienide; THF = tetrahydrofuran) with Na R3 TerNH ( R3 Ter = 2,6(2,4,6-R 3 C 6 H 2 ) 2 C 6 H 3 ; R = Me, Et, iPr) gave the U(III) monoiodide complexes Cp*( R3 TerNH)UI (R = Me, 1-Me; R = Et, 2-Et; R = iPr, 3-iPr). These complexes contain a functionalizable iodide position which reacts favorably with NaBH4 to give the κ 3 -borohydride complexes Cp*( R3 TerNH)U(H 3 BH) (R = Me, 4-Me; R = Et, 5-Et; R = iPr, 6-iPr). All compounds were experimentally characterized by SC-XRD, 1 H and 11 B NMR spectroscopy as well as UV–vis–NIR and FTIR analyses. DFT calculations corroborate the experimental findings, confirming the 5f 3 U(III) configuration across the entire series and revealing an increased U 5f orbital contribution in the borohydride derivatives. All compounds exhibit small but non-negligible U(III)–(η 6 -arene) δ-back-bonding interactions arising from the unpaired 5f electrons. Calculated steric parameters show progressively greater shielding of the U(III) center with increasing bulk of the terphenyl substituents from Me to iPr.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Modeling neutral defects in III-V ternary alloys with a special quasirandom structure: Analysis of As- and III-site point defects in InGaAs

While first-principles density functional theory modeling has become a vital tool to investigate defect properties in semiconductors, the lack of crystalline periodicity in pseudobinary random composition alloys, such as In 1−𝑥 ⁢Ga 𝑥 ⁢As, complicates such analyses. We present a simulation strategy to systematically take into account the variability in the local defect environment in order to predict statistical properties of neutral intrinsic defects in In 1−𝑥⁢ Ga 𝑥 ⁢As. We use a comprehensive sampling from a modest-sized 64-atom special quasirandom structure (SQS) to define a statistically representative set of defects, and use a 512-atom hypercell, a 2 × 2 × 2 supercell of SQS supercells, to achieve cell-size convergence. We articulate an equivalent site principle and describe how it constrains atomic chemical reference energies in computation of defect formation energies in pseudobinary alloys. A simple protocol for estimating reference energies for the Ga and In atoms sharing the III site succeeds in obtaining the equivalence of defects at Ga-sites and In sites in the SQS supercell, (<30 meV differences in average formation energies). For III-site defects, such as the As antisite As III , the statistical variability in formation energies is modest, ≈ 0.1–0.2 eV. The variability in formation energy at As-site defects, such as the As vacancy 𝑣 As , can be much larger, >1 eV. The As antisite is shown to be a low-energy defect and the most likely to be present in as-grown materials, just as in GaAs. All other defects are higher-energy defects unlikely to be important in native material, but potentially important in radiation-damaged material. With a strong variability in defect energies, especially on the As-site, explicit consideration of statistical variability due to compositional randomness will be imperative for meaningful and quantitative comparisons to experiment.

Density functional theory↗
DOE OSTI2025

H-cluster Intermediates and Catalytic Properties of Clostridium pasteurianum [FeFe]-Hydrogenase III

[FeFe]-Hydrogenases are structurally diverse enzymes that catalyze reversible H2 activation at a catalytic cofactor or H-cluster. The H-cluster is a [4Fe-4S] cubane linked by a cysteine thiolate to a diiron subsite containing unique CO, CN-, and dithiomethylamine ligands. The established H-cluster resting state of [4Fe-4S]2+-[FeII-FeI], or Hox, functions in H2 binding and oxidation, or by proton-coupled reduction initiates H2 evolution. In contrast, in Clostridium pasteurianum [FeFe]-hydrogenase III (CpIII) the resting state of the H-cluster is fully oxidized, [4Fe-4S]2+-[FeII-FeII], or Hox+1. To begin to understand if Hox+1 has a role in the mechanism of CpIII, we determined the spectroscopic and redox properties of CpIII H-cluster states under catalytic conditions. CpIII poised in Hox+1 and either equilibrated under 1 atm of H2 or reduced with sodium dithionite, resulted in a mixture of reduced states including Hox (Em8 = -407 mV), Htrans-like [4Fe-4S]+-[FeII-FeII] (Em8 = -418 mV), Hred [4Fe-4S]+-[FeII-FeI], and HredH+ [4Fe-4S]2+-[FeI-FeI] (Em8 = -455-480 mV). Under H2 the population of the Htrans-like state was >20-fold higher than Hox, implicating a role in CpIII catalysis. Unlike other enzymes, there was no spectral evidence of fully reduced states, such as HsredH+ ([4Fe-4S]+-[FeI-FeI]) or Hhyd ([4Fe-4S]+-[FeII-FeII]-H-). Thus, while the H-cluster states of CpIII encompass most of the catalytic intermediates, it is either unable to form HsredH+ and Hhyd, or these states are highly destabilized in CpIII. Thus, these results demonstrate that catalytic intermediates of reduced CpIII differ from the typical intermediates of other catalytic [FeFe]-hydrogenases and may explain the catalytic preference for H2 production.

08 HYDROGEN↗
DOE OSTI2024

Comparison of Americium(III) and Neodymium(III) Monothiophosphate Complexes

Mixed-donor ligands, such as those containing a combination of O/N or O/S, have been studied extensively for the selective extraction of trivalent actinides, especially Am 3+ and Cm3+, from lanthanides during the recycling of used nuclear fuel. Oxygen/sulfur donor ligand combinations also result from the hydrolytic and/or radiolytic degradation of dithiophosphates, such as the Cyanex® class of extractants, that are initially converted to monothiophosphates. To understand potential differences between the binding of such degraded ligands to Nd 3+ and Am 3+ , the monothiophosphate complexes [M(OPS(OEt) 2 ) 5 (H 2 O) 2 ] 2- (M 3+ = Nd 3+ , Am 3+ ) were prepared and characterized by single crystal X-ray diffraction and optical spectroscopy and studied as a function of pressure up ca. 14 GPa using diamond-anvil techniques. Although Nd 3+ and Am 3+ have nearly identical eight-coordinated ionic radii, these structures reveal that while the M-O bond distances in these complexes are nearly equal that the M-S distances are statistically different. Moreover, for [Nd(OPS(OEt) 2 ) 5 (H 2 O) 2 ] 2- , the hypersensitive 4 I 9/2 → 4 G 5 / 2 transition shifts as a function of pressure by -11 cm -1 /GPa. Whereas for [Am(OPS(OEt) 2 ) 5 (H 2 O) 2 ] 2- , the 7 F 0 → 7 F 6 transition shows a slightly stronger pressure dependence with a shift of -13 cm -1 /GPa and also exhibits broadening of the 5f →5f transitions at high pressures. This data likely indicates an increased involvement of the 5f orbitals in bonding to Am 3+ relative to that of Nd 3+ in these complexes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2026

Iodine Close Packing in Hybrid Halide Bismuth(III) and Antimony(III) Semiconductors: (NH 3 (CH 2 ) 7 NH 3 ) 2 Bi 2 I 10 and (NH 3 (CH 2 ) 7 NH 3 ) 2 Sb 2 I 10

Simple features in complex hybrid inorganic–organic crystalline materials provide opportunities for targeted discovery of materials with desired optoelectronic properties. In this study, we report the structure and optoelectronic properties of isostructural (NH 3 (CH 2 ) 7 NH 3 ) 2 Bi 2 I 10 and (NH 3 (CH 2 ) 7 NH 3 ) 2 Sb 2 I 10 . The crystal structures are characterized by corner-connected metal-iodide octahedral chains that form a cubic close-packed iodine inorganic framework. Variable temperature UV–visible diffuse reflectance spectroscopy reveals stark contrasts in the onset of absorption and color changes between the [MX6]3– based structures, due to differences in the interaction of the (NH 3 (CH 2 ) 7 NH 3 ) 2+ organic ammonium cation and the iodine packing of the inorganic framework. Density functional theory (DFT) calculations reveal flat bands reflective of the pseudo-1D crystal structure. Dark microwave conductivity (DMC) and time-resolved microwave conductivity (TRMC) reveal an excitonic character with long carrier lifetimes, consistent with the electronically confined octahedral chains. Comparison of the structural features with those of other diammonium-containing crystals reveals that diammoniumheptane can substitute into structures, displacing inorganic octahedra while retaining a close-packed anion framework. This provides a means for targeting new hybrid materials in which “vacancy-ordering” provides a crystal chemical approach for targeting desirable optoelectronic properties.

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

Synthesis, Structure, and Redox Reactivity of Ni Complexes Bearing a Redox and Acid–Base Non-innocent Ligand with Ni II , Ni III , and Ni IV Formal Oxidation States

Here, a series of Ni complexes bearing a redox and acid–base noninnocent tetraamido macrocyclic ligand, H 4 -(TAML-4) {H 4 -(TAML-4) = 15,15-dimethyl-5,8,13,17-tetrahydro-5,8,13,17-tetraaza-dibenzo[a,g]cyclotridecene-6,7,14,16-tetraone}, with formal oxidation states of Ni II , Ni III , and Ni IV were synthesized and characterized structurally and spectroscopically. The X-ray crystallographic analysis of the Ni complexes revealed a square planar geometry, and the [Ni(TAML-4)] complex with the formal oxidation state of Ni IV was characterized to be [Ni III (TAML-4 •+ )] with the oxidation state of the Ni III ion and the one-electron oxidized TAML-4 ligand, TAML-4 •+ . The Ni III oxidation state and the TAML-4 radical cation ligand, TAML-4 •+ , were supported by X-ray absorption spectroscopy and density functional theory calculations. The reversible interconversions between [Ni II (TAML-4)] 2– and [Ni III (TAML-4)] − and between [Ni III (TAML-4)] − and [Ni III (TAML-4 •+ )] were demonstrated in spectroelectrochemical measurements as well as in chemical oxidation and reduction reactions. The reactivities of [Ni III (TAML-4)] − and [Ni III (TAML-4 •+ )] were then investigated in hydride transfer reactions using NADH analogs. Hydride transfer from 9,10-dihydro-10-methylacridine (AcrH 2 ) to [Ni III (TAML-4 •+ )] was found to proceed via electron transfer (ET) from AcrH 2 to [Ni III (TAML-4 •+ )] with no deuterium kinetic isotope effect (k H /k D = 1.0(2)). In contrast, hydride transfer from AcrH 2 to [NiIII(TAML-4)] − proceeded much more slowly via a concerted proton-coupled electron transfer (PCET) process with k H /k D = 7.0(5). In the latter reaction, an electron and a proton were transferred to the Ni III center and the TAML-4 ligand, respectively. The mechanisms of the ET by [Ni III (TAML-4 •+ )] and the concerted PCET by [Ni III (TAML-4)] − were ascribed to the different redox potentials of the Ni complexes.

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

Elucidation of an Unusually Long Pu–N Bond in a Plutonium(III)-Tetrazolate Complex

Four trivalent, f-element tetrazolate hydrate complexes [M(H 2 O) 9 ](Hdtb) 3 ·nH 2 O (Nd1, n = 7 and Pu1, n = 9; dtb 2– = 1,3-di(tetrazolate-5-yl)benzene) and [M(Hdtb)(H 2 O) 8 ](dtb)·11H 2 O (Nd2 and Pu2) were prepared using metathesis reactions. These complexes contain hydrated M(III) cations, but in the latter complexes, Nd2 and Pu2, one of the water molecules has been displaced by a long interaction between the M(III) cation and a Hdtb – anion. Notably, the Pu(III)–N bond in Pu2, representing the longest IX Pu(III)–N ( IX = nine coordinate) bond reported has a length of 2.8338(15) Å and is slightly shorter than the Nd(III)–N bond length of 2.8425(13) Å in Nd2. Analysis of bond lengths, Wiberg bond indices (WBI), natural localized molecular orbitals (NLMOs), and quantum theory of atoms in molecules (QTAIM) reveals that the metal contribution to the Pu(III)–N bond is marginally greater than that of the Pu(III)–OH 2 bonds in Pu2 and the Nd(III)–N bond in Nd2. Thus, this rather long M–N interaction provides an example where the expectation that An(III) compounds exhibit greater covalency with soft donor ligands compared to harder ligands fails. Furthermore, the absorption spectra of Pu1 and Pu2 further support this observation, highlighting a surprising degree of similarity in their electronic structures.

Covalent bonding↗
DOE OSTI2024

Reconceptualizing the Ir III Role in Metallaphotoredox Catalysis: From Strong Photooxidant to Potent Energy Donor

Dual Ir III /L n Ni II metallaphotoredox catalyzed C(sp 3 )–C(sp 2 ) cross-coupling reactions are widely assumed to proceed by photoinduced single electron transfer steps due to the highly oxidizing Ir III * excited state (Ir III = [Ir(dF(CF 3 )ppy) 2 (dtbbpy)] + [PF 6 ] – ; dF(CF 3 )ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine; L n = dtbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). Using time-resolved absorption and emission spectroscopy, we reveal that energy transfer between Ir III * and various LnNi II precatalysts and intermediates with k q ≥ 10 8 M –1 s –1 also drives catalysis. Specifically, the excited states of L n Ni II dihalide precatalysts/organometallic intermediates accessible by energy transfer appear to drive bond homolysis, halogen radical elimination, and reductive elimination reactions that facilitate formation of cross-coupled products. Energy transfer dynamics consequently circumvent the need for photoinduced electron transfer, thereby extending substrate scopes to coupling partners that cannot be oxidized by Ir III *. Within a cross-electrophile coupling model reaction between 4-bromobenzotrifluoride and bromocyclohexane, energy transfer activates the L n Ni II precatalyst at early reaction times before nucleophilic reductants are present. In the absence of Ir III , direct excitation of L n Ni II (Br) 2 also activates the precatalyst to form a L n Ni II (Br)(Aryl) intermediate. To compare energy transfer and electron transfer kinetics, we determined rate constants for reductive quenching by Br – (k SET = 4.1 × 10 8 M –1 s –1 ) and for the subsequent electron transfer from reduced Ir III•– to L n Ni II (Br) 2 (k SET = 4.1 × 10 7 M –1 s –1 ) using Stern-Volmer analysis and pulse radiolysis, respectively. Energy transfer rate constants are competitive with the electron transfer rate constants and energy transfer is a parallel pathway within metallaphotoredox catalysis. Exploiting the energy transfer mechanism, we demonstrate highly selective cross-electrophile coupling between 4-chlorobenzotrifluoride and bromocyclohexane to form exclusively cross-coupled product. Here, with alkyl-trifluoroborate nucleophiles that do not reductively quench IrIII* emission, transmetalation with L n Ni II (Br/Cl)(Aryl) followed by energy transfer also drives excited state reductive elimination to form C(sp 3 )–C(sp 2 ) cross-coupled product. Similarly, energy transfer rather than Ni II oxidation drives C(sp 2 )–OR reductive elimination, despite the strongly oxidizing ability of Ir III *. In total, these reactions demonstrate energy transfer processes from Ir III * to L n Ni II in metallaphotoredox catalysis that can unlock alternative reactive pathways.

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

Fe(III) reducing bacterial activities in Old Woman Creek wetland sediments, June 2023

To evaluate the Fe(III) reducing microbiological activities in Old Woman Creek Nature Preserve (OWC) wetland sediments, we incubated OWC sediments under anoxic and oxic conditions and with or without Fe(III) amendment [as hydrous ferric oxide (HFO)]. No Fe(III) reduction was observed in heat-deactivated incubations. In non-sterile anoxic incubations, measurement of 0.5 M HCl-extractable Fe(II) indicated that Fe(III) reduction occurred in both Fe(III)-amended and -unamended incubations, indicating that abundant Fe(III) is associated with the OWC sediments. Little Fe(II) accumulated in solution, indicating that the most biogenic Fe(II) adsorbs to the sediments. When air was added to the headspace of non-sterile incubations, Fe(III) reduction was halted and any biogenic Fe(II) that accumulated was oxidized. These experiments were used to guide preparation and analyses of incubations to determine if electrochemical measuements can be used to detect microbiological activities in contrasting terminal electron accepting regimes (i.e., aerobic and Fe(III) reducing conditions). Data package includes methods and data from experiments, including dissolved anion concentrations, dissolved Fe(II) concentrations, and 0.5 M HCl-extractable Fe(II) concentrations. All files are either .txt or .csv and can be opened by any plain text editor application.

EARTH SCIENCE↗
DOE OSTI2024

Bisphenol A degradation by manganese oxides at circumneutral pH: Quantitative evaluation of dissolved Mn(III) species with pyrophosphate

Although trivalent manganese (Mn(III)) species have been recognized as crucial intermediates in the degradation of organic contaminants by Mn oxides, quantitative research on their specific roles remains scarce. Here, our study investigated the degradation processes of an organic pollutant, Bisphenol A (BPA), by dissolved Mn(III) and Mn(III)-bearing oxides, and elucidated the differences of the underlying mechanisms and reaction pathways between several Mn oxides and dissolved Mn(III). Our results indicated that BPA degradation rates with Mn(III)-bearing oxides alone follow the order: δ-MnO 2 >> γ-MnOOH > Mn 3 O 4 . Adding pyrophosphate (PP) significantly enhanced BPA degradation by promoting the formation of Mn(III)-PP complexes and exposing more reactive sites, achieved through destabilizing the crystal structure and mitigating of Mn(II) readsorption, particularly in γ-MnOOH and Mn 3 O 4 . Our kinetic model revealed that heterogeneous degradation by Mn oxides is the predominant reaction pathway, accounting for 61.4 %, 87.8 %, and 73.8 % of the total degraded BPA for δ-MnO 2 , γ-MnOOH, and Mn 3 O 4 , respectively, even in the presence of significant amount of dissolved Mn(III) intermediates due to high PP concentrations. These results offer mechanistic details on BPA degradation by Mn oxides and the influence of ligand concentration, providing helpful insights for optimizing degradation strategies of organic pollutants.

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

V‐Groove Si Nanopatterning for the Direct Epitaxy of Orientation‐Patterned III–V Nonlinear Optical Crystals

Orientation‐patterned (OP) III–V semiconductors—used as quasi‐phase‐matched crystals for nonlinear optics applications—are typically epitaxially grown on expensive III–V substrates using a complex process requiring three separate epitaxy steps. In this work, a method is demonstrated for growing orientation‐patterned III–V crystals on Si substrates through V‐groove nanopatterning and a single epitaxial growth. V‐groove Si allows for suppression of random antiphase domain formation that is typical of III–V growth on (001)‐oriented Si through the use of (111)‐faceted trenches patterned on (001)‐oriented Si substrates. By alternating the directions of the V‐groove trenches between [110] and [10], antiphase boundaries can be selectively induced at the boundaries between the two directions of trenches due to the difference in symmetry between the III–V material and Si. This approach allows for a greatly simplified process for growing OP‐III‐Vs and more broadly is a new, robust approach for precisely patterning antiphase boundaries of arbitrary shape and length scales down to 50 nm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Spectroscopic Properties of Americium(III) in Mineral Acid Media

We report the preparation and optical characterization of three solutions of Am(III) in common aqueous (aq.) mineral acids (HCl, HNO 3 and HBr), including absorption, emission, and Raman vibrational analyses. To our knowledge, this study provides the first detailed absorption spectra of Am(III) spanning the entire UV/Vis/NIR region in these mineral acids reported since the 1960s. Here, using this high-resolution absorption data, provided in an open access format for the broader field, we build on prior work by Carnall and others to provide detailed optical analysis including all transition assignments. This work also includes the first reported absorption spectrum of Am(III) in aq. HBr. Characteristic Am(III) luminescence could be detected from all three samples. These are the first reports of emission from Am(III) in these acid systems, which build on prior emission reports collected from aq. HClO 4 solutions. The acquired emission spectra display anion-dependent shifting of the visible-region transitions by up to 21 nm from their predicted positions, akin to the nephelauxetic effect. The shift magnitude trends linearly according to the acid p K a and more generally according to the transition metal spectrochemical series. These ligand field effects, coupled with luminescence lifetime experiments, indicate that weak Am-X interactions persist in solution.

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

Effect of Fluoride Anions on Nd(III) Electrode Processes and Nd Metal Recovery in LiCl–KCl–NdCl 3

Here, this work investigated the impact of fluoride anions on Nd metal recovery in LiCl–KCl–NdCl 3 electrolytes by introducing LiF at a molar F/Nd ratio of 9 at 773 K. The voltammetric measurements confirmed that the fluoride ions facilitated single-step Nd(III)/Nd reduction by promoting the stability of the Nd(III) state compared to two-step reduction (Nd(III)/Nd(II) and Nd(II)/Nd) in all-chloride electrolytes. The stabilized Nd(III) state in the LiF-containing electrolyte effectively suppressed partial Nd(III)/Nd(II) reduction and the back-dissolution of Nd metal via comproportionation. By suppressing these reactions, high round-trip Coulombic efficiencies of 77–86% were achieved in the LiF-containing electrolyte during selective Nd deposition–removal cycles compared to 53–59% in all-chloride electrolytes. The Faradaic yield for Nd metal recovery was estimated at 38.6% in the LiF-containing electrolyte following long-term electrolysis, more than three times higher than 11.3% in all-chloride electrolytes. These results confirm the beneficial effect of fluoride ions on Nd metal recovery in low-melting chloride-based electrolytes, promising efficient Nd recovery at low temperatures.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Excitation Wavelength-Dependent Emission from Americium(III) in Mineral Acid Solutions

The photoluminescence behavior of trivalent americium, Am(III), in mineral acid solutions is reported under direct-metal excitation at seven high-energy wavelengths in the ultraviolet and visible regions (378-512 nm). This study revealed a dependence of the Am(III)-based visible emission profile on the chosen excitation wavelength. For example, excitation at the more common wavelength of 504 nm produces the two expected emission bands: one at approximately 600 nm (5D1' to 7F0') and another at 690 nm (5D1' to 7F1'). When the excitation wavelength is shifted to 398 nm (targeting the 5D3', 5H7' from 7F0' transitions), the emission occurs almost exclusively at 600 nm. This behavior is unexpected and potentially highlights fundamental knowledge gaps in the current understanding of the intraconfigurational 5f-5f electronic transitions that give rise to Am(III) photoluminescence. Although a full interpretation of these results is limited by the incomplete understanding of Am(III) speciation in mineral acid systems, this study explores several potential explanations for the observed behavior and challenges the widely held assumption of a single emissive Am(III) species.

Americium↗
DOE OSTI2024

Synthesis of porphyrin triads chelated with thallium(III) for studies of ground-state hole/electron transfer

Four target all-porphyrin triads have been prepared for fundamental studies of ground-state hole/electron transfer. Each triad contains thallium(III) porphyrins as bookends, which bear mesityl groups at the three non-linking meso-positions. The central porphyrin is a free base or thallium(III) porphyrin bearing mesityl or pentafluorophenyl groups at the two non-linking meso-positions. The linker is a 4,4 ′ -diphenylethyne unit joined at the porphyrin meso-positions. The net spacer between the two bookend thallium(III) porphyrins thus consists of diphenylethyne–porphyrin–diphenylethyne and is designed as a superexchange element for through-bond hole/electron transfer. The energetics of the superexchange element are tunable given the nature of the substituents and metalation state of the central porphyrin. The synthesis entailed Sonogashira coupling of two building blocks, a free base bis(4-iodophenyl)porphyrin and a mono-ethynylporphinato thallium(III) chloride. Two benchmark porphyrins also were prepared. Absorption spectral comparisons are provided including of the all-thallium(III) monomer, dimer, and triad.

Chemistry↗