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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The Straightening of a River Meander Leads to Extensive Losses in Flow Complexity and Ecosystem Services

To assist river restoration efforts we need to slow the rate of river degradation. This study provides a detailed explanation of the hydraulic complexity loss when a meandering river is straightened in order to motivate the protection of river channel curvature. We used computational fluid dynamics (CFD) modeling to document the difference in flow dynamics in nine simulations with channel curvature (C) degrading from a well-established tight meander bend (C = 0.77) to a straight channel without curvature (C = 0). To control for covariates and slow the rate of loss to hydraulic complexity, each of the nine-channel realizations had equivalent bedform topography. The analyzed hydraulic variables included the flow surface elevation, streamwise and transverse unit discharge, flow velocity at streamwise, transverse, and vertical directions, bed shear stress, stream function, and the vertical hyporheic flux rates at the channel bed. The loss of hydraulic complexity occurred gradually when initially straightening the channel from C = 0.77 to C = 0.33 (i.e., the radius of the channel is three-times the channel width), and additional straightening incurred rapid losses to hydraulic complexity. Other studies have shown hydraulic complexity provides important riverine habitat and is positively correlated with biodiversity. This study demonstrates how hydraulic complexity can be gradually and then rapidly lost when unwinding a river, and hopefully will serve as a cautionary tale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Molecular mechanisms of assembly and TRIP13-mediated remodeling of the human Shieldin complex

The Shieldin complex, composed of REV7, SHLD1, SHLD2, and SHLD3, protects DNA double-strand breaks (DSBs) to promote nonhomologous end joining. The AAA + ATPase TRIP13 remodels Shieldin to regulate DNA repair pathway choice. Here we report crystal structures of human SHLD3–REV7 binary and fused SHLD2–SHLD3–REV7 ternary complexes, revealing that assembly of Shieldin requires fused SHLD2–SHLD3 induced conformational heterodimerization of open (O-REV7) and closed (C-REV7) forms of REV7. We also report the cryogenic electron microscopy (cryo-EM) structures of the ATPγS-bound fused SHLD2–SHLD3–REV7–TRIP13 complexes, uncovering the principles underlying the TRIP13-mediated disassembly mechanism of the Shieldin complex. We demonstrate that the N terminus of REV7 inserts into the central channel of TRIP13, setting the stage for pulling the unfolded N-terminal peptide of C-REV7 through the central TRIP13 hexameric channel. The primary interface involves contacts between the safety-belt segment of C-REV7 and a conserved and negatively charged loop of TRIP13. This process is mediated by ATP hydrolysis-triggered rotatory motions of the TRIP13 ATPase, thereby resulting in the disassembly of the Shieldin complex.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Tuning the Spin Transition and Carrier Type in Rare-Earth Cobaltates via Compositional Complexity

There is growing interest in material candidates with properties that can be engineered beyond traditional design limits. Compositionally complex oxides (CCO), often called high entropy oxides, are excellent candidates, wherein a lattice site shares more than four cations, forming single-phase solid solutions with unique properties. However, the nature of compositional complexity in dictating properties remains unclear, with characteristics that are difficult to calculate from first principles. Here, in this study, compositional complexity is demonstrated as a tunable parameter in a spin-transition oxide semiconductor La 1- x (Nd, Sm, Gd, Y) x/4 CoO 3 , by varying the population x of rare earth cations over 0.00≤ x≤ 0.80. Across the series, increasing complexity is revealed to systematically improve crystallinity, increase the amount of electron versus hole carriers, and tune the spin transition temperature and on-off ratio. At high a population (x = 0.8), Seebeck measurements indicate a crossover from hole-majority to electron-majority conduction without the introduction of conventional electron donors, and tunable complexity is proposed as new method to dope semiconductors. First principles calculations combined with angle resolved photoemission reveal an unconventional doping mechanism of lattice distortions leading to asymmetric hole localization over electrons. Thus, tunable complexity is demonstrated as a facile knob to improve crystallinity, tune electronic transitions, and to dope semiconductors beyond traditional means.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Intramolecular 1,2 C-H Addition of o -Methyl Groups to Form Unique Ruthenium Pincer Tuck-in Complexes

New RPN H P ligands containing 2,4-xylyl (4mXPN H P) and mesityl (MesPN H P) groups on the phosphorus atoms were synthesized. 4mXPN H P reacts with [(cymene)RuCl 2 ] 2 followed by PMe 3 to produce κ 3 -4mXPN H PRu(PMe 3 )Cl 2 . MesPN H P reacts with [(cymene)RuCl 2 ] 2 to produce monomeric κ 3 -MesPN H PRuCl 2 that reacts with CO forming κ 3 -MesPN H PRu(CO)Cl 2 . Surprisingly, dehydrohalogenation of these complexes results in the activation of ortho methyl groups of the pincer ligands, rather than formation of κ 3 -RPNPRuLCl complexes. This results from transient κ 3 -RPNPRuLCl formation followed by 1,2-addition of an ortho C-H bond across the Ru-amide bond. The transient amide complex of κ 4 -4mXPN H PRu(PMe 3 )Cl was trapped with CO forming κ 3 -4mXPNPRu(PMe 3 )(CO)Cl. In contrast, κ 4 -MesPNHPRu(CO)Cl does not react with ligands to trap the expected amide complex of reverse C-H addition. Instead, CO and PMe 3 displace the chloride ligand forming cationic complexes. In both cases, hemi-lability of the pincer ligand was observed spectroscopically. In conclusion, the new complexes serve as precursors to moderately active catalysts for the acceptorless dehydrogenative coupling of n-butanol.

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

Structural studies of intrinsically disordered MLL -fusion protein AF9 in complex with peptidomimetic inhibitors

AF9 (MLLT3) and its paralog ENL(MLLT1) are members of the YEATS family of proteins with important role in transcriptional and epigenetic regulatory complexes. These proteins are two common MLL fusion partners in MLL -rearranged leukemias. The oncofusion proteins MLL-AF9/ENL recruit multiple binding partners, including the histone methyltransferase DOT1L, leading to aberrant transcriptional activation and enhancing the expression of a characteristic set of genes that drive leukemogenesis. The interaction between AF9 and DOT1L is mediated by an intrinsically disordered C-terminal ANC1 homology domain (AHD) in AF9, which undergoes folding upon binding of DOT1L and other partner proteins. We have recently reported peptidomimetics that disrupt the recruitment of DOT1L by AF9 and ENL, providing a proof-of-concept for targeting AHD and assessing its druggability. Intrinsically disordered proteins, such as AF9 AHD, are difficult to study and characterize experimentally on a structural level. In this study, we present a successful protein engineering strategy to facilitate structural investigation of the intrinsically disordered AF9 AHD domain in complex with peptidomimetic inhibitors by using maltose binding protein (MBP) as a crystallization chaperone connected with linkers of varying flexibility and length. The strategic incorporation of disulfide bonds provided diffraction-quality crystals of the two disulfide-bridged MBP–AF9 AHD fusion proteins in complex with the peptidomimetics. These successfully determined first series of 2.1–2.6 Å crystal complex structures provide high-resolution insights into the interactions between AHD and its inhibitors, shedding light on the role of AHD in recruiting various binding partner proteins. We show that the overall complex structures closely resemble the reported NMR structure of AF9 AHD/DOT1L with notable difference in the conformation of the β-hairpin region, stabilized through conserved hydrogen bonds network. These first series of AF9 AHD/peptidomimetics complex structures are providing insights of the protein–inhibitor interactions and will facilitate further development of novel inhibitors targeting the AF9/ENL AHD domain.

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

Epitaxial Thin Film Growth on Recycled SrTiO 3 Substrates Toward Sustainable Processing of Complex Oxides

Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high‐quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO 3 (STO), MgO, LaAlO 3 , a‐Al 2 O 3, and many others. Recent successes in transferring these complex oxides as free‐standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost‐effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high‐resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre‐strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y 3 Fe 5 O 12 ) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high‐quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.

pre-strained STO surfaces↗
DOE OSTI2021

Complexity growth in integrable and chaotic models

We use the SYK family of models with N Majorana fermions to study the complexity of time evolution, formulated as the shortest geodesic length on the unitary group manifold between the identity and the time evolution operator, in free, integrable, and chaotic systems. Initially, the shortest geodesic follows the time evolution trajectory, and hence complexity grows linearly in time. We study how this linear growth is eventually truncated by the appearance and accumulation of conjugate points, which signal the presence of shorter geodesics intersecting the time evolution trajectory. By explicitly locating such “shortcuts” through analytical and numerical methods, we demonstrate that: (a) in the free theory, time evolution encounters conjugate points at a polynomial time; consequently complexity growth truncates at O($\sqrt{N}$), and we find an explicit operator which “fast-forwards” the free N-fermion time evolution with this complexity, (b) in a class of interacting integrable theories, the complexity is upper bounded by O(poly(N)), and (c) in chaotic theories, we argue that conjugate points do not occur until exponential times O(e N ), after which it becomes possible to find infinitesimally nearby geodesics which approximate the time evolution operator. Finally, we explore the notion of eigenstate complexity in free, integrable, and chaotic models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Negative complexity of formation: the compact dimensions strike back

We show that the vacuum-subtracted maximal volume, the proposed holographic dual to complexity of formation, can be negative when contributions from compact directions are included. We construct explicit solutions with arbitrarily negative complexity of formation in asymptotically AdS 4 × S 7 SUGRA. These examples rely critically on the compact directions, specifically the fact that the full eleven-dimensional spacetime is not asymptotically AdS 11 . While there is some ambiguity in the extension of the holographic complexity proposal to the compact directions, we show that the two natural candidates can both have arbitrarily negative complexity of formation in SUGRA solutions. We further find examples in which complexity can even decrease at late times, including cases of both single-sided geometries and two-sided wormholes. In particular, we construct a cosmological wormhole with simultaneously negative and decreasing complexity of formation (as computed by volume) at late times. We find a distinguished role for relevant primaries in these constructions and comment on possible interpretations.

2D Gravity↗
DOE OSTI2020

A comparative look at structural variation among RC–LH1 ‘Core’ complexes present in anoxygenic phototrophic bacteria

All purple photosynthetic bacteria contain RC–LH1 ‘Core’ complexes. The structure of this complex from Rhodobacter sphaeroides, Rhodopseudomonas palustris and Thermochromatium tepidum has been solved using X-ray crystallography. Recently, the application of single particle cryo-EM has revolutionised structural biology and the structure of the RC–LH1 ‘Core’ complex from Blastochloris viridis has been solved using this technique, as well as the complex from the non-purple Chloroflexi species, Roseiflexus castenholzii. It is apparent that these structures are variations on a theme, although with a greater degree of structural diversity within them than previously thought. Furthermore, it has recently been discovered that the only phototrophic representative from the phylum Gemmatimonadetes, Gemmatimonas phototrophica, also contains a RC–LH1 ‘Core’ complex. At present only a low-resolution EM-projection map exists but this shows that the Gemmatimonas phototrophica complex contains a double LH1 ring. This short review compares these different structures and looks at the functional significance of these variations from two main standpoints: energy transfer and quinone exchange.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Structural and spectroscopic characterization of thorium pyrasal complexes

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

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

Spectroscopic and computational investigations of organometallic complexation of group 12 transition metals by methanobactins from Methylocystis sp. SB2

Methanotrophic bacteria catalyze the aerobic oxidation of methane to methanol using Cu-containing enzymes, thereby exerting a modulating influence on the global methane cycle. To facilitate the acquisition of Cu ions, some methanotrophic bacteria secrete small modified peptides known as “methanobactins,” which strongly bind Cu and function as an extracellular Cu recruitment relay, analogous to siderophores and Fe. In addition to Cu, methanobactins form complexes with other late transition metals, including the Group 12 transition metals Zn, Cd, and Hg, although the interplay among solution-phase configurations, metal interactions, and the spectroscopic signatures of methanobactin-metal complexes remains ambiguous. In this study, the complexation of Zn, Cd, and Hg by methanobactin from Methylocystis sp. strain SB2 was studied using a combination of absorbance, fluorescence, extended x-ray absorption fine structure (EXAFS) spectroscopy, and time-dependent density functional theory (TD-DFT) calculations. We report changes in sample absorbance and fluorescence spectral dynamics, which occur on a wide range of experimental timescales and characterize a clear stoichiometric complexation dependence. Mercury L3-edge EXAFS and TD-DFT calculations suggest a linear model for Hg--S coordination, and TD-DFT suggests a tetrahedral model for Zn 2+ and Cd 2+ . We observed an enhancement in the fluorescence of methanobactin upon interaction with transition metals and propose a mechanism of complexation-hindered isomerization drawing inspiration from the wild-type Green Fluorescent Protein active site. Collectively, our results represent the first combined computational and experimental spectroscopy study of methanobactins and shed new light on molecular interactions and dynamics that characterize complexes of methanobactins with Group 12 transition metals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Comparison of the photochemical properties of phthalocyanine and hemiporphyrazine Zn(II) complexes

In DMF (dimethylformamide) solutions containing concentrations of (NEt 4 )Br (Et = ethyl) between 0.001 and 0.05 M both zinc phthalocyanine (Pc) and hemiporphyrazine (Hp) complexes are dissolved and form species [Zn(Hp)(Br)] – , and [Zn(Pc)(Br)] – . The increase in formation of the hemiporphyrazine bromide adduct is revealed by a linear dependence of the UV–Vis absorption spectrum on the Br – concentration whereas, over the same concentration range, absorption measurements indicate the formation of the phthalocyanine bromide adduct in solution. The x-ray and molecular structure of [NEt 4 ][Zn(Pc)(Br)](H 2 O) 0.33 has been determined showing the coordination of the Br – to the metal center. Photo-induced processes of the Zn complexes were investigated with deaerated solutions in a time scale t ≥10 ns. The 355 nm flash irradiation of [Zn(Hp)(Br)] – produced transient spectra which showed a bathochromic shift of the absorption maximum from 460 nm to 440 nm and an increase of the spectrum rate of decay with increasing Br – concentrations. The initial spectrum is attributed to the (nπ*–LLCT Br→Hp )[Zn(Hp)(Br)] – excited state which reacts with H-atom donors forming a radical [Zn(Hp-H)(Br)] •– . On the other hand, a transient spectrum, λ max ~600 nm, grows in a time t ≤0.6 µs when [Zn(Pc)(Br)] – is flash irradiated at 355 nm. The photoreactions of these complexes with SCN – and 2-propanol (IPA) were studied. Despite of the apparent similarity between both complexes, IPA was photo-oxidized by both complexes although by different mechanisms, an electron transfer with [Zn(Pc)(Br)] – and an H atom abstraction with [Zn(Hp)(Br)] – . Finally, the photo-oxidation of SCN– by [Zn(Pc)(Br)] – but not by [Zn(Hp)(Br)] – makes a remarkable difference between the photochemistries of these complexes.

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

Quantitative Separation of Unknown Organic–Metal Complexes by Liquid Chromatography–Inductively Coupled Plasma-Mass Spectrometry

Dissolved organic matter (DOM) is widely recognized to control the solubility and reactivity of trace metals in the environment. However, the mechanisms that govern metal-DOM complexation remain elusive, primarily due to the analytical challenge of fractionating and quantifying metal–organic species within the complex mixture of organic compounds that comprise DOM. Here, we describe a quantitative method for fractionation and element-specific detection of organic–metal complexes using liquid chromatography with online inductively coupled plasma mass spectrometry (LC–ICP-MS). The method implements a post-column compensation gradient to stabilize ICP–MS elemental response across the LC solvent gradient, thereby overcoming a major barrier to achieving quantitative accuracy with LC–ICP-MS. With external calibration and internal standard correction, the method yields concentrations of organic–metal complexes that were consistently within 6% of their true values, regardless of the complex’s elution time. We used the method to evaluate the effects of four stationary phases (C18, phenyl, amide, and pentafluoroylphenyl propyl) on the recovery and separation of environmentally relevant trace metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in Suwannee River Fulvic Acid and Suwannee River Natural Organic Matter. The C18, amide, and phenyl phases generally yielded optimal metal recoveries (>75% for all metals except Pb), with the phenyl phase separating polar species to a greater extent than C18 or amide. We also fractionated organic-bound Fe, Cu, and Ni in oxidized and reduced soils, revealing divergent metal-DOM speciation across soil redox environments. Finally, by enabling quantitative fractionation of DOM-bound metals, our method offers a means for advancing a mechanistic understanding of metal–organic complexation throughout the environment.

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

Determination of the N–H Bond Dissociation Free Energy in a Pyridine(diimine)molybdenum Complex Prepared by Proton-Coupled Electron Transfer

The pyridine(diimine) molybdenum bis(imido) complex, ( iPr PDI)Mo(=NTol) 2 (Tol = 4-methylphenyl) was synthesized by addition of two equivalents of 4-methylphenylazide to a corresponding molybdenum benzene derivative, ( iPr PDI)Mo(η 6 -C 6 H 6 ) ( iPr PDI = 2,6-(2,6-iPr 2 C 6 H 3 N=CMe) 2 C 5 H 3 N). Protonation of ( iPr PDI)Mo(=NTol) 2 with 2,6-lutinidum triflate yielded a cationic molybdenum amido complex, [( iPr PDI)Mo(NHTol)(=NTol)][OTf], which was further transformed into the neutral molybdenum amido complex, ( iPr PDI)Mo(NHTol)(=NTol) by reduction with zinc powder. A series of spectroscopic, synthetic and pK a determination studies along with electrochemical measurements by the protonation-reduction pathway were used to establish an N–H bond dissociation free energy (BDFE) between 65-69 kcal/mol for the molybdenum imido-amido compound, ( iPr PDI)Mo(NHTol)(=NTol). Full molecule DFT studies provided a computed value of 61 kcal/mol. By contrast, reduction of ( iPr PDI)Mo(=NTol) 2 with KC 8 afforded the corresponding anionic molybdenum complex, K[( iPr PDI)Mo(=NTol) 2 ] that has a potassium cation intercalated with the pyridine and the tolyl groups. Protonation of K[( iPr PDI)Mo(=NTol) 2 ] with the weak amidinium acids [TBD(H)][BArF 24 ] (TBD = triazabicyclodecene, BArF 24 = B[3,5-(CF 3 ) 2 C 6 H 3 ] 4 ) also produced the neutral molybdenum amido complex, ( iPr PDI)Mo(NHTol)(=NTol). Measurement of the pKa and oxidation potential of K[( iPr PDI)Mo(=NTol) 2 ] provided a range of 69-73 kcal/mol for the N–H BDFE of ( iPr PDI)Mo(NHTol)(=NTol), in good agreement with the protonation-reduction route and completing the square scheme. The similar pK a and redox potentials obtained from each pathway demonstrate that both sequences are energetically feasible for PCET events. This study on the determination of N–H BDFE of the molybdenum amido complex renders fundamental insight into the N 2 reduction cycle by proton-coupled electron transfer.

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

Phosphine Ligand Binding and Catalytic Activity of Group 10–14 Heterobimetallic Complexes

We report heterobimetallic complexes have attracted much interest due to their broad range of structures and reactivities as well as unique catalytic abilities. Additionally, these complexes can be utilized as single-source precursors for the synthesis of binary intermetallic compounds. An example is the family of bis(pyridine-2-thiolato)dichloro-germanium and tin complexes of group 10 metals (Pd and Pt). The reactivity of these heterobimetallic complexes is highly tunable through substitution of the group 14 element and the neutral ligand bound to the transition metal. Here, we study the binding energies of three different phosphorous-based ligands, PR 3 (R = Bu, Ph, and OPh) by density functional theory and restricted Hartree–Fock methods. The PR 3 ligand-binding energies follow the trend of PBu 3 > PPh 3 > P(OPh) 3 , in agreement with their sigma-bonding ability. These results are confirmed by ligand exchange experiments monitored with 31 P NMR spectroscopy, in which a weaker binding PR 3 ligand is replaced with a stronger one. Furthermore, we demonstrate that the heterobimetallic complexes are active catalysts in the Negishi coupling reaction, where stronger binding PR 3 ligands inhibit access to an active site at the metal center. Similar strategies could be applied to other complexes to better understand their ligand-binding energetics and predict their reactivity as both precursors and catalysts.

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

Magnetism Studies of Bis(acyl)phosphide-Supported Eu 3+ and Eu 2+ Complexes

A series of bis(acyl)phosphide-supported Eu complexes were synthesized (bis(acyl)phosphide = BAP). Here, in this study, BAP ligands proved to be excellent ligands for the synthesis of both Eu 3+ and Eu 2+ molecular complexes. Sodium bis(mesitoyl)phosphide (Na( mes BAP)) and sodium bis(2,4,6-triisopropylbenzoyl)phosphide (Na( tripp BAP)) were employed as ligand precursors for the synthesis of the Eu 3+ complexes Eu(bis(mesitoyl)phosphide) 3 (thf) 2 (Eu( mes BAP) 3 (thf) 2 ) and Eu(bis(2,4,6-triisopropylbenzoyl)phosphide) 3 (Eu( tripp BAP) 3 ), as well as the Eu 2+ complex, Eu(bis(2,4,6-triisopropylbenzoyl)phosphide) 2 (dme) 2 (Eu( tripp BAP) 2 (dme) 2 ) (thf = tetrahydrofuran, dme = 1,2-dimethoxyethane). All complexes were characterized using a combination of UV–vis–NIR–IR and NMR spectroscopies, and single-crystal X-ray diffraction (SC-XRD). The magnetic properties of these three monomeric Eu complexes were investigated by variable-temperature magnetic susceptibility. The magnetic data are typical for these ions, with Eu( tripp BAP) 2 (dme) 2 displaying Curie-type behavior. Both Eu( tripp BAP) 3 and Eu( mes BAP) 3 (thf) 2 possess similar 7 F 0 - 7 F 1 spin–orbit energy gaps and a similar zero-field splitting of the 7 F 1 state.

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

Delineating the Effects of Counterions on the Structural and Vibrational Properties of U(IV) Lindqvist Polyoxometalate Complexes

Herein we conducted a full investigation into the fundamental structural and vibrational properties of uranium(IV) Peacock−Weakley-type lacunary Lindqvist (W 10 ) polyoxometalate (POM) complexes. We recently demonstrated the importance of the secondary lattice elements in tuning the distortion of the D 4d symmetry in W 10 POM complexes, and here, we synthesized eight UW 10 complexes with different alkali metal counterions and evaluated how the composition and packing of counterion species affected complex structural and vibrational properties. Single-crystal X-ray diffraction analysis on complexes 1−8 revealed changes in structural distortion parameters as a function of differences in counterion configurations, while far-infrared and Raman spectra for 1−8 also demonstrated that vibrational mode frequencies were sensitive to changes in counterion composition and packing. To more effectively compare different counterion configurations, we developed counterion effective ionic radius (eIR) as a new structural parameter, and comparisons between structural distortion parameters and eIR values strongly suggested that modulation by the secondary lattice elements can affect structural and vibrational manifolds within POM complexes. Partial least squares (PLS) analysis was used to quantitatively evaluate correlations observed within this investigation, and PLS statistical models showed a strong correlation between counterion eIR and both structural distortion parameters and vibrational mode frequencies.

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

Ambient Synthesis for Fe(II) Polypyridyl Complexes with an Order of Magnitude Increase in Charge-Transfer Excited-State Lifetimes over [Fe(bpy) 3 ] 2+

Replacing precious metals with abundant metals is an important research focus in photochemical energy conversion and storage to meet global energy demands. However, transition metal complexes (TMCs) based on abundant 3d metals typically possess photochemical disadvantages─such as short charge-transfer excited-state lifetimes─and molecular modifications have focused on optimizing the interplay of structure, dynamics, and energetics to overcome their limitations. One strategy to do so is the use of bespoke ligands that can extend the lifetimes of chemically useful excited states. Here, in this study, we report the synthesis and characterization of novel Fe(II) complexes featuring lengthy polypyridyl ligands that can be readily synthesized. Steady-state and transient absorption spectroscopies indicate that these complexes have desirable properties and their excited metal-to-ligand charge-transfer states live an order of magnitude longer than in the benchmark [Fe(bpy) 3 ] 2+ . This lifetime is largely preserved in the heteroleptic complexes, thereby enabling the preparation of asymmetric complexes. Additionally, we apply nonradiative transition theory to explain the long-time decay kinetics. In light of their ease of preparation and reasonable excited-state lifetimes, we suggest the use of these complexes in Fe(II) dye-sensitized solar cells, where the rate of charge injection would be competitive with increased lifetime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗