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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 325 records · Page 18
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DOE OSTI2021

Quasi-operando quantification of Cu(ii) ions in Cu-SSZ-13 catalyst by an NH 3 temperature-programmed reduction method

In this work, a quasi-operando NH3 temperature-programmed reduction method (NH 3 -TPR), with N 2 :Cu = 1:1, is developed to quantify total Cu(II) ions in Cu-SSZ-13 quenched from SCR-relevant reactions, and its accuracy is confirmed by in situ EPR. [Cu(OH)] + -Z and Cu 2+ -2Z can be further distinguished by NH 3 reduction temperatures, and their different reducibility in SCR is revealed.

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

OH radical reactions with the hydrophilic component of sphingolipids

In this article, using the example of model compounds, we studied the reactions resulting from the interaction of OH radicals with the hydrophilic part of sphingolipids. We compared the stopped-flow EPR spectroscopy and pulse radiolysis with optical detection methods to characterize radical intermediates formed in the reaction of OH radicals with glycerol, serinol and N-boc-serinol. Quantum chemical calculations were also performed to help interpret the observed experimental data. It was shown that H-abstraction from the terminal carbon atom is the main process that is realized for all the studied compounds. The presence of the unsubstituted amino group (–NH 2 ) is seen to completely change the reaction properties of serinol in comparison with those observed in glycerol and N-boc serinol.

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

Exchange-biased quantum tunnelling of magnetization in a [Mn 3 ] 2 dimer of single-molecule magnets with rare ferromagnetic inter-Mn 3 coupling

A covalently-linked dimer of two single-molecule magnets (SMMs), [Mn 6 O(O 2 CMe) 6 (1,3-ppmd) 3 ](ClO 4 ) 2 , has been synthesized from the reaction of [Mn 3 O(O 2 CMe) 6 (py) 3 ](ClO 4 ) with 1,3-phenylene-bis(pyridin-2-ylmethanone) dioxime (1,3-ppmdH 2 ). It contains two [Mn III 3 O] +7 triangular units linked by three 1,3-ppmd 2 - groups into an [Mn 3 ] 2 dimer with D 3 symmetry. Solid-state dc and ac magnetic susceptibility measurements showed that each Mn 3 subunit retains its properties as an SMM with an S = 6 ground state. Magnetization vs. dc field sweeps on a single crystal reveal hysteresis loops below 1.3 K exhibiting exchange-biased quantum tunnelling of magnetization (QTM) steps with a bias field of +0.06 T. This is the first example of a dimer of SMMs showing a positive exchange bias of the QTM steps in the hysteresis loops, and it has therefore been subjected to a detailed analysis. Simulation of the loops determines that each Mn3 unit is exchange-coupled with its neighbour primarily through the 1,3-ppmd 2 - linkers, confirming a weak ferromagnetic inter-Mn 3 interaction of J 12 ≈ +6.5 mK ($\hat{H}= -2J\hat{S}_i·\hat{S}_j$ convention). High-frequency EPR studies of a microcrystalline powder sample enable accurate determination of the zero-field splitting parameters of the uncoupled Mn3 SMMs, while also confirming the weak exchange interaction between the two SMMs within each [Mn 3 ] 2 dimer. The combined results emphasize the ability of designed covalent linkers to generate inter-SMM coupling of a particular sign and relative magnitude, and thus the ability of such linkers to modulate the quantum physics. As such, this article supports the feasibility of using designed covalent linkers to develop molecular oligomers of SMMs, or other magnetic molecules, as multi-qubit systems and/or other components of new quantum technologies.

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

Depolymerization of polystyrene under ambient conditions

Depolymerization of the addition polymer polystyrene to monomeric styrene is facilitated by mechanochemical processing at room temperature under ambient atmosphere. The reaction occurs in metal-based milling media in concert with scission of macromolecular chains that generates carbon-centered free-radicals detectable by EPR spectroscopy, although the processing is performed in air.

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

Computational modeling predicts the stability of both Pd + and Pd2 + ion-exchanged into H-CHA

Passive NO x adsorbers (PNA) using Pd/zeolites have emerged as a promising solution for the reduction of cold-start emissions from vehicle exhaust. However, the nature of the active sites and the mechanisms underlying NO x adsorption in Pd/zeolites remain a subject of ongoing investigation. In this study, we employ quantum chemical simulations to investigate the structure of Pd species in cation-exchange sites at isolated Al and Al pairs in the 6-ring and 8-ring of the CHA framework before the introduction of NO x . Our calculations show that the speciation of Pd in these exchange sites strongly depends on the precise Al arrangement within the framework, as well as the operating conditions. Ionically dispersed Pd is found to be the most favorable species over a wide range of oxidizing and reducing conditions. Small oligomers of PdO and metallic Pd do not appear to be competitive at either isolated Al or Al pairs. Notably, our calculations show that ion exchange sites other than next–next–nearest neighbor Al pairs in the 6-ring will be preferentially occupied by Pd + instead of Pd 2+ . The stability of Pd + in the zeolite environment is an interesting contrast with its rareness in molecular Pd compounds. Nonetheless, a detailed analysis of the electronic structure shows that predicted Pd oxidation states are consistent with chemical intuition for all complexes investigated in this study. We also discuss the potential ambiguity in Pd characterization provided by typical experimental techniques such as XANES, EXAFS and UV-Vis, and highlight the need for additional EPR spectroscopy studies to further elucidate the initial Pd speciation in zeolites for PNA applications.

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

Three individually addressable spin qubits in a single molecule

Here, an asymmetric bis-phenol-β-diketone (H 4 L) has been designed as a ligand programmed to promote the assembly of a molecular arrangement composed of three magnetically exchanged [NiCu] pairs, each exhibiting an S = 1/2 spin. The latter are shown by EPR and magnetometry to be good qubit realizations and non-equivalent within the molecule in the solid state, as required for conditional quantum gates.

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

Aromatic and aliphatic hydrocarbon hydroxylation via a formally Ni IV =O oxidant

The reaction of (NMe 4 ) 2 [Ni II (L Ph )(OAc)] (1[OAc], L Ph = 2,2',2''-nitrilo-tris-(N-phenylacetamide); OAc = acetate) with 3-chloroperoxybenzoic acid (m-CPBA) resulted in the formation of a self-hydroxylated Ni III -phenolate complex, 2, where one of the phenyl groups of L Ph underwent hydroxylation. 2 was characterised by UV-Vis, EPR, and XAS spectroscopies and ESI-MS. 2 decayed to yield a previously characterised Ni II -phenolate complex, 3. We postulate that self-hydroxylation was mediated by a formally Ni IV =O oxidant, formed from the reaction of 1[OAc] with m-CPBA, which undergoes electrophilic aromatic substitution to yield 2. This is supported by an analysis of the kinetic and thermodynamic properties of the reaction of 1[OAc] with m-CPBA. Addition of exogenous hydrocarbon substrates intercepted the self-hydroxylation process, producing hydroxylated products, providing further support for the formally Ni IV =O entity. This study demonstrates that the reaction between Ni II salts and m-CPBA can lead to potent metal-based oxidants, in contrast to recent studies demonstrating carboxyl radical is a radical free-chain reaction initiator in Ni II /m-CPBA hydrocarbon oxidation catalysis.

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DOE OSTI2022

Charge transfer in mixed and segregated stacks of tetrathiafulvalene, tetrathianaphthalene and naphthalene diimide: a structural, spectroscopic and computational study

Tetrathiafulvalene (TTF) is a highly tunable electron donor that has been widely studied in charge transfer (CT) complexes, including Bechgaard salts which are superconductors at low temperatures. Its close relative, tetrathianaphthalene (TTN) has received considerably less attention than its TTF counterpart but is potentially a versatile electron donor. Three novel CT complexes containing mixed and segregated stack donor-acceptor (D–A) complexes of tetrathiafulvalene (TTF), tetrathianaphthalene (TTN) and naphthalene diimide (NDI) are reported. We demonstrate a facile mechanochemical synthesis of two salts, TTF–DPNI and TTN–DPNI (DPNI = N,N'-di-(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide), which is uncommon for these materials. Despite the detection of a very low partial charge transfer in the three salts using UV-Vis-NIR, Raman and EPR spectroscopies, we elucidated the properties of the TTN core with support from DFT calculations for the first time. Finally, we highlight the performance of TTN in a CT complex and demonstrate the importance of a combined approach to the characterisation of CT in organic D–A complexes.

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

Conformational dynamicity in a copper( ii ) coordination complex

The geometries of copper coordination complexes are intricately related to their electron transfer capabilities, but the role of dynamics in these processes are not fully understood. We have previously reported CuCl(dpa OMe ), a complex exhibiting conformational fluxionality in its Cu I state and rigidity upon oxidation to Cu II . Here, we report the synthesis and characterization of [CuCl(dpa SMe )] +/0 , a complex exhibiting relative rigidity in its CuI state and structural dynamics upon oxidation to Cu II . The dynamics of [CuCl(dpa SMe )] + were characterized via X-ray diffraction, cyclic voltammetry, and EPR spectroscopy, where temperature-dependent interconversion between trigonal bipyramidal and square pyramidal geometries is observed. Coupling these solid and solution-state characterization data enabled assignment of the coordination geometries involved. As a result, factors impacting these dynamics and their potential implications for electron transfer are discussed.

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

A bis-calix[4]arene-supported [Cu II 16 ] cage

Reaction of 2,2'-bis-p- t Bu-calix[4]arene (H 8 L) with Cu(NO 3 ) 2 ·3H 2 O and N-methyldiethanolamine (Me-deaH 2 ) in a basic dmf/MeOH mixture affords [Cu II 16 (L) 2 (Me-dea) 4 (μ 4 -NO 3 ) 2 (μ-OH) 4 (dmf) 3.5 (MeOH) 0.5 (H 2 O) 2 ](H 6 L)·16dmf·4H 2 O (4), following slow evaporation of the mother liquor. The central core of the metallic skeleton describes a tetracapped square prism, [Cu 12 ], in which the four capping metal ions are the CuII ions housed in the calix[4]arene polyphenolic pockets. The [Cu II 8 ] square prism is held together “internally” by a combination of hydroxide and nitrate anions, with the N-methyldiethanolamine co-ligands forming dimeric [Cu II 2 ] units which edge-cap above and below the upper and lower square faces of the prism. Charge balance is maintained through the presence of one doubly deprotonated H 6 L 2- ligand per [Cu 16 ] cluster. Magnetic susceptibility measurements reveal the predominance of strong antiferromagnetic exchange interactions and an S = 1 ground state, while EPR is consistent with a large zero-field splitting.

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

Isostructural bridging diferrous chalcogenide cores [Fe II (μ-E)Fe II ] (E = O, S, Se, Te) with decreasing antiferromagnetic coupling down the chalcogenide series

Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a few examples reported to date. Here we show that treatment of the ferrous starting material [( tBu pyrpyrr 2 )Fe(OEt 2 )] (1-OEt 2 ) ( tBu pyrpyrr 2 = 3,5- t Bu 2 -bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E = PR 3 results in the neutral phosphine chalcogenide adduct series [( tBu pyrpyrr 2 )Fe(EPR 3 )] (E = O, S, Se; R = Ph; E = Te; R = t Bu) (1-E) without any electron transfer, whereas treatment of the anionic starting material [K] 2 [( tBu pyrpyrr 2 )Fe 2 (μ-N 2 )] (2-N 2 ) with the appropriate chalcogenide transfer source yields cleanly the isostructural ferrous bridging mono-chalcogenide ate complexes [K] 2 [( tBu pyrpyrr 2 )Fe 2 (μ-E)] (2-E) (E = O, S, Se, and Te) having significant deviation in the Fe–E–Fe bridge from linear in the case of E = O to more acute for the heaviest chalcogenide. All bridging chalcogenide complexes were analyzed using a variety of spectroscopic techniques, including 1 H NMR, UV-Vis electronic absorbtion, and 57 Fe Mössbauer. The spin-state and degree of communication between the two ferrous ions were probed via SQUID magnetometry, where it was found that all iron centers were high-spin (S = 2) Fe II , with magnetic exchange coupling between the Fe II ions. Magnetic studies established that antiferromagnetic coupling between the ferrous ions decreases as the identity of the chalcogen is tuned from O to the heaviest congener Te.

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

Magnetic coupling between Fe(NO) spin probe ligands through diamagnetic Ni II , Pd II and Pt II tetrathiolate bridges

Reaction of the nitrosylated-iron metallodithiolate ligand, paramagnetic (NO)Fe(N 2 S 2 ), with [M(CH 3 CN) n ][BF 4 ] 2 salts (M = Ni II , Pd II , and Pt II ; n = 4 or 6) affords di-radical tri-metallic complexes in a stairstep type arrangement ([FeMFe] 2+ , M = Ni, Pd, and Pt), with the central group 10 metal held in a MS 4 square plane. These isostructural compounds have nearly identical ν(NO) stretching values, isomer shifts, and electrochemical properties, but vary in their magnetic properties. Despite the intramolecular Fe∙∙∙Fe distances of ca. 6 Å, antiferromagnetic coupling is observed between {Fe(NO)} 7 units as established by magnetic susceptibility, EPR, and DFT studies. The superexchange interaction through the thiolate sulfur and central metal atoms is on the order of Ni II < Pd II $\ll$ Pt II with exchange coupling constants (J) of -3, -23, and -124 cm -1 , consistent with increased covalency of the M–S bonds (3d < 4d < 5d). This trend is reproduced by DFT calculations with molecular orbital analysis providing insight into the origin of the enhancement in the exchange interaction. Specifically, the magnitude of the exchange interaction correlates surprisingly well with the energy difference between the HOMO and HOMO-1 orbitals of the triplet states, which is reflected in the central metal's contribution to these orbitals. These results demonstrate the ability of sulfur-dense metallodithiolate ligands to engender strong magnetic communication by virtue of their enhanced covalency and polarizability.

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

Light-induced electron spin qubit coherences in the purple bacteria reaction center protein

Photosynthetic reaction center proteins (RCs) provide ideal model systems for studying quantum entanglement between multiple spins, a quantum mechanical phenomenon wherein the properties of the entangled particles become inherently correlated. Following light-generated sequential electron transfer, RCs generate spin-correlated radical pairs (SCRPs), also referred to as entangled spin qubit (radical) pairs (SQPs). Understanding and controlling coherence mechanisms in SCRP/SQPs is important for realizing practical uses of electron spin qubits in quantum sensing applications. The bacterial RC (bRC) provides an experimental system for exploring quantum effects in the SCRP P 865 + Q A − , where P 865 , a special pair of bacteriochlorophylls, is the primary donor, and Q A is the primary quinone acceptor. In this study, we focus on understanding how local molecular environments and isotopic substitution, particularly deuteration, influence spin coherence times (T M ). Using high-frequency electron paramagnetic resonance (EPR) spectroscopy, we observed that the local environment surrounding P 865 and Q A plays a significant role in determining T M . Our findings show that while deuteration led to a modest increase in T M , particularly at low temperatures, but the effect was substantially smaller than predicted by classical nuclear spin diffusion alone. This result is in contrast to our previous study of the photosystem I (PSI) RC, where no increase in T M was observed upon deuteration. Theoretical modeling identified several methyl groups at key distances from the spin centers of both bRC and PSI, and methyl group tunneling at low temperatures has been previously suggested as a mechanism for enhanced spin decoherence. Additionally, our study revealed a strong dependence of spin coherence on the orientation of the external magnetic field, highlighting the influence of the protein microenvironment on spin dynamics. In conclusion, these results offer new insights for optimizing coherence times in quantum system design for quantum information science and sensing applications.

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