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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Intramolecular charge-transfer enhances energy transfer efficiency in carotenoid-reconstituted light-harvesting 1 complex of purple photosynthetic bacteria

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8'-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8'-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Homoleptic U(III) and U(IV) amidate complexes

The syntheses of the first homoleptic U(III) and U(IV) amidate complexes are described here. These can be interconverted by chemical reduction/oxidation, showing an unusual change in coordination number from four in the U(III) complex to eight in the U(IV) complex in the solid state structures.

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

Toxic heavy metal – Pb, Cd, Sn – complexation by the octadentate hydroxypyridinonate ligand archetype 3,4,3-LI(1,2-HOPO)

The toxicity of heavy metals such as lead (Pb), cadmium (Cd) and tin (Sn) has long been known but accidental exposures of large populations to these elements remain unfortunately a topical issue. Chelating agents against Pb, Cd, or Sn poisoning are still limited to classical ligands such as ethylenediamine tetraacetic acid (EDTA). In this paper, we evaluate the ability of 3,4,3-LI(1,2-HOPO) (L 4- ), an octadentate ligand currently under evaluation for actinide decorporation, to bind Pb, Cd and Sn metal ions in aqueous solutions. This ligand forms 1 : 1 complexes with Pb(II), Cd(II) and Sn(IV) as well as bimetallic 2 : 1 species with Pb(II) and Cd(II), all of which were characterized by high resolution mass spectrometry and spectrophotometric titrations. The 3,4,3-LI(1,2-HOPO) ligand exhibits an extreme affinity for Sn(IV) ions (log β 110 > 40), with the complex remaining stable from highly acidic conditions to alkaline media (from 3 M HCl to pH 8). Single crystals of the neutral complex [Sn IV 3,4,3-LI(1,2-HOPO)·3H 2 O] were obtained and its structure determined, revealing a chiral conformation. Finally, although not initially designed for hexacoordinated metals such as Pb(II) and Cd(II), the octadentate ligand shows promise for the in vitro or in vivo sequestration of toxic heavy metals, as evidenced by decorporation experiments performed in mice contaminated with 210 Pb(II) and treated with either EDTA or 3,4,3-LI(1,2-HOPO).

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

Streams, cascades, and pools: various water cluster motifs in structurally similar Ni(ii) complexes

Hydrogen bonding (HB) interactions are well known to impact the properties of water in the bulk and within hydrated materials. A series of Ni(II) complexes based on chelates containing N-(2-aminoethyl)-1-methylimidazole-2-carboxamide have been synthesized and fully characterized by single crystal X-ray diffraction, spectroscopic methods, and thermal analysis. The complexes reveal a variety of water cluster motifs dependent on the packing arrangement in the solid state. A key feature is the orientation of the carboxamide moiety, which leads to the formation of void spaces that accommodate water through HB interactions. The water motifs contain 1D water chains (streams), 2D tapes of infused rings (cascades), and isolated water dimers (pools). The HB motifs in the hydrated structures vary as a function of the crystal packing of the host molecules. Thermal analyses show a correlation between the HB motif in the hydrated crystals and the temperature range of the dehydration process. The conductivity of the hydrated crystals varies as a function of the crystal packing interactions between metal complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Electronic and structural features of octa-coordinated yttrium–ammonia complexes: the first neutral solvated electron precursor with eight ligands and three outer electrons

The neutral and charged yttrium metal–ammonia complexes, [Y(NH3)8]0,±, are investigated using state-of-the-art quantum chemical calculations. The electronic structure of these complexes is described as an Y(NH3)83+ core with two, three, and four electrons orbiting in its periphery. Unlike the so far reported solvated electron precursors containing alkali, alkaline earth or first-row transition metals, yttrium complexes are the only ones which can accommodate eight ammonia ligands and up to four peripheral electrons. For the neutral species, two electrons occupy the diffuse s-type orbital (1s) and one diffuse p-type orbital (1p). For the cationic counterpart one electron is removed from the 1p orbital, while for the anion another electron is added to the 1p shell. The calculated low-lying electronic states with excitation energies up to 2.0 eV populate the 1s, 1p, and 1d outer orbitals. The first ionization energy of Y(NH3)8 is 2.74 eV and its electron affinity is 0.64 eV. The present results suggest that saturated yttrium ammonia solutions will turn into solids (liquid or expanded metals), where a grid of Y(NH3)83+ centers will be surrounded by “free” electrons.

Almeida, Nuno M. S.↗
DOE OSTI2018

A sulphur and uranium fiesta! Synthesis, structure, and characterization of neutral terminal uranium(VI) monosulphide, uranium(VI) η 2 -disulphide, and uranium(IV) phosphine sulphide complexes

Here, three new uranium species (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(=S), (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(η 2 -S 2 ), and (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(S=PMe 3 ) were synthesized and fully characterized by a combination of NMR, IR, and UV/vis–NIR spectroscopies, elemental analysis, and cyclic voltammetry. The solid state structures of (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(=S) and (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(η 2 -S 2 ) were also determined. The compound (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(=S) is the first neutral uranium complex with a terminal sulphido ligand, and (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(S=PMe 3 ) is the first uranium compound with a coordinated phosphine sulphide ligand. The phosphine sulphide adduct, (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(S=PMe 3 ), can be synthesized either by reaction of the uranium(IV) complex (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(thf) with S=PMe 3 or by the reaction of the uranium(VI) terminal sulphido complex (C 5 Me 5 ) 2 U(=N-2,6- i Pr 2 -C 6 H 3 )(=S) with PMe 3 .

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

A mononuclear nonheme {FeNO} 6 complex: synthesis and structural and spectroscopic characterization

While the synthesis and characterization of {FeNO} 7,8,9 complexes have been well documented in heme and nonheme iron models, {FeNO} 6 complexes have been less clearly understood. Herein, we report the synthesis and structural and spectroscopic characterization of mononuclear nonheme {FeNO} 6 and iron(III)–nitrito complexes bearing a tetraamido macrocyclic ligand (TAML), such as [(TAML)Fe III (NO)] - and [(TAML)Fe III (NO 2 )] 2- , respectively. First, direct addition of NO (g) to [Fe III (TAML)] - results in the formation of [(TAML)Fe III (NO)] - , which is sensitive to moisture and air. The spectroscopic data of [(TAML)Fe III (NO)] - , such as 1 H nuclear magnetic resonance and X-ray absorption spectroscopies, combined with computational study suggest the neutral nature of nitric oxide with a diamagnetic Fe center (S = 0). We also provide alternative pathways for the generation of [(TAML)Fe III (NO)] - , such as the iron–nitrite reduction triggered by protonation in the presence of ferrocene, which acts as an electron donor, and the photochemical iron–nitrite reduction. To the best of our knowledge, the present study reports the first photochemical nitrite reduction in nonheme iron models.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thiocyanate complexes of the lanthanides, Am and Cm

In this work, the synthesis and single crystal structures of Am( III ) and Cm( III ) thiocyanate complexes are reported along with an isostructural series of lanthanide thiocyanate complexes. Because the complexes are isostructural, a comparative study of the metal–thiocyanate bonds was conducted using Raman spectroscopy indicating very similar and electrostatic metal–ligand interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Designing molecular building blocks for the self-assembly of complex porous networks

The creation of molecular or colloidal building blocks which can self-assemble into complex, ordered porous structures has been long sought-after, and so are the guiding principles behind this creation. The pursuit of this goal has led to the creation of novel classes of materials like metal organic frameworks (MOFs) and covalent organic frameworks (COFs). In theory, a tremendous number of structures can be formed by these materials due to the variety of geometries available to their building blocks. However, most realized crystal structures tend to be simple or homoporous and typically assemble from building blocks with high degrees of symmetry. Building blocks with low degrees of symmetry suitable for assembly into the more complex structures tend to assemble into polymorphous or disordered structures instead. Here, we use Monte Carlo simulations of patchy vertex-like building blocks to show how the addition of chemical specificity via orthogonally reacting functional sites can allow vertex-like building blocks with even asymmetric geometries to self-assemble into ordered crystallites of various complex structures. In addition to demonstrating the utility of such a strategy in creating ordered, heteroporous structures, we also demonstrate that it can be used as a means for tuning specific features of the crystal structure, accomplishing such aims as the control of relative pore sizes. We also discuss heuristics for properly designing molecules so that they can assemble into target structures.

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

New up-conversion luminescence in molecular cyano-substituted naphthylsalophen lanthanide(iii) complexes

A new naphthylsalophen and its 3:2 ligand-to-lanthanide sandwich-type complexes were isolated. Here, when excited at 380 nm, the complexes display the characteristic metal-centred emission for Nd III , Er III and Yb III . Upon 980 nm excitation, in mixed lanthanide and the Er complexes, Er-centred upconversion emission at 543 and 656 nm is observed, with power densities as low as 2.18 W cm –2 .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Radiation-Induced Effects on the Extraction Properties of Hexa-n-octylnitrilo-triacetamide (HONTA) Complexes of Americium and Europium

The candidate An(III)/Ln(III) separation ligand hexa-n-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions (n-dodecane/0.1 M HNO 3 ) using a solvent test loop in conjunction with cobalt-60 gamma irradiation. The extent of HONTA radiolysis and complimentary degradation product formation was quantified by HPLC-ESI-MS/MS. Further, the impact of HONTA radiolysis on process performance was evaluated by measuring the change in 243 Am and 154 Eu distribution ratios as a function of absorbed gamma dose. HONTA was found to decay exponentially with increasing dose, affording a dose coefficient of d = (4.48 ± 0.19) × 10 –3 kGy –1 . Multiple degradation products were detected by HPLC-ESI-MS/MS with dioctylamine being the dominant quantifiable species. Both 243 Am and 154 Eu distribution ratios exhibited an induction period of ~70 kGy for extraction (0.1 M HNO 3 ) and back-extraction (4.0 M HNO 3 ) conditions, after which both values decreased with absorbed dose. The decrease in distribution ratios was attributed to a combination of the destruction of HONTA and ingrowth of dioctylamine, which is capable of interfering in metal ion complexation. Furthermore, the loss of HONTA with absorbed gamma dose was predominantly attributed to its reaction with the n-dodecane radical cation (R˙ + ). These R˙ + reaction kinetics were measured for HONTA and its 241 Am and 154 Eu complexes using picosecond pulsed electron radiolysis techniques. All three second-order rate coefficients (k) were essentially diffusion limited in n-dodecane indicating a significant reaction pathway: k(HONTA + R˙ + ) = (7.6 ± 0.8) × 10 9 M –1 s –1 , k(Am(HONTA) 2 + R˙ + ) = (7.1 ± 0.7) × 10 10 M –1 s –1 , and k(Eu(HONTA) 2 + R˙ + ) = (9.5 ± 0.5) × 10 10 M –1 s –1 . HONTA-metal ion complexation afforded an order-of-magnitude increase in rate coefficient. Additional nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived (< 100 ns) HONTA radical cation and a second long-lived (µs) species identified as the HONTA triplet excited state. The latter was confirmed by a series of oxygen quenching picosecond pulsed electron measurements, affording a quenching rate coefficient of k( 3 [HONTA]* + O 2 ) = 2.2 × 10 8 M –1 s –1 . Overall, both the HONTA radical cation and triplet excited state are important precursors to the suite of measured HONTA degradation products.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Solvent manipulation of the pre-reduction metal–ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. Herein, we show that the nucleation and growth rates are correlated with the thermodynamics of metal–ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31 P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal–ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles.

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

Observing the three-dimensional dynamics of supported metal complexes

Dynamics are intricately linked with activity and selectivity when it comes to catalysis, as noted for instance in the enzymatic principles of induced fit and allostery, and yet the range of motions heterogeneous catalytic sites are able to undergo is poorly understood. Solid-state nuclear magnetic resonance (NMR) spectroscopy is perhaps the only tool capable of probing the rapid conformational dynamics found in heterogeneous catalysts but has historically been restricted by its low sensitivity, limiting the detail with which structures can be resolved. In this work, we apply solid-state NMR and dynamic nuclear polarization, in combination with density functional theory modeling, to reveal the high-resolution structure and motional freedom of a scandium supported complex in three dimensions. The results are contrasted with the study of the analogous homoleptic complex in the crystalline state, highlighting the impacts that surface structure may have on the dynamics of supported complexes.

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

Vibrational characterization of a diiron bridging hydride complex – a model for hydrogen catalysis

A diiron complex containing a bridging hydride and a protonated terminal thiolate of the form [(m,k 2 - bdtH)(m-PPh 2 )(m-H)Fe 2 (CO) 5 ] + has been investigated through 57 Fe nuclear resonance vibrational spectroscopy (NRVS) and interpreted using density functional theory (DFT) calculations. We report the Fe–mH–Fe wagging mode, and indications for Fe–mD stretching vibrations in the D-isotopologue, observed by 57 Fe-NRVS. Our combined approach demonstrates an asymmetric sharing of the hydride between the two iron sites that yields two nondegenerate Fe–mH/D stretching vibrations. The studied complex provides an important model relevant to biological hydrogen catalysis intermediates. The complex mimics proposals for the binuclear metal sites in [FeFe] and [NiFe] hydrogenases. It is also an appealing prototype for the ‘Janus intermediate’ of nitrogenase, which has been proposed to contain two bridging Fe–H–Fe hydrides and two protonated sulfurs at the FeMo-cofactor. The significance of observing indirect effects of the bridging hydride, as well as obstacles in its direct observation, is discussed in the context of biological hydrogen intermediates.

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

Development of sterically hindered siloxide-functionalized polyoxotungstates for the complexation of 5d-metals

In this study, we extend the family of organosilyl-functionalized trivacant Keggin polyoxotungstates, [PW 9 O 34 (RSiOH) 3 ] 3− (R = n Pr, i Pr, t Bu), through the introduction of bulky aryl and aliphatic silanol substituents, namely phenyl, cyclohexyl and biphenyl. This work was performed in order to study the impact of these large functional groups on the accessibility of the well-defined tridentate coordination site. Coordination of hafnium to these type II hybrid polyoxotungstates was conducted in order to study the ability of the bulkier ligand pockets to support larger cations in comparison to those previously reported (e.g. Ti 4+ , V 3+ , V 5+ , Ge 4+ ). Increased steric hindrance around the coordination site from the biphenyl groups resulted in much longer reaction times for the complexation reaction compared to the other functional groups used, but the impact of our design toward stabilizing reactive species proved limited, as all complexes easily undergo hydrolysis of the Hf-O t Bu bond in the presence of water. As a result, electrochemical investigations of the ligands and hafnium complexes reveal that the redox events centered on the polyoxotungstate core can be tuned by varying the substituents on the silyl fragment, and exhibit a cathodic shift after coordination of the redox inactive tetravalent cation.

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

Mechanistic investigation of the aerobic oxidation of 2-pyridylacetate coordinated to a Ru(ii) polypyridyl complex

A new ruthenium polypyridyl complex, [Ru(bpy) 2 (acpy)] + (acpy = 2-pyridylacetate, bpy = 2,2'-bipyridine), was synthesized and fully characterized. Distinct from the previously reported analog, [Ru(bpy) 2 (pic)] + (pic = 2-pyridylcarboxylate), the new complex is unstable under aerobic conditions and undergoes oxidation to yield the corresponding α-keto-2-pyridyl-acetate (acpyoxi) coordinated to the Ru II center. The reaction is one of the few examples of C–H activation at mild conditions using O 2 as the primary oxidant and can provide mechanistic insights with important implications for catalysis. Theoretical and experimental investigations of this aerobic oxidative transformation indicate that it takes place in two steps, first producing the α-hydroxo-2-pyridyl-acetate analog and then the final product. The observed rate constant for the first oxidation was in the order of 10 -2 h -1 . The reaction is hindered in the presence of coordinating solvents indicating the role of the metal center in the process. Theoretical calculations at the M06-L level of theory were performed for multiple reaction pathways in order to gain insights into the most probable mechanism. Our results= indicate that O 2 binding to [Ru(bpy) 2 (acpy)] + is favored by the relative instability of the six-ring chelate formed by the acpy ligand and the resulting Ru III -OO˙- superoxo is stabilized by the carboxylate group in the coordination sphere. C–H activation by this species involves high activation free energies (ΔG ‡ = 41.1 kcal mol -1 ), thus the formation of a diruthenium μ-peroxo intermediate, [(Ru III (bpy) 2 (O-acpy)) 2 O 2 ] 2+ via interaction of a second [Ru(bpy) 2 (acpy)] + was examined as an alternative pathway. The dimer yields two Ru IV =O centers with a low ΔG ‡ of 2.3 kcal mol -1 . The resulting Ru IV =O species can activate C–H bonds in acpy (ΔG ‡ = 23.1 kcal mol -1 ) to produce the coordinated α-hydroxo-2-pyridylacetate. Further oxidation of this intermediate leads to the α-keto-2-pyridyl-acetate product. The findings provide new insights into the mechanism of C–H activation catalyzed by transition-metal complexes using O 2 as the sole oxygen source.

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

Explorations of the nonheme high-valent iron-oxo landscape: crystal structure of a synthetic complex with an [Fe IV 2 (μ-O) 2 ] diamond core relevant to the chemistry of sMMOH

Methanotrophic bacteria utilize methane monooxygenase (MMO) to carry out the first step in metabolizing methane. The soluble enzymes employ a hydroxylase component (sMMOH) with a nonheme diiron active site that activates O 2 and generates a powerful oxidant capable of converting methane to methanol. It is proposed that the diiron(II) center in the reduced enzyme reacts with O 2 to generate a diferric-peroxo intermediate called P that then undergoes O–O cleavage to convert into a diiron(IV) derivative called Q, which carries out methane hydroxylation. Most (but not all) of the spectroscopic data of Q accumulated by various groups to date favor the presence of an Fe IV 2 (μ-O) 2 unit with a diamond core. The Que lab has had a long-term interest in making synthetic analogs of iron enzyme intermediates. To this end, the first crystal structure of a complex with a Fe III Fe IV (μ-O) 2 diamond core was reported in 1999, which exhibited an Fe∙∙∙Fe distance of 2.683(1) Å. Now more than 20 years later, a complex with an Fe IV 2 (μ-O) 2 diamond core has been synthesized in sufficient purity to allow diffraction-quality crystals to be grown. Finally, its crystal structure has been solved, revealing an Fe∙∙∙Fe distance of 2.711(4) Å for comparison with structural data for related complexes with lower iron oxidation states.

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

Elemental chalcogen reactions of a tetravalent uranium imidophosphorane complex: cleavage of dioxygen

Herein we report the first example of a mononuclear uranium complex, [U 4+ (NP(pip) 3 ) 4 ] (1-U), that selectively reduces dioxygen to produce a terminal oxo complex, [U 6+ O(NP(pip) 3 ) 4 ] (2-U; [NP(pip) 3 ] 1- is tris(piperidinyl)imidophosphorane). Reactions between 1-U and the heavier elemental chalcogens, S 8 or Se 0 , result in six-coordinate U(VI) complexes, [U 6+ (κ 2 -E 3 )(NP(pip) 3 ) 4 ] (E = S (3-U) or Se (4-U)).

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗