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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 OSTI2023

Impact of the Electronic Properties of Chalcogenide Ligands in their Complexation with Uranyl Nitrate Complexes

The idea of covalency being directly correlated with selectivity in f-element separations has gained attention over the years. However, “covalency” as a concept is still under debate as it is not an experimental nor quantum mechanical observable. Regardless, covalency along with ionicity are still the main concepts used to explain the nature of the chemical bond of coordination complexes. Another concept that has gained the attention in the separations community is the hard-soft acid-base (HSAB) theory, which favors soft-donor ligands having the potential to increase selectivity for actinides (An) over the lanthanides (Ln) due to their ability to engage more effectively f-electrons in covalent interactions. However, it has been shown that while using softer donor ligands in fact increased orbital mixing and covalency with the actinides, it compromises the strength of the interaction owing to a decrease in the metal-ligand electrostatic interactions.1 Herein, we study the electronic structure of different types of chalcogenide ligands (LE, E = O, S, Se), their interaction with the uranyl ion, and their complexation free energies. Surprisingly, contrary to the expected order of covalency, i.e. An–LSe > An–LS > An–LO, our results suggest that the degree of covalency and associated complexation free energies depend on the nature of the coordinating moiety rather than solely on the directly coordinated atom. 1) Sadhu, Biswajit, and Michael Dolg. Enhancing actinide (III) over lanthanide (III) selectivity through hard-by-soft donor substitution: exploitation and implication of near-degeneracy-driven covalency. Inorganic Chemistry, 2019, 58, 9738 – 9748.

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

CaMn 3 IV O 4 Cubane Models of the Oxygen‐Evolving Complex: Spin Ground States S <9/2 and the Effect of Oxo Protonation

Abstract We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn 3 IV O 4 and YMn 3 IV O 4 complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen‐evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin‐state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn 3 IV O 4 complexes and variants with protonated oxo moieties need not be S =9/2. Desymmetrization of the pseudo ‐ C 3 ‐symmetric Ca(Y)Mn 3 IV O 4 core leads to a lower S =5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and an S =3/2 spin ground state is observed in CaMn 3 IV O 3 (OH). Our studies complement the observation that the interconversion between the low‐spin and high‐spin forms of the S 2 state is pH‐dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin‐state changes.

Lee, Heui Beom↗
DOE OSTI2018

Rates of Ligand Exchange around the Bis-Oxalato Complex [NpO 2 (C 2 O 4 ) 2 ] 3- Measured by Using Multinuclear NMR Spectroscopy under Neutral to Semi-Alkaline Conditions [Rates of ligand exchange around the bis-oxalato complex NpO2(C2O4)23- measured using multinuclear NMR at neutral to semi-alkaline conditions]

The kinetics of ligand exchange between the free oxalate ion, C 2 O 4 2- , and the bis-oxalato Np V complex, [NpO 2 (C 2 O 4 ) 2 ] 3- , in aqueous solution are reported by using 13 C and 17 O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5–9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13 C and 17 O signals assigned to the free oxalate ion in solution and by applying the Swift–Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. Finally, at pH<8.0, ΔH ≠ =16.9 ±4.9 kJ mol -1 and ΔS≠=-116.3 ±17.1kJ mol -1 K -1 , whereas at pH>8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.

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

Synthesis, Redox, and Spectroscopic Properties of Pd(II) 10,10-Dimethylisocorrole Complexes Prepared via Bromination of Dimethylbiladiene Oligotetrapyrroles

Two brominated 10,10-dimethylisocorrole (10-DMIC) derivatives containing Pd(II) centers have been prepared and characterized. These compounds were prepared via bromination of 10,10-dimethylbiladiene-based oligotetrapyrroles. Bromination of free base 10,10-dimethylbiladiene (DMBil1) followed by metalation with Pd(OAc) 2 , as well as bromination of the corresponding Pd(II) dimethylbiladiene complex (Pd[DMBil1]) provide routes to Pd(II) hexabromo-10,10-dimethyl-5,15-bis(pentafluorophenyl)-isocorrole (Pd[10-DMIC-Br 6 ]) and Pd(II) octabromo-10,10-dimethyl-5,15-bis(pentafluorophenyl)-isocorrole (Pd[10-DMIC-Br 8 ]). The solid-state structures of the two brominated isocorrole complexes are presented, as is that for a new decabrominated dimethylbiladiene derivative (DMBil-Br 10 ). The electronic and spectroscopic properties of the brominated biladiene and isocorrole derivatives were probed using a combination of voltammetric methods and steady-state UV–vis absorption and emission experiments. Data obtained from these experiments allow the properties of the brominated biladiene and isocorrole derivatives to be compared to previously studied biladiene derivatives (i.e., DMBil1 and Pd[DMBil1]). CV and DPV experiments demonstrate that Pd[10-DMIC-Br 6 ] and Pd[10-DMIC-Br 8 ] support well-behaved multielectron redox chemistry, similar to that which has been observed for other nonaromatic tetrapyrroles containing sp 3 -hybridized meso-carbons. Here, spectroscopic experiments reveal that bromination of the dimethylbiladiene core shifts this system’s UV–vis absorption profile to lower energy and that the dimethylisocorrole complexes support panchromatic absorption profiles that extend across the UV–vis and into the near-IR region. Photosensitization experiments demonstrate that unlike previously studied Pd(II) biladiene constructs, DMBil-Br 10 , Pd[10-DMIC-Br 6 ], and Pd[10-DMIC-Br 8 ] support limited triplet excited state chemistry with O 2 , indicating that the novel nonaromatic tetrapyrrole derivatives described in this work may be best suited for applications other than singlet oxygen sensitization.

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

Homoleptic Perchlorophenyl “Ate” Complexes of Thorium(IV) and Uranium(IV)

The reaction of AnCl 4 (DME) n (An = Th, n = 2; U, n = 0) with 5 equiv of LiC 6 Cl 5 in Et 2 O resulted in the formation of homoleptic actinide-aryl “ate” complexes [Li(DME) 2 (Et 2 O)] 2 [Li(DME) 2 ][Th(C 6 Cl 5 ) 5 ] 3 ([Li][1]) and [Li(Et 2 O) 4 ][U(C 6 Cl 5 ) 5 ] ([Li][2]). Similarly, the reaction of AnCl 4 (DME)n (An = Th, n = 2; U, n = 0) with 3 equiv of LiC 6 Cl 5 in Et 2 O resulted in the formation of heteroleptic actinide-aryl “ate” complexes [Li(DME) 2 (Et 2 O)][Li(Et 2 O) 2 ][ThCl 3 (C 6 Cl 5 ) 3 ] ([Li][3]) and [Li(Et 2 O) 3 ][UCl 2 (C 6 Cl 5 ) 3 ] ([Li][4]). Density functional calculations show that the An–C ipso σ-bonds are considerably more covalent for the uranium complexes vs the thorium analogues, in line with past results. Additionally, good agreement between experiment and calculations is obtained for the 13 C ipso NMR chemical shifts in [Li][1] and [Li][3]. Here, the calculations demonstrate a deshielding by ca. 29 ppm from spin–orbit coupling effects originating at Th, which is a direct consequence of 5f orbital participation in the Th–C bonds.

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

Cyclotrimerization of Acetylene in Gas Phase V + (C 2 H 2 ) n Complexes: Detection of Intermediates and Products with Infrared Spectroscopy

Infrared laser spectroscopy and mass spectrometry were used to determine the structures of intermediates and products in the single-atom-catalyzed trimerization of acetylene to form benzene. Complexes of the form V + (C 2 H 2 ) n were produced in the gas phase via laser ablation in a pulsed-nozzle source, size-selected with a mass spectrometer, and studied with infrared laser photodissociation spectroscopy. Density Functional Theory (DFT) calculations were performed in support of the experiments. Single- and doub le-acetylene complexes form V + (C 2 H 2 ) n metallacycle structures. Three-acetylene complexes exhibit a surprising dependence on the acetylene concentration, forming V + (C 2 H 2 ) 3 and (C 2 H 2 )V + (C 4 H 4 ) tri- and dimetallacycle ion structures at low concentration, and eventually V + (benzene) at higher concentrations. Finally, these observations reveal intermediates along the reaction path of acetylene cyclotrimerization to benzene.

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

Computing the Relative Affinity of Chlorophylls a and b to Light-Harvesting Complex II

In plants and algae, the primary antenna protein bound to photosystem II is light-harvesting complex II (LHCII), a pigment–protein complex that binds eight chlorophyll (Chl) a molecules and six Chl b molecules. Chl a and Chl b differ only in that Chl a has a methyl group (–CH 3 ) on one of its pyrrole rings, while Chl b has a formyl group (–CHO) at that position. This blue-shifts the Chl b absorbance relative to Chl a . It is not known how the protein selectively binds the right Chl type at each site. Knowing the selection criteria would allow the design of light-harvesting complexes that bind different Chl types, modifying an organism to utilize the light of different wavelengths. The difference in the binding affinity of Chl a and Chl b in pea and spinach LHCII was calculated using multiconformation continuum electrostatics and free energy perturbation. Both methods have identified some Chl sites where the bound Chl type ( a or b ) has a significantly higher affinity, especially when the protein provides a hydrogen bond for the Chl b formyl group. However, the Chl a sites often have little calculated preference for one Chl type, so they are predicted to bind a mixture of Chl a and b . The electron density of the spinach LHCII was reanalyzed, which, however, confirmed that there is negligible Chl b in the Chl a -binding sites. Finally, it is suggested that the protein chooses the correct Chl type during folding, segregating the preferred Chl to the correct binding site.

chemical calculations↗
DOE OSTI2016

X-ray Emission Spectroscopy of Mn Coordination Complexes Toward Interpreting the Electronic Structure of the Oxygen-Evolving Complex of Photosystem II

X-ray emission (XES) spectroscopy is an attractive technique for analysis of the electronic structure of molecules, materials, and metalloproteins. However, a better understanding of XES results is required. Using a combination of experiment and ground-state density functional theory analysis, we rationalize differences in the X-ray emission spectra of multinuclear Mn complexes. Model compounds, including dinuclear [Mn 2 O 2 L' 4 ](ClO 4 ) 3 (L'= 2,2'-bipyridyl, [1]) and two examples from the Mn 4 O 4 L 6 “cubane” family of model compounds (L = (p-R-C 6 H 4 )PO 2 – , R = OCH 3 [2], CH3 [3] ), were compared with the Oxygen Evolving Complex of Photosystem II. Our analysis demonstrates that changes in the structure of the Mn complexes, resulting in changes to the spin polarization, can introduce significant spectral shifts in compounds of the same formal redox state. The implications of changes in spin polarization for understanding photosynthetic water-splitting catalysis is discussed.

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

Electrochemical Oxidation of Metal–Catechol Complexes as a New Synthesis Route to the High-Quality Ternary Photoelectrodes: A Case Study of Fe 2 TiO 5 Photoanodes

A new electrochemical, solution-based synthesis method to prepare uniform multinary oxide photoelectrodes was developed. This method involves solubilizing multiple metal ions as metal-catechol complexes in a pH condition where they are otherwise insoluble. When some of the catechol ligands are electrochemically oxidized, the remaining metal complexes become insoluble and are deposited as metal-catechol films on the working electrode. The resulting films are then annealed to form crystalline multinary oxide electrodes. Since catechol can serve as a complexing agent for a variety of metal ions, the newly developed method can be used to prepare a variety of multinary oxide films. In the present study, we used this method to prepare n-type Fe 2 TiO 5 photoanodes and investigated their photoelectrochemical properties for use in a photoelectrochemical water splitting cell. We also performed a computational investigation with two goals. The first goal was to investigate small electron polaron formation in Fe 2 TiO 5 . Charge transport in most oxide photoelectrodes involves small polaron hopping, but small polaron formation in Fe 2 TiO 5 has not been examined prior to this work. The second goal was to investigate the effect of substitutional Sn doping at the Fe site on the electronic band structure and the carrier concentration of Fe 2 TiO 5 . Here, the combined experimental and theoretical results presented in this study greatly improve our understanding of Fe 2 TiO 5 for use as a photoanode.

14 SOLAR ENERGY↗
DOE OSTI2022

Surface Immobilization of a Re(I) Tricarbonyl Phenanthroline Complex to Si(111) through Sonochemical Hydrosilylation

A sonochemical-based hydrosilylation method was employed to covalently attach a rhenium tricarbonyl phenanthroline complex to silicon(111). fac-Re(5-(p-Styrene)-phen)(CO) 3 Cl (5-(p-styrene)-phen = 5-(4-vinylphenyl)-1,10-phenanthroline) was reacted with hydrogen-terminated silicon(111) in an ultrasonic bath to generate a hybrid photoelectrode. Subsequent reaction with 1-hexene enabled functionalization of remaining atop Si sites. Attenuated total reflectance–Fourier transform infrared spectroscopy confirms attachment of the organometallic complex to silicon without degradation of the organometallic core, supporting hydrosilylation as a strategy for installing coordination complexes that retain their molecular integrity. Detection of Re(I) and nitrogen by X-ray photoelectron spectroscopy (XPS) further support immobilization of fac-Re(5-(p-styrene)-phen)(CO) 3 Cl. Cyclic voltammetry and electrochemical impedance spectroscopy under white light illumination indicate that fac-Re(5-(p-styrene)-phen)(CO) 3 Cl undergoes two electron reductions. Mott–Schottky analysis indicates that the flat band potential is 239 mV more positive for p-Si(111) co-functionalized with both fac-Re(5-(p-styrene)-phen)(CO) 3 Cl and 1-hexene than when functionalized with 1-hexene alone. XPS, ultraviolet photoelectron spectroscopy, and Mott–Schottky analysis show that functionalization with fac-Re(5-(p-styrene)-phen)(CO) 3 Cl and 1-hexene introduces a negative interfacial dipole, facilitating reductive photoelectrochemistry.

X-ray photoelectron spectroscopy↗