Homoleptic uranium(IV) amidate complexes have been synthesized and applied as single‐source molecular precursors for the chemical vapor deposition of UO2 thin films. These precursors decompose by ...alkene elimination to give highly crystalline phase‐pure UO2 films with an unusual branched heterostructure.
UO2 nanotree: Volatile uranium(IV) amidate complexes are used as single‐source molecular precursors to uranium oxide films. Chemical vapor deposition (CVD) of these single‐source precursors yields crystalline, phase‐pure UO2 films with a fir tree‐like microstructure and a high surface area.
Two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA)3 (2) with KC8 yields the anionic bis(arene) complex K2.2.2cryptandU(TDA)2 (3) (TDA = ...N-(2,6-di-isopropylphenyl)pivalamido). EPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a two-electron reductant toward I2 to form the dinuclear U(III)–U(III) triiodide species K2.2.2cryptand(UI(TDA)2)2(μ-I) (6) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex K2.2.2cryptandU(η7-C7H7)(TDA)2(THF) (7). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion K2.2.2cryptandU(TDA)4 (1-crypt) and U(COT)2, while the addition of COT to complex 2 instead yields the dinuclear U(IV)–U(IV) inverse sandwich complex U(TDA)32(μ-η8:η3-C8H8) (8). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA)4 (4) with KC8 gives the mono(arene) complex K2.2.2cryptandTh(TDA)3(THF) (5). The C–C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.
Uranium nitride complexes are attractive targets for chemists as molecular models for the bonding, reactivity, and magnetic properties of next-generation nuclear fuels, but these molecules are ...uncommon and can be difficult to isolate due to their high reactivity. Here, we describe the synthesis of three new multinuclear uranium nitride complexes, U(BCMA)22(μ-N)(μ-κ1:κ1-BCMA) (7), (U(BIMA)2)2(μ-N)(μ-N i Pr)(K2(μ-η3:η3-CH2CHN i Pr)2 (8), and U(BIMA)22(μ-N)(μ-κ1:κ1-BIMA) (9) (BCMA = N,N-bis(cyclohexyl)methylamidinate, BIMA = N,N-bis(iso-propyl)methylamidinate), from U(III) and U(IV) amidinate precursors. By varying the amidinate ligand substituents and azide source, we were able to influence the composition and size of these nitride complexes. 15N isotopic labeling experiments confirmed the bridging nitride moieties in 7–9 were formed via two-electron reduction of azide. The tetra-uranium cluster 8 was isolated in 99% yield via reductive cleavage of the amidinate ligands; this unusual molecule contains nitrogen-based ligands with formal 1–, 2–, and 3– charges. Additionally, chemical oxidation of the U(IV) precursor U(N3)(BCMA)3 yielded the cationic U(V) species U(N3)(BCMA)3OTf. Magnetic susceptibility measurements confirmed a U(IV) oxidation state for the uranium centers in the three nitride-bridged complexes and provided a comparison of magnetic behavior in the structurally related U(III)-U(IV)-U(V) series U(BCMA)3, U(N3)(BCMA)3, and U(N3)(BCMA)3OTf. At 240 K, the magnetic moments in this series decreased with increasing oxidation state, i.e., U(III) > U(IV) > U(V); this trend follows the decreasing number of 5f valence electrons along this series.
EXAFS provides the capability to interrogate nanoparticle (NP) structure in atomistic detail without relying on long‐range crystallinity. There is a limitation in that EXAFS provides averaged ...structural information, making it difficult to separate a small amount of heterogeneous structure from bulk. In this work, models were developed to extract surface‐specific information from conventional EXAFS measurements collected on UO2 NPs of varying size. Specifically, the surface terminating species of UO2 NPs was determined from comparison of coordination numbers with geometric models while the origin of static disorder was interrogated from user‐defined simulations. Results show that the degree of oxygenation on the NP surface does not significantly deviate from bulk surface and that static disorder is highly enhanced in NP surface layers but cannot be attributed to surface relaxation effects alone. The approach described herein has the potential to be adapted to a range of inorganic NP systems to interrogate surface structure.
Various sizes of UO2 NPs were modeled with user‐defined parameters considering surface termination effect, relaxation, and disorder. The surface coordination of the NPs was backtracked by comparing the EXAFS simulated from the model with actual EXAFS experimental data.
Oral health knowledge among elderly patients McQuistan, Michelle R; Qasim, Assad; Shao, Chong ...
The Journal of the American Dental Association (1939)
146, Številka:
1
Journal Article
Recenzirano
The purpose of this study was to determine the level of oral health knowledge among patients 65 years or older to identify areas in which knowledge gaps exist.
The authors administered the ...Comprehensive Measure of Oral Health Knowledge questionnaire to patients 65 years or older at a university-based dental clinic and examined associations between oral health knowledge scores and participants' demographic and dental characteristics.
Most participants were familiar with basic dental disease prevention and treatment; however, many participants were unfamiliar with concepts pertaining to periodontal disease, oral cancer, and children's oral health.
Advocates for geriatric oral health should educate elderly populations about the risk factors associated with periodontal disease and oral cancer, especially as they become more at risk of experiencing these diseases.
Educational messages aimed at both routine and nonroutine users of dental care should be developed on the basis of universal health literacy principles to facilitate understanding among elderly adults, who have varying literacy levels.
We report the structural properties of ultra-small ThO
2
and UO
2
nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) ...as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior. Characterization using electron microscopy and small-angle X-ray scattering indicates that growth of the ThO
2
and UO
2
NPs was confined by the pores of the COF template, resulting in sub-3 nm particles. X-ray absorption fine structure spectroscopy results indicate that the NPs are best described as ThO
2
and UO
2
materials with unpassivated surfaces. The surface layers of these particles compensate for high surface energy by exhibiting a broader distribution of Th-O and U-O bond distances despite retaining average bond lengths that are characteristic of bulk ThO
2
and UO
2
. The combined synthesis and physical characterization efforts provide a detailed picture of actinide oxide structure at the nanoscale, which remains highly underexplored compared to transition metal counterparts.
ThO
2
and UO
2
nanoparticles synthesized using a COF-5 template exhibit unpassivated surfaces and provide insight into nanoscale properties of actinides.
We report the synthesis of four homoleptic thorium(
iv
) amidate complexes as single-source molecular precursors for thorium dioxide. Each can be sublimed at atmospheric pressure, with the ...substituents on the amidate ligands significantly impacting their volatility and thermal stability. These complexes decompose
via
alkene elimination to give ThO
2
without need for a secondary oxygen source. ThO
2
samples formed from pyrolysis of
C
-alkyl amidates were found to have higher purity and crystallinity than ThO
2
samples formed from
C
-aryl amidates.
Volatile thorium amidates can be converted to ThO
2
in the absence of an external oxygen source, and the thermal properties of these precursors can be readily tuned by modifying the ligand substituents.
Carbon dioxide must be removed from the atmosphere to limit climate change to 2°C or less. The integrated assessment models used to develop climate policy acknowledge the need to implement net ...negative carbon emission strategies, including bioenergy with carbon capture and storage (BECCS), to meet global climate imperatives. The implications of BECCS for the food, water, energy, biodiversity, and social systems (FWEBS) nexus at regional scales, however, remain unclear. Here, we present an interdisciplinary research framework to examine the trade-offs as well as the opportunities among BECCS scenarios and FWEBS on regional scales using the Upper Missouri River Basin (UMRB) as a case study. We describe the physical, biological, and social attributes of the UMRB, and we use grassland bird populations as an example of how biodiversity is influenced by energy transitions, including BECCS. We then outline a “conservation” BECCS strategy that incorporates societal values and emphasizes biodiversity conservation.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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