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21.
Dr. Robert F. Higgins Dr. Thibault Cheisson Dr. Bren E. Cole Dr. Brian C. Manor Dr. Patrick J. Carroll Prof. Eric J. Schelter 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(5):1867-1872
The separation of rare-earth ions from one another is challenging due to their chemical and physical similarities. Nearly all rare-earth separations rely upon small changes in ionic radii to direct speciation or reactivity. Herein, we show that the intrinsic magnetic properties of the rare-earth ions impact the separations of light/heavy and selected heavy/heavy binary mixtures. Using TriNOx3− ([{(2-tBuNO)C6H4CH2}3N]3−) rare-earth complexes, we efficiently and selectively crystallized heavy rare earths (Tb–Yb) from a mixture with light rare earths (La and Nd) in the presence of an external Fe14Nd2B magnet, concomitant with the introduction of a concentration gradient (decrease in temperature). The optimal separation was observed for an equimolar mixture of La:Dy, which gave an enrichment factor of EFLa:Dy=297±31 for the solid fraction, compared to EFLa:Dy=159±22 in the absence of the field, and achieving a 99.7 % pure Dy sample in one step. These results indicate that the application of a magnetic field can improve performance in a molecular separation system for paramagnetic rare-earth cations. 相似文献
22.
Yusen Qiao Haolin Yin Liane M. Moreau Rulin Feng Robert F. Higgins Brian C. Manor Patrick J. Carroll Corwin H. Booth Jochen Autschbach Eric J. Schelter 《Chemical science》2021,12(10):3558
A series of cerium(iv) mixed-ligand guanidinate–amide complexes, {[(Me3Si)2NC(NiPr)2]xCeIV[N(SiMe3)2]3−x}+ (x = 0–3), was prepared by chemical oxidation of the corresponding cerium(iii) complexes, where x = 1 and 2 represent novel complexes. The Ce(iv) complexes exhibited a range of intense colors, including red, black, cyan, and green. Notably, increasing the number of the guanidinate ligands from zero to three resulted in significant redshift of the absorption bands from 503 nm (2.48 eV) to 785 nm (1.58 eV) in THF. X-ray absorption near edge structure (XANES) spectra indicated increasing f occupancy (nf) with more guanidinate ligands, and revealed the multiconfigurational ground states for all Ce(iv) complexes. Cyclic voltammetry experiments demonstrated less stabilization of the Ce(iv) oxidation state with more guanidinate ligands. Moreover, the Ce(iv) tris(guanidinate) complex exhibited temperature independent paramagnetism (TIP) arising from the small energy gap between the ground- and excited states with considerable magnetic moments. Computational analysis suggested that the origin of the low energy absorption bands was a charge transfer between guanidinate π orbitals that were close in energy to the unoccupied Ce 4f orbitals. However, the incorporation of sterically hindered guanidinate ligands inhibited optimal overlaps between Ce 5d and ligand N 2p orbitals. As a result, there was an overall decrease of ligand-to-metal donation and a less stabilized Ce(iv) oxidation state, while at the same time, more of the donated electron density ended up in the 4f shell. The results indicate that incorporating guanidinate ligands into Ce(iv) complexes gives rise to intense charge transfer bands and noteworthy electronic structures, providing insights into the stabilization of tetravalent lanthanide oxidation states.A series of cerium(iv) mixed-ligand guanidinate-amide complexes, {[(Me3Si)2NC(NiPr)2]xCeIV[N(SiMe3)2]3−x}+ (x = 0−3), was prepared by chemical oxidation and studied spectroscopically and computationally, revealing trends in 4f/5d orbital occupancies. 相似文献
23.
Robert F. Higgins Thibault Cheisson Bren E. Cole Brian C. Manor Patrick J. Carroll Eric J. Schelter 《Angewandte Chemie (International ed. in English)》2020,59(5):1851-1856
The separation of rare‐earth ions from one another is challenging due to their chemical and physical similarities. Nearly all rare‐earth separations rely upon small changes in ionic radii to direct speciation or reactivity. Herein, we show that the intrinsic magnetic properties of the rare‐earth ions impact the separations of light/heavy and selected heavy/heavy binary mixtures. Using TriNOx3? ([{(2‐tBuNO)C6H4CH2}3N]3?) rare‐earth complexes, we efficiently and selectively crystallized heavy rare earths (Tb–Yb) from a mixture with light rare earths (La and Nd) in the presence of an external Fe14Nd2B magnet, concomitant with the introduction of a concentration gradient (decrease in temperature). The optimal separation was observed for an equimolar mixture of La:Dy, which gave an enrichment factor of EFLa:Dy=297±31 for the solid fraction, compared to EFLa:Dy=159±22 in the absence of the field, and achieving a 99.7 % pure Dy sample in one step. These results indicate that the application of a magnetic field can improve performance in a molecular separation system for paramagnetic rare‐earth cations. 相似文献
24.
Samuel Braverman Haim Manor 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):357-365
Abstract The synthesis and reactivity of benzyl trifluoromethanesulfinates have been investigated. These esters are easily and almost quantitatively obtained by selective oxidation of the corresponding sulfenates. A study of their behavior has revealed some unique features. In sharp contrast to benzyl arenesulfinates, which undergo ethanolysis with complete sulfur-oxygen bond fission, the corresponding trifluorornethanesulfinates undergo ethanolysis with exclusive carbon-oxygen bond fission, and with a rate enhancement by a factor of 6 powers of ten. The unusual high reactivity of these esters, comparable to that of the corresponding tosylates, is discussed. A kinetic study of the solvent and substituent effects on the rate of solvolysis has been performed. Also in contrast with benzyl arenesulfinates, these esters undergo facile rearrangement to sulfone on heating in polar nonhydroxylic solvents such as acetonitrile, in high yields. The mechanisms of solvolysis and rearrangement are discussed. 相似文献
25.
Let (X,d
X
) be an n-point metric space. We show that there exists a distribution over non-contractive embeddings into trees f: X → T such that for every x ∈ X, where C is a universal constant. Conversely we show that the above quadratic dependence on log n cannot be improved in general. Such embeddings, which we call maximum gradient embeddings, yield a framework for the design of approximation algorithms for a wide range of clustering problems with monotone costs,
including fault-tolerant versions of k-median and facility location. 相似文献
26.
27.
This paper is devoted to the study of quotients of finite metric spaces. The basic type of question we ask is: Given a finite metric space M and α?1, what is the largest quotient of (a subset of) M which well embeds into Hilbert space. We obtain asymptotically tight bounds for these questions, and prove that they exhibit phase transitions. We also study the analogous problem for embeddings into ?p, and the particular case of the hypercube. 相似文献
28.
Shaoguang Zhang Peng Cui Tianchang Liu Qiuran Wang Thomas J. Longo Laura M. Thierer Brian C. Manor Michael R. Gau Patrick J. Carroll Georgia C. Papaefthymiou Neil C. Tomson 《Angewandte Chemie (International ed. in English)》2020,59(35):15215-15219
Despite their connection to ammonia synthesis, little is known about the ability of iron‐bound, bridging nitrides to form N?H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox‐active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N?H bonds via proton‐coupled electron transfer to generate a μ‐amide product. The structurally analogous μ‐silyl‐ and μ‐borylamide complexes were shown to form from the net insertion of the nitride into the E?H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH3 in high yield through a reaction that engages the redox‐activity of the ligand during PCET. 相似文献
29.
Dr. Devrani Mitra Dr. Hideaki Ogata Prof. Wolfgang Lubitz Brian C. Manor Prof. Thomas B. Rauchfuss Dr. Deborah Byrne Dr. Violaine Bonnefoy Prof. Francis E. Jenney Jr. Prof. Michael W. W. Adams Dr. Yoshitaka Yoda Dr. Ercan Alp Dr. Jiyong Zhao Prof. Stephen P. Cramer 《Angewandte Chemie (International ed. in English)》2013,52(2):724-728
30.
We introduce the notion of the scaled Enflo type of a metricspace, and show that for Banach spaces, scaled Enflo type pis equivalent to Rademacher type p. 相似文献