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11.
Jun‐Liang Liu Kasper S. Pedersen Samuel M. Greer Itziar Oyarzabal Abhishake Mondal Stephen Hill Fabrice Wilhelm Andrei Rogalev Alain Tressaud Etienne Durand Jeffrey R. Long Rodolphe Clrac 《Angewandte Chemie (International ed. in English)》2020,59(26):10306-10310
Silicon‐mediated fluoride abstraction is demonstrated as a means of generating the first fluorido‐cyanido transition metal complexes. This new synthetic approach is exemplified by the synthesis and characterization of the heteroleptic complexes, trans‐[MIVF4(CN)2]2? (M=Re, Os), obtained from their homoleptic [MIVF6]2? parents. As shown by combined high‐field electron paramagnetic resonance spectroscopy and magnetization measurements, the partial substitution of fluoride by cyanide ligands leads to a marked increase in the magnetic anisotropy of trans‐[ReF4(CN)2]2? as compared to [ReF6]2?, reflecting the severe departure from an ideal octahedral (Oh point group) ligand field. This methodology paves the way toward the realization of new heteroleptic transition metal complexes that may be used as highly anisotropic building‐blocks for the design of high‐performance molecule‐based magnetic materials. 相似文献
12.
Rational Electrostatic Design of Easy‐Axis Magnetic Anisotropy in a ZnII–DyIII–ZnII Single‐Molecule Magnet with a High Energy Barrier
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Itziar Oyarzabal Prof. Dr. José Ruiz Prof. Dr. José Manuel Seco Dr. Marco Evangelisti Dr. Agustín Camón Prof. Dr. Eliseo Ruiz Dr. Daniel Aravena Prof. Dr. Enrique Colacio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14262-14269
Two novel trinuclear complexes [ZnCl(μ‐L)Ln(μ‐L)ClZn][ZnCl3(CH3OH)]?3 CH3OH (LnIII=Dy ( 1 ) and Er ( 2 )) have been prepared from the compartmental ligand N,N′‐dimethyl‐N,N′‐bis(2‐hydroxy‐3‐formyl‐5‐bromo‐benzyl)ethylenediamine (H2L). X‐ray studies reveal that LnIII ions are coordinated by two [ZnCl(L)]? units through the phenoxo and aldehyde groups, giving rise to a LnO8 coordination sphere with square‐antiprism geometry and strong easy‐axis anisotropy of the ground state. Ab initio CASSCF+RASSI calculations carried out on 1 confirm that the ground state is an almost pure MJ=±15/2 Kramers doublet with a marked axial anisotropy, the magnetic moment is roughly collinear with the shortest Dy?O distances. This orientation of the local magnetic moment of the DyIII ion in 1 is adopted to reduce the electronic repulsion between the oblate electron shape of the MJ=±15/2 Kramers doublet and the phenoxo‐oxygen donor atoms involved in the shortest Dy?O bonds. CASSCF+RASSI calculations also show that the ground and first excited states of the DyIII ion are separated by 129 cm?1. As expected for this large energy gap, compound 1 exhibits, in a zero direct‐current field, thermally activated slow relaxation of the magnetization with a large Ueff=140 K. The isostructural Zn–Er–Zn species does not present significant SMM behavior as expected for the prolate electron‐density distribution of the ErIII ion leading to an easy‐plane anisotropy of the ground doublet state. 相似文献
13.
A new DNA hybridization assay in microwell format for detection of Listeria spp. in foods and environmental samples was developed. This assay uses Listeria-specific oligonucleotide probes labeled with horseradish peroxidase and a photometrically determined end point. Validation studies with 15 different food commodities and a variety of environmental sample types were conducted to compare the performance of this alternative test versus reference methods. Meats, seafood, dairy products, and vegetables comprised the categories of food tested. Food samples were inoculated at 2 levels and refrigerated or frozen for at least 72 h. Uninoculated (negative) control samples were included in each trial. Samples were enriched according to the procedure recommended by either the U.S. Food and Drug Administration (FDA) or the U.S. Department of Agriculture (USDA), Food Safety and Inspection Service (FSIS). Samples enriched for 24 h were transferred to Oxford agar plates and incubated for 24 h. The surface of the plates was then swabbed and any growth present was transferred to phosphate buffer solution for the performance of the DNA assay. A standard confirmation procedure was used to compare the number of positive samples obtained with the DNA method versus reference methods. Statistical analyses of the results indicate that the proposed alternative method performs equally to cultural reference methods. The DNA assay is able to detect as low as 1 colony-forming unit of Listeria in a 25 g food sample, with results available as early as 48 h after the start of sample enrichment. 相似文献
14.
Analysis of the Role of Peripheral Ligands Coordinated to ZnII in Enhancing the Energy Barrier in Luminescent Linear Trinuclear Zn‐Dy‐Zn Single‐Molecule Magnets
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Dr. Jean Pierre Costes Dr. Silvia Titos‐Padilla Itziar Oyarzabal Tulika Gupta Dr. Carine Duhayon Prof. Gopalan Rajaraman Prof. Enrique Colacio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15785-15796
Three new Dy complexes have been prepared according to a complex‐as‐ligand strategy. Structural determinations indicate that the central Dy ion is surrounded by two LZn units (L2? is the di‐deprotonated form of the N2O2 compartmental N,N′‐2,2‐dimethylpropylenedi(3‐methoxysalicylideneiminato) Schiff base. The Dy ions are nonacoordinate to eight oxygen atoms from the two L ligands and to a water molecule. The Zn ions are pentacoordinate in all cases, linked to the N2O2 atoms from L, and the apical position of the Zn coordination sphere is occupied by a water molecule or bromide or chloride ions. These resulting complexes, formulated (LZnX)‐Dy‐(LZnX), are tricationic with X=H2O and monocationic with X=Br or Cl. They behave as field‐free single‐molecule magnets (SMMs) with effective energy barriers (Ueff) for the reversal of the magnetization of 96.9(6) K with τ0=2.4×10?7 s, 146.8(5) K with τ0=9.2×10?8 s, and 146.1(10) K with τ0=9.9×10?8 s for compounds with Zn?OH2, Zn?Br, and Zn?Cl motifs, respectively. The Cole–Cole plots exhibit semicircular shapes with α parameters in the range of 0.19 to 0.29, which suggests multiple relaxation processes. Under a dc applied magnetic field of 1000 Oe, the quantum tunneling of magnetization (QTM) is partly or fully suppressed and the energy barriers increase to Ueff=128.6(5) K and τ0=1.8×10?8 s for 1 , Ueff=214.7 K and τ0=9.8×10?9 s for 2 , and Ueff=202.4 K and τ0=1.5×10?8 s for 3 . The two pairs of largely negatively charged phenoxido oxygen atoms with short Dy?O bonds are positioned at opposite sides of the Dy3+ ion, which thus creates a strong crystal field that stabilizes the axial MJ=±15/2 doublet as the ground Kramers doublet. Although the compound with the Zn?OH2 motifs possesses the larger negative charges on the phenolate oxygen atoms, as confirmed by using DFT calculations, it exhibits the larger distortions of the DyO9 coordination polyhedron from ideal geometries and a smaller Ueff value. Ab initio calculations support the easy‐axis anisotropy of the ground Kramers doublet and predict zero‐field SMM behavior through Orbach and TA‐QTM relaxations via the first excited Kramers doublet, which leads to large energy barriers. In accordance with the experimental results, ab initio calculations have also shown that, compared with water, the peripheral halide ligands coordinated to the Zn2+ ions increase the barrier height when the distortions of the DyO9 have a negative effect. All the complexes exhibit metal‐centered luminescence after excitation into the UV π–π* absorption band of ligand L2? at λ=335 nm, which results in the appearance of the characteristic DyIII (4F9/2→6HJ/2; J=15/2, 13/2) emission bands in the visible region. 相似文献
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[reaction: see text] A simple method for the preparation of fluoroalkyl allylamines or alpha,beta-unsaturated ketones by an olefination reaction of primary enamine phosphonates and aldehydes, followed by selective reduction with hydrides or hydrolysis, is reported. Fluorinated beta-amino nitriles are also obtained by an olefination reaction of primary enamine phosphonates with aldehydes and subsequent addition of metalated acetonitrile. 相似文献
17.
Dr. Jun-Liang Liu Prof. Dr. Kasper S. Pedersen Dr. Samuel M. Greer Dr. Itziar Oyarzabal Dr. Abhishake Mondal Prof. Dr. Stephen Hill Dr. Fabrice Wilhelm Dr. Andrei Rogalev Dr. Alain Tressaud Etienne Durand Prof. Dr. Jeffrey R. Long Dr. Rodolphe Clérac 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10392-10396
Silicon-mediated fluoride abstraction is demonstrated as a means of generating the first fluorido-cyanido transition metal complexes. This new synthetic approach is exemplified by the synthesis and characterization of the heteroleptic complexes, trans-[MIVF4(CN)2]2− (M=Re, Os), obtained from their homoleptic [MIVF6]2− parents. As shown by combined high-field electron paramagnetic resonance spectroscopy and magnetization measurements, the partial substitution of fluoride by cyanide ligands leads to a marked increase in the magnetic anisotropy of trans-[ReF4(CN)2]2− as compared to [ReF6]2−, reflecting the severe departure from an ideal octahedral (Oh point group) ligand field. This methodology paves the way toward the realization of new heteroleptic transition metal complexes that may be used as highly anisotropic building-blocks for the design of high-performance molecule-based magnetic materials. 相似文献