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211.
212.
The use of 1,2‐diselenolato‐1,2‐dicarba‐closo‐dodecaborane(12) dianions [1,2‐(1,2‐C2B10H10)Se2]2? prepared in situ as the dilithium salt may lead to irreproducible results. This is shown by the straightforward synthesis of silanes using the purified and isolated dianions, in contrast with previous less successful attempts. Thus, the reactions of the dianions with dichlorosilanes afford the five‐membered diselenasila cycles containing the SiMe2 or the SiPh2 units, and with 1,2‐dichloro‐tetramethyldisilane the six‐membered cycle containing the Si2Me4 unit. The latter was studied by X‐ray diffraction, and all products were characterized by multinuclear magnetic resonance (1H, 13C, 29Si, 77Se NMR) in solution. Novel isotope effects were detected in 13C and 77Se NMR spectra. Exchange reactions of the five‐ and six‐membered diselanasila cycles with chlorosilanes were studied. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
213.
Resch Laura Karner Anna Sprengel Wolfgang Wrschum Roland Schennach Robert 《Cellulose (London, England)》2022,29(3):1357-1363
Cellulose - In this study, for the first time, the experimental technique of positron annihilation lifetime spectroscopy (PALS) has been applied to monitor in situ the microstructural changes of... 相似文献
214.
Dr. Somnath Dey Dr. Andreas Schönleber Prof. Dr. Sander van Smaalen Dr. Wolfgang Morgenroth Prof. Dr. Finn Krebs Larsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202104151
Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C12H30N8)]3+ ⋅ 3 NO3− is reported to undergo a disorder-order phase transition at Tc1 ≈133 K upon cooling. Temperature-dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below Tc1. The modulation wave vector varies as function of temperature and locks in at Tc3≈98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in Tc1<T<Tc3. Distinctive levels of competitions: trade-off between longer N−H⋅⋅⋅O and shorter C−H⋅⋅⋅O hydrogen bonds; steric constraints to dense C−H⋅⋅⋅O bonds give rise to pronounced modulation of the basic structure. Severely frustrated crystal packing in the incommensurate phase is precursor to optimal balance of intermolecular interactions in the lock-in phase. 相似文献
215.
Olesia I. Kucheriv Dr. Sergii I. Shylin Valerii Y. Sirenko Dr. Vadim Ksenofontov Prof. Wolfgang Tremel Dr. Ioan-Andrei Dascălu Dr. Sergiu Shova Dr. Il'ya A. Gural'skiy 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(44):e202200924
Spin-crossover complexes with multistep transitions attract much attention due to their potential applications as multi-switches and for data storage. A four-step spin crossover is observed in the new iron(II)-based cyanometallic guest-free framework compound Fe(2-ethoxypyrazine)2{Ag(CN)2}2 during the transition from the low-spin to the high-spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct FeII sites which exist due to the packing of the ligand with a bulky substituent. 相似文献
216.
Dr. Dominique Laniel Dr. Florian Trybel Dr. Adrien Néri Yuqing Yin Andrey Aslandukov Dr. Timofey Fedotenko Saiana Khandarkhaeva Dr. Ferenc Tasnádi Dr. Stella Chariton Dr. Carlotta Giacobbe Dr. Eleanor Lawrence Bright Dr. Michael Hanfland Dr. Vitali Prakapenka Prof. Dr. Wolfgang Schnick Prof. Dr. Igor A. Abrikosov Prof. Dr. Leonid Dubrovinsky Prof. Dr. Natalia Dubrovinskaia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202201998
Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. These properties mainly rely on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly attractive. In this study, the phosphorus–nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells, and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. δ-P3N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two compounds are ultra-incompressible, having a bulk modulus of K0=322 GPa for δ-P3N5 and 339 GPa for PN2. Upon decompression below 7 GPa, δ-P3N5 undergoes a transformation into a novel α′-P3N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of α′-P3N5 underlines that a phase space otherwise inaccessible can be explored through materials formed under high pressure. 相似文献
217.
Patrícia Homobono Brito de Moura Wolfgang Brandt Andrea Porzel Roberto Carlos Campos Martins Ivana Correa Ramos Leal Ludger A. Wessjohann 《Molecules (Basel, Switzerland)》2022,27(8)
A rare dihydoxyflavan-epicatechin proanthocyanidin, entcassiflavan-(4β→8)-epicatechin, was isolated from Dalbergia monetaria, a plant widely used by traditional people from the Amazon to treat urinary tract infections. The constitution and relative configuration of the compound were elucidated by HR-MS and detailed 1D- and 2D-NMR measurements. By comparing the experimental electronic circular dichroism (ECD) spectrum with the calculated ECD spectra of all 16 possible isomers, the absolute configuration, the interflavan linkage, and the atropisomers could be determined. 相似文献
218.
Dr Martin Seah, NPL, was the initiator, founder, and first chairman of the Surface Analysis Working Group (SAWG) at the Consultative Committee for Amount of Substance, Metrology in Chemistry and Biology (CCQM) at the Bureau International des Poids et Mesures (BIPM), the international organization established by the Metre Convention. This tribute letter summarizes his achievements during his chairmanship and his long-running impact on the successful work of the group after his retirement. 相似文献
219.
Olga Yuryevna Ridzel Henryk Kalbe Vytautas Astašauskas Pavel Kuksa Alessandra Bellissimo Wolfgang S. M. Werner 《Surface and interface analysis : SIA》2022,54(5):487-500
Reflection electron energy loss spectroscopy (REELS) spectra were measured for seven insulating organic compounds (DNA, Irganox 1010, Kapton, polyethylene [PE], poly(methyl methacrylate) [PMMA], polystyrene [PS] and polytetrafluoroethylene [PTFE]). Optical constants and energy band gaps were extracted from the measured REELS spectra after elimination of multiple electron scattering via a deconvolution and fitting the normalised single scattering energy loss spectra to Drude and Drude–Lindhard model dielectric functions, constrained by the Kramers–Kronig sum and f-sum rules. Satisfactory agreement is found for those optical constants for which literature data exists. For PTFE, the observed features in the optical data correspond to its electronic structure. 相似文献
220.
Wolfgang S.M. Werner Fabian Helmberger Manuel Schürrer Christoph Eisenmenger-Sittner Olga Y. Ridzel 《Surface and interface analysis : SIA》2022,54(7):681-687
Reflection electron energy loss spectra (REELS) were measured for five insulating organic compounds: Kapton, polyethylene (PE), poly(methyl methacrylate) (PMMA), polystyrene (PS) and polytetrafluoroethylene (PTFE), as well as for Ni and Si, in the energy range between 200 and 1600 eV. The average number of surface excitations for a single surface crossing were determined from the experimental data and were found to be considerably smaller than for earlier studied materials, which mainly consisted of elemental metals [Surf. Sci. 486(2001)L461]. The surface excitation parameter, a material parameter used to quantify the relative intensity of surface losses in (photo)electron spectroscopy, was extracted from the data and compared with values found in the literature. The results indicate that surface excitations only have a minor influence on quantification of XPS spectra of polymers. On the other hand, a correction for surface excitations turns out to be essential for measurements of the electron inelastic mean free path of polymers when a metal is used as reference material. 相似文献