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921.
Sieber A Boskovic C Bircher R Waldmann O Ochsenbein ST Chaboussant G Güdel HU Kirchner N van Slageren J Wernsdorfer W Neels A Stoeckli-Evans H Janssen S Juranyi F Mutka H 《Inorganic chemistry》2005,44(12):4315-4325
A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1. 相似文献
922.
923.
Kayed A. Abu Safieh Ahmad M. Abu Mahthieh Mustafa M. El-Abadelah Mikdad T. Ayoub Wolfgang Voelter 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):157-160
Summary. A novel method for the synthesis of a new series of 5-substituted 1,3-dimethyl pyrazolo[4,3-e][1,2,4]triazines is described. The new synthetic strategy is based on the classical Bischler 1,2,4-benzotriazine synthesis. This approach involves the preparation of 5-hydrazinopyrazole from 5-chloro-1,3-dimethyl-4-nitropyrazole
followed by acylation and nitro group reduction to form the corresponding 4-amino-3-(acylhydrazino)pyrazoles. Intramolecular
oxidative cyclization of the latter derivatives, using polyphosphoric acid, produced the respective target pyrazolotriazines. 相似文献
924.
Single crystals of Li4(PO2NH)4 · 4 H2O were obtained by dissolving LiOH and H4(PO2NH)4 · 2 H2O in water and subsequent precipitation with acetone and ethanol followed by slow evaporation of the solvents. The structure of Li4(PO2NH)4 · 4 H2O was solved by single‐crystal X‐ray methods ( (No. 2), a = 489.2(2), b = 853.2(2), c = 880.5(2) pm, α = 101.71(3), β = 102.39(3), γ = 94.88(3)°, Z = 1). The structure is composed of LiO4 tetrahedra and (PO2NH)44? ions. The P4N4 rings of the anions exhibit a slightly distorted chair–1 conformation, which is supported by IR data and has been described by torsion angles, displacement asymmetry parameters and puckering parameters. Via Li+ ions and hydrogen bonds, the tetrametaphosphimate anions are connected forming a three‐dimensional network. 相似文献
925.
Kraft S Hanuschek E Beckhaus R Haase D Saak W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(3):969-978
This paper reports on the potential of titanium compounds as building blocks for supramolecular polygons. Self-assembly reactions of low-valent titanocene units and N-heterocyclic bridging ligands lead to novel titanium-based supramolecular squares. Pyrazine (3), 4,4'-bipyridine (4), and tetrazine (5) were used as bridging ligands, and the acetylene complexes [Cp2Ti{eta2-C2(SiMe3)2}] (1) and [(tBuCp)2Ti{eta2-C2(SiMe3)2}] (2) as sources of titanocene fragments. Molecular rectangles can be synthesized by stepwise reduction of the titanocene dichlorides [Cp(2)TiCl2] and [(tBuCp)2TiCl2] and consecutive coordination of two different bridging ligands. The resulting complexes are the first examples of molecular rectangles containing bent metallocene corner units. Single-crystal X-ray analyses of the tetranuclear compounds revealed the geometric properties of the molecular polygons in the solid state. Comparison of bond lengths and angles in coordinated and free ligands reveals the reduced state of the bridging ligand in the low-valent titanium compounds. The syntheses and properties of these novel, highly air- and moisture-sensitive compounds are discussed. 相似文献
926.
Wolfgang Arendt Giorgio Metafune 《Journal of Mathematical Analysis and Applications》2008,338(1):505-517
We consider a strictly elliptic operator
927.
Céline Degrande Nicolas Greiner Wolfgang Kilian Olivier Mattelaer Harrison Mebane Tim Stelzer Scott Willenbrock Cen Zhang 《Annals of Physics》2013
We advocate an effective field theory approach to anomalous couplings. The effective field theory approach is the natural way to extend the standard model such that the gauge symmetries are respected. It is general enough to capture any physics beyond the standard model, yet also provides guidance as to the most likely place to see the effects of new physics. The effective field theory approach also clarifies that one need not be concerned with the violation of unitarity in scattering processes at high energy. We apply these ideas to pair production of electroweak vector bosons. 相似文献
928.
Dr. Matthias C. Witschel Dr. H. Wolfgang Höffken Michael Seet Dr. Liliana Parra Thomas Mietzner Frank Thater Dr. Ricarda Niggeweg Dr. Franz Röhl Dr. Boris Illarionov Dr. Felix Rohdich Dr. Johannes Kaiser Prof. Dr. Markus Fischer Prof. Dr. Adelbert Bacher Prof. Dr. François Diederich 《Angewandte Chemie (International ed. in English)》2011,50(34):7931-7935
929.
We consider the problem of finding the spectrum of an n × n matrix which arises in the study of a certain model of long-range interactions in a one-dimensional statistical mechanics
system. Our analysis exhibits a curious resemblance of the suitably normalized distribution of eigenvalues to the Marčenko–Pastur
law in the limit n → ∞. 相似文献
930.
Fundamental and practical aspects in the design of nanoscaled SnO2 gas sensors: a status report 总被引:2,自引:0,他引:2
N. Barsan Markus Schweizer-Berberich Wolfgang G?pel 《Fresenius' Journal of Analytical Chemistry》1999,365(4):287-304
Gas sensors based on semiconducting materials have become of great interest to both sensor users and researchers. In this
context, a huge number of publications have appeared in the literature which deal with metal oxide gas sensors, in general,
and with the prototype material SnO2, in particular. The amount of data published grows continuously and has led to a situation in which even experts in this
field tend to lose an overview. The present review describes the reasons for this complexity and outlines unifying concepts
to understand the huge amount of published, mostly empirical data. This leads to a comprehension of gas-sensing phenomena
in both the application and research domains.
Received: 7 December 1998 / Revised: 6 May 1999 / Accepted: 19 May 1999 相似文献