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排序方式: 共有183条查询结果,搜索用时 31 毫秒
91.
G Bender T Wiegand H Eckert R Fröhlich CG Daniliuc C Mück-Lichtenfeld S Ndambuki T Ziegler G Kehr G Erker 《Angewandte Chemie (International ed. in English)》2012,51(35):8846-8849
An enyne-zirconium complex stabilizes molecular magnesium hydride (MgH(2) ) and even a molecular hydride, nC(4) H(9) MgH. These systems feature magnesium olefin π?complexation. 相似文献
92.
93.
Dr. Heng Wang Zhaoyang Zeng Naoya Kawasaki Prof. Hellmut Eckert Dr. Hirofumi Yoshikawa Prof. Kunio Awaga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11235-11240
Rechargeable molecular‐cluster batteries (MCBs) based on the manganese cluster complex [Mn12O12(CH3CH2C(CH3)2COO)16(H2O)4] ([Mn12]) that exhibited a capacity of approximately 200 A h kg?1 in the battery voltage range of 4.0 to 2.0 V were developed. In these batteries, the capacity of approximately 100 A h kg?1 in the range of 4.0–3.0 V is caused by a chemical reduction from [Mn12]0 to [Mn12]8?, whereas the other half in the range of 3.0–2.0 V cannot be explained by a redox change of the Mn ions. We performed the cyclic voltammetry (CV) and 7Li solid‐state NMR measurements on the Mn12‐MCBs to investigate the origin of the capacity below 3.0 V. Pseudo‐rectangular‐shaped CV curves in the range of 3.0–2.0 V demonstrate the presence of an electrical double‐layer (EDL) capacitance in Mn12‐MCBs, which corresponds to approximately 100 A h kg?1. 7Li NMR studies suggest that Li ions form an EDL with electrons in carbon black electrodes in the capacitance voltage range. The capacitance effects are not formed by the single‐carbon electrodes alone, but appear only in the mixture of Mn12 and the carbon black electrodes. This type of coexistence of capacitance effects and redox reaction in one electrochemical cell is quite unusual and can serve as a new working principle for high‐performance energy‐storage devices. 相似文献
94.
Jennifer Malberg Thomas Wiegand Prof. Dr. Hellmut Eckert Dr. Michael Bodensteiner Prof. Dr. Robert Wolf 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(7):2356-2369
The synthesis and structural characterization of the first coordination compounds of bis(diphosphacyclobutadiene) cobaltate anions [M(P2C2R2)2]? is described. Reactions of the new potassium salts [K(thf)3{Co(η4‐P2C2tPent2)2}] ( 1 ) and [K(thf)4{Co(η4‐P2C2Ad2)2}] ( 2 ) with [AuCl(tht)] (tht=tetrahydrothiophene), [AuCl(PPh3)] and Ag[SbF6] afforded the complexes [Au{Co(P2C2tPent2)2}(PMe3)2] ( 3 ), [Au{Co(P2C2Ad2)2}]x ( 4 ), [Ag{Co(P2C2Ad2)2}]x ( 5 ), [Au(PMe3)4][Au{Co(P2C2Ad2)2}2] ( 6 ), [K([18]crown‐6)(thf)2][Au{Co(P2C2Ad2)2}2] ( 7 ), and [K([18]crown‐6)(thf)2][M{Co(P2C2Ad2)2}2] ( 8 : M=Au 9 : M=Ag) in moderate yields. The molecular structures of 2 and 3 , and 6 – 9 were elucidated by X‐ray crystallography. Complexes 4 – 9 were thoroughly characterized by 31P and 13C solid state NMR spectroscopy. The complexes [Au{Co(P2C2Ad2)2}]x ( 4 ) and [Ag{Co(P2C2Ad2)2}]x ( 5 ) exist as coordination polymers in the solid state. The linking mode between the monomeric units in the polymers is deduced. The soluble complexes 1 – 3 , 6 , and 7 were studied by multinuclear 1H‐, 31P{1H}‐, and 13C{1H} NMR spectroscopy in solution. Variable temperature NMR measurements of 3 and 6 in deuterated THF reveal the formation of equilibria between the ionic species [Au(PMe3)4]+, [Au(PMe3)2]+, [Co(P2C2R2)2]?, and [Au{Co(P2C2R2)2}2]? (R=tPent and Ad). 相似文献
95.
Hellmut Haberland Zinetulla Insepov Michael Moseler 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):229-231
Langevin Molecular Dynamics Simulations have been performed in order to understand thin film formation by impact of energetic clusters. The impact of Mo1024 clusters on a Mo surface is simulated at kinetic energies between 1 and 10 eV per atom. The results are in qualitative agreement with the experiments. Due to the high temperature induced locally at the impact zone, the method can be used to form compact, smooth, and strongly adhering thin films on room temperature substrates. 相似文献
96.
NMR investigations on the lithiation and delithiation of nanosilicon-based anodes for Li-ion batteries 总被引:1,自引:0,他引:1
Jan-Henning Trill Chuangqi Tao Martin Winter Stefano Passerini Hellmut Eckert 《Journal of Solid State Electrochemistry》2011,15(2):349-356
Lithiation and delithiation of nanosilicon anodes of 100–200 nm diameter have been probed by ex situ solid-state high-resolution
7Li nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) methods. Samples were charged within pouch
cells up to capacities of 1,500 mAh/g at 0.1 C, and subsequently discharged at the same rate. The NMR spectra reveal important
quantitative information on the local lithium environments during the various stages of the charging/discharging process.
The TEM experiments show that the electrochemical lithiation of nanosilicon particles results in core-shell materials, consisting
of LixSi shells surrounding a core of residual silicon. The NMR spectra yield approximate Li/Si ratios of the lithium silicides
present in the shells, based on the distinct local environments of the various types of 7Li nuclei present. The combination of NMR with TEM gives important quantitative conclusions about the nature of the electrochemical
lithiation process: Following the initial formation of the solid electrolyte interphase layer, which accounts for an irreversible
capacity of 240 mAh/g, lithium silicide environments with intermediate Li concentrations (Li12Si7, Li7Si3, and Li13Si4) are formed at the 500 to 1,000 mAh/g range during the charging process. At a certain penetration depth, further lithiation
does not progress any further toward the interior of the silicon particles but rather leads to the formation of increasing
amounts of the lithium-richest silicide, Li15Si4-type environments. Delithiation does not result in the reappearance of the intermediate-stage phases but rather only changes
the amount of Li15Si4 present, indicating no microscopic reversibility. Based on these results, a detailed quantitative model of nanophase composition
versus penetration depth has been developed. The results indicate the power and potential of solid-state NMR spectroscopy
for elucidating the charging/discharging mechanism of nano-Si anodes. 相似文献
97.
Pfannenschmidt U Johrendt D Behrends F Eckert H Eul M Pöttgen R 《Inorganic chemistry》2011,50(7):3044-3051
The phosphide La(4)Rh(8)P(9) was synthesized from the elements in a bismuth flux. The structure was refined from single crystal diffractometer data: space group Cmcm, a = 1303.1(2), b = 1893.2(2), c = 576.70(6) pm, wR2 = 0.0277, 1380 F(2) values, 65 variables. The rhodium and phosphorus atoms build up a three-dimensional [Rh(8)P(9)] polyanion which leaves larger cages for the three crystallographically independent lanthanum sites. The rhodium atoms have between four and six phosphorus neighbors at Rh-P distance ranging from 229 to 254 pm. Three of the four crystallographically independent phosphorus atoms are isolated (P(3-) units), while the P4 atoms form dimers with double bond character (208 pm P-P). The P(2)(2-) diphosphenide units bond side-on to a Rh3 and end-on to four Rh5 atoms. (31)P magic angle spinning (MAS) NMR spectroscopy is able to resolve three of the four crystallographically distinct phosphorus sites. The doubly bonded phosphorus site P4 is characterized by an axially symmetric shielding tensor of moderate anisotropy Δσ = σ(33) - σ(iso) = 257 ppm. Electronic band structure calculations prove the metallic character and reveal the significant difference between the isolated P(3-) and the phosphorus atoms of the P(2)(2-) units. Magnetic susceptibility measurement reveals Pauli paramagnetism. 相似文献
98.
Hellmut Baumgärtel 《International Journal of Theoretical Physics》2011,50(7):2002-2008
To asymptotic complete scattering systems {M
++V,M
+} on H+:=L2(R+,K{\mathcal{H}}_{+}:=L^{2}(\mathbf{R}_{+},{\mathcal{K}}, d
λ), where M
+ is the multiplication operator on H+{\mathcal{H}}_{+} and V is a trace class operator with analyticity conditions, a decay semigroup is associated such that the spectrum of the generator
of this semigroup coincides with the set of all resonances (poles of the analytic continuation of the scattering matrix into
the lower half plane across the positive half line), i.e. the decay semigroup yields a “time-dependent” characterization of
the resonances. As a counterpart a “spectral characterization” is mentioned which is due to the “eigenvalue-like” properties
of resonances. 相似文献
99.
The radical cations 2-(3-N-butylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-N-oxide (m-BuPYNN) and 4-(ethylammonium)-2,2,6,6-tetramethylpiperidin-1-oxide (EATEP) are successfully intercalated into the layered host structure of CdPS(3) via ion exchange. The reaction proceeds either directly from ethanolic solutions of the radical iodide salt or via a two-stage process involving first the formation of an intermediate tetramethylammonium intercalate. The resulting materials, which are described by the compositional formula Cd(1-x)PS(3){Rad}(2x), are characterized by chemical analysis, X-ray powder diffraction, bulk susceptibility measurements and EPR spectroscopy. Modern single and double resonance solid state NMR techniques are introduced successfully to study the structural modifications of the host lattice and the details of the intermolecular guest/host interactions. (1)H MAS-NMR spectra reveal substantial differences in the unpaired electron spin density distributions within the radical ions intercalated into the host lattice compared to those obtained for the pure radical ion salts, leading to different bulk magnetic properties. The results of (1)H/(31)P double resonance experiments indicate that the orientation of the guest molecules is dominated by Columbic interactions between the radical cations and the negatively charged cadmium vacancies in the host lattice. 相似文献
100.
Juchem C Merkle H Schick F Logothetis NK Pfeuffer J 《Magnetic resonance imaging》2004,22(10):1373-1383
High magnetic fields increase the sensitivity and spectral dispersion in magnetic resonance spectroscopy (MRS). In contrast, spectral peaks are broadened in vivo at higher field strength due to stronger susceptibility-induced effects. Strategies to minimize the spectral line width are therefore of critical importance. In the present study, 1H 2D chemical shift imaging at short echo times was performed in the macaque monkey brain at 7 T. Large brain coverage was obtained at high spatial resolution with voxel sizes down to 50 μl being able to quantify up to nine metabolites in vivo with good reliability. Measured line widths of metabolites decreased from 14.2 to 7.6 Hz with voxel volumes of 3.14 ml to 50 μl (at increased spatial resolution). The line width distribution of the metabolites (7.6±1.6 Hz, ranging from 5.5 to 10 Hz) was considerably smaller compared to that of water (10.6±2.4 Hz) and was also smaller than reported in 1H MRS at 7 T in the human brain. Our study showed that even in well-shimmed areas assumed to have minimal macroscopic susceptibility variations, spectral line widths are tissue-specific exhibiting considerable regional variation. Therefore, an overall improvement of a gross spectral line width — directly correlated with improved spectral quality — can only be achieved when voxel volumes are significantly reduced. Our line width optimization was sufficient to permit clear glutamate (Glu)–glutamine separation, yielding distinct Glu maps for brain areas including regions of greatly different Glu concentration (e.g., ventricles vs. surrounding tissue). 相似文献