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Several 57Fe-labeled ferrocene derivatives and other cyclopentadienyliron complexes were studied by 57Fe and 13C NMR with respect to isotope-induced chemical shifts 1Delta12/13C(57Fe) and the magnitude and sign of coupling constants 1J(57Fe,13C) and 2J(57Fe,1H). The geometries of the complexes were optimized by DFT methods [B3LYP/6-311+G(d,p)] and chemical shifts (GIAO) and coupling constants were calculated at the same level of theory. The trends in calculated 57Fe nuclear shielding agree well with the experimental data and, in the case of coupling constants 1J(57Fe,13C) and 2J(57Fe,1H), both sign and magnitude are correctly reproduced. 相似文献
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A. M. Sheloumov A. A. Koridze M. G. Ezernitskaya P. V. Petrovskii O. L. Tok Z. A. Starikova F. M. Dolgushin A. I. Yanovsky 《Russian Chemical Bulletin》1999,48(9):1767-1773
Reaction of the cluster Os3(μ-CO)(CO)9(μ3-η1:η1:η2-Me3SiC2Me) with HC≡CCOOMe in benzene at 70 °C results in Os3(CO)9{μ3-η1:η1:η2:η2-C(SiMe3)C(Me)C(COOMe)CH× (5), Os3(CO)9{μ3-η1:η1:η2:η2-C(SiMe3)C(Me)C(H)C(COOMe)CH× (6), Os3(CO)9{μ-η1:η1:η4-C(SiMe3)C(Me)C(H)C(COOMe)CH× (7), and Os3(CO)δ{μ3-η1:η1:η4:η1-C(SiMe3)C(Me)C(H)C(COOMe)× complexes (8), containing an osmacyclopentadiene moiety. Complexes5–8 were characterized by1H NMR and IR spectroscopy. The structure of clusters5 and8 was confirmed by X-ray analysis. Complex7 is formed from cluster5 as a result of a new intramolecular rearrangement and complex8 is obtained by decarbonylation of compound6. Complex8 adds PPh3 to give Os3(CO)δ(PPh3){μ-η1:η1:η4-C(SiMe3)C(Me)C(H)C(COOMe)×. 相似文献
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A. A. Koridze A. M. Sheloumov F. M. Dolgushin A. I. Yanovsky P. V. Petrovskii O. L. Tok 《Russian Chemical Bulletin》1998,47(5):995-1000
Reactions of the alkyne cluster Os3(μ-CO)(CO)9(μ3-Me3C2Me) with alkynes Me3SiC≡CR (R=Me, Bun) in refluxing hexane result in the formation of clusters Os3(CO)9{μ3-C(SiMe3)=C(Me)C=C(SiMe3)=C(Me)C=C(SiMe3)R} (2a: R=Me;3a: R=Bun). The dienediyl ligand in these complexes is formed by alkyne-vinylidene coupling, with vinylidene generated in the course of reaction from the alkyne molecule by the acetylene-vinylidene rearrangement involving a 1,2-shift of the Me3Si group. The structure of cluster3a was determined by X-ray structural analysis. The dienediyl ligand is coordinated to three metal atoms of the cluster framework by two π-ethylene bonds with two osmium atoms and two σ-bonds with the third osmium atom with the formation of the osmacyclobutene moiety. The1H and13C NMR study of13CO-enriched samples of clusters2a and3a revealed the stereochemical nonrigidity of these molecules due to the exchange of the hydrocarbon and carbonyl ligands. 相似文献
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One of the aims of temperature-programmed desorption experiments is to facilitate identification of molecular pathways for desorption. The authors provide a rigorous assessment of the difficulty of doing this for H(2)/Si((1-x))Ge(x)(100)-(2x1). An extensive series of density functional calculations using both cluster and slab methods is performed. The resulting desorption barriers are used to compute thermal desorption spectra. A mean-field approximation is used to treat the populations of the various adsites present on the surface. The authors find a number of significant results. First, slab and cluster calculations do not appear to predict consistent differences in desorption barriers between intradimer and interdimer channels. Second, they find that a germanium atom affects the desorption barrier significantly only if it is present at the adsite. A germanium atom adjacent to an adsite or in the second layer influences the desorption barrier negligibly. Both cluster and slab calculations consistently predict a decrease of approximately 0.3-0.4 eV per germanium atom at the adsite. Third, current analysis of thermal desorption spectra in the literature, although yielding good fits to experimental data, is not rigorous. The authors' calculated spectra can be fitted rather well by assuming, as in current analysis of experimental data, three independent second-order channels, even though the underlying molecular pathways used to calculate the spectra are considerably different. Fourth, the authors' results highlight the importance of treating the rearrangement of hydrogen and germanium atoms at the surface during the thermal desorption process. This is generally not taken into account in kinetics modeling of desorption spectra. 相似文献
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Balagurova EV Cheredilin DN Kolomnikova GD Tok OL Dolgushin FM Yanovsky AI Chizhevsky IT 《Journal of the American Chemical Society》2007,129(12):3745-3753
Reactions of the [K]+ salts of the [nido-7,9-C2B9H12]- anion (2) and its C-phenylated derivative [7-Ph-nido-7,9-C2B9H11]- (4) with [OsCl2(PPh3)3] (3) proceed in benzene at ambient temperature with the formation of 16-electron chlorohydrido-Os(IV) exo-nido complexes, [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(mu-H)2-7-R-7,9-C2B9H8] (5: R = H; 6: R = Ph), along with the small amounts of the charge-compensated nido-carboranes [nido-7,9-C2B9H11PPh3] (7) and [7-Ph-nido-7,9-C2B9H10PPh3] (8) as byproducts. However, when carried out under mild heating in ethanol, the reaction of 2 with 3 selectively afforded a 16-electron dihydrido-Os(IV) exo-nido complex [exo-nido-10,11-{(Ph3P)2OsH2}-10,11-(mu-H)2-7,9-C2B9H9] (9). Structures of both complexes 5 and 9 have been confirmed by single-crystal X-ray diffraction studies, which revealed that nido-carboranes in these species function as a bidentate dicarbollide ligands [7-R-nido-7,9-C2B9H10]2- linked to the Os(IV) center via two B-H...Os bonds involving adjacent B-H vertices in the upper CBCBB belt of the carborane cage. Thus, compounds 5 and 9 represent the first structurally characterized exo-nido-metallacarboranes based on meta-dicarbollide-type ligands. Variable-temperature 1H and 31P{1H} NMR experiments indicate that complex 9 is fluxional in solution and shows an unusual exchange between terminal Os-(H)2 and bridging {B-H}2...Os hydrogen atoms. Upon heating in d8-THF at 65 degrees C, complex 9 converts irreversibly to its closo isomer [2,2-(PPh3)2-2,2-H2-closo-2,1,7-OsC2B9H11] (13), which could thus be obtained as a pure crystalline solid. The structure of 13 has been established on the basis of analytical and multinuclear NMR data and a single-crystal X-ray diffraction study. 相似文献
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Characterization of the electronic structure and thermal stability of HfO2/SiO2/Si gate dielectric stack 下载免费PDF全文
X‐ray photoelectron spectroscopy was used to investigate thermal stability of HfO2 on SiO2/Si substrate prepared by atomic layer deposition, followed by annealing at different temperature. Hf silicate and Hf silicide are formed at the interface of HfO2 and SiO2 during deposition. The Hf silicide disappears, while the amount of the Hf silicate is intensified after post‐deposition annealing treatment at 400 °C. Phase separation of the Hf silicate layer occurs when the annealing temperature is over 400 °C, resulting in the Hf silicate decomposition into Si and Hf oxides. Moreover, crystallization at high temperature leads to grain boundaries formation, which deteriorates the gate leakage current, as observed by the electrical measurements. The similar annealing temperature dependence of both internal electric field and the amount of Hf silicate implies that the Hf silicate plays a key role in building up the internal electric field, which is attributed to generation of oxygen vacancies (Vo) in the Hf silicate layer. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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