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91.
Hyungrak Kim 《Journal of solid state chemistry》2005,178(6):1935-1939
The compound Ca14MnP11 crystallizes in the Ca14AlSb11 structure type with the tetragonal space group I41/acd (Z=8) and lattice parameters of , c=20.7565(9) at 90 K. The structure consists of MnP49− tetrahedron, P37− trimer, 4 P3− isolated anions and 14 Ca2+ cations. Similar to other compounds of this structure type containing phosphorous, the P37− trimer has a central P atom that is best modeled in the structure as being equally split between two sites. In addition, there is no additional distortion of the manganese-containing tetrahedron compared with the main group analog, Ca14GaP11, suggesting that the Mn oxidation state is Mn2+. Temperature-dependent magnetic susceptibility shows that the compound is paramagnetic over the entire temperature range measured (2-300 K). The data can be fit with a modified Curie-Weiss law and provide an effective magnetic moment of 5.80 (2) B.M. with a Weiss constant of −2.13(2) K and . This moment is significantly higher than those measured for any of the Mn-containing analogs and is consistent with Mn2+. This result will be discussed in light of the electron counting scheme for Mn compounds of the Ca14AlSb11 structure-type. 相似文献
92.
Guadalupe Fortuño 《Plasma Chemistry and Plasma Processing》1988,8(1):19-34
A parametric study of the etching of Si and SiO2 by reactive ion etching (RIE) was carried out to gain a better understanding of the etching mechanisms. The following fluorocarbons (FCs) were used in order to study the effect of the F-to-Cl atom ratio in the parent molecule to the plasma and the etching properties: CF4, CF3Cl, CF2Cl2, and CFCl3 (FC-14, FC-13, FC-12, and FC-11 respectively). The Si etch rate uniformity across the wafer as a function of the temperature of the wafer and the Si load, the optical emission as a function of the temperature of the load, the etch rate of SiO2 as a function of the sheath voltage, and the mass spectra for each of the FCs were measured. The temperature of the wafer and that of the surrounding Si load strongly influence the etch rate of Si, the uniformity of etching, and the optical emission of F, Cl, and CF2. The activation energy for the etching reaction of Si during CF4 RIE was measured. The etch rate of Si depends more strongly on the gas composition than on the sheath voltage; it seems to be dominated by ion-assisted chemical etching. The etching of photoresist shifted from chemical etching to ion-assisted chemical etching as a function of the F-to-Cl ratio and the sheath voltage. The etch rate of SiO2 depended more strongly on the sheath voltage than on the F-to-Cl ratio. 相似文献
93.
Arturo Battaglia Eleonora Baldelli Gabriele Fontana Andrea Guerrini 《Tetrahedron》2005,61(32):7727-7745
The base induced deprotonation of H-14 of 7-triethylsilyl- (7-TES-) and 7-tert-butoxycarbonyl- (7-BOC-) protected 13-oxo-baccatins gave the corresponding enolates, which were selectively aminated with electrophilic nitrogen donors, such as azodicarboxylates and tosyl azide. In particular, tosyl azide gave the corresponding 7-BOC- and 7-TES-13-oxo-14β-azido-baccatin III. Alternatively, the last compound was prepared via NaN3 induced azidation of the 13-silyl enol ether of 7-TES-13-oxo-baccatin III under oxidative (cerium ammonium nitrate) conditions. The 13-silyl enol ether was obtained in a multistep process by DBU induced silylation of 7-TES-13-oxo-baccatin III. The 7-TES-13-oxo-14β-azido-baccatin III was used as a key intermediate for the synthesis of a new family of antitumour taxanes containing amino based functional groups at the C-14 position, such as: 14β-azido, 14β-amino, 14β-amino 1, 14-carbamate, 14β-amino 1, 14-thiocarbamate, and 14β-amino N-tert-butoxycarbonyl-1,14-carbamate. 相似文献
94.
By14C-labeling it is shown that the ring contraction reaction of 1,4-benzothiazin-2,3-4H-dione (1), leading via benzthiazol-2-carbonic acid (2) finally to benzthiazole (3), proceeds via hydrolytic opening of the thiolactone-bond in1, irrespectively of H+ or OH– catalysis. 相似文献
95.
Jacques Barrau Ghassoub Rima Tajani El Amraoui 《Journal of organometallic chemistry》1998,570(2):8645
The reactions of the divalent species (ArO)2M (Ar=2,4,6-[(CH3)2NCH2]3C6H2; M=Ge, Sn) with either Me3SiN3, elemental S8, Se or transition metal complexes M′(CO)n+1 (M′=Fe, n=4; M′=Cr, W; n=5) (Ph3P)2Pt·C2H4 have resulted in the isolation of either the new stable formal metallanimines (ArO)2M=N–SiMe3, germanethione, -selone (ArO)2Ge=E (E=S, Se) (the expected formations of the stannanethione and -selone were not observed), or the (ArO)2M=M′(CO)n, (ArO)2M=Pt(PPh3)2 complexes, respectively. The direct oxidation of the (ArO)2M species with various oxidizing agents led to the formation of the corresponding metalloxanes [(ArO)2M–O–]2. All of the chalcogenido- and transition metal–metal 14 complexes have been physicochemically and chemically characterized. The reactions of the (ArO)2Ge=E (E=S, Se) compounds with 3,5-di-tert-butyl-1,2-benzoquinone produced, by extrusion of sulfur or selenium, the dioxametalloles corresponding to the formal addition of the divalent species (ArO)2M to the benzoquinone. A substitution reaction of chalcogen (S/Se) has been observed permitting to go from germaneselone to germanethione. 相似文献
96.
The color of a complex number is defined as the number of vertices of the convex hull of powers of that number. This induces a coloring of the unit disk. The structure of the set of points where the color changes is investigated here. It is observed that there is a connection between this fractal set and some family of trinomial equations. Three algorithms for coloring the unit disk are described, the last one (related to the Farey sequence) arising out of a conjecture. This conjecture is formulated and proved in this presentation. 相似文献
97.
Hubert Huppertz 《Journal of solid state chemistry》2004,177(10):3700-3708
This paper reports about two new hydrogen-containing rare-earth oxoborates RE4B6O14(OH)2 (RE=Dy, Ho) synthesized under high-pressure/high-temperature conditions from the corresponding rare-earth oxides, boron oxide, and water using a Walker-type multianvil equipment at 8 GPa and 880 °C. The single crystal structure determination of Dy4B6O14(OH)2 showed: Pbcn, a=1292.7(2), b=437.1(2), , Z=2, R1=0.0190, and wR2=0.0349 (all data). The isotypic holmium species revealed: Pbcn, a=1292.8(2), b=436.2(2), , Z=2, R1=0.0206, and wR2=0.0406 (all data). The compounds exhibit a new type of structure, which is built up from layers of condensed BO4-tetrahedra. Between the layers, the rare-earth cations are coordinated by 7+2 oxygen atoms. Furthermore, we report about temperature-resolved in situ powder diffraction measurements, DTA/TG, and IR-spectroscopic investigations into RE4B6O14(OH)2 (RE=Dy, Ho). 相似文献
98.
The energy transfer from the upper triplet states of diphenylamine, naphthalene and triphenylene to toluene and hexene-1 is studed. Two mechanisms of dissipation transferred energy in solvents are discussed. 相似文献
99.
100.
We present the results of a re-analysis of a previously published carbon isotope data-set related to coralline sponges in the Caribbean Sea. The original interpretation led to the discrimination between a pre-industrial period, with a signal controlled by solar-induced climatic variations, followed by the industrial era, characterized by a progressive δ13C negative shift due to the massive anthropogenic carbon emissions. Our re-analysis allowed to extract from the raw isotopic data evidence of a solar forcing still visible during the industrial era, with a particular reference to the 88-year Gleissberg periods. These signals are related to slope changes in both the δ13C versus time and the δ13C versus carbon emission curves. 相似文献