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911.
Raman and IR-spectroscopic Investigation of Alkyl Derivatives of Arsenic Acid. IV. Vibrational Spectra of Some Dialkylarsinates The Raman and IR spectra of the Na and K salt of the dimethyl- and diethylarsinic acid (in part as hydrate) are discussed. The skeleton C2AsO shows very probably the symmetry C2v. 相似文献
912.
Photoemission measurements with He and Ne resonance lines and Al Kα radiation are reported on bulk samples of the alkali metals Rb, Cs, their suboxides Cs7O, Cs11O3 and (Cs11O3)Rb7. For comparison, the Hel spectrum of the “normal” oxide Cs2O is added. The occurrence of ionic clusters in a metallic matrix is typical for the suboxides. Binding energies, Auger transitions, and electron concentrations are discussed. The spectra of the suboxides show a narrow non-bonding oxygen 2p band at 2.7 eV. Different binding energies are found for Cs atoms in the clusters and for the atoms in the metallic regions of (Cs11O3)Cs10. The compound Cs11O3 consists of ionic [Cs11O3]5? clusters, which are bound by 5 free electrons in accordance with the chemical bond model. 相似文献
913.
Simon A. Llewellyn Malcolm L.H. Green Andrew R. Cowley 《Journal of organometallic chemistry》2005,690(9):2358-2364
The new cobalt (l) acyl compounds, [Co(PMe3)(CO)3(COMe)] 1, [Co(PPhMe2)(CO)3(COMe)] 2, [Co(P(4-Me-C6H4)3)(CO)3(COMe)] 3 and [Co(P(4-F-C6H4)3)(CO)3(COMe)] 4, have been prepared from [Na(Co(CO)4)]. The compound [Co(PCy3)(CO)3(COMe)] 5 has been prepared from [Co(PCy3)(CO)3(Me)] 6. The crystal structures of 5 and 6 are reported. 相似文献
914.
Roberts SA Kellaway IW Taylor KM Warburton B Peters K 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7342-7348
The effect of pH on the adsorption of catalase and lysozyme at the air-water interface has been studied using a combined surface pressure-interfacial shear rheology technique. The results presented show that the rate of development of interfacial phenomena increases as the pH of the subphase approaches the isoelectric point of the protein under investigation. The development of the measured interfacial rheological parameters is due to an increased rate of cross-link formation within the resultant interfacial gel. The formation of the interfacial gels has been modeled using a combination of the Smoluchowski theory for the coagulation of an aerosol or fog and classic rubber elasticity theory. The enhanced rate of cross-link formation at the isoelectric point is a result of an in-surface phase separation brought about by cooperative deionization of the protein molecules near their isoelectric point. Simultaneous measurements of surface pressure and interfacial rheology have enabled us to show that the development of a gel-like interfacial network coincides with observed increases in surface pressure. 相似文献
915.
Uniform catalytic site in Sn-beta-zeolite determined using X-ray absorption fine structure 总被引:1,自引:0,他引:1
Bare SR Kelly SD Sinkler W Low JJ Modica FS Valencia S Corma A Nemeth LT 《Journal of the American Chemical Society》2005,127(37):12924-12932
The Sn silicate zeolite, Sn-beta, has been shown to be an efficient, selective heterogeneous catalyst for Baeyer-Villiger oxidations. Using primarily a multishell fit to extended X-ray absorption fine structure (EXAFS) data, we show that the Sn does not randomly insert into the beta-zeolite structure but rather occupies identical, specific, crystallographic sites. These sites are the T5/T6 sites in the six-membered rings. Moreover, the Sn is substituted in pairs on opposite sides of these six-membered rings. We believe that it is the specific, uniform crystallographic location of the Sn in the beta crystal structure that leads to sites with uniform catalytic activity, and consequently to the high chemical selectivity demonstrated for this catalyst. This manifests itself in the almost enzyme-like selectivity of this catalyst in Baeyer-Villiger oxidations. This uniform site distribution of the Sn suggests that there is likely a symbiotic relationship between the structure-directing agent in the zeolite synthesis and the Sn heteroatoms during the framework formation. 相似文献
916.
The wide-band-gap semiconductor BaZnOS adopts a high-symmetry modification of the SrZnO2 structure type and contains layers of vertex-linked ZnO2S2 tetrahedra, which represent a novel coordination environment for zinc in the solid state. BaZnOS: orthorhombic, space group Cmcm; a = 3.9619(2) angstroms, b = 12.8541(7) angstroms, c = 6.1175(4) angstroms, Z = 4. Diffuse-reflectance spectroscopy measurements reveal a direct band gap of 3.9(3) eV, consistent with the white color and the results of band structure calculations. The band gap is larger than those observed in ZnO and ZnS, consistent with the more ionic nature of BaZnOS. Attempts to dope this compound electronically have so far not proved possible. 相似文献
917.
The title compounds were synthesized from Ln, LnX(3) (Ln = La, Ce; X = Cl, Br), and Sb under an Ar atmosphere at 950 degrees C. They crystallize in the space group P6(3)/m (No. 176) with lattice constants a = 21.232(5) and 20.862(2) Angstroms and c = 4.323(2) and 4.2728(7) Angstroms for La(9)Sb(16)Br(3) and Ce(9)Sb(16)Cl(3), respectively. The solids are the most metal-rich members in the reduced rare earth metal halide family and contain partial structures which are characteristic of reduced halides and intermetallic phases. These are the [Ln(6)X(6)](infinity) hexagon stars, Sb-centered [Ln(3)Sb](infinity) trigonal prismatic columns, and stripes of Sb square meshes. Computational analysis indicates that their electronic structure is valence-precise in the reduced halide part, but electron-deficient in the intermetallic part. Susceptibility and resistivity measurements reveal the metallic nature of the compounds. 相似文献
918.
Bin-Salamon S Brewer S Franzen S Feldheim DL Lappi S Shultz DA 《Journal of the American Chemical Society》2005,127(15):5328-5329
This communication describes the preparation and characterization of a valence tautomer complex covalently attached to gold nanoparticles. Variable-temperature IR spectroscopy is used to determine the equilibrium thermodynamic parameters for the valence tautomerization. These results are compared with a nonsurface combined valence tautomer complex. The results show that surface confinement attenuates both DeltaH degrees and DeltaS degrees . We attribute these changes to a reduced accessible molecular surface area. 相似文献
919.
The synthesis of multivalent neoglycoconjugates with 2,6-diamino-2,6-dideoxyglucose is accomplished by a flexible Ugi multicomponent approach leading to mono-, di- and tri-valent carbohydrate clusters. 相似文献
920.
Timco GA Batsanov AS Larsen FK Muryn CA Overgaard J Teat SJ Winpenny RE 《Chemical communications (Cambridge, England)》2005,(29):3649-3651
Heterometallic wheels can be templated about tertiary amines and imidazoles, leading to new octa-, nona- and deca-nuclear rings. 相似文献