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61.
Ulrich Schubert 《Journal of Sol-Gel Science and Technology》2003,26(1-3):47-55
Organically substituted metal alkoxides can be prepared by reaction of the parent alkoxides with complexing organic compounds. The chemical and structural consequences of such substitutions are discussed in this article. Examples are given showing how functional organic moieties, such as polymerizable groups, can be incorporated into sol-gel materials via the complexing ligands. Major structural differences between silica-based and metal-based hybrid materials originate from the different charge/coordination number ratios of silicon and most metals. This results in a high tendency for the molecular building blocks to aggregate. In many cases, metal oxide clusters are formed which are capped by the organic ligands. Such surface-modified clusters are themselves very valuable condensed matter units for materials syntheses. 相似文献
62.
Meier MA de Gans BJ van den Berg AM Schubert US 《Rapid communications in mass spectrometry : RCM》2003,17(20):2349-2353
Recently, a new multiple-layer matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) sample spotting technique for poly(ethylene glycol), offering improved analysis possibilities, was described. In this contribution the application of ink-jet printing to automated, multiple-layer MALDI-TOFMS sample preparation of synthetic polymers is presented, allowing accurate deposition of matrix, additive and analyte solutions. The new sample preparation technique was evaluated for poly(ethylene glycol) as well as poly(methyl methacrylate) standards, and optimized settings for both synthetic polymers have been obtained. 相似文献
63.
Ulrich Burkert 《Tetrahedron》1979,35(5):691-695
The geometries and energies of polymethyl-1,3-dioxanes were studied by molecular mechanics calculations. Buttressing effects of the Me groups are discussed. The chair/twist conformational equilibrium of 1,3-dioxanes having two syn-axial Me groups in the chair were calculated, and a twist form (the 1,4-twist) is found to be more stable than the chair only for 9 and 14, chair and 2,5-twist form are of comparable energies for 10 and 13, and the chair is considerably favored in 11 and 12. The chair/1,4-twist energy difference of 1 was calculated to be only 16.4 kJ mol?1. Ring inversion of 1 goes through a transition state with C-C-C-O coplanar with a calculated activation enthalpy of 28.3 kJ mol?1. 相似文献
64.
Mass Spectroscopic Observations and Chemical Transport Experiments with the Systems VCl3/Al2Cl6 and VCl2/Al2Cl6 By mass spectrometry the equilibrium VCl3,s + 0.5 Al2Cl6,g ? VAlCl6,g has been determined: ΔH°(298) = 25.6(±0.5) kcal; ΔS°(298) = 23.0(±3) cal/K, ΔCp (assumed) = ?4 cal/K. This is approximately in agreement with results determined by ligand field spectroscopy by ANUNDSKÅS and ØYE (A. and Ø.). For the dimerization of VCl3,g values for ΔH and ΔS have been derived. The molecule VAl2Cl9 assumed by A. and Ø. could not been observed by mass spectrometry. For the VCl2/Al2Cl6 complex, observed by chemical transport, A. and Ø. give the formula VAl3Cl11. This molecule could not been observed by mass spectrometry. This suggests a smaller concentration, compared with the results of A. and Ø. Stabilization of VCl2,s (by metal-nietal-bonds) shifts the reaction to the left, whith explains the lower complex concentration as well as the larger molecular weight of the complex. With chlorides stabilized by stronger metal-metal bonds (MoCl3, MoCl2, Nb3Cl8) AlCl3 complexes are not formed in observable concentrations. The chemical transport of VCl2 with Al2Cl6 needs relatively high temperatures (973 → 873 K). In this case the addition of SiCl4 hinders the attack of the quartz ampoule by Al2Cl6. Using a VCl3 + VCl2 mixture, VCl3 is transported by Al2Cl6 (673 → 623 K) into the colder region. If afterwords the ampoule is reversed, VCl3 again moves into the colder region, but the thermal decomposition of VCl3 at the same time causes that a VCl2-residue remains in the hot region. 相似文献
65.
Gas Molecules Pd2Al2Cl10 and PdAlCl5 as Accompanists of PdAl2Cl8 Mass spectrometric observations using a double cell showed that the reaction of gaseous Al2Cl6 with solid PdCl2 besides the known gaseous complex PdAl2Cl8 gives PdAlCl5 and the unexpected complex Pd2Al2Cl10. For the equilibrium (with ΔCp? ?1 cal/K) ΔH°(298) = 7.5 kcal/Mol and ΔS°(298) = 5.3 ± 2 cl have been obtained. 相似文献
66.
Stamou D Musil C Ulrich WP Leufgen K Padeste C David C Gobrecht J Duschl C Vogel H 《Langmuir : the ACS journal of surfaces and colloids》2004,20(9):3495-3497
We describe a simple method for patterning biomolecular films on surfaces with high resolution. A conventional polymeric resist is structured by electron-beam lithography. The exposed and developed patterns are then used for the directed self-assembly (SA) of a first molecule from solution. Removal of the remaining resist allows the SA of a second species. We illustrate the potential of the approach by assembling on gold (Au) substrates two alkanethiols of contrasting terminal functionality. The patterns have dimensions from the micrometer range down to 40 nm and an edge resolution of 3.5 nm. 相似文献
67.
Chlorothionitrene Complexes of Tungsten. Crystal Structure of [WCl4(NSCl)]2 Tungsten hexachloride reacts with trithiazyl chloride, (NSCl)3, yielding the chlorothionitrene complex [WCl4(NSCl)]2, from which AsPh4[WCl5(NSCl)] can be obtained by reaction with AsPh4Cl. Both complexes are characterized by their i.r. spectra. The crystal structure of [WCl4(NSCl)]2 was determined and refined with X-ray diffraction data (1059 reflexes, R = 0.055). It crystallizes in the monoclinic space group P21/n with the lattice constants a = 1523, b = 904, c = 583 pm and β = 91.35°. In the unit cell there are two centrosymmetric [WCl4(NSCl)]2 molecules in which the W atoms are linked via two chloro bridges; short and long W? Cl distances (244 and 265 pm) alternate in the W2Cl2 ring, the NSCl groups are found in the trans positions to the longer W? Cl bonds. The WNS bond angle (175°) and short bond distances correspond to a formulation . 相似文献
68.
Alkylation of the aza-pseudophenalenone1 with trialkyloxoniumtetrafluoroborates yield the azapseudophenaleniumsalts2 a,2 b, reactions with C-nucleophiles the compounds3 a 3 e, the dihydro-azapseudophenalenone4 reacts with malodinitrile-sodium to5,1 b and1 d with tetrachlorocyclopentadiene to the fulvalenes6 a,6 b,1 b was olefinated withtert. butyl-cyano-ketene to theZ-isomer7.
Meinem lieben Kollegen und Freund, Herrn Prof. Dr.Werner Heimann, Karlsruhe, mit herzlichen Wünschen zum 70. Geburtstag gewidmet. 相似文献
69.
Simon G. Bott Ulrich Kynast Jerry L. Atwood 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(3):241-246
18-crown-6 reacts with TiCl3 in CH2Cl2 to form a complex in which the crown ether functions as a tridentate ligand. Addition of moist hexane affords a molecular complex in which the crown ether functions as a bidentate ligand. A water molecule is bonded directly to the titanium atom and is further hydrogen bonded to three of the oxygen atoms of the crown. The deep blue crystals of the CH2Cl2 adduct belong to the monoclinic space groupP21/n witha=13.481(8),b=8.021(5),c=21.425(9) Å, =97.32(5)°, and
calc = 1.51 g cm–3 forZ=4. Refinement led to a conventionalR value of 0.040 based on 873 observed reflections. The Ti–O bond distances for the crown oxygen atoms are 2.123(8) and 2.154(9) Å, while the oxygen atom of the water molecule is bonded at 2.072(8) Å. The octahedral coordination sphere of the titanium atom is completed by the three chlorine atoms at distances of 2.340(5), 2.352(4), and 2.373(4) Å.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82034 (10 pages). 相似文献
70.
Ulrich Schindewolf 《Angewandte Chemie (International ed. in English)》1978,17(12):887-901
Electrons produced in a gaseous, liquid, or solid solvent are called dissolved electrons or excess electrons. These excess electrons can exist as quasi-free particles of high mobility in a delocalized state, comparable with electrons in a metal; or as bound particles of low mobility they can be localized within narrow limits—in a solvent cavity formed by repulsive forces. Localized electrons can also be solvated like normal ions. Characteristically, such solvated electrons exhibit broad and extensive absorption spectra in the visible to near infrared spectral range. The localized and delocalized states of the excess electrons can be in equilibrium with each other, such that a continuous transition of the properties between the limiting extremes can be observed. The reactions of the excess electrons with suitable acceptors (substrates) are initiated by an attachment-detachment equilibrium A + e? ? A? which is followed by further chemical rearrangements. The rate constants of these reactions vary by more than 15 powers of ten depending on the substrates and the solvents. Most of the properties of excess electrons in solution can be interpreted by means of a model which is easily understandable but quantitatively evaluated only with considerable effort. 相似文献