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981.
Albrecht M Janser I Meyer S Weis P Fröhlich R 《Chemical communications (Cambridge, England)》2003,(23):2854-2855
A huge molecular tetrahedral complex forms quantitatively by self-assembly from four ligands L-H6 and four titanium(IV) ions; in the solid state it encapsulates four [K(DIMF)3]+ units in its interior. 相似文献
982.
Annegrit Rabis Burkhard Ziemer Dirk Wulff‐Molder Manfred Meisel Sebastian Beck 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(4):o247-o250
The title compounds, ethyldiphenylphosphine–dithiomonometaphosphoryl chloride, EtPh2PPS2Cl, C14H15ClP2S2, (I), and tris‐n‐propylphosphine–dithiomonometaphosphoryl chloride and bromide, nPr3PPS2Cl, C9H21ClP2S2, (II), and nPr3PPS2Br, C9H21BrP2S2, (III), respectively, are the first phosphine‐stabilized dithiomonometaphosphoryl halides to be structurally characterized. In the tris‐n‐propylphosphine derivatives, the central PP donor–acceptor bond becomes longer in the order bromo < chloro < fluoro. Substitution of the tris‐n‐propylphosphine group in (II) by the more bulky ethyldiphenylphosphine group also leads to a longer PP bond. These structural features agree with the observed 31P NMR data. In (II) and (III), the central P—P bond coincides with the crystallographic threefold axis, entailing site‐occupational disorder for the S2Y group. 相似文献
983.
The gas-liquid equilibria in hydrogen-1-methylnaphthalene mixtures were experimentally determined at four temperatures from 190 to 430°C and seven pressures from 20 to 250 atm. The Henry constant of hydrogen dissolved in 1-methylnaphthalene was evaluated from the data. A flow apparatus was used to produce the saturated equilibrium phases. The data were found to be consistent with the Gibbs-Duhem equation integrated by the method of orthogonal collocation. Vapor pressures of 1-methylnaphthalene required for the thermodynamic consistency calculations were determined with the same apparatus. Comparison of the new mixture equilibrium data is made with the correlations of Chao and Seader (1961) and Grayson and Streed (1963). 相似文献
984.
The definition of the cyclic polynomial of conjugated hydrocarbons is offered. The combinatorial characteristics of this polynomial are investigated. The most important property of the cyclic polynomial is that it can be used for enumeration of conjugated circuits. 相似文献
985.
Sinnecker S Neese F Noodleman L Lubitz W 《Journal of the American Chemical Society》2004,126(8):2613-2622
The capability of the density functional broken symmetry approach for the calculation of various EPR parameters of exchange coupled metal clusters is demonstrated by studying the experimentally well-investigated [Mn(III)Mn(IV)(mu-O)(2)(mu-OAc)DTNE](2+) complex. Geometry optimizations of the complex in its broken symmetry and high spin states yielded structures with two distinct manganese sites and geometrical parameters in good agreement with the X-ray structure. Exchange coupling constants were calculated from the energy differences between the high spin and broken symmetry states using the Heisenberg spin Hamiltonian. Very good agreement between theory and experiment was achieved with the B3LYP hybrid functional. The g-tensor calculations were performed employing the coupled perturbed Kohn-Sham equations. A strategy for the computation of g-tensor site values is presented and provides single-site g-tensors that are in good agreement with the expectations for Mn(III) and Mn(IV), respectively. Spin projection gave the g-tensor of the coupled manganese complex in very good agreement with the experimental results. Complete (55)Mn hyperfine tensors, including spin-orbit contributions, were calculated and spin-projected. The source of anisotropy in this system could be traced back to the Mn(III) ion in line with the experimental results. The isotropic manganese hyperfine coupling constants were underestimated by factors between 1.4 and 2.5. It is shown that this deficiency is systematic in character and not anchored in the broken symmetry approach. Nuclear quadrupole splitting of the (55)Mn nuclei is shown to be small in this system. In addition, (14)N and (1)H ligand hyperfine data were calculated and compared well with the experimental results. The quality of the extended point-dipole model was demonstrated in application to (1)H anisotropic hyperfine coupling constants. 相似文献
986.
Günther S Esch F del Turco M Africh C Comelli G Kiskinova M 《The journal of physical chemistry. B》2005,109(24):11980-11985
Using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy, we studied the evolution of the structure and chemical state of a Rh(110) surface, modified by K adlayers and exposed to high O2 doses at elevated temperatures. We find that oxygen coadsorption on the K-covered Rh(110) leads to massive reconstruction of the Rh(110) surface. Stable reconstructed (10 x 2) and (8 x 2) segmented phases with a local coverage of more than two oxygen atoms per surface Rh atom were observed. Formation of surface oxide, which coexists with the (10 x 2) and (8 x 2) segmented adsorption phases, is evidenced at the highest O2 doses. The development of strongly reconstructed adsorption phases with oxide-like stoichiometry and surface oxide under UHV conditions is explained in terms of the stabilization of the (1 x 2) reconstruction and promotion of O2 dissociation by the K adatoms. 相似文献
987.
Schlund S Mladenovic M Basílio Janke EM Engels B Weisz K 《Journal of the American Chemical Society》2005,127(46):16151-16158
NMR experiments and theoretical investigations were performed on hydrogen bonded complexes of specifically 1- and 7-15N-labeled adenine nucleosides with carboxylic acids. By employing a freonic solvent of CDClF2 and CDF3, NMR spectra were acquired at temperatures as low as 123 K, where the regime of slow hydrogen bond exchange is reached and several higher-order complexes were found to coexist in solution. Unlike acetic acid, chloroacetic acid forms Watson-Crick complexes with the proton largely displaced from oxygen to the nitrogen acceptor in an ion pairing structure. Calculated geometries and chemical shifts of the proton in the hydrogen bridge favorably agree with experimentally determined values if vibrational averaging and solvent effects are taken into account. The results indicate that binding a second acidic ligand at the adenine Hoogsteen site in a ternary complex weakens the hydrogen bond to the Watson-Crick bound carboxylic acid. However, substituting a second adenine nucleobase for a carboxylic acid in the trimolecular complex leads to cooperative binding at Watson-Crick and Hoogsteen faces of adenosine. 相似文献
988.
Sebastian Ullrich Borislav Kova
evi Xiulan Xie Jrg Sundermeyer 《Angewandte Chemie (International ed. in English)》2019,58(30):10335-10339
It was discovered that phosphazenyl phosphines (PAPs) can be stronger P‐superbases than the corresponding Schwesinger type phosphazene N‐superbases. A simple synthetic access to this class of PR3 derivatives including their homologization is described. XRD structures, proton affinities (PA), and gas‐phase basicities (GB) as well as calculated and experimental pK values in THF are presented. In contrast to their N‐basic counterparts, PAPs are also privileged ligands in transition metal chemistry. In fact, they are currently the strongest uncharged P‐donors known, exceeding classical and more recently discovered ligands such as PtBu3 and imidazolin‐2‐ylidenaminophosphines (IAPs) with respect to their low Tolman electronic parameters (TEPs) and large cone angles. 相似文献
989.
990.