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31.
Ab initio molecular orbital structures and energies of B2F4, B2Cl4, N2O4, and C2O have been calculated for both perpendicular D2d and planar D2h rotamers. The experimental trend toward greater preference for the D2d forms in going from B2F4 to B2Cl4 is reproduced. N2O4 favors the planar conformation, although the rotation barrier is overestimated at the theoretical levels used. The oxalate dianion is calculated to be more stable in the D2d conformation; the experimental planar arrangement in the solid may be due to crystal packing forces. The preferences for one conformation over another are small; analysis indicates that different effects may predominate in each case: π stabilization for B2F4, hyperconjugation for B2Cl4, lone-pair interactions for N2O4, and electrostatic repulsions for C2O. 相似文献
32.
George R. Clark Brian W. Skelton T.Nell Waters 《Journal of organometallic chemistry》1975,85(3):375-394
The crystal structure of tetrakis(methyldiphenylphosphine)iridium(I) tetrafluoroborate with cyclohexane of solvation, [Ir(PPh2Me)4]BF4·C6H12, has been determined from a three-dimensional X-ray analysis. The compound has been analysed in space group C2/c of the monoclinic system. There are twelve molecules (i.e. 1.5 molecules per asymmetric unit) in a cell of dimensions a = 36.804(8), b = 22.93(2), c = 21.676(4) Å, β = 121.41(1)°. Block-diagonal least-squares refinement has given a final R-factor of 0.060 for 7905 reflections having I > 3σ(I).The structure consists of two crystallographically distinct, but structurally similar molecules, one on a general position and one on a crystallographic two-fold axis. The phosphine ligands around the iridium atoms are in a very distorted square-planar arrangement. The reactions of the cation axe discussed in terms of this structure. 相似文献
33.
G.R. Clark T.J. Collins K. Marsden W.R. Roper 《Journal of organometallic chemistry》1983,259(2):215-232
Reaction of HgR2 with OsHCl(CS)(PPh3)3 yields red, five-coordinate, OsRCl-(CS)(PPh3)2 (R = p-tolyl). From this have been derived the compounds OsRX(CS)(PPh3)2 with X = Br, I, S2CNEt2, O2CMe, O2CCF3. These compounds add an additional ligand, MeCN, CO or CNR to form colourless, six coordinate arylthiocarbonyl complexes, which undergo migratory-insertion reactions to form red, dihapto-thioacyl complexes. The crystal structure of a representative example, Os(η2-CSR)(η1-O2CCF3)(CO)PPh3)2 has been determined. The red equant crystals are orthorhombic, space group P212121, a 11.584(1), b 19.184(2), c 18.90(1) Å, V 4199 Å3, Z 4. The structure was solved by conventional heavy-atom methods and refined by full-matrix least-squares employing anisotropic thermal parameters for all non-hydrogen atoms except the carbon atoms of the triphenylphosphines. The final R factor is 0.057 for 2868 observed reflections.The coordination geometry in the monomeric complex is that of an octahedron distorted by the constraints of the ligands. The triphenyl phosphine ligands are mutually trans; the equatorial plane contains carbonyl, monohapto-trifluoroacetate, and dihapto-thioacyl ligands. Bond distances and angles are OsP 2.405, 2.407(4) Å; POsP 173.9(1)°; OsCO 1.83(2) Å; Os-O (trifluoroacetate) 2.206(11) Å; OsC (thioacyl) 1.91(2); OsS 2.513(6); CS 1.72 Å. The CS bond length implies a reduction in bond order from 2.0 to approx. 1.5 upon coordination to the metal.The η2-thioacyl ligand in Os(η2-CSR)Cl(CNR)(PPh3)2 is methylated with methyl triflate and further reaction with LiCl produces the thiocarbene complex OsCl2(C[SMe]R)(CNR)(PPh3)2. 相似文献
34.
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36.
The phase diagram for the binary system K2CrO4CaCrO4 has been determined for CaCrO4 concentrations up to 60 mole%, using the techniques of differential thermal analysis, X-ray diffraction, and drop calorimetry. Essential features of the phase diagram are: the solid-solid phase transition for pure K2CrO4 at 670°C, β-K2CrO4 ? α-K2CrO4; a eutectoid reaction at 14 mole% CaCrO4 and 548°C, β-K2CrO4 ? α-K2CrO4 + K2CrO4 · CaCrO4; a peritectoid event at 50 mole% CaCrO4 and 640°C, β-K2CrO4 + CaCrO4 ? K2CrO4 · CaCrO4; and a eutectic reaction at 51 mole% CaCrO4 and 678°C, L ? β-K2CrO4 + CaCrO4. X-ray diffraction studies lead to the determination of the unit cell dimensions for the K2CrO4 · CaCrO4 double salt, a C-centered monoclinic form with a0 = 7.615(6) Å, b0 = 22.797(15) Å, c0 = 9.777(9) Å, β = 115.45(5)°. 相似文献
37.
Howard C. Clark Anil B. Goel Chun S. Wong 《Journal of organometallic chemistry》1980,190(4):C101-C104
Simple synthetic routes to the mixed ligand complexes PtLL'X2 and PtLL'XY (L' = PEt3; L = phosphine, arsine, etc.; X = Cl and Y = Cl, H or Me) are described; unexpectedly, these display an extensive chemistry without disproportionation, although in some cases ligand scrambling does occur. 相似文献
38.
D. T. Clark M. Z. Abrahman 《Journal of polymer science. Part A, Polymer chemistry》1982,20(7):1717-1728
The composition and gross structural features of plasma polymers formed in the glow regions of an inductively coupled RF plasma with perfluorobenzene and perfluorobenzene/hydrogen mixtures were investigated by ESCA as a function of the operating parameters. The carbon-to-fluorine stoichiometries of the perfluorobenzene polymers are similar and close to those of the starting material but not of the polymers derived from perfluorobenzene/hydrogen mixtures. The rate of film deposition is dependent on the W/FM parameter. Angular and photon energy-dependent studies confirm the vertical homogeneity of the plasma polymer films investigated. 相似文献
39.
Reed M. Izatt Gypzy C. Lindh Peter Huszthy Glen A. Clark R. L. Bruening Jerald S. Bradshaw James J. Christensen 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(5):501-509
The macrocycle-mediated fluxes of alkali, alkaline earth, and several transition metal cations have been determined and compared in a H2O-CH2Cl2-H2O liquid membrane system using four water-insoluble macrocycles containing a dialkylhydrogenphosphate moiety. Transport of alkali metal cations by these ligands was greatest from a source phase pH = 12 or above into an acid receiving phase (pH = 1.5). Very low fluxes were observed for the transport of the alkaline earth cations and all transition metal ions studied except Ag+ and Pb2+ which were transported reasonably well by these new macrocycles.Deceased: September 5, 1987. 相似文献
40.
The spectral properties of selected UV-blocking and UV-transmitting covering materials were characterized by means of a UV-VIS spectroradiometer or a UV-VIS spectrometer to provide researchers and growers with guidelines for selecting suitable materials for use in studying the effects of ambient solar UV radiation on the production of tomatoes and other high-value crops in high tunnels. A survey was made of a wide range of plastic covering materials to identify commercially available products that had the desired characteristics of transmitting high levels of photosynthetically active radiation and of being stable under ambient solar UV radiation. The study was focused on evaluating films that either blocked or transmitted UV wavelengths below 380 nm to determine comparative growth, yield and market quality and to provide a tool for integrated pest management. Based on this survey, two contrasting covering materials of similar thickness (0.152 mm) and durability (4-year polyethylene), one a UV-blocking film and the other a UV-transmitting film, were selected and used to cover two high tunnels at Beltsville, MD. Spectroradiometric measurements were made to determine comparative spectral irradiance in these two high tunnels covered with these materials and under ambient solar UV radiation. Comparative measurements were also made of selected glass and plastic materials that have been used in UV exclusion studies. 相似文献