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971.
Hisanobu Wakita Georg Johansson Magnus Sandström Peter L. Goggin Hitoshi Ohtaki 《Journal of solution chemistry》1991,20(7):643-668
Structures of the complexes formed in aqueous solutions between zinc(II) and iodide ions have been determined from large-angle X-ray scattering, Raman and far-IR measurements. The coordination in the hydrated Zn2+ hexaaqua ion and the first iodide complex, [ZnI]+, is octahedral, but is changed into tetrahedral in the higher complexes, [ZnI2(H2O)2], [ZnI3(H2O)]– and [ZnI4]2–. The Zn-I bond length is 2.635(4)Å in the [ZnI4]2– ion and slightly shorter, 2.592(6)Å, in the two lower tetrahedral complexes. In the octahedral [ZnI(H2O)5]+ complex the Zn-I bond length is 2.90(1)Å. The Zn-O bonding distances in the complexes are approximately the same as that in the hydrated Zn2+ ion, 2.10(1)Å. 相似文献
972.
Peter Schwendt Michal Sivák Andrey E. Lapshin Yury I. Smolin Yury F. Shepelev Dalma Gyepesov 《Transition Metal Chemistry》1994,19(1):34-36
Summary The monoperoxo complexes, M2[VO(HEDTA)(O2)]· 4H2O, where M is K+ or NH
4
+
and H4EDTA is ethylene-diaminetetraacetic acid, were prepared and characterized by Raman and i.r. spectra in the solid state and in aqueous solution. The single crystal X-ray study revealed a pentagonal bipyramidal anion structure with a tetradentate HEDTA(3—) ligand. The decomposition of complexes in aqueous solution to blue vanadium(IV) complexes as end products proceeds via a nonperoxo complex of vanadium. 相似文献
973.
Insertion of the glycosylidene carbenes, derived from the gluco- and the manno-diazirines 1 and 2 , into the Sn? H bond of R3SnH (R = Bu or Ph) leads to the fully substituted stannoglycosides 3 – 8 (53–77%). The 1,2-cis-configurated products are formed preferentially (α-D /β -D ranges from 2.5:1 to 5.1:1 with 1 , and 1:1.3 to 1:4.2 with 2 ). Relative to CH2Cl2, THF favors formation of the equatorial Sn-glycosides. The stannylated (benzyloxy)glucals 9 and 10 were isolated as side products. The reaction of 1 with (Bu3Sn)2 yielded 9 (17% in CH2Cl2; 36% in CCl4) together with the azines 11 and the benzyloxyglucal 12 . NMR Data of the Sn-glycosides 3 – 8 show evidence for an anomeric effect, 1J(C(1),H) being larger in the axial and 1J(Sn,C(1)) larger in the equatorial anomers. 相似文献
974.
Peter M. Pojer 《Tetrahedron letters》1984,25(23):2507-2508
In the absence of deuterium gas, the reaction of deuterated Raney nickel with benzene derivatives, carbonyl compounds, alkenes and activated methylene groups gave either fully deuterated (reduced) products or led to hydrogen-deuterium exchange. 相似文献
975.
A theoretical and experimental treatment of axial dispersion in coiled tubes is presented. The dispersion, δ, is related to the theoretical plate height divided by four times the radius of the tube (H/4r). This parameter, when plotted against the product of the Reynolds number and the Schmidt number (ReSc), accurately predicts maxima in dispersion curves. Variations in the boundary layer thickness and the velocity profile cause the dispersion to pass through a maximum at a constant value of log (De2Sc1·14) equal to 6.13 for unretained solutes (De is the Dean number). A new measure of dispersion is proposed; the reduced dispersion, ? = 256/(Re0.667Sc), is derived from the experimental behavior of dispersion at values of log (De2Sc1·14) smaller than 6.13. The logarithm of ? is found to be approximately zero for 2.2 < log (De2Sc1·14) < 6.1 and to decrease linearly with log (De2Sc1·14) at higher values. Experiments with four solutes that have a wide range of molecular diffusivities are reported. Results agree with theory. 相似文献
976.
Amitava Choudhury Larisa A. Polyakova Ingo Hartenbach Thomas Schleid Peter K. Dorhout 《无机化学与普通化学杂志》2006,632(15):2395-2401
Four related quaternary compounds containing rare‐earth metals have been synthesized employing the molten flux method and metathesis. The reactions of Eu and Rb2S5 with Si and Ge in evacuated fused silica ampoules at 725 °C for 150 h yielded RbEuSiS4 ( I ) and RbEuGeS4 ( II ), respectively. On the other hand, a reaction between CeCl3 and K4Ge4Se10 at 650 °C for 148 h has yielded KCeGeSe4 ( III ) and KPrSiSe4( IV ) was obtained by the reaction of elemental Pr, Si and Se in KCl flux at 850 °C for 168 h. Crystal data for these compounds are as follows: I , orthorhombic, space group P212121 (#19), a = 6.392(1), b = 6.634(2), c = 17.001(3) Å, α = β = γ = 90°, Z = 4; II , monoclinic, space group P21/m (#11), a = 6.498(2), b = 6.689(3), c = 8.964(3) Å, β = 108.647(6)°, Z = 2; III , monoclinic, space group P21 (#4), a = 6.852(2), b = 7.025(2), c = 9.017(3) Å, β = 108.116(2)°, Z = 2; IV , monoclinic, space group P21 (#4), a = 6.736(2), b = 6.943(2), c = 8.990(1) Å, β = 108.262(2)°, Z = 2. The crystal structures of I ‐ IV contain two‐dimensional corrugated anionic layers of the general formula, [LnEQ4]? (Ln = Ce, Pr, Eu; E = Si, Ge and Q = S, Se) alternately piled upon layers of alkali cations. In addition to structural elucidation, Raman and UV‐visible spectroscopy, and magnetic measurements for compound III (KCeGeSe4) are also discussed. 相似文献
977.
R. Q. Topper K. Chung C. M. Boelke D. Louie J. S. Kang R. Hannan T. Kiang L. H. Chan 《Theoretical chemistry accounts》2003,109(4):233-238
2-(Acetylamino)fluorene (AAF), a potent mutagen and a prototypical example of the mutagenic aromatic amines, forms covalent
adducts to DNA after metabolic activation in the liver. A benchmark study of AAF is presented using a number of the most widely
used molecular mechanics and semiempirical computational methods and models. The results are compared to higher-level quantum
calculations and to experimentally obtained crystal structures. Hydrogen bonding between AAF molecules in the crystal phase
complicates the direct comparison of gas-phase theoretical calculations with experiment, so Hartree–Fock (HF) and Becke–Perdew
(BP) density functional theory (DFT) calculations are used as benchmarks for the semiempirical and molecular mechanics results.
Systematic conformer searches and dihedral energy landscapes were carried out for AAF using the SYBYL and MMFF94 molecular
mechanics force fields; the AM1, PM3 and MNDO semiempirical quantum mechanics methods; HF using the 3-21G*and 6-31G* basis
sets; and DFT using the nonlocal BP functional and double numerical polarization basis sets. MMFF94, AM1, HF and DFT calculations
all predict the same planar structures, whereas SYBYL, MNDO and PM3 all predict various nonplanar geometries. The AM1 energy
landscape is in substantial agreement with HF and DFT predictions; MMFF94 is qualitatively similar to HF and DFT; and the
MNDO, PM3 and SYBYL results are qualitatively different from the HF and DFT results and from each other. These results are
attributed to deficiencies in MNDO, PM3 and SYBYL. The MNDO, PM3 and SYBYL models may be unreliable for compounds in which
an amide group is immediately adjacent to an aromatic ring.
Received: 26 May 2002 / Accepted: 12 December 2002 /
Published online: 14 February 2003 相似文献
978.
Peter D. Battle Jonathan C. Burley Clare P. Grey 《Journal of solid state chemistry》2004,177(1):119-125
Polycrystalline samples of the n=2 Ruddlesden-Popper phase La3LiMnO7 have been prepared and characterized. X-ray and neutron diffraction suggest that the structure is tetragonal with a disordered distribution of Li and Mn cations over the octahedral sites, but 6Li MAS NMR shows that the Li and Mn are 1:1 ordered locally. Electron microscopy shows that the stacking of the cation-ordered, perovskite-like bilayers along the crystallographic z-axis is disordered on the distance scale sampled by X-ray and neutron diffraction. Magnetometry data and neutron diffraction data collected at 2 K together suggest that the Mn cations within each structural domain order antiferromagnetically at 14 K, but that the disorder along z prevents the establishment of long-range magnetic order. 相似文献
979.
980.
Peter ?ernoch Petr Štěpánek Miroslav Šlouf Manfred Stamm 《European Polymer Journal》2007,43(4):1144-1153
A systematic study of formation of surface patterns in block copolymer thin layers after their exposure to solvent vapors was performed. The studied effect involves layers of thickness approximately equal to the ordering size of polymers - about 45 nm. Experiments were performed on three styrene - methacrylate derivative block copolymers, synthesized by living anionic polymerization: poly(4-octylstyrene)-block-poly(butyl methacrylate), poly(4-fluorostyrene)-block-poly(butyl methacrylate) and poly(p-octylstyrene)-block-poly(methyl methacrylate). The polymers were exposed to vapors of chloroform, 1,4-dioxane, hexane, acetone and tetrahydrofuran. 相似文献