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171.
Michael MuehlhoferThomas Strassner Eberhardt HerdtweckWolfgang A Herrmann 《Journal of organometallic chemistry》2002,660(2):121-126
Novel bridged platinum(II) biscarbene complexes are reported: 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) (3) and 1,1′-dimethyl-3,3′-ethylene-4-diimidazolin-2,2′-diylidene platinum(II) complexes 4 are directly accessible in high yields starting from platinum halides. The one-pot synthesis obviates the need for multi-step reactions via metal precursors or free carbenes. An X-ray crystal structure of 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) dibromide (3b) confirmed the structural similarity to the known corresponding palladium complexes. Since free 1,1′-di-R-3,3′-methylene-4-diimidazolin-2,2′-diylidenes are only available in low yields this synthetic route provides an easy access to the corresponding carbene complexes. 相似文献
172.
Maria?Victoria Roux Paul?J.?Smith Joel?F.?LiebmanEmail author 《Structural chemistry》2005,16(1):73-75
Despite their seeming simplicity, substituted guanidines have not particularly caught the attention of the thermochemical community. The current paper compares the enthalpy of formation of solid substituted guanidines with correspondingly substituted benzenes, also as solids. 相似文献
173.
煤的孔结构特征对水煤浆性质的影响 总被引:7,自引:3,他引:7
本文选用17种不同变质程度的中国煤,详细研究了煤孔结构特征对煤浆性质的影响。发现煤孔体积通过影响煤在分散体系中的吸水性,从而影响煤之成浆性。但由于不同变质程度煤表面亲水性的显著差异,煤孔体积在影响煤成浆性的能力方面差别很大,这使得煤吸水性和浆体最高煤浓度与煤孔体积并不存在直接的相关性,而是取决于煤孔体积V和以煤-水接触角(θ)的余弦值表示的煤表面亲水性因子的乘积,即煤之有效孔体积:V×cos(θ/ 相似文献
174.
Transmission electron microscopy of freeze fractured and replicated samples (TEM) and polarizing light microscopy (PLM) are
used to investigate the defect structures of the thermotropic and lyotropic mesophases of the non-steroidal antiinflammatory
drug fenoprofen sodium and of the thermotropic mesophase of the nonionic surfactant sucrose oleate (O1570). All mesophases
have a layered, smectic structure. The thermotropic liquid crystal of feno-profen sodium is an interdigitated smectic A phase
(smectic Ad) having the highest viscosity of the investigated samples. The thermotropic mesophase of the sugar ester is also
of the type smectic A, likely to be of subtype smectic A2 (bilayered smectic structure). The lyotropic mesophase is of lamellar
liquid crystalline nature and has a much lower viscosity than the thermotropic mesophases. In the PLM the lyotropic fenoprofen
mesophase has a strong tendency to form a pseudoisotropic texture, indicating a strong tendency to form undisturbed layered
structures. Other textures exhibited in the PLM are fan-shaped texture and maltese-cross texture. Confocal domains, cylinders,
pits and peaks as well as screw dislocations are found in great number in the TEM. However, no greater regions of undisturbed
lamellar arrangement in the lyotropic mesophase could be detected. The only texture of the thermotropic fenoprofen mesophase
visible in the PLM is the fan-shaped texture, indicating confocal domains as predominant structural elements. However, no
confocal domains (tori or Dupin cyclides) are found in the TEM. In the PLM the sugar–ester mesophase exhibited a fan-shaped
texture, maltese crosses and oily streaks as dominant textures. In the TEM only a few +π and −π disclinations and imperfect
confocal domains could be detected. The discrepancies in the appearance of defect structures and textures between the mesophases
as well as the discrepancies in the findings in the PLM and in the TEM investigations are caused by the different sample preparation
and the different viscosities of the mesophases.
Received: 28 May 1997 Accepted: 2 September 1997 相似文献
175.
Synthesis and Structure of Copper(I)Chalcogenolate-2,2′-Bipyridine Complexes [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 and [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 The oligomeric homoleptical copper(I) chalcogenolate compounds [CuS(2,4,6-iPr3C6H2)]x=4,8 and [CuSe(2,4,6-iPr3C6H2)]6 react with 2,2′-bipyridine (Bipy) to yield the tetranuclear complex [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 ( 4 ) and the dinuclear complex [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 ( 5 ). The structures of 4 and 5 were determined by X-ray analysis. In the eight-membered Cu4S4 core of 4 with chair conformation the copper atoms are linked by μ2-bridging selenolate ligands. Only two copper atoms are coordinated by 2,2′bipyridine. The corresponding copper(I) selenolate complex ( 5 ) forms a folded four-membered Cu2Se2 ring with μ2-bridging selenolate ligands. The Cu? Cu distance of 2.52 Å is relatively short. In contrast to the reaction performed with 2,2′-bipyridine, addition of phenantroline to 1 respectively 2 yields a dinuclear complex [CuS(2,4,6-iPr3C6H2)]2(Phen)2 ( 10 ). NMR spectroskopic and cryoscopic measurement of 4 show that this complex dissociates into smaller fragments in solution which undergo rapid exchange reactions. However, corresponding investigations performed on 5 indicate that the solid state structure is maintained in solution. The electrochemical behaviour of 4, 5 and 10 was studied in CH2Cl2 and in any case no reversible redox processes could be observed. 相似文献
176.
Alessandro D'Aprano Ines Dorina Donato Vincenzo Turco Liveri 《Journal of solution chemistry》1989,18(8):785-793
Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered. 相似文献
177.
This article describes the structure determination of five homoleptic d(10) metal-aryl/alkylacetylides [RC triple bond CM] (M=Cu, R=tBu 1, nPr 2, Ph 3; R=Ph, M=Ag 4; Au 5) by using X-ray single-crystal and powder diffraction. Complex 1.C6H6 reveals an unusual Cu20 catenane cluster structure that has various types of tBuC triple bond C-->Cu coordination modes. By using this single-crystal structure as a starting model for subsequent Rietveld refinement of X-ray powder diffraction data, the structure of the powder synthesized from CuI and tBuC triple bond CH was found to have the same structure as 1. Complex 2 has an extended sheet structure consisting of discrete zig-zag Cu4 subunits connected through bridging nPrC triple bond C groups. Complex 3 forms an infinite chain structure with extended Cu-Cu ladders (Cu-Cu=2.49(4)-2.83(2) A). The silver(I) congener 4 is iso-structural to 3 (average Ag-Ag distance 3.11 A), whereas the gold(I) analogue 5 forms a Au...Au honeycomb network with PhC triple bond C pillars (Au-Au=2.98(1)-3.26(1) A). Solid-state properties including photoluminescence, nu(C triple bond C) stretching frequencies and thermal stability of these polymeric systems are discussed in the context of the determined structures. 相似文献
178.
A family of layered bismuth oxyhalides, LI0.5Bi1.5O2X and LIIBiO2X has been reinvestigated. Formation of X1-type Sillén compounds has been established for LI=Li, Na, LII=Ca, Sr, Ba, and X=Cl, Br, I, but the details of their crystal structures are different. While all LI0.5Bi1.5O2X, CaBiO2Br, and CaBiO2I adopt the disordered tetragonal Nd2O2Te structure, all compounds of LII=Sr and Ba are orthorhombic and isostructural to PbSbO2Cl, due to L/Bi cation ordering. Crystal structures have been determined for CaBiO2I, SrBiO2Br, SrBiO2I, and BaBiO2I. We discuss the factors which determine the occurrence and type of cation ordering in the quaternary bismuth and antimony X1-type oxyhalides. We also predict that more isostructural compounds can be prepared with antimony. 相似文献
179.
Mireille Regnier 《BIT Numerical Mathematics》1985,25(2):335-357
Grid file algorithms were suggested in [12] to provide multi-key access to records in a dynamically growing file. We specify here two algorithms and derive the average sizes of the corresponding directories. We provide an asymptotic analysis. The growth of the indexes appears to be non-linear for uniform distributions:O(v
c
) orO(v
), wherec=1+b–1, =1+(s-1)/(sb+1),s is the number of attributes being used,v the file size, andb the page capacity of the system. Finally we give corresponding results for biased distributions and compare transient phases. 相似文献
180.