La6Mo8O33: a new ordered defect scheelite superstructure

The structure of La₆Mo₈O₃₃ has been determined from a triple pattern powder diffraction analysis. Two high-resolution neutron diffraction patterns collected at 1.594 and 2.398 Å and one X-rays were used. This molybdate crystallizes in a non-centrosymmetric monoclinic space group P2₁(N°4), Z=2,a=10.7411(3) Å, b=11.9678(3) Å, c=11.7722(3) Å, β=116.062 (1)°. La₆Mo₈O₃₃ is an unusual ordered defect Scheelite. Hence, it should be described with cation vacancies and an extra oxygen atom following the formula: La₆□₂Mo₈O₃₂₊₁. This extra oxygen atom leads to a pyramidal environment, whereas the other molybdenum atoms present tetrahedral environment. A molybdenum tetrahedral is connecting to the pyramid, forming an [Mo₂O₉] unit.     

疏水性微孔中水的结构和扩散性质的分子模拟

用分子动力学（MD）方法模拟了受限在疏水性微孔中的水的结构与动力学行为.分别考察了孔径、温度和压力对水在孔道方向的密度分布和自扩散系数的影响,计算了不同温度下水的径向分布函数.发现在小孔径的微孔中,随着温度的降低,水分子沿孔道的分布逐渐变得不均匀,最终导致气-液相分离,微孔孔道内有明显的分段现象.受限在小孔径微孔中水的自扩散系数大约为体相流体水的20％～30％,并且随着孔径的减小,自扩散系数也减小.同时还发现沿孔道方向的自扩散系数分量大约为孔径方向的4～5倍.提出了微孔中水自扩散系数的关联模型.     

A theoretical study of substituent effects on the structure of isolated and condensed three-membered rings. A comparison between radicals and parent hydrocarbons

Substituent effects on the structure of radicals and parent hydrocarbons formed by isolated or condensed three-membered rings have been investigated by Hartree-Fock, post-Hartree-Fock and density functional methods. The trends of structural parameters computed for the hydrocarbon systems are in agreement with available experimental data. Substituent effects can be rationalized in terms of interactions between localized orbitals obtained by natural bond analysis. The effects are even larger in free radicals and can be analyzed using the same model. Received: 13 March 1998 / Accepted: 13 July 1998 / Published online: 9 October 1998     

The structure of organic derivatives of hexacoordinated germanium. (O→Ge) chelated bis-(2-oxo-1-hexahydroazepinylmethyl)difluorogermane and bis-(2-oxo-1-hexahydroazepinylmethyl)fluorogermane tetrafluoroborate

Two fluoro derivatives of hexacoordinated germanium containing chelated 2-oxo-1-hexahydroazepinylmethyl ligands were investigated by X-ray diffraction analysis. The coordination polyhedron of the Ge atom in difluoride1 is a somewhat distorted octahedron with the following bond lengths (Å): Ge-F 1.799(2), GeO 2.185(3), and Ge-C 1.945(4). Tetrafluoroborate 2 has an ionic structure; the valence environment of the Ge atom is a distorted trigonal bipyramid open in the direction of the BF ₄ ^– anion. The bond lengths in 2 are: Ge-F 1.792(8), GeO 2.001(4), and Ge-C 1.937(9) Å; the Ge...F(anion) distances are 3.43(1) and 3.68(1) Å. Analysis of the geometry of1,2, and related structures containing hexa-coordinated germanium shows that the parameters of their hypervalent moieties are related to each other by dependences similar to those observed in compounds of pentacoordinated Si and Ge.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1427–1431, August, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (project No 93-03-4855).     

部份层无序铝交联蒙脱土结构的研究

应用非完整晶体的XRD衍射及阳离子交换量的测定等实验数据, 得出了铝交联蒙脱土的三维结构模型. 结构中Al(III)多数以十三聚体形式进入层间, 层间距为1.97 nm, 几率为0.65, 少数以六聚体形式进入层间, 层间距为1.5 nm, 几率为0.25, 其余10%的层间仅为水分子. 并给出了交联柱子在层间的分布与层单元之间的连接方式. 目前通用的以Bragg公式计算所得的d_(001)值来表征交联浆脱土的层间距是不确切的.     

Synthesis, crystal structure, infrared and Raman spectra of Sr5(As2O7)2(AsO3OH)

The new compound Sr₅(As₂O₇)₂(AsO₃OH) was synthesized under hydrothermal conditions. It represents a previously unknown structure type and belongs to a group of a few compounds in the system SrO-As₂O₅-H₂O; (As₂O₇)⁴⁻ besides (AsO₃OH)²⁻ groups have not been described yet. The crystal structure of Sr₅(As₂O₇)₂(AsO₃OH) was determined by single-crystal X-ray diffraction (space group P2₁/n, a=7.146(1), b=7.142(1), , β=93.67(3)°, , Z=4). One of the five symmetrically unique Sr atoms is in a trigonal antiprismatic (Inorg. Chem. 35 (1996) 4708)—coordination, whereas the other Sr atoms adopt the commonly observed (“Collect” data collection software, Delft, The Netherlands, 1999; Methods Enzymol. 276 (1997) 307)—coordination. The position of the hydrogen atom was located in a difference Fourier map and subsequently refined with an isotropic displacement parameter. Worth mentioning is the very short hydrogen bond length O_h-H?O(1) of 2.494(4) Å; it belongs to the shortest known examples where the donor and acceptor atoms are crystallographically different. This hydrogen bond was confirmed by IR spectroscopy. In addition, Raman spectra were collected in order to study the arsenate groups.     

Calorimetric study of the solubilization of cholesterol,retinol and retinal by reversed AOT micelles

Distribution constants and standard enthalpies of transfer of cholesterol, retinol and retinal partitioned between n-heptane and water containing reversed sodium bis(2-ethylhexyl) sulfosuccinate (AOT) micelles as a function of the molar concentration ratio (R=[water]/[AOT]) were evaluated by a calorimetric method. The results indicate that, in spite of the bulky hydrocarbon radical, these solubilizates behave like alcohols with a short alkyl chain. Moreover, cholesterol is always solubilized in the palisade layer of the reversed micelles whereas retinol and retinal are preferentially solubilized in the aqueous pseudophase. The influence of the enthalpic and the entropic contributions to the transfer of the solubilizates from n-heptane to reversed AOT micelles are also considered.     

丝氨酸在蔗糖水溶液中的稀释焓

利用LKB 2277生物活性检测仪分别测定了298.15 K时丝氨酸在不同组成的蔗糖水溶液中的稀释焓, 利用McMillan-Mayer理论,计算了丝氨酸在不同组成的蔗糖水溶液中的焓对相互作用系数,并与其在葡萄糖水溶液中的焓对相互作用系数h2进行了比较.结果表明,丝氨酸在蔗糖和葡萄糖水溶液中的焓对相互作用系数h2都是负值,并且随着糖浓度的增加,h2系数的绝对值逐渐减少.根据溶质-溶质相互作用和溶质-溶剂相互作用对结果进行了解释.     

Structural and energetic consequences of the formation of intramolecular hydrogen bonds

Formation of intramolecular hydrogen bonds leads to structural modifications in the whole molecule, which are discussed on the basis of B3LYP/6-31G(d,p) calculations. The energy and the structure of various hydrogen-bonded and open conformers are considered for two groups of ortho-substituted phenols–N-dimethylaminomethylphenols (Mannich bases) and N-methylbenzylideneamines (Schiff bases). The energy of intramolecular hydrogen bond formation in Mannich bases was corrected for non-bonded interactions within the molecules, based on a thermodynamic cycle. Structural data were used to estimate the fraction of the ortho-quinoid (keto) form in particular tautomers. It is shown that proton transfer in Schiff bases leads to an increase of this fraction to about 40%, while opening of the hydrogen bond in the proton transferred form increases the keto fraction to 70%.