Orthorhombic superstructures within the rare earth strontium-doped cobaltate perovskites: Ln1−xSrxCoO3−δ (Ln=Y, Dy-Yb; 0.750?x?0.875)

A combination of electron, synchrotron X-ray and neutron powder diffraction reveals a new orthorhombic structure type within the Sr-doped rare earth perovskite cobaltates Ln_1−xSr_xCoO_3−δ (Ln=Y³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺and Yb³⁺). Electron diffraction shows a C-centred cell based on a 2√2a_p×4a_p×4√2a_p superstructure of the basic perovskite unit. Not all of these very weak satellite reflections are evident in the synchrotron X-ray and neutron powder diffraction data and the average structure of each member of this series could only be refined based on Cmma symmetry and a 2√2a_p×4a_p×2√2a_p cell. The nature of structural and magnetic ordering in these phases relies on both oxygen vacancy and cation distribution. A small range of solid solution exists where this orthorhombic structure type is observed, centred roughly around the compositions Ln_0.2Sr_0.8CoO_3−δ. In the case of Yb³⁺ the pure orthorhombic phase was only observed for 0.850?x?0.875. Tetragonal (I4/mmm; 2a_p×2a_p×4a_p) superstructures were observed for compositions having higher or lower Sr-doping levels, or for compounds with rare earth ions larger than Dy³⁺. These orthorhombic phases show mixed valence (3+/4+) cobalt oxidation states between 3.2+ and 3.3+. DC magnetic susceptibility measurements show an additional magnetic transition for these orthorhombic phases compared to the associated tetragonal compounds with critical temperatures > 330 K.     

Discotic Metallomesogens: Effects of Sidechains Density in Transition Metal Bis(β-Diketonate) Complexes

The preparation and mesogenic properties of a series of discotic β-diketonate metal complexes are reported. The results show that the density of side chains, positions of side chains, and the geometries of the metal centers play important roles in determining the mesomorphic behaviors and thermodynamic stability of these complexes. In the series of copper complexes 3, all these disc-like molecules with eight alkoxy side chains exhibit columnar hexagonal disordered (D_hd) mesophases. In the series of copper complexes 2 with six side chains, only compounds substituted with longer alkoxy chains (n = C₁₄ or C₁₆) exhibit discotic columnar mesophase. However, in the series of complexes 1, only crystal-to-isotropic transitions were observed. The results showed that induction of liquid crystallinity not only depends on the numbers of side chains (i.e. side chain density), but also on the degree of distribution over the central core. Palladium complexes analogs exhibit similar discotic mesophases, and due to their greater core-core organization, they also have higher clearing points and wider temperature range of mesophases than copper complexes.     

Crystal structure of the thortveitite‐related M phase, (MnxZn1–x)2V2O7 (0.75 < x < 0.913): a combined synchrotron powder and single‐crystal X‐ray study

The determination of the crystal structure of the M phase, (Mn_xZn_1–x)₂V₂O₇ (0.75 < x < 0.913), in the pseudobinary Mn₂V₂O₇–Zn₂V₂O₇ system for x ≃ 0.8 shows that the previously published triclinic unit‐cell parameters for this thortveitite‐related phase do not describe a true lattice for this phase. Instead, single‐crystal X‐ray data and Rietveld refinement of synchrotron X‐ray powder data show that the M phase has a different triclinic structure in the space group P with Z = 2. As prior work has suggested, the crystal structure can be described as a distorted version of the thortveitite crystal structure of β‐Mn₂V₂O₇. A twofold superstructure in diffraction patterns of crystals of the M phase used for single‐crystal X‐ray diffraction work arises from twinning by reticular pseudomerohedry. This superstructure can be described as a commensurate modulation of a pseudo‐monoclinic basis structure closely related to the crystal structure of β‐Mn₂V₂O₇. In comparison with the distortions introduced when β‐Mn₂V₂O₇ transforms at low temperature to α‐Mn₂V₂O₇, the distortions which give rise to the M phase from the β‐Mn₂V₂O₇ prototype are noticeably less pronounced.     

Design Rules for Self‐Assembly of 2D Nanocrystal/Metal–Organic Framework Superstructures

We demonstrate the guiding principles behind simple two dimensional self‐assembly of MOF nanoparticles (NPs) and oleic acid capped iron oxide (Fe₃O₄) NCs into a uniform two‐dimensional bi‐layered superstructure. This self‐assembly process can be controlled by the energy of ligand–ligand interactions between surface ligands on Fe₃O₄ NCs and Zr₆O₄(OH)₄(fumarate)₆ MOF NPs. Scanning transmission electron microscopy (TEM)/energy‐dispersive X‐ray spectroscopy and TEM tomography confirm the hierarchical co‐assembly of Fe₃O₄ NCs with MOF NPs as ligand energies are manipulated to promote facile diffusion of the smaller NCs. First‐principles calculations and event‐driven molecular dynamics simulations indicate that the observed patterns are dictated by combination of ligand–surface and ligand–ligand interactions. This study opens a new avenue for design and self‐assembly of MOFs and NCs into high surface area assemblies, mimicking the structure of supported catalyst architectures, and provides a thorough fundamental understanding of the self‐assembly process, which could be a guide for designing functional materials with desired structure.     

Inclusion chemistry for the modeling of heme proteins

Early attention to the modeling of heme proteins is enhancing the understanding of biochemistry. Those studies are also contributing to the development of techniques for the modeling of still more intricate, multifunctional, variously selective natural systems. Selectivity in simple systems may involve the molecular capability to bind only one of a family of related species or it may mean the ability to select and control one of a number of possible functions of a given bound species. Complicated systems simultaneously combine the two kinds of simple selectivities for two or more different classes of guest, often with synergistic interrelationships. The subject is developed around examples of binary, tertiary, and quarternary complexes designed to model the behavior of monooxygenases.     

上层建筑决定生产力——论官民 官官 民民相争

文章认为,生产力决定生产关系进而决定上层建筑的观点不能成立.官民相争、官官相争、民民相争构成人类社会的三大基本予盾.民主或法治既是从根本上协调三大矛盾的制度装置,也是生产力主体迫使政府供给适合生产力发展要求的生产关系的保证.第一生产力的主体是知识分子.     

一种具有超结构的[Zn(C_2H_8N_2)_3]Cl_2·2H_2O晶体

试图在Eu2O3、Zn粉、HCl、H_2S、Me4NCl、H_2O、CH_3COOH等起始物参加的反应系统中,合成某种二价铕配合物时得到一棱柱状透明[Zn(C2H8N2)3]Cl2 · 2H_2O晶体, 其主要晶体学参数如下：Mr = 350.60,单斜, C2/c, a = 26.3749(7), b =13.9613(5), c =12.9565(4) ?, β = 93.285(1) o, V = 4763.1 ?3, Z = 12, Dx = 1.467g·cm－3, μ(MoKα) = 1.885 mm－1, F(000) = 2208, R = 0.0552。单晶结构分析结果表明本文标题配合物具有一种超结构形式。     

Characterization of Mixed Crystals in the System Cu2MnxCo1−xGeS4 and Investigations of the Tetrahedra Volumes

In a series of investigations on normal tetrahedral compounds we present mixed crystals in the system Cu₂Mn_xCo_1?xGeS₄ (0 < x < 1) and an inspection of their tetrahedra volumes. Cu₂CoGeS₄ crystallizes tetragonal in a stannite type structure, Cu₂MnGeS₄ crystallizes orthorhombic in the wurtzstannite structure type. The crystal structures of Cu₂CoGeS₄ and Cu₂Mn_0.68Co_0.32GeS₄ were refined from single crystal diffraction data. The refinement of Cu₂CoGeS₄ converged to R = 0.0547 and wR2 = 0.0847 for 299 unique reflections. The refinement of Cu₂Mn_0.68Co_0.32GeS₄ converged to R = 0.0481 and wR2 = 0.0877 for 1556 unique reflections. From these data the tetrahedra volumes of the end members and of Cu₂Mn_0.68Co_0.32GeS₄ are calculated. In Cu₂CoGeS₄ tetrahedra [MS₄] are similar in size. In contrast, the differences of the volumes of the polyhedra [MS₄] in the orthorhombic wurtzite superstructure type compounds Cu₂MnGeS₄ and Cu₂Mn_0.68Co_0.32GeS₄ are significant (M = Cu, Mn, (Mn_0.68Co_0.32), Co, Ge). From x = 0 to x = 0.5 the tetragonal structure type dominates while from x = 0.7 to the Cu₂MnGeS₄ end member the products crystallize in the orthorhombic structure type. Melting points of the mixed crystals decrease linearly with increasing manganese content.     

整体煤气化联合循环的煤气饱和系统优化研究

对一个干法进料整体煤气化联合循环(IGCC)的煤气饱和系统进行了研究，分析了相关参数对系统性能的影响，指出了各种可能的煤气饱和系统流程布置方式，在此基础上，构造出一个包括各种可能流程的煤气饱和系统的超级结构，然后，建立起有约束条件的混合整数非线性规划模型，对煤气饱和系统的优化模型进行解算，优化结果给出了最佳的参数值和系统流程．结果表明，优化后IGCC的净效率比原设计方案提高了0．42％．分析揭示了煤气饱和系统的设计对其性能影响的规律性和内在本质．     

Chemistry and thermodynamics of the twin charge-ordering transitions in RBaFe2O5+w series

Thermal and volume parameters of the twin charge-ordering Verwey transitions in RBaFe₂O_5+w (R=a rare-earth element) are summarized as a function of R and w. Their determination is exemplified for case R = Dy, for which also synthesis conditions, phase relations, and refined crystal-structure data for the valence-mixed (Fe^2.5+) and charge-ordered (Fe²⁺ and Fe³⁺) phases are reported. Data for the R=Nd, Sm, Eu and Gd variants with wide ranges of oxygen non-stoichiometry suggest that increasing w decreases ΔS and the temperature of the transition in a manner that is similar to a behavior under increasing concentration of an ideal solution of RBaFe₂O₆ in RBaFe₂O₅. Thermal parameters of the transition for the ideal mixed-valence composition RBaFe₂O_5.000 are estimated from such compositional dependences, varying reasonably smoothly as a function of R (radius, electronegativity, polarizability). Parameter ΔV is the only one that follows the structural discontinuity between the charge-ordered R = Nd and variants with smaller trivalent R ions. The ordering of the d_xz orbitals of the Fe²⁺ ions is thus being achieved at a cost of lowering the symmetry when the R size becomes unfavorably large. A definition of the Verwey transition as a first-order orbital ordering of a valence-mixed phase is suggested.