Molecular Structure of [Cu<Subscript>2</Subscript>(MeCN)<Subscript>2</Subscript>(μ-tpy)<Subscript>2</Subscript>][BPh<Subscript>4</Subscript>]<Subscript>2</Subscript>: A Helical Di-Cuprous Terpyridine Complex

Abstract  The molecular structure of [Cu₂(MeCN)₂(μ-tpy)₂][BPh₄]₂ has been determined. The two terpyridine ligands coordinate to the same Cu(I) center in a bidentate configuration, in which the copper adopted a distorted tetrahedral geometry with the four nitrogen donors. The third ring of each terpyridine ligand forms a bridge with a second Cu(I) center, whose tetrahedral coordination sphere is completed by two acetonitrile ligands. The resulting structure represents a section of a double helix. Crystal data: space group C2/c, a = 27.202(5), b = 12.995(3), c = 23.409(5) ?, β = 123.13(3)°; V = 6930(2) ?³, Z = 4, R = 0.0613, wR ₂ = 0.0946. Graphical Abstract  The molecular structure of [Cu₂(MeCN)₂(μ-tpy)₂][BPh₄]₂ has been determined. The terpyridine ligands coordinate in a bidentate fashion to the same Cu center and monodentate to a second Cu center resulting in a double helical structural motif.      

Locality of connective constants

The connective constant $\mu \left(G\right)$ of a quasi-transitive graph $G$ is the exponential growth rate of the number of self-avoiding walks from a given origin. We prove a locality theorem for connective constants, namely, that the connective constants of two graphs are close in value whenever the graphs agree on a large ball around the origin (and a further condition is satisfied). The proof is based on a generalized bridge decomposition of self-avoiding walks, which is valid subject to the assumption that the underlying graph is quasi-transitive and possesses a so-called unimodular graph height function.     

一些含桥羧基配体的羰基钼(Ⅰ)化合物的NMR研究

化合物(1)[(CO)₄Mo(SPh)₂Mo(CO)₄]同羧酸L反应得到桥羧基配体的羰基钼(Ⅰ)化合物[Bu₄N][(CO)₃Mo(SPh)₂LMo(CO₃)](L=CF₃COO,HCOO,CH₃COO,C₂H₅COO,OOCCH₂CH₂COO,Me₃COO),在室温下测定了它们的¹H,¹³C,⁹⁵MoNMR谱,由于配位基团、对称性及Mo-Mo键长等结构的变化,两者的谱线差别很大,特别是⁹⁵MoNMR更为敏感,即使是不同的羧基也会影响它的化学位移和线宽,其屏蔽和线宽的顺序是Me₃COO^-1 > C₂H₅COO^-1 > CH₃COO^-1 > HCOO^-1 > F3COO^-1。     

用惠斯通电桥测电容器的电容

本文对用惠斯通电桥测电容器的方法进行了研究和论证     

沉淀法制备超细氧化铝粉末过程中的团聚机理和消除办法

采用沉淀法以Al(NO3)3.9H2O和NH3.H2O为原料制备了Al(OH)3干凝胶,经过高温煅烧合成纳米级的α-Al2O3粉末,分析了在制备过程中氧化铝粉末产生团聚的机理,推测了硬团聚的机理模型,并提出了几种消除硬团聚的方法,制备出的α-Al2O3粉末,粒径分布均匀,且无明显团聚,近似球形,平均粒径为70nm。     

An Empirical Comparison of Methods for Computing Bayes Factors in Generalized Linear Mixed Models

Generalized linear mixed models (GLMM) are used in situations where a number of characteristics (covariates) affect a nonnormal response variable and the responses are correlated due to the existence of clusters or groups. For example, the responses in biological applications may be correlated due to common genetic factors or environmental factors. The clustering or grouping is addressed by introducing cluster effects to the model; the associated parameters are often treated as random effects parameters. In many applications, the magnitude of the variance components corresponding to one or more of the sets of random effects parameters are of interest, especially the point null hypothesis that one or more of the variance components is zero. A Bayesian approach to test the hypothesis is to use Bayes factors comparing the models with and without the random effects in question—this work reviews a number of approaches for estimating the Bayes factor. We perform a comparative study of the different approaches to compute Bayes factors for GLMMs by applying them to two different datasets. The first example employs a probit regression model with a single variance component to data from a natural selection study on turtles. The second example uses a disease mapping model from epidemiology, a Poisson regression model with two variance components. Bridge sampling and a recent improvement known as warp bridge sampling, importance sampling, and Chib's marginal likelihood calculation are all found to be effective. The relative advantages of the different approaches are discussed.     

Bridge-disubstituted calix[4]arenes obtained via a new preparative route. Synthesis and structural study

A series of calix[4]arenes bearing various substituents including alkyl, p-bromobenzyl, carboxy and allyl at opposite methylene bridges has been synthesized via successive metallation followed by nucleophilic substitution. In a first step, mono-lithiated calix[4]arenes react with terminal bromoalkanes to give 2-alkylated calix[4]arenes or with CO₂ the respective calixarene-2-carboxylic acid in good yields. A second lithiation step of the monosubstituted products with subsequent attachment of both polar and non-polar substituents yields several new diametrally bridge-disubstituted calix[4]arenes. 2D-NMR measurements establish the disubstituted calixarenes to predominantly adopt the 1,2-alternate conformation in solution. First examples of X-ray crystal structures of the new type of disubstituted calix[4]arenes are described featuring the calix[4]arene also in the rare 1,2-alternate conformation.     

On the aeroelastic transient behaviour of a streamlined bridge deck section in a wind tunnel

The study deals with the transient behaviour of a two degrees of freedom bridge deck section in a wind tunnel under the effect of an initial excitation. Response of the bridge deck section subjected to an initial mechanical excitation and excitation by an upstream gust is investigated separately. Experiments are conducted with three different frequency ratios between the plunge and pitch degrees of freedom. This experimental study shows that transient growth of energy occurs for wind velocities below the onset of flutter, reaching a level higher than 5 times the level of the initial excitation. In high wind conditions, this means that statistical or spectral computation techniques might underestimate the motion amplitude reached by a flexible bridge deck. This emphasises the importance of using temporal techniques under such circumstances.     

表面缺陷对一氧化碳和甲基基团在金红石TiO2(110)表面吸附的影响

本文利用程序升温脱附技术研究了氧空位浓度对甲基基团和CO在R-TiO₂(110)表面吸附的影响. 结果表明,随着氧空位浓度的变化,吸附在桥氧位的甲基基团和吸附在五配位Ti⁴⁺位点上的CO分子的脱附温度呈现了不同的趋势,揭示了表面缺陷可能对R-TiO₂(110)不同位点上的物质吸附具有重要影响.