Oxoniobates Containing Metal Clusters

Metal clusters, discrete or condensed, are characteristic of the structures of many compounds which contain transition metals in low oxidation states. The highly reduced oxoniobates support the concept of condensed clusters. They contain Nb₆O₁₂ clusters which are either isolated or linked at the apices of the Nb₆ octahedra to form oligomeric chains or networks. The analysis of the bonding relationships allows the identification of different types of Nb atoms and thus the quantitative prediction of valence electron concentrations for finite or infinite structures composed of these condensed M₆X₁₂ clusters.     

鲨鱼软骨质量的聚类分析法

用电感耦合等离子体原子发射光谱法（ＩＣＰ－ＡＥＳ）测定了１８个鲨鱼软骨真品中１３个元素含量，对测定结果进行分析和变量聚类分析，抽提５个特征指标，并以谱系数聚类建立了鉴别鲨鱼软骨真伪的数学模式，用３个假冒产品和一个鲨鱼软骨胶囊对其进行检验，结果表明，用无机元素所建立的数学模式不仅能鉴别鲨鱼软骨的真伪，还能区分鲨鱼软骨的部分及不同部位的混合物。     

乙醇对超临界CO2中乙酰乙酸乙酯异构化平衡的影响

超临界流体（SCF）是物质所处的温度和压力同时高于其临界值时的流体．在超临界体系中存在特殊的分子间相互作用，从而使其具有诸如高压缩性、高扩散系数、强溶剂化力等许多独特的性质.在超临界流体研究领域引起人们普遍关注的问题之一是共溶剂效应（cosolventeffect），即在超     

Organometallic Aspects of the Fischer-Tropsch Synthesis

The Fischer-Tropsch Synthesis counts among the industrial-scale processes having a versatile and broad product range, and has for decades offered the most attractive possibility for the use of coal as a source of heating oil and fuels. This conceivably simple reaction, the catalytic hydrogenation of carbon monoxide, generally leads to simple hydrocarbons as well (i.e. short chain olefins) that have been sought as chemical feedstocks since the oil crisis of the seventies, but fails to provide the large-scale, economic process required, due in large part to the minimal selectivity of traditional Fischer-Tropsch processes. In an effort to solve this problem current research in this sector is concerned not only with the optimization of old and the development of new catalytic systems, but also increasingly with the elucidation of numerous relevant reaction mechanisms. This article will discuss, from the viewpoint of an organometallic chemist, the significance of typical model reactions, both with regard to some fundamental aspects of synthesis gas chemistry, and in comparison with previous views concerning the mechanism of the Fischer-Tropsch Synthesis. The importance of various unique classes of complexes that have been studied in the context of Fischer-Tropsch chemistry is also evaluated with regard to their importance in the synthesis of hydrocarbons from carbon monoxide and hydrogen. It emerges that the primary steps of the reductive oligomerization of carbon monoxide are best described by the carbide/methylene mechanism, as originally proposed by Hans Fischer and Franz Tropsch.     

Axiomatizing subcategories of Abelian categories

We investigate how to characterize subcategories of abelian categories in terms of intrinsic axioms. In particular, we find axioms which characterize generating cogenerating functorially finite subcategories, precluster tilting subcategories, and cluster tilting subcategories of abelian categories. As a consequence we prove that any d-abelian category is equivalent to a d-cluster tilting subcategory of an abelian category, without any assumption on the categories being projectively generated.     

An analyticity bound for two-dimensional Ising model at low temperature

We study the coexistence phase in the two-dimensional Ising model. Optimizing the cluster expansion technique, we are able to prove the phase separation phenomenon, with the Onsager value for the surface tension, in a range , where estimates from above the critical within 19% and essentially coincides with the entropic bound.     

Ab initio studies of small AlmFen clusters

The equilibrium geometrical structures of small Al_mFe_n clusters have been determined through ab initio calculation of the cluster total energy at the UB3LYP/Lanl2dz level. For dimers of iron and aluminum, the dissociation energies, the equilibrium atomic distances, and the vibrational frequencies were calculated. The agreement between calculations and experiments is reasonable. The ground stable geometrical structures of Fe₄, FeAl₃, Fe₃Al and Fe₂Al₂ clusters favor three-dimension configurations, but Al₄ tetramers are planar structures. The Al-rich tetramers are more stable than the other two composition tetramers. This is different from that of bulk alloys.     

Formation of Ad-Layers and Clusters on Condensation of Metal Vapors on Solid Surfaces

Synthesis of organometallic materials can be accomplished in many cases by cocondensation of metal atoms and organic molecules at low temperatures. The reaction kinetics is determined by the competition between metal cluster growth and formation of the organometallic compound. Interesting compounds may contain one or more metal atoms; the latter type could be obtained by reaction between a cluster containing the desired number of metal atoms and an organic molecule. A precise knowledge of the events occurring on condensation of metal atoms and cluster formation can therefore be of value in the control of chemical synthesis. These phenomena have been investigated in connection with the study of the growth of thin metallic films, both experimentally and theoretically. Direct observation of the formation of very small clusters is difficult. The good agreement between experimental results and recent calculations for the development of large clusters, however, allows reliable theoretical conclusions for the first stages of adsorption and cluster formation. The present contribution describes experimental work on film growth and relevant theoretical concepts, and an attempt is made to develop applications to organometallic synthesis.     

Reaktivität von Monophosphan-Platin(0)-Verbindungen gegenüber Schwefeldioxid

Reactivity of Monophosphine Platinum(0) Complexes with SO₂ . The addition reaction of (PPh₃)Pt(ViSi) (ViSi = {η²-H₂C?CHSiMe₂}₂O) ( 1 ) with SO₂ gives within 30 min the red SO₂ complex (PPh₃)Pt(η²-H₂C?CHSiMe₂- OSiMe₂CH?CH₂)(SO₂) ( 2 ). A reaction time of 24 h with SO₂ leads to the elimination of the ViSi ligand, and the unstable monomeric intermediate (PPh₃)Pt(SO₂) cyclo- trimerizes to the stable cluster [Pt(PPh₃)(SO₂)]₃ ( 3 ). 3 is also obtained within 30 min by the reaction of (PPh₃)Pt(C₂H₄)₂ ( 4 ) with SO₂. The crystal structure of 3 has been determined; space group P2₁/n, Z = 4, a = 1 606.1(3), b = 1 019.3(1), c = 3 624.6(5) pm, β = 93.67°, R/R_w = 0.102/0.121.