Über Chalkogenidhalogenide des Rheniums: Synthese und Kristallstrukturen der Dreieckscluster Re3E7X7 (E = S,Se; X = Cl,Br)

On Chalcogenide Halogenides of Rhenium: Synthesis and Crystal Structures of the Triangular Clusters Re₃E₇X₇ (E = S, Se; X = Cl, Br) The compounds Re₃E₇X₇ are obtained from rhenium tetrahalides ReX₄, elemental chalcogens and the respective chalcogen halides E₂X₂ or SeX₄ (E = S, Se; X = Cl, Br). Re₃S₇Cl₇, Re₃S₇Br₇ and Re₃Se₇Br₇ are formed in solutions of sulfur or selenium halides or SiBr₄ in form of black crystals and crystallize isotypically in the trigonal space group P31c. Re₃Se₇Cl₇ is formed by solid state reaction of ReCl₄, Se and SeCl₄ or by thermal decomposition of Se₄[ReCl₆], crystallizing as red, in thin layers transparent crystals in the orthorhombic space group Pbcm. The crystal structures consist of discrete positively charged cluster units and halide ions according to the formula [Re₃(μ₃-E)(μ₂-E₂)₃X₆]⁺X^–. In the rhenium triangular clusters the Re–Re distances range from 269,0 to 270,4 pm for the sulfur and from 273,3 to 275,3 pm for the selenium containing compounds. The Re₃ units are capped by chalcogen atoms, three E₂ groups form bridges over the edges of the Re₃ triangles. The trigonal and the orthorhombic structure type show differences in the site symmetry of the clusters (C₃ vs. C_s) and in the stacking sequence of the molecules, which are packed in the motif of a closest packing of spheres.     

Neues zu Oxidchloriden der Seltenen Erden mit Vanadium und Rhenium

New Oxychlorides of the Rare-Earth Metals with Vanadium and Rhenium i) New compounds Ln_12.33V₆O₂₃(OH)Cl₂₀ (Ln = La, Ce) were prepared by heating mixtures of LnCl₃, LnOCl and V₂O₅ (4 : 8 : 3) in evacuated, sealed silica ampoules (850 °C, 4 d). Single crystals could be obtained by chemical vapor transport (T₂ → T₁, T₂ = 900 °C, T₁ = 800 °C, 14 d, p(Cl₂, 298 K) ≈ 70 mbar). The single-crystal study of the lanthanum compound [a = 17.8818(25) Å, c = 4.0567(7) Å, Z = 1, 1035 independent I₀, 70 parameters, R1 = 3.52%] showed that vanadium has CN = 4 (tetrahedrally) and lanthanum has CN = 9 (threefold capped trigonal prismatic). A strong relationship to the structures of the Pr₃NbO₄Cl₆- and the La₂TaO₄Cl₃-type could be discussed. ii) Further we obtained dark red powder of La₃ReO₆Cl₃ by heating (740 °C, 5 d) a mixture of ReO₃ and LaOCl (1 : 3) in sealed silica ampoules under argon atmosphere (p{Ar, 298 K} = 1 atm). This new rhenium-compound crystallizes in the hexagonal space group P6₃/m (No. 176) [a = 9.4164(6) Å, c = 5.4248(4) Å] and is isostructural to La₃WO₆Cl₃.     

Ein neues Praseodymniobat Pr2Nb11O30

A New Praseodymiumniobate Pr₂Nb₁₁O₃₀ By chemical vapor transport (T₂ → T₁, T₂ = 950 °C, T₁ = 900 °C, 3 d) of a mixture of PrOCl and Nb₂O₅ (1 : 1) using 5 mg NH₄Cl as transport agent we obtained the new compound Pr₂Nb₁₁O₃₀. The crystal structure determination [a = 6.2325(5) Å, c = 32.3677(36) Å, Z = 2, 1631 independent I₀, 69 parameters, R1 = 2.07%] shows CN = 8 (twofold capped octahedrally) for Pr, CN = 7 (pentagonal bipyramidally) for Nb(1,2) and CN = 6 (octahedrally) for Nb(3). The structure is closely related to that of Cu₅Ta₁₁O₃₀.     

苏码罐采样预浓缩-GC-MS测定空气中的挥发性有机化合物

采用苏码罐采样技术,预浓缩系统与GC-MS联用,优化了系统的测试条件,建立了测定环境空气中41种挥发性物的监测方法.用于环境空气和室内空气的监测,结果令人满意.     

A first principle study of band structure of III-nitride compounds

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.     

Effective atomic numbers of some vanadium and nickel compounds for total photon interactions using transmission experiments

Effective atomic numbers of V₂O₃,VO₂,VF₃,NH₄VO₃,VF₄,NiF₂,NiCl₂,NiF₂4H₂O,NiCl₂6H₂O,Ni(ClO₄)₂6H₂O were measured in the X-ray energy range 15.746- using an Si(Li) detector. The measured values are compared with the theoretical ones calculated using WinXcom.     

Observation of the Cinnabar Phase in ZnSe at High Pressure

In this paper we describe the results of an energy dispersive X-ray diffraction experiment carried out in the ZnSe 1 m x Te x alloy and pure ZnSe under high pressure. In the downstroke the cinnabar phase is observed between the rocksalt and the zincblende phases. The analysis of the whole series of compositions ( x =0, 0.05, 0.1 and 0.2) enables us to establish its lattice parameters in ZnSe ( a =3.785 + and c =8.844 + at 10.5 GPa). The X-ray diffraction pattern simulation suggests that the internal parameters u and v are close to 0.5, indicating that the cinnabar phase in ZnSe is similar to that observed in GaAs and ZnTe. The cinnabar's stability range decreases as the Te content is reduced.     

Development of plasticised PVC sensing films for the determination of BTEX compounds in aqueous samples

A novel plasticised PVC polymer membrane as a sensing film for the determination of BTEX compounds using ATR-FTIR spectroscopy is demonstrated. A range of 10 plasticised PVC phases have been investigated using toluene and tetrachloroethylene as test analytes. Both analyte enrichment rates and infrared absorbance values were considered when choosing a suitable polymer for sensing. An enhancement in analyte absorbance at the characteristic IR absorption bands was noted as the plasticiser concentration in the film was increased. 2% PVC with 75% diisooctyl azelate was found to show promising results for simultaneous determination of the BTEX compounds. All BTEX analytes can be measured in less than 8 min. A study of a multicomponent sample demonstrated that analyte enrichment times were influenced by the presence of even one additional analyte component in the sample.     

A New Versatile and Sensitive Monitoring System for Liquid Chromatography: Cerate Oxidation and Fluorescence Measurement

Abstract

A new liquid chromatographic detector depends upon the fluorescence measurement of cerium (III) produced from the reaction of cerium (IV) with eluted reducible compounds. It is more sensitive than previous oxidative detectors by more than a factor of 100. The reaction can be varied to discriminate among compounds according to ease of oxidation.