Crystal structure of chloro(dicarbonyl) bis(acetonitrile) (π-2-methallyl) molybdenum(II)

The title compound crystallizes in the monoclinic spacegroup P2₁/m with a = 6.796(9), b = 12.145(14), c = 7.749(8)Å, = 101.86(1)°, and Z = 2. The crystal structure consists of molecules of [MoCl(CO)₂(NCMe)₂(³-C₃H₄Me-2)] with crystallographically imposed C_s symmetry and has a pseudo-octahedral geometry, with the -allyl group trans- to the chloro group and the two cis-carbonyl and acetonitrile groups occupying the equatorial plane.     

Crystal structure of [{MoBr2(O){OPH(OPr i )2}2}2(μ-O)]

[{MoBr₂(O){OPH(OPr ⁱ )₂}₂}₂(μ-O)] (1) crystallizes in the monoclinic space group P2₁/n, with a = 13.063(17) Å, b = 11.818(14) Å, c = 15.889(17) Å, β = 90.30(1)°, Z = 2. The dimeric structure contains a bridging oxygen atom at a crystallographic center of symmetry. Each octahedral molybdenum center has trans-bromide ligands, and two cis-OPH(OPr ⁱ )₂ units, with a terminal oxygen atom trans to one of the OPH(OPr ⁱ )₂ units.     

电感耦合等离子体原子发射光谱(ICP-AES)法测定铅锭中11种杂质元素

研究了用酸分解试样后不需分离基体直接用电感耦合等离子体原子发射光谱(ICP-AES)法测定铅锭中银、铜、铋、砷、锑、锡、锌、铁、镉、镍、铊11种杂质元素的方法。优化了样品前处理条件及仪器检测条件。方法的检出限为0.0012～0.0168μg/mL,回收率为89%～110%,RSD为2.3%～5.0%。方法简便快速,检出限低,精密度和准确度能满足铅锭中杂质元素的检测要求,具有较强的实用性和可操作性,可用于铅锭中杂质元素的测定。     

The effect of γ-irradiation and polymer composition on the stability of PLG polymer and microspheres

The effects of lactide:glycolide ratio and γ-irradiation on the stability characteristics of poly(d,l-lactide-co-glycolide) (dl-PLG) co-polymer and microspheres were studied. Samples containing 50:50, 65:35, 75:25, 85:15 and 95:5 lactide:glycolide were studied as both the raw polymer and microspheres. The samples were characterised and degradation was monitored using a variety of spectroscopic, chromatographic, thermal and particle analysis techniques. The lactide:glycolide ratio was shown to be an important parameter in controlling the degradation of PLG co-polymer, especially in the microspheres, and the raw polymer samples were observed to be less stable than the microspheres. γ-Irradiation was shown to reduce the molecular weight of the PLG samples without significantly affecting the polydispersity, suggesting a random chain scission degradation mechanism. The detrimental effects of γ-irradiation were shown to continue on storage of the samples for 4 weeks in the solid state at ambient and accelerated conditions.     

The structure of tri(cyclohexyl)tin chloride between 108 and 298 K: a compound in which molecular dimensions vary with temperature

Care is necessary when relating physical data obtained at one temperature on compounds showing significant intermolecular interactions to X-ray data obtained at other temperatures. This is revealed by the determination of the structure of tri(cyclohexyl)tin chloride at nine different temperatures between 108 and 298 K. In the crystal, the molecules pack in chains parallel to the c axis with the Sn and Cl atoms close to the plane, with y = 0.25. At low temperature, successive molecules in the chain are related by the glide plane in space group P2(1)/c, and there is significant intermolecular interaction. As the temperature is raised, the Cy(3)SnCl.Sn interactions weaken and the intramolecular Sn-Cl bonds strengthen. At about 248 K, there is an order-disorder transition to space group P2(1)/m with the c axis halved, and at room temperature the structure is best described as comprising discrete molecules, as previously reported. Thus, some of the molecular dimensions, in particular the Sn-Cl bond lengths, are not constant but are functions of temperature.     

A new FeII quaterpyridyl M4L6 tetrahedron exhibiting selective anion binding

A rigid linear bis-bidentate quaterpyridine undergoes metal directed self-assembly with iron(ii) salts yielding M(4)L(6) host-guest complexes; selective anion binding for PF(6)(-) over BF(4)(-) is observed.     

Live lectures or online videos: students’ resource choices in a first-year university mathematics module

In Maths for Business, a mathematics module for non-mathematics specialists, students are given the choice of completing the module content via short online videos, live lectures or a combination of both. In this study, we identify students’ specific usage patterns with both of these resources and discuss their reasons for the preferences they exhibit. In 2015–2016, we collected quantitative data on each student's resource usage (attendance at live lectures and access of online videos) for the entire class of 522 students and employed model-based clustering which identified four distinct resource usage patterns with lectures and/or videos. We also collected qualitative data on students’ perceptions of resource usage through a survey administered at the end of the semester, to which 161 students responded. The 161 survey responses were linked to each cluster and analysed using thematic analysis. Perceived benefits of videos include flexibility of scheduling and pace, and avoidance of large, long lectures. In contrast, the main perceived advantages of lectures are the ability to engage in group tasks, to ask questions, and to learn ‘gradually’. Students in the two clusters with high lecture attendance achieved, on average, higher marks in the module.