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21.
The fractionation technique described in this paper was used to characterize the melting-point, monomer, and blocking distributions for polymers and copolymers. It is different from the molecular-weight fractionation technique in that the fractions are obtained by using a single solvent to extract the solid polymer below its melting point at stepwise-increasing temperatures. The reproducibility of this technique is excellent, and the technique is sufficient to distinguish pellet-to-pellet variation in a commercially available polypropylene. It was used to show the influence of preparation variables on the melting-point distributions of polyethylene and polypropylene and on the monomer and blocking distribution of copolymers, and to distinguish copolymers from blends. 相似文献
22.
Michael Daub;Christoph Haber;Harald Hillebrecht; 《欧洲无机化学杂志》2017,2017(7):1120-1126
The title compounds were obtained by the treatment of MI2 in conc. HI with stoichiometric amounts of [C(NH2)3]2CO3. They show several phase transitions. The Pb/Sn HT phases {[C(NH2)3]2PbI4-I, Pnma, Z = 4, a = 13.04 Å, b = 13.62 Å, c = 9.36 Å} and {[C(NH2)3]2SnI4-I: a = 13.04 Å, b = 13.57 Å, c = 9.45 Å}, as well as [C(NH2)3]2PbI4-II (Pnnm, Z = 8, a = 27.03 Å, b = 9.31 Å, c = 12.92 Å) and [C(NH2)3]2SnI4-II (a = 26.89 Å, b = 9.30 Å, c = 12.94 Å) and also [C(NH2)3]2PbI4-III (P21/n, Z = 8, a = 9.21 Å, b = 26.88 Å, c = 12.68 Å, β = 90.49°) and [C(NH2)3]2SnI4-III (a = 9.28 Å, b = 26.95 Å, c = 12.81 Å, β = 90.76°) are isotypic with each other. For [C(NH2)3]2SnI4 the LT phase realizes a triclinic variant (P1, Z = 4, a = 9.27 Å, b = 12.67 Å, c = 14.44 Å, α = 66.98°, β = 85.88°, γ = 88.26°). The structures are (110)-oriented perovskites A2MX4 with corrugated layers of edge-sharing MI6 octahedra. HT- and MT-forms show a 2+4 pattern of M–I distances. [C(NH2)3]2SnI4-IV represents a new structure type. The different modifications are distinguished by the ordering pattern of the cations and the tilt of the MI6 octahedra. The structural characterizations are amended by vibrational and optical spectroscopy as well as thermal analysis. The band gap of the Sn compound (2.06 eV) makes it a possible candidate as an absorber for the tandem solar cell. For the Pb compound an excitonic absorption peak is observed right below the band gap (2.49 eV) indicating stable excitons at room temperature. 相似文献
23.
Standardized electronic formats for data are needed to efficiently and transparently communicate the results of scientific studies. A format for the unique identification of chemical species is a requirement in the field of chemistry, and the IUPAC International Chemical Identifier (InChI) has been widely adopted for this purpose. The InChI identifier has proved to be very useful. The InChI identifier, however, is currently insufficient to uniquely specify some types of molecular entities at a detailed molecular level needed to fully characterize their chemical nature, to differentiate between chemically distinct conformers, to uniquely identify structures used in quantum chemical calculations, and to completely describe elementary chemical reactions. To address this limitation, we propose an augmented form of InChI, denoted as InChI–ER, which contains additional optional layers that allow the unique and unambiguous identification of molecules at a detailed molecular level. The new layers proposed herein are optional extensions of the existing InChI formalism and, like all other InChI layers, would not interfere with InChI identifiers currently in use. The focus of the present work is the better specification of required molecular entities such as rotational conformations, ring conformations, and electronic states. In companion articles, we propose additional reaction layers using an extended InChI format that will enable the unique identification of elementary chemical reactions, including specification of associated transition states, specification of the changes in bonds that occur during reaction, and classification of reaction types. 相似文献
24.
NbOI3 was obtained from a reaction of Nb2O5, Nb, and I2. Single crystals free from disorder were a by‐product from a reaction with additional CsI. The monoclinic crystal structure (C2, a = 14.624(3) Å, b = 3.9905(8) Å, c = 12.602(3) Å, β = 120.4(3)°, Z = 4, R1(F) = 0.0368, wR2(F2) = 0.0804) represents a new structure type which is built up by distorted octahedral NbI4O2 with unequal O‐atoms in trans‐position. The octahedra are linked to dimers by a common edge of iodine atoms and to double chains by the apical oxygen atoms. A non‐centrosymmetric structure results because the short Nb–O distances point to the same direction and the polar double chains are parallel. The crystal structure of NbOBr3 (NbOCl3‐type, , a = 11.635(6) Å, c = 3.953(2) Å, R1(F) = 0.082, wR2(F2) = 0.174) shows the same polar double chains but the dimeric units Nb2Br6O2 are orthogonal. 相似文献
25.
Synthesis and Crystal Structure of Ti12Sn3O10 – a Low Valent Oxide of Titanium with an Oxidic Network and Intermetallic ”︁Islands”︁”︁ The new ternary compound Ti12Sn3O10 is obtained by the reaction of Ti, TiO2 and Sn at 1500 °C. According to the single crystal structure analysis (cubic, space group Fm3m, a = 13.5652(9) Å, Z = 8, wR2(I) = 0.048, R1(F) = 0.020) the air stable compound represents a new structure type combining structural features of oxides and intermetallics. While tin is surrounded only by titanium the five different Ti atoms have oxidic and metallic coordination spheres as well, explaining the quite low averaged oxidation number. The crystal structure is characterized by a threedimensional net of Ti4O‐tetrahedra and trigonal bipyramides Ti5O. In the voids there are intermetallic ”︁islands”︁”︁ of a composition Ti33Sn6 with a diameter of about 10 Å. 相似文献
26.
Stabilized by the tailor-made coordination in the crystal , B4 tetrahedra were characterized for the first time in a solid-state structure (shown on the right). Some of the Al atoms are replaced by B4 tetrahedra in the cubic τ-boride Ni20AlB14. The B–B distances of 1.681(15) Å are similar to those in the molecular structures of B4Cl4 and B4(tBu)4, which contain tetrahedral B4 units. 相似文献
27.
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29.
Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe3O4) and haematite (α-Fe2O3), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides. 相似文献
30.
烯醇(Ⅱ)氢化 [21] 为醇(Ⅲ),改用Adams催化剂,产率可提高到97%。用高锰酸钾为氧化剂,可以将(Ⅲ)直接氧化为二酸(Ⅳ)。若用发烟硝酸为氧化剂,则产率低,并且不稳定。由Ⅲ的银鹽(Ⅴ)用溴处理得二溴环二辛烷(Ⅵ)。曾试用氮杂萘,叔丁醇,乙醇——氢氧化钠为脱溴氢酸的试剂来处理二溴环二辛烷,未获成功。 相似文献