VICISSITUDES OF LOW-QUARTZ CRYSTAL SETTING OR PITFALLS OF ENANTIOMORPHISM
VICISSITUDES OF LOW-QUARTZ CRYSTAL SETTING OR PITFALLS OF ENANTIOMORPHISM
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DOI：
10.1107/s0567739478001242
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发表时间：
1978-01-01
影响因子：
1.8
通讯作者：
LEPAGE, Y
中科院分区：
文献类型：
--
作者：
DONNAY, JDH;LEPAGE, Y
基于文献研究，以下建议努力结合以前设置低石英晶体的惯例的优点：（1）已知对称轴平行于最小六方晶胞的边缘，将Oz放置在3轴上，将Ox、Oy、Ou放置在宏观2轴上。 (2) 将极轴正向指向 s 和 x 面（如果存在），或指向通过压电测试延伸时产生的正电荷。 (3)将坐标系的手与结构螺钉的手匹配；因此，左旋石英的已知右旋螺杆（RS）的右手坐标系（RHCS）。 (4) 设与结构中的2轴重合的坐标轴为Ox[100]。这些规则导致两种对映体都遵守 Lang 的助记规则并处于 r(+) 设置中，其中 {10{\bar 1}1} 象征主要菱面体 r，由 Iobs(10{\bar 1}1) > Iobs(01{\bar 1}1) 定义。低石英只有一种结构。它应该仅针对 RS (P3121) 和 RHCS 发布：任何人都可以通过在 LHCS 中绘制原子坐标来可视化 LS 对映体。该政策应适用于任何具有已知绝对构型的对映体物质。如果在 RHCS 中确定的晶体结构结果具有 LS，则转换为 LHCS 并发布新坐标，该坐标也符合 RHCS 中的标准 RS，但添加“仅称为 LS”或“观察为 LS”。
Based on a literature study, the following proposals endeavour to combine the advantages of previous conventions for setting low-quartz crystals: (1) Knowing that symmetry axes are parallel to the edges of the smallest hexagonal cell, place Oz along the 3-axis and Ox, Oy, Ou along the macroscopic 2-axes. (2) Direct the polar axes positively toward the s and x faces, if present, or toward the positive charge developed on extension by piezoelectric test. (3) Match the hand of the coordinate system to that of the structural screw; thus, the right-handed coordinate system (RHCS) for the known right screw (RS) of laevorotatory quartz. (4) Let the coordinate axis that coincides with a 2-axis in the structure be Ox[100]. These rules result in both enantiomorphs obeying Lang's mnemonic rule and being in the r(+) setting, in which {10{\bar 1}1} symbolizes the major rhombohedron r, defined by Iobs(10{\bar 1}1) > Iobs(01{\bar 1}1). Low quartz has only one structure. It should be published only for the RS (P3121) and in the RHCS: anyone can visualize the LS enantiomorph by plotting the atomic coordinates in the LHCS. This policy should apply to any enantiomorphous substance with known absolute configuration. If a crystal structure, determined in the RHCS, turns out to have a LS, transform to LHCS and publish the new coordinates, which also fit the standard RS in RHCS, but add, 'Known only as LS' or 'Observed as LS'.