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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Average structures of the disordered β-phase of Pigment Red 170: a single-crystal X-ray diffraction study
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Average structures of the disordered β-phase of Pigment Red 170: a single-crystal X-ray diffraction study

机译：颜料红170无序β相的平均结构：单晶X射线衍射研究

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摘要

The β-phase of the industrially important Pigment Red 170 (β-P.R. 170) has a structure with severe layer stacking disorder. The single-crystal X-ray diffraction pattern consists of a difficult-to-disentangle mix of Bragg diffraction superimposed on rods of diffuse scattering which impede the estimation of accurate Bragg intensities. Two average monoclinic structure models with the same unit-cell dimensions, but different extents of disorder in the layers and different space groups seem plausible, one with the non-conventional space group setting B2_1/g (No. 14, Z0 = 2) and one in P2_1/a (No. 14, Z0 = 4). Disordered molecules related by a translation of 0.158b are present in all layers of the B2_1/g model and in every second layer of the P2_1/a model. Layer-to-layer contacts are practically the same in both models. According to order-disorder theory, both models are valid superposition structures. Structure-factor calculations show that the pattern of strong and weak Bragg reflections is very similar for the two models. R factors indicate that the B2_1/g model is the most economic representation of the average structure. However, given the limitations in data processing, the P2_1/a model should not be discarded and further insight sought from a detailed analysis of the experimental diffuse scattering. The difficulties encountered in this analysis raise the question of whether or not the concept of an average structure is applicable in practice to β-P.R. 170.
机译：工业上重要的颜料红170（β-P.R。170）的β相具有严重的层堆积紊乱的结构。 X射线单晶衍射图谱由难以分辨的布拉格衍射混合物叠加在扩散散射棒上构成，这阻碍了对准确布拉格强度的估计。两种平均单斜结构模型具有相同的晶胞尺寸，但在层和不同空间组中的无序程度不同，似乎是合理的，一种具有非常规空间组设置B2_1 / g（第14号，Z0 = 2），并且P2_1 / a中的第一个（编号14，Z0 = 4）。在B2_1 / g模型的所有层和P2_1 / a模型的每第二层中都存在与0.158b翻译相关的无序分子。两种模型的层间接触实际上是相同的。根据无序理论，两个模型都是有效的叠加结构。结构因子计算表明，两个模型的强布拉格反射和弱布拉格反射的模式都非常相似。 R因子表明B2_1 / g模型是最经济的平均结构表示形式。但是，鉴于数据处理的局限性，不应丢弃P2_1 / a模型，而应从对实验性散射的详细分析中寻求进一步的见解。该分析中遇到的困难提出了一个问题，即平均结构的概念在实践中是否适用于β-P.R。 170。

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