The crystal structure of the organic pigment 2‐monomethyl‐quinacridone (Pigment Red 192, C₂₁H₁₄N₂O₂) was solved from X‐ray powder diffraction data. The resulting average structure is described in space group , Z = 1 with the molecule on the inversion centre. The molecules are arranged in chains. The molecules, which have no inversion symmetry, show orientational head‐to‐tail disorder. In the average structure, the methyl group is disordered and found on both ends of the molecule with an occupancy of 0.5 each. The disorder and the local structure were investigated using various ordered structural models. All models were analysed by three approaches: Rietveld refinement, structure refinement to the pair distribution function (PDF) and lattice‐energy minimization. All refinements converged well. The Rietveld refinement provided the average structure and gave no indication of a long‐range ordering. The refinement to the PDF turned out to be very sensitive to small structural details, giving insight into the local structure. The lattice‐energy minimizations revealed a significantly preferred local ordering of neighbouring molecules along the [01] direction. In conclusion, all methods indicate a statistical orientational disorder with a preferred parallel orientation of molecules in one direction. Additionally, electron diffraction revealed twinning and faint diffuse scattering.

中文翻译：

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通过Rietveld改进，对对分布函数的结构改进和晶格能量最小化研究了单甲基喹ac啶酮的取向紊乱。

从X射线粉末衍射数据解析了有机颜料2-单甲基喹ac啶酮（颜料红192，C ₂₁ H ₁₄ N ₂ O ₂）的晶体结构。将得到的平均结构在空间基团被描述，ž= 1，且分子位于反转中心。分子排列成链状。没有反转对称性的分子表现出定向的头对尾混乱。在平均结构中，甲基是无序的，并且在分子的两端均具有0.5的占有率。使用各种有序结构模型研究了无序和局部结构。所有模型都通过三种方法进行了分析：Rietveld细化，对对分布函数（PDF）的结构细化和晶格能量最小化。所有改进都融合得很好。Rietveld的改进提供了平均结构，没有给出长期有序的迹象。事实证明，对PDF的改进对微小的结构细节非常敏感，可以深入了解本地结构。1个方向。总之，所有方法均表明统计取向异常，分子在一个方向上具有优选的平行取向。另外，电子衍射显示孪晶和微弱的散射。