无序示例-二甲胺阳离子二重无序

DJ_Tokyo

相关软件或概念：Olex2[1] (Version: Olex2-1.5); SHELXL[2] (Version: SHELXL-2019/3); PLATON[3] (Version: 60124); CCDC[4]; CIF[5];Mercury[6]

案例来源：CCDC2338704, DOI: 10.5517/ccdc.csd.cc2jhm2r.

该结构虽然没有AB级警报，不过N原子处差值电子密度及其附近残余峰（Q1）表明该N原子可能存在无序，与之相关的有一个C级警报PLAT094（参阅推文“CheckCIF-PLAT094”），如图1所示。

▲图1 结构详情

用Mercury查看对称元素（参阅视频“Mercury基操-查看对称元素：https://www.bilibili.com/video/BV1U44y1U7ZF”）可知该N原子处于镜面上，如图2所示。

▲图2 对称元素

将Q1定为氮（N1A），对N1和N1A用PART指令进行分组（PART 1和PART 2），设置占有率（20.5和-20.5），并用SADI指令限制使两个无序组分的N–C键等长，SIMU指令限制整个二甲胺原子的各向异性位移参数，最终结果如图3所示。

▲图3 无序处理结果

无序处理前后各项参数指标变化如下：

	Max  Peak	Min  Peak	R1	wR2
未做无序	0.5	-0.2	4.61%	15.11%
无序处理	0.2	-0.2	3.35%	8.66%

视频操作演示请参阅：

单晶结构解析练习68(数据还原)：https://www.bilibili.com/video/BV1W2421T7pJ

参考文献

[1]Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann,H. OLEX2: A complete structure solution,refinement and analysis program. J. Appl. Cryst. 2009, 42, 339–341.

[2](a) Sheldrick, G. M. SHELXL-2019/3, Program for Crystal Structure Refinement,University of Göttingen, Germany, 2019. (b) Sheldrick, G. M. A short history ofSHELX. Acta Cryst. 2008, A64, 112–122. (c) Sheldrick, G. M.Crystal structure refinement with SHELXL.Acta Cryst. 2015, C71, 3–8. (d)Lübben, J.; Wandtke, C. M.; Hübschle, C. B.; Ruf, M.; Sheldrick, G. M.;Dittrich, B. Aspherical scattering factors for SHELXL – model, implementation and application. Acta Cryst. 2019, A75, 50–62.

[3] (a) Spek, A. L. Single-crystal structure validationwith the program PLATON. J. Appl.Cryst. 2003, 36, 7–13. (b) Spek,A. L. Structure validation in chemical crystallography. Acta Cryst. 2009, D65, 148–155. (c) Spek, A. L. What makes a crystal structure reportvalid? Inorg. Chim. Acta 2018, 470, 232–237. (d) Spek, A. L. checkCIFvalidation ALERTS: what they mean and how to respond. Acta Cryst. 2020, E76, 1–11.

[4](a) Allen, F. H. The Cambridge Structural Database: a quarter of a millioncrystal structures and rising. ActaCryst. 2002, B58, 380–388. (b) Allen, F. H. TheCambridge Structural Database: a quarter of a million crystal structures andrising. Acta Cryst. 2016, B72, 171–179.

[5](a) Hall, S. R.; Allen, F. H. Brown, I. D. The Crystallographic InformationFile (CIF): a New Standard Archive File for Crystallography. Acta Cryst. 1991, A47, 655–685. (b)Hall, S. R. The STAR File: A New Format for Electronic Data Transfer andArchiving. J. Chem. Inf. Comput. Sci.1991, 31, 326–333. (c) Hall, S. R.; Spadaccini, N. The STAR File:Detailed Specifications. J. Chem. Inf.Comput. Sci. 1994, 34, 505–508.

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