卟啉氮氢无序

DJ_Tokyo

相关软件或概念：Olex2[1] (Version: Olex2-1.5); PLATON[2] (Version: 261023); SHELXL[3] (Version: SHELXL-2019/3)

卟啉存在如图1所示共振式。

▲图1 卟啉共振式

晶体结构是统计结构，所以在晶体结构中表现为如图2所示无序结构。

▲图2 卟啉无序结构

实际情况下，卟啉骨架并不产生无序，所以表观上其无序由氮上的氢原子表现，如图3所示。

▲图3 卟啉氮氢无序

例如某结构中自由变量精修的两个组分占比约为0.596:0.404，如图4所示。

▲图4 某结构中卟啉氮氢无序

其卟啉环中碳氮键键长如图5所示，基本都在1.37 Å，相差不大，因此改无序处理是合理的。

▲图5 卟啉环中碳氮键键长

参考文献

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[3](a) Sheldrick, G. M. SHELXL-2019/2, 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.