Pseudopolymorphism of Ethylpyrogall[6]arene: Investigating the Role of Solvent in Guiding Self-Assembly of 3D Networks

Recent studies have demonstrated that the r-tctct isomer of ethylpyrogall[6]arene (6EPGR) can be readily isolated as
a minor product of the synthesis of the corresponding tetramer in the form of a 6 DMSO/1 6EPGR clathrate in the hexagonal space
group R-3. Simultaneous studies in our group have led to the isolation of said hexamer as a 12 DMSO/1 6EPGR clathrate in the
same space group. Using powder X-ray diffraction (PXRD) and 13C cross polarization magic angle spinning (CP/MAS) NMR
spectroscopy, we have demonstrated that this 12 DMSO/1 6EPGR pseudopolymorph is, in fact, the precursor to the 6 DMSO/1
6EPGR form. The 6 DMSO/1 6EPGR form can be obtained through simple heating of this 12 DMSO/1 6EPGR precursor, as well
as recrystallization of the precursor from acetone. Furthermore, in light of the data we have obtained using these techniques, in
conjunction with direct observation of the process using a microscope, we suggest that the 6:1 inclusion as prepared by recrystallization
from acetone is more appropriately modeled as containing acetone in addition to DMSO and comment on the relationship between
these pseudopolymorphic forms and the impacts of the two methods of conversion on the structures of the clathrates.

近期研究表明，乙基杯[6]连苯三酚芳烃（ethylpyrogall[6]arene，6EPGR）的r-tctct异构体，可在合成对应四聚体的反应中作为微量副产物，以六方晶系空间群R-3下的6个二甲基亚砜（Dimethyl sulfoxide，DMSO）与1个6EPGR分子构成的包合物形式被分离得到。本课题组同期开展的研究则以相同空间群下的12个DMSO与1个6EPGR分子构成的包合物形式，分离得到了该六聚体。通过粉末X射线衍射（powder X-ray diffraction，PXRD）与碳-13交叉极化魔角旋转核磁共振（CP/MAS NMR）光谱技术，我们证实该12:1 DMSO/6EPGR假多晶型物实为6:1 DMSO/6EPGR晶型的前驱体。6:1 DMSO/6EPGR晶型可通过对该12:1 DMSO/6EPGR前驱体进行简单加热，或从丙酮（acetone）中重结晶该前驱体两种方式获得。此外，结合上述技术获取的实验数据，以及借助显微镜对该转化过程的直接观测结果，我们提出：通过丙酮重结晶制备得到的6:1包合物，除容纳DMSO外还应包含丙酮，该建模方式更为合理；同时我们还讨论了这些假多晶型形式之间的关联，以及两种转化方法对包合物结构的影响。