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

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posted on 01.03.2006 by Philip O. Brown, Gary D. Enright, John A. Ripmeester
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.