Porous framework materials have long been of interest for their applications including catalysis, separation, and gas sorption. The best-known porous materials are polymeric in nature. However, porous molecular materials are also known and exhibit advantageous properties, such as processability without the need to break and make bonds.

Organic molecules of intrinsic microporosity (OMIMs) are one such class of material, in which rigid organic molecules are designed not to pack tightly (so-called frustrated packing). Crystallization of OMIMs is very challenging, but Michael Mastalerz and colleagues, Ruprecht-Karls-Universität Heidelberg, Germany, were able to characterize an OMIM constructed from a D_3h-symmetric π-extended triptycene capped with triptycenylene units, crystallized with mesitylene in four different polymorphs, by single crystal X-ray diffraction.

These crystal structures are among the first reported for OMIMs, and the materials were also investigated by gas sorption. The N₂ sorption isotherm shows a large hysteresis, attributable to the breathing of the material during the sorption process.

• Crystal Structures of a Molecule Designed Not To Pack Tightly,
  Bernd Kohl, Frank Rominger, Michael Mastalerz,
  Chem. Eur. J. 2015.
  DOI: 10.1002/chem.201502847