Figure: Compound 1 self-assembles into a structure with molecule-sized pores

Metal-organic and covalent organic frameworks are porous materials characterized by outstanding thermal stability, high porosities and modular synthesis. Their repeating structures offer a great degree of control over pore sizes, dimensions and surface properties. Similarly precise engineering at the nanoscale is difficult to achieve with discrete molecules, since they rarely crystallize as porous structures. Here we report a small organic molecule that organizes into a noncovalent organic framework with large empty pores. This structure is held together by a combination of [N–H∙∙∙N] hydrogen bonds between the terminal pyrazole rings and [π∙∙∙π] stacking between the electron-rich pyrazoles and electron-poor tetrafluorobenzenes. Such a synergistic arrangement makes this structure stable to at least 250 °C and porous, with an accessible surface area of 1,159m2 g-1. Crystals of this framework adsorb hydrocarbons, CFCs and fluorocarbons—the latter two being ozone-depleting substances and potent greenhouse species—with weight capacities of up to 75%.

See:  Teng-Hao Chen1, Ilya Popov1, Watchareeya Kaveevivitchai1, Yu-Chun Chuang2, Yu-Sheng Chen3, Olafs Daugulis1, Allan J. Jacobson1,4 & Ognjen Sˇ. Miljanic´1, “Thermally robust and porous noncovalent organic framework with high affinity for fluorocarbons and CFCs”, Nat. Commun. 5, 5131, (2014).

Author Affiliations:  1Department of Chemistry, University of Houston, Houston, Texas, USA. 2National Synchrotron Radiation Research Center, Hsinchu, Taiwan. 3Center for Advanced Radiation Sources (ChemMatCARS), The University of Chicago, Chicago, Illinois, USA. 4Texas Center for Superconductivity, Houston, Texas, USA.