Megan O’Shaughnessy, Hang Qu, Xue Wang, Jacob B. Holmes, Lyndon Emsley, Joseph Glover, Roohollah Hafizi, Graeme M. Day, Andrew I. Cooper
High Resolution Image Download MS PowerPoint Slide Porous nonmetal organic frameworks (N-MOFs) are an emerging class of porous materials that can have desirable properties such as stability for iodine capture, proton conductivity, and xenon/ krypton separation. Here, we present the first experimental evidence of polymorphism in porous N-MOFs through the identification of two stable porous phases of a triptycene framework (T.Cl-α and T.Cl-β). We also report single-crystal structures for two isostructural porous N-MOFs (T.Cl-α and T.Br-α). All three polymorphs are porous to carbon dioxide and nitrogen, and T.Cl-α exhibits a remarkable hydrogen uptake of 7.2 mmol g –1 at 77 K and 1 bar. This hydrogen sorption far exceeds most other porous crystals and compares favorably with many MOFs under the same condition. The hydrogen uptake for T.Cl-α is anomalously high for its relatively modest pore volume (0.198 cm 3 g –1 from N 2 isotherms at 77 K), which we attribute to London-dispersion interactions and geometric confinement within subnanometer pores.