Polar Triptycene-Based Nonmetal Organic Frameworks Show Enhanced Hydrogen Adsorption.

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 cm3 g-1 from N2 isotherms at 77 K), which we attribute to London-dispersion interactions and geometric confinement within subnanometer pores.