A permanent mesoporous organic cage with an exceptionally high surface area

Abstract

Recently, porous organic cage crystals have become a real alternative to extended framework materials with high specific surface areas in the desolvated state. Although major progress in this area has been made, the resulting porous compounds are restricted to the microporous regime, owing to the relatively small molecular sizes of the cages, or the collapse of larger structures upon desolvation. Herein, we present the synthesis of a shape-persistent cage compound by the reversible formation of 24 boronic ester units of 12 triptycene tetraol molecules and 8 triboronic acid molecules. The cage compound bears a cavity of a minimum inner diameter of 2.6 nm and a maximum inner diameter of 3.1 nm, as determined by single-crystal X-ray analysis. The porous molecular crystals could be activated for gas sorption by removing enclathrated solvent molecules, resulting in a mesoporous material with a very high specific surface area of 3758 m2 g-1 and a pore diameter of 2.3 nm, as measured by nitrogen gas sorption. Big boronic ester cages: A shape-persistent cuboctahedron can be almost quantitatively formed by a 48-fold one-pot condensation of 12 molecules of a triptycene tetrol with 8 molecules of triboronic acid. The desolvated crystalline material of this cage has a specific surface area of 3758 m2 g-1 and a maximum pore size of 2.3 nm, thus making it mesoporous by the IUPAC definition. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.