Hysteretic Gas Sorption in a Microporous Metal-Organic Framework with Nonintersecting 3D Channels

A permanently porous metal-organic framework (MOF) based on infinite chains of metal ions and angular dicarboxylate ligands was synthesized, and its unusual gas sorption properties were characterized. Zn2+ ions react with 2,7-ndcH(2) (2,7-naphthalenedicarboxylic acid) to produce a double-walled framework, [Zn(2,7-ndc)]. The porous MOF possesses narrow channels in three perpendicular directions. Gas sorption studies using Ar, CO2, H-2, N-2, and O-2 at various temperatures reveal that saturation isotherms show a step-wise adsorption and hysteresis loops that are highly unusual features for microporous materials. The unexpected gas sorption behavior of the microporous MOF is due to the unique arrangement of the pore channels and their narrow passages comparable to the critical dimensions of adsorptive gases. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2010)