Discrimination of Small Gas Molecules through Adsorption: Reverse Selectivity for Hydrogen in a Flexible Metal-Organic Framework

Zn2+ ions react with 3,5-pyridinedicarboxylate (pydc) to form a new metal-organic framework (MOF), [Zn(pydc)(dma)] (dma = N,N'-dimethylacetamide), based on a non interpenetrating (10,3)-a topology. The framework possessing narrow one-dimensional channels is highly flexible, and as a result,- guest-dependent breakthrough-like adsorptions occur under atmospheric pressure. This gate opening requires strong interactions between gas molecules and the adsorbent, and therefore [Zn(pydc)(dma)] shows a reverse selectivity for H-2 at 77 K, which is very unusual in MOFs. At 195 K, only CO2 is selectively adsorbed by this material because of the temperature dependence of the gated adsorption.