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

Zn(2+) 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 noninterpenetrating (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 CO(2) is selectively adsorbed by this material because of the temperature dependence of the gated adsorption.