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

Abstract

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 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 H₂ 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.