Extraordinary Separation of Acetylene-Containing Mixtures in a Honeycomb Calcium-Based MOF with Multiple Active Sites

Acetylene (C₂H₂) separation from multicomponent mixtures is vitally important but industrially challenging for the collection of high-purity C₂H₂. To address this requirement, the reaction between the alkaline-earth Ca²⁺ ions with a dicarboxylate-diazolate linker, 4,6-di(1H-tetrazol-5-yl)isophthalic acid (H₄dtzip), gave rise to a new metal-organic framework (MOF) material [Ca(dtzip)_0.5H₂O]·2H₂O (1). The material presents unique regular tubular channels based on threefolded helical rod-like secondary building units with rich open metal sites and exposed organic hydrogen-bonding N/O acceptors that enhance the interactions with C₂H₂ molecules, endowing significant selectivity for C₂H₂ over C₂H₄ (5.4), C₂H₆ (5.6), CH₄ (30.0), and CO₂ (7.7) at 298 K and 100 kPa. Column breakthrough experiments confirmed the extraordinary C₂H₂ separation performance of the material with the separation time intervals in the range of 18-24 min g^-1 for binary (C₂H₂-C₂H₄, C₂H₂-C₂H₆, C₂H₂-CO₂, and C₂H₂-CH₄) or ternary (C₂H₂-C₂H₄-C₂H₆ and C₂H₂-C₂H₄-CO₂) gas mixtures under dynamic conditions.