Two Microporous Metal–Organic Frameworks with Suitable Pore Size Displaying the High CO₂/CH₄ Selectivity

Two microporous metal–organic frameworks, [Zn₂(HDDCBA)]·2DMF·2H₂O (<b>1</b>) and [Cd₂(DDCBA)·DMA·H₂O]·H₂N­(Me)₂ (<b>2</b>) have been synthesized under solvothermal condition by using a less-exploited symmetrical pentacarboxylate ligand, 3,5-di­(3′, 5′-dicarboxylphenyl)­benozoic acid (H₅L). Both compounds <b>1</b> and <b>2</b> reveal the (5,5)-connected nets based on the binuclear metal clusters and organic linkers. The desolvated structure of <b>1</b> (<b>1a</b>) contains two shapes of 1D channel with suitable pore size and polar system decorated by uncoordinated carboxylate groups. As a result, <b>1a</b> possesses not only high CO₂ loading but also excellent CO₂/CH₄ selectivity at 273 and 298 K. In addition, both compounds display solid-state luminescence stemming from the ligand-centered fluorescence of H₅L