Selective CO2 adsorption in a microporous metal–organic framework with suitable pore sizes and open metal sites

Abstract

Microporous metal–organic frameworks, [H₂N(Me)₂]₂[Zn₄(L)₂(H₂O)_1.5]·5DMF·H₂O (1·DMF) or [H₂N(Me)₂]₂[Zn₄(L)₂(H₂O)_1.5]·4DMA·6H₂O (1·DMA), have been synthesized under solvothermal conditions using an undeveloped asymmetrical pentacarboxylate ligand, 2,4-di(3′,5′-dicarboxylphenyl)benzoic acid (H₅L). Structural analysis demonstrates that 1 is a 3D anionic framework based on two kinds of dinuclear [Zn₂(COO)₅(H₂O)] secondary building units (SBUs), which presents a rare framework constructed from ternary SBUs and shows a new (5,5,5)-connected topology. The desolvated anionic structure of 1·DMF (1a) contains two shapes of 1D channel with suitable pore sizes and a highly polar pore system decorated with open metal sites, diethylammonium cations and carboxylic oxygen atoms, exhibiting multipoint interactions between CO₂ molecules and the framework, resulting in high CO₂ uptake and significant selectivity for CO₂ over CH₄ and N₂. In addition, 1·DMF and 1·DMA display solid-state photoluminescence stemming from the ligand-centered fluorescent emissions of H₅L.