Two-Dimensional Charge-Separated Metal–Organic Framework for Hysteretic and Modulated Sorption

A charge-separated metal–organic framework (MOF) has been successfully synthesized from an imidazolium tricarboxylate ligand, N-(3,5-dicarboxylphenyl)-N′-(4-carboxylbenzyl)­imidazolium chloride (DCPCBImH3Cl), and a zinc­(II) dimeric secondary building unit, namely, DCPCBim-MOF-Zn, which shows an unprecedented 3,6-connected two-dimensional net topology with the point (Schläfli) symbol (42.6)2(44.69.82). The framework contains one-dimensional highly polar channels, and density functional theory calculations show that positive charges are located on the imidazolium/phenyl rings and negative charges on the carboxylate moieties. The charge-separated nature of the pore surface has a profound effect in their adsorption behavior, resulting in remarkable hysteretic sorption of various gases and vapors. For CO2, the hysteretic sorption was observed to occur even up to 298 K. Additionally, trace chloride anions present in the pore channels are able to modulate the gas-sorption behavior.本研究通过咪唑鎓三羧酸配体N-(3,5-二羧基苯基)-N'-(4-羧基苄基)咪唑鎓氯化物（DCPCBImH3Cl）与二聚型锌(II)次级结构基元，成功合成了电荷分离型金属有机框架（metal–organic framework, MOF），并将其命名为DCPCBim-MOF-Zn。该框架展现出前所未有的3,6连接二维网状拓扑结构，其施莱夫利（Schläfli）点符号为(4²·6)²(4⁴·6⁹·8²)。框架内部包含一维高极性通道，密度泛函理论（density functional theory, DFT）计算结果显示，正电荷分布于咪唑鎓/苯环位点，负电荷分布于羧酸酯基团。孔表面的电荷分离特性对其吸附行为产生显著影响，使得该材料对多种气体与蒸气均表现出显著的滞后吸附现象。针对二氧化碳（CO₂），即便在298K的温度下仍可观测到滞后吸附行为。此外，孔道中存在的痕量氯离子能够调控气体吸附性能。