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 (DCPCBImH(3)Cl), 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 (Schlafli) symbol (4(2).6)(2)(4(4).6(9).8(2)). 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.