Metal–organic frameworks (MOFs) have become a mainstay of chemistry and materials research due in large part to the high degree of tunability afforded by different ligand and metal combinations. That tunability can be further exploited through the use of post-synthetic exchange (PSE), where the components of the MOF (either metal cations or organic ligands) can be further modified by metathesis chemistry after the synthesis of the parent MOF, affording MOFs having structures and properties that would otherwise be difficult to achieve by direct synthesis. Two-dimensional (2D) MOFs possess 2D layers formed from coordination bonds between metal clusters and ligands, while adjacent layers are held together via weak Van der Waals or electrostatic interactions, such as π-π interactions. In some cases, these interactions can result in an interlocking motif, where the capping ligand of a layer fills the pore of the adjacent layer below, resulting in a relatively non-porous structure. In this work, we perform both ligand and cation exchange in the non-porous 2D Zn paddlewheel MOF [(Zn2)(bdc)2(iq)2]n, (bdc = 1,4-benzenedicarboxylate, iq = isoquinoline). Despite its measured lack of porosity, we observe evidence of both ligand (isoquinoline to pyridine) and cation (zinc to copper) exchange, suggesting a flexibility in the framework that can accommodate chemical transformations despite being incapable of non-transient adsorption of chemical guests.

Cation and ligand exchange in non-porous 2D metal–organic frameworks

ACS Spring 2022

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