Experimental, Structural, and Computational Investigation of Mixed Metal-Organic Frameworks from Regioisomeric Ligands for Porosity Control

Porosity control and structural analysis of metal-organic frameworks (MOFs) can be achieved using regioisomeric ligand mixtures. While orthodimethoxy-functionalized MOFs yielded highly porous structures and paradimethoxy-functionalized MOFs displayed almost nonporous properties in their N-2 isotherms after evacuation, regioisomeric ligand-mixed MOFs showed variable N-2 uptake amount and surface area depending on the ligand-mixing ratio. The quantity of N-2 absorbed was tuned between 20 and 300 cm(3)/g by adjusting the ligand-mixing ratio. Both experimental analysis and computational modeling were performed to understand the porosity differences between ortho- and paradimethoxy-functionalized MOFs. Detailed structural analysis using X-ray crystallo- graphic data revealed significant differences in the coordination environments of DMOE-[2,3-(OMe)(2)] and DMOF-[2,S-(OMe)(2)] (DMOF = dabco MOF, dabco = 1,4-diazabicyclo[2.2.0]octane). The coordination bond between Zn2+ and carboxylate in the orthofunctionalized DMOF-[2,3-(OMe)(2)] was more rigid than that in the para-functionalized DMOF-[2,5-(OMe)(2)]. Quantum-chemical simulation also showed differences in the coordination environments of Zn secondary building unit surrounded by methoxy-functionalized ligands and pillar ligands. In addition, the binding energy differences between Zn2+ and regioisomeric ligands (orthoand para-dimethoxy-functionalized benzene-1,4-dicarboxylates) explained the rigidity and porosity changes of the mixed MOFs upon evacuation and perfectly matched with experimental N-2 adsorption and X-ray crystallography data.