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

Abstract

Porosity control and structural analysis of metal–organic frameworks (MOFs) can be achieved using regioisomeric ligand mixtures. While ortho-dimethoxy-functionalized MOFs yielded highly porous structures and para-dimethoxy-functionalized MOFs displayed almost nonporous properties in their N2 isotherms after evacuation, regioisomeric ligand-mixed MOFs showed variable N2 uptake amount and surface area depending on the ligand-mixing ratio. The quantity of N2 absorbed was tuned between 20 and 300 cm3/g by adjusting the ligand-mixing ratio. Both experimental analysis and computational modeling were performed to understand the porosity differences between ortho- and para-dimethoxy-functionalized MOFs. Detailed structural analysis using X-ray crystallographic data revealed significant differences in the coordination environments of DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] (DMOF = dabco MOF, dabco = 1,4-diazabicyclo[2.2.0]­octane). The coordination bond between Zn2+ and carboxylate in the ortho-functionalized 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 (ortho- and para-dimethoxy-functionalized benzene-1,4-dicarboxylates) explained the rigidity and porosity changes of the mixed MOFs upon evacuation and perfectly matched with experimental N2 adsorption and X-ray crystallography data.

From zero- to three-dimensional heterobimetallic coordination polymers with the [Pt{SSC-N(CH2COO)2}2]4− metalloligand

“…1,2 In the recent decade, CPs containing more than one metal have attracted significant research interest, as they can exhibit completely different structures and properties than their homometallic analogs, offering new reaction patterns and novel fields of application. [3][4][5][6][7][8] Since the metal-ligand connectivity in these compounds is often difficult to predict and to control, the development of rational synthetic strategies is of fundamental importance. In recent contributions, we have shown that dithiocarbamate-functionalized carboxylates (DTCCs) can coordinate selectively to a to a soft (thiophilic) and a hard (oxophilic) metal center at the same time.…”

Post-synthetic ligand cyclization in metal–organic frameworks through functional group connection with regioisomerism

“…Based on our recent contribution to MOFs with regioisomerism of multiple functional groups, [18][19][20][21][22] a dual-functionalized benzene-1,4-dicarboxylic acid (BDC) ligand with two reactivechemical handles, viz. NH 2 and OH, was designed for cyclization on MOFs (Scheme S1 in ESI †).…”