Thermolabile Cross-Linkers for Templating Precise Multicomponent Metal–Organic Framework Pores

Abstract

While a number of approaches toward multicomponent metal−organic frameworks have been reported, new strategies affording greater structural versatility and molecular precision are needed to replicate the sophisticated active sites found in enzymes.Here, we outline a general method for templating functional groups within framework pores using thermolabile ligand cross-linkers. We show that tertiary ester-based cross-linkers can be used to install welldefined carboxylic acid pairs at precise relative distances and orientations. The tertiary ester linkages remain intact during framework formation but are readily cleaved to reveal free carboxylic acids upon microwave heating. Successful cross-linker synthesis, framework incorporation, and thermolysis is demonstrated using the mesoporous, terphenyl expanded analogues of MOF-74. When short cross-linkers are used, modeling studies show that the carboxylic acids are installed in a single configuration down the pore channels, spaced ∼7 Å apart. These precisely positioned acid pairs can be used as synthetic handles to build up more complex cooperative active sites.

Construction of Macroporous β-Glucosidase@MOFs by a Metal Competitive Coordination and Oxidation Strategy for Efficient Cellulose Conversion at 120 °C

“…In recent years, extensive efforts have been devoted to building MOFs with a macroporous structure through the strategies of ligand extension, − template additives, − and defect formation − in order to overcome the limitation of microporosity. Among them, the ligand extension method could only prepare the 2–20 nm pore size MOF, − which could not meet the mass transfer of the macromolecular substrate (e.g., cellulose).…”

Hierarchical porous metal–organic gels and derived materials: from fundamentals to potential applications

“…[72][73][74][75][76] These reactions became more advanced over time 77 and with the development of chemically more robust frameworks, harsher reaction conditions could be used. 23,78 On the other hand, there was research that described the crosslinking of the organic building blocks pre-synthetically [79][80][81] and post-synthetically 82 for the construction of PolyMOFs 83 and organic gels 84 that used the MOF structure as a template. In parallel to the covalent postsynthetic functionalization, also the coordinative functionalization was established.…”

Tethering Effects in Oligomer-Based Metal–Organic Frameworks

“…Dong, Guan, and co-workers synthesized an amide-tethered aminoterephthalic acid dimer and used this species to grow a crosslinked shell on UiO-66, leading to enhanced CO 2 /CH 4 uptake selectivity . Recently, Xiao and co-workers crosslinked 4,4″-dioxido-[1,1′:4′,1″-terphenyl]-3,3″-dicarboxylic acid to generate dimers connected via ester linkages, which could be thermolyzed to yield free carboxylic acids with precise positioning in an expanded MOF-74-type framework . Beyond these simple dimeric and trimeric linker species, Johnson and co-workers have also synthesized several dimeric and tetrameric MOF linkers bridged by or decorated with polymers, which were used to make IRMOF-1 analogues. , While these studies demonstrate several potential strategies and uses of oligomeric MOFs, they generally have not explored the relationship between the ligand structure and the resulting oligoMOF properties, or by comparison to the molecular and polymeric MOFs.…”