Active Role of Methanol in Post-Synthetic Linker Exchange in the Metal–Organic Framework UiO-66

Abstract

UiO-66 is known as one of the most robust metal-organic framework materials. Nevertheless, UiO-66 has also been shown to undergo post-synthetic exchange of structural linkers with surprising ease in some solvents. To date, the exchange mechanism has not yet been fully elucidated. Here, we show how timeresolved monitoring grants insight into the selected case of exchanging 2-aminoterephthalate into UiO-66 in methanol. Analysis of both the solid and liquid phase, complemented by computational insights, revealed the active role of methanol in the creation and stabilization of dangling linkers. Similar to monocarboxylate defects that can be introduced during UiO-66 synthesis, such dangling linkers undergo fast exchange. The presence of missing linker or missing cluster defects at the start of the exchange process was shown to have no considerable impact on the equilibrium composition. After the exchange process, the incoming 2aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical sub-micron size of UiO-66 crystallites.

Creation of Active Sites in MOF‐808(Zr) by a Facile Route for Oxidative Desulfurization of Model Diesel Oil

“…During this process, possibly EtOH/EtO − pairs replaced formate anion firstly. Then, the intermediate obtained was hydrolyzed into Zr−OH/‐OH 2 (Figure b) …”

Vapor‐Phase Linker Exchange of the Metal–Organic Framework ZIF‐8: A Solvent‐Free Approach to Post‐synthetic Modification

“…In the presence of sodium formate, ZIF‐8 initially grows through nanoparticle aggregation, before transitioning to a linker‐particle attachment . We hypothesize that this growth mode results in defects in the core of the large crystals and that linker exchange initially occurs at these defect sites, as suggested by theoretical calculations for ZIFs and experimentally observed in other MOFs . The resulting local changes in pore polarity and hydrogen bonding capability likely favor the adsorption and incorporation of further CHO‐HIm molecules.…”

Analysis of electrocatalytic metal-organic frameworks

“…For instance, phosphate or acetate buffers that are frequently used electrolytes have been known to cause framework collapse in multiple carboxylate-based frameworks [46]. In an illuminating study, Marreiros et al found that prolonged exposure of UiO-66 to methanol generates missing-linker defects, equilibrating at approximately one missing linker per unit cell [47]. While this does not necessarily lead to framework collapse, the defect makeup and porosity may be altered in an unpredictable way.…”