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 time-resolved monitoring grants insight into the selected case of exchanging 2-minoterephthalate 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 2-aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical sub-micron size of UiO-66 crystallites.
We are grateful to the concerted efforts from the excellent researchers of Ghent University and National Institute of Chemistry in Slovenia! Online version of the paper can be accessed here.