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

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 sol-vents. 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-aminoterephthalic acid 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 metastable states in which dangling linkers are similar to monocarboxylate defects that can be introduced during UiO-66 synthesis, such dangling link-ers undergo fast exchange. The presence of missing linker or missing cluster defects at the start of the ex-change process was shown to have no considerable impact on the equilibrium composition. After the ex-change process, the incoming 2-aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical small crystal size of UiO-66 (≈500nm).