Engineering a highly defective stable UiO-66 with tunable Lewis-Brønsted acidity - The role of the hemilabile linker

The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to maximum 6 defects per cluster in UiO-66. We have synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects, but also as a co-ligand that enhances the stability of the resulting defective framework. Furthermore, upon a post-synthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (3 per formula unit), leaving the Zr-nodes on average 6-fold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly ...