Mixed-Linker Isoreticular Zn(II) Metal-Organic Frameworks as Brønsted Acid-Base Bifunctional Catalysts for Knoevenagel Condensation Reactions.

Multicomponent metal-organic frameworks (MOFs) have received an increasing amount of attention due to their potential to produce new topologies, pore metrics, and functionalities compared to MOFs with a single metal cluster and one organic linker. Herein, five isoreticular Zn MOFs were obtained by mixing two types of linear ditopic linkers in a one-pot solvothermal synthesis. Interestingly, in the resulting Zn MOFs a six-connected cyclic trinuclear Zn(II) cluster and an eight-connected linear trinuclear Zn(II) cluster coexist, leading to an uncommon (6,8)-connected network. Catalytic activities toward the solvent-free Knoevenagel reactions were observed for all of these MOFs. Further experimental and computational studies suggest that they are Brønsted acid-base bifunctional catalysts. Through chemical modifications of dicarboxylate ligands, including their aromatic backbones and substituents, we have successfully implemented reticular chemistry for the modulations of pore sizes, surface areas, and catalytic performances in a series of four-component isoreticular MOFs.