Exploring the Role of Ligand Connectivity in MOFs Mechanical Stability: The Case of MIL-100(Cr)

The key parameters governing the mechanical stability of highly porous materials such as metal-organic frameworks (MOFs) are yet to be clearly understood. This study focuses on the role of the linker connectivity by investigating the mechanical stability of MIL-100(Cr), a mesoporous MOF with a hierarchical structure and a tritopic linker, and comparing it to MIL-101(Cr) having instead a ditopic linker. Using synchrotron X-ray diffraction and infrared spectroscopy, we investigate the high-pressure behavior of MIL-100(Cr) with both solid and fluid pressure transmitting media (PTM). In the case of a solid medium, MIL-100(Cr) undergoes amorphization at about 0.6 GPa, while silicone oil as a PTM delays amorphization until 12 GPa due to the fluid penetration into the pores. Both of these values are considerably higher than those of MIL-101(Cr). MIL-100(Cr) also exhibits a bulk modulus almost ten times larger than that of MIL-101(Cr). This set of results coherently proves the superior stability of MIL-100(Cr) under compression. We ascribe this to the higher connectivity of the organic linker in MIL-100(Cr), which enhances its interconnection between the metal nodes. These findings shed light on the importance of linker connectivity in the mechanical stability of MOFs, a relevant contribution to the quest for designing more robust MOFs.