3-dimensional linker-based metal–organic frameworks for sub-angstrom control and enhanced thermal stability

Abstract

Metal–organic frameworks (MOFs) are some of the best materials for energy-efficient separations, like membranes and adsorption processes, due to their nanoporosity and tunability. To tune a MOF for optimum separation of molecules with sub-angstrom differences in size, which is a common challenge in industrial separations, precise control of the local pore environment is required. Here, we explore the concept of “3-dimensional” linkers, i.e., linkers that contain sterically bulky non-planar cores, as a means to attain sub-angstrom control over MOF pore size and to control structural flexibility. In particular, the introduction of 3-dimensional linkers (3DLs) is shown to hinder global breathing transitions in MOFs. Because these linkers occupy a consistent volume regardless of their orientation, they also allow for precise size-based separation of very similar molecules, such as hexane isomers. Furthermore, we discuss the thermal stability of a subset of these materials, characterized through variable temperature X-ray diffraction and porosity measurements.