The dynamic adaptability of mixed-ligand zinc MOFs: from fundaments to applications

Metal-Organic Frameworks (MOFs) are functional materials composed of metal nodes linked by organic ligands, often displaying empty pores or channels. Their dynamic structural rearrangement upon guest sorption and desolvation makes them uniquely adaptable and suitable for a wide range of applications. In particular, mixedligand Zinc MOFs represent an attractive subset of those materials for their extensive flexibility in coordination and topology. In this review we first discuss the coordination geometries, resulting topologies, and possible structural and dynamic rearrangement modes of different Zn mixed-ligand MOFs families. Like modular tools, the knowledge of these classes and modes make possible the a priori design of tailored materials displaying specific properties. The review follows with a selected list of applications in which the dynamic interplay between framework dynamics and guest molecules properties play an important role. These includes the separation of chemical mixtures of industrial relevance, the controlled release of active pharmaceutical ingredients (APIs) and capture and sensing of hazardous chemicals. We demonstrate the feasibility of this approach by focusing on the PUM (Parma University Materials) family of MOFs, that were specifically engineered to find applications in the controlled release of APIs and smart packaging. These materials are able to trap a wide range of APIs, often more than one at a time, adapting their framework geometry to better allocate guest with different shape and functionalities.