Multi-scale crystal engineering of metal organic frameworks

During the last decade the number of publications related to the synthesis of new metal-organic frameworks or coordination polymers has grown almost exponentially. Many of them are devoted to the study of the correlation between the molecular components (linkers and metal nodes or clusters) and the final properties of the resulting structure. Withal, the field of metal-organic frameworks has also witnessed important advances in the development of synthetic tools to control the particle size and shape and to obtain secondary porosity by applying knowledge from three disciplines: crystallography, coordination chemistry and chemical engineering. These tools allow for crystal engineering beyond the molecular scale extending over the meso and macro scales, so that certain degree of multi-scale design is already possible. In this manner, MOFs' performance have been improved in certain applications by choosing the optimal particle morphology and dimensions that enhance the materials' properties and/or facilitate their implementation on functional devices. This review highlights the latest advances on MOF crystal engineering, with special emphasis on the meso and macro scales. After discussing some general considerations on the fundamentals of MOF crystallization, we examine different synthetic approaches developed in order to tune the MOF particle size, shape and textural properties and the impact this multi-scale MOF crystal engineering has shown so far in different applications. Finally, our view on possible future research directions is outlined.