Unraveling crystal growth of metal-organic frameworks by secondharmonic scattering: from fundamental research to crystal engineering.

Metal-organic frameworks (MOFs) form one of the newest classes of advanced, nanoporous materials. They display a remarkable structural and functional versatility and can be tuned to meet specific technological applications. Although thousands of MOFs have been reported, rational design of MOFs with predictable properties, such as framework structure, size and morphology, is still hindered by a limited understanding of the underlying crystal growth mechanisms. Up to date, the study of crystal growth of MOFs is in an early phase still. The techniques currently used to study crystallization offer fragmented information that it is often hard to combine. In particular the earliest growth events, when nanoscopic clusters form and nuclei initiate crystal growth, remain hard to unveil.  In this project, we propose angle-dependent second harmonic scattering (AD-SHS)as a new method to study crystal growth in MOFs. AD-SHS allows following the complete crystal growth process in situ with a single technique, offering a unique window into the formation of growth species and nuclei and all subsequent stages of the process. Information on size, shape and structure is obtained simultaneously with high time-resolution. A fundamental understanding of the mechanisms involved in the various stages of crystal growth of MOFs will allow us to guide the process to ultimately come to MOFs of desired size, shape and structure.