Materials called metal–organic frameworks (MOFs) have sparked intense interest over the past few decades. In particular, those that form permanently porous architectures have tremendous potential for applications such as chemical sensing, gas storage and catalysis. But techniques for synthesizing these compounds are still often developed through trial and error — in part because the mechanisms that dictate the self-assembly of MOF unit cells from their constituent metal ions and ligands, and their subsequent growth into nanoparticles, are largely unknown and difficult to observe. Writing in the Journal of the American Chemical Society, Patterson et al.1 help to solve this problem by reporting the first observations of the crystallization of MOFs made in real time, using a technique called liquid-cell transmission electron microscopy.
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