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Silver Cluster Formation, Dynamics, and Chemistry in Metal−Organic Frameworks

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posted on 14.10.2009 by Ronald J. T. Houk, Benjamin W. Jacobs, Farid El Gabaly, Noel N. Chang, A. Alec Talin, Dennis D. Graham, Stephen D. House, Ian M. Robertson, Mark D. Allendorf
Synthetic methods used to produce metal nanoparticles typically lead to a distribution of particle sizes. In addition, creation of the smallest clusters, with sizes of a few to tens of atoms, remains very challenging. Nanoporous metal−organic frameworks (MOFs) are a promising solution to these problems, since their long-range crystalline order creates completely uniform pore sizes with the potential for both steric and chemical stabilization. We report a systematic investigation of silver nanocluster formation within MOFs using three representative MOF templates. The as-synthesized clusters are spectroscopically consistent with dimensions ≤1 nm, with a significant fraction existing as Ag3 clusters, as shown by electron paramagnetic resonance. Importantly, we show conclusively that very rapid TEM-induced MOF degradation leads to agglomeration and stable, easily imaged particles, explaining prior reports of particles larger than MOF pores. These results solve an important riddle concerning MOF-based templates and suggest that heterostructures composed of highly uniform arrays of nanoparticles within MOFs are feasible.

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