title: Silver cluster formation, dynamics, and chemistry in metal-organic frameworks.
abstract: 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 < or =1 nm, with a significant fraction existing as Ag(3) 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.
authors.affiliation: Sandia National Laboratories, Livermore, California 94551-0969, USA.
authors.forename: Ronald J T
authors.initials: RJ
authors.lastname: Houk
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Jacobs
authors.forename: Farid
authors.initials: F
authors.lastname: El Gabaly
authors.forename: Noel N
authors.initials: NN
authors.lastname: Chang
authors.forename: A Alec
authors.initials: AA
authors.lastname: Talin
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Graham
authors.forename: Stephen D
authors.initials: SD
authors.lastname: House
authors.forename: Ian M
authors.initials: IM
authors.lastname: Robertson
authors.forename: Mark D
authors.initials: MD
authors.lastname: Allendorf