title: Triosmium clusters on a support: determination of structure by X-ray absorption spectroscopy and high-resolution microscopy.
abstract: The structures of small, robust metal clusters on a solid support were determined by a combination of spectroscopic and microscopic methods: extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning transmission electron microscopy (STEM), and aberration-corrected STEM. The samples were synthesized from [Os(3) (CO)(12) ] on MgO powder to provide supported clusters intended to be triosmium. The results demonstrate that the supported clusters are robust in the absence of oxidants. Conventional high-angle annular dark-field (HAADF) STEM images demonstrate a high degree of uniformity of the clusters, with root-mean-square (rms) radii of 2.03±0.06 Å. The EXAFS OsOs coordination number of 2.1±0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02±0.04 Å. The high-resolution STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining OsOs distances of 2.80±0.14 Å, matching the EXAFS value of 2.89±0.06 Å. IR and EXAFS spectra demonstrate the presence of CO ligands on the clusters. This set of techniques is recommended as optimal for detailed and reliable structural characterization of supported clusters.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Shareghe
authors.initials: S
authors.lastname: Mehraeen
authors.forename: Apoorva
authors.initials: A
authors.lastname: Kulkarni
authors.forename: Miaofang
authors.initials: M
authors.lastname: Chi
authors.forename: Bryan W
authors.initials: BW
authors.lastname: Reed
authors.forename: Norihiko L
authors.initials: NL
authors.lastname: Okamoto
authors.forename: Nigel D
authors.initials: ND
authors.lastname: Browning
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Gates