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Triosmium Clusters on a Support: Determination of Structure by X-ray Absorption Spectroscopy and High-Resolution Microscopy

Authors

  • Shareghe Mehraeen,

    1. Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
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  • Apoorva Kulkarni,

    1. Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
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  • Dr. Miaofang Chi,

    1. Materials Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37830 (USA)
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  • Dr. Bryan W. Reed,

    1. Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (USA)
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  • Norihiko L. Okamoto,

    1. Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
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  • Prof. Nigel D. Browning,

    Corresponding author
    1. Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
    2. Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (USA)
    • Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
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  • Prof. Bruce C. Gates

    Corresponding author
    1. Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
    • Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, California, 95616 (USA), Fax: (+1) 530-752-1031
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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 [Os3(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[BOND]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[BOND]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.

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