Ligand-free osmium clusters supported on MgO. A density functional study
The interactions of Os{sub 4}, Os{sub 5}, and Os{sub 5}C clusters with various sites of a MgO(001) support were investigated theoretically with the aid of a scalar-relativistic density functional cluster model method. Adsorption geometries of C{sub 4{upsilon}} clusters centered above a magnesium cation and the Os atoms oriented either to the nearest surface oxygen anions (A) or between them (B) were considered. The influence of surface V{sub s} and V{sub s}{sup 2{minus}} defects on the adsorption of the clusters was also investigated. The calculated base Os-Os distances in supported Os{sub 5} and Os{sub 5}C square-pyramidal clusters are at most 0.1 {angstrom} longer (2.5--2.6{angstrom}) than the values calculated for the corresponding free osmium cluster but about 0.4{angstrom} (or more) shorter than the values determined by EXAFS spectroscopy for MgO-powder-supported clusters formed by decarbonylation of [Os{sub 5}C(CO){sub 14}]{sup 2{minus}} and shown to retains the Os{sub 5}C frame. The experimental Os-Os distances characterizing the supported clusters are close to the experimental and calculated bond lengths for coordinatively saturated osmium carbonyl clusters; the result favors the suggestion that the supported clusters characterized by EXAFS spectroscopy were not entirely ligand-free. The models reported here are inferred to be too simplified to capture all the pertinent structural details of MgO-powder-supported osmium clusters, but they are sufficient to indicate a significant role of defect sites in the adsorption of supported osmium clusters and, the authors infer, other transition metal clusters.
- Research Organization:
- Technische Univ. Muenchen, Garching (DE)
- Sponsoring Organization:
- Alexander von Humboldt Foundation; US Department of Energy; Deutsche Forschungsgemeinschaft DFG (German Research Partnership)
- DOE Contract Number:
- FG02-87ER13790
- OSTI ID:
- 20050879
- Journal Information:
- Langmuir, Journal Name: Langmuir Journal Issue: 6 Vol. 16; ISSN LANGD5; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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