Chemistry Reference
In-Depth Information
5 Conclusions
This chapter has presented a comprehensive review of the developments of
gas-phase investigations into the structures of small gold clusters and their com-
plexes with the prototypical reactants CO and O
2
. The structural motifs adopted by
the clusters are extremely unusual (when compared, e.g. to transition metal clusters)
with extended two-dimensional flake structures, hollow cages and tetrahedra being
observed. The potential energy surfaces for these clusters provide evidence for
structural isomerism and fluxionality even at reduced temperatures.
The reactivity patterns of the gold clusters with O
2
can be largely rationalised by
simple electron counting metrics, but structural aspects, i.e. the presence of
low-coordinated Au atoms, are more relevant for the reactivity towards carbon
monoxide. Whilst these metrics are not perfect, they do allow for an initial
understanding of the underlying features of gold clusters which encourage the
catalytic CO oxidation. Again, in the characterisation of the gold cluster complexes,
evidence has been presented for the importance of structural isomerism and
fluxionality, which may act as a driving force for reactivity in some cases.
Generally the systems investigated require computational support for assign-
ment of the experimental findings. Thereby, these studies on gold clusters highlight
the vital interplay between gas-phase experimental characterisation and accurate
quantum chemical calculations. As more detailed experimental results,
e.g. spectroscopic data, become available greater demands are placed on the
supporting theory. For example, the 2D to 3D transition in anionic gold clusters
that is experimentally found to occur at Au
12
[
4
] had been a puzzle for theory [
51
]
but can now be correctly described, thanks to more recent developments in density
functional theory which are able to simulate dispersion interactions more accurately
[
5
,
62
,
131
].
Acknowledgments We gratefully acknowledge the contributions from all authors of our original
papers, the “Stichting voor Fundamental Onderzoek der Materie (FOM)” in providing beam time
on FELIX and the skilful assistance of the FELIX staff, in particular A.F.G. van der Meer and
B. Redlich. This work is supported by the Max Planck Society and the Cluster of Excellence
“Unifying Concepts in Catalysis” coordinated by the Technical University Berlin and funded by
the Deutsche Forschungsgemeinschaft (DFG) and through the DFG within the research unit FOR
1282 (FI 893/4). We thank G. Meijer for his continued support.
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