Cluster-support interaction

Under conditions of weak cluster-support interaction the cluster may adopt free-space-like conformations. 

Where the cluster-support interaction is strong, the fluid internal relaxation of the cluster may allow it to adopt a free-space-Uke structure. 

In summary, our study shows the power and the necessity of computational methods in unravelling the structural chemistry of silica-supported metal clusters. It has been shown that the stmcture of such clusters is highly sensitive to the processes by which the cluster-support interaction occurs and not just dependent on the strength of the binding interaction. Further studies are aimed at also investigating the electronic structure of supported clusters and the effects of ligands on cluster structure. 

The ability to conduct EXAFS studies on complexes in non-crystalline phases and in particular on active catalyst systems in situ has been the driving force for much of the development and application of the technique to the analysis of cluster geometry. In the earlier phase of this sort of work, i.e. studies of type (iii), the objective was to identify the cluster species present on the support and the nature of the cluster-support interaction. Three general modes of attachment of cluster complexes to supports have been explored ... 

In each of these it has been shown that in conjunction with other techniques (notably IR spectroscopy) EXAFS spectroscopy can give valuable information about both cluster-support interactions and cluster geometry. 

With oxide-supported cluster complexes, models have been made to mimic the cluster-support interaction, but their reactivity has not been studied. For example, the silica-supported cluster SiCH2CH2PPh20s3H2(CO)io undergoes a decarbonylation reaction, not to give the Os3H2(CO)9(L) species, as occurs in solution, but to give an uncharacterized species which may be of the type 0s3(p2 0)3(C0)x (where M2 0 represents a surface oxygen atom). It should be possible to model the reactivity of such supported complexes. 

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