Stereochemical non-rigid behavior of metal cluster polyhedra

2 Stereochemical non-rigid behavior of metal cluster polyhedra 

Cluster skeleton rearrangements which can be studied by variable temperature NMR spectroscopy are of comparatively low energy and are often characterized by the presence of weak metal-metal interactions within the cluster core or a low-energy pathway between two polyhedra with similar relative energies. Although these low energy skeletal transformations are not the main subject of this article, some key examples will be briefly described. 

The stacked platinum clusters, [Pt (CO)2 ] (n = 6, 9, 12, 15, and 18) consist of trigonal prismatic stacked triangular Pt3 units. The metal-metal bonds within the triangular units are significantly shorter than those between the layers. Variable temperature Pt NMR indicates that the metal polyhedra undergo interconversion between prismatic and antiprismatic structures via the rotation of the triangular units relative to each other. 

Several high-nuclearity rhodium clusters are observed to undergo polyhedral rearrangements on the NMR timescale at ambient temperatures and some gold clus- 

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