Heptanuclear Rh-containing clusters

The structure of the two capped octahedral clusters [MRh6(CO)ie] ( = 3, M = Rh = 2, M = Ni ) are shown in Fig. 13. Both are static in solution at low temperature and their C and Rh NMR spectra have been completely assigned. Despite their overall structural similarity, however, they have quite different CO fluxional processes. These are described below and for M = Ni are related to the asymmetries present for the H2- and //3-COs in the solid-state struc- 

For [NiRh6(CO)i6] (see Fig. 13), there are three CO-exchange processes of increasing energy. 

This closely related pair of clusters illustrates how profoundly different CO flux-ional processes can result. The mechanism of these exchanges can be adequately explained through localized rotations on a particular metal atom, or through exchange of terminal/bridge COs around a particular face, and reflect the asymmetries found in the solid state. 

An unusual cluster, viz. [HOs4Rh3(CO)i5(nbd)2], has recently been isolated from the reaction of [HOs3(CO)n] and [Rh(nbd)Cl]2 the structure consists of an Os-capped Os3Rh3 octahedron H NMR studies suggest that the H is face-bridging 

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