Higher nuclearity Rh-containing clusters 15 metals

For those higher nuclearity clusters which have been structurally characterized (Table 9), there have been few detailed NMR studies and the clusters in Table 9 will be alluded to only when NMR studies have been reported. 

The structure of [RhnS2(CO)32] is shown in Fig. 27. VT C NMR measurements indicate that at 40 °C the cluster is static whereas at -1-180 °C there is exchange of one set of terminal and u-COs but, as the relative intensities of the terminal/jU-COs associated with the inner and outer layers are the same, it is difficult without C- Rh measurements to be sure which of these two sets of groups is exchanging. The direct Rh NMR spectrum of [Rhi7S2(CO)32] has been reported and is consistent with the static structure there are three resonances of relative intensity 1 8 8 from the interstitial and inner/outer Rhs, respectively. In view, however, of the errors in 5( Rh) made by this group on other clusters, the absolute values of the rhodium chemical shifts must be treated with caution, although the resonance from the interstitial Rh is obviously at low field. 

There is spectroscopic and crystallographic evidence that [H tRh22(CO)35] and [H c+iRh22(CO)35] co-crystallize. It was difficult to obtain well resolved NMR spectra because of insolubility but VT H NMR spectra suggested the presence of a high-field H resonance (-18.5 ppm) and a broad multiplet in the C NMR spectrum at 212 ppm. These spectra are, however, rather ill-defined and attempts to 

Low-temperature H NMR studies on [Pt4Rhi8(CO)35] failed to detect a hydride resonance and the absence of a hydride(s) in this formulation is consistent with both space-filling models, which exclude H-coordination to the metal surface, and the lack of reaction with Na2C03. °  

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Table 9. References to higher nuclearity Rh-containing clusters (>15 metals) which have been structurally characterized by X-ray crystallography.

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