Electron counting platinum clusters

In 1977 we reported a method based on graph theory for study of the skeletal bonding topology in polyhedral boranes, carboranes, and metal clusters Q). Subsequent work has shown this method to be very effective In relating electron count to cluster shape for diverse metal clusters using a minimum of computation. Discrete metal clusters treated effectively by this method Include post-transition metal clusters (, ) > osmium carbonyl clusters (O, gold clusters, platinum carbonyl clusters (J., 7 ) > and... 

An important consequence of the nonutilization of tangential orbitals is that platinum clusters often do not obey the normal electron counting rules and appear to be electron deficient (19,21,29,58,75,76). Electron counts are usually intermediate between those found in normal transition metal clusters (58-68) and those observed in gold clusters (58,78), but no satisfactory general electron counting theory has been developed for Pt-containing clusters. In small Pt clusters constructed from PtL2 units, theoretical studies have shown that the total electron count depends on the relative orientation of the... 

Numerous triosmium-platinum clusters have been prepared, many of them derived from Os3Pt(/i-H)2(CO)10(PR3) (1) (40,40a). Although, as discussed in Section III, the participation in cluster bonding of the tangential orbitals of nonconical PtL units may be difficult to predict a priori, the observed tetrahedral skeleton of 1 (40,40a) and nonplanar coordination geometry at the Pt atom suggest that the Pt atom should behave as an 18-electron center. The 58-CVE count therefore implies that the cluster is unsaturated, and this is consistent with EHMO studies (88,98) and the high chemical reactivity of 1. The crystal structures of la (40,40a) and the 58-CVE derivatives 21 (108) and 22 (118) all show unusually short Os(/ -H)Os distances [2.789(1),... 

The electron count in a series of platinum clusters can be seen in Table 2.18. The reason why that occurs appears to be the high energy of the atomic p -orbital. The molecular orbitals derived from this orbital perpendicular to the metal-ligand plane are also high-lying and unavailable for bonding. 

Table 2.18. Electron counting in platinum cluster compounds...

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