Transition metal clusters skeletal electron counting

The examples presented illustrate three points already presented in Sections 2 and 3. The formation of a cluster structure containing specified transition metal and main group atoms depends on (1) the skeletal electron count, (2) the identity of the elements chosen, and (3) the number and type of ligands on the cluster atoms. In addition, the following dramatically shows the wide variety of cluster isomers and stoichiometries that remain to be discovered. 

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... 

Rules for counting the number of skeletal electrons provided by each vertex atom need to be established in order to determine the number of skeletal electrons in polygonal and polyhedral clusters of the post-transition elements. The rules discussed above for polyhedral boranes can be adapted to bare post-transition metal vertices as follows ... 

The metal cluster of [RhioP(CO)22] forms a deltapolyhedron, which has g = 142, as shown in Fig. 19.4.1(d). The skeleton of RhyP(CO)2i I2- is obtained by removal of a vertex transition-metal fragment. The skeletal valence electron count of [RhgPtCOhi]2- gives g = 142 — 12 = 130. 

Development of the concept of the chemical bond from hydrogen to cluster compounds Limitations of the polyhedral skeletal electron pair theory in organometallic cluster chemistry examples in tri- and tetrametallic systems Electron-count versus structural arrangement in clusters based on a cubic transition metal core with bridging main group elements... 

Configurations and bonding in naked clusters formed by the post-transition metals follow a pattern similar to that established for boranes and carboranes discussed in Sect 2.3 i.e. that in c/oso-deltahedra with n vertices there are n -h 1 low-lying skeletal orbitals so the relationship between polyhedral shape and electron count corresponds to that described in Table 2.11. 

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