Clusters of Main Group Elements

Anions fig, where fi = Si, Ge, Sn, Pb, have 2n+A skeletal electrons and hence, according to PSEPT, should adopt nido stmctures, which has been confirmed experimentally, while their derivative clusters [(OC)3M(t) -E9)] (where M = Cr, Mo, W), have closo stmctures (bi-capped Archimedian antiprism) with 2 -I- 2 electrons [267]. Corbett [268] reviewed from the viewpoint of Wade s theory, the stmctures of these and many other mixed-metal clusters, a brief listing of which is given in Table 3.21 (compare with Table 3.20). 

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Ionic clusters of main group elements can also be classified by a similar approach to that used for other clusters. Many such clusters are known they are sometimes called Zintl ions. Examples are shown in Figure 15-21. 

FIGURE 15-21 Ionic Clusters of Main Group Elements (Zintl Ions). (TI7 diagram reprinted with permission from S. Kaskel and J. D. Corbett, Inorg. Chem. 2000,39, 778. 2000, American Chemical Society.)... 

Table 3-10. Selected examples of mixed dusters of transition metal and main group elements and clusters of main group elements containing transition metal atoms (Categories C and D).

Cluster and cage structures are widespread in the chemistry of main group elements, being particularly extensive in the case of boron (Chap. 6). For transition elements the principal... 

Gorling, A., Rosch, N., Ellis, D.E. and Schmidbaur, H. (1991) Electronic structure of main-group-element-centered octahedral gold clusters. Inorganic Chemistry, 30, 3986-3994. 

The Wade rules can be applied to ligand-free cluster compounds of main-group elements. If we postulate one lone electron pair pointing outwards on each of the n atoms, then g — 2n electrons remain for the polyhedron skeleton (g = total number of valence elec-... 

Gonzales-Moraga, G. (1993). Cluster Chemistry. Springer-Verlag, New York. A comprehensive survey of the chemistry of clusters containing transition metals as well as cages composed of main-group elements such as phosphorus, sulfur, and carbon. 

The full understanding of the nature of main-group element clusters will be very difficult to achieve. 

In clusters composed solely of main-group elements, the following electronic relationship between closo, nido, and arachno structures has been found (12, 29) ... 

The electron counting rules of Wade (S3), Williams (117), and Rudolph (118) can serve as a useful concept to explain structure and bonding in a variety of systems which at first glance are very different Zintl phases, boranes and carboranes, transition metal n complexes and carbonyl clusters, nonclassical carbocations, and also n complexes of main-group elements. According to... 

Figure 18. Structures of main-group element (X) centered gold phosphine (L) clusters.

Table 2. Binding energies (eV) of main-group element centered Au clusters.

Current concepts in modem chemistry/Transition metal cluster chemistry/Main group-transition metal mixed clusters/Cluster compounds of main group elements/ Synthetic analogues of the active sites of iron-sulfur proteins... 

I. Synthesis, structure and bonding. II. Clusters with isolated atoms of main group elements, large metal elusters and fluxionality of clusters. III. Homogeneous and heterogeneous eatalysis... 

Of the above four categories, the first two are by far the most documented in high nudearity clusters and share common synthetic methods. Therefore, in the following brief overview of the synthetic methods for transition metal clusters containing main group elements, they will be treated together. The remaining two (C and D) present some peculiar features and will be described separately. 

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