Boron Analogous Clusters of the Type

This section will focus on homonuclear neutral or anionic clusters of the elements aluminum, gallium, indium, and thallium, which have an equal number of cluster atoms and substituents. Thus, they may clearly be distinguished from the metalloid clusters described below, which in some cases have structures closely related to the allotropes of the elements and in which the number of the cluster atoms exceeds the number of substituents. The compounds described here possess only a single non-centered shell of metal atoms. With few exceptions, their structures resemble those of the well-known deltahedral boron compounds such as B4(CMe3)4 [30], B9CI9 [31] or [B H ]2 [32]. The oxidation numbers of the elements in these 

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The initial crystal structures of borohydride complexes of transition metals were obtained in 1967 for Cu(BH4)(PPh3)2 and Zr(BH4)4. The X-ray data for the latter show beautifully symmetric triple hydrogen (tt ) bridges from four borons that tetrahedrally surround M (Figure 13.1). Metalloborane cluster con )lexes of the type [Fe(CO)3]5- B H +4 and HFe(CO)9(BH4) (3) along with [Cp Ru] moieties connected to B H +4 clusters n = 2-A) provide an elegant borane analogy. The... 

The extreme hypoelectronicity of the indium and thallium clusters can be relieved by d-orbital participation from some of the vertex metal atoms. In the case of a normal bare post-transition metal vertex in a metal cluster sucb as those discussed in Section 10.6.1, tbe 12 external electrons may be divided into two types, namely, tbe 10 nonbonding d electrons and tbe 2 electrons of an external lone pair analogous to tbe B-H bonding pair in the polyhedral boranes B H (6 < n < 12). In this way a normal post-transition metal vertex such as indium may be considered to use a four-orbital sp bonding manifold just like light vertex atoms such as boron or carbon. However,... 

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