Polyatomic anions of Ge, Sn, and Pb

In an unusual synthesis, the compound [K(C222)]2Pbio was obtained by oxidation of a solution of Pb94- ions in ethylenediamine with Au1 in the form of [P(C6H5)3AuC1] as the oxidizing agent  

A single-crystal X-ray structure analysis revealed that the intensely brown colored Pbio2- anion has a bicapped square-antiprismatic structure of nearly perfect Dm symmetry. 

The bonding in these polyatomic anions is delocalized, and for the diamagnetic species the bond valence method (see Section 13.4) can be used to rationalize the observed structures. This method is to be applied according to the following rules  

For example, the bond valence (b) of Ge94 is b = 5(8n — g) = [9 x 8 -(9x4+4)] = 16, and the monocapped square-antiprismatic anion is stabilized by six MMM 3c-2e bonds and four M-M 2c-2e bonds. Bonding within the polyhedron involves a resonance hybrid of several canonical forms of the type shown in Fig. 14.6.2. The structures of the polyatomic anions are summarized in Table 14.6.1. 

The polystannide cluster Sn94 (or the related Pb94 ) reacts with Cr(CO)3 (mes) to form a bicapped square-antiprismatic cluster [Sn9Cr(CO)3 ]4  

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