Germanium Zintl ions structure

Most, if not all, solids containing Zintl ions and sequestered alkali metal ions are infinitely stable in the absence of moisture and oxygen. Since the original report of the solid state structures of (crypt-Na+)2(Pbs ) and (crypt-Na )4(Sn9 ) in 1975, " the synthetic use of crypt has now produced compounds containing Zintl ions of germanium, tin, lead, arsenic, antimony, bismuth and tellurium. " ... 

As we can see from the last entry in this table, we have deduced only a rule. In InBi there are Bi-Bi contacts and it has metallic properties. Further examples that do not fulfill the rule are LiPb (Pb atoms surrounded only by Li) and K8Ge46. In the latter, all Ge atoms have four covalent bonds they form a wide-meshed framework that encloses the K+ ions (Fig. 16.26, p. 188) the electrons donated by the potassium atoms are not taken over by the germanium, and instead they form a band. In a way, this is a kind of a solid solution, with germanium as solvent for K+ and solvated electrons. K8Ge46 has metallic properties. In the sense of the 8-A rule the metallic electrons can be captured in K8Ga8Ge38, which has the same structure, all the electrons of the potassium are required for the framework, and it is a semiconductor. In spite of the exceptions, the concept has turned out to be very fruitful, especially in the context of understanding the Zintl phases. 

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