Germanium complexes stereochemistry

On the other hand, for cobalt-germanium complexes, the stereochemistry strongly depends on ligand (Table 3). 

Two factors combine to lend a greater diversity in the stereochemistries exhibited by bivalent germanium, tin and lead compounds, the increased radius of Mn compared with that of Mw and the presence of a non-bonding pair of electrons. When the non-bonding pair of electrons occupies the isotropic valence level s orbital, as in, for example, the complex cations Pb[SC(NH2)2]6+ and Pb[antipyrine]6+, or when they are donated to conductance band levels, as in the binary tin and lead selenides or tellurides or the perovskite ternary phases CsMX3 (M = Sn, Pb X = Cl, Br, I), then the metal coordination is regular. However, in the majority of compounds an apparent vacancy in the coordination sphere of the metal is observed, which is usually ascribed to the presence of the non-bonding pair of electrons in a hybrid orbital and cited as evidence for a stereochemically active lone pair . 

The stereochemistry of displacement of chiral germyl ligand in germanium transition metal complexes [which has been reviewed elsewhere (12)] will also be discussed here, since silicon and germanium resemble each other and since complementary experiments have been undertaken. 

Gielen, M., Dehouck, C., Mokhtar-Jamai, H., Topart, J., Stereochemistry of Four-, Five- and Six-Coordinate Complexes of Group IV Metals, Rev. Silicon Germanium Tin Lead Compounds 1 [1972] 9/33. 

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