Germanium oxide coordination number

Germanium oxide, GeOg differs from Si02 in that in addition to a quartz type structure in which the coordination numbers of germanium and oxygen are respectively 4 and 2, there exists a second modification with a rutile structure (coordination numbers respectively 6 and 3). The reason for the formation of the second structure is not clear, but it may be due to an increased contribution from the ionic form of the GeO bond. 

The monoanionic, bidentate four-electron-donor amidinates are also suitable for stabilizing low oxidation states and/or high coordination numbers at germanium centers. The monosubstituted and mononuclear compound 4, as well as compound 5, have been isolated and were characterized spectroscopically and structurally. 

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