X-ray crystallographic study of some pentacoordinated organogermanium compounds

The X-ray crystallographic structures of 2-(2-phenyl-5-oxo-1,3,2-oxathiagermolan-2-ylthio)acetic acid (2), its pyridinium salt (3), and the pyridinium salt of 2-(2-t-butyl-5-oxo-1,3,2-oxathiagermolan-2-ylthio)acetic acid (1), (4), together with 2-(2-phenyl-1,3,2-oxathiagermolan-2-ylthio)ethanol (5) were determined and compared with that of 1. All of compounds investigated, 2–5, have the TBP-like, pentacoordinated structure. This fact seems to indicate that the driving force of pentacoordination of this type of compounds is the existence of an oxygen atom δ to the germanium atom that readily forms a five membered ring by hypercoordination.