Understanding the Formation of Elemental Germanium by Thermolysis of Sol-Gel Derived Organogermanium Oxide Polymers

Abstract

Thermolysis of organogermanium oxide sol-gel polymers yields germanium oxide-embedded germanium nanocrystals. In the present study, we investigate the influence of different organic substituents, R, on the sol-gel chemistry of organotrichloro- and organotrialkoxygermane precursors and the thermal behavior of the resulting organogermanium oxides (RGeO_1.5)_n. The organic substituent affects the structure of the sol-gel product, with bulky R groups hindering network polymer formation. Cage-like sol-gels formed in the presence of bulky substituents are volatile, while network polymers experience thermolytic cleavage of the Ge–C bond. This cleavage produces a Ge-rich oxide (GeO_1.5)_n, that undergoes thermally induced disproportionation into GeO₂ and elemental Ge. The onset temperature of the disproportionation reaction is profoundly influenced by the nature of the organic substituent. We propose the change in onset temperature arises from a shift in R-group cleavage pathways from radical to β-hydride elimination