From rational design of organometallic precursors to optimized synthesis of core/shell Ge/GeO2 nanoparticles

The synthesis of germanium nanoparticles has been carried out, thanks to the design of novel aminoiminate germanium(II) precursors: (ATI)GeZ (with Z = OMe, NPh2, and ATI = N,N'-diisopropyl-aminotroponiminate) and (Am)2Ge (Am = N,N'-bis(trimethylsilyl)phenyl amidinate). These complexes were fully characterized by spectroscopic techniques as well as single crystal X-ray diffraction. The thermolysis of both complexes yielded NPs which display similar features that are a Ge/GeO2 core/shell structure with a mean diameter close to 5 nm with a narrow size distribution (<15%). Whereas the high temperatures (>300 °C) classically reported in the literature for the preparation of germanium-based NPs were necessary for thermolysis of the complexes (ATI)GeZ, the use of amidinate-based precursors allows the preparation at an unprecedented low temperature (160 °C) for the thermolytic route. As suggested by a mechanistic study, the lower reactivity of (ATI)GeZ (for which the concomitant use of high temperature and acidic reagent is required) was explained in terms of lower ring strain compared to the case of (Am)2Ge.