Metal-encapsulating germanium cage nanoclusters, M@Ge16 (M = lutetium (Lu) and tantalum (Ta)), consist of a single metal atom enclosed within a Ge16 cage and can be regarded as binary cage superatoms (BCSAs) exhibiting enhanced geometric and electronic stability due to dense atomic packing and closed-shell electron configurations. In this study, Lu@Ge16 and Ta@Ge16 were deposited onto hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC)- and fullerene (C60)-modified highly oriented pyrolytic graphite (HOPG) substrates, respectively. Their chemical stability against O2 was evaluated by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Lu@Ge16– on HB-HBC remains intact even after 30 L of O2 exposure, demonstrating better oxidation resistance than the Si16 analogue Lu@Si16. Ta@Ge16+ on C60 undergoes oxidation after exposure to 1.0 × 104 L of O2, indicating cage degradation and partial metal oxidation, although its initial oxidation resistance is comparable to that of Ta@Si16+ on C60. Together with the better oxidative resistivity of Y@Ge16 relative to Y@Si16, these results suggest that the enhanced robustness of Ge-based BCSAs arises from a better spatial match between the larger Y and Lu atoms and the Ge16 cage. This study highlights the critical role of geometric packing in achieving chemically resilient and electronically tunable designer BCSAs.
Osada et al. (Thu,) studied this question.