Alkaline Earth Metal Superatom of W@Si₁₆: Characterization of Group 6 Metal Encapsulating Si₁₆ Cage on Organic Substrates

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si-16) exhibit a superatomic nature, depending on the central M atom owing to the number of valence electrons and charge state on organic substrates. Since M@Si-16 superatom featuring group 4 and 5 transition metal atoms exhibit rare-gas-like and alkali-like characteristics, respectively, group 6 transition metal atoms are expected to show alkaline earth-like behavior. In this study, M@Si-16, comprising a central atom from group 6 (M-VI = Cr, Mo, and W) were deposited on C-60 substrates, and their electronic and chemical stabilities were investigated in terms of their charge state and chemical reactivity against oxygen exposures. In comparison to alkali-like Ta@Si16, the extent of charge transfer to the C-60 substrate is approximately doubled, while the oxidative reactivity is subdued for M-VI@Si-16 on C60, especially for W@Si-16. The results show that a divalent state of MVI@Si-16 (2+) appears on the C-60 substrate, which is consistently calculated to be a symmetrical cage structure of W@Si-16 (2+) in C-3v , revealing insights into the "periodic law" of M@Si-16 superatoms pertaining to the characteristics of alkaline earth metals. [GRAPHICS]