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

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si) 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 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, comprising a central atom from group 6 (M = Cr, Mo, and W) were deposited on C 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@Si, the extent of charge transfer to the C substrate is approximately doubled, while the oxidative reactivity is subdued for M@Si on C, especially for W@Si. The results show that a divalent state of M@Si appears on the C substrate, which is consistently calculated to be a symmetrical cage structure of W@Si in , revealing insights into the "periodic law" of M@Si superatoms pertaining to the characteristics of alkaline earth metals.