Geometric and Electronic Properties of P Atom-Doped Al Nanoclusters: Alkaline-like Superatom of P@Al12

The geometric and electronic characteristics of phosphorus-atom doped aluminum nanoclusters, Al_nP_m (n = 7-17, m = 1 and 2), were investigated through a combination of experiments and theoretical calculations. The size dependences of the ionization energy (E_i) for Al_nP_m NCs exhibit a local minimum of 5.37 eV at Al₁₂P₁, attributed to an endohedral P@Al₁₂ superatom (SA). This SA originates from an excess electron toward the 2P shell closing (40e), coexisting with an exohedral isomer featuring a vertex P atom. The stability of the endohedral P@Al₁₂ is further enhanced in its cationic state compared to the exohedral isomer, when complexed with a fluorine (F) atom, forming an SA salt denoted as P@Al₁₂⁺F^- with an elevated E_i ranging from 6.42 to 7.90 eV. In contrast, for the anionic Al₁₂P₁^-, the exohedral form is found to be more stable than the endohedral one using anion photoelectron spectroscopy and calculations. The geometric and electronic robustness of neutral P@Al₁₂ SAs against electron donation and acceptance is discussed in comparison to rare-gas-like Si@Al₁₂ SAs.