Endohedral Sodium in NaPb12 Clusters: Charge-State-Dependent Stabilization and Electron Counting

Endohedral plumbaspherenes are a growing family of closo lead cages whose known members are typically characterized by transition-metal guests. Herein, we examine sodium as an s-block guest in a Pb12 cage and evaluate how its endohedral stabilization depends on cluster charge. Global structure searches, DFT refinements, and correlated single-point calculations reveal a clear charge-dependent structural response across the NaPb12 series, whereas the neutral charge state favors a crown-like structure, the monoanion selectively stabilizes an endohedral [Na@Pb12]− configuration, and the dianion favors an exohedral sodium arrangement. This preference is consistent with a Wade–Mingos picture in which the Na valence electron contributes to the Pb12 skeletal framework, making the monoanion the 26-electron closo member of the series in a similar fashion to Ca@Pb12. QTAIM and spin-density analyses show distinct charge accommodation across the three charge states, while continuous shape measures and magnetic-response calculations characterize the structural and aromatic response of the Pb12 framework. These results identify [Na@Pb12]− as a charge-state-selected endohedral sodium plumbaspherene, and they show that sodium can participate directly in skeletal electron counting without adopting transition-metal-like bonding. Overall, charge-state control emerges as a simple strategy for tuning guest location and electron counting in endohedral main-group clusters.