Electronic and structural properties of magnesium-doped platinum clusters: superatomic features of the MgPt₉ complex

We address herein a theoretical study of gas phase magnesium-doped platinum clusters (MgPt_n, n = 2-12) using density functional theory, genetic algorithms and the quantum theory of atoms in molecules method of wavefunction analyses. The Mg atom consistently donates electron density to the Pt framework. This electronic charge depletion increases with size before it reaches an asymptotic limit. Among the series, MgPt₉ exhibits enhanced stability, a large HOMO-LUMO gap (1.30 eV), a high adiabatic ionisation potential (6.94 eV) and a filled 1S² 1P⁶ shell, features which indicate a superatomic character of this species. Structural analysis reveals that MgPt₉ forms gradually from MgPt₆ and persists as a core in larger capped clusters. Spin multiplicities vary irregularly, reflecting changes in coordination and electronic degeneracy. Electrostatic potential analysis reveals the presence of σ-holes at low-coordinated Pt sites and at the Mg centre, and thereby a potential catalytic activity. These findings identify MgPt₉ as a candidate superatomic cluster and suggest broader design strategies for bimetallic nanostructures with tunable electronic and chemical properties.