Deciphering σ-aromaticity and transition-metal-directed structural evolution in RuSi12−/RuSi12 clusters: Synergistic photoelectron spectroscopy and <i>ab initio</i> insights

We present a combined photoelectron spectroscopy and multilevel computational study [B3LYP/CCSD(T)] elucidating the geometric/electronic structure and aromatic stabilization of ruthenium-doped silicon clusters. Anion photoelectron spectrum of RuSi12- reveals two distinct detachment features at 3.34 eV [vertical detachment energy (VDE)] and 3.8-4.4 eV, with an adiabatic detachment energy (ADE) of 3.17 eV, indicating significant neutral-state structural reorganization. Theoretical analysis identifies the global minimum as a D2d-symmetric bicapped pentagonal prism, validated by <5.5% deviation between experimental and calculated VDE/ADE. RuSi12 neutral adopts a D6h-symmetric hexagonal prism with elongated Ru-Si bonds (2.64 vs 2.57 Å in anion), demonstrating charge-state-dependent geometric flexibility. Natural population analysis reveals strong Ru-Si charge transfer (-3.487 e on Ru in anion), while molecular orbital and AdNDP/NICS analyses uncover unprecedented σ-aromaticity through 30 delocalized electrons (Hückel 4N + 2, N = 7) and diatropic ring currents. Comparative studies with NbSi12- highlight transition-metal-driven symmetry modulation: Ru's 4d-orbital participation enables adaptable bonding networks (WBI: Ru-Si = 0.44-0.48 vs Si-Si = 0.77-0.86), contrasting with Nb's rigid σ/π-delocalized framework. This work establishes transition-metal doping as a strategic tool for tailoring silicon cluster properties in catalysis and nanoelectronics.