Coexisting Isomers, Charge-State Dependent Bonding, Geometric Reorganization, and Symmetry-Driven Stabilization in RuSi₄^– and RuSi₅^– Clusters

Transition metal (TM)-doped silicon clusters represent critical model systems for understanding the interplay between electronic structures and geometric configurations in nanomaterials. This study combines mass-selected anion photoelectron spectroscopy with multiconfigurational quantum chemical calculations to resolve the structural, electronic, and isomerization dynamics of RuSi₄^- and RuSi₅^- clusters. Photoelectron spectra at 266 nm (4.66 eV) are analyzed alongside density functional theory (B3LYP) and coupled-cluster (CCSD(T)) simulations to determine adiabatic/vertical detachment energies, structural isomers, and reaction pathways. RuSi₄̅ exhibits two coexisting low-energy isomers (Δ<i>E</i> = 0.04/0.13 eV), stabilized kinetically via small thermal barriers, while RuSi₅̅ adopts a <i>C</i>_4v-symmetric tetragonal bipyramid with σ aromaticity. Charge redistribution and Wiberg bond indices calculations critically modulate Ru-Si bonding, with CCSD(T) outperforming B3LYP in predicting energy hierarchies. The work establishes a symmetry-driven framework for predicting structural stability in TM silicides and elucidates kinetic trapping mechanisms relevant to designing functional nanomaterials with tailored electronic properties.