Structural Evolution and Electronic Properties of Ruthenium-Doped Silicon Clusters: Anion Photoelectron Spectroscopy and Theoretical Calculations of Anionic and Neutral RuSi _<i>n</i> ( <i>n</i> = 13–17) Clusters

The structural evolution, electronic properties, and thermodynamic stability of ruthenium-doped silicon clusters (RuSi_<i>n</i>^-, <i>n</i> = 13-17) are systematically investigated through a combination of anion photoelectron spectroscopy and high-level theoretical calculations. Anion photoelectron spectra recorded at 266 nm exhibit size-dependent electronic transitions, with vertical detachment energies (VDEs) ranging from 2.87 to 3.28 eV─the computed VDE values show excellent agreement with the experimental data (deviation <0.11 eV), which validates the structural models. Global minimum structures are identified through a hybrid Crystal Structure AnaLYsis by Particle Swarm Optimization (CALYPSO) and ABCluster search strategy, refined using density functional calculations (DFT) at the B3LYP/def2-TZVPD level, and corroborated by DLPNO-CCSD(T) single-point energy calculations. Both neutral and anionic clusters adopt structural motifs based on a Ru-encapsulating distorted bicapped pentagonal prism, with successive Si atom capping governing geometric evolution and stability. Notable magic-number behavior emerges for anionic RuSi₁₇^- and neutral RuSi₁₄ (compact geometry and favorable electronic configuration). Natural population analysis confirms that Ru acts as an electron acceptor, with charge distributions closely correlating to VDE trends. Energetic descriptors─Ru binding energy (<i>E</i>_b (Ru)) and Si incremental binding energy (Δ<i>E</i>^I (Si))─reveal pronounced size- and charge-state-dependent stability: neutrals exhibit higher <i>E</i>_b (Ru) (9.14-10.15 eV) than anions (6.88-7.91 eV), while positive Δ<i>E</i>^I (Si) values (3.41-5.37 eV for neutrals; 3.87-4.74 eV for anions) confirm that Si incorporation enhances stability. These results underscore the intricate interplay of Ru-Si bonding, geometric configuration, and electronic structure in governing cluster stability, with the charge state serving as a key modulator.