Photoelectron spectroscopic and computational studies of the Pt@Pb₁₀⁻¹ and Pt@Pb₁₂¹⁻/²⁻ anions

A combination of anion photoelectron spectroscopy and density functional theory calculations has elucidated the geometric and electronic structure of gas-phase endohedral Pt/Pb cage cluster anions. The anions, Pt@Pb₁₀⁻¹ and Pt@Pb₁₂¹⁻ were prepared from "preassembled" clusters generated from crystalline samples of [K(2,2,2-crypt)]₂[Pt@Pb₁₂] that were brought into the gas phase using a unique infrared desorption/photoemission anion source. The use of crystalline [K(2,2,2-crypt)]₂[Pt@Pb₁₂] also provided access to K[Pt@Pb(n)](-) anions in the gas phase (i.e., the K⁺ salts of the Pt@Pb(n)²⁻ anions). Anion photoelectron spectra of Pt@Pb₁₀⁻¹, Pt@Pb₁₂¹⁻, and K[Pt@Pb₁₂]¹⁻ are presented. Extensive density functional theory calculations on Pt@Pb₁₀³⁻/²⁻/¹⁻/⁰ and Pt@Pb₁₂²⁻/¹⁻ provided candidate structures and anion photoelectron spectra for Pt@Pb₁₀⁻¹ and Pt@Pb₁₂¹⁻. Together, the calculated and measured photoelectron spectra show that Pt@Pb₁₀⁻¹ and Pt@Pb₁₂²⁻/¹⁻ endohedral complexes maintain their respective D(4d) and slightly distorted I(h) symmetries in the gas phase even for the charge states with open shell character. Aside from the fullerenes, the Pt@Pb₁₂²⁻ endohedral complex is the only bare cluster that has been structurally characterized in the solid state, solution, and the gas phase.