Photoelectron Spectroscopic and Computational Study of Pyridine-Ligated Gold Cluster Anions

Pyridine-ligated gold cluster anions were studied through a combination of negative ion photoelectron spectroscopy and density functional theory calculations. Small gold cluster anions ligated by pyridine, Au_n(py)^- were generated with a ligation cell coupled to a laser vaporization source (LVS). We showed that pyridine is weakly bound (physisorbed) to the Au₂^- moiety of Au₂(py)^- by interactions between its gold atoms and either the hydrogen atoms or the π-ring of pyridine. We also found that pyridine's lone electron pair strongly binds (chemisorbs) to both Au₃(py)^- and Au₄(py)^- through single gold atoms on each of these clusters. Bonding analysis of two isomers of Au₄(py)^- supported the presence of two different ligand binding motifs, these differing in terms of the gold atom to which pyridine binds.