Coordination and Solvation in Gas-Phase Ag+(C2H2)n Complexes Studied with Selected-Ion Infrared Spectroscopy.

Silver-acetylene cation complexes of the form Ag+(C2H2)n (n = 1-9) were produced via laser ablation in a supersonic expansion of acetylene/argon. The ions were mass selected and studied via infrared laser photodissociation spectroscopy in the C-H stretching region (3000-3500 cm-1). Fragmentation patterns indicate that four ligands are strongly coordinated to the metal cation. Density functional theory calculations were performed in support of the experimental data. Together, infrared spectroscopy and theory provide insight into the structure and bonding of these complexes. The Ag+(C2H2)n (n = 1-4) species are shown to be η2-bonded, cation-π complexes with red-shifted C-H stretches on the acetylene ligands. Unlike Cu+(C2H2)n and Au+(C2H2)n complexes, which have a maximum coordination of three, silver cation is tetrahedrally coordinated to four acetylene ligands. Larger complexes (n = 5-9) are formed by solvation of the Ag+(C2H2)4 core with acetylene. Similar to Cu+(C2H2)n and Au+(C2H2)n complexes, acetylene solvation leads to new and interesting infrared band patterns that are quite distinctive from those of the smaller complexes.