Pt<sup>+</sup>(C<sub>2</sub>H<sub>2</sub>)<sub><i>n</i></sub> Complexes Studied with Selected-Ion Infrared Spectroscopy

Platinum cation complexes\nwith multiple acetylene molecules are\nstudied with mass spectrometry and infrared laser spectroscopy. Complexes\nof the form Pt⁺(C₂H₂)_<i>n</i> are produced in a molecular beam by laser vaporization,\nanalyzed with a time-of-flight mass spectrometer, and selected by\nmass for studies of their vibrational spectroscopy. Photodissociation\naction spectra in the C–H stretching region are compared to\nthe spectra predicted for different structural isomers using density\nfunctional theory. The comparison between experiment and theory demonstrates\nthat platinum forms cation−π complexes with up to three\nacetylene molecules, producing an unanticipated asymmetric structure\nfor the three-ligand complex. Additional acetylenes form solvation\nstructures around this three-ligand core. Reacted structures that\ncouple acetylene molecules (e.g., to form benzene) are found by theory\nto be energetically favorable, but their formation is inhibited under\nthe conditions of these experiments by large activation barriers.