Pt⁺(C₂H₂) _n Complexes Studied with Selected-Ion Infrared Spectroscopy

Platinum cation complexeswith multiple acetylene molecules arestudied with mass spectrometry and infrared laser spectroscopy. Complexesof the form Pt+(C2H2)( n ) are produced in a molecular beam by laser vaporization,analyzed with a time-of-flight mass spectrometer, and selected bymass for studies of their vibrational spectroscopy. Photodissociationaction spectra in the C-H stretching region are compared tothe spectra predicted for different structural isomers using densityfunctional theory. The comparison between experiment and theory demonstratesthat platinum forms cation-& pi; complexes with up to threeacetylene molecules, producing an unanticipated asymmetric structurefor the three-ligand complex. Additional acetylenes form solvationstructures around this three-ligand core. Reacted structures thatcouple acetylene molecules (e.g., to form benzene) are found by theoryto be energetically favorable, but their formation is inhibited underthe conditions of these experiments by large activation barriers.