Reactions of Vanadium Dioxide Molecules with Acetylene: Infrared Spectra of VO₂(η²‑C₂H₂)_x (x = 1, 2) and OV(OH)CCH in Solid Neon

Reactions of vanadium dioxide molecules with acetylene have been studied by matrix isolation infrared spectroscopy. Reaction intermediates and products are identified on the basis of isotopic substitutions as well as density functional frequency calculations. Ground state vanadium dioxide molecule reacts with acetylene in forming the side-on-bonded VO₂(η²-C₂H₂) and VO₂(η²-C₂H₂)₂ complexes spontaneously on annealing in solid neon. The VO₂(η²-C₂H₂) complex is characterized to have a ²B₂ ground state with C_2v symmetry, whereas the VO₂(η²-C₂H₂)₂ complex has a ²A ground state with C₂ symmetry. The VO₂(η²-C₂H₂) and VO₂(η²-C₂H₂)₂ complexes are photosensitive. The VO₂(η²-C₂H₂) complex rearranges to the OV­(OH)­CCH molecule upon UV–vis light excitation.