Infrared spectroscopy of coordination and solvation in Cu+(C2H4)n (n = 1–9) complexes

Abstract

Copper-ethylene ion-molecule complexes are produced by laser vaporization of a copper rod in a pulsed supersonic expansion of ethylene and argon. The ions are mass selected and studied via infrared laser photodissociation spectroscopy in the CH stretching region (2600–3400 cm−1). Argon tagging is employed to study the spectra of the n = 1–3 complexes. Spectra of complexes containing four to nine ligands are measured by the elimination of ethylene. Density functional theory calculations are carried out in support of the experimental spectroscopy. The symmetric CH stretches of a free ethylene were found to red shift by about 30 cm−1 in the spectra of Cu+(C2H4) and Cu+(C2H4)2. Cu+(C2H4)3 is found to represent a fully- coordinated copper cation. Its CH stretches are found to blue shift by 10 to 20 cm−1 as a result of steric crowding. In larger complexes, the three-coordinate core ion incorporates additional ethylene "solvent" molecules through cation-π and CH-π interactions. These weak interactions only slightly perturb the vibrations of the external ligands.