An infrared study of CO₂ activation by holmium ions, Ho⁺ and HoO⁺

Abstract

We report a combined experimental and computational study of carbon dioxide activation at gas-phase Ho⁺ and HoO⁺ centres. Infrared action spectra of Ho(CO₂)_<i>n</i>⁺ and [HoO(CO₂)_<i>n</i>]⁺ ion-molecule complexes have been recorded in the spectral region 1700-2400 cm^-1 and assigned by comparison with simulated spectra of energetically low-lying structures determined by density functional theory. Little by way of activation is observed in Ho(CO₂)_<i>n</i>⁺ complexes with CO₂ binding end-on to the Ho⁺ ion. By contrast, all [HoO(CO₂)_<i>n</i>]⁺ complexes <i>n</i> ≥ 3 show unambiguous evidence for formation of a carbonate radical anion moiety, . The signature of this structure, a new vibrational band observed around 1840 cm^-1 for <i>n</i> = 3, continues to red-shift monotonically with each successive CO₂ ligand binding with net charge transfer from the ligand rather than the metal centre.