An infrared study of CO 2 activation by holmium ions, Ho + and HoO .

We report a combined experimental and computational study of carbon dioxide activation at gas-phase Ho + and HoO + centres. Infrared action spectra of Ho(CO 2 ) n + and [HoO(CO 2 ) n ] + 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(CO 2 ) n + complexes with CO 2 binding end-on to the Ho + ion. By contrast, all [HoO(CO 2 ) n ] + complexes n ≥ 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 n = 3, continues to red-shift monotonically with each successive CO 2 ligand binding with net charge transfer from the ligand rather than the metal centre.