CO 2 Activation by Small Copper, Cobalt, and Yttrium Oxide Clusters Probed via Infrared Multiple‐Photon Dissociation Spectroscopy

The interaction of CO 2 with Cu, Co, and Y oxide clusters of different size, composition, and charge is investigated via infrared multiple‐photon dissociation (IR‐MPD) spectroscopy. The IR‐MPD spectra of M x O y (CO 2 ) +/− (M = Cu, Co, Y) complexes reveal the non‐activated binding of CO 2 to all cationic clusters. In contrast, CO 2 is activated by all anions via formation of carbonate‐like CO 3 units. Density functional theory(DFT) calculations on M 2 O 2 +/− model systems suggest that for CO 2 activation in general, the energy difference between the cluster highest occupied molecular orbital (HOMO) and the CO 2 lowest unoccupied molecular orbital (LUMO) is crucial. The binding motif of the activated CO 2 molecule, however, depends on a fine interplay between the nature of the orbitals close to the HOMO and the oxidation state of the metal atoms. CO 3 formation is favored when the cluster HOMO or any energetically close lying molecular orbital (MO) is at least partially localized on one of the cluster oxygen atoms. In contrast, if such MOs are energetically less favorable, η 2 ‐(C,O) and η 2 ‐(O,O) binding to one of the metal atoms can be favored, provided the already positively charged metal atom can transfer electron density, i.e., adopt an even higher oxidation state.