CO₂ Adsorption on Ti₃O₆^-: A Novel Carbonate Binding Motif

CO₂ adsorption on Ti₃O₆^-, which serves as a model for an oxygen vacancy on a titania surface, is studied using infrared photodissociation (IRPD) spectroscopy in combination with density functional theory (DFT) and coupled cluster computations, as well as a recently developed multicomponent artificial force induced reaction method. The IRPD spectra of D₂-tagged [(Ti₃O₆)(CO₂)_n]^-, with n = 1, 2, are reported in the spectral window of 450-2400 cm^-1 and assigned based on a comparison to harmonic IR spectra from the DFT calculations. We find that CO₂ binding leaves the unpaired electron largely unperturbed. The first two CO₂ molecules adsorb chemically to Ti₃O₆^- by incorporating a formally doubly negatively charged, either doubly or triply coordinated O atom to form a bidentate or tridentate bridging carbonate dianion (CO₃^2-), respectively. The latter binding motif exhibits a characteristic IR signature in the form of an intense doublet of peaks near 1400 cm^-1 stemming from two antisymmetric carbonate stretching modes.