Carbon dioxide binding to metal oxides: Infrared spectroscopy of NbO2+(CO2)n and TaO2+(CO2)n complexes.

Graphical abstract Highlights • CO 2 complexes efficiently with NbO 2 + and TaO 2 + relevant to sequestration by MOFs. • DFT simulations allow clear structural determination of MO 2 (CO 2) n + complexes. • Possible M–O–CO 2 type features observed in larger complexes. • No evidence of oxalate structures in CO 2 complexation to NbO 2 + or TaO 2 +. Abstract We report the results of an infrared photodissociation spectroscopy study to determine the structures of gas–phase NbO 2 (CO 2) n + and TaO 2 (CO 2) n + (n = 1–7) ion–molecule complexes. The experimental spectra, recorded in the region of the CO 2 asymmetric stretch using the inert messenger technique, are interpreted in terms of energetically low–lying structures calculated from density functional theory. Together, experiment and simulation provide important new information on CO 2 –binding relevant to prototypical metal–oxide frameworks. Key findings include strong binding of the first two CO 2 ligands to the MO 2 + species and clear evidence for a first solvation shell at n = 4. Some features characteristic of a possible CO 3 ("carbonate") moiety are found in spectra for n ≥ 3 but oxalate structures, observed in some similar systems, appear to be too high in energy to be observed experimentally. CO 2 activation, reactivity and sequestration have long been of interest to Prof Helmut Schwarz, in whose honour this special issue is published on the occasion of his 75th birthday. [ABSTRACT FROM AUTHOR]