Reactions of Copper and Silver Cations with Carbon Dioxide: An Infrared Photodissociation Spectroscopic and Theoretical Study.

The reaction of copper and silver cations with carbon dioxide was studied by mass-selected infrared photodissociation spectroscopy. Quantum chemical calculations were performed on these products, which aided the experimental assignments of the infrared spectra and helped to elucidate the geometrical and electronic structures. The Cu+ and Ag+ cations bind to an oxygen atom of CO2 in an end-on configuration via a charge-quadrupole electrostatic interaction in the [M(CO2)n]+ complexes. The formation of oxide-carbonyl and carbonyl-carbonate structures is not favored for the interaction of CO2 with Cu+ and Ag+. For n = 3 and 4, the n + 0 structure is preferred. [Note on the nomenclature: Using i + j, i denotes the number of CO2 molecules in the first coordination shell, and j denotes the number of CO2 molecules in the second coordination shell.] The two nearly energy-identical n + 0 and (n - 1) + 1 structures coexist in n = 5 and 6. While the six-coordinated structure is favored for [Cu(CO2)n=7,8]+, the n + 0 configuration is dominated in [Ag(CO2)n=7,8]+. The reaction of CO2 with the cationic metal atoms has been compared to that with the neutral and anionic metal atoms, which would have important implications for understanding the interaction of CO2 with reduction catalysts and rationally designing catalysts for CO2 reduction based on cost-effective transition metals.