Carbon dioxide coordination and activation by niobium oxide molecules

Carbon dioxide coordination and activation by niobium oxide molecules were studied by matrix isolation infrared spectroscopy. It was found that the niobium monoxide molecule reacted with carbon dioxide to form the niobium dioxide carbonyl complex NbO(2)(η(1)-CO) spontaneously on annealing in solid neon. The observation of the spontaneous reaction is consistent with theoretical predictions that this carbon dioxide activation process is both thermodynamically exothermic and kinetically facile. In contrast, four niobium dioxide-carbon dioxide complexes exhibiting three different coordination modes of CO(2) were formed from the reactions between niobium dioxide and carbon dioxide, which proceeded with the initial formation of the η(1)-O bound NbO(2)(η(1)-OCO) and NbO(2)(η(1)-OCO)(2) complexes on annealing. The NbO(2)(η(1)-OCO) complex rearranged to the η(2)-O,O bound NbO(2)(η(2)-O(2)C) isomer under visible light irradiation, while the NbO(2)(η(1)-OCO)(2) complex isomerized to the NbO(2)(η(1)-OCO)(η(2)-OC)O structure involving an η(2)-C,O ligand under IR excitation. In these niobium dioxide carbon dioxide complexes, the η(1)-O coordinated CO(2) ligand serves as an electron donor, whereas both the η(2)-C,O and η(2)-O,O coordinated CO(2) ligands act as electron acceptors.