文摘
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 NbO2(畏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鈥揷arbon dioxide complexes exhibiting three different coordination modes of CO2 were formed from the reactions between niobium dioxide and carbon dioxide, which proceeded with the initial formation of the 畏1-O bound NbO2(畏1-OCO) and NbO2(畏1-OCO)2 complexes on annealing. The NbO2(畏1-OCO) complex rearranged to the 畏2-O,O bound NbO2(畏2-O2C) isomer under visible light irradiation, while the NbO2(畏1-OCO)2 complex isomerized to the NbO2(畏1-OCO)(畏2-OC)O structure involving an 畏2-C,O ligand under IR excitation. In these niobium dioxide carbon dioxide complexes, the 畏1-O coordinated CO2 ligand serves as an electron donor, whereas both the 畏2-C,O and 畏2-O,O coordinated CO2 ligands act as electron acceptors.