Matrix Isolation Infrared Spectroscopic And Theoretical Studies On The Reactions Of Beryllium And Diniobium Pentoxide With Oxygen And Carbon Dioxide Gases

The chemical reactions between metal atoms or metal oxides with small molecules havereceived more and more attention in recent years. Investigation of interactions between metalatoms and small molecules such as O₂,CO₂,CO,N₂,H₂and CH₄can provide great significancetoward understanding the mechanism of catalytic activation of O-O, C-O,N-N,H-H and C-Hbonds. For example, ozone is widely used as an oxidant in multiple areas. Metal ozonidecomplexes can serve as ideal models in understanding the mechanism of ozonation in theoxidation reactions at a molecular level. As one of the major combustion products, carbondioxide is known as greenhouse gas which can lead to the serious global climate warming effectswhen it is released into the air, and as an abundant carbon source in the atmosphere as well, theconversion of CO₂into useful chemical materials has drawn increasing attention.In this thesis, we used the matrix-isolation FTIR to investigate the reactions of alkaline earthmetal Be atoms with oxygen and carbon dioxide as well as the reactions of transition metaloxides Nb₂O_<sub>5with carbon dioxide and captured a large number of intermediates. With thecombination of isotopic substitution and density functional theory calculations, products wereassigned. We also analyzed the reaction mechanism by calculating the transition state andpotential energy.The novel results in this thesis are presented as follows:1. The reactions of Be atoms with dioxygen were reinvestigated by matrix isolation infraredabsorption spectroscopy in solid argon. Two interconvertible beryllium ozonide complexes wereprepared and characterized. The BeOBe(η²-O₃) complex was formed on annealing, which ischaracterized to be a side-on bonded ozonide complex with a planar C2vstructure. TheBeOBe(η²-O₃) complex isomerized to the BeOBe(η¹-O₃) isomer under visible light excitation,which is an end-on bonded ozonide complex with planar Cssymmetry. These two isomers areinterconvertible, that is, visible light induces the conversion of the side-on bonded complex tothe end-on bonded isomer, and vice versa on annealing. In addition, evidence is also presentedfor the linear BeOBeOBe cluster.2. Carbon dioxide coordination and activation by beryllium atoms were studied by matrixisolation infrared spectroscopy. Some new complexes were prepared and characterized in solidneon. It was found that the beryllium atoms reacted with carbon dioxide to form the neutralOBeCO, BeOBeCO and η²-O, O bound OCBe(η²-O₂CO) with a planar C2vstructure spontaneously during deposition. The side-on bonded complex OCBe(η²-O₂CO) rearranged toits isomerized structure η²-O,O bound COBe(η²-O₂CO) with the same symmetry under visiblelight irradiation. In addition, evidence is also presented for the cation BeOCO+. Theaforementioned species were identified by isotopic substituted experiments as well as densityfunctional calculations.3. Carbon dioxide coordination and activation by niobium oxide molecules were studied bymatrix isolation infrared spectroscopy. It was found that the niobium monoxide molecule reactedwith carbon dioxide to form the niobium dioxide carbonyl complex NbO₂(η¹-CO) spontaneouslyon annealing in solid neon. The observation of the spontaneous reaction is consistent withtheoretical predictions that this carbon dioxide activation process is both thermodynamicallyexothermic and kinetically facile. In contrast, four niobium dioxide-carbon dioxide complexesexhibiting three different coordination modes of CO₂were formed from the reactions betweenniobium dioxide and carbon dioxide, which proceeded with the initial formation of the η¹-Obound NbO₂(η¹-OCO) and NbO₂(η¹-OCO)2complexes on annealing. The NbO₂(η¹-OCO)complex rearranged to the η²-O,O bound NbO₂(η²-O₂C) isomer under visible light irradiation,while the NbO₂(η¹-OCO)2complex isomerized to the NbO₂(η¹-OCO)(η²-OC)O structureinvolving an η²-C,O ligand under IR excitation. In these niobium dioxide carbon dioxidecomplexes, the η¹-O coordinated CO₂ligand serves as an electron donor, whereas both theη²-C,O and η²-O,O coordinated CO₂ligands act as electron acceptors.