Infrared Photodissociation Spectroscopic Studies On The Metal-Carbon Dioxide Compound Cluster Ions

The chemical transformation of carbon dioxide is of considerable interest because CO2 is a double-faced molecule as a potent green-house gas and an abundant renewable resource for the production of fine chemicals and clean fuels.Metal complexes are widely involved in the catalytic activation and fixation of this robust CO2 molecule.Detailed insights into the catalytic mechanisms of these reactions require structural and energetic information,which is challenging to be completely elucidated from the condensed phase.Recent noteworthy development in this endeavor is the use of gas-phase optical spectroscopy coupled with mass spectrometry at the molecular level to establish clusters model to understand the direct relationships between structure and function,as well as to clarify the pivotal roles played by the ligands,metals,and charging effects.We built an infrared photodissociation(IRPD)spectroscopy,which contains quadrupole mass spectroscopy,low temperature ion trap and time of flight mass spectroscopy,and its sensitivity is about 7 orders higher than the FT-IR absorption spectroscopy.In addition,a new type of ion source is developed on the basis of general laser sputtering ion source,which can produce cluster ions with multiple ligands,and it's very suitable for the study of metal-CO2 complexes.In this thesis,the reaction mechanisms of CO2 with a series of metals have been studied using infrared photodissociation spectroscopy.We interpreted the IR spectra by comparison with quantum chemical calculations.The present findings should have important implications for the catalyst design and the development for the utilization of CO2.Through the study on the interation of CO2 with Cu+ and Ag+,we found that in[M(CO2)n]+(M = Cu,Ag)clusters,the Cu+ and Ag+ cations bind to an oxygen atom of CO2 in an "end-on" configuration via a charge-quadrupole electrostatic interaction.The formation of oxide-carbonyl and carbonyl-carbonate structures is not evidenced in the reaction of CO2 with Cu+ and Ag+.For n= 3 and 4,the n+0 structure is preferred.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.IRPD spectroscopic studies of[YO(CO2)n]+ indicate that the CO2 molecules are weakly coordinated to the metal in the n?3 clusters.A carbonate motif is formed at n = 4,which is retained in all of the lowest-energy isomers of the larger clusters.The experimental observation is consistent with theoretical predictions that the conversion of Y=O and CO2 to carbonate is achieved by donating electrons from the ligands to the metal.Systematical analyses for the effects of different ligands and metals on the coordination-induced CO2 fixation demonstrate that the present system serves as an efficient and rational model for adjusting the CO2 fixation and CO2 emission.IRPD spectroscopic studies of[ZrO(CO2)n]+ reveal that in the n = 1 and 2 clusters,all the CO2 molecules are weakly solvated with metals.Subsequent coordination of CO2 ligands leads to the stabilization of a[ZrO]2+·[CO2]-motif.Theoretical analyses indicate that the metal valence state is elevated with the coodination of CO2 molecules and the ion core is changed from[ZrO]+·[CO2]to[ZrO]2+·[CO2]-,resulting in the CO2 reduction.The present findings would have important implications for understanding and rationally designing CO2 activation and reduction based on cost-effective transition metals.