| Description |
The lanthanides that make up the f-block of the periodic table remain fairly unexplored experimentally such that there is a need for thermochemical information regarding these elements to better understand their reactivity and properties, including, for example, their potential usefulness as catalysts in organometallic and oxidation catalysis. In addition, these heavy elements are difficult to describe theoretically because of spin-orbit and relativistic effects and the many electronic configurations possible from the 4f electrons. Accurate thermochemistry measured from gas-phase experiments, where systems can be probed in isolation from solvent or substrate molecules, can serve as useful benchmarks for evaluating theoretical methods. The work described in this dissertation focuses on examining the gas-phase reactivity and thermochemistry of the lanthanide gadolinium cation (Gd+). Gd+ is found in the middle of the lanthanide series and has a 4f76s15d1 ground state valence electron configuration. This configuration (with two non-4f electrons) is unusual compared with most lanthanide cations, which typically have 4fn6s1 configurations (n corresponding to the remaining valence electrons). Guided ion beam tandem mass spectrometry (GIBMS) is used here to investigate and measure the thermochemistry of the gas-phase activation of H2, O2, and CO2 by Gd+. Potential energy surfaces for the oxidation reactions with O2 and CO2 are characterized in great detail from these experiments. Quantum chemical calculations are performed and provide insight into the electronic states of the species probed in the experiments and a detailed understanding of the reaction mechanisms. Periodic trends are elucidated, where results indicate that Gd+ generally behaves more similarly to the group 3 transition metal cations scandium (Sc+) and yttrium (Y+) than to most lanthanide cations, which is attributable to similarities and differences in the electronic ground states of these ions, respectively. The extensive thermochemistry determined for Gd+ in this work can serve as valuable standards for comparing theoretical calculations against. Moreover, the mechanistic insights provided by these studies for the activation of H2, O2, and CO2 by Gd+ can potentially be useful in understanding the activation in analogous reactions with other metals, where this information can potentially lead to insight beneficial for the design of more effective catalysts. |
