Elucidating the structures of cationic metal-nitrous oxide complexes using infrared action spectroscopy

Thesis

Gas-phase metal ion-molecule complexes provide model environments within which to study fundamental molecular interactions involved in ligand activation and metal ion solvation. These complexes also represent entrance-channel species for catalytic reactions. The ligand of interest in this thesis is nitrous oxide, which accounts for 5% of anthropogenic emissions and is a potent greenhouse gas with a warming potential 300 times greater than carbon dioxide. Thus, there is considerable interest in reducing N₂O emissions particularly via metal-catalysed N₂O reduction. M^+/0/-(N₂O)_n complexes represent entrance-channel species for such reactions and yet, little attention has been given to the structures of M^+/0/-(N₂O)_n complexes. This thesis presents the first experimental investigation on M⁺$(N₂O)_n and M⁺_n(N₂O) complexes studied via infrared action spectroscopy. The infrared spectra are further interpreted and assigned from simulated spectra based on density functional theory (DFT). A range of M⁺(N₂O)_n complexes (M = group 11, group 9, and Li, Al) have been studied in an attempt to draw comparisons between the different M⁺ electron configurations d¹⁰, d⁸, and closed s-shell, respectively). Spectroscopic signatures for N- and O-bound N₂O ligands are observed in all cases however the importance of low-lying electronic states is revealed for the group 9 cations, and insertion complexes inferred for the Li⁺ ion.

Infrared multi-photon dissociation (IRMPD) studies on M⁺_n(N₂O) complexes (M = Au, Co) also present N- and O-bound spectroscopic signatures. However, as the metal cluster size increases, N₂O binds preferentially via the terminal N-atom. Larger clusters represent a more effective energy "bath" facilitating annealing to the lowest energy structure.

Authors: Cunningham, E

• DOI: 10.5287/ora-gozobjy24
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Keywords: Metal-Ligand Complex; Nitrous Oxide; Photodissociation; Cluster Chemistry; Physical Chemistry; Quantum Chemical Calculations; Infrared Spectroscopy