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Reactions of Metal and Metal Oxide Cluster Cations with Small Organic Molecules
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Abstract
The interactions between metal and metal oxide cations and small organic molecules are important in solvation and catalysis. Here, we explore three different gas-phase reactions: C‒H bond activation in ethane by AlxOy+, acetone C=O bond activation by Al+, and solvation of metal cations and dications by acetone. The entrance channel complexes, reaction intermediates and products of these reactions were characterized using photodissociation vibrational spectroscopy coupled with DFT calculations. The results reveal information about the structures of, and the covalent bonds in, the complexes and how the nature of the metal, ion charge, and the number of ligands influence the perturbation of bonds in the ligand. For the C-H activation of ethane by AlxOy+, oxygen-rich species and open-shell cluster ions have smaller barriers, except for Al3O4+. Only entrance channel complexes are observed for oxygen-deficient clusters (Al2O+ and Al3O2+) due to large C-H activation barriers. For Al3O4+(C2H6)3, both the entrance channel complex and C‒H activation intermediate are observed. For oxygen-rich Al4O7+, ethane is favored to bind far from the reactive superoxide group, reducing the reactivity. The observed red shift of the C‒H symmetric stretch in ethane is ~200 cm-1, indicating significant weakening of the proximal C‒H bonds. In the investigation of Al+(acetone)n complexes, computations predict the thermodynamic favorability of the pinacol coupling reaction for n≥3. However, our experimental results reveal the characteristic peak of the pinacolate C-O stretch solely at n=5. Furthermore, the red shift of the C=O stretch and the concurrent blue shift of the CC antisymmetric stretch are also observed. Consistent with anticipated trends, the magnitudes of these shifts decrease with increasing cluster size. When acetone solvates M+/2+ ions, a red shift of the C=O stretch and blue shift of the antisymmetric CC stretch are observed, corresponding to a weakening of the C=O bond and strengthening of the C-C bonds. These shifts decrease as the size of clusters increases, and increase with the charge on the metal ion. A strong correlation of the calculated red shift in the C=O stretch in M+/2+(Ace) with the ionization energy of M+ and M2+ was also discovered.
Type
Dissertation (Open Access)
Date
2024-09
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http://creativecommons.org/licenses/by/4.0/