27Al NMR spectroscopy is a powerful tool for elucidating local geometries at Al sites in liquid and solid-state systems. Even though NMR spectroscopy is a well established and widely used technique, the chemical shift assignments are mostly empirical. Due to the NMR spectral sensitivity to atomic positions and local electron density fluctuations, quantum mechanical calculation of NMR shielding tensor has proven reliable to improve, assess or interpret NMR experimental findings. This project uses information from computed 27Al NMR parameters to improve understanding of phenomena occurring in Al-containing electrolyte solutions at the Hanford Nuclear Reservation. Al species explored included monomeric Td and Oh symmetric species, negatively charged Al dimers and ion paired species. Description of the 27Al shielding tensor response to solvent environment fluctuations and ion-ion interaction (i.e. Al(OH)4--Na+) is explored by combined ab-initio molecular dynamics (AIMD)), configuration ensemble sampling techniques and intermolecular network theory (INT) tools. Exploration of local vibrational, as well as extended solvent contributions to the AIMD time-averaged Al shielding tensor property, was done using the following decomposition scheme: 〈σT〉= 〈σTav〉+ 〈σTvib〉+ 〈σTsolv〉 Correlations between local−electronic properties, structural fluctuations around the Al centers and the theoretically calculated 27Al NMR signatures were obtained.

Exploring Al speciation and interactions in caustic conditions by accurate 27Al NMR shielding tensor calculations

256th National Meeting (2018)

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