Al-alkali ion-pairing interactions and its influence in the 27Al NMR shielding tensor from AIMD ensemble averaging standpoint.
Ernesto Martinez-Baez1, Maxime Pouvreau1 , Carolyn Pearce2 , Gregory K. Schenter2 , Aurora E. Clark1,2
1Washington State University, Pullman, WA, United States
2Pacific Northwest National Laboratory (PNNL), Richland, WA, United States
27Al NMR spectroscopy is a versatile tool for elucidating the local geometries and potential interatomic interactions in Al-containing liquid and solid-state systems. Due to the NMR spectral sensitivity to atomic position and local electron density fluctuations, quantum mechanical calculation of the NMR shielding tensor has proven reliable to improve, assess or interpret NMR experimental observation. This project explores ion pairing interactions between alkali-metals and Al-species present in caustic solutions at the Hanford Nuclear Reservation. Surveyed Al species include monomeric Td (Al(OH)4) and Oh (Al(H2O)3+/6) solvated clusters, and [Al(OH)4 − (Li+,Na+,K +, Rb+, Cs+)] × (H2O)n systems. Description of the 27Al-NMR shielding tensor as a response to solvent fluctuations and ion-ion interaction has been explored by combined ab-initio molecular dynamics (AIMD)), configuration ensemble sampling techniques and intermolecular network theory (INT) tools. Exploration of the local vibrational as well as extended solvent contributions to the AIMD time-averaged Al shielding tensor (??) property was performed using the following decomposition scheme:
Correlations between the local−electronic properties, structural fluctuations around the Al center, and the theoretically calculated 27Al NMR signature has been investigated.