Ab Initio Calculation of Aqueous Aluminum and Aluminum−Carboxylate Complex Energetics and 27Al NMR Chemical Shifts

Abstract

Al3+ hydrolysis in aqueous solution was modeled with ab initio calculations. Structural changes surrounding the cation as protons are removed from the initial Al3+(H2O)6 molecular cluster were predicted. A correlation of the model energy changes and experimental equilibrium constants for these reactions was also found. Calculations of the 27Al NMR chemical shift between the species Al3+(H2O)6 and [Al(OH)4]- were performed to test the feasibility of predicting 27Al NMR chemical shifts in aqueous solution with gas-phase molecular orbital calculations on small clusters. Energetics of Al3+−carboxylic acid complex formation in solution were also calculated using the self-consistent isodensity polarized continuum model (SCIPCM) to account for long-range solvation effects. Comparisons of calculated 27Al NMR chemical shifts in model Al3+−carboxylate complexes to experimentally assigned values were made to test this methodology and previous peak assignments in 27Al NMR spectra of Al3+−carboxylic acid solutions. Re...