Theoretical investigation of the thermodynamic structures and kinetic water-exchange reactions of aqueous Al(III)–salicylate complexes

Abstract

Density functional theory (DFT) calculations were performed on the structures and water-exchange reactions of aqueous Al(III)–salicylate complexes. Based on the four models (gas phase (GP); polarizable continuum model (PCM), which estimates the bulk solvent effect; supermolecule model (SM), which considers the explicit solvent effect, and supermolecule–polarizable continuum model (SM–PCM), which accounts for both types of solvent effects), we systematically conducted this study by examining three different properties of the complexes. (1) The microscopic properties of the aqueous Al(III)–salicylate complexes were studied by optimizing their various structures (including the possible 1:1 mono- and bidentate complexes, cis and trans isomers of the 1:2 bidentate complexes and 1:3 bidentate complexes) at the B3LYP/6-311+G(d, p) level. (2) The 27Al and 13C NMR chemical shifts were calculated using the GIAO method at the HF/6-311+G(d, p) level. The calculation results show that the values obtained with the SM–PCM models are in good agreement with the experimental data available in the literature, indicating that the models we employed are appropriate for Al(III)–salicylate complexes. (3) The water-exchange reactions of 1:1 mono- and bidentate Al(III)–salicylate complexes were simulated using supermolecule models at the B3LYP/6-311+G(d, p) level. The logarithm of the water-exchange rate constant (logkex) of the 1:1 bidentate complex predicted using the “logkex–dAl–OH2” correlation is 4.0, which is in good agreement with the experimental value of 3.7, whereas the calculated range of logkex of the 1:1 monodentate complexes is 1.3–1.9. By effectively combining the results for the thermodynamic static structures with the simulations of the kinetic water-exchange reactions, this work promotes further understanding of the configurations and formation mechanism of Al(III)–salicylate complexes.