Theoretical study of the hydrolysis of aluminum complexes

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>This thesis focuses on the molecular-level chemistry of the solvation of aluminum salts. Fundamental aspects such as, structural characteristics of the aluminum molecules, hydrolysis, acidity, solvation structure, effect of counter ions, and chemical stability are discussed herein. Static computations augmented with the conductor-like screening model (COSMO) were used to investigate hundreds of planar and cyclic configurations of dimeric, trimeric, tetrameric, and pentameric aluminum complexes. Car–Parrinello molecular dynamics (CPMD) calculations were used to expand investigations to aqueous environments. </p><p>This thesis consists of four articles and one additional article. The first paper focuses on the structural analysis of the hydrolysis products of AlCl₃ · 6H₂O. Dimeric, trimeric, and tetrameric aluminum (chloro)hydroxides were investigated in both gas and liquid phase. The liquid environment was modeled by using COSMO.</p><p>The second and the additional paper concentrate on the chemistry of aluminum sulfate complexes. The second article focuses on identifying hydrolysis products of AlCl₃ · 6H₂O in the presence of sulfate (H₂SO₄). The additional paper focuses on the structural characteristics of the hydrolysis products of Al₂ (SO₄)₃ · 18H₂O. Structural information was deduced from the ESI MS results with the aid of computational methods. Detected cationic structures closely resembled the aluminum chlorohydrate analogues introduced in the first paper.</p><p>The third and fourth articles are devoted to the hydrolysis, stability, and dynamics of dimeric and pentameric aluminum (chloro)hydroxides in aquatic environments. During the CPMD simulations, several spontaneous associative hydration reactions were detected in the primary hydration shell of the complexes. Dimeric aluminum chlorohydrates were detected to be stable in liquid conditions, whereas the pentameric aluminum complexes experienced significant topological changes during the simulations. Constrained simulations were used to reveal the role of chloride ions in the hydrolysis processes of dimeric complexes. The effect of the empirical van der Waals corrections to the dynamics of the simulations was also tested for the pentameric system.</p><p>The results of this thesis showed unequivocally that computational chemistry provides effective tools for structural analysis of inorganic complexes such as, aluminum chlorohydrates and sulfates in both gas and liquid phase. In addition, calculations provided answers to the anomalies detected in the experiments. Hence, theoretical methods are highly recommended to be used alongside with conventional experimental methods in the interpretation of the aluminum species in aqueous solutions and to widen the overall chemical perspective of the hydrolysis of aluminum salts. </p></div>