Environment of the Al3+ ion in Water–Acetone Solutions of Aluminum Chloride

Resumo

Water–acetone solutions in the AlCl₃–(CH₃)₂CO–H₂O and AlCl₃–(CH₃)₂CO–H₂O–HCl systems were obtained and studied. In both cases, the solution separated into layers to form liquid fractions of lower and higher density. The IR spectra of the fractions were studied. In the light fraction, no AlCl₃ was present, but hydrogen-bonded acetone–water complexes were detected. The spectra of the heavy fraction exhibited a broad band at ~3020–3040 cm^–1 corresponding to the OH groups of water from aluminum hexahydrate. As the solvent is evaporated, the band narrows down, with its position being retained. The IR spectrum of the obtained solid becomes identical to the IR spectrum of the crystal hydrate AlCl₃.(H₂O)₆. The structures and spectral and energetic parameters of Al(H₂O)₆³⁺, Al(H₂O)₆₊₁₂³⁺, Al((CH₃)₂CO)₆³⁺, Al((CH₃)₂CO)₄³⁺, and (CH₃)₂CO.H₂O were calculated by the density functional theory method (B3LYP/6-31++G(d,p)). Relying on the results, an explanation was proposed for the experimentlly observed absence of acetone molecules in the Al³⁺ first coordination shell.