Proton Magnetic Resonance Coordination-Number Study of AlCl3 in Aqueous Mixtures of Acetone, N,N-Dimethylformamide, Dimethylsulfoxide, Dioxane, Tetrahydrofuran, and Tetramethylurea

Abstract

The coordination number of Al(III) in aqueous mixtures of acetone, dimethylformamide, dimethylsulfoxide, dioxane, tetrahydrofuran, and tetramethylurea was measured over a range of solvent concentrations by a proton magnetic resonance technique. At low temperatures, proton exchange is slowed to such an extent in these mixtures that separate resonance signals are observed for bulk water and water molecules in the Al(III) solvation shell. Coordination numbers were measured by direct integration of the two water signals. The measurements show that in aqueous mixtures of acetone and tetramethylurea, and over a small solvent concentration range, dioxane and tetrahydrofuran, only water solvates Al(III). This was indicated by the value of six molecules obtained for the contribution of water to the Al(III) solvation shell in these mixtures. In aqueous mixtures of dimethylformamide and dimethylsulfoxide, wherein separate signals were also observed for the nonaqueous components, both solvents contribute to the Al(III) solvation shell. No evidence for ion pairing was found in any of the mixtures.