Hydrogen‐1 and aluminum‐27 NMR study of Al(ClO4)3 in aqueous mixtures of dimethylformamide and urea

Abstract

AbstractA competitive solvation study of Al(III) in water–dimethylformamide (DMF) and water–urea mixtures was carried out by 1H and 27Al NMR spectroscopy. At temperatures low enough to slow proton and ligand exchange, separate 1H resonance signals were observed for bulk and coordinated ligand molecules, and for 27Al in different solvation complexes. The 1H NMR data confirmed hexacoordination of Al(III) at all concentrations, monodentate binding at the oxygen atom of both DMF and urea, preferential solvation by both organic ligands, the presence of steric hindrance to complexation, particularly by DMF, and the identification of the complexes responsible for the 27Al spectra. It also showed a non‐equivalence of the amido groups in urea, in both the complex and free states, presumably owing to hindered rotation about the carbon—oxygen bond. In contrast to previous reports, the 27Al spectra for the water–DMF and water–urea solutions showed well resolved signals for the species [Al(H2O)n–6Ln]3+ (n = 0–6; L = DMF or urea), including two isomers for one of the water–urea complexes. The 27Al NMR data reflected the stronger preferential solvation by urea.