Multinuclear magnetic resonance studies of the hydrolysis of aluminium(III). Part 9. Prolonged hydrolysis with aluminium metal monitored at very high magnetic field

Abstract

Aluminium(III) salt solutions hydrolysed by boiling with aluminium metal over extended periods of time have been examined by ²⁷Al n.m.r. spectroscopy and, after drying and redissolution in acetone, by ¹H n.m.r. spectroscopy, both at very high magnetic field. At low hydrolysis ratios, m⩽ 1.4(where m is defined by the stoicheiometric formula AlX_3–m(OH)_m, X being the coanion), the solutions contain the oligomer species observed in base hydrolysis. There are three minor components and one major one whose spectroscopic properties suggest it is the 3,8 trimeric species [Al₃O₂(OH)₄(H₂O)₈]⁺. The fully hydrolysed solutions (m= 2.5) have complex proton spectra which differ between preparations and it is concluded that they contain a hierarchy of species whose structures are related to that of the tridecameric cation but many of which lack the tetrahedrally co-ordinated metal atom. It is not possible to suggest a structure for any individual species but it is made clear for the first time that a wide range of products are formed in these solutions.