Multinuclear magnetic resonance study of the co-ordination of aluminium(III) with glycolic acid in aqueous solution, compared to co-ordination with oxalic and malonic acid

Abstract

The co-ordination of Al^III with glycolic acid in aqueous solution was investigated with the use of ¹H, ¹³C, ¹⁷O, and ²⁷Al n.m.r. techniques. High-field ²⁷Al n.m.r. spectroscopy allowed the observation of 1 : 1, 1 : 2, 1 : 3, and polynuclear complexes of Al^III with glycolic acid. A gradual shift in the ¹H, ¹³C, and ²⁷Al n.m.r. spectra indicated that ionization of the hydroxy group of co-ordinated glycolate starts at pH 3.¹⁷O N.m.r. measurements showed unambiguously the bidentate co-ordination of oxalic, malonic, and glycolic acid with Al^III. Solid-state ²⁷Al ‘magic-angle’ spinning (m.a.s.) and ¹³C cross-polarization (c.p.) m.a.s. n.m.r. spectroscopy were employed to study powdered single crystals of a 2 : 6 aluminium(III)–glycolate complex.