MULTINUCLEAR MAGNETIC-RESONANCE STUDY OF THE COORDINATION OF ALUMINUM(III) WITH TARTARIC ACID IN AQUEOUS-SOLUTION

The coordination of Al(III) with (+)-(2R,3R)-tartaric acid in aqueous solutions at various pH values was investigated with the use of H-1, C-13, O-17 and Al-27 NMR spectroscopy. High-field Al-27 NMR revealed mononuclear 1:1, 1:2, 1:3, and dinuclear 2:2 complexes with both octahedrally and tetrahedrally coordinated Al(III). C-13 and Al-27 chemical shifts showed that deprotonation of the Al(III) coordinated hydroxy groups of tartrate starts already at pH 1.5. The mononuclear 1:3 complex displayed a remarkable stability and symmetry, which is ascribed to the formation of successive hydrogen bonds. The stereospecific formation of the Al(III) complexes was investigated by comparison with rac-(2R,3R/2S,3S) and meso-(2R,3S)-tartaric acid.