A spectroscopic investigation of the complexing ability of catecholate or salicylate derivatives towards aluminium(III)

The coordination of the aluminium(111) cation to 2,3-dihydroxybenzoic acid (2,3-dhba), 5-nitrosalicylic acid (5-nsa), 4-nitrocatechol (4-ncat) and 3,5-dinitrocatechol (3,5-dncat) was studied by pH-potentiometry and by spectroscopic techniques. The stoichiometry of the complexes and their formation constants were determined. NMR spectroscopy allowed us to obtain thermodynamical, dynamical and structural information about the complexes formed in solution. The complexing power of these molecules was compared to that of catechol and salicylic acid. Additionally, the proton exchange rate constant between the phenolic and the phenolate forms of 5-nsa was determined by NMR line-shape analysis. This proton exchange that is usually very fast is considerably slowed down by the formation of an intramolecular hydrogen bond between the carboxylate and the phenolic groups. (C) 2004 Elsevier Ltd. All rights reserved.