Aluminium carboxylates in aqueous solutions. Part 3. Synthesis and solution state of [Al2(cit)2(H2O)6], [Al2(tart)3(H2O)4] and [Al(gluc)(OH)2](H3cit = citric acid, H2tart = tartaric acid, Hgluc = gluconic acid)

Abstract

The complexes [Al₂(cit)₂(H₂O)₆] and [Al₂(tart)₃(H₂O)₄](H₃cit = citric acid, H₂tart = tartaric acid) have been prepared by controlled addition of the relevant α-hydroxycarboxylic acids to Al(OH)₃ while [Al(gluc)(OH)₂](Hgluc = gluconic acid) was obtained by stoichiometric addition of potassium gluconate to a solution of [Al(H₂O)₆]³⁺. The solution state of these complexes was investigated by means of combined IR and ¹H NMR spectroscopies in D₂O, at room temperature. In all cases, solutions were analysed at autogeneous (2.5–4.0) and at physiological pH values, with the aim of checking the agreement between the solution state as predicted from available thermodynamic data and the real, toxicologically relevant, state stemming from spectroscopic observations. The Al^III-citrate system is found to behave according to the thermodynamic expectations down to millimolar metal concentrations. On the contrary, the tartrate and gluconate systems do not agree with thermodynamic predictions, albeit differently, at 0.1 and 0.3 mol dm^–3 analytical concentrations.