MULTINUCLEAR MAGNETIC-RESONANCE STUDIES ON ALUMINUM CHELATES .1. CHELATES WITH CATECHOL AND DISODIUM 4,5-DIHYDROXYBENZENE-1,3-DISULFONATE

The complexation of Al3+ with catechol and tiron (disodium 4,5-dihydro xybenzene-1,3-disulfonate) has been studied by NMR spectroscopy. The c omplexes in-solution at different pH values were identified by multinu clear (Al-27, C-13 and H-1) magnetic resonance spectra. and spectropho tometric and potentiometric data. Aluminium formed 1:1, 1:2 and 1:3 ch elates with both catechol and tiron depending on the pH and ligand con centration. Disproportionation of the 1:1 chelate with tiron at pH 7 g ave a mixture of 1:2 and 1:3 chelates leaving a major amount of alumin ium in an uncomplexed form. Both meridional and facial isomers of [AIL (3)](9-) (Na(2)H(2)L = tiron) have been characterised by C-13 and H-1 NMR. Hydrolysis of the 1:1 AI-L(4-) chelate leading to the formation o f [Al(OH)(4)](-) occurs via the formation of the tetrahedral chelate [ AIL(OH)(2)](3-) (delta 53) as an intermediate. In the Al-catechol (H(2 )cat) system three complex species coexist with [Al(OH)(4)](-) in a 1: 2 mixture at pH 12.5. Unlike in the Al-tiron system, a tetrahedral 1:2 Al-cat chelate (delta 58.5) is also formed during hydrolysis of the o ctahedral 1:2 Al-cat complex.