Back to the list of abstracts
Speciation 98: Abstracts
A. Bodor1, I.Bányai2 and I. Tóth1
1 Department of Inorganic and Analyitical Chemistry,
2 Department of Physical Chemistry, Lajos Kossuth University
(KLTE), H-4010 Debrecen, Hungary
Email: itoth@tigris.klte.hu
Complexes of Al3+ ion have received considerable attention during recent years due to the toxic effect of this metal. Fluoride, oxalate and citrate are important ligands for Al3+ in the aquatic environment. The dynamics of the ligand exchange can be rather different depending on the coordination mode and/or the ligand behavior. In our study we compared the above mentioned mono-, di-, tri- and tetradentate ligands using different dynamic NMR methods (1H-, 13C-, 19F-, 27Al-NMR).
19F-NMR line shape analysis, selective magnetization transfer and 2D-EXSY experiments were carried out to follow the fairly slow dynamic processes between the HF/F- and the monodentate AlFx complexes. This multisite exchange system has a unique feature: the AlF+ species seems to be very inert, even the exchange between AlF2+ and HF takes place without AlF+. We suggest inter- and intramolecular exchange reactions and discuss the mechnism.
The bidentate oxalate ligand seems to be rather inert, there is no detectable exchange between AlOx+, AlOx2-, AlOx33- and the free Ox2- at 25oC. The structural isomers of AlOx2- and their interchange is described using 13C-NMR. The ternary Al3+ - F- - Ox2- system shows a complicated multisite exchange pattern .
Citrate ligand can act three- or four-dentate, non bridging or bridging, resulting in very different kinetics. The Al3(H-1Cit)3(OH)(H2O) is not fluxional in solution.The rate of the ligand exchange reaction between Al(Cit)23- and free citrate is quite slow, kobs=0.25 s-1. The same rate kobs=0.1 s-1 for the Al3(H-1Cit)3(OH)4 and this reaction might be OH- catalysed.
