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Time‐Dependent Solution Speciation of the Al III −Citrate System: Potentiometric and NMR Studies
Author(s) -
Lakatos Andrea,
Bányai István,
Decock Patrick,
Kiss Tamás
Publication year - 2001
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200102)2001:2<461::aid-ejic461>3.0.co;2-e
Subject(s) - chemistry , potentiometric titration , hydroxide , ligand (biochemistry) , genetic algorithm , nuclear magnetic resonance spectroscopy , citric acid , nmr spectra database , inorganic chemistry , carbon 13 nmr , proton nmr , ion , crystallography , stereochemistry , organic chemistry , spectral line , biochemistry , physics , receptor , astronomy , evolutionary biology , biology
Time‐dependent potentiometric and NMR spectroscopic measurements were carried out in the Al III −citric acid system in an equimolar solution and at an excess of ligand in order to monitor the changes in speciation as a function of time. In fresh solutions, the mononuclear 1:1 species [AlLH] + , [AlL], [AlLH −1 ] − and [AlLH −2 ] 2− and the 1:2 complexes [AlL 2 ] 3− , [AlL 2 H −1 ] 4− and [AlL 2 H −2 ] 5− are formed. In agreement with earlier findings ( Inorg. Chem. 1988 , 27 , 2565), these complexes are converted to a large extent into a thermodynamically more stable trinuclear species as the solutions age. Depending on the composition of the initially formed mononuclear species, the formation of the trinuclear species is accompanied either by the consumption or by the liberation of hydroxide ions. NMR spectroscopy was used to confirm the considerable time dependence of the species distribution. The 1 H, 27 Al and 13 C NMR spectra indicated that at equilibrium the trinuclear species [Al 3 (LH −1 ) 3 (OH)] 4− predominates in the pH range 4−7. Oligomerization of the mononuclear species takes place through at least one intermediate complex. At equilibrium, the ligand‐exchange reactions between the trinuclear species, the mononuclear species and free citrate are slow on the NMR time scale.