Back to the list of abstracts
Speciation 98: Abstracts
I. Bodi,1 T. Kiss,2 G. Micera3 and J. Nagy2
1 Biocoordination Chemistry Research
Group of MTA;
2 Department of Inorganic
and Analytical Chemistry, Attila Jozsef University;
3 Department of Chemistry, University of
Sassari, Via Vienna 2, Sassary, Italy
The protonation and the complexation of VO2+ ion by iminodiacetic acid, nitrilotriacetic acid and their phosphonic and mixed carboxylic-phosphonic derivatives, along with the ethylenediamine-tetraacetic acid and its phosphonic derivative have been studied using pH-potentiometric, VIS and ESR techniques at 25 oC and in presence of 0.20 M KCl background electrolyte.
Complexes with extremely high stability have been observed in the VO2+- nitrilotriacetic acid - derivative systems even in strongly acidic media. The formation constants of these complexes have been independently confirmed spectroscopically. For this combined pH-potentiometric-spectrophotometric titrations have been performed, employing the variations occurring in the charge-transfer band of the bismaltol complex of oxovanadium(IV) ion by adding the studied ligand. The stability constants obtained using these various techniques show satisfactory agreement.
A pale blue precipitate occured in the VO2+ phosphonic acid derivative mixtures in acidic solution. The structure and stochiometry of these solid complexes have been determined using elemental analysis and IR-Raman spectroscopy.
The carboxylic phosphonic substitution increases the coordination ability of the ligands, however, the relative stability of these complexes does not increase. This observation can be rationalized on the basis of steric and electrostatic hindrance reasons, which overcompensate the effect of increasing basicity. It has also been concluded that the coordination geometry of the oxovanadium(IV) ion is slightly affected by the phosphonic carboxylic exchange but the coordination sphere becomes more and more distorted with the increase in the number of phosphonic groups.
