Oxovanadium(IV) complexes of quinic acid.: Synthesis, characterization and potentiometric study

The synthesis, characterization and speciation of the VO2+ -quinic acid system is described. Three new solid complexes were obtained: [VO(quin)(H2O)(3)] (I), Na-4[VO(quin)(2)SO4]. 4H2O (II) and Na-6[VO(quin)(2)SO4]. 4H(2)O (III), at pH 3.5, 6 and 12, respectively. They were characterized by elemental analysis, diffuse reflectance, FTIR and Raman spectroscopies, and thermal behavior. Their stability constants were determined at 298 K and at a constant ionic strength of 0.150 M using potentiometric methods. In aqueous solution three different complexes appeared as the main species at the pH values indicated above as shown in the species distribution curves. Up to pH 8 the system behaves as a 2-hydroxyacid/metal-like compound, while at higher pH further deprotonations were observed, which resulted in the formation of sugar-VO2+ -like complexes. UV-Vis spectra were also reported. (C) 2000 Elsevier Science B.V. All rights reserved.