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

The synthesis, characterization and speciation of the VO2+ -quinic acid sys tem 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 (I II), at pH 3.5, 6 and 12, respectively. They were characterized by elementa l analysis, diffuse reflectance, FTIR and Raman spectroscopies, and thermal behavior. Their stability constants were determined at 298 K and at a cons tant ionic strength of 0.150 M using potentiometric methods. In aqueous sol ution three different complexes appeared as the main species at the pH valu es 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 El sevier Science B.V. All rights reserved.