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

Abstract

The synthesis, characterization and speciation of the VO 2+–quinic acid system is described. Three new solid complexes were obtained: [VO(quin)(H 2O) 3] ( I), Na 4[VO(quin) 2SO 4]·4H 2O ( II) and Na 6[VO(quin) 2SO 4]·4H 2O ( 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–VO 2+-like complexes. UV–Vis spectra were also reported.