Vanadium(III) Complexes with Picolinic Acid and Dipicolinic Acid in Aqueous Solution

The complex species formed in aqueous solution (25 ∘C, I = 3.0 mol-dm−3 KCl ionic medium) between V3+ cation and the ligands: picolinic acid (Hpic, HL) and dipicolinic acid (H2dipic, H2L), have been studied potentiometrically and by spectrophotometric measurements. The application of the least-squares computer program LETAGROP to the experimental emf (H) data, taking into account the hydrolytic species of V3+ ion, indicates that under the employed experimental conditions, the formation of the complexes [VL]2+, [V(OH)L]+, [VL2]+, [VL3], [V2OL4] with picolinic acid and the complexes [VL]+, [V(OH)L], [V(OH)2L]−, [V(HL)(L)], and [VL2]− with dipicolinic acid were observed. The stability constants of the complexes formed were determined by potentiometric measurements, and spectrophotometric measurements were done in order to perform a qualitative characterization of the complexes formed in aqueous solution.