Speciation of the vanadium (III) complexes with 6-methylpicolinic acid, salicylic acid and phthalic acid

摘要

The complex species formed in aqueous solutions (25°C, I=3.0 mol·dm-3 KCl ionic medium) between the V(III) cation and the ligands 6-methylpicolinic acid (MePic, HL), salicylic acid (H_2Sal, H_2L) and phthalic acid (H_2Phtha, H_2L) have been studied by potentiometric and spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the experimental emf(H) data, taking into account the hydrolytic species and hydrolysis constants of V(III), indicates that under the employed experimental conditions the complexes [VL]~(2+), [V(OH)L]~+, [V(OH)_2L], [V(OH) _3L]~-, [VL_2]~+, [VL_3] and [V_2OL_4] form in the vanadium(III)-MePic system. Were observed the complexes [VL]~+, [VL_2]~-, [V(OH)L_2]~(2-) and [VL_3]~(3-) in the vanadium(III)-H_2Sal system, and the species [VHL]~(2+), [VL]~+, [V(OH)L], [VHL_2], [VL_2]~-, [V(OH)L_2]~(2-), [V(OH)_2L_2]~(3-) and [VL_3]~(3-) in the vanadium(III)-H_2Phtha system. The stability constants of these complexes were determined by potentiometric measurements, and spectrophotometric measurements were made in order to perform a qualitative characterization of the complexes formed in aqueous solution.