Mixed-ligand complex formation equilibria of vanadium(III) with picolinic and dipicolinic acids with some dicarboxylic acids (oxalic, malonic, and phthalic acids) studied in 3.0 M KCl at 25 °C

The ternary complexes formed between vanadium(III) and picolinic acid (Hpic) and dipicolinic acid (H2dipic) with the dicarboxylic oxalic, malonic, and phthalic acids (H2ox), (H2mal), and (H2phtha) briefly (H2L) were studied in aqueous solution by means of electromotive forces’ measurements emf(H) at 25 °C and 3.0 mol dm−3 KCl as ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, considering the hydrolysis products of the V(III), the acidity constants of the ligands employed, and the formation constants of the binary complexes, obtaining the complexes V(pic)(ox), log β1,1,1,−3 = 5.39(7) and [V(pic)2(ox)]−, log β1,2,1,−4 = 4.3(1); V(pic)(ma), log β1,1,1,−3 = 5.58(5) and [V(pic)2(ox)]−, log β1,2,1,−4 = 5.00(8); V(pic)(phtha), log β1,1,1,−3 = 5.66(6) and [V(pic)2(phtha)]− log β1,2,1,−4 = 4.5(2) in the vanadium(III)-Hpic-H2L system. In the case of the vanadium(III)-H2dipic-H2L system, the complexes [V(dipic)(ox)]−, log1,1,1,−4 β = 9.3(2), [V(dipic)(Hox)(ox)]2−, log β1,1,2,−5 = 11.2(2) and [V(dipic)(ox)2]3−, log β1,1,2,.6 = 5.7 max 7.0; [V(dipic)(ma)]−, log β1,1,1,−4 = 8.7(2), [V(dipic)(Hma)(ma)]2−, log β1,1,2,−5 = 10.3(1) and [V(dipic)(ma)2]3−, log β1,1,2,.6 = 6.9(1); [V(dipic)(phtha)]−, log β1,1,1,−4 = 10.9(1), [V(dipic)(Hphtha)(phtha)]2−, log β1,1,2,−5 = 9.2 max 10.4 and [V(dipic)(phtha)2]3−, log β1,1,2,.6 = 6.9(3) were observed.