Binary and ternary copper(II) complexes with dipicolinic acid and selected bidentate ligands: a potentiometric study

In this work, we present a study on the formation of binary and ternary complexes in the Cu(II)-Dipic-bidentate ligand systems using potentiometric measurements. The bidentate ligands were malonic acid (H2Mal, H2L), phthalic acid (H2Phtha, H2L), and salicylic acid (H2Sal, H2L); the primary ligand was dipicolinic acid (H2Dipic, H2L). The ionic medium used was 1.0 mol dm−3 KNO3 at 25°C and the potentiometric data were analysed with the LETAGROP program. In the binary Cu(II)-Mal system, the complexes Cu(HL)+, CuL, Cu(OH)L−, and Cu(L)22− were detected and, for the Cu(II)-Phtha system the species Cu(HL)+, CuL, Cu(OH)L− were observed. In the ternary Cu(II)-Dipic-Mal and Cu(II)-Dipic-Phtha systems, the LETAGROP analysis showed the formation of the ternary complexes Cu(Dipic)(HL)−, Cu(Dipic)(L)2- and Cu(OH)(Dipic)(L)3-. Finally, in the Cu(II)-Dipic-Sal system, a unique species Cu(Dipic)(HL)− was detected. The species distribution diagrams are briefly discussed.