Potentiometric, Theoretical, and Thermodynamic Studies on Equilibrium Constants of Aurintricarboxylic Acid and Determination of Stability Constants of Its Complexes with Cu2+, Ni2+, Zn2+, Co2+, Hg2+, and Pb2+ Metal Ions in Aqueous Solution

In this study, the dissociation constants of aurintricarboxylic acid (5,5′-((3-carboxy-4-oxocyclohexa-2,5-dienylidene)methylene)bis(2-hydroxybenzoic acid)) (ATA) together with the stability constants of its Cu2+, Ni2+, Zn2+, Co2+, Hg2+, and Pb2+ complexes were studied potentiometrically/theoretically and determined via the SUPERQUAD computer program in aqueous media and at the ionic background of 0.1 mol·dm–3 of NaCl. Moreover, its thermodynamic parameters were determined in different temperatures (298 K, 308 K, and 318 K). It has been perceived that the ATA has five dissociation constants, so for LH5 they are 2.95 (3), 3.04 (4), 3.98 (3), 9.56 (1), and 10.06 (5), respectively. The overall stability constants of its metal complexes were calculated and various formed complexes formulated as M2L, M2HL, M2H2L, M2H3L, and M2H4L between the ATA with Cu2+, Ni2+, Zn2+, Co2+, Hg2+, and Pb2+ ions.