Solution equilibria studies of complexes of divalent metal ions with 2-aminophenol and 3,4-dihydroxybenzoic acid

Abstract

The chelation abilities of 2-aminophenol and 3,4-dihydroxybenzoic acid with divalent metal ions (Cu2+, Be2+, Zn2+, Ni2+, Co2+ and Mn2+) in binary and ternary systems at 37±0.1°C and an ionic strength of 0.15moldm−3 NaCl were systematically investigated by using the potentiometric titration method. The chelating abilities of these complexes were obtained by processing the titration data using the Hyperquad2008 program and the results are presented as stability constants. In a binary system, it was shown that metal complexation involving 3,4-dihydroxybenzoic acid (ligand D) is more stable than the one with 2-aminophenol (ligand A). The stability of the formed metal complexes, both in binary and ternary systems, decreases in the following order: Cu2+>Be2+>Zn2+>Ni2+>Co2+>Mn2+. The tendency of these metals and ligands to form binary or ternary complexes was also evaluated and discussed by calculating their ΔlogKM and logX values. In addition, the distribution of complex species in these systems was graphically presented using the HySS2009 program. UV–Vis spectrophotometry was also performed to qualitatively verify the protonation of these ligands and to confirm the model of the complex formed.