Potentiometric and thermodynamic studies of N, N'-bis(4-hydroxyacetophenone) ethylenediamine and its Cu2+, Ni2+, Co2+, Fe3+, and Mn2+ complexes

Studying the stability constants of metal complexes offers significant insights into their applications in analytical chemistry, pharmaceuticals, catalysis, environmental science, and material science. The protonation constants of N, N'-bis(4-hydroxyacetophenone) ethylenediamine (BHAEN) and the stability constants of a number of transition metal complexes have been studied potentiometrically at 20, 25, 30 and 40oC, in water solution at 0.1 M ionic strength (KNO3), using the mole ratios (1:1) and (2:1), (L:M), where M = Cu2+, Ni2+, Co2+ , Fe3+, and Mn2+. The calculations are performed by operating the computer program SUPERQUAD. From the values of the stability constants of the complexes at the different four temperatures, the thermodynamic functions G, H and S were evaluated. The order of stability of the complexes agrees the Irving - Williams order. The positive values of H for the BHAEN complexes, especially for the most stable complexes species, (ML) in the case with Cu(II) and Fe(III), (MHL) in the case of Ni(II) & Co(II) and (ML2) in the case of Mn(II), reveal that the stability of these species is mainly due to the S values which are highly positive.