Potentiometric and conductometric studies on Fe3+, Ni2+, and Cu2+ complexes with some hydroxamic acid derivatives

Abstract The ionization constants (p K a ) of some hydroxamic acid derivatives were determined potentiometrically in a 50% ethanolic solution applying the Calvin–Bjerrum titration technique as modified by Irving and Rossotti at 25°C, and an ionic strength of 0.1 M NaCl. The stability constants of Fe 3+ , Ni 2+ and Cu 2+ were determined potentiometrically, log  K 1 values being calculated and the free energy change was calculated for the ligands and their chelates. The p K a values were correlated with the Hammett substituent constants and the ionic strength. The relation between the basicity of the ligands and stability constants of complexes is discussed. Conductometric titrations of Fe 3+ , Ni 2+ and Cu 2+ with the hydroxamic acid derivatives were carried out to give further insight into the stoichiometric composition of the complexes formed in the solution.