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

The ionization constants (pK(a)) of some hydroxamic acid derivatives were d etermined potentiometrically in a 50% ethanolic solution applying the Calvi n-Bjerrum titration technique as modified by Irving and Rossotti at 25 degr ees C, and an ionic strength of 0.1 M NaCl. The stability constants of Fe3, Ni2+ and Cu2+ were determined potentiometrically, log K-1 values being ca lculated and the free energy change was calculated for the ligands and thei r chelates. The pK(a) values were correlated with the Hammett substituent c onstants and the ionic strength. The relation between the basicity of the l igands and stability constants of complexes is discussed. Conductometric ti trations of Fe3+, Ni2+ and Cu2+ with the hydroxamic acid derivatives were c arried out to give further insight into the stoichiometric composition of t he complexes formed in the solution. (C) 1999 Elsevier Science S.A. All rig hts reserved.