Potentiometric and theoretical studies of stability constants of glyoxime derivatives and their nickel, copper, cobalt and zinc complexes

The dissociation constants of 1,2-bis(4-methylpiperazine)glyoxime (BMPGH2) and 1,2-bis(4-benzylpiperazine)gly oxime (BBPGH2) were determined in 0.1 mol dm(-3) NaCl and 0.001 mol dm(-3) HCl at 25 degrees C potentiometrically. pK(a) values of BMPGH2 and BBPGH2 were obtained as 2.91, 6.79, 7.97, 10.00 and 3.46, 5.89, 6.77, 9.76, respectively. The protonation order of nitrogen atoms in the BMPGH2 and BBPGH2 were determined using Semi-empirical AM1 method. In various pH conditions, the different complexes formulated as MH6L2, MH5L2, MH4L2, MH3L2, MH2L2, MHL2, ML2, MH-1L2, and MH-2L2 were formed with titration of ligand and Cu, Co, Ni and Zn ions.