Hayati Sari,^a* Muzaffer Can,^a and Mustafa Macit^b
a Gaziosmanpaşa University, Faculty of Art and Sciences, Department of Chemistry, 60250, Tokat, Turkey. E-mail: hsari@gop.edu.tr
^b Ondokuzmayıs University, Department of Chemistry, 55139 Samsun, Turkey

Abstract
The dissociation constants of 1,2-bis(4-methylpiperazine)glyoxime (BMPGH2) and 1,2-bis(4-benzylpiperazine)glyoxime (BBPGH2) were determined in 0.1 mol dm^–3 NaCl and 0.1 mol dm^–3 HCl at 25 °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.

Key words: 1,2-bis(4’-methylpiperazine)glyoxime, 1,2-bis(4’-benzylpiperazine)glyoxime, dissociation constant, stability constants, SUPERQUAD, AM1 method