Potentiometric study of the new synthezised 1-benzyl-4-piperazineglyoxime and 1-methyl-4-piperazineglyoxime and their divalent metal complexes

The deprotonation constants of 1-benzyl-4-piperazineglyoxime (BPGO) and 1-methyl-4-piperazineglyoxime have been determined in 0.1 mol dm(-3) NaCl at 25 degreesC potentiometrically (Molspin). The pK(a) values have been found as 9.79, 7.04 and 3.19 for BPGO and 9.56, 7.62 and 3.01 for MPGO in acidic medium. Protonation order of nitrogen atoms in the ligands has been determined by theoretical calculation (Semi-empirical AM1 method). In various pH conditions, the different complexes, which are formulated as MH6L2, MH5L2, MH4L2, MH3L2, MH2L2, MHL2, ML2, MH-1L2 and MH-2L2 have been formed by titration of the transition metal ions (Cu2+, Co2+, Ni2+ and Zn2+) and ligands mixtures with NaOH. The stabillity constants of each complex have been calculated by SUPERQUAD computer program and general mechanisms have been proposed with regard to the formation of these complexes (MH2nL2 and MH2n-1L2).