Acid-base equilibria of the Zn(II) and Fe(III) complexes with condensation products of 2-acetylpyridine and the dihydrazide of oxalic and malonic acid

Acid-base equilibria of Zn(II) and Fe(III) complexes with N',N'2-bis- [(1E)-1-(2-pyridyl)ethylidene]ethanedihydrazide (ligand L1) and N',N'2-bis[(1E)- -1-(2-pyridyl)ethylidene]propanedihydrazide (ligand L2), i.e., [Fe(L1)Cl2(H2O)], [Fe(L2)Cl(H2O)]2+, [Zn(L1)(H2O)3]+ and [Zn(L2)(H2O)2]2+, which expressed cytotoxic activity, were investigated in aqueous media. The equilibrium constants were determined potentiometrically at 25?C at a constant ionic strength of 0.10 mol/dm3 (Na2SO4). The results showed that at pH < 8 both the Fe(III) complexes studied here have three, while [Zn(L1)(H2O)3]+ and [Zn(L2)(H2O)2]2+ have one and two titratable protons, respectively. Based on the obtained values for the equilibrium constants, protonation schemes of the examined complexes are proposed. U ovom radu su proucavane kiselinsko-bazne ravnoteze u vodenim rastvorima kompleksa Zn(II) i Fe(III) sa N',N'2-bis[(1E)-1-(2-piridil)etiliden]etandihidrazidom (ligand L1) i N',N'2-bis[(1E)-1-(2-piridil)etiliden]propandihidrazidom (ligand L2), tj. [Fe(L1)Cl2(H2O)], [Fe(L2)Cl(H2O)]2+, [Zn(L1)(H2O)3]+, [Zn(L2)(H2O)2]2+, koji pokazuju citotoksicnu aktivnost. Ravnotezne konstante su odredjivane potenciometrijski, na temperaturi 25?C i pri konstantnoj jonskoj jacini 0,10 mol/dm3 Na2SO4. Utvrdjeno je da u intervalu pH < 8 ispitivani Fe(III) kompleksi imaju tri, [Zn(L1)(H2O)3]+ jedan, a [Zn(L2)(H2O)2]2+ dva protona koji mogu da se titrisu. Na osnovu dobijenih vrednosti za konstante, pretpostavljene su i odgovarajuce protonacione sheme.