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

Abstract

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)Cl(2)(H(2)O)], [Fe(L2)Cl(H(2)O)](2+), [Zn(L1)(H(2)O)(3)](+) and [Zn(L2)(H(2)O)(2)](2+), which expressed cytotoxic activity, were investigated in aqueous media. The equilibrium constants were determined potentiometrically at 25 degrees C at a constant ionic strength of 0.10 mol/dm(3) (Na(2)SO(4)). The results showed that at pH lt 8 both the Fe(III) complexes studied here have three, while [Zn(L1)(H(2)O)(3)](+) and [Zn(L2)(H(2)O)(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 proučavane kiselinsko-bazne ravnoteže 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 citotoksičnu aktivnost. Ravnotežne konstante su određivane potenciometrijski, na temperaturi 25°C i pri konstantnoj jonskoj jačini 0,10 mol/dm3 Na2SO4. Utvrđeno je da u intervalu pH lt 8 ispitivani Fe(III) kompleksi imaju tri, [Zn(L1)(H2O)3]+ jedan, a [Zn(L2)(H2O)2]2+ dva protona koji mogu da se titrišu. Na osnovu dobijenih vrednosti za konstante, pretpostavljene su i odgovarajuće protonacione sheme.