PHYSICOCHEMICAL STUDIES ON COMPLEXES OF SOME METALS WITH ISONITROSODIBENZOYL- AND THIODIBENZOYLMETHANE

Abstract

Isonitrosodibenzoylmethane (HL) and Isonitrosothiodibenzoylmethane (HL*) in addition to their metal complexes with Mn(II), Ni(II), Cu(II) Zn(II), Cr(III), Fe(III) and Co(III) were synthesized and analytically characterized. The acid dissociation of HL and HL* and their corresponding complexatidn reactions in solutions of organic solvent-water mixtures at a temperature range of 10-40 oc were studied. The values of the apparent dissociation constants (pKa), thermodynamic acid dissociation constants (TpKa) and true acid dissociation constants (pK rue) of the ligands were evaluated. HL' exhibited higher acidic character compared to HL. The values of the formation constants of the respective metal chelates (log }3) in solution were determined. The formation of metal complexes of HL is seemingly much more favourable than those of HL*. The acid dissociation of the ligands and their corresponding complexation reactions were furtherly subjected to a detailed 0 0 0 thermodynamic investigation. The changes in thermodynamic functions H,G and S accompanying the two processes were estimated, discussed and correlated with the 0 0 various reaction parameters. The electrostatic Xe1 and non-electrostatic Xnonet contributions (X = H, G, S) to the concerned changes in the thermodynamic functions were determined and discussed. The electrostatic contribution does exert a minor role in the acid dissociation of the ligands, whereas its role in the complexation reactions seems to be predominant. The solvation numbers for the acid dissociation of the investigated systems were calculated and found in very good agreement with the entropy changes thereof. Furthermore, it was attempted, to make use of the calculated non­ electrostatic part of enthalpy changes, accounting for the complexation reactions in solution, to approximately determine, the bond energies of metal-oxygen, metal-nitrogen and metal-sulphur, in the examined systems.