Synthesis, characterization, potentiometric and thermodynamic studies of transition metal complexes with 1-benzotriazol-1-yl-1-[(p-methoxyphenyl) hydrazono]propan-2-one

A new series of Mn2+ and Co2+ complexes with 1-benzotriazol-2-yl-1-[(p-methoxyphenyl)-hydrazono]propan-2-one (BMHP) were synthesized and characterized by the elemental analysis, magnetic and different spectral techniques. Proton dissociation constant of the free ligand and the stepwise stability constants of its metal complexes were determined potentiometrically in 0.1 M KC1 and 40% (v/v) ethanol-water. The dissociation constants of the free ligand and its metal complexes were determined at different temperatures and the corresponding thermodynamic parameters were calculated and discussed. The dissociation process was found to be non-spontaneous, endothermic and entropically unfavorable. The changes in the standard Delta G(0) and Delta H-0 accompanying complexation were decreased with increasing metal ionic radius but increased with increasing electronegativity, ionization enthalpy, and hydration enthalpy of the metal ion. The values of (-Delta G(0)) and (-Delta H-0) were in the order: Mn2+< Co2+< Ni2+< Cu2+, in accord with the Irving-Williams order. The complexes were found to be stabilized by both enthalpy and entropy changes and the results suggest that complexation is an enthalpy-driven process. The distribution diagrams of the complexes in solution were evaluated.