Thermodynamics of bis-β-diketonato complexes of Cu(II) and Ni(II)

Abstract

The thermodynamic functions of formation of Cu(II) and Ni(II) complexes of some β-diketones, viz. acetylacetone, benzoylacetone, anisoylacetone and dibenzoylmethane have been determined in 75 vol.% dioxane + 25 vol.% water. The enthalpy changes increase in the order: HBZBZ > HAYAC > HBZAC > HACAC. This is also the order of stability or free energy change. The thermodynamic functions have been separated into temperature dependent and temperature independent components. The increase in the magnitude of -ΔG° and ΔS° and a decrease in the magnitude of -ΔH¯, in water-dioxane medium as compared to water, results from the difference in electrostatic interaction between metal ion and ligand anion in the two media. The thermodynamic parameters have been discussed in relation to the nature of bonding and the symmetry of the metal complexes.