Thermodynamical detection of hydrophobic hydration of tris(2,4-pentanedionato)-cobalt(III) and tris(3,5-heptanedionato)cobalt(III) in water

Abstract

The solubilities of tris(2,4-pentanedionato)cobalt(III) and tris(3,5-heptanedionato)cobalt(III) in water, heptane, and 1,2-ethanediol were determined over the temperature range 5–50 °C and from these data the thermodynamic quantities of solution at 25 °C were estimated. The free energy [Formula: see text], enthalpy [Formula: see text], and entropy [Formula: see text] of transfer of these chelates from heptane to some solvents were calculated from the corresponding thermodynamic quantities of solution. When [Formula: see text] and [Formula: see text] were separately plotted against [Formula: see text], the data of transfer from heptane to water deviated markedly from a correlation obtained for the data of transfer to the solvents other than water. This finding indicates that these chelates are subject to hydrophobic hydration in their aqueous solutions. The solubility of tris(glycinato)cobalt(III) in water was also determined over the temperature range 5–60 °C and its temperature dependence of the solubility is compared with that for the cobalt(III) chelates of the β-diketones. Key words: tris cobalt(III) chelates of β-diketones and glycine, temperature dependence of solubility, thermodynamic parameters of solution, thermodynamic parameters of transfer, hydrophobic hydration.