Enthalpies of Transfer of Single Ions and Metal Complexes from Water to an Aqueous Dioxane Solution

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Abstract
Enthalpies of solution of some 1:1 and 2:1 electrolytes were determined in water and in a dioxane–water mixture (the dioxane content; 0.2 mole fraction or 55.0% w/w) by calorimetry at 25 °C. Enthalpies of transfer (ΔHto) of single ions from water to the dioxane–water mixture were obtained by employing the extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption. Enthalpies of transfer of nickel(II) and copper(II) complexes with glycinate (gly−) and ethylenediamine (en) were also evaluated for [Ni(gly)n](2−n)+ (n=1–3), [Ni(en)n]2+(n=1–3), and [Cu(en)n]2+ (n=1–2) by combining enthalpies of transfer of the relevant single metal ions and ligands with enthalpies of complex formation reactions M+nL=MLn (M=Ni2+ or Cu2+ and L= gly− or en) in water and in the mixture. The enthalpies of transfer of the metal complexes examined here increased almost linearly with an increase in the number of the ligands within the complexes. The values of ΔHto of the ethylenediamine complexes of nickel(II) and copper(II) ions were all negative, as well as those of free Ni2+ and Cu2+ ions. On the other hand, the enthalpies of transfer of the noncharged [Ni(gly)2] and anionic [Ni(gly)3]− complexes were positive, while that of the [Ni(gly)]+ complex was still negative. The result suggested that hydration of the ligands coordinating to the central metal ions plays an essential role in the enthalpies of transfer of the metal complexes from water to the dioxane–water mixture.

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