Abstract
Titration calorimetry is a powerful tool for determining thermodynamic parameters of metal-ion complexation in non-aqueous solvents. By using this method, we could have simultaneously obtained formation constants and enthalpies of not only binary but also ternary metal complexes. The enthalpy and entropy values of metal-ion complexation reflect the change in the solvation number, and thus provide useful information on the coordination structure of metal complexes in solution. In non-aqueous solvent, unlike water, solvent-solvent interaction (solvent structure) in the bulk liquid is generally weak, and solvation steric effect operates upon coordination of bulky solvent molecules to the metal ion. This leads to an enhanced complexation of anionic ligands such as halide ions, even in an aprotic donor solvent that has a stronger donor property than water. Here, the results on the formation thermodynamics and structure of metal-ion complexes will be discussed from the view-point of solvation steric effect.
