Solvation Structures and Solvent Exchange Reactions of Metal Ions in Various Coordinating Solvents

Abstract

Abstract The solvation structures and the reaction mechanisms of the solvent exchange reactions of metal ions are essential aspects of the interactions of the metal ions with the solvent molecules and information about them is necessary to understand the reactivities of the metal ions in solution. The solvation structures in various coordinating solvents were discussed on the basis of the structure parameters determined by the extended X-ray absorption fine structure technique, referring to the ionic size, ionic charge, and electronic configuration of the metal ions and the bulkiness and electron donating ability of the solvent molecules. It was shown that the deficient bulkiness of 1,1,3,3-tetramethylurea leads to a unique variation in the solvation number for a series of 3d-block metal ions and that the strong electron donating ability of propylamine reduces the solvation number. The solvent exchange mechanisms of various metal ions were discussed on the basis of the activation parameters determined by the nuclear magnetic resonance technique, and the effects of the ionic charge, ionic size, and electronic configuration of the metal ions were regularized. The kinetic results for the solvent exchange of the Ni2+ and Mn2+ ions in a series of nitriles revealed the effect of the solvent bulkiness on the variation in the mechanism. The kinetic chelate effect was pointed out on the basis of the activation parameters for the solvent exchange of the divalent first-row transition metal ions in bidentate solvents such as ethylenediamine and trimethylenediamine.