Electrochemical and spectrophotometric study on trivalent neodymium ion in molten binary mixtures of LiCl and alkali earth chlorides

The thermodynamic stability of Nd(III) complexes was studied by electrochemical techniques for molten binary mixtures composed of LiCl and an alkali earth chloride, CaCl₂, SrCl₂, or BaCl₂ at 923 K. The Gibbs free energy change of formation of Nd(III) in the melts was determined. The obtained values showed a good correlation with the polarizing power of solvent cations. The Nd(III) complex was more stable in the melts with low polarizing power. The electronic absorption spectrum of the hypersensitive f-f transition of Nd³⁺ was investigated to obtain information about the structural change of the complex. The estimated oscillator strength of the ⁴G_5/2,²G_7/2 ← ⁴I_9/2 transition and the degree of the energy splitting in electronic energy levels showed different trends upon the polarizing power for each of added alkali earth chloride. This indicates that the coordination environments further from second neighbors could have significant impact on the electronic energy levels of Nd(III) in the mixtures including alkali earth cations.