Spectroscopic and Electrochemical Analyses for Dysprosium Complexes In Potassium Bis(trifluoromethylsulfonyl)amide Melts

Abstract

The coordination states of multivalent dysprosium complexes of potassium bis(trifluoromethylsulfonyl) amide (K[NTf2]) were investigated by Raman spectroscopy. The concentration dependence of the deconvoluted Raman spectra was investigated for 0.23−0.45 mol kg−1 Dy(III), and a mixed sample of Dy(II)/Dy(III) (molar ratio 1/3), in K[NTf2]. Using conventional analysis, the solvation number, n, of the dysprosium complexes was determined to be 4.12 for Dy(II) and 5.09 for Dy(III). The electrochemical behavior of [DyIII(NTf2)5]2– in K[NTf2] melts was also investigated in this study. It is speculated that the first reduction peak at approximately +2.24 V probably corresponds to the formation of [DyII(NTf2)4]2–. Electrochemical analysis revealed that the reduction peak of [DyIII(NTf2)5]2– at approximately +0.81 V at 483 K is based on an electrodeposition reaction from [DyIII(NTf2)5]2– to Dy(0). The diffusion coefficient and activation energy of [DyIII(NTf2)5]2– in K[NTf2] melts were measured in the range 473–493 K by semi-integral and semi-differential analyses. Furthermore, the nucleation behavior of [DyIII(NTf2)5]2– was evaluated using chronoamperometry. The results indicated that the nucleation mechanism of Dy nuclei changed from instantaneous to progressive nucleation when the overpotential became more negative than the deposition potential of Dy(0). The electrodeposits were identified as mostly the metallic state by X-ray photoelectron spectroscopy.