Spectroscopic, electrochemical, and spectroelectrochemical investigations of several solute species in molten sodium chloroaluminates

Spectroscopy, electrochemistry, and spectro-electrochemistry (SEC) (primarily UV-visible) have been used to study the behavior of solute species in the molten sodium chloroaluminate melts. The utilities of two fiber optic probing techniques, fiber optic cables connected to the dry box and a fiber optic probe for in situ studies, have been demonstrated. The Raman, UV-visible, and electron spin resonance (ESR) spectroelectrochemical behavior of chloranil in basic melt [<50 mole percent (m/o) AICI₃] and the UV-visible and ESR spectroelectrochemical behavior of chloranil in acidic melt (>50 m/o AICI₃) has been examined. The chloranil is electrochemically reduced in the basic melt via two one electron transfers. The results indicate that the radical anion intermediate exists as a complex with AICI₃ (or Al₂Cl₇^-) in both basic and acidic melts. UV-visible spectroscopic and spectroelectrochemical studies of NbCl₅ in the basic melt showed that a Nb^2.33+ cluster is electrochemically generated in the fourth reduction and that it is further generated chemically by the disproportionation reaction of Nb⁴⁺, produced in the first wave, to Nb⁵⁺ and Nb³⁺, the latter of which then decomposes to give the cluster. The cluster was shown to be less soluble at higher temperatures. The UV-visible spectroscopic and spectroelectrochemical behavior of potassium hexachlororhenate(IV) was studied. The initial voltammograms show a new wave to grow in at a potential more positive than the [ReCl₆]^2- reduction. The resulting voltammogram, consisting of three reduction and two oxidation waves, does not change further. Spectroelectrochemical results indicate that this first reduction is due to the [Re₂Cl₉]^2-/[Re₂Cl₈]^2- couple. The second wave is believed to be due to the reductions of both [ReCl₆]^2- and [Re₂Cl₈]^2-. The results are complicated by the instability of rhenium (III).