Spectroscopy, Electrochemistry, and Spectroelectrochemistry of Rhenium Chlorides in the AlCl3 ‐ NaClsat Melt

Abstract

The electrochemical and UV-visibie spectroscopic and spectroelectrochemical behavior of rhenium(IV), added as K~ReCI~, and the metal-metal bonded rhenium(III) complexes, [Bu~N]~Re~CI~ and Re~CI~, was studied in the A1C13-NaClsa t melt at 175~ In the initial voltammograms of solutions containing [ReCl~] 2-a new wave grows in at a potential more positive than the [ReC16] ~-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 [ReCI~]~-/[Re2CI~] ~-couple. The second wave is believed to be due to the reductions of both [ReCI~] 2-and [Re2CI~] 2-. The results are complicated by the instability of the intermediates as well as the disproportionation of Re, C1, to [ReCI~] ~-and rhenium metal.

Reactions and speciation of technetium and rhenium in chloride melts: a spectroscopy study

“…The spectra recorded in NaCl-CsCl melt at 600 C and in NaCl-KCl melt at 700 C after several hours of chlorination exhibited only a single band between 29 000 and 30 000 cm À1 with essentially no absorbance in the visible region. Similar spectra were reported 25 for AlCl 3 -NaCl melts containing very low concentration of [ReCl 6 ] 2À . At present we can therefore only postulate that the reaction of rhenium with HCl in molten chlorides leads to the formation of very small amounts of [ReCl 6 ] 2À .…”

“…Higher intensity band corresponding to the first spin-allowed transition, 4 A 2g ! 4 T 2g , is expected around 30 000 cm À1 and was observed by Hodrogiannis and Mamantov 25 for very dilute (9.9 10 À4 mol dm 3 ) solutions of K 2 ReCl 6 in AlCl 3 -NaCl melt at 175 C. No reaction was observed between rhenium and chlorine in LiCl-KCl melt at 480 C. The experiments were then repeated in the LiCl-KCl and NaCl-KCl melts at 650 and 700 C, respectively. The reactions were slower than in NaCl-CsCl melt, Table 2, and the spectra recorded in LiCl-KCl and NaCl-KCl systems were rather different, Fig.…”

“…Subsequent spectroscopic studies of rhenium in chloride systems have been mainly limited to the low-temperature ionic systems. Strubinger et al [22][23][24] have investigated rhenium(III) and (IV) species in room temperature were also reported in AlCl 3 -NaCl melts at 175 C. 25 In all the above work rhenium was introduced into the melts by dissolving various rhenium chloride salts, so there was no information on the formation of rhenium chlorides from other starting compounds, e.g., metal or oxides. Spectroscopic properties of technetium in molten salt systems (either high-or low-temperature) have not been previously reported.…”

Excessive consumption mechanism of hydrazine in the reaction with ReO4−: Re species evolution and ReO2·nH2O-catalyzed decomposition

“…The 301 nm absorption peak was assigned to the Re( iv ) species, 25–28 but the exact form of the Re( iv ) species could not be confirmed. The current consensus is that ReO(OH) 2 °/ReO(OH) 3 − species are forms of ReO 2 (S) dissolved in water, 29,30 and the solubility of ReO 2 (S) would increase from 1 × 10 −6 mol L −1 at pH 8 to 1 × 10 −4 mol L −1 at pH 10.…”

“…3a ([N during an induction period. The 301 nm absorption peak was assigned to the Re(IV) species, [25][26][27][28] but the exact form of the Re(IV) species could not be confirmed. The current consensus is that ReO(OH) 2 °/ReO (OH) 3…”