Rhenium and technetium (VI) and meso-(VII) species

Abstract

Spectrophotometric study shows that less than 35 per cent of normal perrhenate converts to a meso form in 15 M base, and Kf ~ 0[middle dot]1. The species absrobs at 260 m[mu] ([epsilon] = 6,400) and near 310 m[mu] ([epsilon] ~ 1,400), overlapping the normal perrhenate features. Reflectance spectra on an isolable barium salt, Ba3(ReO5)2, confirm this resolution of the curve components. The variation of the barium salt solubility with concentration of aqueous hydroxide ion is consistent with the equilibrium deduced from spectrophotometry. Hydration is found for this salt and does not require the postulation of a dimeric form (to maintain 6-coordination); nor does this postulate seem to fit the equilibrium data or the i.r. absorption. No detectable amount of a comparable mesopertechnetate species is found in aqueous media of any alkalinity. However, pertechnetate fused in sodium hydroxide does give new absorption at 345, 420 and (~ 570) m[mu] (of relative [epsilon] ca. 8/4/1), which is probably due to meso (or, ortho) species. Attempts to isolate a (VI) salt, BaTcO4, from hydrazine-reduced (VII) in alkaline aqueous media, result in mixtures. Disproportionation of the intermediate state forms TcO2, and incidental BaCO3 gives "products" of high Tc/Ba ratio. The red intermediate is more likely to be a Tc(V) species.