...from 1966 which reports the use of CsCl as a "precipitating solution" for perrhenate.
Rate of oxygen exchange between the perrhenate ion and water (Murmann, J. Phys. Chem.1967 71 4974-978)
From the text:
Preparation of Materials. NaRe04 enriched inO18 was prepared from a concentrated (1 g of Re/ml) solution of HRe04 (S. W. Shattuck Co.) by mixing with an equal volume of 8 X 018-enriched water, redistilled from KMn04. After equilibration for 2 hr, which was known from previous work to cause complete exchange, reagent grade Na2C03(s) was slowly added in slight excess. Then a small excess of HRe04 was added until it was just acidic after boiling. The solution was filtered and concentrated to half its initial volume under vacuum at room temperature and AR acetone (50 ml/g of Re) added. It was filtered to remove a trace of insoluble material and AR ethyl ether added (200 ml/g of Re). After 2 hr at 0° the white precipitate was collected, washed with anhydrous ether, and dried at 70° under vacuum for 2 days. Yield was 80-90% of theory. Analysis2 for Re gave 68.2% (calculated for NaRe04, 68.16). The analysis only shows the compound to be essentially pure; it would not indicate the presence of eatalytically important impurities. In order to clarify this point, NaRe04 was prepared through recrystallized AgRe0418 by reaction with the stoichiometric amount of AR NaCl. After removal of the AgCl, the solution was evaporated until crystallization occurred and the product was removed and dried under vacuum. The two preparations of NaRe04 showed identical (±1%) rates of oxygen exchange in both the acidic and basic regions. LiCl, NaCl, and LiN03 stock solutions were prepared from AR solids and the filtered solutions analyzed for content by standard methods. The CsC1-H20 precipitating solution was made by adding ca. 25 g of AR CsCl to 50 ml of filtered solution.
= new reply since forum marked as read
