The perrhenate ion is the
anion with the formula ReO− 4, or a compound containing this ion. The perrhenate anion is tetrahedral, being similar in size and shape to
perchlorate and the valence
isoelectronicpermanganate. The perrhenate anion is stable over a broad pH range and can be precipitated from solutions with the use of organic cations. At normal pH, perrhenate exists as metaperrhenate (ReO− 4), but at high pH mesoperrhenate (ReO3− 5) forms. Perrhenate, like its conjugate acid
perrhenic acid, features rhenium in the
oxidation state of +7 with a d0 configuration. Solid perrhenate salts takes on the color of the cation.[1]
Preparation
Typical perrhenate salts are the alkali metal derivatives and
ammonium perrhenate. These salts are prepared by oxidation of rhenium compounds with nitric acid followed by neutralization of the resulting perrhenic acid.[2][3][4] Addition of
tetrabutylammonium chloride to aqueous solutions of sodium perrhenate gives tetrabutylammonium perrhenate, which is soluble in organic solvents.[5]
Reactions of perrhenates
Basicity
Perrhenate anion is a weaker base than Cl− or Br− but stronger than ClO− 4 or BF− 4. Silver perrhenate reacts with
trimethylsilyl chloride to give the silyl "ester" (CH3)3SiOReO3.[6]
Condensation
Perrhenate may undergo condensation with formation of small rhenium
polyoxometalate Re4O2− 15[7] where one central Re has octahedral oxygen coordination while 3 other are tetrahedral.
Reaction with sulfide
With sulfide sources such as
hydrogen sulfide, ReO− 4 converts to tetrathioperrhenate anion ReS− 4. An intermediate is [ReO3S]−.[8]
Redox
Unlike the related permanganate, perrhenate is nonoxidising. Replacement of some
oxo ligands induces redox however. Thus the perrhenate ion reacts with the
cyanide to give trans-[ReO2(CN)43−. Treatment of tetrabutylammonium perrhenate with
trimethylsilyl chloride produces the
oxychloride of Re(V):[5]
The chemistry of the perrhenate ion is similar to that of the
pertechnetate ion TcO− 4. For this reason, perrhenate is sometimes used as a carrier for trace levels of pertechnetate, for instance in nuclear medicine scanning procedures. Perrhenate is also used as a safer alternative to pertechnetate for nuclear waste vitrification studies, such as volatility[9] or encapsulation in solids.[10]
^
abDilworth, J. R.; Hussain, W.; Hutson, A. J.; Jones, C. J.; McQuillan, F. S. (1997). "Tetrahalo Oxorhenate Anions". Inorganic Syntheses. pp. 257–262.
doi:
10.1002/9780470132623.ch42.
ISBN9780470132623.
^Kühn, Fritz E.; Santos, Ana M.; Herrmann, Wolfgang A. (2005). "Organorhenium(VII) and Organomolybdenum(VI) Oxides: Syntheses and Application in Olefin Epoxidation". Dalton Transactions (15): 2483–91.
doi:
10.1039/b504523a.
PMID16025165.