Rhenium(VII) oxide is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula Re₂ O₇. This yellowish solid is the anhydride of HOReO₃.

Perrhenic acid Perrhenic acid is the chemical compound with the formula . It is obtained by evaporating aqueous solutions of . Conventionally, perrhenic acid is considered to have the formula , and a species of this formula forms when rhenium(VII) oxide sublime ...

, Re₂O₇·2H₂O, is closely related to Re₂O₇. Re₂O₇ is the raw material for all rhenium compounds, being the volatile fraction obtained upon roasting the host ore.

Structure

Solid Re₂O₇ consists of alternating octahedral and tetrahedral Re centres. Upon heating, the polymer cracks to give molecular (nonpolymeric) Re₂O₇. This molecular species closely resembles

manganese heptoxide Manganese(VII) oxide (manganese heptoxide) is an inorganic compound with the formula Mn2O7. This volatile liquid is highly reactive. It is a dangerous oxidizer and was first described in 1860. It is the acid anhydride of permanganic acid. Prop ...

, consisting of a pair of ReO₄ tetrahedra that share a vertex, i.e., O₃Re–O–ReO₃.

Synthesis and reactions

Rhenium(VII) oxide is formed when metallic rhenium or its oxides or sulfides are oxidized at in air. Re₂O₇ dissolves in water to give

perrhenic acid Perrhenic acid is the chemical compound with the formula . It is obtained by evaporating aqueous solutions of . Conventionally, perrhenic acid is considered to have the formula , and a species of this formula forms when rhenium(VII) oxide sublime ...

. Heating Re₂O₇ gives

rhenium dioxide Rhenium(IV) oxide or rhenium dioxide is the inorganic compound with the formula ReO2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure. Synthesis and reactions It forms v ...

, a reaction signalled by the appearance of the dark blue coloration:O. Glemser "Rhenium" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1476-85. :Re₂O₇ → 2ReO₂ + 1.5O₂ Using tetramethyltin, it converts to methylrhenium trioxide ("MTO"), a catalyst for oxidations: :Re₂O₇ + 2Sn(CH₃)₄ → CH₃ReO₃ + (CH₃)₃SnOReO₃ In a related reaction, it reacts with hexamethyldisiloxane to give the siloxide: :Re₂O₇ + 2O(Si(CH₃)₃)₂ → 2(CH₃)₃SiOReO₃

Uses

Hydrogenation catalyst

Rhenium(VII) oxide finds some use in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

as a catalyst for ethenolysis, carbonyl reduction and amide reduction.

References

{{Oxides Rhenium compounds Acidic oxides Hydrogenation catalysts