Rhenium trioxide or rhenium(VI) oxide is an

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

with the formula ReO₃. It is a red solid with a metallic lustre that resembles

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

in appearance. It is the only stable trioxide of the Group 7 elements ( Mn, Tc, Re).

Preparation and structure

Rhenium trioxide can be formed by reducing

rhenium(VII) oxide Rhenium(VII) oxide is the inorganic compound with the formula Rhenium, Re2oxide, O7. This yellowish solid is the anhydride of HOReO3. Perrhenic acid, Re2O7·2H2O, is closely related to Re2O7. Re2O7 is the raw material for all rhenium compounds, b ...

with

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

at 200 °C or elemental

rhenium Rhenium is a chemical element; it has symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

at 400 °C. :Re₂O₇ + CO → 2 ReO₃ + CO₂ :3 Re₂O₇ + Re → 7 ReO₃ Re₂O₇ can also be reduced with dioxane. Rhenium trioxide crystallizes with a primitive

cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

, with a

lattice parameter A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has ...

of 3.742 Å (374.2 pm). The structure of ReO₃ is similar to that of

perovskite Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as , known as the perovskite (stru ...

(ABO₃), without the large A cation at the centre of the unit cell. Each rhenium center is surrounded by an

octahedron In geometry, an octahedron (: octahedra or octahedrons) is any polyhedron with eight faces. One special case is the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. Many types of i ...

defined by six oxygen centers. These octahedra share corners to form the 3-dimensional structure. The coordination number of O is 2, because each oxygen atom has 2 neighbouring Re atoms., p. 1047.

Properties

Physical properties

ReO₃ is unusual for an oxide because it exhibits very low

resistivity Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity i ...

. It behaves like a

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

in that its resistivity decreases as its temperature decreases. At 300 K, its resistivity is 100.0 nΩ·m, whereas at 100 K, this decreases to 6.0 nΩ·m, 17 times less than at 300 K.

Chemical properties

Rhenium trioxide is insoluble in water, as well as dilute acids and bases. Heating it in base results in disproportionation to give and , while reaction with acid at high temperature affords . In concentrated nitric acid, it yields perrhenic acid. Upon heating to 400 °C under vacuum, it undergoes disproportionation: : 3 ReO₃ → Re₂O₇ + ReO₂ Rhenium trioxide can be

chlorinated In chemistry, halogenation is a chemical reaction which introduces one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. ...

to give rhenium trioxide chloride: : Rhenium trioxide serves as host for the intercalation of one and two equivalents of lithium. Lithium can be incorporated using butyl lithium: : : Re remains octahedral before and after intercalation, but the framework distorts.

Uses

Hydrogenation catalyst

Rhenium trioxide finds some use in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

as a

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

for amide reduction.

References

{{Oxides Rhenium compounds Hydrogenation catalysts Transition metal oxides