Rhenium trioxide or rhenium(VI) oxide is an

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 chemis ...

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

copper Copper is a chemical element with the symbol Cu (from la, cuprum) 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 pink ...

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 with

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

at 200 °C or elemental rhenium 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 unit cell, with a lattice parameter 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 (XIIA2+VIB4+X2−3), known a ...

(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 (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

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 specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...

. It behaves like a

metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...

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 In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...

to give and , while reaction with acid at high temperature affords . In concentrated nitric acid, it yields

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 ...

. Upon heating to 400 °C under vacuum, it undergoes

:G. Glemser "Rhenium (VI) Oxide" Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 2. p. 1482. : 3 ReO₃ → Re₂O₇ + ReO₂

Uses

Hydrogenation catalyst

Rhenium trioxide 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 Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

for amide reduction.

References

{{Oxides Rhenium compounds Hydrogenation catalysts Transition metal oxides