Rhenium(VII) oxide
Rhenium(VII) oxide (Re2O7), also known as dirhenium heptoxide, is the chemical compound with the formula Re2O7. It is the highest oxide of rhenium, and notable for being volatile. It is a pale yellow solid that readily dissolves in water to form perrhenic acid (HReO4).
Properties:
Rhenium(VII) oxide is a hygroscopic solid. It exists as discrete Re2O7 molecules in the solid state. These molecules feature two rhenium atoms, each tetrahedrally coordinated to four oxygen atoms. One oxygen atom bridges the two rhenium centers. It is soluble in water, forming perrhenic acid. It also dissolves in certain organic solvents.
Synthesis:
Rhenium(VII) oxide is typically prepared by oxidizing rhenium metal at high temperatures in an atmosphere of oxygen.
Reactions:
When dissolved in water, Re2O7 forms perrhenic acid.
Re2O7 + H2O → 2 HReO4
It reacts with metal oxides to form perrhenates. For example, reaction with sodium oxide produces sodium perrhenate.
Re2O7 + Na2O → 2 NaReO4
Uses:
Rhenium(VII) oxide is primarily used as a precursor to other rhenium compounds. It is also employed as a catalyst in some chemical reactions.
Safety:
Like other rhenium compounds, rhenium(VII) oxide is generally considered to have low toxicity, although appropriate care should be taken during handling. Skin and eye contact should be avoided, and inhalation of dust or vapors should be minimized.