chemistry

Rhenium compounds

Rhenium compounds is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Rhenium compounds rather than just read about it. In short: Rhenium compounds are compounds formed by the transition metal rhenium (Re). Rhenium can form in many oxidation states, and compounds are known for every oxidation state from −3 to +7 except −2, although the oxidation states +7, +4, and +3 are the most common.

Key takeaways

Rhenium compounds belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Rhenium compounds to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rhenium compounds from memory before moving on to harder problems.

Reference excerpt

Rhenium compounds are compounds formed by the transition metal rhenium (Re). Rhenium can form in many oxidation states, and compounds are known for every oxidation state from −3 to +7 except −2, although the oxidation states +7, +4, and +3 are the most common. Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates. These are white, water-soluble compounds. The tetrathioperrhenate anion [ReS4]− is possible.

Chalcogenides

Oxides

Rhenium(IV) oxide (or rhenium dioxide) is an oxide of rhenium, 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. It forms via comproportionation:

2 Re2O7 + 3 Re → 7 ReO2 Single crystals are obtained by chemical transport, using iodine as the transporting agent. At high temperatures it undergoes disproportionation. It forms perrhenates with alkaline hydrogen peroxide and oxidizing acids. In molten sodium hydroxide it forms sodium rhenate. Rhenium(VI) oxide, or rhenium trioxide, is another oxide of rhenium. It is the only stable group 7 trioxide. It has an appearance somewhat like copper. It can be formed by reducing rhenium(VII) oxide with carbon monoxide at 200 °C or elemental rhenium at 400 °C. 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 (ABO3), without the large A cation at the centre of the unit cell. Each rhenium center is surrounded by an octahedron 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. Rhenium(VII) oxide, or rhenium heptoxide, is another oxide of rhenium. It is the anhydride form of perrhenic acid, and is the raw material for all rhenium compounds. 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, consisting of a pair of ReO4 tetrahedra that share a vertex, i.e., O3Re–O–ReO3.

Other chalcogenides Rhenium disulfide is a sulfide with the formula ReS2. It has a layered structure where atoms are strongly bonded within each layer. The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material. It is a two-dimensional (2D) group VII transition metal dichalcogenide (TMD). ReS2 was isolated down to monolayers which is only one unit cell in thickness for the first time in 2014. ReS2 is found in nature as the mineral rheniite. It can be synthesized from the reaction between rhenium and sulfur at 1000 °C, or the decomposition of rhenium(VII) sulfide at 1100 °C:

Re + 2 S → ReS2 Re2S7 → 2 ReS2 + 3 S Rhenium diselenide (ReSe2) also has a layered structure, although, contrary to the other dichalcogenides, rhenium ditelluride does not. In addition, rhenium also forms a heptoxide, which can be produced by the direct reaction of those elements, or through the reaction of ReO4− and H2S in 4N HCl.

Perrhenates

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 isoelectronic permanganate. 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. These salts are prepared by oxidation of rhenium compounds with nitric acid followed by neutralization of the resulting perrhenic acid. Addition of tetrabutylammonium chloride to aqueous solutions of sodium perrhenate gives tetrabutylammonium perrhenate, which is soluble in organic solvents.

Halides Rhenium can form at least four fluorides, of which rhenium heptafluoride is the most common. This is the only thermally stable metal heptafluoride. It has a pentagonal bipyramidal structure similar to IF7, and can be prepared by the direct reaction of the elements at 400 °C. Combining this with additional rhenium metal at 300 °C in a pressure vessel would produce rhenium hexafluoride. It is one of the seventeen known binary hexafluorides. Both of these fluorides have a very low melting point. In addition to this, rhenium also forms a pentafluoride, which form yellow-green crystals, and a tetrafluoride, which forms blue crystals. The most common rhenium chlorides are ReCl6, ReCl5, ReCl4, and ReCl3. Unlike fluorine, chlorine cannot oxidize rhenium past +V; the hexachloride is made from the hexafluoride and the heptachloride is entirely unknown. Rhenium(III) chloride (ReCl3 or sometimes written as Re3Cl9), is a dark-red hygroscopic solid, prepared from rhenium(V) chloride and insoluble in ordinary solvents. Historically, the trichloride is one of the earliest cluster compounds with recognizable metal-metal multiple bonds. Indeed, all the chlorides feature extensive Re-Re bonding, which appears characteristic of rhenium in oxidation states lower than VII. Salts of [Re2Cl8]2− feature a quadruple metal-metal bond. The metal-metal bonds and antibonds lie close to the Fermi level in many dinuclear chlororhenate complexes; both oxidized and reduced derivatives with lesser bond order (some of them mixed-valence) are known. Rhenium(III) bromide also adopts the same structure, and is a black lustrous crystalline solid. It can be obtained by the direct reaction between rhenium metal and bromine at 500 °C under nitrogen:

6 Re + 9 Br2 → 2 Re3Br9 Rhenium also forms two iodides, rhenium tetraiodide, which can be reduced from perrhenic acid with hydrogen iodide, and rhenium triiodide, which forms from the decomposition of this. Like tungsten and molybdenum, with which it shares chemical similarities, rhenium forms a variety of oxyhalides. The oxychlorides are most common, and include ReOCl4, ReOCl3.

Organometallic compounds

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Rhenium compounds

Start with the simplest possible case. Write down what Rhenium compounds claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Rhenium compounds before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Rhenium compounds ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Rhenium compounds

In research: Rhenium compounds appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Rhenium compounds in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Rhenium compounds is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical compounds by element, Rhenium compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Rhenium compounds outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Rhenium compounds in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rhenium compounds means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Rhenium compounds out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rhenium compounds in simple terms?

Why does Rhenium compounds matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Rhenium compounds?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Rhenium compounds.