chemistry

Iron(III) fluoride

Iron(III) fluoride 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 Iron(III) fluoride rather than just read about it. In short: Iron(III) fluoride, also known as ferric fluoride, are inorganic compounds with the formula FeF3(H2O)x where x = 0 or 3. They are mainly of interest by researchers, unlike the related iron(III) chloride.

Key takeaways

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

Reference excerpt

Iron(III) fluoride, also known as ferric fluoride, are inorganic compounds with the formula FeF3(H2O)x where x = 0 or 3. They are mainly of interest by researchers, unlike the related iron(III) chloride. Anhydrous iron(III) fluoride is white, whereas the hydrated forms are light pink.

Chemical and physical properties Iron(III) fluoride is a thermally robust, antiferromagnetic solid consisting of high spin Fe(III) centers, which is consistent with the pale colors of all forms of this material. Both anhydrous iron(III) fluoride as well as its hydrates are hygroscopic.

Structure The anhydrous form adopts a simple structure with octahedral Fe(III)F6 centres interconnected by linear Fe-F-Fe linkages. In the language of crystallography, the crystals are classified as rhombohedral with an R-3c space group. The structural motif is similar to that seen in ReO3. Although the solid is nonvolatile, it evaporates at high temperatures, the gas at 987 °C consists of FeF3, a planar molecule of D3h symmetry with three equal Fe-F bonds, each of length 176.3 pm. At very high temperatures, it decomposes to give FeF2 and F2. Two crystalline forms—or more technically, polymorphs—of FeF3·3H2O are known, the α and β forms. These are prepared by evaporation of an HF solution containing Fe3+ at room temperature (α form) and above 50 °C (β form). The space group of the β form is P4/m, and the α form maintains a P4/m space group with a J6 substructure. The solid α form is unstable and converts to the β form within days. The two forms are distinguished by their difference in quadrupole splitting from their Mössbauer spectra.

Preparation, occurrence, reactions Anhydrous iron(III) fluoride is prepared by treating virtually any anhydrous iron compound with fluorine. More practically and like most metal fluorides, it is prepared by treating the corresponding chloride with hydrogen fluoride:

FeCl3 + 3 HF → FeF3 + 3 HCl It also forms as a passivating film upon contact between iron (and steel) and hydrogen fluoride. The hydrates crystallize from aqueous hydrofluoric acid. The material is a fluoride acceptor. With xenon hexafluoride it forms [XeF5]+[FeF4]−. Pure FeF3 is not yet known among minerals. However, hydrated form is known as the very rare fumarolic mineral topsøeite. Generally a trihydrate, its chemistry is slightly more complex: FeF[F0.5(H2O)0.5]4·H2O.

Applications The primary commercial use of iron(III) fluoride in the production of ceramics. Some cross coupling reaction are catalyzed by ferric fluoride-based compounds. Specifically the coupling of biaryl compounds are catalyzed by hydrated iron(II) fluoride complexes of N-heterocyclic carbene ligands. Other metal fluorides also catalyse similar reactions. Iron(III) fluoride has also been shown to catalyze chemoselective addition of cyanide to aldehydes to give the cyanohydrins.

Safety The anhydrous material is a powerful dehydrating agent. The formation of ferric fluoride may have been responsible for the explosion of a cylinder of hydrogen fluoride gas.

References

External links

National Pollutant Inventory—Fluoride and compounds fact sheet CAMEO Chemicals: Database of Hazardous Materials

Illustrations

Worked examples

Example 1 — a first encounter with Iron(III) fluoride

Start with the simplest possible case. Write down what Iron(III) fluoride 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 Iron(III) fluoride 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 Iron(III) fluoride 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 Iron(III) fluoride

In research: Iron(III) fluoride 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 Iron(III) fluoride 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: Iron(III) fluoride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fluorides, Iron(III) compounds, Metal halides, so understanding it makes those chapters shorter.
In everyday life: Look for Iron(III) fluoride 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 Iron(III) fluoride in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Iron(III) fluoride 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 Iron(III) fluoride out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Iron(III) fluoride in simple terms?

Why does Iron(III) fluoride 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 Iron(III) fluoride?

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 Iron(III) fluoride.