chemistry

Roussin's red salt

Roussin's red salt 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 Roussin's red salt rather than just read about it. In short: Roussin's red salt is the inorganic compound with the formula K2[Fe2S2(NO)4]. This metal nitrosyl was first described by Zacharie Roussin in 1858, making it one of the first synthetic iron-sulfur clusters.

Key takeaways

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

Reference excerpt

Roussin's red salt is the inorganic compound with the formula K2[Fe2S2(NO)4]. This metal nitrosyl was first described by Zacharie Roussin in 1858, making it one of the first synthetic iron-sulfur clusters.

Structure and bonding Roussin's red salt anion is an edge-shared bitetrahedron, wherein a pair Fe(NO)2 units are bridged by a pair of sulfide ligands. The Fe-NO bonds are linear indicating NO is acting as a three electron donor. The diamagnetic compound obeys the 18-electron rule. The dark red colour of the complex is attributed to a number of charge-transfer interactions between the iron core and nitrosyl ligands.

Synthesis

The French chemist Z. Roussin first prepared this salt while investigating reactions between nitroprusside ion ([Fe(CN)5NO]2−) and sulfur. The salt can be prepared by the reaction of sulfide salts with iron nitrosyl halides:

Fe2I2(NO)4 + 2 Li2S → Li2Fe2S2(NO)4 + 2 LiI Another way to obtain Roussin's red salt is to alkalize a solution of the related compound Roussin's black salt, K[Fe4S3(NO)7], using a suitable base:

2 K[Fe4S3(NO)7] + 4 KOH → 3 K2[Fe2S2(NO)4] + 2 Fe(OH)2 + 2 NO Another obtaining procedure consists of reacting sodium (or potassium) nitrite, ascorbic acid, ferrous sulfate, sodium sulfide and sodium (or potassium) hydroxide in this order. Ascorbic acid works both as an acidulant and as a reducing agent, converting nitrite into nitrous acid and then reducing it to nitrogen monoxide, which will then bind to iron ions forming nitrosyl complexes, which will react with sulfide in a basic medium giving Roussin's red salt.

2 FeSO4 + 4 HNO2 + 3 C6H8O6 + 2 Na2S + 2 NaOH → Na2[Fe2S2(NO)4] + 3 C6H6O6 + 2 Na2SO4 + 6 H2O

To obtain the "esters", the salt is alkylated:

Li2Fe2S2(NO)4 + 2 RX → Fe2(SR)2(NO)4 + 2 LiX Esters can also be easily be prepared from the reaction of Fe2I2(NO)4 with the thiol or thiosulfate.

Occurrence and potential applications It is found in nature as its "esters" with the formula Fe2(SR)2(NO)4, where "R" is any alkyl group. In addition Roussin's red salt is discussed in the fields of microbiology and food science due to its mutagenic properties. The ester derivative are being investigated as nitric oxide donors in biology and medicine, due to the relatively low toxicity and good stability of Roussin's red salt.Photodissociation of the compound induces the release of NO, thereby sensitizing target cells to exposure to radiation.

Illustrations

Worked examples

Example 1 — a first encounter with Roussin's red salt

Start with the simplest possible case. Write down what Roussin's red salt 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 Roussin's red salt 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 Roussin's red salt 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 Roussin's red salt

In research: Roussin's red salt 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 Roussin's red salt 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: Roussin's red salt is common in secondary-school and first-year university syllabi. It links to neighbouring topics Iron complexes, Nitrosyl complexes, Sulfur compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Roussin's red salt 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Roussin's red salt” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Roussin's red salt in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Roussin's red salt 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 Roussin's red salt out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Roussin's red salt in simple terms?

Why does Roussin's red salt 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 Roussin's red salt?

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 Roussin's red salt.