chemistry

Pentacyanocobaltate

Pentacyanocobaltate 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 Pentacyanocobaltate rather than just read about it. In short: In chemistry, pentacyanocobaltate is the coordination complex with the formula [Co(CN)5]3−. When crystallized with a quaternary ammonium cation, it can be obtained as a yellow solid.

Key takeaways

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

Reference excerpt

In chemistry, pentacyanocobaltate is the coordination complex with the formula [Co(CN)5]3−. When crystallized with a quaternary ammonium cation, it can be obtained as a yellow solid. Pentacyanocobaltate attracted attention as an early example of a metal complex that reacts with hydrogen. It contains low-spin cobalt(II), with a doublet ground state.

Synthesis and structure Aqueous solutions of pentacyanocobaltate are produced by the addition of five or more equivalents of a cyanide salt to a solution of a cobalt(II) salt. Initially this reaction produces insoluble cobalt dicyanide, but this solid dissolves in the presence of the excess cyanide. Pentacyanocobaltate forms within seconds. When prepared using a quaternary ammonium (quat) cyanide, crystals can be obtained with the formula (quat)3[Co(CN)5]. According to X-ray crystallography, the salt features square pyamidal [Co(CN)5]3−.

Reactions Solutions of [Co(CN)5]3− undergo a variety of reactions. The complex attracted attention in the 1940s for its reactivity toward hydrogen, which is now understood to produce a cobalt hydride:

2[Co(CN)5]3− + H2 → 2 [Co(CN)5H]2− When allowed to stand as a dilute solution for several minutes, the complex reacts with water to give two Co(III) derivatives:

2[Co(CN)5]3− + H2O → [Co(CN)5H]3− + [Co(CN)5OH]3− In concentrated solution, the complex dimerizes:

2[Co(CN)5]3− → [(NC)5Co−Co(CN)5]6− These complexes catalyze the selective reduction of conjugated dienes, probably through an allyl intermediate. With benzyl chloride and related alkylating agents, Co(III) alkyls are formed:

2[Co(CN)5]3− + C6H5CH2Cl → [Co(CN)5CH2C6H5]3− + [Co(CN)5Cl]3−

References

Illustrations

Worked examples

Example 1 — a first encounter with Pentacyanocobaltate

Start with the simplest possible case. Write down what Pentacyanocobaltate 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 Pentacyanocobaltate 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 Pentacyanocobaltate 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 Pentacyanocobaltate

In research: Pentacyanocobaltate 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 Pentacyanocobaltate 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: Pentacyanocobaltate is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anions, Cobalt(II) compounds, Cobalt complexes, so understanding it makes those chapters shorter.
In everyday life: Look for Pentacyanocobaltate 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 “Pentacyanocobaltate” →

Affiliate

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

How to study Pentacyanocobaltate in 20 minutes

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

Frequently asked questions

What is Pentacyanocobaltate in simple terms?

In chemistry, pentacyanocobaltate is the coordination complex with the formula [Co(CN)5]3−. When crystallized with a quaternary ammonium cation, it can be obtained as a yellow solid.

Why does Pentacyanocobaltate 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 Pentacyanocobaltate?

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 Pentacyanocobaltate.