chemistry

Zeise's salt

Zeise's 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 Zeise's salt rather than just read about it. In short: Zeise's salt, potassium trichloro(ethylene)platinate(II) hydrate, is the chemical compound with the formula K[PtCl3(C2H4)]·H2O. The anion of this air-stable, yellow, coordination complex contains a ethylene as a ligand bound to the Pt.

Key takeaways

Zeise's 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 Zeise's salt to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Zeise's salt from memory before moving on to harder problems.

Reference excerpt

Zeise's salt, potassium trichloro(ethylene)platinate(II) hydrate, is the chemical compound with the formula K[PtCl3(C2H4)]·H2O. The anion of this air-stable, yellow, coordination complex contains a ethylene as a ligand bound to the Pt. The salt is of historical importance in the area of organometallic chemistry as one of the first examples of a transition metal alkene complex and is named for its discoverer, William Christopher Zeise.

Preparation This compound was originally prepared by Zeise by heating mixtures of platinum chlorides and potassium chloride in ethanol. Under suitable conditions, the ethanol converts to sufficient ethylene to allow the formation of the salt. The hydrate can be more readily prepared by treating a solution of K2[PtCl4] and ethylene with a catalytic amount of SnCl2. The water of hydration can be removed in vacuo. Zeise's salt is commercially available as a hydrate.

Structure The anion is the component of this salt that is of interest. In the anion Pt is bound to (or "coordinated to") four ligands: three chlorides (Cl-) and ethylene (C2H4). The PtCl3 group is nearly planar and bisects the C=C bond of the ethylene ligand, which is oriented in a perpendicular manner. Both carbons of the ethylene are bonded to Pt, an interaction described as η2. The Pt-Cl bond trans to ethylene is 234 pm in length, while the other two Pt-Cl bonds are near 230 pm. In Zeise's salt and related compounds, the alkene rotates about the metal-alkene bond with a modest activation energy. Analysis of the barrier heights indicates that the π-bonding between most metals and the alkene is weaker than the σ-bonding.

History Zeise's salt was one of the first organometallic compounds to be reported. It was discovered by William Christopher Zeise, a professor at the University of Copenhagen, who prepared this compound in 1830 while investigating the reaction of PtCl4 with boiling ethanol. Following careful analysis he proposed that the resulting compound contained ethylene. Justus von Liebig, a highly influential chemist of that era, often criticised Zeise's proposal, but Zeise's proposal was decisively supported in 1868 when Birnbaum prepared the complex using ethylene. Zeise's salt received a great deal of attention during the second half of the 19th century because chemists could not explain its molecular structure. This question remained unanswered until the determination of its X-ray crystal structure in the 20th century. Zeise's salt stimulated much scientific research in the field of organometallic chemistry and would be key in defining new concepts in chemistry.

Related compounds Zeise's dimer, [(η2-C2H4)PtCl2]2, derived from Zeise's salt by elimination of KCl followed by dimerisation. COD-platinum dichloride, (cyclooctadiene)PtCl2, derived from platinum(II) chloride and 1,5-cyclooctadiene, is a common platinum(II) alkene complex. Many other ethylene complexes have been prepared. For example, ethylenebis(triphenylphosphine)platinum(0), [(C6H5)3P]2Pt(H2C=CH2), wherein the platinum is three-coordinate and in oxidation state 0 (Zeise's salt is a derivative of platinum(II)).

Dichloro(ethylene)(α-methylbenzylamine)platinum(II) (PtCl2(C2H4)(PhCH(NH2)Me) is a chiral derivative of Zeise's salt that is used for the chiral resolution of alkenes.

References

Illustrations

Worked examples

Example 1 — a first encounter with Zeise's salt

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

In research: Zeise's 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 Zeise's 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: Zeise's salt is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkene complexes, Chlorides, Chloro complexes, so understanding it makes those chapters shorter.
In everyday life: Look for Zeise's 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.

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How to study Zeise's salt in 20 minutes

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

Frequently asked questions

What is Zeise's salt in simple terms?

Why does Zeise's 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 Zeise's 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 Zeise's salt.