chemistry

Krogmann's salt

Krogmann'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 Krogmann's salt rather than just read about it. In short: Krogmann's salt is a linear chain compound consisting of stacks of tetracyanoplatinate. Sometimes described as molecular wires, Krogmann's salt exhibits highly anisotropic electrical conductivity.

Key takeaways

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

Reference excerpt

Krogmann's salt is a linear chain compound consisting of stacks of tetracyanoplatinate. Sometimes described as molecular wires, Krogmann's salt exhibits highly anisotropic electrical conductivity. For this reason, Krogmann's salt and related materials are of some interest in nanotechnology.

History and nomenclature Krogmann's salt was first synthesized by Klaus Krogmann in the late 1960s. Krogmann's salt most commonly refers to a platinum metal complex of the formula K2[Pt(CN)4X0.3] where X is usually bromine (or sometimes chlorine). Many other non-stoichiometric metal salts containing the anionic complex [Pt(CN)4]n− can also be characterized.

Structure and physical properties

Krogmann's salt is a series of partially oxidized tetracyanoplatinate complexes linked by the platinum-platinum bonds on the top and bottom faces of the planar [Pt(CN)4]n− anions. This salt forms infinite stacks in the solid state based on the overlap of the dz2 orbitals. Krogmann's salt has a tetragonal crystal structure with a Pt-Pt distance of 2.880 angstroms, which is much shorter than the metal-metal bond distances in other planar platinum complexes such as Ca[Pt(CN)4]·5H2O (3.36 angstroms), Sr[Pt(CN)4]·5H2O (3.58 angstroms), and Mg[Pt(CN)4]·7H2O (3.16 angstroms). The Pt-Pt distance in Krogmann's salt is only 0.1 angstroms longer than in platinum metal. Each unit cell contains a site for Cl−, corresponding to 0.5 Cl− per Pt. However, this site is only filled 64% of the time, giving 0.32 Cl− per Pt in the actual compound. Because of this, the oxidation number of Pt does not rise above +2.32. Krogmann's salt has no recognizable phase range and is characterized by broad and intense intervalence bands in its electronic spectra.

Chemical properties One of the most widely researched properties of Krogmann's salt is its unusual electric conductance. Because of its linear chain structure and overlap of the platinum d z 2 {\displaystyle d_{z^{2}}} orbitals, Krogmann's salt is an excellent conductor of electricity. This property makes it an attractive material for nanotechnology.

Preparation The usual preparation of Krogmann's salt involves the evaporation of a 5:1 molar ratio mixture of the salts K2[Pt(CN)4] and K2[Pt(CN)4Br2] in water to give copper-colored needles of K2[Pt(CN)4]Br0.32·2.6 H2O.

5K2[Pt(CN)4] + K2[Pt(CN)4Br2] + 15.6 H2O → 6K2[Pt(CN)4]Br0.32·2.6 H2O Because excess PtII or PtIV complex crystallizes out with the product when the reactant ratio is changed, the product is therefore well defined, although non-stoichiometric.

Uses Krogmann's salt nor any related material has found any commercial applications.

References

Worked examples

Example 1 — a first encounter with Krogmann's salt

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

In research: Krogmann'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 Krogmann'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: Krogmann's salt is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical compounds containing metal–metal bonds, Cyanides, Electrical conductors, so understanding it makes those chapters shorter.
In everyday life: Look for Krogmann'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 Krogmann's salt in 20 minutes

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

Frequently asked questions

What is Krogmann's salt in simple terms?

Krogmann's salt is a linear chain compound consisting of stacks of tetracyanoplatinate. Sometimes described as molecular wires, Krogmann's salt exhibits highly anisotropic electrical conductivity.

Why does Krogmann'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 Krogmann'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 Krogmann's salt.