physics

Inner sphere electron transfer

Inner sphere electron transfer is a physics 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 Inner sphere electron transfer rather than just read about it. In short: Inner sphere electron transfer (IS ET) or bonded electron transfer is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants. In inner sphere electron transfer, a ligand bridges the two metal redox centers during the electron transfer event.

Key takeaways

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

Reference excerpt

Inner sphere electron transfer (IS ET) or bonded electron transfer is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants. In inner sphere electron transfer, a ligand bridges the two metal redox centers during the electron transfer event. Inner sphere reactions are inhibited by large ligands, which prevent the formation of the crucial bridged intermediate. Thus, inner sphere ET is rare in biological systems, where redox sites are often shielded by bulky proteins. Inner sphere ET is usually used to describe reactions involving transition metal complexes and most of this article is written from this perspective. However, redox centers can consist of organic groups rather than metal centers. The bridging ligand could be virtually any entity that can convey electrons. Typically, such a ligand has more than one lone electron pair, such that it can serve as an electron donor to both the reductant and the oxidant. Common bridging ligands include the halides and the pseudohalides such as hydroxide and thiocyanate. More complex bridging ligands are also well known including oxalate, malonate, and pyrazine. Prior to ET, the bridged complex must form, and such processes are often highly reversible. Electron transfer occurs through the bridge once it is established. In some cases, the stable bridged structure may exist in the ground state; in other cases, the bridged structure may be a transiently-formed intermediate, or else as a transition state during the reaction. The alternative to inner sphere electron transfer is outer sphere electron transfer. In any transition metal redox process, the mechanism can be assumed to be outer sphere unless the conditions of the inner sphere are met. Inner sphere electron transfer is generally enthalpically more favorable than outer sphere electron transfer due to a larger degree of interaction between the metal centers involved, however, inner sphere electron transfer is usually entropically less favorable since the two sites involved must become more ordered (come together via a bridge) than in outer sphere electron transfer.

Taube's experiment The discoverer of the inner sphere mechanism was Henry Taube, who was awarded the Nobel Prize in Chemistry in 1983 for his pioneering studies. A particularly historic finding is summarized in the abstract of the seminal publication.

"When Co(NH3)5Cl++ is reduced by Cr++ in M [meaning 1 M] HClO4, 1 Cl− appears attached to Cr for each Cr(III) which is formed or Co(III) reduced. When the reaction is carried on in a medium containing radioactive Cl, the mixing of the Cl− attached to Cr(III) with that in solution is less than 0.5%. This experiment shows that transfer of Cl to the reducing agent from the oxidizing agent is direct…" The paper and the excerpt above can be described with the following equation:

[CoCl(NH3)5]2+ + [Cr(H2O)6]2+ → [Co(NH3)5(H2O)]2+ + [CrCl(H2O)5]2+ The point of interest is that the chloride that was originally bonded to the cobalt, the oxidant, becomes bonded to chromium, which in its +3 oxidation state, forms kinetically inert bonds to its ligands. This observation implies the intermediacy of the bimetallic complex [Co(NH3)5(μ-Cl)Cr(H2O)5]4+, wherein "μ-Cl" indicates that the chloride bridges between the Cr and Co atoms, serving as a ligand for both. This chloride serves as a conduit for electron flow from Cr(II) to Co(III), forming Cr(III) and Co(II).

See also Inner sphere complex Outer sphere electron transfer Solvated electron

References

Worked examples

Example 1 — a first encounter with Inner sphere electron transfer

Start with the simplest possible case. Write down what Inner sphere electron transfer claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Inner sphere electron transfer 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 Inner sphere electron transfer 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 Inner sphere electron transfer

In research: Inner sphere electron transfer appears in physics 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 Inner sphere electron transfer 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: Inner sphere electron transfer is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electron, Physical chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Inner sphere electron transfer 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 Inner sphere electron transfer in 20 minutes

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

Frequently asked questions

What is Inner sphere electron transfer in simple terms?

Why does Inner sphere electron transfer matter?

Because it connects several physics 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 Inner sphere electron transfer?

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 Inner sphere electron transfer.