chemistry

Trimethylindium

Trimethylindium 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 Trimethylindium rather than just read about it. In short: Trimethylindium, often abbreviated to TMI or TMIn, is the organoindium compound with the formula In(CH3)3. It is a colorless, pyrophoric solid.

Key takeaways

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

Reference excerpt

Trimethylindium, often abbreviated to TMI or TMIn, is the organoindium compound with the formula In(CH3)3. It is a colorless, pyrophoric solid. Unlike trimethylaluminium, but akin to trimethylgallium, TMI is monomeric.

Preparation TMI is prepared by the reaction of indium trichloride with methyl lithium.

InCl3 + 3 LiMe → Me3In.OEt2 + 3 LiCl

Properties Compared to trimethylaluminium and trimethylgallium, InMe3 is a weaker Lewis acid. It forms adducts with secondary amines and phosphines. A complex with the heterocyclic triazine ligand (PriNCH2)3 forms a complex with 6-coordinate In, where the C-In-C angles are 114°-117° with three long bonds to the tridentate ligand with N-In-N angles of 48.6° and long In-N bonds of 278 pm.

Structure In the gaseous state InMe3 is monomeric, with a trigonal planar structure, and in benzene solution it is tetrameric. In the solid state there are two polymorphs, a tetragonal phase which is obtained, for example, by sublimation and a lower density rhombohedral phase discovered in 2005, when InMe3 re-crystallised from hexane solution. In the tetragonal form InMe3 is tetrameric as in benzene solution and there is bridging between tetramers to give an infinite network. Each indium atom is five coordinate, in a distorted trigonal planar configuration, the three shortest bonds (ca. 216 pm) are those in the equatorial plane, with longer axial bonds, 308 pm for the In-C bonds joining the InMe3 units to form the tetramers and 356 pm for the In-C linking the tetramers into an infinite network. The solid state structures of GaMe3 and TlMe3 are similar. The association in the solid state accounts for the high melting point of 89°–89.8 °C compared to triethylindium which melts at −32 °C. The rhombohedral form of InMe3 consists of cyclic hexamers with 12 membered (InC)6 rings in an extended chair conformation. The hexamers are interlinked into an infinite network. Indium atoms are five coordinate the equatorial In-C distances average 216.7pm almost identical to the average for the tetragonal form, and the axial bonds are 302.8pm joining the InMe3 units into hexamers and 313.4 pm linking the hexamers to form the infinite network.

Application to microelectronics Indium is a component of several compound semiconductors, including as InP, InAs, InN, InSb, GaInAs, InGaN, AlGaInP, AlInP, and AlInGaNP. These materials are prepared by metalorganic vapour phase epitaxy (MOVPE) and TMI is the preferred source for the indium component. High purity in TMI (99.9999% pure or greater) is essential for many of these applications. For some materials, electron mobilities are observed as high as 287,000 cm²/Vs at 77 K and 5400 cm²/Vs at 300 K, and background carrier concentration as low as 6×1013 cm−3.

Vapor pressure equation The vapor pressure equation log P (Torr) = 10.98–3204/T (K) describes TMI within a wide range of MOVPE growth conditions.

Safety TMI is pyrophoric.

References

External links Interesting research notes by Linus Pauling in re: Trimethylindium and its structure; Notebook # 19, Page 049, August 1955. Interactive Vapor Pressure Chart for metalorganics.

Illustrations

Worked examples

Example 1 — a first encounter with Trimethylindium

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

In research: Trimethylindium 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 Trimethylindium 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: Trimethylindium is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical vapour deposition precursors, Indium compounds, Methyl complexes, so understanding it makes those chapters shorter.
In everyday life: Look for Trimethylindium 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 Trimethylindium in 20 minutes

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

Frequently asked questions

What is Trimethylindium in simple terms?

Trimethylindium, often abbreviated to TMI or TMIn, is the organoindium compound with the formula In(CH3)3. It is a colorless, pyrophoric solid.

Why does Trimethylindium 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 Trimethylindium?

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 Trimethylindium.