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

pyrophoric A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...

solid. Unlike

trimethylaluminium Trimethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( CH3)6 (abbreviated as Al2Me6 or TMA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industriall ...

, but akin to

trimethylgallium Trimethylgallium, often abbreviated to TMG or TMGa, is the organogallium compound with the formula Ga(CH3)3. It is a colorless, pyrophoric liquid. Unlike trimethylaluminium, TMG adopts a monomeric structure. When examined in detail, the monomeric ...

, TMI is monomeric.

Preparation

TMI is prepared by the reaction of

indium trichloride Indium(III) chloride is the chemical compound with the formula Indium, InChlorine, Cl3. This salt (chemistry), salt is a white, flaky solid with applications in organic synthesis as a Lewis acid. It is also the most available soluble derivative ...

with

methyl lithium Methyllithium is the simplest organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in s ...

. : InCl₃ + 3LiMe → Me₃In^.OEt₂ + 3LiCl

Properties

Compared to

and

, InMe₃ is a weaker

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

. It forms adducts with secondary

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

s and

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

s. A complex with the heterocyclic

triazine Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common. Structure The triazines have planar six-membered benzene-like ring but ...

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 Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

solution it is tetrameric.''CVD of compound semiconductors, Precursor Synthesis, Development and Applications'', Anthony C. Jones, Paul O'Brien, John Wiley & Sons, 2008, 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 Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...

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.''Inorganic Chemistry'', (2d edition), Catherine E. Housecroft, Alan G. Sharpe, Pearson Education, 2005, , 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 In organic chemistry, cyclohexane conformations are any of several three-dimensional shapes adopted by molecules of cyclohexane. Because many compounds feature structurally similar six-membered rings, the structure and dynamics of cyclohexane are ...

. 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 semiconductor Semiconductor materials are nominally small band gap insulators. The defining property of a semiconductor material is that it can be compromised by doping it with impurities that alter its electronic properties in a controllable way. Because of ...

s, including as InP, InAs,

InN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they also provided accommo ...

InSb Indium antimonide (InSb) is a crystalline compound made from the elements indium (In) and antimony (Sb). It is a narrow- gap semiconductor material from the III- V group used in infrared detectors, including thermal imaging cameras, FLIR systems, ...

GaInAs Gainas (Greek: Γαϊνάς) was a Gothic leader who served the Eastern Roman Empire as ''magister militum'' during the reigns of Theodosius I and Arcadius. Gainas began his military career as a common foot-soldier, but later commanded the bar ...

InGaN Indium gallium nitride (InGaN, ) is a semiconductor material made of a mix of gallium nitride (GaN) and indium nitride (InN). It is a ternary group III/group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of in ...

AlGaInP Aluminium gallium indium phosphide (, also AlInGaP, InGaAlP, GaInP, etc.) is a semiconductor material that provides a platform for the development of novel multi-junction photovoltaics and optoelectronic devices, as it spans a direct bandgap fro ...

, AlInP, and AlInGaNP. These materials are prepared by

metalorganic vapour phase epitaxy Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...

(

MOVPE Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...

) and TMI is the preferred source for the

indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts p ...

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 Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases ...

equation log P (Torr) = 10.98–3204/T (K) describes TMI within a wide range of

growth conditions.

Safety

TMI is

.Chemistry of Materials (2000);

References

External links

Interesting research notes
by

Linus Pauling Linus Carl Pauling (; February 28, 1901August 19, 1994) was an American chemist, biochemist, chemical engineer, peace activist, author, and educator. He published more than 1,200 papers and books, of which about 850 dealt with scientific top ...

in re: Trimethylindium and its structure; ''Notebook # 19, Page 049'', August 1955.
Interactive Vapor Pressure Chart for metalorganics
{{Indium compounds Chemical vapour deposition precursors Indium compounds Methyl complexes