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23.4C: Gallium, Indium, and Thallium

  • Page ID
    34552
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    Learning Objectives

    In this lecture you will learn the following

    • Chemistry of gallium and indium.
    • How to stabilize M—M multiple bonds.

    Organometallic compounds of gallium and indium

    Trialkylgallium compounds are mild Lewis acids, so the corresponding metathesis reaction in ether produces the complex (C2H5)2OGa(C2H5)3. Similarly excess use of C2H5Li leads to the salt, Li[Ga(C2H5)4].

    Alkylindium and alkylthalium compounds may be prepared similar to gallium analogs. InMe3 is monomeric in the gas phase and in the solid the bond lengths indicate that association is very weak. Partial hydrolysis of TlMe3 yields the linear (MeTiMe]+ion, which is isoelectronic and isostructural with HgMe2.

    CpIn and CoTl exist as monomers in the gas phase but are associated in solids {Inert-pair effect is displayed for In and Tl}. CpTl is useful as a synthetic reagent in organometallic chemistry because it is not as highly reducing as NaCp.

    Species of the type R4E2(single E-E bond) and [R4E2] - (with E-E bond order of 1.5) can be prepared for Ga and In with bulky R groups (R = (Me3Si)2CH, 2,4,6-iPr3C6H2), and reduction of [(2,4,6-iPr3C6H2)4Ga2] to [(2,4,6-iPr3C6H2)4Ga2] - is accompanied by a shortening of the Ga—Ga bond from 252-234 pm.

    Using even bulkier substituents, it is possible to prepare gallium(I) compounds, RGa starting from GaI. No structural data are yet available for these monomers
    (We are working on it).

    Crystallized as dimer but reverts to monomer when dissolved in cyclohexane.

    Interest in organometallic comounds of Ga, In and Tl is mainly because of their potential use as precursors to semiconducting materials such as GaAs and InP. Volatile compounds can be used in the growth of thin films by MOCVD (metal organic chemical vapor deposition) or MOVPE (metal organic vapor phase epitaxy) techniques. Precursors include appropriate Lewis base adducts of metal alkyls, e.g. Me3Ga.NMe3 and Me3In.PEt3. Thermal decomposition of gaseous precursors result in semiconductors (III-V semiconductors) which can be deposited in thin films.

    III-V semiconductors: Derive their name from the old groups 13 and 15, and include AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs and InSb. Off these GaAs is of the greatest commercial interest. Although Si is probably the most important commercial semiconductor, a major advandage of GaAs over Si is that the charge carrier mobility is much greater. This makes GaAs suitable for high-speed electronic devices.

    Another important difference is that GaAs exhibits a fuly allowed electronic transition between valence and conduction bands (i.e. it is direct band gap semiconductor) whereas Si is an indirect band gap semiconductor. The consequence of difference is that GaAs (also other III-V types) are more suited than Si for use in optoelectronic devices, since light is emitted more efficiently. The III-Vs have important applications in light-emitting diodes (LEDs).

    Problems

    1. Predict the structure of monomeric, Cp3Ga; polymeric Cp3In and CpIn.

      Solution:
      See the articles Organometallics 1985, 4, 751.
      Inorg. Chem. 1972, 11, 2832.
      Organometallics 1988, 7, 105.

    2. The reaction of [(R3C)4Ga4] ( R = a bulky substituent) (i) with I2 in boiling hexane results in the formation of [(R3C)GaI]2(ii) and [(R3C)GaI2]2(iii). Draw the structure and state the oxidation state for (i) - (iii).

      Solution:
    3. The I2 oxidation of [(tBu}4In4] leads to the formation of the InII compound [(tBu}4In4I4] in which each indium atom retains a tetrahedral environment. Draw the correct structure.

      Solution:

    Contributors and Attributions

    http://nptel.ac.in/courses/104101006/9


    23.4C: Gallium, Indium, and Thallium is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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