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Gallium(III) chloride

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Gallium(III) chloride
Names
Other names
Gallium(III) chloride, Trichlorogallium, Trichlorogallane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.033.268 Edit this at Wikidata
RTECS number
  • LW9100000
UNII
  • InChI=1S/3ClH.Ga/h3*1H;/q;;;+3/p-3 checkY
    Key: UPWPDUACHOATKO-UHFFFAOYSA-K checkY
  • InChI=1/3ClH.Ga/h3*1H;/q;;;+3/p-3
    Key: UPWPDUACHOATKO-DFZHHIFOAO
  • Cl[Ga](Cl)Cl
Properties
GaCl3
Appearance colorless crystals
Density 2.47 g/cm3
2.053 g/cm3 at melting point
Melting point 77.9 °C (172.2 °F; 351.0 K)
Boiling point 201 °C (394 °F; 474 K)
very soluble
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
3
0
1
Flash point Non-flammable
Related compounds
Other anions
 Gallium(III) fluoride
Gallium(III) bromide
Gallium(III) iodide
Other cations
 Aluminium chloride
Indium(III) chloride
Thallium(III) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Gallium trichloride is the chemical compound with the formula GaCl3. Solid gallium trichloride exists as a dimer with the formula Ga2Cl6.[1] It is colourless and soluble in virtually all solvents, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium and a reagent in organic synthesis.[2]

As a Lewis acid, GaCl3 is milder than aluminium trichloride. Gallium(III) is easier to reduce than Al(III), so the chemistry of reduced gallium compounds is more extensive than for aluminium. Ga2Cl4 is known whereas the corresponding Al2Cl4 is not. The coordination chemistry of Ga(III) and Fe(III) are similar, and gallium(III) compounds have been used as diamagnetic analogues of ferric compounds.

Preparation

Gallium trichloride can be prepared from the elements, heating gallium metal in a stream of chlorine, and purifying the product by sublimation under vacuum.[3][4]

2 Ga + 3 Cl2 → 2 GaCl3

It can also be prepared from the gallium oxide by heating with thionyl chloride:[5]

Ga2O3 + 3 SOCl2 → 2 GaCl3 + 3 SO2

Structure

The dimeric structure involving two chlorine bridging atoms with the gallium atoms essentially tetrahedrally coordinated by chlorine is surprising, as the chlorides of the two members of group 13 above and below gallium, AlCl3 and InCl3 both contain 6 coordinate metal atoms in a three dimensional structure. As a consequence of its structure where there are no significant lattice forces, gallium trichloride has the lowest melting point of all of the aluminium, gallium and indium trihalides. The formula of Ga2Cl6 is often written as Ga2(μ-Cl)2Cl4. In the gas phase the dimers dissociate to trigonal planar monomers.

Complexes

Gallium is the lightest member of Group 13 to have a full d shell, (gallium has the electronic configuration Ar 3d10 4s2 4p1) below the valence electrons that could take part in d-π bonding with ligands. The low oxidation state of Ga in Ga(III)Cl3, along with the low electronegativity and hight polarisability, allow Ga(III)Cl3 to behave as a "Soft Acid" in terms of the HSAB theory. The strength of the bonds between gallium halides and ligands have been extensively studied. What emerges is:

With a chloride ion as ligand the tetrahedral GaCl4− ion is produced, the 6 coordinate GaCl63− cannot be made. Compounds like KGa2Cl7 that have a chloride bridged anion are known[6] In a molten mixture of KCl and GaCl3, the following equilibrium exists:

2 GaCl4− Ga2Cl7− + Cl−

Use in detection of solar neutrinos

110 tons of gallium trichloride solution was used in the GALLEX experiment performed by Laboratori Nazionali del Gran Sasso in Italy to detect solar neutrinos. In this experiment, isotope germanium-71 was produced and its decay measured.[7]

See also

References

  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  • "Gallium". WebElements Periodic Table.
  1. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  2. ^ Yamaguchi, M.; Shibasaki, M. Gallium Trichloride" in Encyclopedia of Reagents for Organic Synthesis 2005; John Wiley & Sons. doi:10.1002/047084289X.rn00118u
  3. ^ S.C. Wallwork I.J.Worral J.Chem. Soc 1965,1816
  4. ^ Kovar, R. A. "Gallium Trichloride" Inorganic Syntheses, 1977, volume XVII, pp 167-172. ISBN 0-07-044327-0
  5. ^ H.Hecht, G.Jander, H.Schlapmann Z. Anorg. Allgem. Chem. Vol.254, p.255 (1947)
  6. ^ J H von Barner Inorg Chem 1985 24 1686
  7. ^ David R. Lide, ed. Handbook of Chemistry and Physics, 85th Edition, Internet Version 2005. CRC Press, 2005.
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