Gallium trichloride

Gallium trichloride

Names
Other names Gallium(III) chloride, Trichlorogallium, Trichlorogallane
Identifiers
CAS Number	13450-90-3
ChemSpider	24229
Jmol interactive 3D	Image
PubChem	26010
RTECS number	LW9100000
UNII	4Y6GQD4915
InChI InChI=1S/3ClH.Ga/h3*1H;/q;;;+3/p-3 Key: UPWPDUACHOATKO-UHFFFAOYSA-K InChI=1/3ClH.Ga/h3*1H;/q;;;+3/p-3 Key: UPWPDUACHOATKO-DFZHHIFOAO
SMILES Cl[Ga](Cl)Cl
Properties
Chemical formula	Cl3Ga
Molar mass	176.07 g·mol^−1
Appearance	colorless crystals deliquescent
Density	2.47 g/cm^3 2.053 g/cm^3 at melting point
Melting point	77.9 °C (172.2 °F; 351.0 K) (anhydrous) 44.4 °C (hydrate)
Boiling point	201 °C (394 °F; 474 K)
Solubility in water	very soluble
Solubility	soluble in benzene, CCl4, CS2
Hazards
NFPA 704	0 3 1
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	4700 mg/kg (rat, oral)
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).
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Infobox references

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, even alkanes, which is truly 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 high 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:

• GaCl₃ is a weaker Lewis acid than AlCl₃ towards N and O donors e.g. pyridine
• GaCl₃ is a stronger Lewis acid than AlCl₃ towards thioethers e.g. dimethyl sulfide, Me₂S

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⁻ $\overrightarrow{\leftarrow}$ Ga₂Cl₇⁻ + Cl⁻

Use in detection of solar neutrinos

110 tons of gallium trichloride aqueous solution was used in the GALLEX and GNO experiments performed at Laboratori Nazionali del Gran Sasso in Italy to detect solar neutrinos. In these experiments, germanium-71 was produced by neutrino interactions with the isotope gallium-71 (which has a natural abundance of 40%), and the subsequent beta decays of germanium-71 were measured.^[7]

See also

• Gallium halides

References

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
• "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.

External links

• "Emergency First Aid Treatment Guide - Gallium Trichloride". United States Environmental Protection Agency.