Gallium(III) bromide

Gallium(III) bromide (GaBr₃) is a chemical compound, and one of four gallium trihalides.

Gallium(III) bromide (dimer)

Names
Other names gallium tribromide
Identifiers
CAS Number	13450-88-9 Y
3D model (JSmol)	Interactive image
ChemSpider	75315 Y
ECHA InfoCard	100.033.267
EC Number	236-609-5
PubChem CID	83477
CompTox Dashboard (EPA)	DTXSID2065466
InChI InChI=1S/3BrH.Ga/h3*1H;/q;;;+3/p-3 Y Key: SRVXDMYFQIODQI-UHFFFAOYSA-K Y InChI=1/3BrH.Ga/h3*1H;/q;;;+3/p-3 Key: SRVXDMYFQIODQI-DFZHHIFOAJ
SMILES Br[Ga](Br)Br
Properties
Chemical formula	GaBr3
Molar mass	309.435 g/mol
Appearance	white powder
Density	3.69 g/cm3
Melting point	121.5 °C (250.7 °F; 394.6 K)
Boiling point	278.8 °C (533.8 °F; 552.0 K)
Solubility in water	soluble
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
NFPA 704 (fire diamond)	4 0 0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Introduction

Gallium(III) bromide is, at room temperature and atmospheric pressure, a white, crystalline powder which reacts favorably and exothermically with water.^[1] Solid gallium tribromide is stable at room temperature and can be found primarily in its dimeric form.^[2] GaBr₃ can form an intermediate halide, Ga₂Br_7; however, this is not as common as with GaCl₃. It is a member of the gallium trihalide group and is similar to GaCl₃, and GaI₃, but not GaF₃, in its preparation and uses.^[2] GaBr₃ is a milder Lewis acid than AlBr₃, and has more versatile chemistry due to the comparative ease of reducing gallium, but is more reactive than GaCl₃.^[3]

GaBr₃ is similar spectroscopically to aluminum, indium, and thallium trihalides excluding trifluorides.^[4]

Preparation

One method of preparing GaBr₃ is to heat elemental gallium in the presence of bromine liquid under vacuum.^[5] Following the highly exothermic reaction, the mixture is allowed to rest and then subjected to various purifying steps. This method from the turn of the twentieth century remains a useful way of preparing GaBr_3. Historically, gallium was obtained by electrolysis of its hydroxide in solution of potassium hydroxide, however today it is obtained as a byproduct of aluminium and zinc production.

GaBr₃ can be synthesized by exposing gallium to bromine in an environment free of water, oxygen and grease.^[5][6] The result is a gas which must be crystallized in order to form bromide purchased by laboratories. Below is the equation:

2 Ga(s) + 3 Br₂(l) → 2 GaBr₃(g)

Structure

Extended crystal structure of GaBr₃

The GaBr₃ monomer has trigonal planar geometry, but when it forms the dimer Ga₂Br₆ the geometry around the gallium center distorts to become roughly tetrahedral. As a solid, GaBr₃ forms a monoclinic crystalline structure with a unit cell volume of 524.16 ų. Additional specifications for this unit cell are as follows: a = 8.87 Å, b = 5.64 Å, c =11.01 Å, α = 90˚, β = 107.81˚, γ = 90˚.^[7]

Complexes

Gallium is the lightest group 13 metal with a filled d-shell, and has an electronic configuration of ([Ar] 3d¹⁰ 4s² 4p¹) below the valence electrons that could take part in d-π bonding with ligands. The somewhat high oxidation state of Ga in Ga(III)Br₃, low electronegativity, and high polarizability allow GaBr₃ to behave as a "soft acid" in terms of the Hard-Soft-Acid-Base (HSAB) theory. The Lewis acidity of all the gallium trihalides, GaBr₃ included, has been extensively studied thermodynamically, and the basicity of GaBr₃ has been established with a number of donors.^[2]

GaBr₃ is capable of accepting an additional Br⁻ ion or unevenly splitting its dimer to form [GaBr₄]⁻, a tetrahedral ion of which crystalline salts can be obtained.^[2][8] This ionic complex is further capable of binding to . The Br⁻ ion can be just as easily substituted with a neutral ligand. Typically these neutral ligands, with form GaBr₃ L and sometimes GaBr₃L₂, will form a tetrahedral bipyramidal geometric structure with the Br in an equatorial position due to their large effective nuclear charge.^[2] Additionally, GaBr₃ can be used as a catalyst in certain oxidative addition reactions.

Uses

GaBr₃ is used as a catalyst in organic synthesis, with similar mechanism to GaCl_3. However, due to its greater reactivity, it is sometimes disfavored because of the greater versatility of GaCl₃.^[2] GaBr₃ as well as other gallium trihalides and group 13 metal trihalides can be used as catalysts in the oxidative addition of organic compounds. It has been verified that the GaBr₃ dimer cleaves unevenly into [GaBr₄]⁻ and [GaBr₂]⁺.^[8] The entire mechanism is uncertain partly because intermediate states are not always stable enough for study, and partially because GaBr₃ is studied less frequently than GaCl₃. Ga(III) itself is a useful Lewis acid for organic reactions because its full d-electron shell makes it able to accept variable numbers of ligands, but will readily give up ligands if conditions prove favorable.

See also

• GaCl₃
• Catalysis

References

1. "Gallium(III) bromide". Sigma Aldrich Catalogue. Sigma Aldrich Company.
2. King, Bruce R. (1994). Encyclopedia of Inorganic Chemistry. New York: Wiley. pp. 1265–1267. ISBN 978-0-471-93620-6.
3. Kiyokawa, Kensuke; Yasuda, Makoto; Baba, Akio (2010-04-02). "Cyclopropylmethylation of Benzylic and Allylic Chlorides with Cyclopropylmethylstannane Catalyzed by Gallium or Indium Halide". Organic Letters. 12 (7): 1520–1523. doi:10.1021/ol100240b. ISSN 1523-7060. PMID 20218636.
4. Downs, A.J. (199). Chemistry of Aluminium Gallium Indium and Thallium. Springer Science & Business Media. p. 133.
5. Johnson, W. C.; Parsons, J. B. (1929-01-01). "The Preparation of Gallium Tribromide and Gallium Triiodide". The Journal of Physical Chemistry. 34 (6): 1210–1214. doi:10.1021/j150312a007. ISSN 0092-7325.
6. Downs, A.J. (199). Chemistry of Aluminium Gallium Indium and Thallium. Springer Science & Business Media. p. 133.
7. Troyanov, S.I.; Krahl, T.; Kemnitz, E. (2004). "Crystal structures of GaX₃ (X = Cl, Br, I) and AlI₃". Zeitschrift für Kristallographie. 219 (2): 88–92. Bibcode:2004ZK....219...88T. doi:10.1524/zkri.219.2.88.26320. S2CID 101603507.
8. El-Hellani, Ahmad; Monot, Julien; Guillot, Régis; Bour, Christophe; Gandon, Vincent (2013-01-07). "Molecular versus Ionic Structures in Adducts of GaX3 with Monodentate Carbon-Based Ligands". Inorganic Chemistry. 52 (1): 506–514. doi:10.1021/ic302440g. ISSN 0020-1669. PMID 23256783.