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Gallium(III) bromide (dimer)
Names


Other names gallium tribromide
Identifiers
CAS Number	13450-88-9
3D model (JSmol)	Interactive image
ChemSpider	75315
ECHA InfoCard	100.033.267
EC Number	236-609-5
PubChem CID	83477
CompTox Dashboard (EPA)	DTXSID2065466
InChI InChI=1S/3BrH.Ga/h31H;/q;;;+3/p-3Key: SRVXDMYFQIODQI-UHFFFAOYSA-K InChI=1/3BrH.Ga/h31H;/q;;;+3/p-3Key: SRVXDMYFQIODQI-DFZHHIFOAJ
SMILES Br(Br)Br
Properties
Chemical formula	GaBr₃
Molar mass	309.435 g/mol
Appearance	white powder
Density	3.69 g/cm
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 , 100 kPa). N verify (what is ?) Infobox references

Chemical compound

Gallium(III) bromide (Ga Br₃) is a chemical compound, and one of four gallium trihalides.

Introduction

Gallium(III) bromide is, at room temperature and atmospheric pressure, a white, crystalline powder which reacts favorably and exothermically with water. Solid gallium tribromide is stable at room temperature and can be found primarily in its dimeric form. 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. 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.

GaBr₃ is similar spectroscopically to aluminum, indium, and thallium trihalides excluding trifluorides.

Preparation

One method of preparing GaBr₃ is to heat elemental gallium in the presence of bromine liquid under vacuum. 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. 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

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 Å. 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˚.

Complexes

Gallium is the lightest group 13 metal with a filled d-shell, and has an electronic configuration of ( 3d 4s 4p) 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.

GaBr₃ is capable of accepting an additional Br ion or unevenly splitting its dimer to form , a tetrahedral ion of which crystalline salts can be obtained. 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. 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. 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 and . 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.

References

"Gallium(III) bromide". Sigma Aldrich Catalogue. Sigma Aldrich Company.
^ King, Bruce R. (1994). Encyclopedia of Inorganic Chemistry. New York: Wiley. pp. 1265–1267. ISBN 978-0-471-93620-6.
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.
Downs, A.J. (199). Chemistry of Aluminium Gallium Indium and Thallium. Springer Science & Business Media. p. 133.
^ 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.
Downs, A.J. (199). Chemistry of Aluminium Gallium Indium and Thallium. Springer Science & Business Media. p. 133.
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.
^ 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.