There are three sets of gallium halides, the trihalides where gallium has
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
+3, the intermediate halides containing gallium in
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
s +1, +2 and +3 and some unstable monohalides, where gallium has
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
+1.
Trihalides
All four trihalides are known. They all contain gallium in the +3 oxidation state. Their proper names are gallium(III) fluoride, gallium(III) chloride, gallium(III) bromide and gallium(III) iodide.
;
GaF3
:GaF
3 is a white solid which sublimes before it melts, with an estimated melting point above 1000 °C. It contains 6 co-ordinate gallium atoms with a three-dimensional network of GaF
6 octahedra
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...
sharing common corners.
;
GaCl3,
GaBr3 and
GaI3
:These all have lower melting points than GaF
3, (
GaCl3 mp 78 °C, GaBr
3 mp 122 °C, GaI
3 mp 212 °C) reflecting the fact that their structures all contain dimers with 4 coordinate gallium atoms and 2 bridging halogen atoms. Thus, this halides have molecular formula Ga
2Cl
6, Ga
2Br
6, Ga
2I
6, respectively. They are all
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
s, forming mainly 4 co-ordinate adducts.
GaCl3 is the most commonly used trihalide.
Intermediate halides
Intermediate chlorides, bromides and iodides exist. They contain gallium in oxidation states +1, +2 and +3.
;Ga
3Cl
7
:This compound contains the Ga
2Cl
7− ion, which has a structure similar to the
dichromate, Cr
2O
72−, ion with two tetrahedrally coordinated gallium atoms sharing a corner. The compound can be formulated as gallium(I) heptachlorodigallate(III), Ga
I Ga
III2Cl
7.
:
;GaCl
2, GaBr
2 and GaI
2
:These are the best known and most studied intermediate halides. They contain gallium in oxidation states +1 and +3 and are formulated Ga
IGa
IIIX
4. The dihalides are unstable in the presence of water
disproportionating to gallium metal and gallium(III) entities. They are soluble in aromatic solvents, where arene complexes have been isolated and the arene is
η6 coordinated to the Ga
+ ion. With some ligands, L, e.g. dioxane, a neutral complex, Ga
2X
2L
2, with a gallium-gallium bond is produced. These compounds have been used as a route into gallium chain and cluster compounds.
;Ga
2Br
3 and Ga
2I
3
:These are formulated Ga
I2 Ga
II2Br
6 and Ga
I2 Ga
II2I
6 respectively. Both anions contain a gallium-gallium bond where gallium has a formal oxidation state of +2. The Ga
2Br
62− anion is eclipsed like the In
2Br
62− anion in In
2Br
3 whereas the Ga
2I
62− anion is isostructural with Si
2Cl
6 with a staggered conformation.
Monohalides
None of the monohalides are stable at room temperature. The previously reported GaBr and GaI produced from fusing gallium with the trihalide have been shown to be mixtures of metallic gallium with, respectively, Ga
2Br
3 and Ga
2I
3.
;GaCl and GaBr
:GaCl and GaBr have been produced in the gas form from the reaction of HX and molten gallium using a special reactor. They have been isolated by quenching the high temperature gas at 77 K. GaCl is reported as a red solid that
disproportionates
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
above 0 °C. Both GaCl and GaBr produced in this way can be stabilised in suitable solvents. The metastable solutions formed in this way have been used as precursors to numerous gallium cluster compounds.
:In the
HVPE
Hydride vapour phase epitaxy (HVPE) is an epitaxial growth technique often employed to produce semiconductors such as GaN, GaAs, InP and their related compounds, in which hydrogen chloride is reacted at elevated temperature with the group-III metal ...
production of
GaN
The word Gan or the initials GAN may refer to:
Places
*Gan, a component of Hebrew placenames literally meaning "garden"
China
* Gan River (Jiangxi)
* Gan River (Inner Mongolia),
* Gan County, in Jiangxi province
* Gansu, abbreviated ''Gā ...
, GaCl is produced by passing HCl gas over molten gallium which is then reacted with NH
3 gas.
;GaI
:
GaI
Gai or GAI may refer to:
People
Given name or nickname
* GAI (musician) (born 1987), Chinese hip-hop musician
* Gai Assulin (born 1991), Israeli footballer
* Gai Brodtmann (born 1963), Australian politician
* Gai Eaton (1921–2010), Brit ...
is produced as a reactive green powder, which has been hailed as a "versatile reagent for the synthetic chemist".
[Baker R.J., Jones C. Dalton Trans. 2005 Apr 21;(8):1341-8] The chemical structure of the reagent termed
‘GaI’ produced from reacting gallium metal with iodine in toluene using ultrasound has only recently been investigated using 69/71Ga solid-state NMR and a tentative structure assigned which includes gallium metal atoms,
0">a0sub>2
asup>+
4">aI4sup>−.
Anionic halide complexes
Salts containing GaCl
4−, GaBr
4− and GaI
4− are all known. Gallium is very different from
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts p ...
in that it is only known to form 6 coordinate complexes with the fluoride ion. This can be rationalised by the smaller size of gallium (ionic radii of Ga(III) 62 pm, In(III) 80 pm).
Salts containing the Ga
2Cl
62− anion, where gallium has an oxidation state of +2, are known.
General references
WebElements#
#
Footnotes
{{Gallium compounds
Gallium compounds
Metal halides
Mixed_valence_compounds