Gallium trichloride is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the formula GaCl
3. Solid gallium trichloride exists as a
dimer
Dimer may refer to:
* Dimer (chemistry), a chemical structure formed from two similar sub-units
** Protein dimer, a protein quaternary structure
** d-dimer
* Dimer model, an item in statistical mechanics, based on ''domino tiling''
* Julius Dimer ...
with the formula Ga
2Cl
6. 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
Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...
and a reagent in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
.
As a
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 ...
, GaCl
3 is milder than
aluminium trichloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
. Gallium(III) is easier to reduce than Al(III), so the chemistry of reduced gallium compounds is more extensive than for aluminium. Ga
2Cl
4 is known whereas the corresponding Al
2Cl
4 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
Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...
metal in a stream of
chlorine
Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
, and purifying the product by sublimation under vacuum.
:2 Ga + 3 Cl
2 → 2 GaCl
3
It can also be prepared from by heating
gallium oxide with
thionyl chloride
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...
:
:Ga
2O
3 + 3 SOCl
2 → 2 GaCl
3 + 3 SO
2
Gallium metal reacts slowly with hydrochloric acid. This reaction produces
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas slowly.
Structure
As a solid, it adopts a bitetrahedral structure with two bridging chlorides. Its structure resembles that of
aluminium tribromide
Aluminium bromide is any chemical compound with the empirical formula AlBrx. Aluminium tribromide is the most common form of aluminium bromide. It is a colorless, sublimable hygroscopic solid; hence old samples tend to be hydrated, mostly as al ...
. In contrast
AlCl3 and
InCl3 feature contain 6 coordinate metal centers. As a consequence of its molecular nature and associated low
lattice energy
In chemistry, the lattice energy is the energy change upon formation of one mole of a crystalline ionic compound from its constituent ions, which are assumed to initially be in the gaseous state. It is a measure of the cohesive forces that bind ...
, gallium trichloride has a lower melting point vs the aluminium and indium trihalides. The formula of Ga
2Cl
6 is often written as Ga
2(μ-Cl)
2Cl
4. In the gas phase the dimers dissociate to
trigonal planar
In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands a ...
monomers.
Complexes
Gallium
Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...
is the lightest member of Group 13 to have a full ''d'' shell, (gallium has the electronic configuration
Argon">Ar.html" ;"title="Argon.html" ;"title="nowiki/>Argon">Ar">Argon.html" ;"title="nowiki/>Argon">Ar3''d''
10 4''s''
2 4''p''
1) below the valence electrons that could take part in ''d''-π bonding with ligands.
The low oxidation state of Ga in Ga(III)Cl
3, along with the low electronegativity and high polarisability, allow GaCl
3 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:
*GaCl
3 is a weaker
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 ...
than AlCl
3 towards N and O donors e.g.
pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...
*GaCl
3 is a stronger
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 ...
than AlCl
3 towards
thioethers
In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A sul ...
e.g.
dimethyl sulfide
Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...
, Me
2S
With a chloride ion as ligand the tetrahedral GaCl
4− ion is produced, the 6 coordinate GaCl
63− cannot be made. Compounds like KGa
2Cl
7 that have a chloride
bridged
Bridging may refer to:
Construction
* Building of bridges across a gap
* Cross bracing used between joists to stabilize them
Electronics and computing
* In electronics, using a low source impedance to drive a large load impedance for maximum vol ...
anion are known.
[J H von Barner Inorg Chem 1985 24 1686]
In a molten mixture of KCl and GaCl
3, the following equilibrium exists:
:2 GaCl
4− Ga
2Cl
7− + Cl
−
Uses
Organic synthesis
Gallium trichloride is a
Lewis acid catalyst, such as in the
Friedel–Crafts reaction
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions ...
, and is also used in
carbogallation reactions of compounds with a carbon-carbon triple bond. It is a precursor to
organogallium reagents. It is also used as a catalyst in many organic reactions.
Detection of solar neutrinos
110 tons of gallium trichloride aqueous solution was used in the
GALLEX
GALLEX or Gallium Experiment was a radiochemical neutrino detection experiment that ran between 1991 and 1997 at the Laboratori Nazionali del Gran Sasso (LNGS). This project was performed by an international collaboration of French, German, Itali ...
and GNO experiments performed at
Laboratori Nazionali del Gran Sasso
Laboratori Nazionali del Gran Sasso (LNGS) is the largest underground research center in the world. Situated below Gran Sasso mountain in Italy, it is well known for particle physics research by the INFN. In addition to a surface portion of the ...
in Italy to detect
solar neutrino
A solar neutrino is a neutrino originating from nuclear fusion in the Sun's core, and is the most common type of neutrino passing through any source observed on Earth at any particular moment. Neutrinos are elementary particles with extremely smal ...
s. In these experiments,
germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...
-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.
[David R. Lide, ed. ''Handbook of Chemistry and Physics, 85th Edition'', Internet Version 2005. CRC Press, 2005.]
See also
*
Gallium halides
References
*
*
External links
*
{{DEFAULTSORT:Gallium Trichloride
Inorganic compounds
Gallium compounds
Chlorides
Metal halides