Gallium trichloride
Encyclopedia
Gallium trichloride is the chemical compound
with the formula GaCl3. Solid gallium trichloride exists as a dimer with the formula Ga2Cl6. It is colourless and soluble in virtually all solvents, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium
and a reagent in organic synthesis
.
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.
metal in a stream of chlorine
, and purifying the product by sublimation under vacuum.
It can also be prepared from the gallium oxide by heating with thionyl chloride
:
monomers.
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 hight 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:
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
In a molten mixture of KCl and GaCl3, the following equilibrium exists:
experiment performed by Laboratori Nazionali del Gran Sasso
in Italy to detect solar neutrino
s. In this experiment, isotope germanium
-71 was produced and its decay measured.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula GaCl3. Solid gallium trichloride exists as a dimer with the formula Ga2Cl6. It is colourless and soluble in virtually all solvents, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
and a reagent in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
.
As a Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
, 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 galliumGallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
metal in a stream of chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, and purifying the product by sublimation under vacuum.
- 2 Ga + 3 Cl2 → 2 GaCl3
It can also be prepared from the gallium oxide by heating with thionyl chloride
Thionyl chloride
Thionyl chloride is an inorganic compound with the formula SOCl2. It is a reactive chemical reagent used in chlorination reactions. It is a colorless, distillable liquid at room temperature and pressure that decomposes above 140 °C. Thionyl chloride is sometimes confused with sulfuryl...
:
- 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 planarTrigonal planar
In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of a triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to...
monomers.
Complexes
GalliumGallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
is the lightest member of Group 13 to have a full d shell, (gallium has the electronic configuration Ar
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
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
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
and hight polarisability, allow Ga(III)Cl3 to behave as a "Soft Acid" in terms of the HSAB theory
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....
. The strength of the bonds between gallium halides and ligands have been extensively studied. What emerges is:
- GaCl3 is a weaker Lewis acidLewis acid]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
than AlCl3 towards N and O donors e.g. pyridine - GaCl3 is a stronger Lewis acidLewis acid]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
than AlCl3 towards thioethers e.g. dimethyl sulfideDimethyl sulfideDimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...
, Me2S
With a chloride ion as ligand the tetrahedral GaCl4
In a molten mixture of KCl and GaCl3, the following equilibrium exists:
- 2 GaCl4
− 
Ga2Cl7− + Cl−
Use in detection of solar neutrinos
110 tons of gallium trichloride solution was used in the GALLEXGALLEX
GALLEX or Gallium Experiment was a radiochemical neutrino detection experiment that ran between 1991 and 1997 at the Laboratori Nazionali del Gran Sasso...
experiment performed by Laboratori Nazionali del Gran Sasso
Laboratori Nazionali del Gran Sasso
Laboratori Nazionali del Gran Sasso is a particle physics laboratory of the INFN, situated near the Gran Sasso mountain in Italy, between the towns of L'Aquila and Teramo, about 120 km from Rome. In addition to a surface portion of the laboratory, there are extensive underground facilities...
in Italy to detect solar neutrino
Solar neutrino
Electron neutrinos are produced in the Sun as a product of nuclear fusion. By far the largest fraction of neutrinos passing through the Earth are Solar neutrinos....
s. In this experiment, isotope germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
-71 was produced and its decay measured.