Gallium(III) chloride

Gallium(III) chloride can be prepared from the elements by heating gallium metal in a stream of chlorine at 200 °C and purifying the product by sublimation under vacuum.{{cite book |author1=Roger A. Kovar |author2=J. A. Dilts |title=Inorganic Syntheses Volume 17 |date=1977 |publisher=McGraw‐Hill |isbn=9780470131794 |pages=167–172 |url=https://doi.org/10.1002/9780470132487.ch45 |language=en |chapter=Gallium Trichloride}}{{cite encyclopedia |last= Gray|first=Floyd |author-link= |editor-last= |editor-first= |editor-link= |encyclopedia=Kirk-Othmer Encyclopedia of Chemical Technology |title=Gallium and Gallium Compounds

|url= |access-date= |language=en|edition= |year=2013|publisher= |series= |volume= |location= |id= |isbn=9780471238966|issn= |oclc= |doi=10.1002/0471238961.0701121219010215.a01.pub3}}

:2 Ga + 3 Cl₂ → 2 GaCl₃

It can also be prepared from by heating gallium oxide with thionyl chloride:{{cite journal |author1=H. Hecht |author2=G. Jander |author3=H. Schlapmann |title=Über die Einwirkung von Thionylchlorid auf Oxyde |journal=Zeitschrift für anorganische Chemie |date=1947 |volume=254 |issue=5-6 |pages=255–264 |doi=10.1002/zaac.19472540501 |trans-title=On the effect of thionyl chloride on oxides |language=en}}

:Ga₂O₃ + 3 SOCl₂ → 2 GaCl₃ + 3 SO₂

Gallium metal reacts slowly with hydrochloric acid, producing hydrogen gas.{{cite encyclopedia |last=Greber|first=Jörg |author-link= |editor-last= |editor-first= |editor-link= |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |title=Gallium and Gallium Compounds

|url= |access-date= |language=en|edition= |year=2000|publisher= |series= |volume= |location= |id= |isbn=9783527306732|issn= |oclc= |doi=10.1002/14356007.a12_163}} Evaporation of this solution produces the monohydrate.{{cite journal |author1=Jacques Roziere |author2=Marie-Thérèse Roziere-Bories |author3=Alain Manteghetti |author4=Antoine Potier |title=Hydrates des halogenures de gallium. II Spectroscopie de vibration des complexes coordinés GaX3•H2O (X = Cl ou Br) |journal=Canadian Journal of Chemistry |date=1974 |volume=52 |issue=18 |pages=3274–3280 |doi=10.1139/v74-483 |language=fr}}

As a solid, it adopts a bitetrahedral structure with two bridging chlorides. Its structure resembles that of aluminium tribromide. In contrast AlCl₃ and InCl₃ feature contain 6 coordinate metal centers. As a consequence of its molecular nature and associated low lattice energy, gallium(III) chloride has a lower melting point vs the aluminium and indium trihalides. The formula of Ga₂Cl₆ is often written as Ga₂(μ-Cl)₂Cl₄.{{cite journal |author1=Sergey I. Troyanov |author2=Thoralf Krahl |author3=Erhard Kemnitz |title=Crystal structures of GaX3 (X = Cl, Br, I) and AlI3 |journal=Zeitschrift für Kristallographie - Crystalline Materials |date=2004 |volume=219 |issue=2 |pages=88–92 |doi=10.1524/zkri.219.2.88.26320 |language=en}}

In the gas-phase, the dimeric (Ga₂Cl₆) and trigonal planar monomeric (GaCl₃) are in a temperature-dependent equilibrium, with higher temperatures favoring the monomeric form. At 870 K, all gas-phase molecules are effectively in the monomeric form.{{cite journal |author1=Viacheslav I. Tsirelnikov |author2=Boris V. Lokshin |author3=Petr Melnikov |author4=Valter A. Nascimento |title=On the Existence of the Trimer of Gallium Trichloride in the Gaseous Phase |journal=Zeitschrift für anorganische und allgemeine Chemie |date=2012 |volume=638 |issue=14 |pages=2335–2339 |doi=10.1002/zaac.201200282 |language=en}}

In the monohydrate, the gallium is tetrahedrally coordinated with three chlorine molecules and one water molecule.

Gallium(III) chloride is a diamagnetic and deliquescent colorless white solid that melts at 77.9 °C and boils at 201 °C without decomposition to the elements. This low melting point results from the fact that it forms discrete Ga₂Cl₆ molecules in the solid state. Gallium(III) chloride dissolves in water with the release of heat to form a colorless solution, which when evaporated, produces a colorless monohydrate, which melts at 44.4 °C.{{cite journal |author1=J. Burgess |author2=J. Kijowski |title=Enthalpies of solution of chlorides and iodides of gallium(III), indium(III), thorium(IV) and uranium(IV) |journal=Journal of Inorganic and Nuclear Chemistry |date=1981 |volume=43 |issue=11 |pages=2649–2652 |doi=10.1016/0022-1902(81)80592-1 |language=en}}

Gallium 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 high polarisability, allow GaCl₃ to behave as a "soft acid" in terms of the HSAB theory.{{cite book |last1=Housecroft |first1=Catherine E. |last2=Sharpe |first2=Alan G. |title=Inorganic Chemistry |edition=5th |year=2018 |orig-year=2001 |publisher=Pearson Education |location=Harlow, Essex |isbn=978-1-292-13414-7}} The strength of the bonds between gallium halides and ligands have been extensively studied. What emerges is:{{Greenwood&Earnshaw2nd|pages=237–239}}

• GaCl₃ is a weaker Lewis acid than AlCl₃ towards N and O donors e.g. pyridine
• GaCl₃ is a stronger Lewis acid than AlCl₃ towards thioethers e.g. dimethyl sulfide, Me₂S

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.{{cite journal |author1=Jens H. Von Barner |title=Potentiometric and Raman spectroscopic study of the complex formation of gallium(III) in potassium chloride-aluminum chloride melts at 300C |journal=Inorganic Chemistry |date=1985 |volume=24 |issue=11 |pages=1686–1689 |doi=10.1021/ic00205a019 |language=en}}

In a molten mixture of KCl and GaCl₃, the following equilibrium exists:

:2 GaCl₄⁻ {{eqm}} Ga₂Cl₇⁻ + Cl⁻

When dissolved in water, gallium(III) chloride dissociates into the octahederal [Ga(H₂O)₆]³⁺ and Cl⁻ ions forming an acidic solution, due to the hydrolysis of the hexaaquogallium(III) ion:{{cite journal |author1=Scott A. Wood |author2=Iain M. Samson |title=The aqueous geochemistry of gallium, germanium, indium and scandium |journal=Ore Geology Reviews |date=2006 |volume=28 |issue=1 |pages=57–102 |doi=10.1016/j.oregeorev.2003.06.002 |language=en}}

:[Ga(H₂O)₆]³⁺ → [Ga(H₂O)₅OH]²⁺ + H⁺ (pK_a = 3.0)

In basic solution, it hydrolyzes to gallium(III) hydroxide, which redissolves with the addition of more hydroxide, possibly to form Ga(OH)₄⁻.

Gallium(III) chloride is a Lewis acid catalyst, such as in the Friedel–Crafts reaction, which is able to substitute more common lewis acids such as ferric chloride. Gallium complexes strongly with π-donors, especially silylethynes, producing a strongly electrophilic complex. These complexes are used as an alkylating agent for aromatic hydrocarbons.

It is also used in carbogallation reactions of compounds with a carbon-carbon triple bond. It is also used as a catalyst in many organic reactions.

It is a precursor to organogallium reagents. For example, trimethylgallium, an organogallium compound used in MOCVD to produce various gallium-containing semiconductors, is produced by the reaction of gallium(III) chloride with various alkylating agents, such as dimethylzinc, trimethylaluminium, or methylmagnesium iodide.{{ cite journal |author1=Kraus, C. A. |author2=Toonder, F. E. | title = Trimethyl Gallium, Trimethyl Gallium Etherate and Trimethyl Gallium Ammine | journal = PNAS | year = 1933 | volume = 19 | issue = 3 | pages = 292–8 | doi = 10.1073/pnas.19.3.292 | pmc = 1085965 | pmid = 16577510 | bibcode = 1933PNAS...19..292K |doi-access=free }}{{cite book | last1= Foster | first1=Douglas F. | last2= Cole-Hamilton|first2=David J. | title=Inorganic Syntheses | chapter=Electronic Grade Alkyls of Group 12 and 13 Elements|pages =29–66|volume=31|year=1997|doi=10.1002/9780470132623.ch7| isbn=978-0-471-15288-0 }}{{cite patent |country=WO |number=2014078263 |inventor= Liam P. Spencer, James C. Stevens, Deodatta Vinayak Shenai-Khatkhate |status=application |title=Methods of producing trimethylgallium |pubdate=2014-05-22 |gdate= |fdate=2013-11-12 |pridate=2012-11-14 |assign1= |assign2= |url=}}

Gallium(III) chloride is an intermediate in various gallium purification processes, where gallium(III) chloride is fractionally distilled or extracted from acid solutions.

110 tons of gallium(III) chloride aqueous solution was used in the GALLEX and GNO experiments performed at Laboratori Nazionali del Gran Sasso in Italy to detect solar neutrinos. In these experiments, germanium-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.

• Gallium halides

• {{Greenwood&Earnshaw}}

• {{cite web | url = http://yosemite.epa.gov/oswer/ceppoehs.nsf/firstaid/13450-90-3?OpenDocument | publisher = United States Environmental Protection Agency | title = Emergency First Aid Treatment Guide - Gallium Trichloride | url-status = dead | archive-url = https://web.archive.org/web/20041112081035/http://yosemite.epa.gov/oswer/CeppoEHS.nsf/firstaid/13450-90-3?OpenDocument | archive-date = 2004-11-12 }}

{{Gallium compounds}}

{{Chlorides}}

{{DEFAULTSORT:Gallium Trichloride}}

Category:Inorganic compounds

Category:Gallium compounds

Category:Chlorides

Category:Metal halides