Английская Википедия:Gallium compounds
Шаблон:Short description Шаблон:Category see also Gallium compounds are compounds containing the element gallium. These compounds are found primarily in the +3 oxidation state. The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners indium and thallium. For example, the very stable GaCl2 contains both gallium(I) and gallium(III) and can be formulated as GaIGaIIICl4; in contrast, the monochloride is unstable above 0 °C, disproportionating into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as GaS (which can be formulated as Ga24+(S2−)2) and the dioxan complex Ga2Cl4(C4H8O2)2.[1] There are also compounds of gallium with negative oxidation states, ranging from -5 to -1, most of these compounds being magnesium gallides (MgxGay).
Aqueous chemistry
Strong acids dissolve gallium, forming gallium(III) salts such as [[gallium(III) nitrate|Шаблон:Chem]] (gallium nitrate). Aqueous solutions of gallium(III) salts contain the hydrated gallium ion, Шаблон:Chem.[2]Шаблон:Rp Gallium(III) hydroxide, Шаблон:Chem, may be precipitated from gallium(III) solutions by adding ammonia. Dehydrating Шаблон:Chem at 100 °C produces gallium oxide hydroxide, GaO(OH).[3]Шаблон:Rp
Alkaline hydroxide solutions dissolve gallium, forming gallate salts (not to be confused with identically named gallic acid salts) containing the Шаблон:Chem anion.[4][2]Шаблон:Rp[5] Gallium hydroxide, which is amphoteric, also dissolves in alkali to form gallate salts.[3]Шаблон:Rp Although earlier work suggested Шаблон:Chem as another possible gallate anion,[6] it was not found in later work.[5]
Oxides and chalcogenides
Gallium reacts with the chalcogens only at relatively high temperatures. At room temperature, gallium metal is not reactive with air and water because it forms a passive, protective oxide layer. At higher temperatures, however, it reacts with atmospheric oxygen to form gallium(III) oxide, Шаблон:Chem.[4] Reducing Шаблон:Chem with elemental gallium in vacuum at 500 °C to 700 °C yields the dark brown gallium(I) oxide, Шаблон:Chem.[3]Шаблон:Rp Шаблон:Chem is a very strong reducing agent, capable of reducing [[sulfuric acid|Шаблон:Chem]] to [[hydrogen sulfide|Шаблон:Chem]].[3]Шаблон:Rp It disproportionates at 800 °C back to gallium and Шаблон:Chem.[7]
Gallium(III) sulfide, Шаблон:Chem, has 3 possible crystal modifications.[7]Шаблон:Rp It can be made by the reaction of gallium with hydrogen sulfide (Шаблон:Chem) at 950 °C.[3]Шаблон:Rp Alternatively, Шаблон:Chem can be used at 747 °C:[8]
- 2 Шаблон:Chem + 3 Шаблон:Chem → Шаблон:Chem + 6 Шаблон:Chem
Reacting a mixture of alkali metal carbonates and Шаблон:Chem with Шаблон:Chem leads to the formation of thiogallates containing the Шаблон:Chem anion. Strong acids decompose these salts, releasing Шаблон:Chem in the process.[7]Шаблон:Rp The mercury salt, Шаблон:Chem, can be used as a phosphor.[9]
Gallium also forms sulfides in lower oxidation states, such as gallium(II) sulfide and the green gallium(I) sulfide, the latter of which is produced from the former by heating to 1000 °C under a stream of nitrogen.[7]Шаблон:Rp
The other binary chalcogenides, Шаблон:Chem and Шаблон:Chem, have the zincblende structure. They are all semiconductors but are easily hydrolysed and have limited utility.[7]Шаблон:Rp
Nitrides and pnictides
Шаблон:Multiple image Gallium reacts with ammonia at 1050 °C to form gallium nitride, GaN. Gallium also forms binary compounds with phosphorus, arsenic, and antimony: gallium phosphide (GaP), gallium arsenide (GaAs), and gallium antimonide (GaSb). These compounds have the same structure as ZnS, and have important semiconducting properties.[2]Шаблон:Rp GaP, GaAs, and GaSb can be synthesized by the direct reaction of gallium with elemental phosphorus, arsenic, or antimony.[7]Шаблон:Rp They exhibit higher electrical conductivity than GaN.[7]Шаблон:Rp GaP can also be synthesized by reacting Шаблон:Chem with phosphorus at low temperatures.[10]
Gallium forms ternary nitrides; for example:[7]Шаблон:Rp
Similar compounds with phosphorus and arsenic are possible: Шаблон:Chem and Шаблон:Chem. These compounds are easily hydrolyzed by dilute acids and water.[7]Шаблон:Rp
Halides
Шаблон:Main article Gallium(III) oxide reacts with fluorinating agents such as HF or [[fluorine|Шаблон:Chem]] to form gallium(III) fluoride, Шаблон:Chem. It is an ionic compound strongly insoluble in water. However, it dissolves in hydrofluoric acid, in which it forms an adduct with water, Шаблон:Chem. Attempting to dehydrate this adduct forms Шаблон:Chem. The adduct reacts with ammonia to form Шаблон:Chem, which can then be heated to form anhydrous Шаблон:Chem.[3]Шаблон:Rp
Gallium trichloride is formed by the reaction of gallium metal with chlorine gas.[4] Unlike the trifluoride, gallium(III) chloride exists as dimeric molecules, Шаблон:Chem, with a melting point of 78 °C. Eqivalent compounds are formed with bromine and iodine, [[gallium(III) bromide|Шаблон:Chem]] and [[gallium(III) iodide|Шаблон:Chem]].[3]Шаблон:Rp
Like the other group 13 trihalides, gallium(III) halides are Lewis acids, reacting as halide acceptors with alkali metal halides to form salts containing Шаблон:Chem anions, where X is a halogen. They also react with alkyl halides to form carbocations and Шаблон:Chem.[3]Шаблон:Rp
When heated to a high temperature, gallium(III) halides react with elemental gallium to form the respective gallium(I) halides. For example, Шаблон:Chem reacts with Ga to form Шаблон:Chem:
- 2 Ga + Шаблон:Chem Шаблон:Eqm 3 GaCl (g)
At lower temperatures, the equilibrium shifts toward the left and GaCl disproportionates back to elemental gallium and Шаблон:Chem. GaCl can also be produced by reacting Ga with HCl at 950 °C; the product can be condensed as a red solid.[2]Шаблон:Rp
Gallium(I) compounds can be stabilized by forming adducts with Lewis acids. For example:
- GaCl + Шаблон:Chem → Шаблон:Chem
The so-called "gallium(II) halides", Шаблон:Chem, are actually adducts of gallium(I) halides with the respective gallium(III) halides, having the structure Шаблон:Chem. For example:[4][2]Шаблон:Rp[11]
- GaCl + Шаблон:Chem → Шаблон:Chem
Hydrides
Like aluminium, gallium also forms a hydride, Шаблон:Chem, known as gallane, which may be produced by reacting lithium gallanate (Шаблон:Chem) with gallium(III) chloride at −30 °C:[2]Шаблон:Rp
- 3 Шаблон:Chem + Шаблон:Chem → 3 LiCl + 4 Шаблон:Chem
In the presence of dimethyl ether as solvent, Шаблон:Chem polymerizes to Шаблон:Chem. If no solvent is used, the dimer Шаблон:Chem (digallane) is formed as a gas. Its structure is similar to diborane, having two hydrogen atoms bridging the two gallium centers,[2]Шаблон:Rp unlike α-[[aluminium hydride|Шаблон:Chem]] in which aluminium has a coordination number of 6.[2]Шаблон:Rp
Gallane is unstable above −10 °C, decomposing to elemental gallium and hydrogen.[12]
Organogallium compounds
Шаблон:Main Organogallium compounds are of similar reactivity to organoindium compounds, less reactive than organoaluminium compounds, but more reactive than organothallium compounds.[13] Alkylgalliums are monomeric. Lewis acidity decreases in the order Al > Ga > In and as a result organogallium compounds do not form bridged dimers as organoaluminium compounds do. Organogallium compounds are also less reactive than organoaluminium compounds. They do form stable peroxides.[14] These alkylgalliums are liquids at room temperature, having low melting points, and are quite mobile and flammable. Triphenylgallium is monomeric in solution, but its crystals form chain structures due to weak intermolecluar Ga···C interactions.[13]
Gallium trichloride is a common starting reagent for the formation of organogallium compounds, such as in carbogallation reactions.[15] Gallium trichloride reacts with lithium cyclopentadienide in diethyl ether to form the trigonal planar gallium cyclopentadienyl complex GaCp3. Gallium(I) forms complexes with arene ligands such as hexamethylbenzene. Because this ligand is quite bulky, the structure of the [Ga(η6-C6Me6)]+ is that of a half-sandwich. Less bulky ligands such as mesitylene allow two ligands to be attached to the central gallium atom in a bent sandwich structure. Benzene is even less bulky and allows the formation of dimers: an example is [Ga(η6-C6H6)2] [GaCl4]·3C6H6.[13]
See also
- Organogallium chemistry
- Category:Gallium compounds
- Aluminium compounds
- Indium compounds
- Germanium compounds
References
Шаблон:Gallium compounds Шаблон:Chemical compounds by element
- ↑ Greenwood and Earnshaw, p. 240
- ↑ 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 Шаблон:Cite book
- ↑ 3,0 3,1 3,2 3,3 3,4 3,5 3,6 3,7 Шаблон:Cite book
- ↑ 4,0 4,1 4,2 4,3 Шаблон:Cite book
- ↑ 5,0 5,1 Шаблон:Cite journal
- ↑ Шаблон:Cite book
- ↑ 7,0 7,1 7,2 7,3 7,4 7,5 7,6 7,7 7,8 Шаблон:Cite book
- ↑ Шаблон:Cite book
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite book
- ↑ Шаблон:Cite book
- ↑ Шаблон:Cite book
- ↑ 13,0 13,1 13,2 Greenwoood and Earnshaw, pp. 262–5
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
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