Aluminum connections
Aluminum compounds are the chemical compounds of the metallic element aluminum . Many aluminum compounds occur naturally as minerals . After silicon and oxygen, aluminum is the third most common and therefore the most common metallic element in the earth's crust ; accordingly, aluminum compounds also occur, e.g. B. the aluminosilicates , often.
In almost all of its compounds, aluminum is trivalent and the electropositive partner. All naturally occurring aluminum compounds and all commercially available aluminum compounds are those with the oxidation state +3. In the triple positively charged aluminum ion Al 3+ , the ion has the electron configuration of neon with 10 electrons. The ion radius is very small - Al 3+ can be counted among the smallest ions at all, since the compounds of the somewhat smaller B 3+ and the even more highly charged ions (such as Si 4+ or Ti 4+ ) are more covalent than ionic. In the HSAB concept, Al 3+ is one of the hard Lewis acids and therefore forms particularly stable compounds with the hard Lewis bases fluoride F - and oxide O 2− . In many compounds, aluminum (III) has either the coordination number four or six. With the coordination number six often occurs the octahedral coordination, with the coordination number four the tetrahedral, z. B. in the aluminosilicates .
Compounds of trivalent aluminum are mostly colorless. The exceptions also include compounds that are used to detect the aluminum ion: the cobalt-containing Thénards Blue , the fluorescent compound with Morin and the colored lakes of Alizarin S and aluminon . The colorlessness of most aluminum compounds can be explained by the closed neon electron shell of Al 3+ , which hardly participates in electron transitions.
Compounds of trivalent aluminum
Overview of important binary connections
| hydrogen |
Carbon group group 14 (IVA) |
Nitrogen group group 15 (VA) |
Chalcogenes Group 16 (VIA) |
Halogens group 17 (VIIA) |
|---|---|---|---|---|
| Hydrogen Aluminum (Alan) | ||||
| Aluminum carbide Al 4 C 3 | Aluminum nitride AlN | Aluminum oxide Al 2 O 3 | Aluminum fluoride AlF 3 | |
| Aluminum phosphide AlP | Aluminum sulfide Al 2 S 3 | Aluminum chloride AlCl 3 | ||
| Aluminum arsenide AlAs | Aluminum selenide Al 2 Se 3 | Aluminum bromide AlBr 3 | ||
| Aluminum antimonide AlSb | Aluminum telluride Al 2 Te 3 | Aluminum iodide AlI 3 |
Oxides, hydroxides, silicates
The aluminum oxide Al 2 O 3 occurs naturally in different forms: α-Al 2 O 3 as corundum or sapphire and - colored red by chrome - as ruby . γ-Al 2 O 3 is called alumina. The oxide-hydroxide AlO (OH) also occurs naturally as boehmite γ-AlOOH or more rarely as diaspore α-AlOOH, the aluminum hydroxide Al (OH) 3 as bayerite , gibbsite (hydrargillite) γ-Al (OH) 3 and north strandite . Aluminum ore bauxite , which contains gibbsite, boehmite and diaspore, is primarily used for aluminum extraction . In the kaolinite Al 2 (OH) 4 [Si 2 O 5 ] there are alternating silicate layers [Si 2 O 5 ] x 2− with tetrahedral Si (IV) and octahedral layers with sixfold and octahedral coordinated Al 3+ . In the frequently occurring layered silicate pyrophyllite Al 2 (OH) 2 [Si 2 O 5 ] 2 , the Al octahedral layer is linked with tetrahedral layers on both sides.
In aluminosilicates , e.g. For example, in mica (e.g. muscovite K Al 2 [AlSi 3 O 10 (OH) 2 ]), sillimanite , mullite , feldspars (e.g. potassium feldspar K [AlSi 3 O 8 ]) and zeolites , silicon is partially through Al 3+ replaced. Like silicon, the aluminum ion is tetrahedrally surrounded by oxide ions.
Halides and related compounds
In aluminum fluoride , the fluoride ions form distorted F6 octahedra around the aluminum ion, with each fluoride ion being linked to two aluminum ions, so that a three-dimensional networked structure is built up. In contrast, aluminum chloride forms a layer structure. It sublimes at 180 ° C. and is present in the gas phase as the dimer Cl 2 AlCl 2 AlCl 2 . In aluminum bromide and aluminum iodide such dimeric molecules occur Al 2 Br 6 and Al 2 I 6 on the coordination number of four in the solid state.
Anhydrous aluminum chloride serves as a catalyst in Friedel-Crafts alkylation and Friedel-Crafts acylation .
Halido complexes
A technically important complex compound is sodium hexafluoroaluminate Na 3 AlF 6 , which is used as an electrolyte component in fused-salt electrolysis for aluminum production in the Hall-Héroult process , but which also occurs naturally as a rare mineral, cryolite .
Other aluminum (III) salts
The aluminum sulfate Al 2 (SO 4 ) 3 , which occurs naturally as a rather rare mineral alunogen , is used as a flocculant in water treatment . The various aluminum phosphates include the aluminum orthophosphate AlPO 4 and the aluminum metaphosphate Al (PO 3 ) 3 . The aluminum stearate is used as a thickener .
Sucralfate , the aluminum salt of sucrose sulfate , is used as a drug, e.g. B. for the treatment of duodenal ulcers .
Aluminum hydrides
Aluminum hydride (AlH 3 ) x , also known as alan, has a polymeric structure and is hardly soluble. It breaks down into the elements above 100 ° C. As a reducing agent, especially in organic chemistry, are lithium aluminum hydride LiAlH 4 (lithium aluminum hydride) and sodium aluminum hydride NaAlH 4 (sodium alanate) is important. They can be used to reduce carbonyl compounds. Substituted hydrides are derived from them, lithium triethoxyaluminum hydride LiAl (OEt) 3 H is z. B. used as a mild reducing agent.
Organic aluminum compounds
Among the organoaluminum compounds there are important catalysts, e.g. B. the Tebbe reagent , the methylaluminoxane and the Ziegler-Natta catalysts .
Aluminum carbide and aluminum nitride
Aluminum carbide Al 4 C 3 reacts with water to form methane . The only nitride in aluminum is aluminum nitride AlN; it can be represented from the elements.
Aluminum compounds with oxidation states +1 and +2
Aluminum (II) compounds
At high temperatures, aluminum and Al 2 O 3 can form aluminum (II) oxide AlO.
Aluminum (I) compounds
If the vapors of the aluminum (III) halides AlF 3 , AlCl 3 and AlBr 3 are reduced at high temperatures with aluminum, the aluminum (I) halides aluminum (I) fluoride AlF, aluminum (I) chloride AlCl, aluminum ( I) -Bromide AlBr and aluminum (I) -iodide AlI can be obtained. They are also formed at 1000 ° C from liquid aluminum and hydrogen halide. There is an adduct of the aluminum (I) iodide AlI with triethylamine , Al 4 I 4 (NEt 3 ) 4 . Aluminum (I) oxide can also be obtained at high temperatures.
Alloys of aluminum
Some alloys of aluminum have a defined stoichiometry, e.g. B. that of lithium with the composition LiAl, and can therefore be regarded as intermetallic compounds . Al is the electronegative partner to lithium .
Individual evidence
- ↑ Ionic Radii (in Picometers) of the Most Common oxidation States
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , pp. 965-966.
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 969.
- ↑ http://www.acros.com/myBrochure/brochure_aluminum_v5.pdf
