Aluminium tribromide

Aluminium bromide

Names
Preferred IUPAC name Aluminium bromide
Other names Aluminic bromide Aluminium(III) bromide Aluminium tribromide
Identifiers
CAS Number	7727-15-3 Y 7784-11-4 hexahydrate Y
3D model (Jmol)	Interactive image
ChemSpider	22818 Y 9040513 hemi(acetyl bromide) Y 9499890 ethanethiol Y
ECHA InfoCard	100.028.891
EC Number	231-779-7
PubChem CID	24409 11062022 tertikis(tetrachloromethane) 10865226 hemi(acetyl bromide) 11324936 ethanethiol 6093832 tris(pyridine)
RTECS number	BD0350000
UN number	1725
InChI InChI=1S/Al.3BrH/h;3*1H/q+3;;;/p-3 Y Key: PQLAYKMGZDUDLQ-UHFFFAOYSA-K Y InChI=1/Al.3BrH/h;3*1H/q+3;;;/p-3 Key: PQLAYKMGZDUDLQ-DFZHHIFOAT
SMILES Br[Al](Br)Br
Properties
Chemical formula	AlBr3 Al2Br6
Molar mass	266.69 g/mol
Appearance	white to pale yellow crystalline solid
Odor	pungent
Density	3.205 g/cm3
Melting point	97.8 °C (208.0 °F; 370.9 K)
Boiling point	265 °C (509 °F; 538 K)
Solubility in water	reacts
Solubility	slightly soluble in methanol, diethyl ether, acetone
Structure
Crystal structure	monoclinic
Hazards
EU classification (DSD) (outdated)	not listed
NFPA 704	1 3 1
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1598 mg/kg (oral, rat)
Related compounds
Other anions	aluminium trichloride aluminium triiodide
Other cations	boron tribromide
Related compounds	iron(III) bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Aluminium(III) bromide

Aluminium bromide is any chemical compound with the empirical formula AlBr_x. The species called "aluminium tribromide," is the most common aluminium bromide. It is a colorless, sublimable hygroscopic solid, although older samples tend to be hydrated.

The dimeric form of aluminium tribromide (Al₂Br₆) predominates in the solid state, solutions in noncoordinating solvents (e.g. CS₂), in the melt, and the gas phase. Only at high temperatures do these dimers break up into monomers:

The species aluminium monobromide forms from the reaction of HBr with Al metal at high temperature. It disproportionates near room temperature:

This reaction is reversed at temperatures higher than 1000 °C. Aluminium monobromide has been crystallographically characterized in the form the tetrameric adduct Al₄Br₄(NEt₃)₄ (Et = C₂H₅). This species is electronically related to cyclobutane. Theory suggest that the diatomic aluminium monobromide condenses to a dimer and then a tetrahedral cluster Al₄Br₄, akin to the analogous boron compound.

Al₂Br₆ consists of two AlBr₄ tetrahedra that share a common edge. The molecular symmetry is D_2h.

The monomer AlBr₃, observed only in the vapor, can be described as trigonal planar, D_3h point group. The atomic hybridization of aluminium is often described as sp². The Br-Al-Br bond angles are 120 °.

By far the most common form of aluminium bromide is Al₂Br₆. This species exists as hygroscopic colorless solid at standard conditions. Typical impure samples are yellowish or even red-brown due to the presence of iron-containing impurities. It is prepared by the reaction of HBr with Al:

Alternatively, the direct bromination occurs also:

Al₂Br₆ dissociates readily to give the strong Lewis acid, AlBr₃. Regarding the tendency of Al₂Br₆ to dimerize, it is common for heavier main group halides to exist as aggregates larger than implied by their empirical formulae. Lighter main group halides such as boron tribromide do not show this tendency, in part due to the smaller size of the central atom.