Aluminum trifluoride

Aluminium fluoride

Crystal structure
Names
Other names Aluminium(III) fluoride Aluminum trifluoride
Identifiers
CAS Number	7784-18-1 Y 32287-65-3 (monohydrate) Y 15098-87-0 (trihydrate) Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:49464 Y
ChemSpider	2039 Y
ECHA InfoCard	100.029.137
PubChem CID	2124
RTECS number	BD0725000
InChI InChI=1S/Al.3FH/h;3*1H/q+3;;;/p-3 Y Key: KLZUFWVZNOTSEM-UHFFFAOYSA-K Y InChI=1/Al.3FH/h;3*1H/q+3;;;/p-3 Key: KLZUFWVZNOTSEM-DFZHHIFOAC
SMILES F[Al](F)F
Properties
Chemical formula	AlF3
Molar mass	83.977 g/mol (anhydrous) 101.992 g/mol (monohydrate) 138.023 (trihydrate)
Appearance	white, crystalline solid odorless
Density	3.10 g/cm3 (anhydrous) 2.17 g/cm3 (monohydrate) 1.914 g/cm3 (trihydrate)
Melting point	1,290 °C (2,350 °F; 1,560 K) (anhydrous) (sublimes)
Solubility in water	5.6 g/L (0 °C) 6.7 g/L (20 °C) 17.2 g/L (100 °C)
Magnetic susceptibility (χ)	-13.4·10−6 cm3/mol
Refractive index (nD)	1.3767 (visible range)
Structure
Crystal structure	Rhombohedral, hR24
Space group	R3c, No. 167
Lattice constant	a = 0.49254 nm, c = 1.24477 nm
Lattice volume (V)	0.261519
Formula units (Z)	6
Thermochemistry
Specific heat capacity (C)	75.1 J/mol·K
Std molar entropy (So298)	66.5 J/mol·K
Std enthalpy of formation (ΔfHo298)	−1510.4 kJ/mol
Gibbs free energy (ΔfG˚)	-1431.1 kJ/mol
Hazards
EU classification (DSD) (outdated)	No classification according to EU Regulation (EC) No. 1272/2008.
R-phrases (outdated)	–
S-phrases (outdated)	–
NFPA 704	0 0 0
US health exposure limits (NIOSH):
PEL (Permissible)	none
REL (Recommended)	2 mg/m3
IDLH (Immediate danger)	N.D.
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 fluoride (AlF₃) is an inorganic compound used primarily in the production of aluminium. This colorless solid can be prepared synthetically but also occurs in nature as minerals rosenbergite and oskarssonite.

The majority of aluminium fluoride is produced by treating alumina with hydrogen fluoride gas at 700 °C:

Alternatively, it is manufactured by thermal decomposition of ammonium hexafluoroaluminate. For small scale laboratory preparations, AlF₃ can also be prepared by treating aluminium hydroxide or aluminium metal with HF.

Aluminium fluoride trihydrate is found in nature as the rare mineral rosenbergite. The non-hydrated form appears as the mineral oskarssonite.

Its structure adopts the rhenium trioxide motif, featuring distorted AlF₆octahedra. Each fluoride is connected to two Al centers. Because of its 3-dimensional polymeric structure, AlF₃ has a high melting point. The other trihalides of aluminium in the solid state differ, AlCl₃ has a layer structure and AlBr₃ and AlI₃, are molecular dimers. Also they have low melting points and evaporate readily to give dimers. In the gas phase aluminium fluoride exists as trigonal molecules of D_3h symmetry. The Al-F bond lengths of this gaseous molecule are 163 pm.

Aluminium fluoride is an important additive for the production of aluminium by electrolysis. Together with cryolite, it lowers the melting point to below 1000 °C and increases the conductivity of the solution. It is into this molten salt that aluminium oxide is dissolved and then electrolyzed to give bulk Al metal.