Aluminium sulfide

Aluminium sulfide
Other names Aluminum sulfide
Identifiers
CAS number	1302-81-4 Y
PubChem	16684788
ChemSpider	140154 Y
Jmol-3D images	Image 1
SMILES [Al+3].[Al+3].[S-2].[S-2].[S-2]
InChI InChI=1S/2Al.3S/q2*+3;3*-2 Y Key: COOGPNLGKIHLSK-UHFFFAOYSA-N Y InChI=1/2Al.3S/q2*+3;3*-2 Key: COOGPNLGKIHLSK-UHFFFAOYAY
Properties
Molecular formula	Al2S3
Molar mass	150.158 g/mol
Appearance	gray solid
Density	2.32 g/cm3
Melting point	1100 °C
Boiling point	1500 °C (sublimes)
Solubility in water	decomposes
Solubility in other solvents	none
Hazards
MSDS	MSDS
EU classification	not listed
NFPA 704	0 4 2
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Aluminium sulfide or aluminium sulphide is a chemical compound with the formula Al₂S₃. This colorless species has an interesting structural chemistry, existing in several forms. The material is sensitive to moisture, hydrolyzing to hydrated aluminium oxides/hydroxides.^[1] This can begin when the sulfide is exposed to the atmosphere. The hydrolysis reaction generates gaseous hydrogen sulfide (H₂S).

Crystal structure

More than six crystalline forms of aluminium sulfide are known and only some are listed below. Most of them have rather similar, wurtzite-like structures, and differ by the arrangement of lattice vacancies, which form ordered or disordered sublattices.^[2][3]

The β and γ phases are obtained by annealing the most stable α-Al₂S₃ phase at several hundred degrees Celsius.^[4] Compressing aluminium sulfide to 2–65 kbar results in the δ phase where vacancies are arranged in a superlattice of tetragonal symmetry.^[5]

Unlike Al₂O₃, in which the Al(III) centers occupy octahedral holes, the more expanded framework of Al₂S₃ stabilizes the Al(III) centers into one third of the tetrahedral holes of a hexagonally close-packed arrangement of the sulfide anions. At higher temperature, the Al(III) centers become randomized to give a "defect wurtzite" structure. And at still higher temperatures stabilize the γ-Al₂S₃ forms, with a structure akin to γ-Al₂O₃.

Molecular derivatives of Al₂S₃ are not known. Mixed Al-S-Cl compounds are however known. Al₂Se₃ and Al₂Te₃ are also known.

Preparation

Aluminium sulfide is readily prepared by ignition of the elements

2 Al + 3 S → Al₂S₃

This reaction is extremely exothermic and it is not necessary or desirable to heat the whole mass of the sulfur-aluminium mixture; (except possibly for very small amounts of reactants). The product will be created in a fused form; it reaches a temperature greater than 1100 °C and may melt its way through steel. The cooled product is very hard.

References