Aluminium sulfide

Aluminium sulfide

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Names
Other names Aluminum sulfide
Identifiers
CAS Number	1302-81-4 N
ChemSpider	140154 Y
Jmol 3D model	Interactive image
PubChem	16684788
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
SMILES [Al+3].[Al+3].[S-2].[S-2].[S-2]
Properties
Chemical formula	Al2S3
Molar mass	150.158 g/mol
Appearance	gray solid
Density	2.02 g/cm3
Melting point	1,100 °C (2,010 °F; 1,370 K)
Boiling point	1,500 °C (2,730 °F; 1,770 K) sublimes
Solubility in water	decomposes
Solubility	insoluble in acetone
Structure
Crystal structure	trigonal
Thermochemistry
Specific heat capacity (C)	105.1 J/mol K
Std molar entropy (So298)	116.9 J/mol K
Std enthalpy of formation (ΔfHo298)	-724 kJ/mol
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Aluminum 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. 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.

Form	Symmetry	Space group	a (A)	c (A)	ρ (g/cm3)
α	Hexagonal		6.423	17.83	2.32
β	Hexagonal	P63mc	3.579	5.829	2.495
γ	Trigonal		6.47	17.26	2.36
δ	Tetragonal	I41/amd	7.026	29.819	2.71

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

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.