Lithium nitride

Lithium nitride is an inorganic compound with the chemical formula Li₃N. It is the only stable alkali metal nitride. It is a reddish-pink solid with a high melting point.^[1]

Lithium nitride

Unit cell ball and stick model of lithium nitride __ Li+     __ N3−
Names
Preferred IUPAC name Lithium nitride
Other names Trilithium azanide Trilithium nitride
Identifiers
CAS Number	26134-62-3 Y
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:30525 N
ChemSpider	19054984
ECHA InfoCard	100.043.144
EC Number	247-475-2
Gmelin Reference	1156
PubChem CID	520242 erroneous
CompTox Dashboard (EPA)	DTXSID80894085
InChI InChI=1S/3Li.N Key: IDBFBDSKYCUNPW-UHFFFAOYSA-N InChI=1S/3Li.N/q;;+1;-1 Key: AJUFTLIHDBAQOK-UHFFFAOYSA-N
SMILES [Li]N([Li])[Li] [Li+].[Li][N-][Li]
Properties
Chemical formula	Li3N
Molar mass	34.83 g·mol−1
Appearance	Red-purple or reddish-pink crystals or powder
Density	1.270 g/cm3
Melting point	813 °C (1,495 °F; 1,086 K)
Solubility in water	reacts
log P	3.24
Structure
Crystal structure	see text
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	reacts with water to release ammonia
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H260, H314
Precautionary statements	P223, P231+P232, P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P335+P334, P363, P370+P378, P402+P404, P405, P501
NFPA 704 (fire diamond)	0 2 W
Related compounds
Other anions	Lithium phosphide Lithium arsenide Lithium fluoride Lithium oxide Tetralithiomethane Lithium carbide
Other cations	Sodium nitride Potassium nitride Copper(I) nitride Silver nitride Thallium(I) nitride Calcium nitride
Related compounds	Ammonia Lithium amide Lithium imide
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

Preparation and handling

Lithium nitride is prepared by direct reaction of elemental lithium with nitrogen gas:^[2]

6 Li + N₂ → 2 Li₃N

Instead of burning lithium metal in an atmosphere of nitrogen, a solution of lithium in liquid sodium metal can be treated with N₂.

Lithium nitride is an extremely strong base, so it must be protected from moisture as it reacts violently with water to produce ammonia:

Li₃N + 3 H₂O → 3 LiOH + NH₃

Structure and properties

• alpha-Li₃N (stable at room temperature and pressure) has an unusual crystal structure that consists of two types of layers: one layer has the composition Li₂N⁻ contains 6-coordinate N centers and the other layer consists only of lithium cations.^[3]

Two other forms are known:

• beta-Li₃N, formed from the alpha phase at 0.42 GPa has the sodium arsenide (Na₃As) structure;
• gamma-Li₃N (same structure as lithium bismuthide Li₃Bi) forms from the beta form at 35 to 45 GPa.^[4]

Lithium nitride shows ionic conductivity for Li⁺, with a value of c. 2×10⁻⁴ Ω⁻¹cm⁻¹, and an (intracrystal) activation energy of c. 0.26 eV (c. 24 kJ/mol). Hydrogen doping increases conductivity, whilst doping with metal ions (Al, Cu, Mg) reduces it.^[5][6] The activation energy for lithium transfer across lithium nitride crystals (intercrystalline) has been determined to be higher, at c. 68.5 kJ/mol.^[7] The alpha form is a semiconductor with band gap of c. 2.1 eV.^[4]

Reactions

Reacting lithium nitride with carbon dioxide results in amorphous carbon nitride (C₃N₄), a semiconductor, and lithium cyanamide (Li₂CN₂), a precursor to fertilizers, in an exothermic reaction.^[8][9]

Under hydrogen at around 200°C, Li₃N will react to form lithium amide.^[10]

Li₃N + 2 H₂ → 2LiH + LiNH₂

At higher temperatures it will react further to form ammonia and lithium hydride.

LiNH₂ + H₂ → LiH + NH₃

Lithium imide can also be formed under certain conditions. Some research has explored this as a possible industrial process to produce ammonia since lithium hydride can be thermally decomposed back to lithium metal.

Lithium nitride has been investigated as a storage medium for hydrogen gas, as the reaction is reversible at 270 °C. Up to 11.5% by weight absorption of hydrogen has been achieved.^[11]