Lithium nitride

Overview
Lithium nitride is a compound of lithium and nitrogen with the formula Li3N. It is the only stable alkali metal nitride. The solid is a red or purple color, has a high melting point and is ionic. It has an unusual crystal structure which consists of two different types of layer, one sheet, composition Li2N, containing 6 coordinate lithium ions and the other consisting only of lithium ions. Solid lithium nitride is a fast ion conductor and has the highest conductivity of any inorganic lithium salt. It has been studied extensively as a solid electrolyte and an anode material for use in batteries. . It can be formed by direct reaction of the elements, either by burning lithium metal in pure nitrogen gas or by reacting nitrogen gas with lithium dissolved in liquid sodium metal. The second method gives a purer product. Lithium nitride reacts violently with water to produce ammonia:

Li3N (s) + 3 H2O (l) → 3 LiOH (aq) + NH3 (g)

All ionic nitrides display this pattern, due to the N3 &minus; ion being an extremely strong Bronsted base. It easily qualifies as a superbase. It is, in fact, a stronger base than the hydride ion, so deprotonates hydrogen itself:

Li3N (s) + 2 H2 (g) → LiNH2 (s) + 2 LiH (s).

Lithium nitride is being investigated as a potential storage medium for hydrogen gas, as the reaction is reversible at 270oC. Up to 11.5% by weight absorption of hydrogen has been achieved.