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.[1]. 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[2]. 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− 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[3].