Rapid Microwave Synthesis, Characterization and Reactivity of Lithium Nitride Hydride, Li₄NH.

Lithium nitride hydride, Li₄NH, was synthesised from lithium nitride and lithium hydride over minute timescales, using microwave synthesis methods in the solid state for the first time. The structure of the microwave-synthesised powders was confirmed by powder X-ray diffraction [tetragonal space group 4₁; = 4.8864(1) Å, = 9.9183(2) Å] and the nitride hydride reacts with moist air under ambient conditions to produce lithium hydroxide and subsequently lithium carbonate. Li₄NH undergoes no dehydrogenation or decomposition [under Ar] below 773 K. A tetragonal-cubic phase transition, however, occurs for the compound at . 770 K. The new high temperature (HT) phase adopts an -fluorite structure (space group ; = 4.9462(3) Å) with N and H ions disordered on the 4 sites. Thermal treatment of Li₄NH under nitrogen yields a stoichiometric mixture of lithium nitride and lithium imide (Li₃N and Li₂NH respectively).