Rapid Microwave Synthesis, Characterization and Reactivity of Lithium Nitride Hydride, Li(4)NH

Lithium nitride hydride, Li(4)NH, 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 I4(1)/a; a = 4.8864(1) Å, c = 9.9183(2) Å] and the nitride hydride reacts with moist air under ambient conditions to produce lithium hydroxide and subsequently lithium carbonate. Li(4)NH undergoes no dehydrogenation or decomposition [under Ar((g))] below 773 K. A tetragonal–cubic phase transition, however, occurs for the compound at ca. 770 K. The new high temperature (HT) phase adopts an anti-fluorite structure (space group Fm [Formula: see text] m; a = 4.9462(3) Å) with N(3−) and H(−) ions disordered on the 4a sites. Thermal treatment of Li(4)NH under nitrogen yields a stoichiometric mixture of lithium nitride and lithium imide (Li(3)N and Li(2)NH respectively).