Mixed metal imides and amides

Two independent studies rapidly followed considering the alternative pathway to mixed imides in the Li-Mg-N-H system, namely combining magnesium amide with lithium hydride [84, 85]. The two studies differed in the ratios of starting materials considered. The former took the 1 2 ratio of amide hydride and by analogy to Eq. (16.22) sought to liberate hydrogen as a by-product of mixed imide formation, viz. Eq. (16.23) (hereafter referred to as the 1 2 reaction based on the Mg(NH2)2 LiH ratio)  

By contrast to the 1 2 reaction, however, it was proposed that the equivalent 3 8 reaction was an ammonia-mediated one by analogy to the findings that had been made in the Li-N-H system [85, 97]. Hence, Mg(NH2)2 first decomposes to Mg3N2 -1- NH3 followed by the reaction of ammonia with LiH to produce Li(NH2) that reacts further with LiH to yield the imide (Eq. 16.28)  

4NH3 -I- 4LiH 4L1NH2 -1- 4H2 4LiNH2 -I- 4LiH 4Li2NH -1- 4H, 

Mg3N2 alone certainly confirm that without Li2NH the uptake reaction will not proceed under 10 MPa H2 at 200 °C and the authors maintain that nanosized (ball-milled) Mg3N2 mixed intimately with the produced amide is essential if the ammonia-mediated hydrogenation is to occur. 

5 Anti-La203 structure of Li2Ca(NH)2. Li (smallest spheres) and Ca (light spheres) are coordinated to (NH) in a tetrahedral and octahedral geometry respectively. The disordered H positions are not shown. 

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