Insights into the Rb-Mg-N-H System: An Ordered Mixed Amide/Imide Phase and a Disordered Amide/Hydride Solid Solution

The crystal structure of a mixed amide-imide phase, RbMgND2ND, has been solved in the orthorhombic space group Pnma (a = 9.55256(31), b = 3.70772(11) and c = 10.08308(32) Å). A new metal amide-hydride solid solution, Rb(NH2)xH(1–x), has been isolated and characterized in the entire compositional range. The profound analogies, as well as the subtle differences, with the crystal chemistry of KMgND2ND and K(NH2)xH1–x are thoroughly discussed. This approach suggests that the comparable performances obtained using K- and Rb-based additives for the Mg(NH2)2-2LiH and 2LiNH2–MgH2 hydrogen storage systems are likely to depend on the structural similarities of possible reaction products and intermediates.