The ternary imide Li2Mg(NH)(2) is considered to be one of the most promising on-board hydrogen storage materials due to its high reversible hydrogen capacity of 5.86 wt%, favorable thermodynamic properties and good cycling stability. In this work, Li2Mg(NH)(2) was synthesized by dynamically dehydrogenating a mixture of Mg(NH2)(2)-2LiH up to 280 C under different gas (Ar and H-2) and pressures (0-9.0 bar). The crystal structure of Li2Mg(NH)(2) was found to depend on the gas back pressure in the dehydrogenation process. The crystal structure of Li2Mg(NH)(2) and the dehydrogenation/rehydrogenation properties of the Mg(NH2)(2)-2LiH system strongly depend on the gas back pressure in the dehydrogenation process due to the effect of the pressure on the dehydrogenation kinetics. This study provides a new approach for improving the hydrogen storage properties of the amide hydride systems. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.