We have designed a new synthesis method for the complex Mg2NiR4 hydride, based on the direct reaction of simple hydrides under high-pressure and moderate-temperature conditions. A well-crystallized sample was obtained in a piston-cylinder hydrostatic press at moderate pressures of 2 GPa and temperatures around 750 degrees C from mixtures of MgH2 and Ni enclosed in gold capsules. X-ray and neutron powder diffraction analysis were used to identify the purity of the samples and provide an accurate description of the crystal structure features. Mg2NiH4 hydride shows a monoclinic symmetry with space group C2/c (No. 15). Thermogravimetric analysis (TGA) and differential scanning calorimetry (Dsc) have been carried out to determine the hydrogen desorption temperature, the hydrogen contents and the cyclability of the compound under a hydrogen pressure of 10 atm. These studies reveal two different desorption temperatures that correspond to the loss of the labile hydrogen H3 leading to a stable hexagonal structure (Mg2NiH3) followed by the complete hydrogen desorption to give Mg2Ni. The cyclability of the hydride was studied through 10 cycles at a hydrogen pressure of 10 atm; a slight loss of reversibility was observed due the progressive oxidation to MgO due to traces of oxygen adsorbed within the DSC chamber. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.