Results for (La,Mg)Ni-3.5 and (La,Mg)(Ni,Al)(3.5) systems synthesized by metallurgical and mechanochemical techniques are reported. Powder X-ray and neutron diffraction combined with Rietveld refinements and profile analysis show that depending on the applied synthesis method various structurally related phases can be obtained for the same nominal composition. The hexagonal A(2)B(7)-type structure incorporating aluminum, with the refined composition La0.77Mg0.23Ni3.41Al0.09, has been identified. Al atoms occupy 12% of the 6h site within the LaNi5 slabs. This intermetallic phase absorbs hydrogen (deuterium) when exposed to 10 bar of H-2 (D-2) gas at room temperature. The H(D)-containing phase expands isotropically and retains the original symmetry of the parent compound. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.