Mg(AlH4)(2) was produced as a nanocrystalline powder by metathesis of NaAlH4 and MgCl2. Starting with a structure estimation which was developed from an evaluation of FIR data and comparison of structural properties of two solvent adducts, quantum chemical calculations were performed on the density functional theory (DFT) level. The calculated atomic positions were used to simulate an X-ray powder diffraction pattern, based on a trigonal unit cell. The simulated pattern was congruent to experimental data. Thus, magnesium alanate exhibits a CdI2 layer structure, the layers being formed by Mg atoms occupying the Cd sites and AlH4 tedrahedra occupying the sites of the iodine atoms in CdI2.