The binary alkaline-earth aluminides AEAl₂ (AE = Ca and Sr) and AEAl₄ (AE = Ca-Ba) have been synthesized from the elements and investigated via powder X-ray diffraction experiments. CaAl₂ adopts the cubic MgCu₂-type structure (Fd3̅m), while SrAl₂ crystallizes in the orthorhombic KHg₂-type (Imma). LT-CaAl₄ crystallizes with the monoclinic CaGa₄-type (C2/m), while HT-CaAl₄, SrAl₄, and BaAl₄ adopt the tetragonal BaAl₄-type structure (I4/mmm). The close structural relation of the two CaAl₄ polymorphs was established using a group-subgroup relation in the Bärnighausen formalism. In addition to the room-temperature and normal pressure phase of SrAl₂, a high-pressure/high-temperature phase has been prepared using multianvil techniques, and its structural and spectroscopic parameters were determined. Elemental analysis by inductively coupled plasma mass spectrometry showed that no significant impurities with other elements besides the weighed ones are present and the chemical compositions match the synthesized ones. The title compounds have been furthermore investigated by ²⁷Al solid-state magic angle spinning NMR experiments to validate the crystal structure and to gain information about the influence of the composition on the electron transfer and the NMR characteristics. This has also been investigated from a quantum chemical point of view using Bader charges, while the stabilities of the binary compounds in the three phase diagrams (Ca-Al, Sr-Al and Ba-Al) have been studied by calculations of formation energies per atom.

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