Ternary magnesium gallides – synthesis, crystal chemistry and properties of CaMgGa, SrMgGa, BaMgGa and YbMgGa

The gallides CaMgGa, SrMgGa, BaMgGa and YbMgGa were synthesized from the elements in sealed tantalum ampoules in muffle furnaces. The phase purity of the samples was checked by powder X‐ray diffraction. CaMgGa and YbMgGa crystallize with the ZrNiAl type structure, space group P 6‾ ${\bar 6}$ 2m, whereas SrMgGa and BaMgGa adopt an ordering variant of the Cu2Sb/PbFCl type, space group P4/nmm. The structures of SrMg0.884(7)Ga1.116(7) (a=459.23(9), c=792.43(12) pm, wR2=0.0371, 226 F2 values, 11 variables) and YbMgGa (a=774.55(7), c=411.95(4) pm, wR2=0.0329, 342 F2 values, 15 variables) were refined from single crystal X‐ray diffractometer data. Refinement of the occupancy parameters indicated a small degree of Mg/Ga mixing on the 2a site for the strontium compound. The [MgGa] substructures in both compounds are composed of condensed Mg@Ga4 tetrahedra with 4×287 pm Mg−Ga in SrMg0.884Ga1.116 vs 2×282 and 2×296 pm in YbMgGa. The SrMgGa structure has a stacking of layers of edge‐sharing Mg@Ga4 and Sr4 tetrahedra. Electronic structure calculations indicate a net charge transfer from strontium and magnesium to gallium. YbMgGa completes the series of REMgGa gallides. Temperature dependent magnetic susceptibility studies reveal weak Pauli paramagnetism, confirming divalent ytterbium.