Abstract
Abstract The gallides Ca3Ni4Ga4 and Sr3Ni3Ga4 were synthesized from arc-melted NixGay precursor alloys and the respective alkaline earth metal in sealed niobium tubes in an induction furnace. Redetermination of the Ca3Ni4Ga4 structure from X-ray single crystal diffractometer data confirmed the X-ray powder data: Na3Pt4Ge4 type, I4̅3m, a=740.6(1) pm, wR2=0.0245, 169 F2 values, 9 variables. The nickel atoms build tetrahedral Ni4 clusters (256 pm Ni–Ni) that are end-on coordinated by gallium atoms (234 pm Ni–Ga). These [Ni4Ga4] units show a bcc packing and leave cavities Ca@Ga4Ni4Ga4 for the calcium atoms. Sr3Ni3Ga4 crystallizes with a new structure type: R3m, a=1039.8(2), c=698.2(1) pm, wR2=0.1048, 636 F2 values, 23 variables. The structure shows twinning by inversion with a domain ratio of 79/21. The structures of Sr3Ni3Ga4 and Ca3Ni4Ga4 are related by a group–subgroup scheme (R3m is a translationengleiche subgroup of I4̅3m). The 8c Ni and Ga subcell sites split into site 3a and 9b each. This allows formation of ordered Ni3Ga tetrahedra (264 pm Ni–Ga) along with ordered gallium vacancies.
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