MgAuGa and MgAu₂Ga: first representatives of the Mg-Au-Ga system

MgAuGa is the first ternary representative of the Mg-Au-Ga system. It adopts the Fe₂P structure type (Pearson symbol hP9) and closely resembles hexa­gonal Mg₂Ga through a direct group-subgroup relationship. MgAu₂Ga also crystallizes hexa­gonally and is isotypic with Na₃As. It adopts the structure of another binary compound, viz. Mg₃Au (hP8), but shows an unexpected distribution of Mg, Au, and Ga among the atomic positions of the asymmetric unit compared to Mg₃Au.

The low-temperature form of calcium gold stannide, CaAuSn

The low-temperature form of CaAuSn has an EuAuGe-type structure (space group Imm2), with a = 4.5261 (7) Å, b = 7.1356 (11) Å and c = 7.8147 (11) Å. This structure is one of the two parent structures of its high-temperature polymorph (ca 873 K), which is an inter­growth structure of the EuAuGe- and SrMgSi-type structures in a 2:3 ratio.