Crystal structures and new perspectives on Y₃Au₄ and Y₁₄Au₅₁

Y₃Au₄ (triyttrium tetragold) and Y₁₄Au₅₁ (tetradecayttrium henpentacontagold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R-3 and P6/m, adopting the Pu₃Pd₄ and Gd₁₄Ag₅₁ structure types, respectively (Pearson symbols hR42 and hP65). A variety of binary R-Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu₃Pd₄ type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca₃Au₄, Pr₃Au₄, Nd₃Au₄, Gd₃Au₄, and Th₃Au₄. Sm₆Au₇ is suspected to be Sm₃Au₄ due to identical symmetry and close unit-cell parameters. The Pu₃Pd₄ structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd₁₄Ag₅₁ type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y₃Au₄ can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y₁₄Au₅₁, this structure is more complex and is best described in terms of polyhedral `pinwheels' around the tunnel forming polyhedra along the c axis.