ErPtAs crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to six equivalent Pt(1) and six equivalent As(1) atoms to form a mixture of face and edge-sharing ErAs6Pt6 cuboctahedra. In the second Er site, Er(2) is bonded to six equivalent Pt(1) and six equivalent As(1) atoms to form a mixture of distorted face and edge-sharing ErAs6Pt6 cuboctahedra. Pt(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent As(1) atoms. As(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent Pt(1) atoms.
ErPtAs crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to six equivalent Pt(1) and six equivalent As(1) atoms to form a mixture of face and edge-sharing ErAs6Pt6 cuboctahedra. All Er(1)-Pt(1) bond lengths are 3.21 Å. All Er(1)-As(1) bond lengths are 3.01 Å. In the second Er site, Er(2) is bonded to six equivalent Pt(1) and six equivalent As(1) atoms to form a mixture of distorted face and edge-sharing ErAs6Pt6 cuboctahedra. All Er(2)-Pt(1) bond lengths are 2.99 Å. All Er(2)-As(1) bond lengths are 3.19 Å. Pt(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent As(1) atoms. All Pt(1)-As(1) bond lengths are 2.47 Å. As(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent Pt(1) atoms.