ErCuTe2 crystallizes in the trigonal P3m1 space group. Er(1) is bonded to three equivalent Te(1) and three equivalent Te(2) atoms to form distorted ErTe6 octahedra that share corners with six equivalent Cu(1)Te4 tetrahedra, edges with six equivalent Er(1)Te6 octahedra, and edges with three equivalent Cu(1)Te4 tetrahedra. Cu(1) is bonded to one Te(1) and three equivalent Te(2) atoms to form distorted CuTe4 tetrahedra that share corners with six equivalent Er(1)Te6 octahedra, corners with six equivalent Cu(1)Te4 tetrahedra, and edges with three equivalent Er(1)Te6 octahedra. The corner-sharing octahedral tilt angles range from 22-57°. There are two inequivalent Te sites. In the first Te site, Te(1) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Er(1) and one Cu(1) atom. In the second Te site, Te(2) is bonded to three equivalent Er(1) and three equivalent Cu(1) atoms to form distorted edge-sharing TeEr3Cu3 octahedra.
ErCuTe2 crystallizes in the trigonal P3m1 space group. Er(1) is bonded to three equivalent Te(1) and three equivalent Te(2) atoms to form distorted ErTe6 octahedra that share corners with six equivalent Cu(1)Te4 tetrahedra, edges with six equivalent Er(1)Te6 octahedra, and edges with three equivalent Cu(1)Te4 tetrahedra. All Er(1)-Te(1) bond lengths are 3.01 Å. All Er(1)-Te(2) bond lengths are 3.14 Å. Cu(1) is bonded to one Te(1) and three equivalent Te(2) atoms to form distorted CuTe4 tetrahedra that share corners with six equivalent Er(1)Te6 octahedra, corners with six equivalent Cu(1)Te4 tetrahedra, and edges with three equivalent Er(1)Te6 octahedra. The corner-sharing octahedral tilt angles range from 22-57°. The Cu(1)-Te(1) bond length is 2.64 Å. All Cu(1)-Te(2) bond lengths are 2.61 Å. There are two inequivalent Te sites. In the first Te site, Te(1) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Er(1) and one Cu(1) atom. In the second Te site, Te(2) is bonded to three equivalent Er(1) and three equivalent Cu(1) atoms to form distorted edge-sharing TeEr3Cu3 octahedra.