ErCuPbSe3 crystallizes in the orthorhombic Pnma space group. Er(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form ErSe6 octahedra that share corners with two equivalent Er(1)Se6 octahedra, edges with two equivalent Er(1)Se6 octahedra, and edges with four equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. Cu(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra and edges with four equivalent Er(1)Se6 octahedra. Pb(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Er(1), two equivalent Cu(1), and two equivalent Pb(1) atoms. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to two equivalent Er(1), one Cu(1), and two equivalent Pb(1) atoms. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Er(1), one Cu(1), and two equivalent Pb(1) atoms.
ErCuPbSe3 crystallizes in the orthorhombic Pnma space group. Er(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form ErSe6 octahedra that share corners with two equivalent Er(1)Se6 octahedra, edges with two equivalent Er(1)Se6 octahedra, and edges with four equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. Both Er(1)-Se(1) bond lengths are 2.85 Å. Both Er(1)-Se(2) bond lengths are 2.88 Å. Both Er(1)-Se(3) bond lengths are 2.84 Å. Cu(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra and edges with four equivalent Er(1)Se6 octahedra. The Cu(1)-Se(2) bond length is 2.48 Å. The Cu(1)-Se(3) bond length is 2.44 Å. Both Cu(1)-Se(1) bond lengths are 2.52 Å. Pb(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. Both Pb(1)-Se(1) bond lengths are 3.17 Å. Both Pb(1)-Se(2) bond lengths are 3.14 Å. Both Pb(1)-Se(3) bond lengths are 3.18 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Er(1), two equivalent Cu(1), and two equivalent Pb(1) atoms. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to two equivalent Er(1), one Cu(1), and two equivalent Pb(1) atoms. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Er(1), one Cu(1), and two equivalent Pb(1) atoms.