Er2PbSe4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one Se(2), two equivalent Se(4), and three equivalent Se(3) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-62°. In the second Er site, Er(2) is bonded to one Se(4), two equivalent Se(2), and three equivalent Se(1) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-62°. Pb(1) is bonded in a 7-coordinate geometry to one Se(2), two equivalent Se(1), two equivalent Se(3), and two equivalent Se(4) atoms. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Er(2) and two equivalent Pb(1) atoms to form distorted edge-sharing SeEr3Pb2 square pyramids. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to one Er(1), two equivalent Er(2), and one Pb(1) atom. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to three equivalent Er(1) and two equivalent Pb(1) atoms. In the fourth Se site, Se(4) is bonded in a 5-coordinate geometry to one Er(2), two equivalent Er(1), and two equivalent Pb(1) atoms.
Er2PbSe4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one Se(2), two equivalent Se(4), and three equivalent Se(3) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-62°. The Er(1)-Se(2) bond length is 2.83 Å. Both Er(1)-Se(4) bond lengths are 2.90 Å. There is one shorter (2.82 Å) and two longer (2.84 Å) Er(1)-Se(3) bond lengths. In the second Er site, Er(2) is bonded to one Se(4), two equivalent Se(2), and three equivalent Se(1) atoms to form a mixture of corner and edge-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-62°. The Er(2)-Se(4) bond length is 2.87 Å. Both Er(2)-Se(2) bond lengths are 2.80 Å. There is one shorter (2.84 Å) and two longer (2.86 Å) Er(2)-Se(1) bond lengths. Pb(1) is bonded in a 7-coordinate geometry to one Se(2), two equivalent Se(1), two equivalent Se(3), and two equivalent Se(4) atoms. The Pb(1)-Se(2) bond length is 3.33 Å. Both Pb(1)-Se(1) bond lengths are 3.22 Å. Both Pb(1)-Se(3) bond lengths are 3.31 Å. Both Pb(1)-Se(4) bond lengths are 3.17 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Er(2) and two equivalent Pb(1) atoms to form distorted edge-sharing SeEr3Pb2 square pyramids. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to one Er(1), two equivalent Er(2), and one Pb(1) atom. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to three equivalent Er(1) and two equivalent Pb(1) atoms. In the fourth Se site, Se(4) is bonded in a 5-coordinate geometry to one Er(2), two equivalent Er(1), and two equivalent Pb(1) atoms.