BaErAgSe3 crystallizes in the orthorhombic Cmcm space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent Se(2) and six equivalent Se(1) atoms. Er(1) is bonded to two equivalent Se(2) and four equivalent Se(1) 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 Ag(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 45°. Ag(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form AgSe4 tetrahedra that share corners with two equivalent Ag(1)Se4 tetrahedra and edges with four equivalent Er(1)Se6 octahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to three equivalent Ba(1), two equivalent Er(1), and one Ag(1) atom. In the second Se site, Se(2) is bonded to two equivalent Ba(1), two equivalent Er(1), and two equivalent Ag(1) atoms to form a mixture of distorted corner and edge-sharing SeBa2Er2Ag2 octahedra. The corner-sharing octahedra are not tilted.
BaErAgSe3 crystallizes in the orthorhombic Cmcm space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent Se(2) and six equivalent Se(1) atoms. Both Ba(1)-Se(2) bond lengths are 3.27 Å. There are four shorter (3.49 Å) and two longer (3.59 Å) Ba(1)-Se(1) bond lengths. Er(1) is bonded to two equivalent Se(2) and four equivalent Se(1) 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 Ag(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 45°. Both Er(1)-Se(2) bond lengths are 2.91 Å. All Er(1)-Se(1) bond lengths are 2.94 Å. Ag(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form AgSe4 tetrahedra that share corners with two equivalent Ag(1)Se4 tetrahedra and edges with four equivalent Er(1)Se6 octahedra. Both Ag(1)-Se(1) bond lengths are 2.63 Å. Both Ag(1)-Se(2) bond lengths are 2.67 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to three equivalent Ba(1), two equivalent Er(1), and one Ag(1) atom. In the second Se site, Se(2) is bonded to two equivalent Ba(1), two equivalent Er(1), and two equivalent Ag(1) atoms to form a mixture of distorted corner and edge-sharing SeBa2Er2Ag2 octahedra. The corner-sharing octahedra are not tilted.