AgErSe2 is Caswellsilverite-like structured and crystallizes in the tetragonal P4/mmm space group. Er(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form ErSe6 octahedra that share corners with six equivalent Er(1)Se6 octahedra, edges with four equivalent Er(1)Se6 octahedra, and edges with eight equivalent Ag(1)Se6 octahedra. The corner-sharing octahedra are not tilted. Ag(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form AgSe6 octahedra that share corners with six equivalent Ag(1)Se6 octahedra, edges with four equivalent Ag(1)Se6 octahedra, and edges with eight equivalent Er(1)Se6 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to four equivalent Er(1) and two equivalent Ag(1) atoms to form SeEr4Ag2 octahedra that share corners with six equivalent Se(1)Er4Ag2 octahedra, edges with four equivalent Se(1)Er4Ag2 octahedra, and edges with eight equivalent Se(2)Er2Ag4 octahedra. The corner-sharing octahedra are not tilted. In the second Se site, Se(2) is bonded to two equivalent Er(1) and four equivalent Ag(1) atoms to form SeEr2Ag4 octahedra that share corners with six equivalent Se(2)Er2Ag4 octahedra, edges with four equivalent Se(2)Er2Ag4 octahedra, and edges with eight equivalent Se(1)Er4Ag2 octahedra. The corner-sharing octahedra are not tilted.
AgErSe2 is Caswellsilverite-like structured and crystallizes in the tetragonal P4/mmm space group. Er(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form ErSe6 octahedra that share corners with six equivalent Er(1)Se6 octahedra, edges with four equivalent Er(1)Se6 octahedra, and edges with eight equivalent Ag(1)Se6 octahedra. The corner-sharing octahedra are not tilted. Both Er(1)-Se(2) bond lengths are 2.84 Å. All Er(1)-Se(1) bond lengths are 2.89 Å. Ag(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form AgSe6 octahedra that share corners with six equivalent Ag(1)Se6 octahedra, edges with four equivalent Ag(1)Se6 octahedra, and edges with eight equivalent Er(1)Se6 octahedra. The corner-sharing octahedra are not tilted. Both Ag(1)-Se(1) bond lengths are 2.84 Å. All Ag(1)-Se(2) bond lengths are 2.89 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to four equivalent Er(1) and two equivalent Ag(1) atoms to form SeEr4Ag2 octahedra that share corners with six equivalent Se(1)Er4Ag2 octahedra, edges with four equivalent Se(1)Er4Ag2 octahedra, and edges with eight equivalent Se(2)Er2Ag4 octahedra. The corner-sharing octahedra are not tilted. In the second Se site, Se(2) is bonded to two equivalent Er(1) and four equivalent Ag(1) atoms to form SeEr2Ag4 octahedra that share corners with six equivalent Se(2)Er2Ag4 octahedra, edges with four equivalent Se(2)Er2Ag4 octahedra, and edges with eight equivalent Se(1)Er4Ag2 octahedra. The corner-sharing octahedra are not tilted.