AgErSe2 crystallizes in the orthorhombic P2_12_12_1 space group. Er(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 43-52°. Ag(1) is bonded in a 4-coordinate geometry to two equivalent Se(1) and two equivalent Se(2) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Er(1) and two equivalent Ag(1) atoms to form a mixture of distorted edge and corner-sharing SeEr3Ag2 trigonal bipyramids. In the second Se site, Se(2) is bonded to three equivalent Er(1) and two equivalent Ag(1) atoms to form a mixture of distorted edge and corner-sharing SeEr3Ag2 trigonal bipyramids.
AgErSe2 crystallizes in the orthorhombic P2_12_12_1 space group. Er(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 43-52°. There are a spread of Er(1)-Se(1) bond distances ranging from 2.82-2.86 Å. There is one shorter (2.84 Å) and two longer (2.85 Å) Er(1)-Se(2) bond lengths. Ag(1) is bonded in a 4-coordinate geometry to two equivalent Se(1) and two equivalent Se(2) atoms. Both Ag(1)-Se(1) bond lengths are 2.73 Å. Both Ag(1)-Se(2) bond lengths are 2.70 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Er(1) and two equivalent Ag(1) atoms to form a mixture of distorted edge and corner-sharing SeEr3Ag2 trigonal bipyramids. In the second Se site, Se(2) is bonded to three equivalent Er(1) and two equivalent Ag(1) atoms to form a mixture of distorted edge and corner-sharing SeEr3Ag2 trigonal bipyramids.