BaErAgS3 crystallizes in the monoclinic C2/m space group. Ba(1) is bonded in a 7-coordinate geometry to two equivalent S(1), two equivalent S(3), and three equivalent S(2) atoms. Er(1) is bonded to one S(4), two equivalent S(2), and three equivalent S(1) atoms to form ErS6 octahedra that share  a cornercorner with one Er(1)S6 octahedra, corners with two equivalent Ag(1)S4 trigonal pyramids, edges with four equivalent Er(1)S6 octahedra, and edges with two equivalent Ag(1)S4 trigonal pyramids. The corner-sharing octahedra are not tilted. Ag(1) is bonded to one S(2), one S(3), and two equivalent S(4) atoms to form distorted AgS4 trigonal pyramids that share corners with two equivalent Er(1)S6 octahedra, corners with five equivalent Ag(1)S4 trigonal pyramids, edges with two equivalent Er(1)S6 octahedra, and  an edgeedge with one Ag(1)S4 trigonal pyramid. The corner-sharing octahedral tilt angles are 84°. There are four inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to two equivalent Ba(1) and three equivalent Er(1) atoms. In the second S site, S(2) is bonded to three equivalent Ba(1), two equivalent Er(1), and one Ag(1) atom to form distorted SBa3Er2Ag octahedra that share corners with four equivalent S(3)Ba4Ag2 octahedra, edges with two equivalent S(4)Er2Ag4 octahedra, edges with four equivalent S(2)Ba3Er2Ag octahedra, and  a faceface with one S(3)Ba4Ag2 octahedra. The corner-sharing octahedral tilt angles range from 41-57°. In the third S site, S(3) is bonded to four equivalent Ba(1) and two equivalent Ag(1) atoms to form SBa4Ag2 octahedra that share corners with four equivalent S(4)Er2Ag4 octahedra, corners with eight equivalent S(2)Ba3Er2Ag octahedra, edges with two equivalent S(3)Ba4Ag2 octahedra, and faces with two equivalent S(2)Ba3Er2Ag octahedra. The corner-sharing octahedral tilt angles range from 41-57°. In the fourth S site, S(4) is bonded to two equivalent Er(1) and four equivalent Ag(1) atoms to form SEr2Ag4 octahedra that share corners with four equivalent S(3)Ba4Ag2 octahedra, edges with two equivalent S(4)Er2Ag4 octahedra, and edges with four equivalent S(2)Ba3Er2Ag octahedra. The corner-sharing octahedral tilt angles are 51°.
BaErAgS3 crystallizes in the monoclinic C2/m space group. Ba(1) is bonded in a 7-coordinate geometry to two equivalent S(1), two equivalent S(3), and three equivalent S(2) atoms. Both Ba(1)-S(1) bond lengths are 3.24 Å. Both Ba(1)-S(3) bond lengths are 3.08 Å. There is one shorter (3.24 Å) and two longer (3.28 Å) Ba(1)-S(2) bond lengths. Er(1) is bonded to one S(4), two equivalent S(2), and three equivalent S(1) atoms to form ErS6 octahedra that share  a cornercorner with one Er(1)S6 octahedra, corners with two equivalent Ag(1)S4 trigonal pyramids, edges with four equivalent Er(1)S6 octahedra, and edges with two equivalent Ag(1)S4 trigonal pyramids. The corner-sharing octahedra are not tilted. The Er(1)-S(4) bond length is 2.80 Å. Both Er(1)-S(2) bond lengths are 2.74 Å. There are two shorter (2.75 Å) and one longer (2.77 Å) Er(1)-S(1) bond length. Ag(1) is bonded to one S(2), one S(3), and two equivalent S(4) atoms to form distorted AgS4 trigonal pyramids that share corners with two equivalent Er(1)S6 octahedra, corners with five equivalent Ag(1)S4 trigonal pyramids, edges with two equivalent Er(1)S6 octahedra, and  an edgeedge with one Ag(1)S4 trigonal pyramid. The corner-sharing octahedral tilt angles are 84°. The Ag(1)-S(2) bond length is 2.76 Å. The Ag(1)-S(3) bond length is 2.58 Å. Both Ag(1)-S(4) bond lengths are 2.68 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to two equivalent Ba(1) and three equivalent Er(1) atoms. In the second S site, S(2) is bonded to three equivalent Ba(1), two equivalent Er(1), and one Ag(1) atom to form distorted SBa3Er2Ag octahedra that share corners with four equivalent S(3)Ba4Ag2 octahedra, edges with two equivalent S(4)Er2Ag4 octahedra, edges with four equivalent S(2)Ba3Er2Ag octahedra, and  a faceface with one S(3)Ba4Ag2 octahedra. The corner-sharing octahedral tilt angles range from 41-57°. In the third S site, S(3) is bonded to four equivalent Ba(1) and two equivalent Ag(1) atoms to form SBa4Ag2 octahedra that share corners with four equivalent S(4)Er2Ag4 octahedra, corners with eight equivalent S(2)Ba3Er2Ag octahedra, edges with two equivalent S(3)Ba4Ag2 octahedra, and faces with two equivalent S(2)Ba3Er2Ag octahedra. The corner-sharing octahedral tilt angles range from 41-57°. In the fourth S site, S(4) is bonded to two equivalent Er(1) and four equivalent Ag(1) atoms to form SEr2Ag4 octahedra that share corners with four equivalent S(3)Ba4Ag2 octahedra, edges with two equivalent S(4)Er2Ag4 octahedra, and edges with four equivalent S(2)Ba3Er2Ag octahedra. The corner-sharing octahedral tilt angles are 51°.