CsTb2Ag3Se5 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. Tb(1) is bonded to one Se(2), two equivalent Se(1), and three equivalent Se(3) atoms to form TbSe6 octahedra that share  a cornercorner with one Tb(1)Se6 octahedra, corners with four equivalent Ag(2)Se4 tetrahedra, edges with four equivalent Tb(1)Se6 octahedra, edges with two equivalent Ag(1)Se4 tetrahedra, and edges with three equivalent Ag(2)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. There are two inequivalent Ag sites. In the first Ag site, 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, corners with four equivalent Ag(2)Se4 tetrahedra, and edges with four equivalent Tb(1)Se6 octahedra. In the second Ag site, Ag(2) is bonded to two equivalent Se(1) and two equivalent Se(3) atoms to form distorted AgSe4 tetrahedra that share corners with four equivalent Tb(1)Se6 octahedra, corners with two equivalent Ag(1)Se4 tetrahedra, corners with two equivalent Ag(2)Se4 tetrahedra, edges with three equivalent Tb(1)Se6 octahedra, and  an edgeedge with one Ag(2)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 7-59°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Tb(1), one Ag(1), and two equivalent Ag(2) atoms. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Tb(1), and two equivalent Ag(1) atoms. In the third Se site, Se(3) is bonded to one Cs(1), three equivalent Tb(1), and two equivalent Ag(2) atoms to form a mixture of distorted corner and edge-sharing SeCsTb3Ag2 octahedra. The corner-sharing octahedral tilt angles are 61°.
CsTb2Ag3Se5 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. Both Cs(1)-Se(2) bond lengths are 3.63 Å. Both Cs(1)-Se(3) bond lengths are 3.69 Å. All Cs(1)-Se(1) bond lengths are 3.81 Å. Tb(1) is bonded to one Se(2), two equivalent Se(1), and three equivalent Se(3) atoms to form TbSe6 octahedra that share  a cornercorner with one Tb(1)Se6 octahedra, corners with four equivalent Ag(2)Se4 tetrahedra, edges with four equivalent Tb(1)Se6 octahedra, edges with two equivalent Ag(1)Se4 tetrahedra, and edges with three equivalent Ag(2)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. The Tb(1)-Se(2) bond length is 2.89 Å. Both Tb(1)-Se(1) bond lengths are 2.93 Å. There is one shorter (2.91 Å) and two longer (2.96 Å) Tb(1)-Se(3) bond lengths. There are two inequivalent Ag sites. In the first Ag site, 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, corners with four equivalent Ag(2)Se4 tetrahedra, and edges with four equivalent Tb(1)Se6 octahedra. Both Ag(1)-Se(1) bond lengths are 2.73 Å. Both Ag(1)-Se(2) bond lengths are 2.64 Å. In the second Ag site, Ag(2) is bonded to two equivalent Se(1) and two equivalent Se(3) atoms to form distorted AgSe4 tetrahedra that share corners with four equivalent Tb(1)Se6 octahedra, corners with two equivalent Ag(1)Se4 tetrahedra, corners with two equivalent Ag(2)Se4 tetrahedra, edges with three equivalent Tb(1)Se6 octahedra, and  an edgeedge with one Ag(2)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 7-59°. There is one shorter (2.72 Å) and one longer (2.79 Å) Ag(2)-Se(1) bond length. Both Ag(2)-Se(3) bond lengths are 2.71 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Tb(1), one Ag(1), and two equivalent Ag(2) atoms. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Tb(1), and two equivalent Ag(1) atoms. In the third Se site, Se(3) is bonded to one Cs(1), three equivalent Tb(1), and two equivalent Ag(2) atoms to form a mixture of distorted corner and edge-sharing SeCsTb3Ag2 octahedra. The corner-sharing octahedral tilt angles are 61°.