KTb2CuS4 crystallizes in the orthorhombic Cmcm space group. K(1) is bonded in a 6-coordinate geometry to two equivalent S(3) and four equivalent S(2) atoms. Tb(1) is bonded to one S(3), two equivalent S(1), and three equivalent S(2) atoms to form TbS6 octahedra that share corners with three equivalent Tb(1)S6 octahedra,  a cornercorner with one Cu(1)S4 tetrahedra, edges with five equivalent Tb(1)S6 octahedra, and edges with two equivalent Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 0-38°. Cu(1) is bonded to two equivalent S(2) and two equivalent S(3) atoms to form CuS4 tetrahedra that share corners with two equivalent Tb(1)S6 octahedra, corners with two equivalent Cu(1)S4 tetrahedra, and edges with four equivalent Tb(1)S6 octahedra. The corner-sharing octahedral tilt angles are 5°. There are three inequivalent S sites. In the first S site, S(1) is bonded in a square co-planar geometry to four equivalent Tb(1) atoms. In the second S site, S(2) is bonded to two equivalent K(1), three equivalent Tb(1), and one Cu(1) atom to form a mixture of distorted corner, edge, and face-sharing SK2Tb3Cu octahedra. The corner-sharing octahedral tilt angles are 65°. In the third S site, S(3) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent Tb(1), and two equivalent Cu(1) atoms.
KTb2CuS4 crystallizes in the orthorhombic Cmcm space group. K(1) is bonded in a 6-coordinate geometry to two equivalent S(3) and four equivalent S(2) atoms. Both K(1)-S(3) bond lengths are 3.13 Å. All K(1)-S(2) bond lengths are 3.26 Å. Tb(1) is bonded to one S(3), two equivalent S(1), and three equivalent S(2) atoms to form TbS6 octahedra that share corners with three equivalent Tb(1)S6 octahedra,  a cornercorner with one Cu(1)S4 tetrahedra, edges with five equivalent Tb(1)S6 octahedra, and edges with two equivalent Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 0-38°. The Tb(1)-S(3) bond length is 2.72 Å. Both Tb(1)-S(1) bond lengths are 2.83 Å. There are two shorter (2.73 Å) and one longer (2.78 Å) Tb(1)-S(2) bond length. Cu(1) is bonded to two equivalent S(2) and two equivalent S(3) atoms to form CuS4 tetrahedra that share corners with two equivalent Tb(1)S6 octahedra, corners with two equivalent Cu(1)S4 tetrahedra, and edges with four equivalent Tb(1)S6 octahedra. The corner-sharing octahedral tilt angles are 5°. Both Cu(1)-S(2) bond lengths are 2.34 Å. Both Cu(1)-S(3) bond lengths are 2.36 Å. There are three inequivalent S sites. In the first S site, S(1) is bonded in a square co-planar geometry to four equivalent Tb(1) atoms. In the second S site, S(2) is bonded to two equivalent K(1), three equivalent Tb(1), and one Cu(1) atom to form a mixture of distorted corner, edge, and face-sharing SK2Tb3Cu octahedra. The corner-sharing octahedral tilt angles are 65°. In the third S site, S(3) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent Tb(1), and two equivalent Cu(1) atoms.