KTm2Cu3Se5 crystallizes in the orthorhombic Cmcm space group. K(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. Tm(1) is bonded to one Se(1), two equivalent Se(2), and three equivalent Se(3) atoms to form TmSe6 octahedra that share  a cornercorner with one Tm(1)Se6 octahedra, corners with four equivalent Cu(1)Se4 tetrahedra, edges with four equivalent Tm(1)Se6 octahedra, edges with two equivalent Cu(2)Se4 tetrahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 35°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(2) and two equivalent Se(3) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Tm(1)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with three equivalent Tm(1)Se6 octahedra, and  an edgeedge with one Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-63°. In the second Cu site, Cu(2) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(2)Se4 tetrahedra, corners with four equivalent Cu(1)Se4 tetrahedra, and edges with four equivalent Tm(1)Se6 octahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent Tm(1), and two equivalent Cu(2) atoms. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to two equivalent K(1), two equivalent Tm(1), one Cu(2), and two equivalent Cu(1) atoms. In the third Se site, Se(3) is bonded to one K(1), three equivalent Tm(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge and corner-sharing SeKTm3Cu2 octahedra. The corner-sharing octahedral tilt angles are 53°.
KTm2Cu3Se5 crystallizes in the orthorhombic Cmcm space group. K(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. Both K(1)-Se(1) bond lengths are 3.37 Å. Both K(1)-Se(3) bond lengths are 3.35 Å. All K(1)-Se(2) bond lengths are 3.46 Å. Tm(1) is bonded to one Se(1), two equivalent Se(2), and three equivalent Se(3) atoms to form TmSe6 octahedra that share  a cornercorner with one Tm(1)Se6 octahedra, corners with four equivalent Cu(1)Se4 tetrahedra, edges with four equivalent Tm(1)Se6 octahedra, edges with two equivalent Cu(2)Se4 tetrahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 35°. The Tm(1)-Se(1) bond length is 2.75 Å. Both Tm(1)-Se(2) bond lengths are 2.81 Å. There is one shorter (2.78 Å) and two longer (2.89 Å) Tm(1)-Se(3) bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(2) and two equivalent Se(3) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Tm(1)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with three equivalent Tm(1)Se6 octahedra, and  an edgeedge with one Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-63°. There is one shorter (2.51 Å) and one longer (2.54 Å) Cu(1)-Se(2) bond length. Both Cu(1)-Se(3) bond lengths are 2.45 Å. In the second Cu site, Cu(2) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(2)Se4 tetrahedra, corners with four equivalent Cu(1)Se4 tetrahedra, and edges with four equivalent Tm(1)Se6 octahedra. Both Cu(2)-Se(1) bond lengths are 2.41 Å. Both Cu(2)-Se(2) bond lengths are 2.61 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent Tm(1), and two equivalent Cu(2) atoms. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to two equivalent K(1), two equivalent Tm(1), one Cu(2), and two equivalent Cu(1) atoms. In the third Se site, Se(3) is bonded to one K(1), three equivalent Tm(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge and corner-sharing SeKTm3Cu2 octahedra. The corner-sharing octahedral tilt angles are 53°.