K2Dy4Cu4Se9 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 7-coordinate geometry to one Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There are two inequivalent Dy sites. In the first Dy site, Dy(1) is bonded to one Se(3), two equivalent Se(2), and three equivalent Se(1) atoms to form DySe6 octahedra that share  a cornercorner with one Dy(2)Se6 octahedra, corners with four equivalent Cu(1)Se4 tetrahedra, edges with four equivalent Dy(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 39°. In the second Dy site, Dy(2) is bonded to one Se(3), two equivalent Se(5), and three equivalent Se(4) atoms to form DySe6 octahedra that share  a cornercorner with one Dy(1)Se6 octahedra, corners with two equivalent Dy(2)Se6 octahedra,  a cornercorner with one Cu(2)Se4 tetrahedra, edges with five equivalent Dy(2)Se6 octahedra, and edges with two equivalent Cu(2)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 0-39°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Dy(1)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with three equivalent Dy(1)Se6 octahedra, and  an edgeedge with one Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-63°. In the second Cu site, Cu(2) is bonded to one Se(2), one Se(4), and two equivalent Se(3) atoms to form CuSe4 tetrahedra that share  a cornercorner with one Dy(2)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with two equivalent Dy(1)Se6 octahedra, and edges with two equivalent Dy(2)Se6 octahedra. The corner-sharing octahedral tilt angles are 8°. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to one K(1), three equivalent Dy(1), and two equivalent Cu(1) atoms to form distorted SeKDy3Cu2 octahedra that share corners with two equivalent Se(4)K2Dy3Cu octahedra and edges with four equivalent Se(1)KDy3Cu2 octahedra. The corner-sharing octahedral tilt angles are 41°. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to two equivalent K(1), two equivalent Dy(1), one Cu(2), and two equivalent Cu(1) atoms. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to two equivalent K(1), one Dy(1), one Dy(2), and two equivalent Cu(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent K(1), three equivalent Dy(2), and one Cu(2) atom to form distorted SeK2Dy3Cu octahedra that share corners with two equivalent Se(1)KDy3Cu2 octahedra and edges with four equivalent Se(4)K2Dy3Cu octahedra. The corner-sharing octahedral tilt angles are 41°. In the fifth Se site, Se(5) is bonded in a square co-planar geometry to four equivalent Dy(2) atoms.
K2Dy4Cu4Se9 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 7-coordinate geometry to one Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. The K(1)-Se(1) bond length is 3.28 Å. Both K(1)-Se(2) bond lengths are 3.51 Å. Both K(1)-Se(3) bond lengths are 3.30 Å. Both K(1)-Se(4) bond lengths are 3.31 Å. There are two inequivalent Dy sites. In the first Dy site, Dy(1) is bonded to one Se(3), two equivalent Se(2), and three equivalent Se(1) atoms to form DySe6 octahedra that share  a cornercorner with one Dy(2)Se6 octahedra, corners with four equivalent Cu(1)Se4 tetrahedra, edges with four equivalent Dy(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 39°. The Dy(1)-Se(3) bond length is 2.83 Å. Both Dy(1)-Se(2) bond lengths are 2.85 Å. There is one shorter (2.85 Å) and two longer (2.93 Å) Dy(1)-Se(1) bond lengths. In the second Dy site, Dy(2) is bonded to one Se(3), two equivalent Se(5), and three equivalent Se(4) atoms to form DySe6 octahedra that share  a cornercorner with one Dy(1)Se6 octahedra, corners with two equivalent Dy(2)Se6 octahedra,  a cornercorner with one Cu(2)Se4 tetrahedra, edges with five equivalent Dy(2)Se6 octahedra, and edges with two equivalent Cu(2)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 0-39°. The Dy(2)-Se(3) bond length is 2.81 Å. Both Dy(2)-Se(5) bond lengths are 2.94 Å. There are two shorter (2.86 Å) and one longer (2.92 Å) Dy(2)-Se(4) bond length. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Dy(1)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with three equivalent Dy(1)Se6 octahedra, and  an edgeedge with one Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-63°. Both Cu(1)-Se(1) bond lengths are 2.47 Å. There is one shorter (2.50 Å) and one longer (2.60 Å) Cu(1)-Se(2) bond length. In the second Cu site, Cu(2) is bonded to one Se(2), one Se(4), and two equivalent Se(3) atoms to form CuSe4 tetrahedra that share  a cornercorner with one Dy(2)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with two equivalent Dy(1)Se6 octahedra, and edges with two equivalent Dy(2)Se6 octahedra. The corner-sharing octahedral tilt angles are 8°. The Cu(2)-Se(2) bond length is 2.62 Å. The Cu(2)-Se(4) bond length is 2.49 Å. Both Cu(2)-Se(3) bond lengths are 2.46 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to one K(1), three equivalent Dy(1), and two equivalent Cu(1) atoms to form distorted SeKDy3Cu2 octahedra that share corners with two equivalent Se(4)K2Dy3Cu octahedra and edges with four equivalent Se(1)KDy3Cu2 octahedra. The corner-sharing octahedral tilt angles are 41°. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to two equivalent K(1), two equivalent Dy(1), one Cu(2), and two equivalent Cu(1) atoms. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to two equivalent K(1), one Dy(1), one Dy(2), and two equivalent Cu(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent K(1), three equivalent Dy(2), and one Cu(2) atom to form distorted SeK2Dy3Cu octahedra that share corners with two equivalent Se(1)KDy3Cu2 octahedra and edges with four equivalent Se(4)K2Dy3Cu octahedra. The corner-sharing octahedral tilt angles are 41°. In the fifth Se site, Se(5) is bonded in a square co-planar geometry to four equivalent Dy(2) atoms.