U8CoSe17 crystallizes in the triclinic P1 space group. There are eight inequivalent U sites. In the first U site, U(1) is bonded in a 8-coordinate geometry to one Se(12), one Se(13), one Se(15), one Se(17), one Se(2), one Se(3), one Se(5), and one Se(9) atom. In the second U site, U(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(12), one Se(13), one Se(15), one Se(17), one Se(4), one Se(6), and one Se(9) atom. In the third U site, U(3) is bonded in a 8-coordinate geometry to one Se(1), one Se(10), one Se(11), one Se(14), one Se(16), one Se(17), one Se(4), and one Se(7) atom. In the fourth U site, U(4) is bonded in a 8-coordinate geometry to one Se(10), one Se(11), one Se(14), one Se(16), one Se(17), one Se(2), one Se(3), and one Se(8) atom. In the fifth U site, U(5) is bonded in a 8-coordinate geometry to one Se(1), one Se(11), one Se(13), one Se(17), one Se(2), one Se(3), one Se(4), and one Se(9) atom. In the sixth U site, U(6) is bonded in a 8-coordinate geometry to one Se(1), one Se(10), one Se(12), one Se(14), one Se(17), one Se(2), one Se(3), and one Se(4) atom. In the seventh U site, U(7) is bonded in a 8-coordinate geometry to one Se(12), one Se(14), one Se(15), one Se(16), one Se(5), one Se(6), one Se(7), and one Se(8) atom. In the eighth U site, U(8) is bonded in a 8-coordinate geometry to one Se(11), one Se(13), one Se(15), one Se(16), one Se(5), one Se(6), one Se(7), and one Se(8) atom. Co(1) is bonded in an octahedral geometry to one Se(10), one Se(5), one Se(6), one Se(7), one Se(8), and one Se(9) atom. There are seventeen inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one U(2), one U(3), one U(5), and one U(6) atom. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one U(1), one U(4), one U(5), and one U(6) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one U(1), one U(4), one U(5), and one U(6) atom. In the fourth Se site, Se(4) is bonded in a rectangular see-saw-like geometry to one U(2), one U(3), one U(5), and one U(6) atom. In the fifth Se site, Se(5) is bonded to one U(1), one U(7), one U(8), and one Co(1) atom to form SeU3Co trigonal pyramids that share  a cornercorner with one Se(17)U6 octahedra,  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(10)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(15)U4 trigonal pyramid, corners with two equivalent Se(16)U4 trigonal pyramids, corners with three equivalent Se(8)U3Co trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(6)U3Co trigonal pyramid,  an edgeedge with one Se(9)U3Co trigonal pyramid, and  an edgeedge with one Se(15)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 53°. In the sixth Se site, Se(6) is bonded to one U(2), one U(7), one U(8), and one Co(1) atom to form SeU3Co trigonal pyramids that share  a cornercorner with one Se(17)U6 octahedra, corners with three equivalent Se(7)U3Co tetrahedra,  a cornercorner with one Se(10)U3Co trigonal pyramid,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid,  a cornercorner with one Se(15)U4 trigonal pyramid, corners with two equivalent Se(16)U4 trigonal pyramids,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(8)U3Co trigonal pyramid,  an edgeedge with one Se(9)U3Co trigonal pyramid, and  an edgeedge with one Se(15)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 54°. In the seventh Se site, Se(7) is bonded to one U(3), one U(7), one U(8), and one Co(1) atom to form SeU3Co tetrahedra that share  a cornercorner with one Se(17)U6 octahedra,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid,  a cornercorner with one Se(9)U3Co trigonal pyramid,  a cornercorner with one Se(16)U4 trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids, corners with three equivalent Se(6)U3Co trigonal pyramids,  an edgeedge with one Se(10)U3Co trigonal pyramid,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(8)U3Co trigonal pyramid, and  an edgeedge with one Se(16)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 54°. In the eighth Se site, Se(8) is bonded to one U(4), one U(7), one U(8), and one Co(1) atom to form distorted SeU3Co trigonal pyramids that share  a cornercorner with one Se(17)U6 octahedra,  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(9)U3Co trigonal pyramid,  a cornercorner with one Se(16)U4 trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids, corners with three equivalent Se(5)U3Co trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(10)U3Co trigonal pyramid,  an edgeedge with one Se(6)U3Co trigonal pyramid, and  an edgeedge with one Se(16)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 53°. In the ninth Se site, Se(9) is bonded to one U(1), one U(2), one U(5), and one Co(1) atom to form distorted SeU3Co trigonal pyramids that share  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(10)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(6)U3Co trigonal pyramid, and  a faceface with one Se(17)U6 octahedra. In the tenth Se site, Se(10) is bonded to one U(3), one U(4), one U(6), and one Co(1) atom to form distorted SeU3Co trigonal pyramids that share  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(9)U3Co trigonal pyramid, corners with two equivalent Se(16)U4 trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(8)U3Co trigonal pyramid, and  a faceface with one Se(17)U6 octahedra. In the eleventh Se site, Se(11) is bonded in a rectangular see-saw-like geometry to one U(3), one U(4), one U(5), and one U(8) atom. In the twelfth Se site, Se(12) is bonded in a rectangular see-saw-like geometry to one U(1), one U(2), one U(6), and one U(7) atom. In the thirteenth Se site, Se(13) is bonded in a rectangular see-saw-like geometry to one U(1), one U(2), one U(5), and one U(8) atom. In the fourteenth Se site, Se(14) is bonded in a rectangular see-saw-like geometry to one U(3), one U(4), one U(6), and one U(7) atom. In the fifteenth Se site, Se(15) is bonded to one U(1), one U(2), one U(7), and one U(8) atom to form distorted SeU4 trigonal pyramids that share corners with two equivalent Se(17)U6 octahedra, corners with two equivalent Se(7)U3Co tetrahedra,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid, corners with two equivalent Se(8)U3Co trigonal pyramids, corners with two equivalent Se(9)U3Co trigonal pyramids,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(6)U3Co trigonal pyramid, and  an edgeedge with one Se(16)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 38°. In the sixteenth Se site, Se(16) is bonded to one U(3), one U(4), one U(7), and one U(8) atom to form SeU4 trigonal pyramids that share corners with two equivalent Se(17)U6 octahedra,  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(8)U3Co trigonal pyramid, corners with two equivalent Se(10)U3Co trigonal pyramids, corners with two equivalent Se(5)U3Co trigonal pyramids, corners with two equivalent Se(6)U3Co trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(8)U3Co trigonal pyramid, and  an edgeedge with one Se(15)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 38°. In the seventeenth Se site, Se(17) is bonded to one U(1), one U(2), one U(3), one U(4), one U(5), and one U(6) atom to form SeU6 octahedra that share  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids, corners with two equivalent Se(16)U4 trigonal pyramids,  a faceface with one Se(10)U3Co trigonal pyramid, and  a faceface with one Se(9)U3Co trigonal pyramid.
U8CoSe17 crystallizes in the triclinic P1 space group. There are eight inequivalent U sites. In the first U site, U(1) is bonded in a 8-coordinate geometry to one Se(12), one Se(13), one Se(15), one Se(17), one Se(2), one Se(3), one Se(5), and one Se(9) atom. The U(1)-Se(12) bond length is 3.02 Å. The U(1)-Se(13) bond length is 2.97 Å. The U(1)-Se(15) bond length is 2.96 Å. The U(1)-Se(17) bond length is 3.10 Å. The U(1)-Se(2) bond length is 2.95 Å. The U(1)-Se(3) bond length is 3.03 Å. The U(1)-Se(5) bond length is 2.90 Å. The U(1)-Se(9) bond length is 2.88 Å. In the second U site, U(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(12), one Se(13), one Se(15), one Se(17), one Se(4), one Se(6), and one Se(9) atom. The U(2)-Se(1) bond length is 2.93 Å. The U(2)-Se(12) bond length is 2.97 Å. The U(2)-Se(13) bond length is 2.97 Å. The U(2)-Se(15) bond length is 2.99 Å. The U(2)-Se(17) bond length is 3.08 Å. The U(2)-Se(4) bond length is 3.00 Å. The U(2)-Se(6) bond length is 2.94 Å. The U(2)-Se(9) bond length is 2.86 Å. In the third U site, U(3) is bonded in a 8-coordinate geometry to one Se(1), one Se(10), one Se(11), one Se(14), one Se(16), one Se(17), one Se(4), and one Se(7) atom. The U(3)-Se(1) bond length is 3.02 Å. The U(3)-Se(10) bond length is 2.87 Å. The U(3)-Se(11) bond length is 2.99 Å. The U(3)-Se(14) bond length is 2.97 Å. The U(3)-Se(16) bond length is 2.98 Å. The U(3)-Se(17) bond length is 3.11 Å. The U(3)-Se(4) bond length is 2.95 Å. The U(3)-Se(7) bond length is 2.91 Å. In the fourth U site, U(4) is bonded in a 8-coordinate geometry to one Se(10), one Se(11), one Se(14), one Se(16), one Se(17), one Se(2), one Se(3), and one Se(8) atom. The U(4)-Se(10) bond length is 2.87 Å. The U(4)-Se(11) bond length is 3.00 Å. The U(4)-Se(14) bond length is 2.97 Å. The U(4)-Se(16) bond length is 2.98 Å. The U(4)-Se(17) bond length is 3.10 Å. The U(4)-Se(2) bond length is 3.02 Å. The U(4)-Se(3) bond length is 2.95 Å. The U(4)-Se(8) bond length is 2.92 Å. In the fifth U site, U(5) is bonded in a 8-coordinate geometry to one Se(1), one Se(11), one Se(13), one Se(17), one Se(2), one Se(3), one Se(4), and one Se(9) atom. The U(5)-Se(1) bond length is 2.91 Å. The U(5)-Se(11) bond length is 2.87 Å. The U(5)-Se(13) bond length is 2.88 Å. The U(5)-Se(17) bond length is 2.98 Å. The U(5)-Se(2) bond length is 2.90 Å. The U(5)-Se(3) bond length is 2.92 Å. The U(5)-Se(4) bond length is 2.91 Å. The U(5)-Se(9) bond length is 2.96 Å. In the sixth U site, U(6) is bonded in a 8-coordinate geometry to one Se(1), one Se(10), one Se(12), one Se(14), one Se(17), one Se(2), one Se(3), and one Se(4) atom. The U(6)-Se(1) bond length is 2.91 Å. The U(6)-Se(10) bond length is 2.96 Å. The U(6)-Se(12) bond length is 2.88 Å. The U(6)-Se(14) bond length is 2.88 Å. The U(6)-Se(17) bond length is 2.99 Å. The U(6)-Se(2) bond length is 2.92 Å. The U(6)-Se(3) bond length is 2.91 Å. The U(6)-Se(4) bond length is 2.91 Å. In the seventh U site, U(7) is bonded in a 8-coordinate geometry to one Se(12), one Se(14), one Se(15), one Se(16), one Se(5), one Se(6), one Se(7), and one Se(8) atom. The U(7)-Se(12) bond length is 2.91 Å. The U(7)-Se(14) bond length is 2.92 Å. The U(7)-Se(15) bond length is 3.02 Å. The U(7)-Se(16) bond length is 3.13 Å. The U(7)-Se(5) bond length is 3.07 Å. The U(7)-Se(6) bond length is 3.05 Å. The U(7)-Se(7) bond length is 2.86 Å. The U(7)-Se(8) bond length is 2.85 Å. In the eighth U site, U(8) is bonded in a 8-coordinate geometry to one Se(11), one Se(13), one Se(15), one Se(16), one Se(5), one Se(6), one Se(7), and one Se(8) atom. The U(8)-Se(11) bond length is 2.92 Å. The U(8)-Se(13) bond length is 2.92 Å. The U(8)-Se(15) bond length is 3.13 Å. The U(8)-Se(16) bond length is 3.02 Å. The U(8)-Se(5) bond length is 2.86 Å. The U(8)-Se(6) bond length is 2.84 Å. The U(8)-Se(7) bond length is 3.06 Å. The U(8)-Se(8) bond length is 3.07 Å. Co(1) is bonded in an octahedral geometry to one Se(10), one Se(5), one Se(6), one Se(7), one Se(8), and one Se(9) atom. The Co(1)-Se(10) bond length is 2.36 Å. The Co(1)-Se(5) bond length is 2.59 Å. The Co(1)-Se(6) bond length is 2.58 Å. The Co(1)-Se(7) bond length is 2.57 Å. The Co(1)-Se(8) bond length is 2.56 Å. The Co(1)-Se(9) bond length is 2.34 Å. There are seventeen inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one U(2), one U(3), one U(5), and one U(6) atom. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one U(1), one U(4), one U(5), and one U(6) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one U(1), one U(4), one U(5), and one U(6) atom. In the fourth Se site, Se(4) is bonded in a rectangular see-saw-like geometry to one U(2), one U(3), one U(5), and one U(6) atom. In the fifth Se site, Se(5) is bonded to one U(1), one U(7), one U(8), and one Co(1) atom to form SeU3Co trigonal pyramids that share  a cornercorner with one Se(17)U6 octahedra,  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(10)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(15)U4 trigonal pyramid, corners with two equivalent Se(16)U4 trigonal pyramids, corners with three equivalent Se(8)U3Co trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(6)U3Co trigonal pyramid,  an edgeedge with one Se(9)U3Co trigonal pyramid, and  an edgeedge with one Se(15)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 53°. In the sixth Se site, Se(6) is bonded to one U(2), one U(7), one U(8), and one Co(1) atom to form SeU3Co trigonal pyramids that share  a cornercorner with one Se(17)U6 octahedra, corners with three equivalent Se(7)U3Co tetrahedra,  a cornercorner with one Se(10)U3Co trigonal pyramid,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid,  a cornercorner with one Se(15)U4 trigonal pyramid, corners with two equivalent Se(16)U4 trigonal pyramids,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(8)U3Co trigonal pyramid,  an edgeedge with one Se(9)U3Co trigonal pyramid, and  an edgeedge with one Se(15)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 54°. In the seventh Se site, Se(7) is bonded to one U(3), one U(7), one U(8), and one Co(1) atom to form SeU3Co tetrahedra that share  a cornercorner with one Se(17)U6 octahedra,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid,  a cornercorner with one Se(9)U3Co trigonal pyramid,  a cornercorner with one Se(16)U4 trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids, corners with three equivalent Se(6)U3Co trigonal pyramids,  an edgeedge with one Se(10)U3Co trigonal pyramid,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(8)U3Co trigonal pyramid, and  an edgeedge with one Se(16)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 54°. In the eighth Se site, Se(8) is bonded to one U(4), one U(7), one U(8), and one Co(1) atom to form distorted SeU3Co trigonal pyramids that share  a cornercorner with one Se(17)U6 octahedra,  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(9)U3Co trigonal pyramid,  a cornercorner with one Se(16)U4 trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids, corners with three equivalent Se(5)U3Co trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(10)U3Co trigonal pyramid,  an edgeedge with one Se(6)U3Co trigonal pyramid, and  an edgeedge with one Se(16)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 53°. In the ninth Se site, Se(9) is bonded to one U(1), one U(2), one U(5), and one Co(1) atom to form distorted SeU3Co trigonal pyramids that share  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(10)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(6)U3Co trigonal pyramid, and  a faceface with one Se(17)U6 octahedra. In the tenth Se site, Se(10) is bonded to one U(3), one U(4), one U(6), and one Co(1) atom to form distorted SeU3Co trigonal pyramids that share  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(9)U3Co trigonal pyramid, corners with two equivalent Se(16)U4 trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(8)U3Co trigonal pyramid, and  a faceface with one Se(17)U6 octahedra. In the eleventh Se site, Se(11) is bonded in a rectangular see-saw-like geometry to one U(3), one U(4), one U(5), and one U(8) atom. In the twelfth Se site, Se(12) is bonded in a rectangular see-saw-like geometry to one U(1), one U(2), one U(6), and one U(7) atom. In the thirteenth Se site, Se(13) is bonded in a rectangular see-saw-like geometry to one U(1), one U(2), one U(5), and one U(8) atom. In the fourteenth Se site, Se(14) is bonded in a rectangular see-saw-like geometry to one U(3), one U(4), one U(6), and one U(7) atom. In the fifteenth Se site, Se(15) is bonded to one U(1), one U(2), one U(7), and one U(8) atom to form distorted SeU4 trigonal pyramids that share corners with two equivalent Se(17)U6 octahedra, corners with two equivalent Se(7)U3Co tetrahedra,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid, corners with two equivalent Se(8)U3Co trigonal pyramids, corners with two equivalent Se(9)U3Co trigonal pyramids,  an edgeedge with one Se(5)U3Co trigonal pyramid,  an edgeedge with one Se(6)U3Co trigonal pyramid, and  an edgeedge with one Se(16)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 38°. In the sixteenth Se site, Se(16) is bonded to one U(3), one U(4), one U(7), and one U(8) atom to form SeU4 trigonal pyramids that share corners with two equivalent Se(17)U6 octahedra,  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(8)U3Co trigonal pyramid, corners with two equivalent Se(10)U3Co trigonal pyramids, corners with two equivalent Se(5)U3Co trigonal pyramids, corners with two equivalent Se(6)U3Co trigonal pyramids,  an edgeedge with one Se(7)U3Co tetrahedra,  an edgeedge with one Se(8)U3Co trigonal pyramid, and  an edgeedge with one Se(15)U4 trigonal pyramid. The corner-sharing octahedral tilt angles are 38°. In the seventeenth Se site, Se(17) is bonded to one U(1), one U(2), one U(3), one U(4), one U(5), and one U(6) atom to form SeU6 octahedra that share  a cornercorner with one Se(7)U3Co tetrahedra,  a cornercorner with one Se(5)U3Co trigonal pyramid,  a cornercorner with one Se(6)U3Co trigonal pyramid,  a cornercorner with one Se(8)U3Co trigonal pyramid, corners with two equivalent Se(15)U4 trigonal pyramids, corners with two equivalent Se(16)U4 trigonal pyramids,  a faceface with one Se(10)U3Co trigonal pyramid, and  a faceface with one Se(9)U3Co trigonal pyramid.