K2Bi8Se13 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 7-coordinate geometry to one Se(3), two equivalent Se(1), two equivalent Se(6), and two equivalent Se(7) atoms. There are four inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one Se(4), one Se(6), two equivalent Se(2), and two equivalent Se(7) atoms to form a mixture of corner and edge-sharing BiSe6 octahedra. The corner-sharing octahedra are not tilted. In the second Bi site, Bi(2) is bonded to two equivalent Se(1) and three equivalent Se(3) atoms to form BiSe5 square pyramids that share corners with two equivalent Bi(3)Se6 octahedra and edges with four equivalent Bi(2)Se5 square pyramids. The corner-sharing octahedral tilt angles are 67°. In the third Bi site, Bi(3) is bonded to one Se(1), one Se(2), two equivalent Se(4), and two equivalent Se(6) atoms to form BiSe6 octahedra that share  a cornercorner with one Bi(3)Se6 octahedra, corners with two equivalent Bi(4)Se6 octahedra, corners with two equivalent Bi(2)Se5 square pyramids,  an edgeedge with one Bi(4)Se6 octahedra, edges with two equivalent Bi(3)Se6 octahedra, and edges with four equivalent Bi(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the fourth Bi site, Bi(4) is bonded to one Se(7), two equivalent Se(4), and three equivalent Se(5) atoms to form a mixture of corner and edge-sharing BiSe6 octahedra. The corner-sharing octahedral tilt angles are 5°. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent K(1), one Bi(3), and two equivalent Bi(2) atoms to form distorted SeK2Bi3 trigonal bipyramids that share  a cornercorner with one Se(2)Bi6 octahedra, corners with two equivalent Se(4)Bi5 square pyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(7)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids,  an edgeedge with one Se(7)K2Bi3 trigonal bipyramid, edges with two equivalent Se(1)K2Bi3 trigonal bipyramids, edges with two equivalent Se(6)K2Bi3 trigonal bipyramids, and edges with three equivalent Se(3)KBi3 trigonal pyramids. The corner-sharing octahedra are not tilted. In the second Se site, Se(2) is bonded to two equivalent Bi(3) and four equivalent Bi(1) atoms to form SeBi6 octahedra that share corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with four equivalent Se(7)K2Bi3 trigonal bipyramids, edges with two equivalent Se(2)Bi6 octahedra, edges with four equivalent Se(4)Bi5 square pyramids, edges with two equivalent Se(7)K2Bi3 trigonal bipyramids, and edges with four equivalent Se(6)K2Bi3 trigonal bipyramids. In the third Se site, Se(3) is bonded to one K(1) and three equivalent Bi(2) atoms to form SeKBi3 trigonal pyramids that share corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(7)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids, edges with three equivalent Se(1)K2Bi3 trigonal bipyramids, and edges with two equivalent Se(3)KBi3 trigonal pyramids. In the fourth Se site, Se(4) is bonded to one Bi(1), two equivalent Bi(3), and two equivalent Bi(4) atoms to form SeBi5 square pyramids that share corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with three equivalent Se(6)K2Bi3 trigonal bipyramids, edges with two equivalent Se(2)Bi6 octahedra, edges with two equivalent Se(4)Bi5 square pyramids,  an edgeedge with one Se(6)K2Bi3 trigonal bipyramid, and edges with two equivalent Se(7)K2Bi3 trigonal bipyramids. In the fifth Se site, Se(5) is bonded in a distorted T-shaped geometry to three equivalent Bi(4) atoms. In the sixth Se site, Se(6) is bonded to two equivalent K(1), one Bi(1), and two equivalent Bi(3) atoms to form SeK2Bi3 trigonal bipyramids that share corners with three equivalent Se(4)Bi5 square pyramids, corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(7)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids, edges with two equivalent Se(2)Bi6 octahedra,  an edgeedge with one Se(4)Bi5 square pyramid,  an edgeedge with one Se(6)K2Bi3 trigonal bipyramid, edges with two equivalent Se(1)K2Bi3 trigonal bipyramids, and edges with two equivalent Se(7)K2Bi3 trigonal bipyramids. In the seventh Se site, Se(7) is bonded to two equivalent K(1), one Bi(4), and two equivalent Bi(1) atoms to form distorted SeK2Bi3 trigonal bipyramids that share corners with two equivalent Se(2)Bi6 octahedra, corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids,  an edgeedge with one Se(2)Bi6 octahedra, edges with two equivalent Se(4)Bi5 square pyramids,  an edgeedge with one Se(1)K2Bi3 trigonal bipyramid, edges with two equivalent Se(6)K2Bi3 trigonal bipyramids, and edges with two equivalent Se(7)K2Bi3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 3°.
K2Bi8Se13 crystallizes in the monoclinic C2/m space group. K(1) is bonded in a 7-coordinate geometry to one Se(3), two equivalent Se(1), two equivalent Se(6), and two equivalent Se(7) atoms. The K(1)-Se(3) bond length is 3.35 Å. Both K(1)-Se(1) bond lengths are 3.34 Å. There is one shorter (3.51 Å) and one longer (3.59 Å) K(1)-Se(6) bond length. Both K(1)-Se(7) bond lengths are 3.46 Å. There are four inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one Se(4), one Se(6), two equivalent Se(2), and two equivalent Se(7) atoms to form a mixture of corner and edge-sharing BiSe6 octahedra. The corner-sharing octahedra are not tilted. The Bi(1)-Se(4) bond length is 2.98 Å. The Bi(1)-Se(6) bond length is 3.00 Å. Both Bi(1)-Se(2) bond lengths are 3.05 Å. Both Bi(1)-Se(7) bond lengths are 2.87 Å. In the second Bi site, Bi(2) is bonded to two equivalent Se(1) and three equivalent Se(3) atoms to form BiSe5 square pyramids that share corners with two equivalent Bi(3)Se6 octahedra and edges with four equivalent Bi(2)Se5 square pyramids. The corner-sharing octahedral tilt angles are 67°. Both Bi(2)-Se(1) bond lengths are 2.99 Å. There is one shorter (2.71 Å) and two longer (2.92 Å) Bi(2)-Se(3) bond lengths. In the third Bi site, Bi(3) is bonded to one Se(1), one Se(2), two equivalent Se(4), and two equivalent Se(6) atoms to form BiSe6 octahedra that share  a cornercorner with one Bi(3)Se6 octahedra, corners with two equivalent Bi(4)Se6 octahedra, corners with two equivalent Bi(2)Se5 square pyramids,  an edgeedge with one Bi(4)Se6 octahedra, edges with two equivalent Bi(3)Se6 octahedra, and edges with four equivalent Bi(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. The Bi(3)-Se(1) bond length is 2.76 Å. The Bi(3)-Se(2) bond length is 3.19 Å. Both Bi(3)-Se(4) bond lengths are 3.08 Å. Both Bi(3)-Se(6) bond lengths are 2.87 Å. In the fourth Bi site, Bi(4) is bonded to one Se(7), two equivalent Se(4), and three equivalent Se(5) atoms to form a mixture of corner and edge-sharing BiSe6 octahedra. The corner-sharing octahedral tilt angles are 5°. The Bi(4)-Se(7) bond length is 3.03 Å. Both Bi(4)-Se(4) bond lengths are 3.03 Å. All Bi(4)-Se(5) bond lengths are 2.87 Å. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent K(1), one Bi(3), and two equivalent Bi(2) atoms to form distorted SeK2Bi3 trigonal bipyramids that share  a cornercorner with one Se(2)Bi6 octahedra, corners with two equivalent Se(4)Bi5 square pyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(7)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids,  an edgeedge with one Se(7)K2Bi3 trigonal bipyramid, edges with two equivalent Se(1)K2Bi3 trigonal bipyramids, edges with two equivalent Se(6)K2Bi3 trigonal bipyramids, and edges with three equivalent Se(3)KBi3 trigonal pyramids. The corner-sharing octahedra are not tilted. In the second Se site, Se(2) is bonded to two equivalent Bi(3) and four equivalent Bi(1) atoms to form SeBi6 octahedra that share corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with four equivalent Se(7)K2Bi3 trigonal bipyramids, edges with two equivalent Se(2)Bi6 octahedra, edges with four equivalent Se(4)Bi5 square pyramids, edges with two equivalent Se(7)K2Bi3 trigonal bipyramids, and edges with four equivalent Se(6)K2Bi3 trigonal bipyramids. In the third Se site, Se(3) is bonded to one K(1) and three equivalent Bi(2) atoms to form SeKBi3 trigonal pyramids that share corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(7)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids, edges with three equivalent Se(1)K2Bi3 trigonal bipyramids, and edges with two equivalent Se(3)KBi3 trigonal pyramids. In the fourth Se site, Se(4) is bonded to one Bi(1), two equivalent Bi(3), and two equivalent Bi(4) atoms to form SeBi5 square pyramids that share corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with three equivalent Se(6)K2Bi3 trigonal bipyramids, edges with two equivalent Se(2)Bi6 octahedra, edges with two equivalent Se(4)Bi5 square pyramids,  an edgeedge with one Se(6)K2Bi3 trigonal bipyramid, and edges with two equivalent Se(7)K2Bi3 trigonal bipyramids. In the fifth Se site, Se(5) is bonded in a distorted T-shaped geometry to three equivalent Bi(4) atoms. In the sixth Se site, Se(6) is bonded to two equivalent K(1), one Bi(1), and two equivalent Bi(3) atoms to form SeK2Bi3 trigonal bipyramids that share corners with three equivalent Se(4)Bi5 square pyramids, corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(7)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids, edges with two equivalent Se(2)Bi6 octahedra,  an edgeedge with one Se(4)Bi5 square pyramid,  an edgeedge with one Se(6)K2Bi3 trigonal bipyramid, edges with two equivalent Se(1)K2Bi3 trigonal bipyramids, and edges with two equivalent Se(7)K2Bi3 trigonal bipyramids. In the seventh Se site, Se(7) is bonded to two equivalent K(1), one Bi(4), and two equivalent Bi(1) atoms to form distorted SeK2Bi3 trigonal bipyramids that share corners with two equivalent Se(2)Bi6 octahedra, corners with two equivalent Se(1)K2Bi3 trigonal bipyramids, corners with two equivalent Se(6)K2Bi3 trigonal bipyramids, corners with two equivalent Se(3)KBi3 trigonal pyramids,  an edgeedge with one Se(2)Bi6 octahedra, edges with two equivalent Se(4)Bi5 square pyramids,  an edgeedge with one Se(1)K2Bi3 trigonal bipyramid, edges with two equivalent Se(6)K2Bi3 trigonal bipyramids, and edges with two equivalent Se(7)K2Bi3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 3°.