Si19Te8 crystallizes in the trigonal R3c space group. There are seven inequivalent Si sites. In the first Si site, Si(1) is bonded to one Si(3), one Si(5), one Si(6), one Te(1), and one Te(2) atom to form SiSi3Te2 trigonal bipyramids that share  a cornercorner with one Si(5)Si4 tetrahedra, corners with two equivalent Si(3)Si3Te tetrahedra, corners with three equivalent Si(4)Si3Te tetrahedra,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(6)Si3Te2 trigonal bipyramid, and corners with two equivalent Si(7)Si3Te trigonal pyramids. In the second Si site, Si(2) is bonded to three equivalent Si(3), one Te(3), and one Te(4) atom to form distorted SiSi3Te2 trigonal bipyramids that share corners with three equivalent Si(5)Si4 tetrahedra, corners with three equivalent Si(1)Si3Te2 trigonal bipyramids, corners with three equivalent Si(6)Si3Te2 trigonal bipyramids, and corners with three equivalent Si(7)Si3Te trigonal pyramids. In the third Si site, Si(3) is bonded to one Si(1), one Si(2), one Si(5), and one Te(2) atom to form distorted SiSi3Te tetrahedra that share  a cornercorner with one Si(4)Si3Te tetrahedra,  a cornercorner with one Si(5)Si4 tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra, corners with two equivalent Si(3)Si3Te tetrahedra,  a cornercorner with one Si(6)Si3Te2 trigonal bipyramid, corners with two equivalent Si(1)Si3Te2 trigonal bipyramids, and  a cornercorner with one Si(7)Si3Te trigonal pyramid. In the fourth Si site, Si(4) is bonded to one Si(5), one Si(6), one Si(7), and one Te(1) atom to form distorted SiSi3Te tetrahedra that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Si(5)Si4 tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra, corners with two equivalent Si(6)Si3Te2 trigonal bipyramids, corners with three equivalent Si(1)Si3Te2 trigonal bipyramids, and corners with two equivalent Si(7)Si3Te trigonal pyramids. In the fifth Si site, Si(5) is bonded to one Si(1), one Si(3), one Si(4), and one Si(7) atom to form SiSi4 tetrahedra that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Si(4)Si3Te tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra,  a cornercorner with one Si(1)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid, corners with three equivalent Si(6)Si3Te2 trigonal bipyramids, and  a cornercorner with one Si(7)Si3Te trigonal pyramid. In the sixth Si site, Si(6) is bonded to one Si(1), one Si(4), one Si(7), one Te(1), and one Te(4) atom to form distorted SiSi3Te2 trigonal bipyramids that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra, corners with two equivalent Si(4)Si3Te tetrahedra, corners with three equivalent Si(5)Si4 tetrahedra,  a cornercorner with one Si(1)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid, corners with two equivalent Si(6)Si3Te2 trigonal bipyramids, and  a cornercorner with one Si(7)Si3Te trigonal pyramid. In the seventh Si site, Si(7) is bonded to one Si(4), one Si(5), one Si(6), and one Te(3) atom to form distorted SiSi3Te trigonal pyramids that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Si(5)Si4 tetrahedra, corners with two equivalent Si(4)Si3Te tetrahedra,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(6)Si3Te2 trigonal bipyramid, corners with two equivalent Si(1)Si3Te2 trigonal bipyramids, and corners with two equivalent Si(7)Si3Te trigonal pyramids. There are four inequivalent Te sites. In the first Te site, Te(4) is bonded in a 4-coordinate geometry to one Si(2) and three equivalent Si(6) atoms. In the second Te site, Te(1) is bonded in a trigonal non-coplanar geometry to one Si(1), one Si(4), and one Si(6) atom. In the third Te site, Te(3) is bonded to one Si(2) and three equivalent Si(7) atoms to form distorted TeSi4 tetrahedra that share corners with three equivalent Si(3)Si3Te tetrahedra, corners with three equivalent Si(4)Si3Te tetrahedra, corners with three equivalent Si(5)Si4 tetrahedra, and corners with three equivalent Si(6)Si3Te2 trigonal bipyramids. In the fourth Te site, Te(2) is bonded in a distorted bent 120 degrees geometry to one Si(1) and one Si(3) atom.
Si19Te8 crystallizes in the trigonal R3c space group. There are seven inequivalent Si sites. In the first Si site, Si(1) is bonded to one Si(3), one Si(5), one Si(6), one Te(1), and one Te(2) atom to form SiSi3Te2 trigonal bipyramids that share  a cornercorner with one Si(5)Si4 tetrahedra, corners with two equivalent Si(3)Si3Te tetrahedra, corners with three equivalent Si(4)Si3Te tetrahedra,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(6)Si3Te2 trigonal bipyramid, and corners with two equivalent Si(7)Si3Te trigonal pyramids. The Si(1)-Si(3) bond length is 2.40 Å. The Si(1)-Si(5) bond length is 2.39 Å. The Si(1)-Si(6) bond length is 2.35 Å. The Si(1)-Te(1) bond length is 2.77 Å. The Si(1)-Te(2) bond length is 3.07 Å. In the second Si site, Si(2) is bonded to three equivalent Si(3), one Te(3), and one Te(4) atom to form distorted SiSi3Te2 trigonal bipyramids that share corners with three equivalent Si(5)Si4 tetrahedra, corners with three equivalent Si(1)Si3Te2 trigonal bipyramids, corners with three equivalent Si(6)Si3Te2 trigonal bipyramids, and corners with three equivalent Si(7)Si3Te trigonal pyramids. All Si(2)-Si(3) bond lengths are 2.39 Å. The Si(2)-Te(3) bond length is 3.10 Å. The Si(2)-Te(4) bond length is 2.64 Å. In the third Si site, Si(3) is bonded to one Si(1), one Si(2), one Si(5), and one Te(2) atom to form distorted SiSi3Te tetrahedra that share  a cornercorner with one Si(4)Si3Te tetrahedra,  a cornercorner with one Si(5)Si4 tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra, corners with two equivalent Si(3)Si3Te tetrahedra,  a cornercorner with one Si(6)Si3Te2 trigonal bipyramid, corners with two equivalent Si(1)Si3Te2 trigonal bipyramids, and  a cornercorner with one Si(7)Si3Te trigonal pyramid. The Si(3)-Si(5) bond length is 2.40 Å. The Si(3)-Te(2) bond length is 2.62 Å. In the fourth Si site, Si(4) is bonded to one Si(5), one Si(6), one Si(7), and one Te(1) atom to form distorted SiSi3Te tetrahedra that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Si(5)Si4 tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra, corners with two equivalent Si(6)Si3Te2 trigonal bipyramids, corners with three equivalent Si(1)Si3Te2 trigonal bipyramids, and corners with two equivalent Si(7)Si3Te trigonal pyramids. The Si(4)-Si(5) bond length is 2.39 Å. The Si(4)-Si(6) bond length is 2.36 Å. The Si(4)-Si(7) bond length is 2.39 Å. The Si(4)-Te(1) bond length is 2.63 Å. In the fifth Si site, Si(5) is bonded to one Si(1), one Si(3), one Si(4), and one Si(7) atom to form SiSi4 tetrahedra that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Si(4)Si3Te tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra,  a cornercorner with one Si(1)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid, corners with three equivalent Si(6)Si3Te2 trigonal bipyramids, and  a cornercorner with one Si(7)Si3Te trigonal pyramid. The Si(5)-Si(7) bond length is 2.40 Å. In the sixth Si site, Si(6) is bonded to one Si(1), one Si(4), one Si(7), one Te(1), and one Te(4) atom to form distorted SiSi3Te2 trigonal bipyramids that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Te(3)Si4 tetrahedra, corners with two equivalent Si(4)Si3Te tetrahedra, corners with three equivalent Si(5)Si4 tetrahedra,  a cornercorner with one Si(1)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid, corners with two equivalent Si(6)Si3Te2 trigonal bipyramids, and  a cornercorner with one Si(7)Si3Te trigonal pyramid. The Si(6)-Si(7) bond length is 2.35 Å. The Si(6)-Te(1) bond length is 2.64 Å. The Si(6)-Te(4) bond length is 3.10 Å. In the seventh Si site, Si(7) is bonded to one Si(4), one Si(5), one Si(6), and one Te(3) atom to form distorted SiSi3Te trigonal pyramids that share  a cornercorner with one Si(3)Si3Te tetrahedra,  a cornercorner with one Si(5)Si4 tetrahedra, corners with two equivalent Si(4)Si3Te tetrahedra,  a cornercorner with one Si(2)Si3Te2 trigonal bipyramid,  a cornercorner with one Si(6)Si3Te2 trigonal bipyramid, corners with two equivalent Si(1)Si3Te2 trigonal bipyramids, and corners with two equivalent Si(7)Si3Te trigonal pyramids. The Si(7)-Te(3) bond length is 2.70 Å. There are four inequivalent Te sites. In the first Te site, Te(4) is bonded in a 4-coordinate geometry to one Si(2) and three equivalent Si(6) atoms. In the second Te site, Te(1) is bonded in a trigonal non-coplanar geometry to one Si(1), one Si(4), and one Si(6) atom. In the third Te site, Te(3) is bonded to one Si(2) and three equivalent Si(7) atoms to form distorted TeSi4 tetrahedra that share corners with three equivalent Si(3)Si3Te tetrahedra, corners with three equivalent Si(4)Si3Te tetrahedra, corners with three equivalent Si(5)Si4 tetrahedra, and corners with three equivalent Si(6)Si3Te2 trigonal bipyramids. In the fourth Te site, Te(2) is bonded in a distorted bent 120 degrees geometry to one Si(1) and one Si(3) atom.