KTh(SbSe3)2 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one Se(2), one Se(3), one Se(5), two equivalent Se(1), two equivalent Se(4), and two equivalent Se(6) atoms. Th(1) is bonded in a 9-coordinate geometry to one Se(1), one Se(2), two equivalent Se(4), two equivalent Se(6), and three equivalent Se(5) atoms. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded in a 5-coordinate geometry to one Se(4), two equivalent Se(2), and three equivalent Se(3) atoms. In the second Sb site, Sb(2) is bonded to one Se(2), one Se(6), two equivalent Se(1), and two equivalent Se(3) atoms to form distorted edge-sharing SbSe6 octahedra. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent K(1), one Th(1), and two equivalent Sb(2) atoms. In the second Se site, Se(2) is bonded to one K(1), one Th(1), one Sb(2), and two equivalent Sb(1) atoms to form distorted SeKThSb3 trigonal bipyramids that share  a cornercorner with one Se(6)K2Th2Sb square pyramid, corners with two equivalent Se(4)K2Th2Sb square pyramids, corners with two equivalent Se(2)KThSb3 trigonal bipyramids, edges with two equivalent Se(4)K2Th2Sb square pyramids, and edges with two equivalent Se(6)K2Th2Sb square pyramids. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one K(1), two equivalent Sb(2), and three equivalent Sb(1) atoms. In the fourth Se site, Se(4) is bonded to two equivalent K(1), two equivalent Th(1), and one Sb(1) atom to form distorted SeK2Th2Sb square pyramids that share corners with four equivalent Se(6)K2Th2Sb square pyramids, corners with two equivalent Se(2)KThSb3 trigonal bipyramids, edges with two equivalent Se(4)K2Th2Sb square pyramids, edges with two equivalent Se(6)K2Th2Sb square pyramids, and edges with two equivalent Se(2)KThSb3 trigonal bipyramids. In the fifth Se site, Se(5) is bonded in a 5-coordinate geometry to one K(1), three equivalent Th(1), and one Se(5) atom. In the sixth Se site, Se(6) is bonded to two equivalent K(1), two equivalent Th(1), and one Sb(2) atom to form SeK2Th2Sb square pyramids that share corners with four equivalent Se(4)K2Th2Sb square pyramids,  a cornercorner with one Se(2)KThSb3 trigonal bipyramid, edges with two equivalent Se(4)K2Th2Sb square pyramids, edges with two equivalent Se(6)K2Th2Sb square pyramids, and edges with two equivalent Se(2)KThSb3 trigonal bipyramids.
KTh(SbSe3)2 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one Se(2), one Se(3), one Se(5), two equivalent Se(1), two equivalent Se(4), and two equivalent Se(6) atoms. The K(1)-Se(2) bond length is 3.53 Å. The K(1)-Se(3) bond length is 3.46 Å. The K(1)-Se(5) bond length is 3.65 Å. There is one shorter (3.32 Å) and one longer (3.86 Å) K(1)-Se(1) bond length. There is one shorter (3.33 Å) and one longer (3.62 Å) K(1)-Se(4) bond length. There is one shorter (3.42 Å) and one longer (3.43 Å) K(1)-Se(6) bond length. Th(1) is bonded in a 9-coordinate geometry to one Se(1), one Se(2), two equivalent Se(4), two equivalent Se(6), and three equivalent Se(5) atoms. The Th(1)-Se(1) bond length is 3.05 Å. The Th(1)-Se(2) bond length is 3.13 Å. There is one shorter (2.97 Å) and one longer (3.15 Å) Th(1)-Se(4) bond length. There is one shorter (3.02 Å) and one longer (3.09 Å) Th(1)-Se(6) bond length. There are a spread of Th(1)-Se(5) bond distances ranging from 3.07-3.20 Å. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded in a 5-coordinate geometry to one Se(4), two equivalent Se(2), and three equivalent Se(3) atoms. The Sb(1)-Se(4) bond length is 2.68 Å. There is one shorter (2.67 Å) and one longer (3.04 Å) Sb(1)-Se(2) bond length. There are a spread of Sb(1)-Se(3) bond distances ranging from 2.84-3.38 Å. In the second Sb site, Sb(2) is bonded to one Se(2), one Se(6), two equivalent Se(1), and two equivalent Se(3) atoms to form distorted edge-sharing SbSe6 octahedra. The Sb(2)-Se(2) bond length is 3.29 Å. The Sb(2)-Se(6) bond length is 2.70 Å. There is one shorter (2.67 Å) and one longer (3.09 Å) Sb(2)-Se(1) bond length. There is one shorter (2.76 Å) and one longer (3.29 Å) Sb(2)-Se(3) bond length. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent K(1), one Th(1), and two equivalent Sb(2) atoms. In the second Se site, Se(2) is bonded to one K(1), one Th(1), one Sb(2), and two equivalent Sb(1) atoms to form distorted SeKThSb3 trigonal bipyramids that share  a cornercorner with one Se(6)K2Th2Sb square pyramid, corners with two equivalent Se(4)K2Th2Sb square pyramids, corners with two equivalent Se(2)KThSb3 trigonal bipyramids, edges with two equivalent Se(4)K2Th2Sb square pyramids, and edges with two equivalent Se(6)K2Th2Sb square pyramids. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one K(1), two equivalent Sb(2), and three equivalent Sb(1) atoms. In the fourth Se site, Se(4) is bonded to two equivalent K(1), two equivalent Th(1), and one Sb(1) atom to form distorted SeK2Th2Sb square pyramids that share corners with four equivalent Se(6)K2Th2Sb square pyramids, corners with two equivalent Se(2)KThSb3 trigonal bipyramids, edges with two equivalent Se(4)K2Th2Sb square pyramids, edges with two equivalent Se(6)K2Th2Sb square pyramids, and edges with two equivalent Se(2)KThSb3 trigonal bipyramids. In the fifth Se site, Se(5) is bonded in a 5-coordinate geometry to one K(1), three equivalent Th(1), and one Se(5) atom. The Se(5)-Se(5) bond length is 2.54 Å. In the sixth Se site, Se(6) is bonded to two equivalent K(1), two equivalent Th(1), and one Sb(2) atom to form SeK2Th2Sb square pyramids that share corners with four equivalent Se(4)K2Th2Sb square pyramids,  a cornercorner with one Se(2)KThSb3 trigonal bipyramid, edges with two equivalent Se(4)K2Th2Sb square pyramids, edges with two equivalent Se(6)K2Th2Sb square pyramids, and edges with two equivalent Se(2)KThSb3 trigonal bipyramids.