K3TaNbCu3S8 crystallizes in the monoclinic C2 space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a body-centered cubic geometry to one S(3), one S(4), one S(7), one S(8), two equivalent S(5), and two equivalent S(6) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one S(2), one S(4), two equivalent S(1), and three equivalent S(7) atoms. In the third K site, K(3) is bonded in a 7-coordinate geometry to one S(1), one S(3), two equivalent S(2), and three equivalent S(8) atoms. Ta(1) is bonded to one S(1), one S(3), one S(5), and one S(7) atom to form TaS4 tetrahedra that share  an edgeedge with one Cu(3)S4 tetrahedra and edges with two equivalent Cu(1)S4 tetrahedra. Nb(1) is bonded to one S(2), one S(4), one S(6), and one S(8) atom to form NbS4 tetrahedra that share  an edgeedge with one Cu(4)S4 tetrahedra and edges with two equivalent Cu(2)S4 tetrahedra. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(3), one S(5), and one S(7) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(3)S4 tetrahedra and edges with two equivalent Ta(1)S4 tetrahedra. In the second Cu site, Cu(2) is bonded to one S(2), one S(4), one S(6), and one S(8) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(4)S4 tetrahedra and edges with two equivalent Nb(1)S4 tetrahedra. In the third Cu site, Cu(3) is bonded to two equivalent S(3) and two equivalent S(5) atoms to form distorted CuS4 tetrahedra that share corners with four equivalent Cu(1)S4 tetrahedra and edges with two equivalent Ta(1)S4 tetrahedra. In the fourth Cu site, Cu(4) is bonded to two equivalent S(4) and two equivalent S(6) atoms to form distorted CuS4 tetrahedra that share corners with four equivalent Cu(2)S4 tetrahedra and edges with two equivalent Nb(1)S4 tetrahedra. There are eight inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one K(3), two equivalent K(2), one Ta(1), and one Cu(1) atom. In the second S site, S(2) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(3), one Nb(1), and one Cu(2) atom. In the third S site, S(3) is bonded in a 5-coordinate geometry to one K(1), one K(3), one Ta(1), one Cu(1), and one Cu(3) atom. In the fourth S site, S(4) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Nb(1), one Cu(2), and one Cu(4) atom. In the fifth S site, S(5) is bonded in a 5-coordinate geometry to two equivalent K(1), one Ta(1), one Cu(1), and one Cu(3) atom. In the sixth S site, S(6) is bonded in a 5-coordinate geometry to two equivalent K(1), one Nb(1), one Cu(2), and one Cu(4) atom. In the seventh S site, S(7) is bonded to one K(1), three equivalent K(2), one Ta(1), and one Cu(1) atom to form distorted SK4TaCu octahedra that share  a cornercorner with one S(8)K4NbCu octahedra, corners with two equivalent S(7)K4TaCu octahedra, and edges with two equivalent S(7)K4TaCu octahedra. The corner-sharing octahedral tilt angles range from 0-69°. In the eighth S site, S(8) is bonded to one K(1), three equivalent K(3), one Nb(1), and one Cu(2) atom to form distorted SK4NbCu octahedra that share  a cornercorner with one S(7)K4TaCu octahedra, corners with two equivalent S(8)K4NbCu octahedra, and edges with two equivalent S(8)K4NbCu octahedra. The corner-sharing octahedral tilt angles range from 0-69°.
K3TaNbCu3S8 crystallizes in the monoclinic C2 space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a body-centered cubic geometry to one S(3), one S(4), one S(7), one S(8), two equivalent S(5), and two equivalent S(6) atoms. The K(1)-S(3) bond length is 3.49 Å. The K(1)-S(4) bond length is 3.49 Å. The K(1)-S(7) bond length is 3.33 Å. The K(1)-S(8) bond length is 3.32 Å. There is one shorter (3.36 Å) and one longer (3.55 Å) K(1)-S(5) bond length. There is one shorter (3.36 Å) and one longer (3.55 Å) K(1)-S(6) bond length. In the second K site, K(2) is bonded in a 7-coordinate geometry to one S(2), one S(4), two equivalent S(1), and three equivalent S(7) atoms. The K(2)-S(2) bond length is 3.23 Å. The K(2)-S(4) bond length is 3.68 Å. There is one shorter (3.54 Å) and one longer (3.63 Å) K(2)-S(1) bond length. There are a spread of K(2)-S(7) bond distances ranging from 3.34-3.42 Å. In the third K site, K(3) is bonded in a 7-coordinate geometry to one S(1), one S(3), two equivalent S(2), and three equivalent S(8) atoms. The K(3)-S(1) bond length is 3.23 Å. The K(3)-S(3) bond length is 3.67 Å. There is one shorter (3.55 Å) and one longer (3.62 Å) K(3)-S(2) bond length. There are a spread of K(3)-S(8) bond distances ranging from 3.33-3.43 Å. Ta(1) is bonded to one S(1), one S(3), one S(5), and one S(7) atom to form TaS4 tetrahedra that share  an edgeedge with one Cu(3)S4 tetrahedra and edges with two equivalent Cu(1)S4 tetrahedra. The Ta(1)-S(1) bond length is 2.29 Å. The Ta(1)-S(3) bond length is 2.31 Å. The Ta(1)-S(5) bond length is 2.31 Å. The Ta(1)-S(7) bond length is 2.30 Å. Nb(1) is bonded to one S(2), one S(4), one S(6), and one S(8) atom to form NbS4 tetrahedra that share  an edgeedge with one Cu(4)S4 tetrahedra and edges with two equivalent Cu(2)S4 tetrahedra. The Nb(1)-S(2) bond length is 2.29 Å. The Nb(1)-S(4) bond length is 2.32 Å. The Nb(1)-S(6) bond length is 2.32 Å. The Nb(1)-S(8) bond length is 2.31 Å. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(3), one S(5), and one S(7) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(3)S4 tetrahedra and edges with two equivalent Ta(1)S4 tetrahedra. The Cu(1)-S(1) bond length is 2.33 Å. The Cu(1)-S(3) bond length is 2.37 Å. The Cu(1)-S(5) bond length is 2.38 Å. The Cu(1)-S(7) bond length is 2.35 Å. In the second Cu site, Cu(2) is bonded to one S(2), one S(4), one S(6), and one S(8) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(4)S4 tetrahedra and edges with two equivalent Nb(1)S4 tetrahedra. The Cu(2)-S(2) bond length is 2.33 Å. The Cu(2)-S(4) bond length is 2.37 Å. The Cu(2)-S(6) bond length is 2.38 Å. The Cu(2)-S(8) bond length is 2.35 Å. In the third Cu site, Cu(3) is bonded to two equivalent S(3) and two equivalent S(5) atoms to form distorted CuS4 tetrahedra that share corners with four equivalent Cu(1)S4 tetrahedra and edges with two equivalent Ta(1)S4 tetrahedra. Both Cu(3)-S(3) bond lengths are 2.37 Å. Both Cu(3)-S(5) bond lengths are 2.36 Å. In the fourth Cu site, Cu(4) is bonded to two equivalent S(4) and two equivalent S(6) atoms to form distorted CuS4 tetrahedra that share corners with four equivalent Cu(2)S4 tetrahedra and edges with two equivalent Nb(1)S4 tetrahedra. Both Cu(4)-S(4) bond lengths are 2.37 Å. Both Cu(4)-S(6) bond lengths are 2.35 Å. There are eight inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one K(3), two equivalent K(2), one Ta(1), and one Cu(1) atom. In the second S site, S(2) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(3), one Nb(1), and one Cu(2) atom. In the third S site, S(3) is bonded in a 5-coordinate geometry to one K(1), one K(3), one Ta(1), one Cu(1), and one Cu(3) atom. In the fourth S site, S(4) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Nb(1), one Cu(2), and one Cu(4) atom. In the fifth S site, S(5) is bonded in a 5-coordinate geometry to two equivalent K(1), one Ta(1), one Cu(1), and one Cu(3) atom. In the sixth S site, S(6) is bonded in a 5-coordinate geometry to two equivalent K(1), one Nb(1), one Cu(2), and one Cu(4) atom. In the seventh S site, S(7) is bonded to one K(1), three equivalent K(2), one Ta(1), and one Cu(1) atom to form distorted SK4TaCu octahedra that share  a cornercorner with one S(8)K4NbCu octahedra, corners with two equivalent S(7)K4TaCu octahedra, and edges with two equivalent S(7)K4TaCu octahedra. The corner-sharing octahedral tilt angles range from 0-69°. In the eighth S site, S(8) is bonded to one K(1), three equivalent K(3), one Nb(1), and one Cu(2) atom to form distorted SK4NbCu octahedra that share  a cornercorner with one S(7)K4TaCu octahedra, corners with two equivalent S(8)K4NbCu octahedra, and edges with two equivalent S(8)K4NbCu octahedra. The corner-sharing octahedral tilt angles range from 0-69°.