K2MgNb2(CuS2)4 crystallizes in the triclinic P1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one Mg(1), one S(1), one S(3), one S(4), one S(5), and two equivalent S(7) atoms. In the second K site, K(2) is bonded in a 6-coordinate geometry to one S(2), one S(3), one S(4), one S(6), and two equivalent S(8) atoms. Mg(1) is bonded in a 3-coordinate geometry to one K(1), one S(3), one S(4), and one S(6) atom. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 4-coordinate geometry to one S(1), one S(3), one S(6), and one S(8) atom. In the second Nb site, Nb(2) is bonded to one S(2), one S(4), one S(5), and one S(7) atom to form distorted NbS4 tetrahedra that share  an edgeedge with one Cu(1)S4 tetrahedra,  an edgeedge with one Cu(2)S4 tetrahedra, and edges with two equivalent Cu(4)S4 tetrahedra. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(2), one S(5), and one S(6) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(2)S4 tetrahedra, corners with two equivalent Cu(4)S4 tetrahedra, and  an edgeedge with one Nb(2)S4 tetrahedra. In the second Cu site, Cu(2) is bonded to one S(1), one S(2), one S(7), and one S(8) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(1)S4 tetrahedra, corners with two equivalent Cu(4)S4 tetrahedra, and  an edgeedge with one Nb(2)S4 tetrahedra. In the third Cu site, Cu(3) is bonded in a 4-coordinate geometry to one S(1), one S(3), one S(6), and one S(8) atom. In the fourth Cu site, Cu(4) is bonded to one S(2), one S(4), one S(5), and one S(7) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(1)S4 tetrahedra, corners with two equivalent Cu(2)S4 tetrahedra, and edges with two equivalent Nb(2)S4 tetrahedra. There are eight inequivalent S sites. In the first S site, S(1) is bonded in a distorted trigonal bipyramidal geometry to one K(1), one Nb(1), one Cu(1), one Cu(2), and one Cu(3) atom. In the second S site, S(2) is bonded in a distorted pentagonal planar geometry to one K(2), one Nb(2), one Cu(1), one Cu(2), and one Cu(4) atom. In the third S site, S(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Nb(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 Mg(1), one Nb(2), and one Cu(4) atom. In the fifth S site, S(5) is bonded in a 4-coordinate geometry to one K(1), one Nb(2), one Cu(1), and one Cu(4) atom. In the sixth S site, S(6) is bonded in a 5-coordinate geometry to one K(2), one Mg(1), one Nb(1), one Cu(1), and one Cu(3) atom. In the seventh S site, S(7) is bonded in a 5-coordinate geometry to two equivalent K(1), one Nb(2), one Cu(2), and one Cu(4) atom. In the eighth S site, S(8) is bonded in a 5-coordinate geometry to two equivalent K(2), one Nb(1), one Cu(2), and one Cu(3) atom.
K2MgNb2(CuS2)4 crystallizes in the triclinic P1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one Mg(1), one S(1), one S(3), one S(4), one S(5), and two equivalent S(7) atoms. The K(1)-Mg(1) bond length is 3.75 Å. The K(1)-S(1) bond length is 3.22 Å. The K(1)-S(3) bond length is 3.60 Å. The K(1)-S(4) bond length is 3.60 Å. The K(1)-S(5) bond length is 3.27 Å. There is one shorter (3.25 Å) and one longer (3.54 Å) K(1)-S(7) bond length. In the second K site, K(2) is bonded in a 6-coordinate geometry to one S(2), one S(3), one S(4), one S(6), and two equivalent S(8) atoms. The K(2)-S(2) bond length is 3.25 Å. The K(2)-S(3) bond length is 3.55 Å. The K(2)-S(4) bond length is 3.51 Å. The K(2)-S(6) bond length is 3.48 Å. There is one shorter (3.37 Å) and one longer (3.44 Å) K(2)-S(8) bond length. Mg(1) is bonded in a 3-coordinate geometry to one K(1), one S(3), one S(4), and one S(6) atom. The Mg(1)-S(3) bond length is 2.52 Å. The Mg(1)-S(4) bond length is 2.48 Å. The Mg(1)-S(6) bond length is 2.48 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 4-coordinate geometry to one S(1), one S(3), one S(6), and one S(8) atom. The Nb(1)-S(1) bond length is 2.42 Å. The Nb(1)-S(3) bond length is 2.34 Å. The Nb(1)-S(6) bond length is 2.46 Å. The Nb(1)-S(8) bond length is 2.32 Å. In the second Nb site, Nb(2) is bonded to one S(2), one S(4), one S(5), and one S(7) atom to form distorted NbS4 tetrahedra that share  an edgeedge with one Cu(1)S4 tetrahedra,  an edgeedge with one Cu(2)S4 tetrahedra, and edges with two equivalent Cu(4)S4 tetrahedra. The Nb(2)-S(2) bond length is 2.34 Å. The Nb(2)-S(4) bond length is 2.36 Å. The Nb(2)-S(5) bond length is 2.31 Å. The Nb(2)-S(7) 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(2), one S(5), and one S(6) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(2)S4 tetrahedra, corners with two equivalent Cu(4)S4 tetrahedra, and  an edgeedge with one Nb(2)S4 tetrahedra. The Cu(1)-S(1) bond length is 2.53 Å. The Cu(1)-S(2) bond length is 2.29 Å. The Cu(1)-S(5) bond length is 2.28 Å. The Cu(1)-S(6) bond length is 2.33 Å. In the second Cu site, Cu(2) is bonded to one S(1), one S(2), one S(7), and one S(8) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(1)S4 tetrahedra, corners with two equivalent Cu(4)S4 tetrahedra, and  an edgeedge with one Nb(2)S4 tetrahedra. The Cu(2)-S(1) bond length is 2.34 Å. The Cu(2)-S(2) bond length is 2.41 Å. The Cu(2)-S(7) bond length is 2.33 Å. The Cu(2)-S(8) bond length is 2.36 Å. In the third Cu site, Cu(3) is bonded in a 4-coordinate geometry to one S(1), one S(3), one S(6), and one S(8) atom. The Cu(3)-S(1) bond length is 2.33 Å. The Cu(3)-S(3) bond length is 2.52 Å. The Cu(3)-S(6) bond length is 2.38 Å. The Cu(3)-S(8) bond length is 2.42 Å. In the fourth Cu site, Cu(4) is bonded to one S(2), one S(4), one S(5), and one S(7) atom to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(1)S4 tetrahedra, corners with two equivalent Cu(2)S4 tetrahedra, and edges with two equivalent Nb(2)S4 tetrahedra. The Cu(4)-S(2) bond length is 2.33 Å. The Cu(4)-S(4) bond length is 2.40 Å. The Cu(4)-S(5) bond length is 2.35 Å. The Cu(4)-S(7) bond length is 2.35 Å. There are eight inequivalent S sites. In the first S site, S(1) is bonded in a distorted trigonal bipyramidal geometry to one K(1), one Nb(1), one Cu(1), one Cu(2), and one Cu(3) atom. In the second S site, S(2) is bonded in a distorted pentagonal planar geometry to one K(2), one Nb(2), one Cu(1), one Cu(2), and one Cu(4) atom. In the third S site, S(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Nb(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 Mg(1), one Nb(2), and one Cu(4) atom. In the fifth S site, S(5) is bonded in a 4-coordinate geometry to one K(1), one Nb(2), one Cu(1), and one Cu(4) atom. In the sixth S site, S(6) is bonded in a 5-coordinate geometry to one K(2), one Mg(1), one Nb(1), one Cu(1), and one Cu(3) atom. In the seventh S site, S(7) is bonded in a 5-coordinate geometry to two equivalent K(1), one Nb(2), one Cu(2), and one Cu(4) atom. In the eighth S site, S(8) is bonded in a 5-coordinate geometry to two equivalent K(2), one Nb(1), one Cu(2), and one Cu(3) atom.