K4MgNb2(CuS4)2 crystallizes in the monoclinic C2 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 6-coordinate geometry to two equivalent S(1) and four equivalent S(4) atoms. In the second K site, K(2) is bonded in a 8-coordinate geometry to two equivalent S(2), two equivalent S(4), and four equivalent S(3) atoms. In the third K site, K(3) is bonded in a 8-coordinate geometry to two equivalent S(2), two equivalent S(4), and four equivalent S(1) atoms. In the fourth K site, K(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent S(1), and four equivalent S(2) atoms. Mg(1) is bonded in a 4-coordinate geometry to two equivalent K(4), two equivalent S(2), and two equivalent S(3) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form NbS4 tetrahedra that share edges with two equivalent Cu(1)S4 tetrahedra. In the second Nb site, Nb(2) is bonded to two equivalent S(3) and two equivalent S(4) atoms to form NbS4 tetrahedra that share edges with two equivalent Cu(2)S4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form distorted CuS4 tetrahedra that share edges with two equivalent Nb(1)S4 tetrahedra. In the second Cu site, Cu(2) is bonded to two equivalent S(3) and two equivalent S(4) atoms to form distorted CuS4 tetrahedra that share edges with two equivalent Nb(2)S4 tetrahedra. There are four inequivalent S sites. In the first S site, S(1) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(3), one Nb(1), and one Cu(1) atom. In the second S site, S(2) is bonded in a 7-coordinate geometry to one K(2), one K(3), two equivalent K(4), one Mg(1), one Nb(1), and one Cu(1) atom. In the third S site, S(3) is bonded in a 3-coordinate geometry to two equivalent K(2), one Mg(1), one Nb(2), and one Cu(2) atom. In the fourth S site, S(4) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(1), one Nb(2), and one Cu(2) atom.
K4MgNb2(CuS4)2 crystallizes in the monoclinic C2 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 6-coordinate geometry to two equivalent S(1) and four equivalent S(4) atoms. Both K(1)-S(1) bond lengths are 3.45 Å. There are two shorter (3.40 Å) and two longer (3.58 Å) K(1)-S(4) bond lengths. In the second K site, K(2) is bonded in a 8-coordinate geometry to two equivalent S(2), two equivalent S(4), and four equivalent S(3) atoms. Both K(2)-S(2) bond lengths are 3.51 Å. Both K(2)-S(4) bond lengths are 3.58 Å. There are two shorter (3.42 Å) and two longer (3.66 Å) K(2)-S(3) bond lengths. In the third K site, K(3) is bonded in a 8-coordinate geometry to two equivalent S(2), two equivalent S(4), and four equivalent S(1) atoms. Both K(3)-S(2) bond lengths are 3.73 Å. Both K(3)-S(4) bond lengths are 3.43 Å. There are two shorter (3.44 Å) and two longer (3.60 Å) K(3)-S(1) bond lengths. In the fourth K site, K(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent S(1), and four equivalent S(2) atoms. Both K(4)-Mg(1) bond lengths are 3.38 Å. Both K(4)-S(1) bond lengths are 3.15 Å. There are two shorter (3.29 Å) and two longer (3.59 Å) K(4)-S(2) bond lengths. Mg(1) is bonded in a 4-coordinate geometry to two equivalent K(4), two equivalent S(2), and two equivalent S(3) atoms. Both Mg(1)-S(2) bond lengths are 2.50 Å. Both Mg(1)-S(3) bond lengths are 2.44 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form NbS4 tetrahedra that share edges with two equivalent Cu(1)S4 tetrahedra. Both Nb(1)-S(1) bond lengths are 2.32 Å. Both Nb(1)-S(2) bond lengths are 2.38 Å. In the second Nb site, Nb(2) is bonded to two equivalent S(3) and two equivalent S(4) atoms to form NbS4 tetrahedra that share edges with two equivalent Cu(2)S4 tetrahedra. Both Nb(2)-S(3) bond lengths are 2.39 Å. Both Nb(2)-S(4) bond lengths are 2.31 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form distorted CuS4 tetrahedra that share edges with two equivalent Nb(1)S4 tetrahedra. Both Cu(1)-S(1) bond lengths are 2.33 Å. Both Cu(1)-S(2) bond lengths are 2.48 Å. In the second Cu site, Cu(2) is bonded to two equivalent S(3) and two equivalent S(4) atoms to form distorted CuS4 tetrahedra that share edges with two equivalent Nb(2)S4 tetrahedra. Both Cu(2)-S(3) bond lengths are 2.41 Å. Both Cu(2)-S(4) bond lengths are 2.34 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(3), one Nb(1), and one Cu(1) atom. In the second S site, S(2) is bonded in a 7-coordinate geometry to one K(2), one K(3), two equivalent K(4), one Mg(1), one Nb(1), and one Cu(1) atom. In the third S site, S(3) is bonded in a 3-coordinate geometry to two equivalent K(2), one Mg(1), one Nb(2), and one Cu(2) atom. In the fourth S site, S(4) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(1), one Nb(2), and one Cu(2) atom.