K4MgMn4O8 crystallizes in the triclinic P1 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(5) atoms. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(4), and two equivalent O(7) atoms. In the third K site, K(3) is bonded in a 6-coordinate geometry to one O(4), one O(7), two equivalent O(2), and two equivalent O(6) atoms. In the fourth K site, K(4) is bonded in a 4-coordinate geometry to two equivalent O(3) and two equivalent O(8) atoms. Mg(1) is bonded to one O(3), one O(8), and two equivalent O(1) atoms to form distorted MgO4 tetrahedra that share  a cornercorner with one Mn(4)O5 square pyramid, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and  an edgeedge with one Mn(1)O5 trigonal bipyramid. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(6), two equivalent O(1), and two equivalent O(5) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(2)O5 square pyramids,  an edgeedge with one Mg(1)O4 tetrahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. In the second Mn site, Mn(2) is bonded to one O(5), two equivalent O(2), and two equivalent O(6) atoms to form edge-sharing MnO5 square pyramids. In the third Mn site, Mn(3) is bonded in a 5-coordinate geometry to one O(7), two equivalent O(3), and two equivalent O(8) atoms. In the fourth Mn site, Mn(4) is bonded to one O(8), two equivalent O(4), and two equivalent O(7) atoms to form distorted MnO5 square pyramids that share  a cornercorner with one Mg(1)O4 tetrahedra and edges with two equivalent Mn(4)O5 square pyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent K(1), two equivalent Mg(1), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one K(1), one K(2), two equivalent K(3), and two equivalent Mn(2) atoms to form distorted OK4Mn2 octahedra that share edges with two equivalent O(7)K3Mn3 octahedra, edges with two equivalent O(2)K4Mn2 octahedra, and edges with two equivalent O(5)K2Mn3 square pyramids. In the third O site, O(3) is bonded to two equivalent K(4), one Mg(1), and two equivalent Mn(3) atoms to form distorted OK2MgMn2 trigonal bipyramids that share corners with two equivalent O(7)K3Mn3 octahedra, corners with four equivalent O(8)K2MgMn3 octahedra,  an edgeedge with one O(8)K2MgMn3 octahedra, edges with two equivalent O(3)K2MgMn2 trigonal bipyramids, and  a faceface with one O(8)K2MgMn3 octahedra. The corner-sharing octahedral tilt angles range from 23-54°. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one K(3), two equivalent K(2), and two equivalent Mn(4) atoms. In the fifth O site, O(5) is bonded to two equivalent K(1), one Mn(2), and two equivalent Mn(1) atoms to form OK2Mn3 square pyramids that share edges with two equivalent O(2)K4Mn2 octahedra and edges with two equivalent O(5)K2Mn3 square pyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent K(3), one Mn(1), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded to one K(3), two equivalent K(2), one Mn(3), and two equivalent Mn(4) atoms to form distorted OK3Mn3 octahedra that share corners with two equivalent O(3)K2MgMn2 trigonal bipyramids, edges with two equivalent O(8)K2MgMn3 octahedra, edges with two equivalent O(7)K3Mn3 octahedra, and edges with two equivalent O(2)K4Mn2 octahedra. In the eighth O site, O(8) is bonded to two equivalent K(4), one Mg(1), one Mn(4), and two equivalent Mn(3) atoms to form distorted OK2MgMn3 octahedra that share corners with four equivalent O(3)K2MgMn2 trigonal bipyramids, edges with two equivalent O(8)K2MgMn3 octahedra, edges with two equivalent O(7)K3Mn3 octahedra,  an edgeedge with one O(3)K2MgMn2 trigonal bipyramid, and  a faceface with one O(3)K2MgMn2 trigonal bipyramid.
K4MgMn4O8 crystallizes in the triclinic P1 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(5) atoms. The K(1)-O(2) bond length is 2.84 Å. There is one shorter (2.86 Å) and one longer (3.05 Å) K(1)-O(1) bond length. There is one shorter (2.54 Å) and one longer (2.56 Å) K(1)-O(5) bond length. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(4), and two equivalent O(7) atoms. The K(2)-O(2) bond length is 2.81 Å. There is one shorter (2.65 Å) and one longer (2.67 Å) K(2)-O(4) bond length. There is one shorter (2.72 Å) and one longer (2.76 Å) K(2)-O(7) bond length. In the third K site, K(3) is bonded in a 6-coordinate geometry to one O(4), one O(7), two equivalent O(2), and two equivalent O(6) atoms. The K(3)-O(4) bond length is 3.05 Å. The K(3)-O(7) bond length is 2.97 Å. There is one shorter (2.78 Å) and one longer (2.81 Å) K(3)-O(2) bond length. There is one shorter (2.84 Å) and one longer (2.87 Å) K(3)-O(6) bond length. In the fourth K site, K(4) is bonded in a 4-coordinate geometry to two equivalent O(3) and two equivalent O(8) atoms. There is one shorter (2.61 Å) and one longer (2.63 Å) K(4)-O(3) bond length. There is one shorter (2.67 Å) and one longer (2.71 Å) K(4)-O(8) bond length. Mg(1) is bonded to one O(3), one O(8), and two equivalent O(1) atoms to form distorted MgO4 tetrahedra that share  a cornercorner with one Mn(4)O5 square pyramid, corners with two equivalent Mg(1)O4 tetrahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and  an edgeedge with one Mn(1)O5 trigonal bipyramid. The Mg(1)-O(3) bond length is 2.00 Å. The Mg(1)-O(8) bond length is 2.04 Å. There is one shorter (1.99 Å) and one longer (2.00 Å) Mg(1)-O(1) bond length. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(6), two equivalent O(1), and two equivalent O(5) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(2)O5 square pyramids,  an edgeedge with one Mg(1)O4 tetrahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The Mn(1)-O(6) bond length is 2.25 Å. There is one shorter (2.17 Å) and one longer (2.51 Å) Mn(1)-O(1) bond length. There is one shorter (2.06 Å) and one longer (2.07 Å) Mn(1)-O(5) bond length. In the second Mn site, Mn(2) is bonded to one O(5), two equivalent O(2), and two equivalent O(6) atoms to form edge-sharing MnO5 square pyramids. The Mn(2)-O(5) bond length is 2.14 Å. There is one shorter (2.02 Å) and one longer (2.03 Å) Mn(2)-O(2) bond length. There is one shorter (2.05 Å) and one longer (2.06 Å) Mn(2)-O(6) bond length. In the third Mn site, Mn(3) is bonded in a 5-coordinate geometry to one O(7), two equivalent O(3), and two equivalent O(8) atoms. The Mn(3)-O(7) bond length is 2.10 Å. There is one shorter (2.10 Å) and one longer (2.11 Å) Mn(3)-O(3) bond length. There is one shorter (2.23 Å) and one longer (2.26 Å) Mn(3)-O(8) bond length. In the fourth Mn site, Mn(4) is bonded to one O(8), two equivalent O(4), and two equivalent O(7) atoms to form distorted MnO5 square pyramids that share  a cornercorner with one Mg(1)O4 tetrahedra and edges with two equivalent Mn(4)O5 square pyramids. The Mn(4)-O(8) bond length is 2.14 Å. There is one shorter (1.99 Å) and one longer (2.00 Å) Mn(4)-O(4) bond length. There is one shorter (2.06 Å) and one longer (2.07 Å) Mn(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent K(1), two equivalent Mg(1), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one K(1), one K(2), two equivalent K(3), and two equivalent Mn(2) atoms to form distorted OK4Mn2 octahedra that share edges with two equivalent O(7)K3Mn3 octahedra, edges with two equivalent O(2)K4Mn2 octahedra, and edges with two equivalent O(5)K2Mn3 square pyramids. In the third O site, O(3) is bonded to two equivalent K(4), one Mg(1), and two equivalent Mn(3) atoms to form distorted OK2MgMn2 trigonal bipyramids that share corners with two equivalent O(7)K3Mn3 octahedra, corners with four equivalent O(8)K2MgMn3 octahedra,  an edgeedge with one O(8)K2MgMn3 octahedra, edges with two equivalent O(3)K2MgMn2 trigonal bipyramids, and  a faceface with one O(8)K2MgMn3 octahedra. The corner-sharing octahedral tilt angles range from 23-54°. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one K(3), two equivalent K(2), and two equivalent Mn(4) atoms. In the fifth O site, O(5) is bonded to two equivalent K(1), one Mn(2), and two equivalent Mn(1) atoms to form OK2Mn3 square pyramids that share edges with two equivalent O(2)K4Mn2 octahedra and edges with two equivalent O(5)K2Mn3 square pyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent K(3), one Mn(1), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded to one K(3), two equivalent K(2), one Mn(3), and two equivalent Mn(4) atoms to form distorted OK3Mn3 octahedra that share corners with two equivalent O(3)K2MgMn2 trigonal bipyramids, edges with two equivalent O(8)K2MgMn3 octahedra, edges with two equivalent O(7)K3Mn3 octahedra, and edges with two equivalent O(2)K4Mn2 octahedra. In the eighth O site, O(8) is bonded to two equivalent K(4), one Mg(1), one Mn(4), and two equivalent Mn(3) atoms to form distorted OK2MgMn3 octahedra that share corners with four equivalent O(3)K2MgMn2 trigonal bipyramids, edges with two equivalent O(8)K2MgMn3 octahedra, edges with two equivalent O(7)K3Mn3 octahedra,  an edgeedge with one O(3)K2MgMn2 trigonal bipyramid, and  a faceface with one O(3)K2MgMn2 trigonal bipyramid.