KMgMn4O8 crystallizes in the triclinic P1 space group. K(1) is bonded in a 7-coordinate geometry to one O(8), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. Mg(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form distorted MgO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra,  a cornercorner with one Mn(3)O6 octahedra,  an edgeedge with one Mn(1)O6 octahedra, and  an edgeedge with one Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 65-69°. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. In the second Mn site, Mn(2) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(8), and two equivalent O(6) atoms. In the third Mn site, Mn(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, edges with two equivalent Mn(3)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. In the fourth Mn site, Mn(4) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), and two equivalent O(7) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(3), and one Mn(4) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Mn(1), and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(2), and one Mn(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent K(1), one Mn(4), and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent K(1), one Mn(3), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to two equivalent K(1), one Mn(1), and two equivalent Mn(4) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one K(1), one Mn(2), and two equivalent Mn(3) atoms.
KMgMn4O8 crystallizes in the triclinic P1 space group. K(1) is bonded in a 7-coordinate geometry to one O(8), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. The K(1)-O(8) bond length is 3.02 Å. There is one shorter (3.02 Å) and one longer (3.36 Å) K(1)-O(5) bond length. There is one shorter (2.96 Å) and one longer (3.22 Å) K(1)-O(6) bond length. There is one shorter (2.96 Å) and one longer (3.35 Å) K(1)-O(7) bond length. Mg(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form distorted MgO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra,  a cornercorner with one Mn(3)O6 octahedra,  an edgeedge with one Mn(1)O6 octahedra, and  an edgeedge with one Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 65-69°. The Mg(1)-O(1) bond length is 1.93 Å. The Mg(1)-O(2) bond length is 1.95 Å. The Mg(1)-O(3) bond length is 1.94 Å. The Mg(1)-O(4) bond length is 1.96 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. The Mn(1)-O(2) bond length is 1.98 Å. The Mn(1)-O(7) bond length is 1.93 Å. There is one shorter (2.04 Å) and one longer (2.35 Å) Mn(1)-O(4) bond length. There is one shorter (1.99 Å) and one longer (2.04 Å) Mn(1)-O(5) bond length. In the second Mn site, Mn(2) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(8), and two equivalent O(6) atoms. The Mn(2)-O(3) bond length is 1.98 Å. The Mn(2)-O(4) bond length is 1.99 Å. The Mn(2)-O(8) bond length is 1.95 Å. There is one shorter (1.96 Å) and one longer (2.12 Å) Mn(2)-O(6) bond length. In the third Mn site, Mn(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, edges with two equivalent Mn(3)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. The Mn(3)-O(1) bond length is 1.96 Å. The Mn(3)-O(6) bond length is 1.94 Å. There is one shorter (2.01 Å) and one longer (2.44 Å) Mn(3)-O(2) bond length. There is one shorter (1.98 Å) and one longer (2.03 Å) Mn(3)-O(8) bond length. In the fourth Mn site, Mn(4) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), and two equivalent O(7) atoms. The Mn(4)-O(1) bond length is 1.97 Å. The Mn(4)-O(3) bond length is 1.97 Å. The Mn(4)-O(5) bond length is 1.95 Å. There is one shorter (1.96 Å) and one longer (2.12 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 one Mg(1), one Mn(3), and one Mn(4) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Mn(1), and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(2), and one Mn(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent K(1), one Mn(4), and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent K(1), one Mn(3), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to two equivalent K(1), one Mn(1), and two equivalent Mn(4) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one K(1), one Mn(2), and two equivalent Mn(3) atoms.